08cutting_2_6_f - Cutting processes 2.008 Design &...

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1 2.008-spring-2004 S.Kim 1 2.008 Design & Manufacturing II Spring 2004 Metal Cutting II 2.008-spring-2004 S.Kim 2 Cutting processes ± Objectives ± Product quality: surface, tolerance ± Productivity: MRR , Tool wear ± Physics of cutting ± Mechanics ± Force, power ± Tool materials ± Design for manufacturing 2.008-spring-2004 S.Kim 3 Orthogonal cutting in a lathe Rake angle Shear angle T o : depth of cut Shear plane Assume a hollow shaft 2.008-spring-2004 S.Kim 4 Velocity diagram in cutting zone () φ sin c V α cos s V α φ cos V = = α φ cos φ sin r c t o t V c V = = = α φ cos φ Vsin c V = α φ cos φ sin r c t o t V c V = = = Cutting ratio: r <1 2.008-spring-2004 S.Kim 5 E. Merchant’s cutting diagram α φ R F t F c F n F s F N α β Source: Kalpajkian F t F c β−α 2.008-spring-2004 S.Kim 6 α ) β Rcos( φ φ sin t F φ cos c F s F + = = φ cos t F φ sin c F n F + = β sin R F = β cos R N = ( ) β tan μ = Angle Friction β = 2 μ 0.5 : Typcially < < FBD of Forces α tan t F c F α tan c F t F N F μ + = = α - β sin R Ft = - β cos R Fc =
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2 2.008-spring-2004 S.Kim 7 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 β 2 α 45 φ o + = () α φ tan cot φ ac cd bc γ + = + = 2.008-spring-2004 S.Kim 8 Shear Angle 2 β 2 α 45 φ o + = Fs Fc φ w sin φ A Fs As Fs τ = = σ s As Fs = α ) β Rcos( φ φ sin t F φ cos c F s F + = = α - β cos R Fc = Maximize shear stress Minimize Fc 0 d d τ = ϕ 0 d dFc = 2.008-spring-2004 S.Kim 9 Power s s V F : shearing for Power V F c : input Power c V F : friction via dissipated Power V t w V F u o s s s = : shearing for energy Specific V t w V F u o c f = : friction for energy
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This note was uploaded on 02/23/2012 for the course MECHANICAL 2.008 taught by Professor Jung-hoonchun during the Spring '04 term at MIT.

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08cutting_2_6_f - Cutting processes 2.008 Design &amp;...

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