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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
*
* Source: Kalpakjian, Manufacturing Engineering and Technology
*
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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
* Source: Kalpakjian, Manufacturing Engineering and Technology
*
* 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)
* Source: Kalpakjian, Manufacturing Engineering and Technology
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
*
* Source: Kalpakjian, Manufacturing Engineering and Technology
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* Source: Kalpakjian, Manufacturing Engineering and Technology
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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
* Source: Kalpakjian, Manufacturing Engineering and Technology
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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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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.hemsaw.com/Videolinkpages/x-vVideopg.htm
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Sand 0.5 radiiBelt sender
Bore 1 radius
Drill hole 1 diameter
Mill out 2X1.5X4Mill width to 2
Mill two ends to length 4
Manual vertical mill
Saw stock to ~4.125Horizontal band saw
OperationMachine
* Source: http://www.hemsaw.com/Videolinkpages/x-vVideopg.htm
*
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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.hemsaw.com/Videolinkpages/x-vVideopg.htm
*
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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.hemsaw.com/Videolinkpages/x-vVideopg.htm
*
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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.hemsaw.com/Videolinkpages/x-vVideopg.htm
*
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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/jet-index.html (WMH Tool Group)
*
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Process plan
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
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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
Drill hole 1 diameter
-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
Mill two ends to length 4
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