1. 2.008 Design & ManufacturingII
Spring 2004
Metal Cutting I
2.008-spring-2004
S.Kim

2. Today, February 25th ▪ HW#2 due before the class, #3 out on
the web after the class.
▪ Math Formulae, handout
▪ Lab groups fixed, and thank you.
▪ group report!!!
▪ Metal cutting demo
▪ Cutting physics
2.008-spring S.Kim

3. A lathe of pre WWII 2.008-spring-2004 S.Kim 3 HEADSTOCK SPINDLE
TALL STOCK
LOCK LEVER
RAM LOCK
TOOLPOST T-SLOT
COMPOUND
HANDWHEEL
TALL STOCK
HANDWHEEL
WAYS
LEAD SCREW
CROSS SLIDE
HANDWHEEL
CHIP PAN
CARRIAGE
HANDWHEEL
HANDWHEE
PEDESTAL
TALL STOCK
PEDESTAL
2.008-spring S.Kim

4. Material removal processes
▪ Cost : 
▪ Expensive $100 -
$10,000
▪ Quality: 
▪ Very high
▪ Flexibility:
▪ Any shape under the
sun
▪ Rate: 
▪ Slow
2.008-spring S.Kim

5. Surface roughness by machining
Roughness (Ra)
Process
Flame cutting
Snagging (coarse grinding)
Sawing
Planing, shaping
Average application
Less frequent application
Drilling
Chemical machining
Electrical-discharge machining
Milling
Broaching
Reaming
Electron-beam machining
Laser machining
Electrochemical machining
Turning, boring
Barrel finishing
Electrochemical machining
Roller burnishing
Grinding
Honing
Electropolishing
Polishing
Lapping
Superfinishing
Kalpakjian
2.008-spring S.Kim

6. (arithmetical average)
Machined Surface
Flaw
Waviness
height
Rough
Medium
Avg.
Better than Avg.
Fine
Very fine
Extremely fine
Lay direction
Roughness
width
Roughness
height
Waviness
width
Roughness-width cutoff
Waviness
height
Waviness
width
Roughness-
width cutoff
Roughness height
(arithmetical average)
Roughness-
width
inch
Lay
2.008-spring S.Kim

7. Cutting processes  Why do we study cutting physics?
 Product quality: surface, tolerance
 Productivity: MRR , Tool wear
 Physics of cutting
 Mechanics
 Force, power
 Tool materials
 Design for manufacturing
2.008-spring S.Kim

8. Cutting Tools 2.008-spring-2004 S.Kim 8 Top view Right side view
Tool shank
Tool shank
Rake face
Rake face
Side-cutting-edge
Cutting edge
angle
Flank face
Nose radius
End-cutting-edge
angle
Side-cutting-edge
Right side view
Front view
Back-rake
angle
End-relief
Side-rake
angle
angle
Side-relief
angle
Flank face
2.008-spring S.Kim

9. Cutting process modeling
 Methods: Modeling and Experiments
 Key issues
 How does cutting work?
 What are the forces involved?
 What affect does material properties have?
 How do the above relate to power
requirements, MRR, wear, surface?
2.008-spring S.Kim

10. Orthogonal cutting in a lathe
Assume a hollow shaft
Shear plane
Shear angle
To: depth of cut
Rake angle
2.008-spring S.Kim

11. Cutting tool and workpiece..
Shiny surface
Rough surface
Secondary shear zone
Chip
Rake
angle
Tool face
Tool
Primary shear zone
Flank
Relief or
clearance angle
Shear plane
Shear angle
Workpiece
2.008-spring S.Kim

12. Varying rake angle α:
- α α = 0
2.008-spring S.Kim

13. Basic cutting geometry
▪ We will use the orthogonal model
Continuity
Rake angle, α
Chip
V⋅to = Vc⋅tc
tc: chip thickness
to: depth of cut
Tool
Shear angle
Cutting ratio: r <1
2.008-spring S.Kim

14. Velocity diagram in cutting zone
Law of sines
2.008-spring S.Kim

15. Forces and power ▪ FBD at the tool-workpiece contact
▪ What are the forces involved
▪ Thrust force, Ft
▪ Cutting force, Fc
▪ Resultant force, R
▪ Friction force, F
▪ Normal Force, N
▪ Shear Force, Fs, Fn
2.008-spring S.Kim

16. E. Merchant’s cutting diagram
Chip
Tool
Workpiece
Source: Kalpajkian
2.008-spring S.Kim

17. FBD of Forces
Friction Angle
Typcially:
2.008-spring S.Kim

18. Analysis of shear strain
▪ What does this mean:
▪ Low shear angle = large shear strain
▪ Merchant’s assumption: Shear angle adjusts
to minimize cutting force or max. shear stress
▪ Can derive:
2.008-spring S.Kim

19. Shear angle (area of shear plane, shear strength)
2.008-spring S.Kim

20. Things to think about ▪ As rake angle decreases ior frict on increases
▪ Shear angle decreases
▪ Chip becomes thicker
▪ Thicker chip = more energy dissiipat on via shear
▪ More shear = more heat generation
▪ Temperature increase!!!
2.008-spring S.Kim

21. Power shearing+ friction Power input Power for shearing
Specific energy for shearing
MRR
Power dissipated via friction
Specific energy for friction
Total specific energy
Experimantal data
2.008-spring S.Kim

22. Specific energy (rough estimate)
Approximate Energy Requirements in Cutting
Operations (at drive motor, corrected for 80%
efficiency; multiply by 1.25 for dull tools).
Specific energy
Material
Aluminum alloys
Cast irons
Copper alloys
High-temperature alloys
Magnesium alloys
Nickel alloys
Refractory alloys
Stainless steels
Steels
Kalpakjian
2.008-spring S.Kim

23. Example
▪ Consider the turning with a rod, from 1.25 inch diameter to 1.0.
▪ to; depth of cut, inch
▪ f; feed rate, inch/rev
▪ ω; spindle speed, 1000 rpm
▪ uf;spe ifc ic energy for i fr c it on
▪ us;specific energy for shear, 0.35 hp min/In3
▪ 1 hp = 550 ft.lbf/s
▪ How many passes?
▪ Tools speed?
▪ Time to make this part?
▪ V c max?
▪ Max power needed?
▪ Initial cutting force?
2.008-spring S.Kim

24. Cutting zone pictures continuous secondary shear BUE
serrated discontinuous
Kalpakjian
2.008-spring S.Kim