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

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Presentation on theme: "2.008-spring-2004 S.Kim 1 2.008 Design & Manufacturing II Spring 2004 Metal Cutting I."— Presentation transcript:

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

2 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


4 2.008-spring-2004 S.Kim 4 Material removal processes Cost : Expensive $100 - $10,000 Quality: Very high Flexibility: Any shape under the sun Rate: Slow

5 Surface roughness by machining Roughness (Ra) Process Flame cutting Snagging (coarse grinding) Sawing Planing, shaping 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 spring-2004 S.Kim 5 Average application Less frequent application

6 Machined Surface Rough Medium Avg. Better than Avg. Fine Very fine Extremely fine inch Waviness height Roughness height Roughness width Waviness height Flaw Waviness width Roughness height (arithmetical average) Roughness- width cutoff Waviness width Roughness- width cutoff Roughness- width Lay direction Lay spring-2004 S.Kim 6

7 2.008-spring-2004 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

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

9 2.008-spring-2004 S.Kim 9 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? Cutting process modeling

10 Orthogonal cutting in a lathe spring-2004 S.Kim 10 Assume a hollow shaft Shear plane Shear angle T o : depth of cut Rake angle

11 2.008-spring-2004 S.Kim 11 Cutting tool and workpiece.. Rough surface Chip Primary shear zone Secondary shear zone Shiny surface Tool face Flank Relief or clearance angle Tool Shear planeShear angle Workpiece Rake angle

12 2.008-spring-2004 S.Kim 12 Varying rake angle α: - α α = 0

13 2.008-spring-2004 S.Kim 13 Basic cutting geometry We will use the orthogonal model Continuity Cutting ratio: r <1 V t o = V c t c t c : chip thickness t o : depth of cut Rake angle, α Tool Chip Shear angle

14 2.008-spring-2004 S.Kim 14 Velocity diagram in cutting zone Law of sines

15 2.008-spring-2004 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

16 2.008-spring-2004 S.Kim 16 E. Merchant s cutting diagram Source: Kalpajkian Workpiece Chip Tool

17 2.008-spring-2004 S.Kim 17 FBD of Forces Friction Angle Typcially:

18 2.008-spring-2004 S.Kim 18 Analysis of shear strain What does this mean: Low shear angle = large shear strain Merchants assumption: Shear angle adjusts to minimize cutting force or max. shear stress Can derive:

19 2.008-spring-2004 S.Kim 19 Shear angle (area of shear plane, shear strength)

20 2.008-spring-2004 S.Kim 20 Things to think about As rake angle decreasesior frict on increases Shear angle decreases Chip becomes thicker Th icker chip = more energy dissiipat on via shear More shear = more heat generation Temperature increase!!!

21 2.008-spring-2004 S.Kim 21 Power Power input shearing+ friction Power for shearing Specific energy for shearing Power dissipated via friction Specific energy for friction Total specific energy Experimantal data MRR

22 2.008-spring-2004 S.Kim 22 Specific energy (rough estimate) Kalpakjian Specific energy Approximate Energy Requirements in Cutting Operations (at drive motor, corrected for 80% efficiency; multiply by 1.25 for dull tools). Aluminum alloys Cast irons Copper alloys High-temperature alloys Magnesium alloys Nickel alloys Refractory alloys Stainless steels Steels Material

23 2.008-spring-2004 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/In 3 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?

24 2.008-spring-2004 S.Kim 24 Cutting zone pictures Kalpakjian continuous secondary shear BUE serrated discontinuous

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