hmewrk_02_sol - Solution Homework #2: Injection Molding...

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Solution Homework #2: Injection Molding 2.008 Design and Manufacturing II Spring 2004 Out: February 18 th Due: February 25 th Problem 1: What are the design considerations in replacing a metal container for carbonated beverages with plastic bottles? Think about the functional requirements and explain how the design of a plastic container differs from that of a metal can. Solution While the functional requirements, naturally, are almost the same for metal and plastic containers (remember: functional requirements are “what you want” and solution- neutral), the design parameters to fulfill the functional requirements may differ. In particular the following differences can be stated: o Since plastic is a cheap material and less dense than metal, the urge for a material- saving design is not as strong as when using aluminum. o Special attention has to be paid to the permeability of plastic. In order to conserve the gas for a long period of time (less than 15% loss in 120 days, from the lecture), a special processing with low permeability plastic is necessary. o Plastic is not as strong as metal. The wall thickness can be increased, small corrugation or, better, a wavy structure (like small coke bottles) can be used. The bottom is usually thick to provide rigidity and a save stand. o Because plastic is easier to form into complicated shapes than cans, it became more feasible to make them more aesthetically and ergonomically pleasing; hence, soda in bottles again, but now with grippy sides. Also scaling up the size is feasible. o In principle, plastic didn’t eat that much of Al cans, but replaced most of the glass bottles.
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Consider the injection molded L-bracket made of Polycarbonate shown in Figure 1. You are asked to find the mold design with the parting line that leads to the minimum possible clamping force to mold the part. 10mm x z y Plane B Gate C 6 mm 6mm 1 mm 1 mm 3mm Plane A Figure 1: L-bracket part drawings a) What would be the minimum clamping force required for this part? Indicate the location of gate and the location of parting line/plane for the minimum clamping force design. Assume that the peak injection pressure is 6,000 psi. Also discuss the potential problems in producing the part with this design. b) You soon realize that the minimum clamping force is not as important as the quality of the part and productivity of the process (as long as the machine has enough clamping force). i) What would be a better position of the parting line/plane and gate and direction of injection molding? Why? ii) What is the clamping force required for the new design? Solution a) The minimum cross-sectional area projected on the parting plane A will require the minimum clamping force. A
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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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hmewrk_02_sol - Solution Homework #2: Injection Molding...

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