first edition: - airwalkbooks.comairwalkbooks.com/images/pdf/pdf_67_1.pdf · 9 abrasive processes:...

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(For B.E. Mechanical Engineering Students)

Dr. S.Ramachandran,M.E., Ph.D.,

Professor and Head

Dr. S. Ramesh, B.E., M.Tech (IIT-M), Ph.D.,

PrincipalAnnai Mathammal Sheela

Engineering College,Erumapatty,

Namakkal (DT)

R. Thamarai Kannan,M.Tech.,

Assistant ProfessorDepartment of Mechanical

EngineeringSathyabama University

Jeppiaar Nagar, Chennai - 600 119

AIR WALK PUBLICATIONS(Near All India Radio)

80, Karneeshwarar Koil Street,Mylapore, Chennai - 600 004.Ph.: 2466 1909, 94440 81904

Email: [email protected]

First Edition: 23-10-2013

© All Rights Reserved by the Publisher

This book or part thereof should not be reproduced inany form without the written permission of the publisher.

Price : Rs. 400/-

Copies can be had from :

AIR WALK PUBLICATIONS(Near All India Radio)80, Karneeshwarar Koil Street,Mylapore, Chennai - 600 004.

Ph.: 2466 1909, 9444 08 1904

Books will be door delivered after payment into AIR WALKPUBLICATIONS A/c No. 801620100001454 (IFSC: BKID0008016)Bank of India, Santhome branch, Mylapore, Chennai - 4 (or)

S.Ramachandran, A/c.No.482894441 (IFSC:IDIB000S201), IndianBank, Sathyabama University Branch, Chennai - 600119.

ISBN : 978-81-924031-3-7

Typeset by: aksharaa muthra aalayam, Chennai - 18. Ph.: 044-2436 4303

Printed at: Abinayaram Printers, Chennai - 4. Ph.: 044-2466 1909, 9444 08 1904

Dedicated to

Our Parents

Books available inall book stalls with

attractive discounts

��

(For B.E. Mechanical Engineering Students)

(As per Anna University New Revised Syllabus)

Dr. S.Ramachandran,M.E., Ph.D.,

Professor and Head

Dr. S. Ramesh, B.E., M.Tech (IIT-M), Ph.D.,

PrincipalAnnai Mathammal Sheela

Engineering College,Erumapatty,

Namakkal (DT)

R. Thamarai Kannan,M.Tech.,

Assistant ProfessorDepartment of Mechanical

EngineeringSathyabama University

Jeppiaar Nagar, Chennai - 600 119

AIR WALK PUBLICATIONS(Near All India Radio)

80, Karneeshwarar Koil Street,Mylapore, Chennai - 600 004.Ph.: 2466 1909, 94440 81904

Email: [email protected]

© All Rights Reserved by the Publisher

This book or part thereof should not be reproduced inany form without the written permission of the publisher.

Copies can be had from :

AIR WALK PUBLICATIONS(Near All India Radio)80, Karneeshwarar Koil Street,Mylapore, Chennai - 600 004.

Ph.: 2466 1909, 9444 08 1904

Books will be door delivered after payment into AIR WALKPUBLICATIONS A/c No. 801620100001454 (IFSC: BKID0008016)Bank of India, Santhome branch, Mylapore, Chennai - 4 (or)

S.Ramachandran, A/c.No.482894441 (IFSC:IDIB000S201), IndianBank, Sathyabama University Branch, Chennai - 600119.

Typeset by: aksharaa muthra aalayam, Chennai - 18. Ph.: 044-2436 4303

Printed at: Abinayaram Printers, Chennai - 4. Ph.: 044-2466 1909, 9444 08 1904

Dedicated to

Our Parents

Books available inall book stalls with

attractive discounts

First Edition: 23-10-2013Second Edition: 02-02-2016

ISBN : 978-93-84893-01-9

Anna University SyllabusMANUFACTURING TECHNOLOGY – II

Unit I Theory of Metal Cutting 9

Introduction: Material removal processes, types of machinetools - theory of metal cutting: chip formation, orthogonal cutting,cutting tool materials, tool wear, tool life, surface finish, cuttingfluids.

Unit II Centre Lathe and Special Purpose Lathes 9

Centre lathe, constructional features, cutting tool geometry,various operations, taper turning methods, thread cutting methods,special attachments, machining time and power estimation.Capstan and turret lathes - automats - single spindle, Swiss type,automatic screw type, multi spindle - Turret Indexing mechanism,Bar feed mechanism.

Unit III Other Machine Tools 9

Reciprocating machine tools: shaper, planer, slotter - Milling:types, milling cutters, operations - Hole making: drilling - Quillmechanism, Reaming, Boring, Tapping - Sawing machine: hacksaw, band saw, circular saw; broaching machines; broachconstruction -push, pull, surface and continuous broachingmachines.

Unit IV Abrasive Processes and Gear Cutting 9

Abrasive processes: grinding wheel - specifications andselection, types of grinding process - cylindrical grinding, surfacegrinding, centreless grinding - honing, lapping, super finishing,polishing and buffing, abrasive jet machining - Gear cutting,forming, generation, shaping, hobbing.

Unit V CNC Machine Tools and Part Programming 9

Numerical control (NC) machine tools - CNC: types,constructional details, special features - design considerations ofCNC machines for improving machining accuracy - structuralmembers - slide ways - linear bearings - ball screws - spindle drivesand feed drives. Part programming fundamentals - manualprogramming - computer assisted part programming.

Total Number of Periods: 45 Periods

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITYIII Year B.Tech. M.E.I-Sem

MACHINE TOOLS (PRODUCTION TECHNOLOGY – II)

UNIT – I

Elementary treatement of metal cutting theory – Element ofcutting process – Geometry of single point tool and angles chipformation and types of chips – built up edge and its effects chipbreakers. Mechanics of orthogonal cutting –Merchant’s Forcediagram, cutting forces – cutting speeds, feed, depth of cut, toollife, coolants, machinability – Tool materials.

Kinematic schemes of machine tools – Constructionalfeatures of speed gear box and feed gear box.

UNIT – II

Engine lathe – Principle of working, specification of lathe –types of lathe – work holders tool holders – Box tools Taper turningthread turning – for Lathes and attachments.

Turret and capstan lathes – collet chucks – other workholders – tool holding devices – box and tool layout.

Principal features of automatic lathes – classification –Single spindle and multi-spindle automatic lathes – tool layout andcam design.

UNIT – III

Shaping slotting and planing machines – Principles ofworking – Principal parts – specification classification, operationsperformed. Kinematic scheme of the shaping slotting and planningmachines, machining time calculations.

UNIT – IV

Drilling and Boring Machines – Principles of working,specifications, types, operations performed – tool holding devices –twist drill – Boring machines – Fine boring machines – Jig Boringmachine. Deep hole drilling machine. Kinematics scheme of thedrilling and boring machines

T P C

4+1* 0 4

UNIT – V

Milling machine – Principles of working – specifications –classifications of milling machines – Principal features ofhorizontal, vertical and universal milling machines – machiningoperations Types geometry of milling cutters – milling cutters –methods of indexing – Accessories to milling machines, kinematicscheme of milling cutters – milling cutters – methods of indexing.

UNIT – VI

Grinding machine – Fundamentals – Theory of grinding –classification of grinding machine – cylindrical and surface grindingmachine – Tool and cutter grinding machine – special types ofgrinding machines – Different types of abrasives – bondsspecification of a grinding wheel and selection of a grinding wheelKinematic scheme of grinding machines.

UNIT - VII

Lapping, honing and broaching machines – comparison togrinding – lapping and honing. Kinematics scheme of Lapping,Honing and Broaching machines. Constructional features of speedand feed Units, machining time calculations

UNIT - VIII

Principles of design of Jigs and fixtures and uses.Classification of Jigs & Fixtures – Principles of location andclamping – Types of clamping & work holding devices. Typicalexamples of jigs and fixtures.

CONTENTS

Chapter 1THEORY OF METAL CUTTING

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.11.1.1 Types of motion in machining . . . . . . . . . . . . . 1.2

1.2 Metal Removal Processes. . . . . . . . . . . . . . . . . . . . . 1.3

1.2.1 Classification of Metal Removal Processes. . . 1.3

1.2.2 Chip forming Processes . . . . . . . . . . . . . . . . . . . 1.3

1.2.3 Turning, Boring and other LatheOperations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3

1.2.3.1 Machining parameters and related terms in turning operation. . . . . . . . . . . . . . . . . . 1.7

1.2.4 Shaping, Planing and Slotting . . . . . . . . . . . . 1.10

1.2.4.1 Machining Parameters in Shaping, Planing. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.12

1.2.5 Drilling and Reaming . . . . . . . . . . . . . . . . . . . 1.14

1.2.5.1 Machining Parameters for Drilling . . . . 1.15

1.2.6 Milling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.15

1.2.6.1 Machining Parameters in Milling. . . . . . 1.18

1.2.7 Broaching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.19

1.2.8 Thread Cutting . . . . . . . . . . . . . . . . . . . . . . . . . 1.20

1.2.8.1 Machining Parameters in thread cutting 1.21

1.2.9 Grinding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.22

1.2.10 Honing and Lapping . . . . . . . . . . . . . . . . . . . 1.22

1.2.11 Gear Cutting . . . . . . . . . . . . . . . . . . . . . . . . . . 1.23

(a) Formed Cutter method . . . . . . . . . . . . . . . . . . 1.23

(b) Generating Method . . . . . . . . . . . . . . . . . . . . . 1.23

1.3 Types of Machine / Cutting Tools . . . . . . . . . . . . 1.24

1.4 Parts and Nomenclature of Single Point CuttingTool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.26

1.4.1 Tool Signature . . . . . . . . . . . . . . . . . . . . . . . . . 1.31

1.4.2 Influence of Tool angles in machining . . . . . 1.32

1.5 Theory of Metal Cutting. . . . . . . . . . . . . . . . . . . . . 1.35

1.5.1 Mechanics of Metal Cutting and Chip formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.35

1.5.2 Chip Formation . . . . . . . . . . . . . . . . . . . . . . . . 1.37

1.5.3 Methods of Metal Cutting Processes . . . . . . 1.38

1.5.3.1 Differences between orthogonal and obliquecutting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.40

1.5.4 Types of Chips . . . . . . . . . . . . . . . . . . . . . . . . . 1.41

1.5.4.1 Variables affecting type of chip . . . . . . . 1.41

1.5.4.2 Continuous Chips . . . . . . . . . . . . . . . . . . . 1.41

1.5.4.3 Continuous Chips with Built up Edges. 1.43

1.5.4.4 Discontinuous Chips . . . . . . . . . . . . . . . . . 1.44

1.5.4.5 Chip Breakers . . . . . . . . . . . . . . . . . . . . . . 1.47

1.5.6 Geometry of Chip Formation . . . . . . . . . . . . . 1.48

1.6 Cutting Tool Materials . . . . . . . . . . . . . . . . . . . . . . 1.67

1.6.1 Desirable Properties of Cutting Tools . . . . . 1.67

(i) Hot Hardness . . . . . . . . . . . . . . . . . . . . . . . . . . 1.68

(ii) Wear Resistance. . . . . . . . . . . . . . . . . . . . . . . . 1.68

(iii) Toughness . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.69

(iv) Mechanical and Thermal Shock Resistance 1.69

(v) Friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.70

(vi) Chemical reaction/affinity between the Tooland Workpiece . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.70

(vii) Availability and Manufacture . . . . . . . . . . . 1.70

(viii) High Thermal Conductivity . . . . . . . . . . . . 1.70

(ix) Coefficient of Thermal expansion . . . . . . . . . 1.70

(x) Tool Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.70

1.6.2 Types of Cutting Tool Materials . . . . . . . . . . 1.71

(i) Carbon Tool Steels or Carbon Steels . . . . . . 1.71

(ii) Medium Alloy Steels. . . . . . . . . . . . . . . . . . . . 1.72

Contents 1 Manufacturing Technology - II2

(iii) High Speed Steels (HSS) . . . . . . . . . . . . . . . 1.72

(iv) Cast Alloys (or) Stellites . . . . . . . . . . . . . . . . 1.74

(v) Cemented Carbide Tools . . . . . . . . . . . . . . . . . 1.74

(vi) Ceramic Tools . . . . . . . . . . . . . . . . . . . . . . . . . 1.76

(vii) Diamond Cutting Tools . . . . . . . . . . . . . . . . 1.77

1.7 Tool Wear. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.79

1.7.1 Tool Wear Mechanisms . . . . . . . . . . . . . . . . . . 1.80

1.7.2 Types of Tool Damage in Cutting . . . . . . . . . 1.85

Flank Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.86

Crater Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.87

1.7.3 Tool Failure. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.88

1.7.4 Measurement of Wear . . . . . . . . . . . . . . . . . . . 1.89

1.8 Tool Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.89

1.8.1 Tool failure Criterion. . . . . . . . . . . . . . . . . . . . 1.90

1.8.2 Factors affecting Tool Life . . . . . . . . . . . . . . . 1.91

1.8.3 Machining Cost. . . . . . . . . . . . . . . . . . . . . . . . . 1.96

1.8.4 Machinability. . . . . . . . . . . . . . . . . . . . . . . . . . . 1.97

1.8.4.1 Factors affecting machinability . . . . . . . . 1.98

1.9 Surface Finish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.98

1.10 Cutting Fluids . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.104

1.11 Solved Problems in Cutting Forces . . . . . . . . . 1.110

CHAPTER - 2Centre Lathe and Special Purpose Lathe

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1

2.1.1 Principle of working of Lathe . . . . . . . . . . . . . 2.1

2.2 Types of Lathes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2

2.2.1 Speed lathe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3

2.2.2 Engine lathe or Centre lathe . . . . . . . . . . . . . . 2.3

2.2.3 Bench Lathe . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4

2.2.4 Tool room lathe . . . . . . . . . . . . . . . . . . . . . . . . . 2.4

2.2.5 Special purpose lathe . . . . . . . . . . . . . . . . . . . . 2.5

2.2.6 Capstan and Turret lathes. . . . . . . . . . . . . . . . 2.5

2.2.7 Automatic lathes . . . . . . . . . . . . . . . . . . . . . . . . 2.6

2.2.8 Numerically controlled lathes. . . . . . . . . . . . . . 2.6

2.3 Size and Specification of a Centre Lathe . . . . . . . 2.7

2.4 Centre Lathe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.82.4.1 Constructional features of centre lathe . . . . . 2.8

2.4.1.1 Bed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.10

2.4.1.2 Head stock . . . . . . . . . . . . . . . . . . . . . . . . . 2.11

2.4.1.3 Tail stock . . . . . . . . . . . . . . . . . . . . . . . . . . 2.12

2.4.1.4 Carriage . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.13

2.4.1.4. Tool post . . . . . . . . . . . . . . . . . . . . . . . . . . 2.15

2.4.1.5. Apron. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.18

2.4.2 Feed mechanisms . . . . . . . . . . . . . . . . . . . . . . . 2.19

2.4.2.1 End Gear Train . . . . . . . . . . . . . . . . . . . . 2.20

Tumbler Gear mechanism . . . . . . . . . . . . . . . . . . 2.21

2.4.2.2 Feed gear box . . . . . . . . . . . . . . . . . . . . . . 2.22

2.4.2.3 Feed rod and Lead screw Drive Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.23

Feed rod or Feed shaft. . . . . . . . . . . . . . . . . . . . . 2.23

Lead screw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.24

2.4.2.4 Apron mechanism . . . . . . . . . . . . . . . . . . . 2.24

2.4.2.4.1 Half nut mechanism (Thread cuttingmechanism). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.26

2.4.3 Head stock mechanisms . . . . . . . . . . . . . . . . . 2.27

2.5 Lathe Accessories and Attachments . . . . . . . . . . . 2.332.5.1 Lathe Accessories . . . . . . . . . . . . . . . . . . . . . . . 2.34

(a) Lathe centres . . . . . . . . . . . . . . . . . . . . . . . . . . 2.34

(b) Chucks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.35

(i) Three jaw or Universal chuck . . . . . . . . . . . . 2.37


(ii) Four Jaw chuck . . . . . . . . . . . . . . . . . . . . . . . 2.38

(iii) Collet chuck . . . . . . . . . . . . . . . . . . . . . . . . . . 2.39

(iv) Magnetic chuck . . . . . . . . . . . . . . . . . . . . . . . . 2.40

(c) Face plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.41

(d) Angle plates . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.41

(e) Catch plate and carriers (dogs) . . . . . . . . . . . 2.42

(f) Mandrels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.43

(g) Steady Rest . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.45

(h) Follower rest. . . . . . . . . . . . . . . . . . . . . . . . . . . 2.46

2.6 Cutting Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.472.6.1 Classification of cutting tools (single point

cutting tool) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.47

2.6.2 Factors affecting cutting Tool efficiency . . . . 2.48

2.6.3 Types of tools . . . . . . . . . . . . . . . . . . . . . . . . . . 2.49

(i) Forged tool (solid tool). . . . . . . . . . . . . . . . . . . 2.49

(ii) Brazed tip tool. . . . . . . . . . . . . . . . . . . . . . . . . 2.49

(iii) Fastened tip tool (Mechanical fastening) . . 2.50

(iv) Tool bit and Tool holders . . . . . . . . . . . . . . . 2.50

(v) Tools for method of operation . . . . . . . . . . . . 2.52

(a) Turning Tool . . . . . . . . . . . . . . . . . . . . . . . . . . 2.52

(b) Chamfer Tool . . . . . . . . . . . . . . . . . . . . . . . . . . 2.53

(c) Boring Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.53

(d) External Thread Cutting Tool . . . . . . . . . . . . 2.54

(e) Internal Thread Cutting Tool. . . . . . . . . . . . . 2.55

(f) Facing Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.55

(g) Grooving tool . . . . . . . . . . . . . . . . . . . . . . . . . . 2.55

(h) Parting Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.56

(i) Right Hand Tool . . . . . . . . . . . . . . . . . . . . . . . 2.56

(j) Left Hand Tool . . . . . . . . . . . . . . . . . . . . . . . . . 2.57

(k) Round Nose Tool . . . . . . . . . . . . . . . . . . . . . . . 2.57

2.6.4 Cutting Tool Geometry . . . . . . . . . . . . . . . . . . 2.57

2.6.4.1 Single Point Cutting Tool terms andGemoetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.58

(a) Back rake angle . . . . . . . . . . . . . . . . . . . . . . . 2.60

(b) Side Rake Angles . . . . . . . . . . . . . . . . . . . . . . 2.60

(c) End Relief Angle (Clearance Angle) . . . . . . . 2.61

(d) Side Relief Angle. . . . . . . . . . . . . . . . . . . . . . . 2.61

(e) End cutting Edge Angle . . . . . . . . . . . . . . . . . 2.62

(f) Side cutting edge Angle (Lead Angle) . . . . . . 2.62

(g) Lip Angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.63

2.6.4.2 Chip Breaker . . . . . . . . . . . . . . . . . . . . . . . 2.63

2.7 Lathe Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.64

2.7.1 Centering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.64

2.7.2 Plain or Straight Turning . . . . . . . . . . . . . . . 2.65

(i) Rough turning . . . . . . . . . . . . . . . . . . . . . . . . . 2.66

(ii) Finish Turning . . . . . . . . . . . . . . . . . . . . . . . . 2.67

2.7.3 Shoulder Turning (or) Step turning . . . . . . . 2.67

2.7.4 Taper Turning . . . . . . . . . . . . . . . . . . . . . . . . . 2.67

2.7.5 Eccentric Turning. . . . . . . . . . . . . . . . . . . . . . . 2.69

2.7.6 Cam Turning . . . . . . . . . . . . . . . . . . . . . . . . . . 2.70

2.7.7 Chamfering . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.70

2.7.8 Facing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.71

2.7.9 Knurling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.72

2.7.10 Filing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.73

2.7.11 Polishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.74

2.7.12 Grooving or Necking . . . . . . . . . . . . . . . . . . . 2.74

2.7.13 Parting-Off . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.75

2.7.14 Spinning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.75

2.7.15 Spring Winding . . . . . . . . . . . . . . . . . . . . . . . 2.76

2.7.16 Forming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.76

2.7.17 Drilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.77

2.7.18 Reaming. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.78


2.7.19 Boring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.78

2.7.20 Counter boring, counter sinking and spot-facing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.79

2.7.21 Tapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.80

2.7.22 Under cutting . . . . . . . . . . . . . . . . . . . . . . . . . 2.80

2.7.23 Taper boring . . . . . . . . . . . . . . . . . . . . . . . . . . 2.81

2.7.24 Milling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.81

2.7.25 Grinding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.81

2.8 Taper Turning Methods . . . . . . . . . . . . . . . . . . . . . 2.81

2.8.1 Taper turning by using a form tool . . . . . . . 2.82

2.8.2 Compound rest swiveling method . . . . . . . . . 2.83

2.8.3 Set over or tailstock offset Method . . . . . . . 2.84

2.8.4 Taper turning attachment method . . . . . . . . 2.86

2.8.5 Template and tracer attachment . . . . . . . . . . 2.87

2.8.6 Combination of longitudinal and cross feed. 2.88

2.9 Thread Cutting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.882.9.1 Change Gear Calculations. . . . . . . . . . . . . . . . 2.90

2.9.2 Types of Gear connections . . . . . . . . . . . . . . . 2.92

2.9.3 Metric Thread on English Lead Screw. . . . . 2.95

2.9.4 Procedure for cutting external thread. . . . . . 2.97

2.9.5 Cutting Internal thread procedure . . . . . . . 2.102

2.9.6 Cutting Left hand threads . . . . . . . . . . . . . . 2.102

2.9.7 Cutting Tapererd threads . . . . . . . . . . . . . . . 2.103

2.9.8 Square thread cutting . . . . . . . . . . . . . . . . . . 2.103

2.9.9 Cutting Multiple Start threads . . . . . . . . . . 2.104

2.10 Special Attachments . . . . . . . . . . . . . . . . . . . . . . 2.1052.10.1 Milling Attachment . . . . . . . . . . . . . . . . . . . 2.105

2.10.2 Grinding Attachment . . . . . . . . . . . . . . . . . . 2.106

2.10.3 Gear cutting on Lathe. . . . . . . . . . . . . . . . . 2.107

2.11 Machining Time and Power Calculation. . . . . 2.107

2.12 Capstan and Turret Lathe . . . . . . . . . . . . . . . . . 2.1162.12.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . 2.116

2.12.2 Capstan and Turret lathe . . . . . . . . . . . . . 2.117

2.12.2.1 Principle parts of Capstan and Turretlathe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.119

2.12.3 Types of Turret Lathes. . . . . . . . . . . . . . . . 2.124

2.12.4 Difference between Capstan - Turret latheand Engine Lathe. . . . . . . . . . . . . . . . . . . . . . 2.125

2.12.5 Difference between Capstan and Turret lathe . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.127

2.12.6 Size and specification of Turret Lathe. . . 2.128

2.12.7 Work holding devices . . . . . . . . . . . . . . . . . 2.129

2.12.8 Tool holding devices . . . . . . . . . . . . . . . . . . 2.131

2.12.9 Turret Tools . . . . . . . . . . . . . . . . . . . . . . . . . 2.139

2.12.10 Tooling layout for Capstan and Turret Lathes . . . . . . . . . . . . . . . . . . . . . . . . . 2.139

2.13 Automats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.150

2.14 Automation Mechanisms on Capstan and TurretLathes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.167

2.14.1 Turret Indexing Mechanism or GenevaMechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.167

2.14.2 Bar Feeding Mechanism . . . . . . . . . . . . . . . 2.169

CHAPTER - 3Other Machine Tools

3.1 Reciprocating Machine Tools . . . . . . . . . . . . . . . . . . 3.1

3.2 Shaper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1

3.3 Parts of a shaper. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6

3.4 Shaper drive mechanisms. . . . . . . . . . . . . . . . . . . . . 3.8

3.5 Feed Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.15


3.6 Work holding devices in shaper. . . . . . . . . . . . . . 3.16

3.7 Shaper Operations . . . . . . . . . . . . . . . . . . . . . . . . . 3.20

3.8 Shaper tools (Shaper cutting tools) . . . . . . . . . . . 3.23

3.9 Shaper Cutting Speed, Feed and Depth of Cut 3.26

3.10 Planing Machine . . . . . . . . . . . . . . . . . . . . . . . . . . 3.28

3.11 Planer Size and Specifications . . . . . . . . . . . . . . 3.33

3.12 Main parts of a planer . . . . . . . . . . . . . . . . . . . . 3.33

3.13 Driving mechanism. . . . . . . . . . . . . . . . . . . . . . . . 3.36

3.14 Electrical drive: (Table drive by reversibleElectric motor). . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.38

3.15 Types of tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.40

3.16 Planer operations . . . . . . . . . . . . . . . . . . . . . . . . . 3.42

3.17 Slotter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.44

3.18 Specification of slotter . . . . . . . . . . . . . . . . . . . . . 3.46

3.19 Drives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.46

3.20 Feed mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 3.48

3.21 Work holding devices . . . . . . . . . . . . . . . . . . . . . . 3.50

3.22 Slotter tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.52

3.23 Slotter operations . . . . . . . . . . . . . . . . . . . . . . . . . 3.52

3.24 Milling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.55

3.25 Milling Machine . . . . . . . . . . . . . . . . . . . . . . . . . . 3.55

3.26 Size and specification of milling machine . . . . 3.64Comparison between plain and universal millingmachine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.65

3.27 Work holding devices . . . . . . . . . . . . . . . . . . . . . . 3.65

3.28 Cutter holding device (or) Tool holding device 3.70

3.29 Milling Machine Attachments. . . . . . . . . . . . . . . 3.71

3.30 Milling Cutters . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.731. Plain milling cutter . . . . . . . . . . . . . . . . . . . . . 3.74

2. Side milling cutter . . . . . . . . . . . . . . . . . . . . . . 3.75

3. End Mill Cutters . . . . . . . . . . . . . . . . . . . . . . . 3.76

4. Angle milling cutter . . . . . . . . . . . . . . . . . . . . . 3.77

5. Form milling cutters . . . . . . . . . . . . . . . . . . . . 3.78

6. Metal slitting saw cutters . . . . . . . . . . . . . . . . 3.78

7. T-slot milling cutters . . . . . . . . . . . . . . . . . . . . 3.79

8. Fly cutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.79

3.31 Nomenclature of plain milling cutter . . . . . . . . . 3.79

3.32 Cutter Angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.81

3.33 Fundamentals of the milling process. . . . . . . . . 3.82

1. Peripheral milling . . . . . . . . . . . . . . . . . . . . . . . . . 3.83

(i) Up milling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.84

(ii) Down milling. . . . . . . . . . . . . . . . . . . . . . . . . . 3.84

2. Face milling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.85

3.34 Milling Operations . . . . . . . . . . . . . . . . . . . . . . . . . 3.85

(i) Plain (or) Slab milling . . . . . . . . . . . . . . . . . . 3.86

(ii) Face milling . . . . . . . . . . . . . . . . . . . . . . . . . 3.86

(iii) Angular milling . . . . . . . . . . . . . . . . . . . . . . . 3.86

(iv) Straddle Milling . . . . . . . . . . . . . . . . . . . . . . . 3.87

(v) Gang Milling . . . . . . . . . . . . . . . . . . . . . . . . . . 3.87

(vi) End Milling. . . . . . . . . . . . . . . . . . . . . . . . . . . 3.88

(vii) Form Milling . . . . . . . . . . . . . . . . . . . . . . . . . 3.88

(viii) Gear Cutting . . . . . . . . . . . . . . . . . . . . . . . . 3.89

(ix) T-slot milling . . . . . . . . . . . . . . . . . . . . . . . . . 3.89

(x) Side Milling . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.89

3.35 Indexing (or) Dividing Heads . . . . . . . . . . . . . . . 3.89

3.36 Indexing Method . . . . . . . . . . . . . . . . . . . . . . . . . . 3.92

3.37 Hole Making . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.93

3.37.1 Drilling Machine . . . . . . . . . . . . . . . . . . . . . . 3.93

3.37.2 Classification of drilling machine . . . . . . . . 3.93

3.38 Specification of drilling machine . . . . . . . . . . . . 3.102

3.39 Feed mechanism. . . . . . . . . . . . . . . . . . . . . . . . . . 3.102


3.40 Drilling operations . . . . . . . . . . . . . . . . . . . . . . . 3.103(i) Drilling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.104

(ii) Reaming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.106

(iii) Boring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.106

(iv) Counter boring . . . . . . . . . . . . . . . . . . . . . . . 3.106

(v) Counter sinking . . . . . . . . . . . . . . . . . . . . . . . 3.107

(vi) Spot facing . . . . . . . . . . . . . . . . . . . . . . . . . . 3.107

(vii) Tapping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.107

(viii) Grinding . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.108

(ix) Lapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.108

(x) Trepanning . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.108

3.41 Drill Tool Nomenclature . . . . . . . . . . . . . . . . . . 3.109

3.42 Drill holding devices. . . . . . . . . . . . . . . . . . . . . . 3.112

3.43 Reaming tools . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.115

3.43.1 Types of Reamers. . . . . . . . . . . . . . . . . . . . . 3.116

3.44 Tapping Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.117

3.45 Drilling parameters calculations. . . . . . . . . . . . 3.121

3.46 Solved Problems . . . . . . . . . . . . . . . . . . . . . . . . . 3.124

3.47 Boring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.126

3.47.1 Types of boring machines . . . . . . . . . . . . . . 3.126

3.48 Horizontal boring machine . . . . . . . . . . . . . . . . 3.127

3.49 Vertical Boring Machine: (VBM) . . . . . . . . . . . 3.130

3.50 Horizontal boring machine operations. . . . . . . 3.134

3.51 Vertical boring machine operations . . . . . . . . . 3.135

3.52 Boring cutting tools . . . . . . . . . . . . . . . . . . . . . . 3.136

3.53 Precision boring machine. . . . . . . . . . . . . . . . . . 3.137

3.54 Jig boring machine . . . . . . . . . . . . . . . . . . . . . . . 3.138

3.55 Sawing Machines . . . . . . . . . . . . . . . . . . . . . . . . 3.140

3.56 Selection of Blade for Sawing Machine . . . . . 3.143

3.57 Broaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1443.57.1 Types of broaching machines . . . . . . . . . . . 3.145

3.58 Size and specification of broaching machines. 3.152

3.59 Tool Nomenclature. . . . . . . . . . . . . . . . . . . . . . . . 3.153

3.60 Broaching Operations . . . . . . . . . . . . . . . . . 3.156-157

CHAPTER - 4Abrasive Processes and Gear Cutting

4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1

4.2.1 Abrasives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2

4.2.2 Natural Abrasives . . . . . . . . . . . . . . . . . . . . . . . 4.4

(i) Sandstone or solid quartz. . . . . . . . . . . . . . . . . 4.4

(ii) Emery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5

(iii) Corundum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5

(iv) Diamonds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5

(v) Garnet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5

4.2.3 Artificial Abrasives . . . . . . . . . . . . . . . . . . . . . . 4.6

(i) Silicon Carbide (SiC). . . . . . . . . . . . . . . . . . . . . 4.6

(ii) Aluminium oxide Al2O3 . . . . . . . . . . . . . . . . . 4.7

(iii) Boron carbide . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7

(iv) Cubic Boron Nitride (CBN) . . . . . . . . . . . . . . 4.8

4.2.4 Abrasive grain size or Grit Number andGeometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9

4.3 Grinding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10

4.3.1 Principle of Grinding. . . . . . . . . . . . . . . . . . . . 4.11

4.3.2 Mechanics of Grinding . . . . . . . . . . . . . . . . . . 4.12

4.4 Grinding Wheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.14

4.4.1 Characteristics of Grinding wheel . . . . . . . . . 4.15

4.4.1.1 Type of abrasive used . . . . . . . . . . . . . . . 4.15

4.4.1.2 Grain size or Grit size. . . . . . . . . . . . . . . 4.15

4.4.1.3 Wheel Grade and Hardness . . . . . . . . . . 4.15

4.4.1.4 Grain spacing or structure . . . . . . . . . . . 4.16

4.4.1.5 Type of Bond. . . . . . . . . . . . . . . . . . . . . . . 4.17


(a) Vitrified bond . . . . . . . . . . . . . . . . . . . . . . . . . . 4.18

(b) Silicate bond. . . . . . . . . . . . . . . . . . . . . . . . . . . 4.19

(c) Shellac bond . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.20

(d) Rubber bonding . . . . . . . . . . . . . . . . . . . . . . . . 4.21

(e) Bakelite or Resinoid bond. . . . . . . . . . . . . . . . 4.22

(f) Oxychloride bond . . . . . . . . . . . . . . . . . . . . . . . 4.22

4.4.1.6 Size and shape . . . . . . . . . . . . . . . . . . . . . 4.23

4.4.2 Mounted wheels . . . . . . . . . . . . . . . . . . . . . . . . 4.26

4.5 Specification and selection of Grinding wheel . . 4.264.5.1 Standard marking system of Grinding

wheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.26

4.5.2 Selection of Grinding wheels . . . . . . . . . . . . . 4.27

4.6 Glazing, Loading and Gumming of Grindingwheels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.32

(i) Glazing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.32

(ii) Loading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.32

(iii) Gumming. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.33

4.7 Dressing and Truing of Grinding wheel. . . . . . . 4.33(i) Dressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.33

(ii) Truing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.36

4.8 Balancing of Grinding Wheel . . . . . . . . . . . . . . . . 4.36

4.9 Mounting of Grinding Wheels . . . . . . . . . . . . . . . 4.37

4.10 Parameters In Grinding. . . . . . . . . . . . . . . . . . . . 4.39

4.11 Types of Grinding Machines and Processes . . . 4.40

4.11.1 Rough grinders . . . . . . . . . . . . . . . . . . . . . . . . 4.42

(a) Floor stand grinder and bench grinder . . . . 4.42

(b) Portable and Flexible shaft grinder . . . . . . . 4.43

(c) Swing frame grinder . . . . . . . . . . . . . . . . . . . . 4.43

(d) Abrasive belt grinders . . . . . . . . . . . . . . . . . . . 4.44

4.11.2 Precision grinding machines . . . . . . . . . . . . . 4.45

4.11.3 Cylindrical grinding (centre type)machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.45

(i) Traverse grinding . . . . . . . . . . . . . . . . . . . . . . . 4.47

(ii) Plunger type grinding. . . . . . . . . . . . . . . . . . . 4.47

4.11.3.1 Plain centre type grinder. . . . . . . . . . . . 4.48

Parts of plain centre type grinder . . . . . . . . . . . 4.48

4.11.3.2 Universal centre type grinder . . . . . . . . 4.50

4.11.3.3 Plunge-centre type grinding machine . . 4.52

4.11.4 Centre-less type grinding machines . . . . . . 4.52

(i) Through feed. . . . . . . . . . . . . . . . . . . . . . . . . . . 4.54

(ii) In-feed centreless grinding (plunge cut grinding) . . . . . . . . . . . . . . . . . . . . . . 4.55

(iii) End-feed centreless grinding. . . . . . . . . . . . . 4.56

4.11.5 Internal Grinders . . . . . . . . . . . . . . . . . . . . . . 4.57

(i) Work rotating type or chucking type . . . . . . . 4.58

(ii) Planetary type . . . . . . . . . . . . . . . . . . . . . . . . . 4.59

(iii) Centreless internal grinding . . . . . . . . . . . . . 4.60

4.11.6 Surface grinding machines . . . . . . . . . . . . . . 4.61

(i) Planar or reciprocating table type . . . . . . . . . 4.63

(ii) Rotary table type. . . . . . . . . . . . . . . . . . . . . . . 4.64

4.11.7 Tool and cutter grinder . . . . . . . . . . . . . . . . 4.66

4.11.8 Special grinding machines . . . . . . . . . . . . . . 4.68

4.12 Microfinishing Processes . . . . . . . . . . . . . . . . . . . . 4.70

4.12.1 Honing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.71

4.12.1.1 Honing tool . . . . . . . . . . . . . . . . . . . . . . . . . 4.72

4.12.2 Lapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.74

4.12.2.1 Methods of lapping. . . . . . . . . . . . . . . . . 4.75

(i) Individual piece lapping . . . . . . . . . . . . . . . . . 4.76

(ii) Matched piece lapping . . . . . . . . . . . . . . . . . . 4.76

(iii) Hand lapping . . . . . . . . . . . . . . . . . . . . . . . . . 4.76

(iv) Machine lapping. . . . . . . . . . . . . . . . . . . . . . . 4.77

4.12.2.2 Types of lapping operations . . . . . . . . . 4.79

4.12.3 Super finishing . . . . . . . . . . . . . . . . . . . . . . . . 4.80

4.13 Buffing and polishing . . . . . . . . . . . . . . . . . . . . . . 4.81


4.13.1 Polishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.82

4.13.2 Buffing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.83

4.14 Abrasive Jet Machining (AJM). . . . . . . . . . . . . . 4.84

4.15 Gear Cutting and Manufacture . . . . . . . . . . . . . 4.89

4.15.2 Gear manufacturing methods . . . . . . . . . . . . 4.89

(i) Non machining process (forming process) . . . 4.89

(ii) Machining process . . . . . . . . . . . . . . . . . . . . . . 4.90

4.15.3 Form cutting processes . . . . . . . . . . . . . . . . . 4.90

4.15.3.1 Gear cutting using End cutter/End millin milling machine . . . . . . . . . . . . . . . . . . . . . . . . 4.91

4.15.3.2 Procedure for spur gear cutting in millingmachine by formed cutter . . . . . . . . . . . . . . . . . . . 4.93

4.15.3.4 Indexing and dividing heads. . . . . . . . . 4.93

4.15.3.5 Indexing methods . . . . . . . . . . . . . . . . . . 4.95

Simple Indexing . . . . . . . . . . . . . . . . . . . . . . . . . . 4.97

Compound Indexing. . . . . . . . . . . . . . . . . . . . . . . . 4.98

Differential Indexing . . . . . . . . . . . . . . . . . . . . . . . 4.99

4.15.4 Helical gear milling by form disc cutter . 4.102

4.15.5 Gear cutting by a single point cutting tool(Formed tool) . . . . . . . . . . . . . . . . . . . . . . . . . . 4.105

4.15.6 Gear cutting by formed end mill. . . . . . . . 4.105

4.15.7 Gear cutting by shear speed process . . . . 4.106

4.15.8 Gear cutting by template method . . . . . . . 4.106

4.15.9 Gear generating processes . . . . . . . . . . . . . 4.107

4.15.9.1 Gear planing process (Rack cuttergenerating process). . . . . . . . . . . . . . . . . . . . . . . . 4.108

4.15.9.2 Gear shaping process (pinion cuttergenerating method) . . . . . . . . . . . . . . . . . . . . . . . 4.110

4.15.9.3 Gear hobbing process . . . . . . . . . . . . . . 4.113

Gear hobbing machines. . . . . . . . . . . . . . . . . . . . 4.117

4.15.10 Gear forming (Non machining methods) 4.119

4.15.10.1 Casting . . . . . . . . . . . . . . . . . . . . . . . . . 4.119

4.15.10.2 Hot rolling . . . . . . . . . . . . . . . . . . . . . . 4.119

4.15.10.3 Stamping . . . . . . . . . . . . . . . . . . . . . . . 4.119

4.15.10.4 Powder-metallurgy . . . . . . . . . . . . . . . 4.120

4.15.10.5 Extruding . . . . . . . . . . . . . . . . . . . . . . . 4.120

4.15.10.6 Coining . . . . . . . . . . . . . . . . . . . . . . . . . 4.120

Chapter 5CNC Machine Tools and Part Programming

5.1 Numerical Control (NC) Machine Tools. . . . . . . . . 5.1

5.2 CNC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2

5.5 CNC System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3

5.6 Basic components of CNC system. . . . . . . . . . . . . . 5.5

5.7 Standard Axes of Machine Tool . . . . . . . . . . . . . . . 5.8

5.8 Feed Back Device . . . . . . . . . . . . . . . . . . . . . . . . . . 5.14

5.9 Classification of CNC Systems . . . . . . . . . . . . . . . 5.14

5.10 Classification of CNC Based on Feed Back Control 5.15

5.11 Open Loop Control System . . . . . . . . . . . . . . . . . 5.15

5.12 Closed loop control system. . . . . . . . . . . . . . . . . . 5.17

5.13 Classification of CNC based on motion controlsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.19

5.13.1 Point to Point (Positional) control system (PTP) . 5.20

5.13.2 Straight line Paraxial Motion control system(or) Straight Cut control system: . . . . . . . . . 5.22

5.13.3 Contouring control system (Continuous pathcontrol system): . . . . . . . . . . . . . . . . . . . . . . . . . 5.22

5.14 Interpolators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.25

5.15 Absolute Positioning System . . . . . . . . . . . . . . . . 5.26

5.16 Incremental coordinate system . . . . . . . . . . . . . . 5.28

5.17 CNC controllers . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.29

5.17.1 Functions of CNC Controllers . . . . . . . . . . . 5.30

5.18 Direct Numerical Control (DNC system) . . . . . . 5.31


5.18.1 Components of DNC system. . . . . . . . . . . . . 5.32

5.18.2 Advantages of DNC . . . . . . . . . . . . . . . . . . . . 5.34

5.19 Design consideration of CNC machines forimproving machining accuracy . . . . . . . . . . . . . 5.34

5.19.1 Factors affecting CNC machine’s accuracy 5.35

5.19.2 Factors to be considered for testing theperformance of a CNC machine . . . . . . . . . . . 5.35

5.20 Control System Design . . . . . . . . . . . . . . . . . . . . 5.36

5.20.1 Analog Control System . . . . . . . . . . . . . . . . . 5.37

5.20.2 Digital Control System . . . . . . . . . . . . . . . . . 5.37

5.20.3 Punched tape (or) Magnetic Tape (or)Pendrive (USB) (or) CD . . . . . . . . . . . . . . . . . . 5.38

5.20.4 Open loop vs Closed loop system . . . . . . . . 5.38

5.20.5 Linear vs Rotary Transducers . . . . . . . . . . . 5.39

5.21 Mechanical System Design . . . . . . . . . . . . . . . . . 5.39

5.22 Main Structural Members of CNC MachineTools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.40

5.23 Slides and Slideways (or) Guide Ways . . . . . . . 5.44

5.24 Friction Slideways (Wear resistant slideways) 5.46

5.24.1 V-slideways . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.49

5.24.2 Flat and Dovetail Slideways . . . . . . . . . . . . 5.50

5.24.3 Cylindrical guideways . . . . . . . . . . . . . . . . . . 5.50

5.25 Anti Friction Linear Motion (LM) Guideways . 5.51

5.25.1 Recirculating linear ball bearings (forslide ways) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.51

5.25.2 Recirculating Ball Bush (for slide ways) . . 5.52

5.25.3 Recirculating Ball Screw and nut (forslideways) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.53

5.26 Hydrostatic Type Slideways . . . . . . . . . . . . . . . . 5.56

5.27 Aerostatic Slideways. . . . . . . . . . . . . . . . . . . . . . . 5.57

5.28 Spindle Drives and Feed Drives . . . . . . . . . . . . . 5.57

5.29 Work Holding Devices. . . . . . . . . . . . . . . . . . . . . . 5.64

5.29.1 Requirements of work holding devices . . . . 5.66

5.29.2 Linear Pallet shuttle . . . . . . . . . . . . . . . . . . . 5.66

5.29.3 Rotary Pallet . . . . . . . . . . . . . . . . . . . . . . . . . 5.68

5.30 Tool Holding Devices. . . . . . . . . . . . . . . . . . . . . . . 5.70

5.30.1 Spindle Tooling. . . . . . . . . . . . . . . . . . . . . . . . 5.70

5.31 Automatic Tool Changers . . . . . . . . . . . . . . . . . . . 5.74

5.31.2 Tool Magazine - Turret. . . . . . . . . . . . . . . . . 5.75

5.31.3 Chain Type Tool Magazine . . . . . . . . . . . . . 5.76

5.31.4 Tool changing . . . . . . . . . . . . . . . . . . . . . . . . . 5.77

5.32 Feed Back Devices. . . . . . . . . . . . . . . . . . . . . . . . . 5.795.32.3.1 Linear Transducers. . . . . . . . . . . . . . . . . 5.81

1. Glass scales with line grating . . . . . . . . . . . . 5.82

2. Ferranti system (using Moire Fringe effect) . 5.83

3. Binary Coded Scale . . . . . . . . . . . . . . . . . . . . . 5.84

4. Inducto syn . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.85

5.32.3.2 Rotary transducer (Angular positionmeasuring transducer) . . . . . . . . . . . . . . . . . . . . . 5.86

(a) Absolute Encoder . . . . . . . . . . . . . . . . . . . . . . . 5.86

(b) Incremental encoder . . . . . . . . . . . . . . . . . . . . 5.88

Resolver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.90

5.33 Machining Centers. . . . . . . . . . . . . . . . . . . . . . . . . 5.91

5.33.1 Vertical Machining Centre: (VMC) . . . . . . . 5.92

5.33.2 Horizontal Machining Centre: (HMC). . . . . 5.92

5.33.3 Universal Machining Centre . . . . . . . . . . . . 5.93

5.34 Tooling for CNC Machines. . . . . . . . . . . . . . . . . . 5.94

5.35 Part Programming Fundamentals for CNCMachines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.100

5.35.1 Types of Words (or) Codes in CNC . . . . . 5.102

5.35.2 Standard Formats in Programming: . . . . . 5.110


1. Word Address Format . . . . . . . . . . . . . . . . . . 5.110

2. Tab sequential Format . . . . . . . . . . . . . . . . . . 5.112

3. Fixed Block Format . . . . . . . . . . . . . . . . . . . . 5.112

5.36 Manual Part Programming . . . . . . . . . . . . . . . . 5.1135.36.1 Part programming for PTP (Point to Point)

machining: . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.116

5.36.2 Part programming for machining along curvedsurface (Turning Operation). . . . . . . . . . . . . . 5.121

5.36.3 Part programming for Milling operations: 5.138

5.36.4 Subroutines (Macros) (L code) . . . . . . . . . . 5.144

5.36.5 Canned Cycles: [(or) Fixed cycle (or)Standardised cycle] . . . . . . . . . . . . . . . . . . . . . 5.152

5.36.6 Non-standarised Fixed cycles . . . . . . . . . . . 5.159

1. Do-Loops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.159

2. Parametric Subroutines . . . . . . . . . . . . . . . . . 5.160

3. Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.162

5.36.7 Mirroring . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.163

5.37 Computer Assisted Part Programming (CAP) 5.1641. APT [Automatically Programmed Tools] . . . 5.167

2. ADAPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.167

3. EXAPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.167

5.38 APT Language. . . . . . . . . . . . . . . . . . . . . . . . . . . 5.168

5.39 Four Types of Apt Statements . . . . . . . . . . . . . 5.168

5.40 Geometry Statement. . . . . . . . . . . . . . . . . . . . . . 5.169

5.41 Motion Statements . . . . . . . . . . . . . . . . . . . . . . . 5.178

5.42 Postprocessor Statements. . . . . . . . . . . . . . . . . . 5.183

5.43 Auxiliary Statement: . . . . . . . . . . . . . . . . . . . . . 5.1845.37.3 Macro Statement in APT . . . . . . . . 5.193 to 194


Chapter 1

THEORY OF METAL CUTTING

1.1 INTRODUCTION

Machining is a manufacturing process whichinvolves forcing of a cutting tool through the excessmaterial of the work piece thereby removing theunwanted material in the form of chips, so as to obtainthe final desired shape and size to the work piece. It maybe emphasized that the cutting tool never peels off chipsor the excess material from the work piece, but the chipsare generated because of plastic deformation of metal justahead of the cutting edge of the tool. Machining isnormally the most expensive manufacturing processbecause more energy is consumed and a lot of wastematerial is generated in the process. Still, machining iswidely used because,

It delivers very good dimensional accuracy and goodsurface finish.

Machine tools does not require elaborate tooling.

Machining can be employed to all engineeringmaterials.

It can also generate accurate contours with hightolerances.

The wear of tool is not costly, if it is kept withinlimit.

Large number of parameters can be suitablycontrolled during machining.

1.1.1 Types of motion in machiningFor machining, it is necessary to have relative

motions between the work piece and tool. Two types ofrelative motions are necessary. For example, to drill ahole, we have to rotate the drill or work piece and besidesthis, we have to press the drill against the work piece.The first motion (i.e rotation of drill or work piece) iscalled the primary or cutting motion and the secondmotion (pressing of drill) is called feed motion.

In turning a circular cylinder on lathe, the cuttingmotion is obtained by rotation of the workpiece, and feedmotion forms the motion of tool parallel or perpendicularto work piece axis and normal to the cutting motion. Thecutting speed is the rate of primary cutting motion andit determines the rate at which the material is beingremoved.

In all machine tools, the primary cutting motion ispowered. Apart from small machines with hand feeds,feed motions on most of the machine tools are alsopowered. Auxiliary or handling motion helps to handlingand clamping of the work piece in the machine, advancingthe cutting tool to engage the work piece, positioning thetool in desired orientation with respect to workpiece,disengaging tool, withdrawing tool, removing machinedwork piece. On manually operated machine tools,auxiliary motions are performed manually by operator. Inautomatic machine tools, the auxiliary motions arecarried out in the required sequence by the machineitself.

Theory of Metal Cutting 1.1 Manufacturing Technology - II1.2

Chapter 1

THEORY OF METAL CUTTING

1.1 INTRODUCTION

Machining is a manufacturing process whichinvolves forcing of a cutting tool through the excessmaterial of the work piece thereby removing theunwanted material in the form of chips, so as to obtainthe final desired shape and size to the work piece. It maybe emphasized that the cutting tool never peels off chipsor the excess material from the work piece, but the chipsare generated because of plastic deformation of metal justahead of the cutting edge of the tool. Machining isnormally the most expensive manufacturing processbecause more energy is consumed and a lot of wastematerial is generated in the process. Still, machining iswidely used because,

It delivers very good dimensional accuracy and goodsurface finish.

Machine tools does not require elaborate tooling.

Machining can be employed to all engineeringmaterials.

It can also generate accurate contours with hightolerances.

The wear of tool is not costly, if it is kept withinlimit.

Large number of parameters can be suitablycontrolled during machining.

1.1.1 Types of motion in machiningFor machining, it is necessary to have relative

motions between the work piece and tool. Two types ofrelative motions are necessary. For example, to drill ahole, we have to rotate the drill or work piece and besidesthis, we have to press the drill against the work piece.The first motion (i.e rotation of drill or work piece) iscalled the primary or cutting motion and the secondmotion (pressing of drill) is called feed motion.

In turning a circular cylinder on lathe, the cuttingmotion is obtained by rotation of the workpiece, and feedmotion forms the motion of tool parallel or perpendicularto work piece axis and normal to the cutting motion. Thecutting speed is the rate of primary cutting motion andit determines the rate at which the material is beingremoved.

In all machine tools, the primary cutting motion ispowered. Apart from small machines with hand feeds,feed motions on most of the machine tools are alsopowered. Auxiliary or handling motion helps to handlingand clamping of the work piece in the machine, advancingthe cutting tool to engage the work piece, positioning thetool in desired orientation with respect to workpiece,disengaging tool, withdrawing tool, removing machinedwork piece. On manually operated machine tools,auxiliary motions are performed manually by operator. Inautomatic machine tools, the auxiliary motions arecarried out in the required sequence by the machineitself.

Theory of Metal Cutting 1.1 Manufacturing Technology - II1.2 www.airwalkpublications.com

1.2 METAL REMOVAL PROCESSES

Metal removal process is a manufacturing processby which a work piece is given (i) a desired shape (ii)a desired size and (iii) a desired surface finish.

To achieve one or all of these, the excess materialfrom the work piece is removed in the form of chips withthe help of some properly shaped and sized tools. Themetal removal processes are chip forming processes.

1.2.1 Classification of Metal Removal Processes

Metal removal processes are broadly classified intotwo categories.

(i) Chip forming (Metal Cutting / Removal)Processes: Examples are Turning, Boring,Shaping, Planing, Slotting, Drilling, Reaming,Milling, Broaching, Thread Cutting, Grinding,Honing, Gear cutting etc.,

(ii) Chipless Forming Processes: Examples areRolling, Spinning, Forging, Extrusion, Stampingetc.,

1.2.2 Chip forming Processes

Chip forming processes are manufacturing processesin which the desired shape, size and surface finish ofwork piece is obtained by separating layer from parentworkpiece in the form of chips, whereas in chiplessforming processes no chips are formed.

1.2.3 Turning, Boring and other Lathe Operations

Traditional machining operations like turning,boring, facing, grooving, thread cutting, drilling,chamfering etc are carried out on a machine tool called

Lathe. Lathe is one of the most important machine inany workshop. Its main objective is to remove materialfrom outside by rotating the work against a cutting tool.The various Lathe Operations are discussed as below.

Turning: Turning is a machining operation forgenerating external surfaces of revolution (cone-shaped orcylindrical shaped) on the workpiece. In turning, work isrotated where as tool has a linear motion, parallel to theaxis of the work. In this operation, the work is held eitherin the chuck or between centers and the longitudinal feedis given to the tool either by hand or power. Turningoperation is shown in Fig. 1.1. The turning operation inwhich there are steps on the work is called step turningas shown in Fig 1.2

Facing: When the feed motion of the tool is axial i.eparallel to the work piece axis, a cylindrical surface isgenerated. If on the other hand, feed motion is radial(normal to the axis of rotation), an end face or shoulderis produced. This operation is called facing as shown inFig. 1.3.

W ork

ChuckChuck

W ork

Fig 1.3 FacingFig 1.1 Plain turning

Chuck

W ork

Fig 1.2 Step turning


Boring: Boring is a machining operation for generatinginternal surface of revolution i.e., it is an operation ofenlarging of a hole already made in workpiece with thehelp of a single point tool called boring tool. Boring toolis held in the tool post and fed into the work by handor power by movement of carriage. Boring is shown inFig. 1.4

Drilling: Drilling is an operation of making a hole in aworkpiece with the help of a drill. In this operation, thework piece is held in the chuck and drill is held in thetail stock. The drill is fed manually into the rotatingworkpiece by rotating the tailstock hand wheel. Drillingis shown in Fig. 1.5.

Reaming: Reaming is an operation of finishing thepreviously drilled hole. In this operation as shown in Fig.1.6, a reamer tool is held in tail stock and it is fed intothe hole in the similar way as for drilling.

Undercutting or Grooving: It is an operation ofmaking a groove on the body of work, by feeding the toolperpendicular to the axis of the workpiece. In this

operation as shown in Fig 1.7, a tool of appropriate shapeis fed into the rotating work piece upto the desired depthat right angles to the centre line of the work piece.

Threading: It is an operation of cutting helical grooves(threads) on the external cylindrical surface of workpieceas shown in Fig. 1.8. The work is held in a chuck orbetween centers and the threading tool (V-tool) is fedlongitudinally to the rotating workpiece. The longitudinalfeed is equal to the pitch of the thread to be cut.

C huck

W ork

Boring tool

Fig 1.4 Boring Fig 1.5 Drilling

C huck

W ork

D rill

Chuck

W ork

Tool

Fig 1.7 Under cutting

Chuck

W orkReam er

Fig 1.6 Ream ing

W ork

Fig 1.8 Threading

Threading V -Tool

W ork

KnurlingTool

Fig 1.9 Knurling


Knurling: Knurling is a process of impressing diamondshaped or straight line pattern on to the surface of awork piece. The diamond shaped pattern or impressionsare called knurls. In this operation, a knurled tool ismoved longitudinally to a rotating workpiece. Theprojection on the knurled tool reproduces depressions onthe work surface as shown in Fig. 1.9.

1.2.3.1 Machining parameters and related terms inturning operation

The different machining parameters or variables inturning are discussed below (Refer Fig. 1.10)

Cutting speed (V): Cutting speed is the relativevelocity between work piece and cutting edge of toolresponsible for cutting action. It is given by relationship

V DN1000

in m/min

where D Diameter of work at engagement

N Rotational speed of work in RPM

Uncut chip thickness: It is the thickness of the layerof material being removed by the cutting tool in thedirection of the feed motion. The feed in turning isnormally expressed in mm per revolution.

Uncut chip thickness t f cos s

where f Feed per revolution.

s Side cutting edge angle of turning tool.

Depth of cut: It is the normal distance between themachined and unmachined surfaces measured along anormal to the machined surface. In turning, it is theradial distance between machined and unmachinedsurface. From the Fig. 1.10, the cutting edge engagementis ‘b’ while the depth of cut is ‘d’, hence,

Depth of Cut d b cos s

Area of Uncut Chip: It is the cross sectional areaAc of the layer of the work being machined.

Area of Uncut chip Ac f d.

Metal removal rate (Rw: It is the volume of material

being removed per unit time from the work piece.

Rw 1000 f d V in mm3/min

Here, f, d are in mm, V is in m/min

Machining time: If L is the length of workpiece to beturned, then the time of cutting Tc per pass is given by

W ork piece

Direction of rotation

b

d

fTool

Position of Tool at start

Position of Tool afterone revolution

s

Fig 1.10 Geometry of Cut in Turning


Time Tc L/f N

In machining, however tool is not positioned indirect contact with the work piece at the start of cut. Itis kept at a small distance away from the job. This iscalled approach allowance or approach length la. Then,

The Machining Time Tm L la

f N

Problem 1.1 Evaluate the machining time for turning of a100 mm diameter rod to 92 mm diameter over a length of60 mm at a spindle speed of 500 RPM. The maximum depthof cut is limited to 3 mm and the feed f is 0.5 mm per rev.

The side cutting edge angle of the tool is 30. Approach

allowance 5 mm. Also calculate cutting speed for each pass.

Given: Initial diameter Di 100 mm, Final diameter

Df 92 mm, Length L 60 mm,

Speed N 500 RPM, d 3 mm,

f 0.5 mm/rev, s 30, la 5 mm

Solution

Total diameter to be reduced

Di Df 100 92 8 mm

Diameter reduced in one pass d 2 3 2 6 mm

No. of pass required to reduce 8 mm 2 pass.

One Rough pass of 3 mm depth of cut and onefinish pass of 1 mm depth of cut.

3 2 1 2 8 mm

Cutting Speed for 1st rough pass

V1 DiN

1000

100 5001000

157.1 m/min

Cutting Speed for 2nd finish pass

V2 Di 6 N

1000

94 5001000

147.6 m/min

Since for both the passes, the spindle speed andfeed are common

Machining time Tm No. of passes L la

f N

Tm 2 60 50.5 500

2.4 mins

1.2.4 Shaping, Planing and Slotting

Shaping is a machining operation for generatingflat surface by means of single point cutting toolreciprocating over a stationary work piece. The feedmotion is intermittent i.e. imparted to the work piece atthe end of each stroke. The reciprocating motion of thetool is obtained either by the crank and slotted leverquick return motion mechanism or whitworth quickreturn motion mechanism. The shaping action is shownin the Fig. 1.11. The surfaces produced in shaping maybe horizontal, vertical or inclined. Shaping is performedon the machine tool called shaper. In general, shaper canproduce any surface composed of straight line elements.

Some of examples of the parts produced by shapingoperation are shown in Fig. 1.12


Planing is a machining operation similar to shapingoperation primarily intended to produce plane and flatsurfaces by a single point cutting tool. The fundamentaldifference between a shaping and planing is that inplaning the work which is supported on the tablereciprocates past the stationary cutting tool and the feedis supplied by the lateral movement of the tool, whereasin shaping the tool which is mounted upon the ramreciprocates and the feed is given by the crosswisemovement of the table. Planing operations are carried onmachine tool called “planer”.

Slotting operation falls into the category of shaping andplaning. The major difference between a slotting andshaping is that in a slotting, the ram holding the toolreciprocates in a vertical axis, whereas in shaping theram holding the tool reciprocates in a horizontal axis. Avertical shaper and slotter are almost similar to eachother as regards their construction, operation and use.Slotting operation is used for cutting grooves, keyways,slots of various shapes, for cutting internal and externalgears etc.

1.2.4.1 Machining Parameters in Shaping, Planing

In shaping or planing, the cutting speed V varieseven in a single stroke. Cutting speed V is calculatedas follows.

Cutting Speed V N L 1

1000 in m/min

where N : No. of Complete Strokes per minute (oneworking stroke return stroke)

L : Length of stroke in mm;

(a) Grooved block (b) Dovetail slide

(c) Guide grib(d) V-block

1.12 Parts produced on a shaper

W ork P iece

f

d

ToolTool m otion

Fig 1.11 Shaping Action


: Ratio of time taken in return stroke to timetaken in cutting stroke.

Depth of Cut d: Depth of cut is equal to the normaldistance between the unmachined and machined surfacemeasured along a normal to the machined surface.

Nominal feed rate f is equal to the movement givento the workpiece in a shaper (or to the tool in planer) ina direction normal to other cutting velocity direction.

Area of uncut chip Ac f d

Metal removal rate Rw f d Lw N

Machining time Tm Bw

f N For Shaping

where Lw : Length of workpiece along stroke

Bw : Width of the workpiece

Machining Time for Planer

Tm Bw

fs

lsVc

1

Bw

fs tr.

where ls Length of stroke

fs Feed per stroke

Vc Average cutting speed in m/min

Average cutting speed to average returnspeed ratio

tr Time for reversal of work table.

1.2.5 Drilling and ReamingDrilling is a machining operation in which a hole

is produced or enlarged by use of a cutting tool calleddrill, usually having more than one cutting edge. Theprimary cutting motion is a rotary motion given to eitherwork piece or to drill and the feed motion is a translationmotion given to drill as shown in Fig. 1.13. The cuttingaction is done by the cutting edges on the end face.

Reaming is a hole finishing process. The motion of toolis similar as in case of drilling. Cutting edges of a reamerare on its periphery. These cutting edges are eitherstraight or helical.

Fig 1.13 Drilling Action

Drill

W ork piece

ft

b

b


1.2.5.1 Machining Parameters for Drilling

Cutting Speed V D N

1000 in m/min

where D Drill diameter in mmN Speed of drill in RPMd Depth of Cut d D/2

Feed f Feed per revolution of drill (or) movementof drill along its axis in one revolution.

Uncut chip thickness tc f cos

90 where 2 is point angle of drill.

Area of Uncut chip Ac f D/n 2

where n No. of cutting edges.

Metal removal rate Rw D2 f N

4 in mm3/min

Machining time Tm L

f N

where L Length of hole.

1.2.6 Milling

Milling is a machining process in which flat as wellas curved surfaces are produced by rotating multi-edgescutting tools called milling cutters and the work is fedpast it. The work piece is rigidly mounted on the machinetable and the cutter is on the spindle or arbor. The workis fed slowly past the cutter while the cutter revolves atfairly high speed. The main milling operations are

Slab milling,

Face milling,

Slot milling,

Form milling,

Angular milling etc.

These may be classified into two types i.e peripheralmilling and face milling. The operations are shown inFig. 1.14.

W ork piece

Cutter

(a)S lab m illing (b)Profile milling

(c) Gang milling (d) M illing with angle cutte r

(a) Slot m illing w ith end mill (b) Face m illing

Fig 1.14(b) End milling Operations on a Vertical Milling M achine

Fig 1.14(a) Peripheral milling Operations on a Horizontall Milling M achine


Following are the two methods commonly used inmilling operations.

(a) Conventional or up milling: In this method, thework is fed in a direction opposite to the rotation of themilling cutter Fig. No. 1.15 (a)

(b) Climb or down milling: In this method, the workis fed in the direction of rotation of cutter. Fig 1.15 (b)

Fig 1.15 (c) shows that the chips produced are notuniform in cross section. In up milling, each tooth startswith a minimum thickness and ends with maximumthickness (of the chip). In down milling, the reverse

happens i.e. each tooth starts with the maximumthickness and ends up with minimum. Total volume ofthe chip for a cut by a tooth is same in both the cases.

1.2.6.1 Machining Parameters in Milling

Cutting Speed V : It is the circumferential speedof cutter.

Cutting Speed V D N

1000 in m/min

where D Cutter diameter in mm,

N Speed of cutter in RPM.

In slab milling, the work piece is fixed on themachine table and feed motion is given by table whichis expressed in mm/min. If F is table feed in mm/minand f is feed per tooth of cutter, then.

f F

nc N mm/rev/tooth


Table S top

Cutte r

Conventional m illing

W ork

(a) Up m illingFig. 1.15. M illing Operation

TableS top

Cutte rC limb m illing

W ork

(b) Down m illingFig. 1.15. M illing Operation

t- dep th of cut

(c) Total cross - sectiona l a rea o f the uncut chipFig. 1.15. M illing Operation

Following are the two methods commonly used inmilling operations.

(a) Conventional or up milling: In this method, thework is fed in a direction opposite to the rotation of themilling cutter Fig. No. 1.15 (a)

(b) Climb or down milling: In this method, the workis fed in the direction of rotation of cutter. Fig 1.15 (b)

Fig 1.15 (c) shows that the chips produced are notuniform in cross section. In up milling, each tooth startswith a minimum thickness and ends with maximumthickness (of the chip). In down milling, the reverse

happens i.e. each tooth starts with the maximumthickness and ends up with minimum. Total volume ofthe chip for a cut by a tooth is same in both the cases.

1.2.6.1 Machining Parameters in Milling

Cutting Speed V : It is the circumferential speedof cutter.

Cutting Speed V D N

1000 in m/min

where D Cutter diameter in mm,

N Speed of cutter in RPM.

In slab milling, the work piece is fixed on themachine table and feed motion is given by table whichis expressed in mm/min. If F is table feed in mm/minand f is feed per tooth of cutter, then.

f F

nc N mm/rev/tooth


Table S top

Cutte r

Conventional m illing

W ork

(a) Up m illingFig. 1.15. M illing Operation

TableS top

Cutte rC limb m illing

W ork

(b) Down m illingFig. 1.15. M illing Operation

t- dep th of cut

(c) Total cross - sectiona l a rea o f the uncut chipFig. 1.15. M illing Operation

www.airwalkpublications.com

where nc No.of cutting edges or teeth on cutter.

w Width of work piece

d Depth of cut

Plane Area of cut Ac w d

Metal removal rate Rw w d F in mm3/min

Machining Time Tm lw A a1 a2

F

l2, Length of workpiece in the feed direction.

a1 and a2, over travels at beginning and end of cut.

A [D d] d

1.2.7 Broaching

Broaching is a machining operation in which amultitooth cutter called a broach is pushed or pulled overthe surface to be machined while keeping a desired

interference between broach teeth and the surface.Generally it is a single stroke operation. Broaching isgenerally limited to the removal of 6 mm of stock or less.A continuous Broaching Operation is shown in Fig 1.17.

1.2.8 Thread CuttingTapping and die cutting are machining operations

in which internal and external screw threads areproduced by the helical (cutting) motion of multi-pointtools called taps and dies respectively. Taps and dies canbe visualized as helical broaches. Nowadays thread rollingis very popular in manufacture of components like screwand bolts.

A schematic of cutting threads on a Lathe Machineis shown in Fig.1.18 by using a ‘V’ tool.

W ork piece

a2 a1

Fig 1.16 Approach Length and Over Travel in slab milling

Cutter Cutter

A

Unloading

Broach Suppo rt

Com ponentLoading

Suppo rt

Fixtures

Fig 1.17 A Continuous Broaching M achine


Let Nl Speed of lead screw in RPM,

Ns Speed of lathe spindle in RPM,

P, Pitch of thread to be cut and

l, Pitch of the lead screw.

Then, Ns P Nl l

Gear ratio Ns

Nl

lP

Pitch of lead screw

Pitch of thread to be cut

1.2.8.1 Machining Parameters in thread cutting

Cutting speed V D N

1000 in m/min.

D : Diameter of tool (tap of die) and

N : Speed of tool in RPM.

Feed Per min (f P N

Machining Time (Tm lw lt

f

Where P Pitch of thread

lw Length of surface of work

lt Length of tool

1.2.9 GrindingGrinding is a machining operation in which a

multi-edged rotating abrasive tool called grinding wheelremoves excess material from the work piece. Grindingis finishing operation removing material usually 0.25 to0.5 mm in most operations and accuracy in dimensionsis in order of 0.000025 mm. Typical grinding operationsare shown in Fig. 1.19.

Grinding operations are broadly classified as roughor non precision grinding and precision grinding.

1.2.10 Honing and LappingHoning and Lapping are fine finishing operations.

Very little stock is removed during these operations. Theyare used to correct dimensional and geometricalinaccuracies and to obtain high surface finish.


Head stock Chuck W ork piecep

Tool

Lead screwCarriageL

Changegears

Fig 1.18 A Schem atic View of Thread Cutting on Lathe

.

... ..... ...

..... .

.

....

.

....

.

......

.... ...

.. ..

...... .

....

.............

Fig 1.19 Basic kinds of precision grinding

Honing is fine finishing operation in which abrasivesticks are used as tool which rotate and simultaneouslyreciprocate on the surface of the workpiece and slowlyabrade the work piece surface to the desired finish andaccuracy. Though honing can be performed on lathes anddrilling machines, special honing machines, bothhorizontal and vertical are often used.

Lapping is a fine finishing operation in which a lapmade of material softer than the work piece lightly rubsabrasive particles against work piece. Flat or curvedsurface can be lapped.

1.2.11 Gear Cutting

Gears are important elements in mechanicaltransmission of power. Gears may be manufactured bycasting, stamping, machining or by powder metallurgicalprocesses. The most common and accurate method ofproduction of gears is by machining. The various methodsof machining gears are:

(a) Formed Cutter method

(i) By a formed disc cutter or formed end mill inmilling machine.

(ii) By a formed single point tool in shaping orplaning machine.

(iii) Formed cutter in a broaching machine.

(b) Generating Method

(i) By a rack tooth cutter in gear cutting machine.

(ii) By a pinion cutter in a gear cutting machine.

(iii) By a hob cutter in a gear cutting machine.

(iv) By a bevel gear generator.

1.3 TYPES OF MACHINE / CUTTING TOOLS

In metal cutting process chip removal is performedeither by cutting tools having distinct cutting edges or byabrasives used in grinding wheels, abrasive sticks,abrasive cloth etc.

Metal cutting tools are broadly classified as:

(a) Single point cutting tools.

(b) Multi point cutting tools.

A single point cutting tool has a wedge like actionand are used in lathe, shaping and slotting machines.

Two or more single point cutting tools whenarranged together as a unit in a specific manner formsa multipoint cutting tool and are used in milling machine,broaching machine etc.

A machine tool is a power driven device in whichenergy is utilized in deformation of material for shaping,sizing or processing a product by removing the excessmaterial in the form of chips.

Machine tools are generally used for two purpose.

(i) To produce certain forms on workpiece.

(ii) To produce finished surfaces on workpiece

The forms of the surfaces produced depend upon theshape of the cutting tool and the relative path of motionbetween the cutter and work piece.

Machine tools can be classified as


I. Based on type of surface generated(a) Machine Tools for Cylindrical Work: Examplesare

Lathes

Capstan and Turret lathes

Boring machine

Cylindrical Surface grinder.

(b) Machine Tools for flat surface work: Examplesare

Planer

Shaper

Slotter

Broaching by using single point cutting tool

Milling machine

Surface grinding machine by multipointcutting tool.

II. Types of Production(a) General Purpose or basic Machine Tools:Examples are

Lathes

Shaper

Drilling machines

Milling machine

Grinding machine

Planing machines etc.,

(b) Production Machine Tools: Examples are


Production milling machine

Multiple head drilling machine etc.

(c) Special Purpose or Single Purpose MachineTools: Examples are

Gear generators

Camshaft grinders

Piston turning lathes

Thread rolling machines etc.

(d) Flexible Manufacturing System (FMS):Examples:

Machining Centers

Versatile Machines and Robots

AGV’s (Automated Guided Vehicles) etc.,

1.4 PARTS AND NOMENCLATURE OF SINGLE

POINT CUTTING TOOL

The various parts of a single point cutting tool areshank, neck, face, base, heel, cutting edge or lip flank,point, height and width. A single point tool is shown inFig 1.20.

Parts of Single Point Cutting Tool

Shank : Shank is the main body of the tool at oneend of which the cutting portion is formed.

Neck : The portion which is reduced in section toform necessary cutting edges and angles iscalled the neck.


I. Based on type of surface generated(a) Machine Tools for Cylindrical Work: Examplesare

Lathes


Boring machine

Cylindrical Surface grinder.

(b) Machine Tools for flat surface work: Examplesare

Planer

Shaper

Slotter

Broaching by using single point cutting tool

Milling machine

Surface grinding machine by multipointcutting tool.

II. Types of Production(a) General Purpose or basic Machine Tools:Examples are

Lathes

Shaper

Drilling machines

Milling machine

Grinding machine

Planing machines etc.,

(b) Production Machine Tools: Examples are


Production milling machine

Multiple head drilling machine etc.

(c) Special Purpose or Single Purpose MachineTools: Examples are

Gear generators

Camshaft grinders

Piston turning lathes

Thread rolling machines etc.

(d) Flexible Manufacturing System (FMS):Examples:

Machining Centers

Versatile Machines and Robots

AGV’s (Automated Guided Vehicles) etc.,

1.4 PARTS AND NOMENCLATURE OF SINGLE

POINT CUTTING TOOL

The various parts of a single point cutting tool areshank, neck, face, base, heel, cutting edge or lip flank,point, height and width. A single point tool is shown inFig 1.20.

Parts of Single Point Cutting Tool

Shank : Shank is the main body of the tool at oneend of which the cutting portion is formed.

Neck : The portion which is reduced in section toform necessary cutting edges and angles iscalled the neck.


Face : Face of the tool is the surface across whichthe chips travel as they are formed and isvisible to the operator when looking downat the top from above.

Base : Base is the surface on which the tool rests.

Heel : Heel also known as lower face is thehorizontal surface at the end of the base inthe neck portion which do not participate incutting process.

Cuttingedge

: Cutting edge or lip is the portion of the faceedge along which the chip is separated fromthe workpiece.

Standard Angles of Single Point Cutting ToolThese are angles which depend upon the shape of

tool. These are described below.

(i) Side rake angle: Side rake angle is the angle bywhich the face of the tool is inclined side-ways whereasthe back rack angle is the angle by which the face ofthe tool is inclined towards back.

The side rake angle is theangle between the tool face and aline parallel to its base andmeasured in a plane right anglesto the base and at right angles tothe centre line of the point of thetool (side cutting edge).

The side rack angle of a tooldetermines the tool thicknessbehind the cutting edge.

(ii) Back rake angle: Back rake angle is the anglebetween the face of the tool and a line parallel to thebase of the shank in a plane parallel to the centre lineof the point (or parallel to the side cutting edge) and atright angles to the base.

If the inclination of face backwards is downwards,the back rake angle is positive, and if the slope isupwards, then the angle is negative.

End Cutting Edge Angle

Nose Angle

Side cuttingEdge AngleFaceCutting

Edge

Neck

Face

Shank

Back Rake Angle

FlankLip Angle

BaseHeel

Clearance Angle

End Relief Angle

Point

Height

Side Relief Angle

Side Rake Angle

wid th

Fig 1.20 Single point cutting tool

(a)

(b)(c )


Height

S ide Relief Angle

Side Rake Angle

width

(b)Fig. 120

Face : Face of the tool is the surface across whichthe chips travel as they are formed and isvisible to the operator when looking downat the top from above.

Base : Base is the surface on which the tool rests.

Heel : Heel also known as lower face is thehorizontal surface at the end of the base inthe neck portion which do not participate incutting process.

Cuttingedge

: Cutting edge or lip is the portion of the faceedge along which the chip is separated fromthe workpiece.

Standard Angles of Single Point Cutting ToolThese are angles which depend upon the shape of

tool. These are described below.

(i) Side rake angle: Side rake angle is the angle bywhich the face of the tool is inclined side-ways whereasthe back rack angle is the angle by which the face ofthe tool is inclined towards back.

The side rake angle is theangle between the tool face and aline parallel to its base andmeasured in a plane right anglesto the base and at right angles tothe centre line of the point of thetool (side cutting edge).

The side rack angle of a tooldetermines the tool thicknessbehind the cutting edge.

(ii) Back rake angle: Back rake angle is the anglebetween the face of the tool and a line parallel to thebase of the shank in a plane parallel to the centre lineof the point (or parallel to the side cutting edge) and atright angles to the base.

If the inclination of face backwards is downwards,the back rake angle is positive, and if the slope isupwards, then the angle is negative.


Nose Angle


Edge

Neck

Face

Shank

Back Rake Angle

FlankLip Angle

BaseHeel

Clearance Angle

End Relief Angle

Point

Height

Side Relief Angle

Side Rake Angle

wid th

Fig 1.20 Single point cutting tool

(a)

(b)(c )


Height

S ide Relief Angle

Side Rake Angle

width

(b)Fig. 120


This angle helpsin turning the chipaway from the workpiece.

Back rake angleaffects the direction ofchip flow. Tool lifeincreases and cuttingforce is reduced by increasing back rake angle.

Increasing the rake angle facilitates easy flow ofchip which increases tool life, improves surface finish andreduces cutting force. Increasing rake angle alsominimizes size and effect of built up edges, cuttingtemperature, cutting force and power consumption. As aresult better surface is obtained. Higher rake anglemakes the point weak which may induce tool chatter.

(iii) End relief angle: End relief angle is provided ontool to provide clearance between the workpiece and thetool so as to prevent the rubbing of workpiece with endflake of tool. It is the angle between the surface of theflank immediately below the point and a line drawn fromthe point perpendicular to the base.

Excessive relief angle reduces the strength of tool,therefore, it should not be too large. Generally its valuevaries from 6 to 10

(iv) Side relief angle: Side relief angle is provided onthe tool to provide clearance between its flank and theworkpiece surface. It is the angle between the surface ofthe flank immediately below the point and a plane atright angles to the centre line of the point of the tool.

This angle must be large enough for turning operationsto allow for feed helix angle on the shoulder of workpiece.

(v) End cutting edge angle: It provides clearancebetween the toolcutting edge andworkpiece, and theside cutting edgeangle is responsiblefor turning the chipaway from thefinished surface.Side cutting edgeangle is the anglebetween the straight cutting edge on the side of the tooland side of the tool shank. It provides the major cuttingaction and should, therefore, be kept as sharp as possible.Too much of this angle causes chatter.

(vi) Nose Angle: It is the angle between the sidecutting edge and the end cutting edge.

(vii) Nose radius: It is provided to remove the fragilecorner of the tool. It increases the tool life and improvessurface finish.

(viii) Clearance angle: It is the angle between theportion of the flank adjacent to the base and the planeperpendicular to the base. This angle providesfree-cutting action, minimises tool forces and decreasescutting temperature. Excessive clearance angle may causechatter and excessive tool wear.


Face Back Rake Angle

FlankLip Angle

BaseHeel

C learance Angle

End Relie f Angle

Point

(c)Fig. 1.20

Fig. 1.20 (a)


Nose Angle


Edge

Neck Shank

(ix) Lip Angle: It is the angle between the tool faceand the ground end surface of flank. It is usually between60 and 80

1.4.1 Tool Signature

Tool signature is numerical method of identificationof tool standardized by American Standards Association(ASA) according to which the seven elements comprisingsignature of a single point tool are always stated in thefollowing order:

(i) Back rake angle

(ii) Side rake angle

(iii) End relief angle

(iv) Side relief angle

(v) End cutting edge angle

(vi) Side cutting edge angle, and

(vii) Nose radius.

Symbols of degrees of angles and units for noseradius are omitted and only numerical values of thosecomponents are indicated.

Example: A tool specified with the following as perASA 8-16-7-7-8-16-6 has the following angles.

8 Back rake angle, 16 side rake, 7 end relief,

7 side relief, 8 end cutting edge, 16 side cutting edgeangles and 6 mm nose radius.

1.4.2 Influence of Tool angles in machining

1. Rake Angle

Rake angle has the following functions.

Helps in flow of chip in convenient direction.

Reduces cutting force and helps to increase tool lifeand reduce power consumption.

Improves surface finish.

Amount of Rake angle to be given depends upon thefollowing parameters.

Type of material being cut: Small rake angle isgiven for harder material and large rake angle isgiven for soft material.

Type of Tool Material used: High speed tools (eg.cemented carbide) are given minimum or negativerake angle to increase tool strength.

Depth of Cut: Higher the depth of cut lower shouldbe rake angle. Smaller depth of cut have high rakeangle tools.

Rigidity of the tool holder and condition of machine:An improperly supported tool and old machineshould have tool with large rake angle to reducecutting pressure.

Rake angle may be positive, zero or negative asshown in Fig 1.21.

A tool has positive rake when the face of toolslopes away from the cutting edges and slants towardsthe back or side of the tool.


Fig. 1.20 (a)


Nose Angle


Edge

Neck Shank

A tool has zero rake when the face of tool has no

slope and in the same plane or parallel to upper surface

of shank. Turning brass usually have zero rake tools.

Zero rake increases strength of tool and prevents cutting

edge from digging into the work.

A tool has negative rake when the face of the tool

slopes away from the cutting edge and slants upwards

towards the back or side of tool. It is used in turning

metal with cemented carbide tipped tool in mass

production.

Advantages of negative rake angle Point of application of cutting force is changed from

weak to stronger section.

Can work at very high speed.

Increases tool life and reduces tool wear.

Increases lip angle and hence permits higher depthof cut.

2. Clearance angle

Clearance angle prevents the flank from rubbingagainst the surface of work allowing only cutting edge tocome in contact with the workpiece.

Front clearance angle prevents front flank of toolfrom rubbing work piece. It is large for large workdiameter.

Side clearance angle prevents the side of the toolfrom rubbing work when longitudinal feed is given.Larger feed requires large side clearance angle.

3. Nose radius

Nose radius clears feed marks caused by previousshearing action.

It increases strength of cutting edge and henceincrease tool life.

High heat dissipation.

4. Side cutting edge angle

Increases tool life and force distribution on widersurface.

Helps in greater cutting speed.

Improves surface finish and quickly dissipates heat

Usually its value is 15

4. End Cutting edge Angle

It is given to prevent the trailing front cutting edgeof tool from rubbing against work piece. Its value variesbetween 8 to 15. High value of this, weakens tools.

R

T

R

TT

Fig. 1.21. Positive, zero and negative rake R-Rake, T-Thrust


5. Lip AngleLip angle influences the strength of cutting edge.

Lip angle directly depends upon rake and clearance angle.Large lip angle helps in machining harder metals, givinghigh depth of cut, increases tool life and improvesdissipation of heat.

1.5 THEORY OF METAL CUTTING

1.5.1 Mechanics of Metal Cutting and Chipformation.

Any metal cutting process involves workpiece, tool

(including holding devices), chips and cutting fluid. For

removing the metal, a wedge shaped tool is considered

stationary and the work piece moves to the right. The

area of metal in front of tool gets compressed causing

high temperature shear. The stress in workpiece just

ahead of the cutting tool reaches ultimate strength and

particles shears to form chip elements. Fig 1.22 (a)

shows position of tool in relation to work in order to cut

metal. There are three basic angles of importance-rake

angle, clearance angle and setting angle.

The outward or shearing movement of eachsuccessive is arrested by work hardening and themovement is transferred to the next element. The processis continuous and repetitive to give continuous chip whichis compressed, burnished and slightly serrated top sidecaused by shearing action.

The place of element shearing is called shear plane.Thus chip is formed by plastic deformation of grainstructure of metal along the shear plane. The deformationoccurs along a narrow band across the shear plane.

The structure beginselongating along AB below shearplane and continue elongatingtill it completely deforms alongthe line CD above shear planeas shown in Fig 1.22(b) andchip is born. The region betweenAB and CD is called shear zoneor primary deformation zone.

Actually lines AB and CD are not parallel and mayproduce wedge-shape which is thicker near the tool faceat the right than at the left.

Because of this, Curling of the chip occurs inmetal cutting. Also the non uniform distribution of theforces at the chip-tool interface and on the shear plane,the shear plane is curved slightly downward causingcurling of the chip from the cutting face of tool.


III

III

Shear P laneChip Tool

Rake Angle( )

Clearance Angle( )Shear

Angle( )

Setting Angle

Depth of Cut

W orkA

B

Fig. 1.22 (a) Position of tool in relation to work.

BA

D C

Chip

Tool

Fig.1.22 (b) Shear zone during metal cutting

Observations in any cutting operation

Metal is cut by removal of chips either continuousribbon or discontinuous chips. Chip is thicker thanthe actual depth of cut and correspondinglyshortened.

Hardness of chip is greater than the hardness ofparent material

There is no flow of metal at right angles todirection of flow.

Flow lines on side and back of chip indicatesshearing mechanism. Front surface is smooth dueto burnishing action.

Lot of heat is generated in the process of cuttingdue to friction between the chip and tool. Frictioncan be reduced by using sharp cutting edge, goodtool finish, good tool geometry, using cutting fluidetc.

In front of cutting tool point, generally no crack isobserved. Due to strain hardening, the hardness ofmetal in chip, the built up edge and near thefinished surface is usually greater than that for themetal.

Sometimes a built up edge is formed at the tip ofthe tool and it significantly alters the cuttingprocess. It deteriorates the surface finish and rateof tool wear is increased.

1.5.2 Chip Formation

Chip formation has already been explained inmechanism of metal cutting. All machining processesinvolve formation of chips by deforming the work material

on the surface of the job with the help of a cutting tool.The extent of deformation that the material suffers notonly determines the type of the chip but also determinesthe quality of the machined surface, cutting forces,temperature developed and dimensional accuracy of thejob. Depending upon the tool geometry, cutting conditionsand work material, a large variety of chip shapes andsizes are produced during different machining operations.

1.5.3 Methods of Metal Cutting Processes

Metal Cutting processes are generally classified intotwo types.

(i) Orthogonal cutting process (Two dimensional)

(ii) Oblique cutting process (Three dimensional)

Orthogonal cutting process is one in which thecutting face of the tool is 90 to the line of action or pathof the tool. In other words, the edge of tool isperpendicular to the cutting velocity vector as shown inFig. 1.23(a)


Feed90

o

Rake

Knife edge

Feed

60o Rake

Roughing

Depth of cut

(a) O rthogonal (b) Oblique

Fig. 1.23. Orthogonal and Oblique cutting

Oblique cutting process is one in which the cuttingface is inclined at an angle less than 90 to the path ofthe tool, the cutting action is known as oblique as shownin Fig 1.23(b)

Fig 1.24 shows the chip flow in orthogonal and

oblique cutting. In orthogonal cutting the chip coils in a

tight, flat spiral where as in oblique cutting the chip

flows sideways in a long curl. Angle’s i and nc are of

importance in oblique cutting. In orthogonal cutting

i 0 & nc 0. Orthogonal cutting is used for knife

turning, broaching and slotting where as bulk machining

is done by oblique cutting.

1.5.3.1 Differences between orthogonal and obliquecutting.

S.No.

Orthogonal Cutting Oblique Cutting

1. The cutting edge of thetool remains at 90 tothe direction of feed (ofthe tool or the work)

The cutting edge of thetool remains inclined atan acute angle todirection of feed.

2. The chip flows in adirection normal to thecutting edge of the tool.

The chip flow is notnormal but at an angle to the normal to thecutting edge.

3. The cutting edge clearsthe width of the workpiece on either ends.

The cutting edge may ormay not clear the widthof the workpiece.

4. Only two components ofcutting force which areperpendicular to eachother are acting on tool.

Three components ofcutting forceperpendicular to eachother acts on the tool.

5. Maximum chip thicknessoccurs at the middle.

Maximum chip thicknessmay not occur at middle.,

6. The shear force acts on asmaller area, so shearforce per unit area ismore.

The shear force acts on alarge area, hence shearforce per unit area issmaller.

7. Tool life is smaller thanthat in oblique cutting.

Tool life is higher thanorthogonal cutting.

8. The cutting edge isbigger than the width ofcut.

The cutting edge issmaller than the widthof cut.


v

c

o

vw

ork

Ch i

p

o

ab

c

di

nc

(c) Oblique

Fig. 1.24. Direction of chip flow in orthogonal and oblique cutting.

(a) Orthogonal (b) Oblique

1.5.4 Types of Chips

The chips are broadly classified into threecategories:

(i) Continuous Chip

(ii) Continuous chip with built up edges.

(iii) Discontinuous Chip

1.5.4.1 Variables affecting type of chipThe type of chip produced in a particular operation

depends upon the following variables.

Properties of material being cut (i.e ductile orbrittle)

Cutting speed

Depth of cut

Feed rate

Rake angle

Type and way of application of cutting fluid

Surface roughness of the tool face.

Coefficient of friction between the chip and toolinterface

Temperature of the chip on the tool face.

Nature of cutting i.e. continuous or intermittent

1.5.4.2 Continuous Chips

During the cutting of ductile materials like low

carbon steel, copper, brass, aluminium alloys etc., a

continuous ribbon type chip is produced. The pressure of

tool makes the material ahead of the cutting edge deform

plastically. It undergoes compression and shear. The

material then slides over the tool rake face for some

distance and then leaves the tool. Friction between the

chip and tool may produce secondary deformation on chip.

The plastic zone ahead of the tool edge is called the

Primary Zone of deformation and the deformation

Zone on the rake face is usually called Secondary Zone

of deformation as shown in Fig. 1.25(a). Both these

zones and the sliding of chip on rake face produce heat.

The extent of primary zone deformation depend upon.

(i) Cutting speed (ii) Rake angle of tool(iii) Friction on rake face (iv) Work materialcharacteristics.

With large rake angle tools, the chip formation is

gradual and material suffers less overall deformation.

Cutting forces are also low. With small or negative rake

angle tools, the material suffers more severe deformation

with large cutting forces.

At high cutting speed, the thickness of the primary

zone of deformation shrinks i.e it becomes narrower.


Prim ary zone of deform ation

Secondary zone of deform ation

W ork piece

Tool

Chip

Fig.1.25 (a) Continuous chip

Conditions favorable for continuous chip are

(i) Ductile Material

(ii) Large rake angle

(iii) High cutting speed

(iv) Small depth of cut

(v) Small feed rate

(vi) Efficient way of applying cutting fluid to preventbuilt up edge

(vii) Low coefficient of friction at chip tool interface

(viii) Polished face of the cutting tool

(ix) Use of material having low coefficient friction ascutting tool, (Ex) cemented carbide.

Continuous chips pose difficulty while machining, itgets wrapped over the machined portion of work if notquickly disposed. So during machining a device known as“Chip Breaker” is attached over the tool post (near thetool nose) which breaks the chip into smaller fragments.

1.5.4.3 Continuous Chips with Built up Edges.

The temperature is high at the interface betweenthe chip and the tool during cutting. As the chip movesover the tool face due to the high normal load on the toolface, high temperature and high coefficient of frictionbetween chip and tool interface, a portion of chip getswelded on the tool face forming the embryo of built upedge (BUE). The strain hardened chip is so hard thatnow it becomes part of the cutting edge and starts cuttingthe material. Since this built up edge is irregular inshape, the surface produced becomes rough. As themachining continues, more and more chip material getswelded on the embryo built up edge, this increases its

size and ultimately, it becomes unstable and gets shearedoff. This cycle is repeated. During the unstable stage,some fragments of the built up edge are carried alongthe under surface of chip while some escape along theflank thus worsening the surface finish of the machinedsurface. [Fig. 1.25(b)]

However there is a remedy. Increasing in cuttingspeed, increases the interface temperature which softensthe built up edge. As a result, the critical size of thebuilt up edge completely disappears. Fig 1.26 shows theformative cycle of built up edge. After the embryo of builtup edge reaches the final stage,. it is sheared off. Againthe embryo is formed and the whole cycle is repeated.

1.5.4.4 Discontinuous ChipsDiscontinuous chips are produced during the cutting

of brittle material like cast iron, brasses etc containinghigher % of Zinc. The chip formation mechanism isdifferent from that of ductile material. A slight plasticdeformation produced by a small advance of the cuttingtool edge into the job leads to a crack formation in thedeformation Zone. With further advance of the cutting


W ork piece

Built up edge

BUE = Built Up Edge

Fragem ents of B U E

Fig.1.25 (b) Continuous chip with B U E

tool, the crack travels and a small lump of material startsmoving up the rake face as shown in Fig. 1.27.

The force and constraints of motion acting on thelump make the crack propagate towards the surface, andthus a small fragment of chip gets detached. As the toolmoves further, this sequence is repeated.

Following are conditions at which discontinuouschips are formed

Use of brittle material

Smaller negative rake angle

Large chip thickness i.e. large depth of cut andhigh feed rate.


W ork piece

Tool

Chips

Fig.1.25 (c) Discontinuous chip

Chip

Tool

W ork piece

Initiation of B U E

(a) nitiation of B U E I

Chip Tool

W ork piece

Grow th of B U E

(b) Growth of B U E

Chip Tool

W ork piece

Fragments of B U E

(c) Breaking of B U E

Fig. 1.26. Formation of Built up Edge and Fragmentation

Fig. 1.27. Formation of Discontinuous C hip.

Tool Tool Tool

W ork piece W ork piece W ork piece

(a) (b) (c)

Initialdeformation Crack

Formation

Chipsegment

Low cutting speeds

Dry cutting i.e. cutting without use of cutting fluid.

1.5.4.5 Chip BreakersChip breakers are important components of tool

design particularly when tool has to cut ductile materialslike low carbon steels, copper, aluminium, low zincbrasses etc. These materials produce long continuouschips which are difficult to handle and occupy largevolumes. Such chips fouls the tool, clutter up the machineand work place and are difficult to remove. These chipsare to be broken into small pieces for ease of handlingand to prevent it from becoming hazardous. Hence chipbreakers are used to break this continuous chips intosmall pieces. The general types of chip breakers are

(i) Step type

(ii) Groove type

(iii) Clamp type.

These types are shown in Fig. 1.28

In general shop practice, the chips are broken bythe following methods.

(i) By a stepped type breaker in which a step isground on the face of the tool along the cuttingedge.

(ii) By clamping a piece of sheet metal in the path ofthe coil.

(iii) By a clamp type breaker in which a thin carbideplate is brazed or screwed on the face of tool.

(iv) By a groove type breaker in which a small grooveis ground behind the cutting edge.

1.5.6 Geometry of Chip Formation

When a wedge shaped tool is pressed against theworkpiece, chip is produced by deformation of materialahead of cutting edge because of shearing action takingplace in a zone known as shear plane. This shear planeseparates the deformed and undeformed material.

The Geometry of chip formation is shown in theFig. 1.29(a)

Considering the Geometry of chip formation wehave the following.

Vc : Velocity of tool against workpiece (CuttingVelocity).

AB : Shear plane.

t : Depth of Cut (Feed in turning operation)

tc : Chip thickness

Vt : Velocity of chip relative to tool acting along toolface.

Vs : Velocity of chip relative to workpiece alongshear plane


Step type Groove type Clam p typeFig. 1.28 Ch ip Breakers

Considering the principles of kinematics, the three

velocity vectors (Vt, Vc, Vs) form a closed velocity triangle

ABD as shown in Fig. 1.29(b). Also from the kinematics,

the vector sum of cutting velocity Vc and chip velocity

Vt is equal to the shear velocity vector Vs

1.5.6.1 Velocity Relationships

[Fig. 1.29 (b)]

From Right Angle triangle ACD , BDC we have

DC Vc sin ; DC Vt cos

From above relation, we have

Vc sin Vt cos

So, Vt Vc sin

cos ...(1)

Similarly, from right angle triangle AED , AEB we

have

AE Vc cos ; AE Vs cos

Vc cos Vs cos

So, Vs Vc cos

cos ...(2)

1.5.6.2 Shear Plane angle and chip Thicknessratio

The chip thickness ratio is defined as the ratio of

depth of cut t to the chip thickness tc

Chip thickness ratio r ttc


t

B Tool

VC

tCV S

-G A

E

V t

Fig.1.29.(a) Geom etry of Chip formation

Chip

V C

V t

B

C

V S

A

E

D

Fig.1.29.(b) Cutting velocities triang le

From the Geometry of Fig. 1.29(a) we see thatAE perpendicular to tool chip interface represents tc i.e.

Chip Thickness.

From right angle triangles ABG & ABE we have

AB t

sin , AB

tccos

dividing the above two equations we have

ABAB

t/sin

tc/cos

i.e. ttc

sin

cos r

. . . r

ttc

r ttc

sin

cos cos sin sin

. . . cos cos cos sin sin

r cos cos sin sin sin

r cos cos sin sin

sin 1

r cos tan

r sin 1

r cos tan

1 r sin

. . . tan r cos

1 r sin

(or) Shear Angle tan 1

r cos 1 r sin

...(1.3)


(Here the term 1r

is termed as chip reduction

coefficient or chip compression factor and is denotedby K)

The cutting ratio or chip thickness ratio is alwaysless than unity and can be evaluated by measuring chipthickness and depth of cut. But it is difficult to measurechip thickness precisely due to roughness on back surfaceof chip.

The chip reduction coefficient can also be estimatedin a different manner by measuring the length of thechip (lc

Volume of metal removed Volume of Chip.

So, t b l tc bc lc c ...(1.4)

(Here t, b, l, being thickness or depth, width,length and density of metal cut and ‘c’ standing suffixfor chip).

If width of chip is same as workpiece i.e b bc, and

density is same for both ie c we have

t l tc lc

ttc

lcl

We know ttc

r so, r ttc

lcl

[chip thickness ratio

or cutting ratio]

Also density of metal can be used to find the chip

reduction coefficient r t b

m ...(1.5)

where m is Weight per unit length of metal.

1.5.6.3 Force Analysis in Metal Cutting Fig 1.30 shows a turning operation with oblique

cutting. In this the cutting edge ab makes an angle withthe direction of feed. The metal being cut undergoescutting forces. These forces are resolved in three mutuallyperpendicular direction as shown in Fig. 1.30.

The three forces are

(i) Feed Force Fd: It is horizontal component of the

cutting force, acting in the direction of feed of the tool.It is acting tangent to the generated surface.

(ii) Thrust force Fr: It is reaction force between the

tool and the work piece acting in radial directionperpendicular to feed direction.

(iii) Main cutting force Fc: It is the vertical

component of the cutting force acting in vertical direction.

The resultant force R Fd2 Fr

2 Fc2

Orthogonal CuttingFig 1.31 shows an orthogonal cutting process. In

this process, the cutting force has two components only,one in the feed direction Fd and other in vertical

direction - cutting force Fc

The two components of forces Fd, Fc and forces

acting on chip are shown in Fig. 1.31(a).

As the cutting tool moves along the feed direction,the metal gets plastically deformed along the shear planeand the chip moves along the rake surface of tool anddue to roughness of chip, frictional Force F is acting onthe tool.

Following are the forces developed.

Force F : It is the Frictional resistance of chipacting on tool.

Force N : It is reaction provided by the tool.


c

a

bFd

F r

Feed

Fc

F y

F z

F x

R

Fig.1.30. Forces in oblique Turning

F c

Fa

F d

Feed

Fs

F nF cF d

Tool

Feed

W orkpiece

NF

Chip

Fig. 1.31. Orthogonal Turning.(a)

Force Fs : It is shear force on metal.

Force Fn : It is normal to shear plane and it isbacking up force causing compressivestress on the shear plane.

Fig 1.32 shows the free body diagram of forcesacting on chip.

Here the Resultant

R Fn2 Fs

2 ; R F2 N2

Both R and R are equal in magnitude and opposite

in direction and are collinear since chip is in equilibrium.

1.5.6.4 Force analysis in orthogonal cutting(Merchant Circle diagram and Theory)

From a fixed geometry of the cutting tool, thereexists a definite relationship among the above mentionedforces (section 1.5.6.3)

The components of forces could be measured by adynamometer and all the forces could be calculated.

Merchant represented these forces in a circle,known as Merchants circle diagram shown in Fig 1.33.

Following are the assumptions made in merchantsto workout force relations.

(i) Tool is perfectly sharp and there is no contactalong the clearance face.

F s

Fn

R

F

R �

N

Chip

Fig. 1.32. Free body diagram


Fig. 1.33 M erchant Circle diagram.

(ii) The shear surface is a plane extending upwardfrom the cutting edge.

(iii) The cutting edge is a straight line.

(iv) The chip does not flow to either side.

(v) The depth of cut is constant.

(vi) Width of the tool is greater than that of workpiece.

(vii) The work moves relative to tool with uniformvelocity.

(viii) A continuous chip is produced with no built upedge.

(ix) Plain strain condition exists i.e width of chipremains equal to width of the workpiece.

In the Fig 1.33 we have

back rake angle

shear angle

angle of friction ;

Forces Fd and Fc can be measured by dynamometer

Shear angle can be measured by photomicrographor by measuring thickness of chip and depth of cut.(discussed earlier).

Once the Fd, Fc, and are known, all the other

components of forces acting on the chip can bedetermined by the geometry shown in Fig 1.33. We candraw the following figures from Fig 1.33 and findrelations.

From the Fig 1.34(a) we have from the geometry

Fs AB AC BC ; Fc AD ; Fn BE

Fs AB Fc cos Fd sin

Fn BE Fc sin Fd cos ...(1.6)

Again from Fig 1.34(a) we have

Fc R cos [From le ADE ]

Fs R cos [From le ABE]

So R Fs

cos ...(1.7)

Substituting R in Fc we get

Fc Fs

cos cos

...(1.8)

or Fs Fc cos

cos ...(1.9)


Fd

F c

c

ed

f

F

N

b

a

R

o

(b)

-

Fd

Fs

Fc

Fn

D

C

B

A

R

(a)E

Fig. 1.34. Geometry of Forces

From Fig 1.34(b) we have.

N ab oe od de

N Fc cos Fd sin

Since F ao be

ef fb cd fb

F Fc sin Fd cos ...(1.10)

Let coefficient of friction, then we have

F N

Coefficient of friction

FN

Fc sin Fd cos

Fc cos Fd sin ...(1.11)

dividing the numerator and denominator by cos we get

Coefficient of friction Fc tan Fd

Fc Fd tan ...(1.12)

Condition For maximum cutting forceFrom the equation (1.8) we have

Fc Fs

cos cos

where Fs shear force

Fs shear stress Area of shear plane

Fs s b tsin ...(1.13)

Substituting 1.13 in 1.8 we get

Fc s b tsin

cos

cos ...(1.14)

For maximum Fc, we have

d Fc

d 0

d Fc

d

dd

s b t

sin

cos cos

0

s b t cos dd

1sin cos

0

d Fc

d s b t cos

cos cos sin sin

sin cos 2

0

(or) cos cos sin sin 0

cos [ ] 0

[. . . cos A B sin A sin B cos A cos B]

cos 2 0 cos /2[. . . cos /2 0]

2 /2

or Shear Angle 4

2

2 ...(1.15)


From Fig 1.34(b) we have.

N ab oe od de

N Fc cos Fd sin

Since F ao be

ef fb cd fb

F Fc sin Fd cos ...(1.10)

Let coefficient of friction, then we have

F N

Coefficient of friction

FN

Fc sin Fd cos

Fc cos Fd sin ...(1.11)

dividing the numerator and denominator by cos we get

Coefficient of friction Fc tan Fd

Fc Fd tan ...(1.12)

Condition For maximum cutting forceFrom the equation (1.8) we have

Fc Fs

cos cos

where Fs shear force

Fs shear stress Area of shear plane

Fs s b tsin ...(1.13)

Substituting 1.13 in 1.8 we get

Fc s b tsin

cos

cos ...(1.14)


d Fc

d 0

d Fc

d

dd

s b t

sin

cos cos

0

s b t cos dd

1sin cos

0

d Fc

d s b t cos

cos cos sin sin

sin cos 2

0

(or) cos cos sin sin 0

cos [ ] 0

[. . . cos A B sin A sin B cos A cos B]

cos 2 0 cos /2[. . . cos /2 0]

2 /2

or Shear Angle 4

2

2 ...(1.15)


The above relationship is based on EarnestMerchant Theory and also called as “ModifiedMerchant Theory”, which makes the followingconclusions.

1. The stress is maximum at the shear plane and itremains constant.

2. The shear takes place in a direction in which theenergy required for shearing is minimum.

Merchant modified the relationship desired byEarnest - Merchant, by assuming that the shear stressalong the shear plane varies linearly with normal stress.It is given as

s 0 K n ...(1.6)

Where s Shear stress

0 Static stress

n Normal stress

K constant

Equation 1.14 becomes,

Fc 0 K n b tsin

cos

cos


d Fc

d 0, we get cos 2 K

or 2 cos 1 K

Shear Angle cos 1 K

2

2

2 ...(1.17)

1.5.6.5 Lee and Shaffer Theory

According to Lee and Shaffer Theory, the shearoccurs on a single plane. So, for a cutting processaccording to this theory,

(i) The Material ahead of the cutting tool, behave asideal plastic material.

(ii) The chip does not get hardened.

(iii) The chip and parent work-material are separatedby shear plane.

According to Lee and Shaffer Theory

4 ...(1.18)

The relation was further modified by taking intoaccount factor based on changes due to built up edgeformation.

4 ...(1.19)

1.5.6.6 Power and workdone in cutting process

Let Pc Horse Power (HP) in kW required for cutting.

Pm Gross Horse Power HP in kW of the motor.

PI Idle Horse power ie Horse Power consumedwhile running idle in kW

Vc Cutting Velocity

Work done in cutting W Fc Vc in Nm/s or Watt

...(1.20)

Where Fc Cutting Force in N


Work done in shear Ws Fs Vs ...(1.21)

Where Fs Shear force and

Vs Velocity of chip relative to work in m/s.

Work done in friction Wf Ff V

Ff Frictional force,

V Velocity of chip relative to cutting tool in m/s.

Now Total work done in cutting W Ws Wf

Fc Vc Fs Vs Ff V ...(1.22)

Also cutting Power in Pc Fc Vc

60 75 1.36 kW

...(1.23)

Here Fc Vc is workdone in kgm/min.

Or Force of Cutting Fc Pc 6120

Vc ...(1.24)

Here Fc is in kg, Vc in m/min, Pc in kW

Also we have Pc Pm PI ...(1.25)

Mechanical Tool efficiency (tool Pc

Pm ...(1.26)

1.5.6.7 Stress and Strain in Chip

Let avg Average Shear Stress on Shear plane

As Area of Shear Plane

w Width of the chip

t Thickness of chip

We have Shear Stress s Fs

As where Fs Shear

force

We know that As w.t

sin

s Fs sin

w t ...(1.27)

From the equation 1.6 we have

Fs Fc cos Fd sin

s [Fc cos Fd sin ] sin

w.t

Shear Stress s Fc cos sin Fd sin2

w.t ...(1.28)

1.5.6.8 Shear Strain in Cutting

Let us consider the chip consists of a large numberof element as shown in Fig. 1.35

Let x Thickness of each element

s Displacement of each element through shearplane

e Strain

We know that Strain e sx

ACx

AB BC

x

e ABx

BCx


Work done in shear Ws Fs Vs ...(1.21)

Where Fs Shear force and

Vs Velocity of chip relative to work in m/s.

Work done in friction Wf Ff V

Ff Frictional force,

V Velocity of chip relative to cutting tool in m/s.

Now Total work done in cutting W Ws Wf

Fc Vc Fs Vs Ff V ...(1.22)

Also cutting Power in Pc Fc Vc

60 75 1.36 kW

...(1.23)

Here Fc Vc is workdone in kgm/min.

Or Force of Cutting Fc Pc 6120

Vc ...(1.24)

Here Fc is in kg, Vc in m/min, Pc in kW

Also we have Pc Pm PI ...(1.25)

Mechanical Tool efficiency (tool Pc

Pm ...(1.26)

1.5.6.7 Stress and Strain in Chip

Let avg Average Shear Stress on Shear plane

As Area of Shear Plane

w Width of the chip

t Thickness of chip

We have Shear Stress s Fs

As where Fs Shear

force

We know that As w.t

sin

s Fs sin

w t ...(1.27)


Fs Fc cos Fd sin

s [Fc cos Fd sin ] sin

w.t

Shear Stress s Fc cos sin Fd sin2

w.t ...(1.28)

1.5.6.8 Shear Strain in Cutting

Let us consider the chip consists of a large numberof element as shown in Fig. 1.35

Let x Thickness of each element

s Displacement of each element through shearplane

e Strain

We know that Strain e sx

ACx

AB BC

x

e ABx

BCx


x tan 90

x

x tan x

e tan tan 90 ...(1.29)

e tan cot

sin cos

cos sin

e sin sin cos cos

sin cos

e sin [sin cos cos sin ] cos [cos cos sin sin ]

sin cos

. . . sin A B sin A cos B cos A sin B

cos A B cos A cos B sin A sin B

e sin2 cos sin cos sin cos2 cos cos sin sin

sin cos

e cos [sin2 cos2 ]

sin cs

strain e cos

sin cos

... (1.30)


VS VC cos

cos

Substituting (1.2) in 1.30

Strain e Vs

Vc sin

Vs e Vc sin ... (1.31)

1.5.6.9 Energy in cutting

Total energy consumed per unit time in cutting

Energy E Fc Vc ... (1.32)

Total energy consumed per unit volume of metalremoved

Em E

Vc w t

Fc Vc

Vc w t

Fc

w t ... (1.33)

The total energy required per unit volume of metalremoved is

ETot Es Ef Ea Em

where Es Shear energy per unit volume

Ef Specific friction energy

Tool

xs

x

s

-

A B C D

90-

O

x

s

Fig.1.35. Shear Strain.


Ea Surface energy per unit volume(negligible)

Em Momentum energy per unit volume(negligible)

Es s Vs

Vc sin and Ef

Fw tc ... (1.34)

Practically all the energy required in metal cuttingis consumed in the plastic deformation on the shear planeand the friction between chip and tool.

1.6 CUTTING TOOL MATERIALS

The materials having certain specific properties andcharacteristics are used as tool materials. Tool materialis harder than the material to be cut. Type of cuttingtool material to be used depends upon.

(i) Physical and chemical properties of metal to becut

(ii) Type of manufacturing process ie eitherTurning, Milling, Grinding etc.

(iii) Rate of production & volume of production.

(iv) Condition of the machine tool.

(v) Complexity of tool and material to be cut.

1.6.1 Desirable Properties of Cutting Tools

The various and important properties of cuttingtools are

(i) Hot Hardness

(ii) Wear resistance

(iii) Mechanical and Thermal shock resistance

(iv) Toughness

(v) Friction properties between tools & workpiece

(vi) Chemical reactivity between tool and workpiece

(vii) Ease of availability and manufacture

(viii) High thermal conductituty

(ix) Low coefficient of thermal expansion

(x) Cost of tool.

The most important proporties of tool material arehot hardness, wear resistance and toughness

(i) Hot Hardness

Hot Hardness is a measure of the ability of a toolmaterial to retain its hardness even at elevatedtemperature without loosing its cutting edge. In metalcutting, heat is generated during the process due to whichthe hardness of the cutting material reduces andconsequently the cutting ability of the tool (or the cuttingedge of the tool) will reduce. Therefore, it is a veryimportant factor for any materials to be used as a cuttingmaterial. In practice, the harness is increased by addingelement like chromium, molybdenum, vanadium,tungsten.

(ii) Wear Resistance

Wear means loss of material. Wear of tools iscaused by abrasion, adhesion and diffusion. Abrasiveaction is because of flow of chip over the rake face underhigh pressure and rubbing action of the machined surfacewith tool flank. Adhesion is gradual loss of tool material


when its particles adhere to the chip or machined surfaceand get torn away. Diffusion wear is due to transfer ofatoms of hard alloy constituents of tool material into workor chip materials resulting in heating of tool.

A wornout tool will have following effects

(i) Poor surface finish dimensional tolerence onwork piece.

(ii) Increase in cutting force and thus increase inpower consumption.

(iii) Increase in temperature and vibration.

Therefore tools must have high wear resistance.

(iii) Toughness

Toughness is the ability of a material to absorbdeformation energy before fracture. Tougher the material,higher the ability of material to absorb impact loads andintermittent cuts. It is however observed from experiencethat materials which are wear resistant and have highhot hardness are also more brittle and therefore lesstough.

(iv) Mechanical and Thermal Shock Resistance

If a material has high hardness, its resistance towear is more. But increase in hardness, renders it toshock, because it loses toughness and fracture underimpact load easily. There is shock load to the tool whenit just engages with the work and at regular interval ifthe cutting is intermittent. Therefore, the tool materialshould have high mechanical and thermal shockresistance.

(v) Friction

There should be low friction between the tool and

workpiece since the friction generates heat. The

coefficient of friction between the tool and work piece

should be as low as possible.

(vi) Chemical reaction/affinity between the Tooland Workpiece

If there is a high affinity of work material with tool

material, the tool will wear out easily and hence the tool

material should have less affinity or no affinity with work

material.

(vii) Availability and Manufacture

A tool material with the above mentioned properties

must be easily available or can be easily manufactured.

If its manufacture is very hard, it may not be of much

use to the machining.

(viii) High Thermal Conductivity

Tool material should have high thermal conductivity

so that the heat generated during cutting is easily

removed from the chip-tool interface.

(ix) Coefficient of Thermal expansionTool material should have low coefficient of thermal

expansion to avoid distortion during heat treatment.

(x) Tool Cost

The cost of material is also an important factor for

its selection as tool material. Tool material should be of

low cost.


1.6.2 Types of Cutting Tool Materials

The various types of cutting tool materials are:

(i) Carbon tool steels or carbon steels.

(ii) Medium alloy steels or Alloy tool steels

(iii) High Speed Steels (HSS)

(iv) Cast alloys (or) Stellites

(v) Cemented Carbide tool Materials

(vi) Oxide or Ceramic tool Materials

(vii) Diamond

(i) Carbon Tool Steels or Carbon Steels

The composition of general carbon steels are Carbon0.8 to 1.3%, Manganese - 0.1 to 0.4% and Silicon - 0.1to 0.4%. Few alloying elements are added to improveproperties of Carbon Steels. These are Vanadium andChromium. The composition of Carbon-Vanadium Steelsand Carbon Chromium Steels are:

(i) Carbon Steels : 0.8 to 1.3% C, 0.1 to 0.4% Mn,0.1to 0.4% Si

(ii) Carbon-VanadiumSteels

: 0.8 to 1.3% C, 0.1 to 0.4% Mn,0.1 to 0.4% Si, 0.15-0.25% V

(iii) Carbon-Chromium Steels

: 0.8 to 1.3% C, 0.1 to 0.4% Mn,0.1 to 0.4% Si, 0.40-0.60% Cr

Characteristics of Carbon Steels

Carbon Steels have low hot hardness and poorhardenability. They can be worked upto 200 to250C. At higher temperature, they loose hardnessrapidly.

Carbon Steels are used for Cutting soft materialslike Wood, Plastic, Aluminium, Copper etc.,

Carbon steels are used for making Taps and Coredrills for machining soft materials and for makingwood working tools.

Effect of alloying element:

Tungsten increases the wear resistance

Chromium and Manganese improves hardenability.

Vanadium increases toughness by giving heattreatment.

(ii) Medium Alloy Steels

In medium alloy steels, alloying elements likeTungsten, Chromium, Molybdenum are added to improvehardenability. The carbon content in these alloy steel isaround 1.2 to 1.3%. Higher Carbon content increaseshardness and wear resistance. Tools of these material canwork between 250C to 300C and speed is 20 to 40%more than carbon steels. These steels materials are usedin making drills, taps and reamers.

(iii) High Speed Steels (HSS)The composition of High Speed Steel is 18%

Tungsten, 5.5% Chromium 0.7%, Carbon and smallamount of Manganese, Vanadium and Silicon. This HSSsteel was developed by Fredenck W.Taylor and M.White.It can work upto 600C at 40 m/min.

HSS is of three types:

(i) High Tungsten HSS

(ii) High Molybdenum HSS

(iii) Tungsten-Molybdenum HSS.


The composition of the above HSS is given below:

(i) High Tungsten HSS : 18% W, 4% Cr, 1% V,0.6% C & Balance Fe

(ii) High Molybdenum HSS : 1% W, 4.5% Cr, 1.5% V,8.5% Mo, 0.8% C andBalance Fe.

(iii) Tungsten-Molybdenum HSS

: 6% W, 4% Cr, 2% V,6% Mo and Balance Fe

Characteristics of HSS High Tungsten HSS is the best of the above three

for all purpose tool steels.

Tungsten and Molybdenum increase the hothardness.

Vanadium iron Carbide tools are very hardconstituents of HSS and imparts high wearresistance to tool at all temperatures.

To increase the cutting efficiency, 2 to 5% of Cobaltis added. One of the composition 2% W, 4% Cr, 2%V, 12% Cobalt are called Super high SpeedSteels. Because of heavy cost, it is used for heavycut operations only.

HSS hot hardness is quite high so it retains thecutting ability upto 600C at 40 m/min.

HSS has high wear resistance and goodhardenability.

Uses: HSS is used in Drill, Broaches, Reamers,Milling Cutters, Taps, Lathe Cutting Tools, Gearhobs etc.

(iv) Cast Alloys (or) StellitesStellites or cast alloys are non-ferrous alloy

containing Tungsten, Chromium, Cobalt and Carbon usedfor cutting tools. These alloys contain no iron and hencecannot be shaped because they cannot be heat treated.They are casted into final shape. They are casted from atemperature about 1300C. The Chemical Composition ofthese cast alloys are 12 to 17% W, 30 to 35% Cr, 45 to55% Co, 2 to 4% C.

Characteristics of Stellites Cast alloys are not hard at room temperature but

becomes very hard above 1000F (hardness morethan HSS)

Cast alloys are very brittle hence not widely used.

Cast alloys have less toughness but more wearresistance than HSS and allow cutting speed thricethan that of HSS.

Uses: Used in manufacture of Valve seats, Push rodsheets and Erosion shield of steam turbine etc.

(v) Cemented Carbide ToolsThe main constituents of cemented carbide tools is

tungsten carbide (WC). This material was discovered byMoissan. Tungsten carbide materials are produced bypowder metallurgy by pressing and bonding. Cementedcarbide tools are of three types.

(i) Straight Cemented Carbides: Containing tungstencarbide held in matrix of Cobalt. These are more ductileand less brittle.


(ii) Titanium-tungsten Cemented Carbides:Consisting of solid grains, solid solution of tungstencarbide in carbide of titanium and surplus grains oftungsten carbide all bonded by cobalt in cobalt matrix.

Symbolically given by WC Co WC TiC. Theseare very brittle.

(iii) Titanium-Tantalum-Tungsten CementedCarbide: Consists of grains of solid solution of carbideof titanium, tantalum and tungsten and surplus grainsof tungsten carbide cemented together by CobaltSymbolically: WC Co WC TiCTaC

Characteristics of Cemented Carbide Tools

These tools have / are

High hardness, heat resistance, wear resistance,high hot hardness.

These tools can be used upto 1000C

High thermal conductivity and low thermalexpansion compared to steel.

No plastic flow to stress upto 3500 N/mm2

Low impact resistance.

Very expensive.

Operate at cutting speed upto 45 to 360 m/min.

These are very brittle and hence rigidly supportedand have low shock resistance.

Uses: Used to machine cast iron, non-ferrous andlight metal and alloys, non-metallic materials likerubber, glass, plastics, plastics carbon electrodes, in

machining unhardened carbon and alloy steels, heatresistance steels and super alloys workpieces.

Generally cutting tools are six inches in length andhave square cross sections, but carbide toolsconsists of shank made in steel and at one end ithas cemented carbide piece called bits and aredivided into 2 groups namely brazed tip carbidetools and throw away inserts.

(vi) Ceramic Tools

Ceramic tools are also called cemented oxides. Themain constituent of ceramic tools are aluminium, tauxite(a dehydrated alumina) converted into crystalline formcalled alpha aluminium. Fine grains are obtained fromthe precipitation of alumina (in powder form) and tooltips are produced by hot or cold pressing of the powder.(sintering process at 1600 1700C). Certain amount ofmagnesium oxide or titanium oxide are used along withsome binder.

Characteristics of ceramic tools

They have very high compressive strength. It isquite brittle.

Low heat conductivity, so no coolant is requiredduring machining.

Have high strength and hot hardness upto1200C.

Have low coefficient of friction and hence low heatgenerated.

Have 2 to 5 times more cutting speed than othertools.


Advantages

Very high cutting speed so low machining time.

High tool life with large depth of cuts.

Low wear rate and hence high dimensionalaccuracy with high surface finish.

Low cost of production.

Disadvantages

High initial cost-40 to 200% more than carbidetools.

High rigidity of machine tools is required.

More power required since high speed and feedrate.

Tools are brittle so proper tool geometry, holdingdevices are to be used.

Application

Turning, boring and facing at high speeds, used forfinishing operation on non-ferrous and ferrousmetals, machining of casting and hard steels.

Cermets are ceramic metal combinations of Iron,Chromium, Titanium and other metals, added toaluminium oxide and boron carbide. The brittlenessof the ceramic tools is considerably reduced.

(vii) Diamond Cutting Tools

Diamond is the hardest known material today. They

are used in cutting tools. Diamond is of four

classes-carbons, ballar, boarts and ornamental stones.

Cutting tools are made from boarts which are single

crystal, less clear and fault free.

Characteristics of diamond

They are very hard, hence very brittle.

They are abrasion resistant with low coefficient offriction and low thermal coefficient of expansion.

They burn to Co2 at 800C

They cannot take shock loads.

High heat conductivity and poor electricalconductor.

Advantages

Very high production rate with close tolerance, highsurface finish.

Small depth of cut can be given (0.215 micron).

Cost of grinding is reduced.

Chances of built up edge formation is nil.

Disadvantages

Very high cost.

Interrupted cut machining is not possible.

Machine tool should have high rigidity.

Cannot be used for machining beyond 800C.

Exclusively used for shallow cuts.

Applications

Used for machining non metals like rubber,ceramic, graphite and plastic.

Used for machining precious metals like Platinum,Gold and Silver, Soft metals like Copper, Brass,Zinc alloys.


1.7 TOOL WEAR

A new or newly ground tool has sharp cutting edges

and smooth flanks. During machining operation it is

subjected to cutting forces, temperatures, sliding action,

mechanical and thermal shocks. Under these severe

conditions, the tools gradually wear out and even

fractures, necessitating a tool change.

This tool wear causes the following effects

The cutting forces increases.

The dimensional accuracy of the work decreases.

The surface roughness of work increases.

Increase in the temperature between tool andworkpiece.

The tool-work-machine starts vibrating.

The work piece/tool may get damaged.

Loss of production and increase in cost.

Hence the study of tool wear is very important. The

tool wear occurs at two places on a cutting tool.

(i) At the cutting edge and the principal flank of thetool.

(ii) At the rake face of the tool. Refer Fig 1.36.

The wear at the flank is called flank wear and

the wear at the rake face is called crater wear.

1.7.1 Tool Wear Mechanisms

Some of the important tool wear mechanisms of ahard tool are:

(i) Shearing at High Temperature

(ii) Diffusion Wear.

(iii) Adhesive Wear (Attrition Wear)

(iv) Abrasive Wear

(v) Fatigue Wear

(vi) Electrochemical effect

(vii) Oxidation effect


Crater w ear Crater w idth

Flank wearFlank wearheight

(a)

Fig. 1.36. Tool Wear

A

B B ��B ��B �

Crater w ear

Flank wear

ABC-Originalcross-section

AB B B C-Cross-sectionof worn out tool

� ��

(b)

C

1.7 TOOL WEAR

A new or newly ground tool has sharp cutting edges

and smooth flanks. During machining operation it is

subjected to cutting forces, temperatures, sliding action,

mechanical and thermal shocks. Under these severe

conditions, the tools gradually wear out and even

fractures, necessitating a tool change.

This tool wear causes the following effects

The cutting forces increases.

The dimensional accuracy of the work decreases.

The surface roughness of work increases.

Increase in the temperature between tool andworkpiece.

The tool-work-machine starts vibrating.

The work piece/tool may get damaged.

Loss of production and increase in cost.

Hence the study of tool wear is very important. The

tool wear occurs at two places on a cutting tool.

(i) At the cutting edge and the principal flank of thetool.

(ii) At the rake face of the tool. Refer Fig 1.36.

The wear at the flank is called flank wear and

the wear at the rake face is called crater wear.

1.7.1 Tool Wear Mechanisms

Some of the important tool wear mechanisms of ahard tool are:

(i) Shearing at High Temperature

(ii) Diffusion Wear.

(iii) Adhesive Wear (Attrition Wear)

(iv) Abrasive Wear

(v) Fatigue Wear

(vi) Electrochemical effect

(vii) Oxidation effect




(a)


A

B B ��B ��B �

Crater w ear

Flank wear



� ��

(b)

C


1.7.1.1 Shearing at High TemperatureThe strength of hard metal decreases at high

temperatures. The shear yield stress becomes smaller athigh temperature than at room temperature. Though themetal sliding over it has lower yield stress, nevertheless,the chip may got so much work hardened as to be ableto exert frictional stress sufficient to cause yielding byshear of the hard tool metal. The higher the temperatureat the interface, the greater is the effect as shown in Fig.1.37.

1.7.1.2 Diffusion WearWhen a sliding metal is in contact with another

metal, the temperature is very high and the alloying atom

from harder metal starts diffusing into the softer matrix,

thereby increasing the hardness and abrasiveness of the

soft material. Also atoms from softer material diffuse into

the harder medium thus weakening the surface layer of

the tool. Diffusion process is highly dependent upon the

temperature. Diffusion process doubles for an increase of

temperature of order of 20C in machining using HSS

tools. Fig 1.38 shows diffusion process.

1.7.1.3 Adhesive Wear (Attrition Wear)When a soft metal slide over a hard metal such

that it always presents a newly formed surface to the

same portion of the hard metal. Due to friction, high

temperature and pressure, particles of soft material

adhere to a few high spots of the hard metal as shown

in Fig 1.39. As a result, flow of the softer metal over

the surface of the hard metal becomes irregular or less

laminar and contact between the two becomes less

continuous. More particles join up to form “Built up

edge”. These Built up edges when grow up are torn out

from the surface. This process continues and appears as

if the surface of hard metal is nibbled and looks uneven.

Chip m otionShear stress dueto chip

Chip

Tool

Shearing o fa ridge

M achinedsurface

Fig. 1.37. Wear by Plastic Yielding and Shear.


Steel ch ip

Chip

Tool

Fig. 1.38. Diffusion W ear Process

C

HSS

HSS Tool

.

1.7.1.4 Abrasive Wear

The softer metal sliding over the surface of theharder metal may contain appreciable concentrations ofhard particles (Eg). Casting may have sand particles.Under such condition, hard particles act as small cuttingedges like those of a grinding wheel on the surface of ahard metal which in due course, is wornout throughabrasion (Fig. 1.40). Also the particles of the hard toolmetal, which intermittently get torn out from its surfaceare dragged along the tool surface or rolled over. Theseparticles plough grooves into the surface of the hard toolmetal.

1.7.1.5 Fatigue Wear

Asperities are formed when two surface slides incontact with each other under pressure. These asperitiesinterlocks with each other. Due to friction, compressive

Chip

Chip

Tool

Fig. 1.39. Adhesive Wear M echan ism .

W eld

W eld

Tool

Tool particlewelded to chip


Chip

Chip

Tool

Fig. 1.40. Abrasive Wear M echanism .

Tool

Hard partic lein chip& m achined surface

M achined surface

Chip

Chip Flow

Tool

Fig. 1.41. Fatigue Wear Mechanism.

Tool

Tension

Com pression

Force by chip

stress is developed on one side of asperity and tensilestress on the other side (Fig 1.41). After the asperitiesof a given pair has moved over or through each other,the above stresses are relieved. New pair of asperitiesare soon formed and the stress cycle is repeated. Thusthe material of the hard metal near the surface undergoescyclic stresses. This phenomenon causes surface cracksand ultimately crumbling of hard metal. The variablethermal stresses due to high temperature also contributeto fatigue wear.

1.7.1.6 Electrochemical Effect

Due to the high temperatures existing on tool chipinterface, a thermoelectric EMF is set up in closed circuitdue to formation of junction at the chip tool interfaceassisting the tool wear.

1.7.1.7 Oxidation Effect

Grooves and notches are formed at rake face andflank due to the reaction of sliding portion of chip andmachined surface with atmospheric oxygen to formabrasive oxides causing wear.

1.7.1.8 Chemical decomposition

Local chemical reaction may occur that weaken thetool material through formation of weak compounds ordissolution of the bond between the binder and the hardconstituents of carbide tool. These weakened particles areeasily torn away by the aspirities of the chip or onmachined surface.

1.7.2 Types of Tool Damage in Cutting

The main types of Tool Wear / Damage are

(i) Flank Wear

(ii) Crater Wear

(iii) Groove formation

Flank Wear(Refer Fig 1.36)

The wear at the side and end of flank of tool is

called Flank wear. Flank wear is caused by the rubbing

action of the machined surface. The worn out region is

called wear land. Wear land is not of uniform width. It

is widest at a point farthest from the nose. When

diffusion becomes predominant wear mode on the flank,




(a)


A

B B ��B ��B �

Crater w ear

Flank wear



� ��

(b)

C

a critical wear land is formed and accelerating wear rate

takes place and then Rapid wear. It is advisable to

change the tool well before the on-set of the rapid wear

in order to avoid catastrophic tool failure. A typical wear

curve for cutting is shown in Fig 1.42

Crater WearCrater Wear occurs on the rake face of tool in the

form of a pit called crater. It is formed at a distance fromthe cutting edge. It is a temperature dependentphenomenon caused by diffusion, adhesion etc. Fig 1.43shows the radius of curvature Rc, depth of crater KT,

width of crater KB KM and the distance of the start of

the crater from the tool tip KM change with time. The

crater significantly reduces the strength of the tool andmay lead to total failure.

1.7.3 Tool Failure

Tool failure is said to have occurred when a tool isunable to produce desired shape, size and finish on thework piece. A tool failure can occur due to any one ofthe following.

(i) Loss of form stability due to high temperatureand stresses.

(ii) Mechanical breakage of tool.

Tim e

Wid

th o

f fla

nk w

ear

Initial rapid wear

Constant rate wear region

Rapid wearC

O C T

B

Fig. 1.42. A Typical Wear Curve for a Cutting Tool.


A

KB

K M

K B

K T

R C

K T

R C

(a)

Tim e

Val

ue o

f Cha

ract

ristic

A

(b)

Fig.1.43. Progress of Crater W ear

(iii) By the process of gradual wear on flank.

1.7.4 Measurement of Wear

Tool wear can be measured by any one of thefollowing methods with different degree of accuracy andconvenience.

(i) Measurement of height of Wear land.

(ii) Measurement of Volume (or depth).

(iii) Measurement of loss of weight of the tool.

(iv) Diamond Indentor technique.

(v) Radioactive technique.

1.8 TOOL LIFE

Tool life is defined as the time elapsed between twosuccessive grinding of tool (or) the time for which acutting edge or a cutting tool can be usefully employedwithout grinding (in case of HSS tools) or replacement(in the case of throwaway carbide or oxide inserts) iscalled as tool life.

The other ways of expressing tool life are

(i) Machine time: Tool life is the total time ofoperation of this machine tool.

(ii) Actual cutting time: The tool life is the timeelapsed during which the tool is actually cutting,between two successive grindings.

(iii) Volume of metal: Once a certain volume of metalis removed, the life of the tool is assumed to beover.

1.8.1 Tool failure Criterion

The various criterion for judging tool failure are:

(i) Complete Failure

A tool is continued to be used until it can cut theworkpiece. So when a tool fails to cut, then the tool hasto be ground.

(ii) Flank Failure

The wear on the flank causes the reduction in depthof cut. The work piece becomes taper if the cutting iscontinued. Therefore, if the wear on flank reaches certainheight, the tool is removed and reground. This is mostgeneral criterion of tool failure.

Flank wear is measured in Maker’s microscope.

(iii) Finish Failure

When the surface roughness of the workpiecereaches a certain high value, then the cutting of the toolis discontinued and regrinding is done. This criterionbecomes specially important when close fitting is requiredbetween the mating surfaces. Due to rough and unevensurfaces, the fitting may not be very close.

(iv) Size Failure

A tool is said to be failed when there is a changein the dimension of the finished work piece by a certainspecified value.

(v) Cutting Force Failure

If the cutting forces are increased by certainamount, the tool is said to be failed and regrounded.


1.8.2 Factors affecting Tool Life

The various factors which affect the tool life are

(i) Cutting Speed

(ii) Depth of Cut

(iii) Feed rate

(iv) Tool material properties

(v) Tool geometry

(vi) Work material properties

(vii) Type of cutting fluid and method of application

(viii) Rigidity of machine-tool-workpiece system

(ix) Nature of cutting.

(i) Cutting Speed

Cutting speed is one of the important factor whichaffects the tool life. The temperature increases with theincrease in the cutting speed which reduces the hardnessof tool and increases the flank and crater wears therebyreducing the tool life.

Frederick W.Taylor conducted number ofexperiments and derived an empirical relationshipbetween tool life and the cutting speed given by

VTn C ...(1.35)

Where V Cutting speed in m/min

T Tool life in min

n Tool life index [depending upon tool andwork material and cutting environments]

C Constant

In equation if T 1 then V C

Here the constant C can be physically interpretedas the cutting speed for which the tool life is one minute.

In Taylor’s equation the tool life equation becomesstraight line on log-log scale as shown in Fig. 1.44 i.elog V n log T log C ...(1.36)

The values of n for different tool materials are:

n 0.2 to 0.25 for HSS

0.25 to 0.45 for Carbide Tools

0.4 to 0.55 for Ceramic Tools

Equation 1.35 may be generalized to include the

effects of feed f and depth of cut d.

VTn f n1 dn2 C1

Where n, n1, n2, C1 are constants depending upon

tool and work material, tool geometry and type of coolant

used etc.


Tool life T (m in)

Cut

ting

spee

d V

(m/m

in)

Log

V

Log V+n Log T = Log C

Log T

Fig.1.44. Tool life Vs Cutting speed

(ii) Effect of Feed rate and depth of cut

With the increase in the feed rate and depth of cutthe tool life decreases. The life of the cutting tool isinfluenced by the amount of metal removed by the toolper minute which in turn depends upon the feed rate anddepth of cut.

The effect of feed and depth of cut on tool life forcemented carbide tool and low carbon steel combinationis given by:

V T0.2 260

f0.35 t0.08

Where V Cutting Speed in m/min

T Tool life in min

f Feed in mm/min

t Depth of cut in mm

(iii) Effect of Tool Material

Fig 1.45 shows the tool life variation againstcutting speed for different tool materials. The tool life isgreatest for ceramic tools and lowest for HSS.

(iv) Effect of work material hardness andmicrostructure

A general emphirical relationship between thehardness and cutting speed for a given tool is given as

VH1.7 Constant

Where V Permissible cutting speedH Brinell hardness number % reduction in size

If hardness is more, corresponding velocity shouldbe less as given by the expression.

Micro structure of work material affects the tool life.As percentage of pearlite increase, the tool life decreasesat any and every cutting speed.

(v) Effect of Cutting Fluid

As the tool cuts the work piece, a lot of heat isgenerated due to friction and rubbing. Heat producedduring metal cutting is carried away from the tool andworkpiece by means of cutting fluid. It also reduces thefriction between the chip tool interface and increases thetool life.

An empirical relationship between tool life andtemperatures of chip tool interface has been establishedand is given as

T n K

Where T Tool life in min Interface Temperature in Cn An exponent indexK Constant

30

60

150

300

90

1 2 3 5 10 20 30 50 100Tool life,T, m in

Fig. 1.45 Effect Tool material Cutting Speed on Tool life

Idea l

Ceram ic toolCarbide tool

H igh speed stee l tool


(vi) Tool Geometry

Tool geometry having various angles influences thelife of the tool.

Back rake angle affects the shear angle, shearstrain and cutting force.

High back rake reduces cutting force but makes thewedge thinner and rise in temperatureconsequently more wear rate and lower tool life.

Negative back rake increases cutting force but thewedge becomes more stronger.

Therefore optimum back rake angle should be usedand its range is 5 to 10.

Principle cutting edge angle also affects the tool life.

For the tool with 90 cutting edge angle (orthogonalcutting), the cutting edge is impact loaded over asmall area and hence the cutting force is very highthere by reduces the life of tool.

For the tool with less cutting edge angle (obliquecutting) the tool experiences cutting force graduallyand over a larger area and hence tool is safer andhas more life.

(vii) Rigidity of Workpiece-Machine tool System

If the rigidity of workpiece-machine tool system islow, higher the vibration of the system and higher thechances of tool failure. The vibration induces chipping oftool (specifically brittle tools), because of impact loadingon the tool due to intermittent cutting. Its rigidity is veryhigh then the damping is more and vibration is less and

less chatter and more life. Chatter causes fatigue orcatastrophic failure of tool.

(viii) Nature of Cutting

Sometimes the job is such that cutting edge has tofrequently enter and exit from the cut as for example inturning a work piece having longitudinal slots(Intermittent Cutting). Each entrance and exit gives animpact on the cutting edge than can shorten the tool life,especially if the tool material is hard or brittle.

(ix) Effect of nose radius of tool

Nose radius of the tool improves tool life andsurface finish of the workpiece. A relationship betweencutting speed, tool life and nose radius is given below.

VT0.09 300 R0.25

Where R Nose radius in mm

T Tool life in min

V Cutting speed in m/min

Nose radius has an optimum value at which toollife is maximum beyond which the tool life reduces.Larger nose radius means more contact area which inturnincreases friction there by reducing life of tool.

1.8.3 Machining Cost

Cost of machining involves the following cost

(i) Machining cost (cutting cost ormachine/operating cost)

(ii) Tool cost (Tool cost and Grinding Cost)

(iii) Idle cost (or) non productive cost.


(vi) Tool Geometry

Tool geometry having various angles influences thelife of the tool.

Back rake angle affects the shear angle, shearstrain and cutting force.

High back rake reduces cutting force but makes thewedge thinner and rise in temperatureconsequently more wear rate and lower tool life.

Negative back rake increases cutting force but thewedge becomes more stronger.

Therefore optimum back rake angle should be usedand its range is 5 to 10.

Principle cutting edge angle also affects the tool life.

For the tool with 90 cutting edge angle (orthogonalcutting), the cutting edge is impact loaded over asmall area and hence the cutting force is very highthere by reduces the life of tool.

For the tool with less cutting edge angle (obliquecutting) the tool experiences cutting force graduallyand over a larger area and hence tool is safer andhas more life.

(vii) Rigidity of Workpiece-Machine tool System

If the rigidity of workpiece-machine tool system islow, higher the vibration of the system and higher thechances of tool failure. The vibration induces chipping oftool (specifically brittle tools), because of impact loadingon the tool due to intermittent cutting. Its rigidity is veryhigh then the damping is more and vibration is less and

less chatter and more life. Chatter causes fatigue orcatastrophic failure of tool.

(viii) Nature of Cutting

Sometimes the job is such that cutting edge has tofrequently enter and exit from the cut as for example inturning a work piece having longitudinal slots(Intermittent Cutting). Each entrance and exit gives animpact on the cutting edge than can shorten the tool life,especially if the tool material is hard or brittle.

(ix) Effect of nose radius of tool

Nose radius of the tool improves tool life andsurface finish of the workpiece. A relationship betweencutting speed, tool life and nose radius is given below.

VT0.09 300 R0.25

Where R Nose radius in mm

T Tool life in min


Nose radius has an optimum value at which toollife is maximum beyond which the tool life reduces.Larger nose radius means more contact area which inturnincreases friction there by reducing life of tool.

1.8.3 Machining Cost

Cost of machining involves the following cost

(i) Machining cost (cutting cost ormachine/operating cost)

(ii) Tool cost (Tool cost and Grinding Cost)

(iii) Idle cost (or) non productive cost.


Total cost per piece CTot Cm CI CT CG

Where CM Machining cost C1 D L

1000 VS

Where C1 Direct labor cost Over head cost inRs/min

D Diameter of work piece machined in mm

L Length of machining in mm


S Feed in mm/rev

CI Idle cost C1 Idle time per piece

CT Tool changing cost

C1 Tool failure per workpiece T1.

Where T1 Tool changing time.

CG Tool grinding cost per piece

Tool cost per grind No. of failures per piece.

Optimum Tool life for minimum cost is

Topt 1n

1 C1 T1 C2

C1

Where C2 Tool cost per grind

also VTn Constant (Taylor equation)

1.8.4 Machinability

The term machinability is used to refer to the easewith which a given workpiece material can be machinedunder a given set of cutting conditions. It is of

considerable economic importance for a productionengineer to know in advance the machinability of a workmaterial, so that its processing can be efficiently planned.

1.8.4.1 Factors affecting machinability

The various factors affecting machinability are

(i) Chemical and physical properties of workmaterial.

(ii) Microstructure of work material.

(iii) Mechanical properties of work material.

(iv) Geometry of Tool (Various angles and noseradius)

(v) Rigidity of tool and machine.

(vi) Type of tool material.

(vii) Nature of operation and cutting condition.

1.9 SURFACE FINISH

A surface can be characterised by its topographyand microstructure. The topography describes its microgeometrical properties or texture in terms of roughness,waviness and lay. Microstructure describes the depth andnature of the altered material zone just below the surface.

Surface finish (or surface texture) refers to thefollowing properties of a machined surface as shown inFig. 1.46.

Roughness: Roughness consists of relativelyclose-spaced or fine surface irregularities, mainly in theform of feed marks left by cutting tool on the machinedsurface. The mean height or depth is measured over a 1mm cut off length or roughness sampling length.


Waviness: It consists of all surface irregularities whose

spacing is greater than the roughness sampling length.

Vibration, chatter and tool or workpiece deflections due

to cutting loads and cutting temperature may cause

waviness.

Lay: Lay denotes the predominate direction of the

surface irregularities. The lay is usually specified with

respect to an edge called the reference edge of workpiece.

Surface flaws: These are random spaced irregularities

i.e those which occur at some particular location on the

surface or at widely varying intervals. Flaws could be due

to inherent defects such as inclusions, cracks, blow-holes

etc.

1.9.1 Factors affecting surface finish

The factors which affects the surface finish are:

(i) Cutting tool geometry

(ii) Workpiece geometry

(iii) Machine tool rigidity

(iv) Workpiece material

(v) Cutting condition (speed, feed and depth of cut)

(vi) Tool material.

(i) Cutting Tool Geometry

The various angles rake, relief, cutting edge and

nose radius directly affects the surface finish on the

workpiece.

(ii) Workpiece Geometry

Long slender workpiece have low stiffness against

both static and dynamic forces. As a result waviness

effects are more in long work than small workpieces


A

(a)

Lay

Inclusion

Blow hole

B

Cut off length

Valleys Mean line

B Magnified Peaks

Roughness spacing

Waviness spacing

(b)

(c)

A Magnified

Fig. 1.46. E lem ents of Surface Texture

Waviness height

(iii) Machine Tool RigidityA sufficient high rigid machine produce less

vibration which inturn reduces the waviness in workpieceand produce high surface finish.

(iv) Workpiece Material

Chemical composition, hardness, microstructure andmetallurgical properties of the workpiece material largelyaffects the surface finish of workpiece. (eg) steel having0.1% or less carbon produce build up edge and therebyspoil surface finish.

(v) Cutting ConditionHigh speed cutting produces better surface finish

than at low cutting speed. Feed also affects the surfacefinish. A coarse feed produces rough surface and fine feedproduces good surface finish. Also depth of cut directlyaffects the surface finish. Light depth of cut produces finesurface finish, while heavy depth of a cut produces roughsurface.

(vi) Tool MaterialDifferent tool material have different hot hardness,

toughness and frictional behavior which affects thesurface finish

1.9.2 Measurement of RoughnessFollowing are the parameters measured in surface

roughness (Fig. 1.47)

(i) Overall height hmax

Overall height is height of separation between

upper and lower surface line occurring within sampling

length (L)

hmax Lp Lv

(ii) Leveling depth hp

It is the mean height of profile above the mean line

Lm. Mathematically

hp 1L

0

L

ydx

(iii) Centre Line Average hCLA

It is defined as the arithmetic average of the

deviation of the profile above and below the mean line

Lm

hCLA 1L

0

L

|Y| dx


Lp

Lm

Lv

yhp

hm ax

L

X

Fig. 1.47. M easures of Surface Roughness.

Y

(iv) Root mean Square Value hRms

It is defined as geometrical average value of thedeviation of the profile above and below mean line.

hRms

1L

0

L

y2 dx

1/2

1.9.3 Specification of Surface RoughnessISO recommendation on surface roughness in

machining specification is given in the Fig 1.48

Symbols are described as below:

a hCLA or centre line average value;

b Production method heat treatment andcontinuing

C Sampling length

d Direction of lay

e Machining allowance

The symbol d can take following symbols.

– When lay is parallel to plane of view

– The lay is perpendicular to plane of view

X – The lay is in 2 directions

M – The lay is multi-directional

C – The lay is circular

R – The lay is radial

1.10 CUTTING FLUIDS

In metal cutting process, heat is generated due toplastic deformation of metal, friction between chip andrake face of tool and rubbing between the flank and work.This increases the temperature of both tool andworkpiece. The temperature affects the tool life causingtool failure and surface finish of the workpiece isdeteriorated. Hence cutting fluids are used to remove theheat produced.

1.10.1 Functions of cutting fluids

The main functions of cutting fluids are:

(i) To cool the cutting tool and increase the tool life.

(ii) To cool the workpiece and helps in lubrication ofmachine.

(iii) To reduce the friction between the chip and thetool.

(iv) To flush away the chip to keep the cutting regionfree.

(v) To produce the machined surface free fromcorrosion.

(vi) Reduce the cutting forces and energy consumption.

60o

60o

e d

a

bc

Fig . 1.48. Drawing Sym bols for Surface Roughness in M achin ing


1.10.2 Properties of Good Cutting fluid

A good cutting fluid should have the followingcharacteristic properties.

(i) Good Lubricating Qualities

A cutting fluid should have good lubricatingproperty to remove the chip from touching and adheringto the tool face and preventing formation of built up edge.

(ii) High heat absorbing capacity or coolingcapacity

A good cutting fluid will remove more heat andremove the heat quickly thus reducing the temperaturebetween tool and workpiece.

(iii) Rust resistance

Cutting fluid should prevent rusting of work, toolor machine.

(iv) Cutting fluid should have low viscosity so thatchip and dirt easily settles.

(v) Cutting fluid should not be toxic in nature.

(vi) Cutting fluid should have high chemical stabilitysuch that it can be used for longer time.

(vii) Cutting fluid should have high flash point

(viii) It should not be harmful to worker or operator

(ix) It should be non flammable

(x) It should not produce smoke or foam easily

(xi) It should not produce bad smell

(xii) It should be of low cost.

1.10.3 Types of Cutting Fluids

Cutting fluids are of the following types:

(i) Solid based cutting fluids: It may be included inthe work material itself or applied on the chip tool interfacewith some liquid mainly to facilitate machining by reducingfriction. Ex. graphite, molybdenum disulphide etc.

(ii) Straight cutting fluid: These are of three types

(i) Mineral oils (ii) Fatty oils (iii) Combination ofmineral and fatty oils.

These oil have good lubricating properties but poorheat absorption quality and are used for low cuttingspeeds.

(iii) Oil with additives: The beneficial effects ofmineral oils can be improved with the help of additiveswhich are generally compounds of sulphur or chlorine.Addition of sulphur compounds reduces chances of chipwelding on tool rake face.

The additives and function are given below:

Additive Function(i) Mineral oils and other

hydrocarbonBase oil

(ii) Polyglycoether (watersoluble)

Emulsifier

(iii) Aliphatic amines(water soluble)

Neutralizing agent

(iv) Aliphatic amines inneutralized form

Corrosion protection

(v) Sulfonates Corrosion protection,pressure additive

(vi) Fatly acid amides Lubricity Improvement


Additive Function(vii) Sulphur / Phosphorous

additivesPressure additives

(viii) Aldehyde Derivatives Biocides

(iv) Water Soluble Cutting FluidsThese are also called water based cutting fluids.

These comprise of mineral oils, fat mixtures and

emulsifiers added to water. The oil is held in the form

of microscopic droplets (colloidal) in water, which assumes

a white milky appearance. Because of water, these have

very good cooling effects. Mixture is prepared in different

ratios of cutting oil and water to get the desired heat

transfer and lubricating characteristics.

1.10.4 Composition of Cutting FluidsA cutting fluid may contain the following.

Base oil

Emulsifier

Corrosion Inhibitor

Lubricating-antiwear-extreme pressure additives

Neutralising agents

Biocides and Fungicides

Foam inhibitors

Stabilizing agent.

Table 1.1 shows the different types of coolants and

lubricants used for different type of operations.


1.10.5 Method of applying cutting fluid

The method of applying a cutting fluid is very

important if one wants to use full benefit and to conserve

it or reduce its wastage. The various methods are

(i) Nozzle-pump tank method: A pump is mounted on

the tank containing fluid and outlet of pump is connected

to nozzle through flexible hose. The nozzle directs the

stream of fluid at desired point.

(ii) Mist application: In this method fluid is passed

through a specially designed nozzle so that it forms very

fine droplets of cutting fluid or produce a mist of size 5

to 25 m directed at cutting zone.

(iii) High jet method: A narrow jet at high velocity is

directed at the flank surface of the tool. It is the most

recent method.

1.11 SOLVED PROBLEMS IN CUTTING FORCES

Problem 1.2 A dynamometer measures the following feed

force 100 kgs, cutting force 375 kgs, rake angle 12,Chip thickness ratio 0.3, Find the following (i) Shear

Angle (ii) Shear force (iii) Coefficient of friction (iv) Compressive force at shear plane. (Apr/May 2012 .AU)

Given:

Feed force (Fd 100 kgs, cutting force

Fc 375 kgs, rake Angle 12 Chip thickness ratio

r 0.3


Solution:

(i) Shear Angle

We know that tan r cos

1 r sin (from Eqn. 1.3)

Shear Angle tan 1

0.3 cos 121 0.3 sin 12

tan 1 [0.3129]

Shear Angle 17.38

(ii) Shear force Fs

Shear force Fs FC cos Fd sin

(From Eqn. 1.6)

375.cos 17.38 100 sin 17.38

Fs 328 kgs

(iii) Normal or Compressive force Fn

Compressive force Fn FC sin Fd cos (From Eqn. 1.6)

375 sin 17.38 100 cos 17.38

Fn 207.45 kgs

(iv) Coefficient of friction

We know that coefficient of friction

FC tan Fd

FC Fd tan (From Eqn. 1.12)

375 tan 12 100375 100 tan 12

0.508

0.508

Friction Angle tan 1 tan 10.508 26.93

Problem 1.3 In orthogonal cutting process which has depth

of cut 0.3 mm, Chip thickness ratio 0.5, Width of cut

6 mm, Cutting Velocity 60 m/min, cutting force parallel

to cutting velocity 1200 N, Cutting force normal to cutting

velocity 160 N, Rake angle 12. Determine the shear

Angle, Resultant cutting force, Power required for cutting,coefficient of friction, force component parallel to shear plane? (Apr-2013-AU)

Given:

Depth of cut t1 0.3 mm, Chip thickness ratio

r 0.5, Width of cut b 6 mm, Cutting Velocity

Vc 60 m/min, Cutting force Parallel to cutting velocity

Fc 1200 N, Cutting force normal to cutting Velocity

Fd 160 N, Rake angle 12

Solution

(i) Shear Angle


1 r sin

0.5 cos 121 0.5 sin 12

Shear Angle tan 1

0.5 cos 121 0.5 sin 12

tan 10.5458

28.62

(ii) Resultant Cutting Force F

We know that F Fc2 Fd

2 12002 1602

F 1210 N


Solution:

(i) Shear Angle


1 r sin (from Eqn. 1.3)

Shear Angle tan 1

0.3 cos 121 0.3 sin 12

tan 1 [0.3129]

Shear Angle 17.38

(ii) Shear force Fs

Shear force Fs FC cos Fd sin

(From Eqn. 1.6)

375.cos 17.38 100 sin 17.38

Fs 328 kgs

(iii) Normal or Compressive force Fn

Compressive force Fn FC sin Fd cos (From Eqn. 1.6)

375 sin 17.38 100 cos 17.38

Fn 207.45 kgs

(iv) Coefficient of friction

We know that coefficient of friction

FC tan Fd

FC Fd tan (From Eqn. 1.12)

375 tan 12 100375 100 tan 12

0.508

0.508

Friction Angle tan 1 tan 10.508 26.93

Problem 1.3 In orthogonal cutting process which has depth

of cut 0.3 mm, Chip thickness ratio 0.5, Width of cut

6 mm, Cutting Velocity 60 m/min, cutting force parallel

to cutting velocity 1200 N, Cutting force normal to cutting

velocity 160 N, Rake angle 12. Determine the shear

Angle, Resultant cutting force, Power required for cutting,coefficient of friction, force component parallel to shear plane? (Apr-2013-AU)

Given:

Depth of cut t1 0.3 mm, Chip thickness ratio

r 0.5, Width of cut b 6 mm, Cutting Velocity

Vc 60 m/min, Cutting force Parallel to cutting velocity

Fc 1200 N, Cutting force normal to cutting Velocity

Fd 160 N, Rake angle 12

Solution

(i) Shear Angle


1 r sin

0.5 cos 121 0.5 sin 12

Shear Angle tan 1

0.5 cos 121 0.5 sin 12

tan 10.5458

28.62

(ii) Resultant Cutting Force F

We know that F Fc2 Fd

2 12002 1602

F 1210 N


(iii) Power required for cutting P

Power P Fc Vc

P 1200 60 72,000 Nm/min

P 72000

60 1200 Nm/sec 1200 watts

Power P 1.2 kW

(iv) Coefficient of Friction

We know that

Fc tan Fd

Fc Fd tan

1200 tan 12 1601200 160 tan 12

0.356.

Friction Angle tan 1 tan 1 0.356 19.59

(v) Force Component Parallel to shear plane Fs

We know that Fs Fc cos Fd sin

1200 cos 28.62 160 sin 28.62

Fs 976.74 N

Problem 1.4 The machining of a steel with a tool havingsignature 0-12-6-8-8-90-1 mm ORS shaped tool has the

following observations. Feed 0.7 mm/rev, depth of cut

3 mm, cutting speed 60 m/min, Shear Angle 15.Power consumed while in machining 6 kW and idle power

1 kW. Calculate (i) The cutting force, (ii) Chip thickness

ratio, (iii) Normal pressure on the chip (iv) Chip thickness.

Given:

From tool signature we have rake angle 12Feed f 0.7 mm/rev, depth of cut d 3 mm, cutting

speed Vc 60 m/min, Shear Angle 15.

Power for machining P 6 kW, Idle Power

PI 1 kW.

Solution

(i) Cutting Force Fc

Net Cutting Power Pc P PI 6 kW 1 kW

Pc 5 kW

We know Power Pc Fc Vc

50 103 Fc 60

60

Vc 60 m/min

6060

m/sec

Cutting force Fc 50 103

60 60 50 kN

(ii) Chip thickness ratio r

We know tan r cos

1 r sin

tan 15 r cos 12

1 r sin 12

0.268 r 0.978

1 0.208 r

0.268 r 0.978 0.208 0.268

r 0.2593


(iii) Normal Pressure on the chip

Pressure P Force FcChip Area

Fc

w t

here w Depth of cut 3 mm

t Feed 0.7 mm

Pressure P 50 103

3 0.7 23.81 kN/mm2

(iv) Chip Thickness tc

tc Feed

Chip thickness ratio

0.70.2593

2.7 mm

Problem 1.5 A seamless tube 40 mm outside diameter isturned orthoganally. The following data are obtained. Rake

angle 40, Cutting Speed 25 m/min, feed

0.15 mm/rev. Length of Chip ( 1 rev) 60 mm. Cutting

force 300 kg, feed force 100 Kg. Calculate (i) Coefficient

of friction (ii) Shear Angle (iii) Velocity of Chip along toolface (iv) Chip thickness.

Given:

Diameter of tube D 40 mm, Rake angle 40, Feed f 0.15 mm/rev, Cutting Speed Vc 25 m/min,

Length of Chip (rev) 60 mm, Fd 100 kg, Fc 300 kg

Solution

(i) Coefficient of friction

Fc tan Fd

Fc Fd tan

300 tan 40 100300 100 tan 40

1.628

(ii) Shear Angle


1 r sin


r t1

t2

l1l2

60

D

60 D

60

40 0.4775

tan 0.4775 cos 40

1 0.4775 sin 40

0.36580.6931

0.5265

Shear Angle tan 1 0.5265 27.77

(iii) Chip Velocity Vf

Vf Vc r 25 0.4775 11.94 m/min

(iv) Chip Thickness t2

r t1t2

; t2 t1

r

0.150.4775

0.314 mm

Problem 1.6 In orthogonal cutting of Mild steel rod ofdiameter 200 mm and depth of cut 1.5 mm with a cuttingspeed of 50 m/min and feed of 0.3 mm/rev, the following

were obtained, cutting force 200 kg, Feed force 50 kg,

Chip thickness 0.35 mm, Contact length 1 mm, Net

Power 2.5 kW and Back rake angle 15. Calculate the

shear strain and strain energy per unit volume, normalpressure. (Nov/Dec-2012 -AU)

Given:

Diameter of rod D 200 mm; Depth o f cut

d 1.5 mm, Cutting Speed Vc 50 m/min, Feed

f 0.3 mm/rev, Cutting force Fc 200 kg, Feed force


(iii) Normal Pressure on the chip

Pressure P Force FcChip Area

Fc

w t

here w Depth of cut 3 mm

t Feed 0.7 mm

Pressure P 50 103

3 0.7 23.81 kN/mm2

(iv) Chip Thickness tc

tc Feed


0.70.2593

2.7 mm

Problem 1.5 A seamless tube 40 mm outside diameter isturned orthoganally. The following data are obtained. Rake

angle 40, Cutting Speed 25 m/min, feed

0.15 mm/rev. Length of Chip ( 1 rev) 60 mm. Cutting

force 300 kg, feed force 100 Kg. Calculate (i) Coefficient

of friction (ii) Shear Angle (iii) Velocity of Chip along toolface (iv) Chip thickness.

Given:

Diameter of tube D 40 mm, Rake angle 40, Feed f 0.15 mm/rev, Cutting Speed Vc 25 m/min,

Length of Chip (rev) 60 mm, Fd 100 kg, Fc 300 kg

Solution

(i) Coefficient of friction

Fc tan Fd

Fc Fd tan

300 tan 40 100300 100 tan 40

1.628

(ii) Shear Angle


1 r sin


r t1

t2

l1l2

60

D

60 D

60

40 0.4775

tan 0.4775 cos 40

1 0.4775 sin 40

0.36580.6931

0.5265

Shear Angle tan 1 0.5265 27.77

(iii) Chip Velocity Vf

Vf Vc r 25 0.4775 11.94 m/min

(iv) Chip Thickness t2

r t1t2

; t2 t1

r

0.150.4775

0.314 mm

Problem 1.6 In orthogonal cutting of Mild steel rod ofdiameter 200 mm and depth of cut 1.5 mm with a cuttingspeed of 50 m/min and feed of 0.3 mm/rev, the following

were obtained, cutting force 200 kg, Feed force 50 kg,

Chip thickness 0.35 mm, Contact length 1 mm, Net

Power 2.5 kW and Back rake angle 15. Calculate the

shear strain and strain energy per unit volume, normalpressure. (Nov/Dec-2012 -AU)

Given:

Diameter of rod D 200 mm; Depth o f cut

d 1.5 mm, Cutting Speed Vc 50 m/min, Feed

f 0.3 mm/rev, Cutting force Fc 200 kg, Feed force


Fd 50 kg, Chip thickness t2 0.35 mm, Contact length

L 1 mm, Net Power 2.5 kW, Back rake Angle

15

Solution:

(i) To Calculate Shear Angle


1 r sin

Chip thickness ratio r t1t2

0.3

0.35 0.857

Shear Angle tan 1

0.857 cos 151 0.857 sin 15

0.6775

tan 1 [0.6775 ] 34.12

(ii) Shear Strain e

We know that Shear Strain

e cos

sin cos

(from Eqn. 1.30)

e cos 15

sin 34.12 cos 34.12 15

0.966

0.561 0.6545 2.631

Shear Strain e 2.631

(iii) Shear Stress s

Shear Force Fs Fc cos Fd sin (Eqn.1.6)

200 cos 34.12 50 sin 34.12

137.53 kg

Shear Stress s Shear ForceShear Area

Fs sin

w.t

(From Eqn. 1.27)

137.53 sin 34.12

1.5 0.3 171.43 kg/mm2

s 171.43 9.81 1681.7 N/mm2

Shear Velocity Vs Vc cos

cos (From Eqn. 1.2)

50 cos 15

cos 34.12 15 73.8 m/min

(iv) Shear Energy Es

Shear Energy Es s Vs

Vc sin (From Eqn. 1.34)

Shear Energy 1681.7 73.850 sin 34.12

4425 N/mm2

(v) Normal Pressure

Fc

Area of chip

200Feed Depth

200

0.3 1.5 444.44 kg/mm2

Normal Pressure 4.44 kN/mm2

Problem 1.7 In an orthogonal cutting operation on aworkpiece of width 2.5 mm, the uncut chip thickness was0.25 mm and the tool rake angle was zero degree. It wasobserved that the chip thickness was 1.25 mm. The cuttingforce was measured to be 900 N and the thrust force was


found to be 810 N.(i) Find Shear Angle(ii) If the Coefficient of friction between the chip and toolwas 0.5, what is the machining constant Cm?

(Anna Univ Nov. 2010)

Given:

Width w 2.5, Uncut chip thickness

t1 0.25 mm, Rake Angle 0, Chip thickness

t2 1.25 mm, Cutting force Fc 900 N, Thrust Force

Fd 810 N, Coefficient of friction 0.5

Solution

(i) To find Shear Angle

Chip Thickness ratio r t1

t2

0.251.25

0.2

Shear Angle

tan r cos

1 r sin

tan 1

r cos 1 r sin

tan 1

0.2 cos 01 0.2 sin 0

tan 1 [0.2] 11.31

Shear Angle 11.31

(ii) To find Machining Constant Cm

Machining Constant Cm 2

Shear Force Fs Fc cos Fd sin

900 cos 11.31 810 sin 11.31

Fs 723.67 N

Shear Stress s Shear force

Area

Fs sin w.t1

s 723.67 sin 11.31

2.5 0.25 227.1 N

Coefficient of friction tan

tan 1 tan 10.5 26.565


2 11.31 26.565 0

Cm 49.185

Problem 1.8 In an orthogonal machining with a tool rake

angle of 10, the chip thickness was found to be 3 mm when

the uncut chip thickness is set to 0.5 mm. Find the ShearAngle and friction angle [Assume Merchant formula isholding good for the machining].

Given:

Rake Angle 10, Chip thickness t2 3 mm,

Uncut chip thickness t1 0.5 mm

(i) Shear Angle


t2

0.53

0.167

Shear Angle : tan r cos

1 sin

tan 1

r cos 1 r sin


found to be 810 N.(i) Find Shear Angle(ii) If the Coefficient of friction between the chip and toolwas 0.5, what is the machining constant Cm?

(Anna Univ Nov. 2010)

Given:

Width w 2.5, Uncut chip thickness

t1 0.25 mm, Rake Angle 0, Chip thickness

t2 1.25 mm, Cutting force Fc 900 N, Thrust Force

Fd 810 N, Coefficient of friction 0.5

Solution

(i) To find Shear Angle


t2

0.251.25

0.2

Shear Angle

tan r cos

1 r sin

tan 1

r cos 1 r sin

tan 1

0.2 cos 01 0.2 sin 0

tan 1 [0.2] 11.31

Shear Angle 11.31

(ii) To find Machining Constant Cm


Shear Force Fs Fc cos Fd sin

900 cos 11.31 810 sin 11.31

Fs 723.67 N

Shear Stress s Shear force

Area

Fs sin w.t1

s 723.67 sin 11.31

2.5 0.25 227.1 N

Coefficient of friction tan

tan 1 tan 10.5 26.565


2 11.31 26.565 0

Cm 49.185

Problem 1.8 In an orthogonal machining with a tool rake

angle of 10, the chip thickness was found to be 3 mm when

the uncut chip thickness is set to 0.5 mm. Find the ShearAngle and friction angle [Assume Merchant formula isholding good for the machining].

Given:

Rake Angle 10, Chip thickness t2 3 mm,

Uncut chip thickness t1 0.5 mm

(i) Shear Angle


t2

0.53

0.167

Shear Angle : tan r cos

1 sin

tan 1

r cos 1 r sin


tan 1

0.167 cos 101 0.167 sin 10

tan 1 0.16450.971

9.613

(ii) According to Merchant Theory [ Friction angle]

2 /2

2 9.613 10 90

Friction Angle 80.77

Problem 1.9 In orthogonal machining of a tube in lathewhose outer diameter is 80 mm and wall thickness of 4 mmto reduce its length. The speed of workpiece is 150 rpm andlongitudinal feed is 0.4 mm/rev, cutting ratio is 0.25 withtangential force of 1000 N and axial force of 500 N. Findchip velocity and power consumed? (Apr-2008-AU)

Given:

Outer diameter Do 80 mm, Wall thickness

tw 4 mm, N 150 rpm, f 0.4 mm/rev, Cutting ratio

0.25, Fc 1000 N, Fd 500 N

Solution

1. Chip Velocity

Cutting ratio Velocity of Chip

Velocity of workpiece

Velocity of workpiece V D N in m/min

Where D Mean diameter

D Do di

2

di Do 2tw 80 2 4 72 mm

D 80 72

2 76 mm

Velocity of workpiece V 76 150 35814 mm/min

V 35.814 m/min

Velocity of Chip Vc 0.25 35.814 8.954 m/min

Power Consumed P Fc V

P 1000 35.814

60 570 watts

Problem 1.10 In an orthogonal cutting of a mild steel,

following were observed cutting force 1200 N, Feed force

500 N, Cutting velocity 100 m/min Rake Angle 12and shear plane angle is 20. Determine the following

(i) Shear velocity (ii) Chip flow Velocity (iii) Work done perminute in shearing and against friction (iv) show that workinput is sum of work done in shearing and friction.

Given:

Cutting force Fc 1200 N, Feed force Fd 500 N,

Cutting Velocity Vc 100 mm/min. rake angle 12

Shear Angle 20

Solution

(i) Shear Velocity Vs

Vs Vc cos

cos ...(From eqn. 1.2)


Vs 100 cos 12

cos 20 12 98.78 m/min

(ii) Chip flow velocity Vt

Vt Vc sin

cos ...(From Eqn. 1.1)

Vt 100 sin 20

cos 20 12 34.54 m/min

(iii) Work done in Shearing and Friction

Work done in shear Ws Fs Vs.

Fs Fc cos Fd sin 1200 cos 20 500 sin 20

Fs 956.62 N

Ws 956.62 98.78

60 1575 W

Friction Force Ff Fd cos Fc sin

500 cos 12 1200 sin 12

Ff 738.57 N

Work done in friction WF Ff Vt 738.57 34.54

60

425.17 W

(iv) Total workdone W

Ws WF 1575 425.17 2000 W

Work input WI Fc V 1200 100

60 2000 W

Hence WI W

Problems on Tool life and wear.Problem 1.11 The Taylor tool-life equation for machiningC-40 steel with a HSS cutting tool at a feed of 0.2 mm/rev

and a depth of cut of 2 mm is given by VTn C Where n

and c are constants. The following V and T observationshave been noted.

V, m/min – 25 35

T, min – 90 20

Calculate (i) n and C (ii) Hence recommend the cuttingspeed for a desired tool life of 60 min (Anna Univ. May 2011)

Given:

Feed f 0.2 mm/rev, d 2 mm ; Taylors Eqn.

VTn C, V1 25 m/min, V2 35 m/min,

T1 90 min, T2 20 min

Solution

(i) To find n & C

According to Taylors Eqn. VTn C

V1T1n C V2 T2

n

25 90n 35 20n

9020

n

3525

4.5n 1.4

n log 4.5 log 1.4


n log 1.4log 4.5

0.223

Now

V1T1n C

C 25 900.223 68.192

(ii) To find Cutting Speed at 60 min

Given: T3 60 min

Again V3 T3n C

V3 68.192

600.223 27.37 m/min

Cutting Speed V3 27.37 m/min

Problem 1.12 A HSS tool gave a tool life of 120 min at15 m/min and 25 min at 70 m/mm. Calculate (i) C and

n for Taylor’s equation. (ii) Cutting Speed for minimum lifesay 1 min?

Given:

T1 120 min, V1 15 m/min, T2 25 min, V2 70 m/min

Solution

(i) To find C and n for Taylor’s Equation.

We know that VTn C

V1 T1n V2 T2

n

15 120n 70 25n

12025

n

7015

n log 4.8 log 4.67

n log 4.67log 4.8

0.9825

Now, V1 T1n C

C 15 1200.9825 1655.33

The Taylor Equation is VT0.9825 1655.33

(ii) Cutting Speed for Minimum Tool life say 1 min

VT0.9825 1655.33 (T 1 min)

V 10.9825 1655.33

V 1655.33 m/min

Problem 1.13 The tool life equation for HSS and carbide

tool are given as follows. Carbide: VT0.3 C1 and HSS Tool:

VT0.2 C2. If the tool life is 100 min at 50 m/min, Compare

the tool life of both tools at 150 m/min.

Given:

For HSS tool VT0.2 C2 and

For Carbide Tool VT0.3 C1

T 100 min at V 150 m/min

Solution:

(i) To Find C1 & C2

VT0.2 C2


50 1000.2 C2

VT0.3 C1

50 1000.3 C1

C2 125.6 ; C1 199.1

To Find T1 & T2 at 150 m/min

For Carbide Tool: VT0.3 C1

150 T10.3 199.1

T1 199.1150

1/0.3

2.57 min

HSS Tool VT0.2 C2

150 T20.2 125.6

T2 125.6150

1/0.2

0.412 min

T1

T2

2.570.412

6.24

Life of Carbide Tool is 6.24 Times life of HSS tool.

Problem 1.14 The modified Taylor equation for a Carbide

tool is given as VT0.3 f0.4 d0.2 C. It was obtained a tool

life of 100 min under the following condition.

V 50 m/min, f 0.5 mm d 1 mm. Calculate the effect of tool

of life if feed is increased by 20%, Speed by 15% and depthof cut by 50% together. (Nov/Dec-2009 - AU)

Given:

VT0.3 f0.4 d0.2 C, T 100 min, V 50 m/min,

f 0.5 mm, d 1 mm

Solution

(i) To Find the Constant C

C VT0.3 f0.4 d0.2

C 50 1000.3 0.50.4 10.2 150.854

(ii) Effect on Tool life

Increase in Feed

20% f1 f 20

100 f 1.2 f 1.2 0.5

f1 0.6

Increase in Speed 15% V1 1.15V 1.15 50 57.5

Increase in depth of cut 50% d1 1.5 d 1.5 1 1.5

V1 T10.3 f1

0.4 d10.2 C

57.5 T1

0.3

0.60.4 1.50.2 150.854.

life T1

150.854

57.5 0.60.4 1.50.2

1/0.3

150.85450.833

1/0.3

2.967 1/0.3

life T1 37.56 mins

The effect on tool life is

T T1 100 37.56 62.44 min

Tool life is reduced by 62.44 mins.


Solved Question PaperAnna University

ME 2252 - Manufacturing Technology - IIApril / May - 2010

(Part – A)

1. How do you classify tool wear?

For answer refer Short Question and Answer No.1.29

2. Define Tool Life.

For answer refer short question and answer No.1.30

Part – B

11. (a) (i) Discuss the various types of chipsproduced during metal machining.

For answer refer section 1.5.4, 1.5.4.2, 1.5.4.3,1.5.4.4.

(ii) State the parameters that influence tool lifeand discuss.

For answer refer section 1.8.2

(b) (i) What is meant by orthogonal cutting andoblique cutting.

For answer refer section 1.5.3, 1.5.3.1

(ii) Explain ‘Merchant force circle’ along withassumptions.

For answer refer section 1.5.6.4

ME 2252 – Manufacturing Technology - IINov/Dec - 2010

Part - A

1. What are the objectives and functions of cuttingfluids?

For answer refer short question and answerNo.1.41.

2. Briefly explain the effect of rake angle duringcutting.


Part - B

11. (a) In an orthogonal cutting operation on aworkpiece of width 2.5 mm, the uncut chipthickness was 0.25 mm and the tool rake anglewas zero depths. It was observed that the chipthickness was 1.25 mm. The cutting force wasmeasured to be 900 N and the thrust force wasfound to be 810 N (i) find shear angle (ii) Ifthe coefficient of friction between the chip andthe tool was 0.5, what is the machiningconstant Cm?

For answer refer solved problem No.1.7

(b) (i) Describe the different types of chips withneat sketches.



Solved Question PaperAnna University

ME 2252 - Manufacturing Technology - IIApril / May - 2010

(Part – A)

1. How do you classify tool wear?

For answer refer Short Question and Answer No.1.29

2. Define Tool Life.

For answer refer short question and answer No.1.30

Part – B

11. (a) (i) Discuss the various types of chipsproduced during metal machining.


(ii) State the parameters that influence tool lifeand discuss.


(b) (i) What is meant by orthogonal cutting andoblique cutting.

For answer refer section 1.5.3, 1.5.3.1

(ii) Explain ‘Merchant force circle’ along withassumptions.

For answer refer section 1.5.6.4

ME 2252 – Manufacturing Technology - IINov/Dec - 2010

Part - A

1. What are the objectives and functions of cuttingfluids?


2. Briefly explain the effect of rake angle duringcutting.


Part - B

11. (a) In an orthogonal cutting operation on aworkpiece of width 2.5 mm, the uncut chipthickness was 0.25 mm and the tool rake anglewas zero depths. It was observed that the chipthickness was 1.25 mm. The cutting force wasmeasured to be 900 N and the thrust force wasfound to be 810 N (i) find shear angle (ii) Ifthe coefficient of friction between the chip andthe tool was 0.5, what is the machiningconstant Cm?


(b) (i) Describe the different types of chips withneat sketches.



(ii) Mention the functions of cutting fluids.


ME - 2252 - Manufacturing Technology - IIApril / May 2011

(Part – A)

1. Compare orthogonal and oblique cutting.

For answer refer section 1.5.3.1 (or) short questionand answer No.1.16

2. Define Tool life.

For answer refer short question and answer No.1.30.

Part – B

11. (a) (i) Describe the mechanism of metalcutting.


(ii) Discuss the various types of chips producedduring metal machining.

For answer refer section 1.5.4, 1.5.4.2, 1.5.4.3,1.5.4.4

(b) (i) The taylor tool life equation for machiningC 40 steels with a HSS cutting tool at a feedof 0.2 mm/min and a depth of cut of 2 mm is

given by VTn C where n & C are constants. Thefollowing V and T observations are made.

V m/min 25 35

T min 90 20

Calculate: (i) n and C (ii) Hence recommend thecutting speed for a desired tool life of 60 min.


(ii) List the various tool materials used in industry.State the optimum temperature of each of thetool materials.

For answer refer section No.1.6.2.

ME 2252 - Manufacturing Technology - IINov/Dec - 2011

Part - A

1. State any two situation where positive rakeangle is recommended during turning.


2. Name any two reasons for flank wear in cuttingtools.

(i) High coefficient of friction tool material.

(ii) High rake angle.

(Part – B)

11. (a) (i) Discuss the advantages and limitationsof the following cutting tool materials 1.Cemented carbides 2. Cubic Boron nitride.Also state the desirable characteristics of acutting tool material.

(a) Desirable characteristics of cutting tool - refersection 1.6.1

(b) Cemented Carbide Tools: Refer Section 1.6.2 (V)


(c) Cubic Boron nitride (CBN): It consists of atomsof boron and nitrogen, and is the hardest next todiamond.

Features:

1. It is having high hardness.

2. High Thermal Conductivity.

3. High Tensile Strength.

4. A thin layer of CBN is applied on cementedcarbide tools to obtain high machiningperformance.

5. It can be made in terms of indexable inserts instandard forms and size called “BOROZON”.

(ii) With the help of sketches explain the followingtypes of chips produced during metalmachining.(i) Continuous Chips(ii) Continuous chips with built up edges.

For Answer refer section 1.5.4.2, 1.5.4.3

(b) (i) With help of a sketch, show crater wear andflank wear on a cutting tool.


(ii) Explain types and applications of differenttypes of cutting tools.

For answer refer section 1.3.

(iii) Enumerate the factors that effect the cuttingtemperature during machining.Factors affecting the cutting temperation duringmachining are:

(a) Cutting tool geometry (various angles like rakeangle, cutting edge angle, relief angle, lip angle,nose radius).(b) Work piece and tool material.(c) Machine tool rigidity(d) Cutting condition (speed, feed and depth of cut)(e) Microstructure of work piece and tool material(f) Nose Radius of the cutting tool.


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