introduction (2)

Chapter IChapter I

©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

Overview of processes

Cutting processes

INTRODUCTION

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Manufacturing Technology I Metal casting (Sand casting and other casting processes) Materials Joining (Arc welding, TIG, EBW, PAW, etc.) Bulk deformation (Metal Forming – Forging, Rolling, Extrusion) Sheet metal processes (Shearing, bending, drawing, etc.) Manufacturing of plastic materials (Injection molding, etc).

Manufacturing Technology II (Material removal process) Metal Cutting or Mechanical Abrasion Centre lathe and special purpose lathes Shaper, Planer, Slotter, Milling, Drilling, Broaching, Gear cutting,

etc. Grinding, Honing, Lapping, etc. CNC and DNC

INTRODUCTION – CONTD.

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Machining – produces finished products with high degree of accuracy.

Conventional machining Utilizes cutting tools (harder than workpiece material). Needs a contact between the tool and workpiece. Needs a relative motion between the tool and workpiece.

Absence of any of these elements – makes the process a unconventional or nontraditional one.

Big boon to modern manufacturing industries. The need for higher productivity, accuracy and surface

quality – led to combination of two or more machining actions, called hybrid machining processes.

HISTORY OF MACHINING

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In ancient days – hand tools (stones, bones or stick). Later – hand tools of elementary metals (bronze or iron) Till 17th Century – tools were either hand operated or driven

mechanically by very elementary methods. Wagons, ships, furniture, etc. – were produced. Introduction of water, steam and electricity – power driven

machine tools Caused a big revolution in 18th and 19th centuries. 1953 – Numerical control machine tools – enhanced the

product productivity and accuracy.

TRADITIONAL OR CONVENTIONAL MACHINING

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METAL CUTTING PROCESSES

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ABRASIVE MACHINING

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Cylindrical grinding

Flat surface grinding

ABRASIVE MACHINING

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Centreless grinding

NTM ProcessesNTM ProcessesFour basic groups of material removal using NTM processes

◦Chemical: Chemical reaction between a liquid reagent and workpiece

results in etching◦Electrochemical

An electrolytic reaction at workpiece surface for removal of material

◦Thermal High temperature in very localized regions evaporate

materials, for example, EDM◦Mechanical

High-velocity abrasives or liquids remove materials

Limitations of Conventional Limitations of Conventional Machining ProcessesMachining ProcessesMachining processes that involve chip

formation have a number of limitations◦Large amounts of energy◦Unwanted distortion◦Residual stresses◦Burrs ◦Delicate or complex geometries may be difficult or impossible

NEED FOR UNCONVENTIONAL MACHINING

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• Greatly improved thermal, mechanical and chemical properties of modern materials – Not able to machine thru conventional methods. (Why???)

• Ceramics & Composites – high cost of machining and damage caused during machining – big hurdles to use these materials.

• In addition to advanced materials, more complex shapes, low rigidity structures and micro-machined components with tight tolerances and fine surface finish are often needed.

• To meet these demands, new processes are developed.• Play a considerable role in aircraft, automobile, tool, die and

mold making industries.

NEED FOR UNCONVENTIONAL MACHINING

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• Very high hardness and strength of the material. (above 400 HB.)• The work piece is too flexible or slender to support the cutting or

grinding forces.• The shape of the part is complex, such as internal and external

profiles, or small diameter holes.• Surface finish or tolerance better than those obtainable

conventional process.• Temperature rise or residual stress in the work piece are

undesirable.

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UNCONVENTIONAL MACHINING PROCESSES - CLASSIFICATION

Electrical

MECHANICAL BASED PROCESSES

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1. Working principles

2. Equipment used

3. Process parameters

4. MRR

5. Variation in techniques used

6. Applications

AJM

WJM

AWJM

USM

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ELECTRICAL BASED PROCESSES

1. Working principle

2. Equipment used


4. Surface finish & MRR

5. Electrode/Tool

6. Power & Control circuits

7. Tool wear

8. Dielectric

9. Flushing

10. Applications

Electrical

EDM

WEDM

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CHEMICAL & ELECTROCHEMICAL BASED PROCESSES


2. Etchants & Maskants

3. Techniques of applying maskants


5. Surface finish & MRR

6. Electrical circuits in case of ECM

7. Applications

CHM

ECM

ECG

ECH

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THERMAL BASED PROCESSES


2. Equipment used

3. Types

4. Beam control techniques

5. Applications

LBM

PAM

EBM

MECHANICAL BASED UNCONVENTIONAL PROCESSES

USM – thru mechanical abrasion in a medium (solid abrasive particles suspended in the fluid)

WJM – Cutting by a jet of fluid

AWJM – Abrasives in fluid jet.

IJM – Ice particles in fluid jet.Abrasives or ice – Enhances

cutting action.

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THERMAL BASED UNCONVENTIONAL PROCESSES

Thru – melting & vaporizing

Many secondary phenomena – surface cracking, heat affected zone and striations.

Heat Source:Plasma – EDM and PBM.Photons – LBM Electrons – EBMIons – IBMMachining medium:

different for different processes.

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CHEMICAL & ELECTROCHEMICAL BASED UNCONVENTIONAL PROCESSES

CHM – uses Chemical dissolution action in an etchant.

ECM – uses Electrochemical dissolution action in an electrolytic cell.

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19.1 Introduction19.1 IntroductionNon-traditional machining (NTM) processes

have several advantages◦Complex geometries are possible◦Extreme surface finish◦Tight tolerances◦Delicate components◦Little or no burring or residual stresses◦Brittle materials with high hardness can be machined

◦Microelectronic or integrated circuits (IC) are possible to mass produce

Conventional End Milling vs. NTMConventional End Milling vs. NTMTypical machining parameters

◦Feed rate (5 – 200 in./min.)◦Surface finish (60 – 150 in) AA – Arithmetic

Average◦Dimensional accuracy (0.001 – 0.002 in.)◦Workpiece/feature size (25 x 24 in.); 1 in. deep

NTM processes typically have lower feed rates and require more power consumption

The feed rate in NTM is independent of the material being processed

Table 19-1 Summary of NTM ProcessesTable 19-1 Summary of NTM Processes

Chemical Machining

Etching:

Chemical reaction between reagent (in gas, solution, or paste form)

and workpiece.

Main uses:

- Shallow, wide cavities on plates, forgings, castings reduce weight

- Electronics manufacturing (wafer fabrication)

- Hydrogen Flouride, Hydrofloric acid: etching of glass

Photo-Chemical Machining

Main uses:

- Flat springs, metal bookmarks, encoder wheels, lead frames for IC chips,

sieves for medical applications, microwave oven filters, heat-sinks for PCBs

(i) Clean (ii) Apply resist (iii) UV exposure (iv) Development (v) Etching (v) Stripping(i) Clean (ii) Apply resist (iii) UV exposure (iv) Development (v) Etching (v) Stripping

Electrochemical Machining (ECM)

Reverse of electro-plating (workpiece is anode)

Main uses:

- Dies and glass-making molds, turbine and compressor blades, Holes, Deburring

Due to low forces on tool,ECM can be used to makeholes at very large angle toa surface – an example is

shown in the turbine nozzleholes in the figure here.[source: www.barber-nichols.com]

Due to low forces on tool,ECM can be used to makeholes at very large angle toa surface – an example is

shown in the turbine nozzleholes in the figure here.[source: www.barber-nichols.com]

Electro-Discharge Machining (EDM)

[source: iprod.auc.dk]

- Sparks between electrode-workpiece- Dielectric flushes the metal powder

- Inexpensive, precise, complex shapes- Workpiece must be a conductor

[source: www.magnix.co.kr]

Electrode EDM

Wire-cut EDM

Laser cutting

Light Amplification by Stimulated Emission of Radiation

- High energy density (small focus area)- Uses: Cutting, welding, precision holes- Common lasers: CO2, Nd:YAG- Continuous power or Pulsed (more precise)

Nd:YAG laser cut:larger dia andheat-affected zone

Femtosecond laser cut:smaller diameter,lower thermal damage

Microscope image of laser cut hole

Nd:YAG laser cut:larger dia andheat-affected zone

Femtosecond laser cut:smaller diameter,lower thermal damage

Microscope image of laser cut hole

Ultrasonic Machining

~powersupply

Nozzle Abrasiveslurry

Transducer

Up-down vibration of toolhammers the abrasive particlesagainst workpiece, causing cutting

~powersupply


Transducer

~powersupply


Transducer

Up-down vibration of toolhammers the abrasive particlesagainst workpiece, causing cutting

Main uses of USM: - Welding plastics (package sealing) - Wire-bonding (IC chips) - Machining brittle materials

Water-Jet, Abrasive Water-Jet Machining

- Workpiece is fractured by impact from high pressure (~400 MPa) water-jet

- No heat no thermal stress, damage

Common applications:

- Fast and precise cutting of fabrics- Vinyl, foam coverings of car dashboard panels- Plastic and composite body panels used in the interior of cars- Cutting glass and ceramic tiles

19.4 Electrical Discharge 19.4 Electrical Discharge MachiningMachiningElectrical discharge machining (EDM)

removes metal by discharging electric current from a pulsating DC power supply across a thin interelectrode gap

The gap is filled by a dielectric fluid, which becomes locally ionized

Two different types of EDM exist based on the shape of the tool electrode◦Ram EDM/ sinker EDM◦Wire EDM

Figure 19-21 EDM or spark erosion machining of metal, using high-frequency spark discharges in a dielectric, between the shaped tool (cathode) and the work (anode). The table can make X-Y movements.

EDM ProcessesEDM Processes

Slow compared to conventional machining

Produce a matte surface

Complex geometries are possible

Often used in tool and die making

Figure 19-22 Schematic diagram of equipment for wire EDM using a moving wire electrode.

EDM ProcessesEDM Processes

Figure 19-24 (above) SEM micrograph of EDM surface (right) on top of a ground surface in steel. The spherical nature of debris on the surface is in

evidence around the craters (300 x).

Figure 19-23 (left) Examples of wire EDM workpieces made on NC machine (Hatachi).

Effect of Current on-time and Effect of Current on-time and Discharge Current on Crater SizeDischarge Current on Crater SizeMRR = (C I)/(Tm

1.23),Where MRR – material removal rate in in.3/min.; C – constant of proportionality equal to 5.08 in US customary units; I – discharge current in amps; Tm – melting temperature of workpiece material, 0F.

Example:A certain alloy whose melting point = 2,000 0F is to be

machined in EDM. If a discharge current = 25A, what is the expected metal removal rate?

MRR = (C I)/(Tm1.23) = (5.08 x 25)/(2,0001.23)

= 0.011 in.3/min.

Figure 19-25 The principles of

metal removal for EDM.

Effect of Current on-time and Effect of Current on-time and Discharge Current on Crater SizeDischarge Current on Crater Size

From Fig 19 – 25: we have the conclusions:◦Generally higher duty cycles with higher

currents and lower frequencies are used to maximize MRR.

◦Higher frequencies and lower discharge currents are used to improve surface finish while reducing MRR.

◦Higher frequencies generally cause increased tool wear.

Considerations for EDMConsiderations for EDMGraphite is the most widely used tool

electrodeThe choice of electrode material depends on

its machinability and coast as well as the desired MRR, surface finish, and tool wear

The dielectric fluid has four main functions◦Electrical insulation◦Spark conductor◦Flushing medium◦Coolant

Table 19-5 Melting Temperatures for Selected EDM Table 19-5 Melting Temperatures for Selected EDM Workpiece MaterialsWorkpiece Materials

Advantages and Disadvantages Advantages and Disadvantages of EDMof EDM

AdvantagesApplicable to all

materials that are fairly good electrical conductors

Hardness, toughness, or brittleness of the material imposes no limitations

Fragile and delicate parts

DisadvantagesProduces a hard

recast surfaceSurface may

contain fine cracks caused by thermal stress

Fumes can be toxic

Electron and Ion MachiningElectron and Ion Machining Electron beam

machining (EBM) is a thermal process that uses a beam of high-energy electrons focused on the workpiece to melt and vaporize a metal

Ion beam machining (IBM) is a nano-scale machining technology used in the microelectronics industry to cleave defective wafers for characterization and failure analysis

Figure 19-26 Electron-beam machining uses a high-energy electron beam (109 W/in.2)

Laser-Beam MachiningLaser-Beam Machining

Laser-beam machining (LBM) uses an intensely focused coherent stream of light to vaporize or chemically ablate materials

Figure 19-27 Schematic diagram of a laser-beam machine, a thermal NTM process that can micromachine any material.

Plasma Arc Cutting (PAC)Plasma Arc Cutting (PAC)Uses a superheated

stream of electrically ionized gas to melt and remove material

The process can be used on almost any conductive material

PAC can be used on exotic materials at high rates

Figure 19-29 Plasma arc machining or cutting.

Thermal DeburringThermal DeburringUsed to remove

burrs and fins by exposing the workpiece to hot corrosive gases for a short period of time

Thermal deburring can remove burrs or fins from almost any material but is especially effective with materials of low thermal conductivity

Figure 19-31 Thermochemical machining process for the removal of burrs and fins.

What is manufacturing?

• Application of physical and chemical processes to alter the geometry, properties, and/or appearance of a given starting material to make parts or products.

• Also includes assembly of parts into products.

• Goal: to achieve a product

• Transformation of materials into items of greater value (added value) by processing and/or assembly operations

• Goal: to make money through a product

A Technical Process: An Economic Process:

Cutting processes to manufacture parts from sheets & plates

Purpose to manufacture parts by cutting from sheets and plates:•Fast to manufacture•Parts are low in cost

– Helps drive costs for assembled products down•From low to high quantities•Simple to complex parts•Parts can later be formed (bent) to make more complex shapes

Major cutting processes• Mechanical processes:

– Machining and grinding (will cover in later classes)– Shearing, blanking, and punching (sheet metalworking operations)– Ultrasonic machining (USM)– Water jet cutting (WJC or hydrojet)– Abrasive water jet cutting (AWJC or abrasive hydrojet)

• Electrochemical process:– Electrochemical Machining (ECM)

• Thermal Energy Processes– Ram electric discharge machining (Ram EDM)– Wire electric discharge machining (Wire EDM)– Electron beam machining (EBM)– Laser beam machining (LBM)– Plasma arc cutting (PAC) or plasma arc machining (PAM)– Air carbon arc cutting– Oxyfuel Cutting (OFC) or flame cutting

• Chemical Processes:– Chemical Machining (CHM)

Red indicates non-traditional processes

Definition of sheets and plates

Sheets: thickness is 1/64” (0.04 mm) to 1/4” (6 mm).

Plates: thickness is greater than: 1/4” (6mm)


Importance of Nontraditional Processes

• Need to machine newly developed metals and non metals with special properties that make them ‑difficult or impossible to machine by conventional methods

• Need for unusual and/or complex part geometries that cannot readily be accomplished by conventional machining

• Need to avoid surface damage that often accompanies conventional machining

Shearing, Blanking, and Punching

• Three principal operations in pressworking that cut sheet metal: – Shearing– Blanking– Punching


Shearing Operation• (a) Side view of the operation; (b) front view

of power shears equipped with inclined upper cutting blade


Dies for Sheet Metal Processes

Most pressworking operations are performed with conventional punch and die tooling‑ ‑

• Usually custom designed for the particular part‑Note: • Tooling cost is higher than cutting machines

that require no tooling• Tooling wears out so needs continual

replacement

• Components of a punch and die for a blanking operation

Punch and Die Components

• Components of a punch and die for a punch operation

Die

Punch


Blanking and Punching• Blanking (a) - sheet metal cutting to separate

piece (called a blank) from surrounding stock• Punching (b) - similar to blanking except cut

piece is scrap, called a slug


Press

• For punching/blanking and bending operations

• Have to feed material manually into correct position

(photo courtesy of Greenerd Press & Machine Company, Inc.)


CNC Turret Press

• Advantage: – Automatic positioning

of punch and dies– Can be used for

punching/blanking and bending operations

• Disadvantage: – Tooling cost is high


Uses high pressure, high velocity stream of water directed at work surface for cutting

Water Jet Cutting (WJC) or Hydrojet Cutting


WJC & Applications• Usually automated by CNC or industrial

robots to manipulate nozzle along desired trajectory

• Water also acts as a cooling agent• Can cut complex shaped parts• Used to cut narrow slits in flat stock such as

plastic, textiles, composites, floor tile, carpet, leather, and cardboard

• Not suitable for brittle materials (e.g., glass)


Abrasive Water Jet Cutting (AWJC)

• Most common for cutting metal• Abrasive particles are added to jet stream for

quicker cutting• Slower than laser cutting, but produces a

cleaner finish• Note that the water jet cut is tapered


Material removal by anodic dissolution, using electrode (tool) in close proximity to work but separated by a rapidly flowing electrolyte

Electrochemical Machining (ECM)


Electrochemical Machining Processes

• Electrical energy used in combination with chemical reactions to remove material

• Reverse of electroplating• Work material must be a conductor• Processes:

– Electrochemical machining (ECM)– Electrochemical deburring (ECD)– Electrochemical grinding (ECG)


ECM OperationMaterial is depleted from anode workpiece

(positive pole) and transported to a cathode tool (negative pole) in an electrolyte bath

Electrolyte flows rapidly between two poles to carry off depleted material, so it does not plate onto tool

• Electrode materials: Cu, brass, or stainless steel• Tool has inverse shape of part

– Tool size and shape must allow for the gap


Electric Discharge Machining (EDM)


EDM Operation• One of the most widely used nontraditional processes• Shape of finished work surface produced by a shape of

electrode tool• Can be used only on electrically conducting work

materials • Requires dielectric fluid, which creates a path for each

discharge as fluid becomes ionized in the gap. • Metal is melted/vaporized by the series of electrical

discharges• Can be very precise and produces a very good surface

finish


Work Materials in EDM

Work materials must be electrically conducting

Hardness and strength of work material are not factors in EDM

Material removal rate depends on melting point of work material


Special form of EDM uses small diameter wire as electrode to cut a narrow kerf in work

Wire EDM


Operation of Wire EDM

Work is fed slowly past wire along desired cutting path, like a bandsaw operation

CNC used for motion controlWhile cutting, wire is continuously advanced

between supply spool and take up spool to ‑maintain a constant diameter

Dielectric fluid is required– Applied using nozzles directed at tool work ‑

interface or submerging workpart


Wire EDM Applications

• Ideal for stamping die components– Since kerf is so narrow, it is often possible to fabricate

punch and die in a single cut

• Other tools and parts with intricate outline shapes, such as lathe form tools, extrusion dies, and flat templates


Dental part cut from nitinol material by wire EDM


Uses the light energy from a laser to remove material by vaporization and ablation

Laser Beam Machining (LBM)


LBM Applications

• Drilling, slitting, slotting, scribing, and marking operations

• Drilling small diameter holes down to 0.025 ‑mm (0.001 in)

• Generally used on thin stock• Work materials: metals with high hardness

and strength, soft metals, ceramics, glass and glass epoxy, plastics, rubber, cloth, and wood


Laser beam cutting operation performed on sheet metal

(photo courtesy of PRC Corp.).


Uses plasma stream operating at very high temperatures to cut metal by melting

Plasma Arc Cutting (PAC)


Operation of PAC• Plasma = a superheated, electrically ionized

gas• PAC temperatures: 10,000C to 14,000C

(18,000F to 25,000F)• Plasma arc generated between electrode in

torch and anode workpiece• The plasma flows through water cooled ‑

nozzle that constricts and directs stream to desired location


Applications of PAC

• Most applications of PAC involve cutting of flat metal sheets and plates

• Hole piercing and cutting along a defined path • Comparable to laser cutting, but cuts are

usually is more course• Can cut any electrically conductive metal • Most frequently cut metals: carbon steel,

stainless steel, aluminum


Important: Water Jet, Laser, Plasma

• Need to start the cut away from the wanted cut to prevent a rough surface irregularity where the cut starts

Starting cut Wanted cut

Summary of Cutting Processes for Sheets and Plates in terms of Quality & Cost

Quality

(In terms of tolerances & surface finish

Cost

Punching/ Blanking

Plasma

Water Jet

Wire EDM

Machining

Laser

Comparison: sheet and plate cutting

1. Plasma2. Laser3. Waterjet


Main criteria for comparison:

1.Materials

2.Cost (much determined by speed)

3.Quality

4.Productivity


Processes Material Thickness Quality Cost NotePlasma All electrically

conductive materials

Gauge to 2 in Poor Low Need high power

Laser A variety of materials

¼ in and thinner

Middle Middle Problem with reflective materials

Waterjet A variety of materials, usually soft material

Highest High

Cost: decided by the speed.

introduction (2)

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