Impact of Material Properties and Strain Hardening on Bending & Cutting in Manufacturing, Quizzes of Mechanical Engineering

Download Impact of Material Properties and Strain Hardening on Bending & Cutting in Manufacturing and more Quizzes Mechanical Engineering in PDF only on Docsity! Page 1 of 10 Name_____________________________ GEORGIA INSTITUTE OF TECHNOLOGY George W. Woodruff School of Mechanical Engineering ME 6222 MANUFACTURING PROCESSES AND SYSTEMS Fall 2008 Quiz #3 – On-campus November 17 Directions: • Books, notes, and devices that communicate are prohibited. • You may use any type of calculator. • There are two (2) problems. • Answer the problems in the space provided in the examination packet. • You must turn in the entire examination packet. • The exam is one class period long. Page 2 of 10 Problem #1 (one-half credit) Consider the bending of a sheet of metal to produce a part with a specified final angle. Note: I am interested in your understanding of the mechanics and materials science, rather than just a manipulation of the equations. Using the figure below, discuss the effect of the following on the punch angle and punch force: a) An increase in the thickness of the material b) A decrease in the yield point of the material t re punchtensile 21 1 + = eelastic = σyield/E ( )ααμα cossincos2 2 +⎟ ⎠ ⎞ ⎜ ⎝ ⎛= l MF b tan(2α) = μ Power = Force * speed Linearly strain-hardening material keyield += σσ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ += y y b bt M σ σσ 1 2 21 12 ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ +⎟ ⎠ ⎞ ⎜ ⎝ ⎛ +=⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ Δ y y punch punch Et tr σ σσ α α 121 2 Page 5 of 10 Problem #2 (one-half credit) Consider the orthogonal cutting of a strain-hardening copper alloy. You have two samples of the alloy - one that has not undergone strain hardening, and one that has been strain hardening. For this examination, you may assume that the machining operation does NOT further strain harden the metal. The cutting power, cutting velocity, rake angle (α) which is positive in sign, and depth of cut (t0) are held constant for the two materials. Discuss the effect of the strain hardening on the following, being as quantitative as possible: a) Shear plane angle (φ) b) Chip thickness ratio (r) Problem #2 Student answer Page 6 of 10 Problem #2 Student answer (continued) Page 7 of 10 Taylor’s tool life equation VTn = C V = velocity (m/min) or (ft/min) T = tool life (min) Revolutions per unit time N (rev/unit time) = V/πD V = velocity D = diameter Machining time for turning on a lathe tm = L/fN L = axial length of cut F = feed rate N = revolutions per time period Single point turning cost per piece Cp = tmRm + tiRm + tsRs/Ns + tcRm(tm/T) + [tgRg+Dg](tm/T) + Cr Cr = cost/weight * (part weight + (1-S)*scrap weight) t = time ( ) n gggmc n m cm DRtRt n CRV ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ++⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − = 11 ( ) mgggmccm RDRtRtnT /1 1 ++⎟ ⎠ ⎞ ⎜ ⎝ ⎛ −= n c tm t n CV ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − = 11 ctm tn T ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ −= 11