[metalworking] machining

8/7/2019 [Metalworking] Machining

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Machining processes

2.810 Fall 2003

Professor Tim Gutowski


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OutlineBasic Machine Configuration1

Basic Mechanics1

Geometry1,3

Production machining1,2,3,4,5

Environmental Issues


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Readings1. Kalpakjian Ch.20-26

2. Simplified Time Estimation Bookletfor Basic Machining Operations

3. Design for Machining handout

4. Single minute exchange of dies

(SMED) handout

5. A Job Shop handout


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OutlineBasic Machine Configuration1

n Single point machining

w Turning, boring, trepanning, planingn Multiple point machining

wDrilling, milling, reaming, sawing, broaching,

grinding


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Machining processes

Horizontal Slab mill ing Face mill ing End milling

Cutter Arbor

Arbor

Spindle

Spindle

End mill

Shank

Turning

Mill ing

* Source: Kalpakjian, Manufacturing Engineering and Technology

*

*

Grinding

Grinding

wheel

DGrains

Workpiecev

V


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Horizontal-spindle surface grinderMachine Tools

Column

Base

Head

Table

Saddle

Knee

*

Spindle

speed

selector

Feed

change

gearbox

Compound rest and

slides (swivels) ApronBed

Lead screw

Feed rod

Headstock

Spindle

Cross slideWays

Carriage

Center

Tailstock quill

Tailstock

Basic Lathe

Vertical-Spindle Mil l

*


*


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OutlineBasic Mechanics1

n Power, Forces

n Heat, Tool materials, Rate limits

n New Technology to reduce these effects

See Video on Plastic Deformation


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Basic Machining Mechanism

Approximation

us ~ H (Hardness)

t0

tc

Shear plane Shear angle

Tool

V

Chip

Workpiece

+-

Rakeangle

)42(6

1

u

42du

u80%)to(65uu

uenergyspecific

vol

work

workdt

d(work)PowerVF

p

p

frictionworkplasticS

S

=

+=

==

===

H


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Specific energy, uS


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Hence we have the approximation;

Power = Hardness * MRR

MRR is the Material Removal Rate or d(Vol)/dt

Since Power is P = F * V

and MRR can be written as,d(Vol)/dt = A * V

Where A is the cross-sectional area of the undeformed chip, we can getan estimate for the cutting force as,

F = H ANote that this approximation is the cutting force in the cutting direction.You may want to use the specific cutting energy us given in Table20.1 of Kalpakjian in place of the Hardness value in the aboveequations.

Basic Machining Mechanism


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Cutting Force Directions in Milling

Fp

Fcn

Fc

Fcn

FpFc

FcnFc

Fp

Fcn

Fp

Fc

Fc ~ H Ac

(Tangential Cutting Force ~

Chip Cross-section Hardness)


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Feed per Tooth and MRR

f = feed per tooth (m)w = width of cut (m)

v (m/s)

= rotational rate (rpm)

Consider the workpiece moving into the cutter at rate v. The travel in time tis v*t. During the same time, the cutter would rotate t times and the

workpiece would see 4t cutter teeth. In general, a cutter may have Nteeth, so the feed per tooth is

f = v / NThe material removal rate (MRR) is,

MRR = v w d

where d is the depth of the tool into the workpiece.

Top view of face millingWith 4 tooth cutter

Side view


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Ex) Face milling of Al Alloy

w

d =D

vwN = 4 (number of teeth)D = 2 (cutter diameter)

Let w = 1 (width of cut), d=0.1 (depth of cut)f = 0.007 (feed per tooth),

vs = 2500 ft/min (surface speed; depends oncutting tool material; here, we must have acoated tool such as TiN or PCD)

The rotational rate for the spindle is = vs/ D = 4775 rpm

Now, we can calculate vw, workpiece velocity,

f = vw/ N => vw= 134 [in/min]

Material removal rate, MRR = vw*w*d = 13.4 [in3/min]

Power requirement, P = us*MRR = 5.36 [hp]Cutting force / tooth, F ~ us*d*f = 111 [lbf]

us from Table 20.1; Note 1 [hp min/in3] = 3.96*105 [psi]


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Ex) Turning a stainless steel barf

D=1

d

Tool

Recommended feed = 0.006 (Table 22.2)Recommended surface speed = 1000 ft/min

= 1000 ft/min = 3820 rpm1 1ft/12

Material removal rate, MRR = 0.10.006(13820) = 7.2 [in3/min]

Power requirement, P = us*MRR = 1.9*7.2 = 13.7 [hp]

Cutting force / tooth, F ~ us*d*f = (1.9*3.96*105)*(0.1*0.006)

= 450 [lbf]

us from Table 20.1; Note 1 [hp min/in3] = 3.96*105 [psi]

Let d = 0.1


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Temperature Rise in Cutting

Adiabatic Temperature Rise: cp T = uS

Note : uS ~ H, HardnessTadiabatic > Tmelt (Al & Steel)

Interface Temperature:

T = 0.4 (H / cp)(v f / )0.33

v = cutting speedf = feed = thermal diffusivity of workpieceNote v f / = Pe = convection/conduction

Typical temperature distributionin the cutting zone


*

* Reference: N. Cook, Material Removal Processes


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Cutting tool materials & process conditions

Temperature (F)

Hardness(HRA)

HRC

Feed (in/rev)

Cuttingspeed(ft/min)

m/min

Year

Machiningtime(m

in)


Cutting Speed (ft/min)

Too

llife(min)


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Limits to MRR in Machining1. Spindle Power for rigid, well supported parts

2. Cutting Force may distort part, break delicate

tools3. Vibration and Chatter lack of sufficient rigidity inthe machine, workpiece and cutting tool may resultin self-excited vibration

4. Heat heat build-up may produce welding, poor

surface finish, excessive work hardening; can bereduced with cutting fluid

See Video on Rate Limits In Machining


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Typical Material Removal Rate10 -4 10 -3 10 -2 10 -1 1 10 102

EBM 1 EDM 1,2

Grinding3

Machining

Creep Feed2

Grinding

LASER3

Chem. Mill ing2

[cm3/sec]

25A, 6um RM S1Rough mil l ingof Al > 35hp

1m X 1m areaNote: 1cm3/ sec = 3.67 in3/min

* References: 1. Advanced Methods of Machining, J.A.McGeough, Chapman and Hall, 1988

2. Manufacturing Engineering and Technology, S. Kalpakjian, Addison-Wesley, 19923. Laser Machining, G. Chryssolouris , Springer-Verlag, 1991


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Hexapod Milling Machines

Tool

Linear actuator

StewartPlatform

*

* Source: http://macea.snu.ac.kr/eclipse/background/background.html

Hexapod machining center(Ingersoll, USA)

Schematics


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High speed Machining and AssemblyHigh Speed Machined aluminum parts are replacing built-upparts made by forming and assembly (riveting) in the aerospaceindustry. The part below was machined on a 5-axis Makino(A77) at Boeing using a 8-15k rpm spindle speed, and a feed of240 ipm vs 60 ipm conventional machining. This part replaces abuild up of 25 parts. A similar example exists for the F/A-18bulkhead (Boeing, St. Louis) going from 90 pieces (sheetmetalbuild-up) to 1 piece. High speed machining is able to cut wallsto 0.020 (0.51mm) without distortion. Part can be fixturedusing window frame type fixture.

MRR = f d * N w


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OutlineGeometry1,3

n Micro-geometry: tolerance, surface finish

n Macro-geometry: 5 axes, form tools vs. software


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Micro-geometryExcellent surface finish and dimensionprecision are possible.

Compare machining tolerances with otherprocesses.n See figure 22.15 and 35.25 of Kalpakjian

Compare surface finish with other processes,and various applications.n See figure 22.14 and 35.26 of Kalpakjian

Why is machining so good?


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Variation Vs Part Size


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Macro-geometryMachine tool configuration

number of axes, spindles, serial and parallel

configurationsCutter geometry

Form tool, cutter radius, inserts, tool changers

Software

flexibility, geometrical compensation, look aheaddynamics compensation


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* Source: Reintjes, Numerical Control


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Column

Base

Head

Table

Saddle

Knee

*



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Simple Classification Scheme for

Part Geometry

Primary RotationalPrimary Rotationalw ith secondary Primary Planar

Primary Planar withsecondary

Primary Rotationaland Planar

Primary Rotational andPlanar with secondary

Secondary


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Pop quiz; how would you

make a gun stock?

See video


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Production MachiningPart Fixturing and Production Equipment

n Quick Release Fixtures, Quick Tool Changes, SMED (notesfrom Shigeo Shingo), Multiple Spindles, Modular Equipment

n See Chapter 24 of Kalpakjian

Machining Systems

n Job Shop, Flow Shop, Cellular Machining, Machining Centers,Flexible Automation (FMS), Transfer Lines

n See Chapter 39 of Kalpakjian

Process Planning and Time Estimationn See Simplified Time Estimation for Machining and DFM

rules


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Part Fixturing for Prismatic PartsJob Shopn Vise Jaws / T-slot

n

Bolt clamps / T-slotn Direct bolt to plate / T-slot

Productionn Special work holding jaws and clamps

w Soft jaws, custom jaws, stops, mechanical clamps,

hydraulic clamps, pneumatic clamps, magnetic chuckn Multiple parts fixtures and indexing heads

w Tombstones, trunnion, indexing heads


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Job shop fixturing

Vise Faceplate on lathe

T-slot & clamps on m ill


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Production

8-station Vise

http://www.te-co.com/toolex/html/10a.html

Quad-Vert ical combinat ion Chuck

http://www.royalworkholding.com/RM3.html

Indexing Trunnion

http://www.royalworkholding.com

Modular Fixtures

http://www.royalworkholding.com/RM3.html

Hydraulic Pallet Fixture

http://www.royalworkholding.com

Collet Index Fixture

http://www.cuttingtoolmall.com/catalog/standard.cfm?FamilyID=225205


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SMEDSingle-Minute-Exchange-Die

w Shigeo Shingo, A Study of the ToyotaProduction Systems

n Stage1: Separating Internal and ExternalSetup

n Stage2: Converting Internal to ExternalSetup

n Stage3: Streamlining all aspects of thesetup operation


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Machining Systems Classification

Job

Shop

FlowShop

CNCJob

Shop

CellularMachining

Machining Center

TransferLine

Automation of Work station/ Transfer

SystemF

low

Free

Transfer

Syn

chronous


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Job shop


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Flow Shop

L

M

D GL M

A A

L M G G

L D

Receiving

Shipping


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Flexible Manufacturing System


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Transfer line



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VMMachining Cell

S

L

L

HM

VM

G

Finalinspection

Finishedpart cart

Raw materialcart

Worker position

Worker path

Part movement

Decoupler(Kanban square)

OUT


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Process planningHow would you machine this part?

Assumption:1. We begin with a stock size of 2.5 X 2.25 X 122. This will be manufactured in a job shop for very low quantity

We will use:- A bandsaw to roughly cut the stock to size- A manual vertical mill to create the planar features and the holes- A belt sander to sand the radii ( assuming the tolerance is not

very high)


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Sand 0.5 radiiBelt sender

Bore 1 radius

Drill hole 1 diameter

Mill out 2X1.5X4

Mill width to 2

Mill two ends to length 4

Manual vertical mill

Saw stock to ~4.125Horizontal band saw

OperationMachine

* Source: http://www.jettools.com/Catalog/Metalworking/CatalogPages/HVBS56M.html

*


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Bore 1 radius


Mill out 2X1.5X4

Mill width to 2




OperationMachine

*

* Source: http://www.hemsaw.com/Videolinkpages/x-vVideopg.htm


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Bore 1 radius


Mill out 2X1.5X4Mill width to 2




OperationMachine


*


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Bore 1 radius


Mill out 2X1.5X4

Mill width to 2




OperationMachine


*


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Bore 1 radius


Mill out 2X1.5X4

Mill width to 2




OperationMachine


*


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Bore 1 radius


Mill out 2X1.5X4

Mill width to 2




OperationMachine


*


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Bore 1 radius


Mill out 2X1.5X4

Mill width to 2




OperationMachine

* Source: http://www.jettools.com/jet-index.html (WMH Tool Group)

*


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Process plan


Bore 1 radius


Mill out 2X1.5X4

Mill width to 2




OperationMachine


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Time estimation (minutes)

0.08

0.20

0.20

-

0.20

0.20

0.20

0.23

Fixture

-

2

2

2

22

-

-

2

-

ToolChange

0.20R

0.21F

0.96R

0.01F

0.03

0.05

0.040.01

2.19R

0.93F

0.46R

0.67F

0.13R

0.75F

2.02

Run (R=Rough,F=Finish)

Sand 0.5 radii

V = 0.05 in3

A = 0.79 in2

, P = 3.14in

Bore 1 radius

V = 0.79 in3

A = 1.57 in2, P = 7.28in


-Center drill

-Pilot drill

-Pilot drill 63/64

-Ream

Mill out 2X1.5X4

V = 12 in3

A = 14 in2, P = 15in

Mill width to 2

V = 2.5 in3

A = 10 in2, P = 13in


V = 0.703 in3

A = 11.25 in2, P = 19in

Saw stock to ~4.125

A = 5.6525 in2, P = 9 in

Operation (V = Volume, A= Area, P = Perimeter)

0.10D, 0.05I

0.06M, 0.06M

0.24D, 0.05I

0.06M

0.21D, 0.05I

0.17M

0.50D, 0.05I

0.13M, 0.13M

0.43D, 0.05I,

0.13M

0.63D, 0.05I,

0.13M

0.30D, 0.05I

Deburr/Inspect/

Measure

Belt sender

Manual vertical

mil l

Horizontal bandsaw

Machine


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Summary Times (minutes)

Fixture Tool Change Run (R=Rough, F=Finish) Deburr/Inspect/Measure

1.31 12 6.08 2.58 3.63

Total Time 25.6 minutes


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Environmental issues

Waste material

Energy

n Machine, material (embodied energy),temperature controlled environment

Lubricants and hydraulic fluids

Cutting Fluidsn Dry machining


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Production machining energyVs production rate

Ref. Toyota

[metalworking] machining

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