1 Printed name: On my honor, I pledge that I have neither received nor provided improper assistance in the completion of this test. Signature: GEORGIA INSTITUTE OF TECHNOLOGY George W. Woodruff School of Mechanical Engineering ME 4210 MANUFACTURING PROCESSES AND ENGINEERING Spring 2011 Test #3 April 13 Be sure to list all assumptions. Write legibly. One, two-sided page of hand-written notes is allowed; it must be handed in with your worked solutions (put your name on your sheet of notes). Otherwise, the test is closed book and notes. This test is 50 minutes long. Use the data provided with the test for all calculations. Show your work and write your answers in the exam in the space after the questions. You may write on both sides of the test.2 Problem #1 (20 points) Consider a molten thermoplastic polymer at a constant temperature. You notice that when you increase the pressure on it, its viscosity (resistance to flow) increases. - Why? Your answer should discuss the concepts of physics and chemistry involved. Start your answer to Problem #1 here:3 Problem #2 (20 points) Consider the extrusion of a solid rod of a thermoplastic polymer of diameter, d, at velocity, v. You notice that when the rod emerges from the die, the diameter is larger than d. - Why does the diameter increase? - What could you do to reduce this die increase in diameter? Your answers should discuss the concepts of physics and chemistry involved. Start your answer to Problem #2 here:4 Problem #3 (60 points) Consider the injection molding of a flat plate that is 75 mm in diameter and 3 mm thick. The sprue that feeds the part can be modeled as a cylinder that is 5 mm in diameter and 50 mm long. - What should the RPM of the screw be to make a shot in 6 seconds? - What is the longest time available to make that shot? The barrel has a diameter of 28 mm. The reciprocating screw, which rotates, has a channel depth of 4 mm, a channel width of 21 mm, and a flight angle of 18 degrees. The axial length of pumping section of the screw is 1.1 m long. The polymer has a viscosity of 450 N-s/m2. The back pressure on the screw while the shot is being prepared is 8 MPa. The temperature of the polymer injected into a mold at 225ºC. The mold is maintained at 38ºC. The plastic much reach a temperature of 115ºC before it can be removed from the mold. The density of the polymer is 990 kg/m3, its specific heat is 1600 J/kg-K, and its thermal conductivity is 0.25 W/m-K. Start your answer to Problem #3
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