GOALI: Development of Advanced Molding Technology for Polymer Micro-/Nano-Fabrication

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This Grant Opportunities for Academic Liaison with Industry (GOALI) research project is to investigate thermoplastic polymer-based molding technologies, i.e. high speed/ high pressure (thin wall) injection molding, and micro-embossing, because of their great potential for low cost mass production. In high speed/high pressure (thin wall) injection molding, the polymer melt may flow under a pressure twice as much as in conventional injection molding, and the shear rate can be more than 10 times higher. Current commercial simulation codes which are typically used to evaluate moldability and cycle time do not accurately predict mold filling at these extremely high pressures and shear rates. An experimental data base of the high shear rate and high pressure rheology of polycarbonate will be created and used as input in a commercial software called C-MOLD. The effect of high shear stresses on mold wear and 'molded-in' stresses will also be investigated in detail. C-MOLD will be used to simulate the molding of micro-scale features. The simulation software is capable of predicting flow patterns, pressures and shear stresses on the mold surface. In micro-embossing, the plan is to carry out detailed thermorheological study around the glass transition temperature of selected polymers. The molding cycle will be designed according to the rheological behavior of polymers, instead of arbitrarily chosen molding temperatures. The thermorheology results will also be used in FEM simulation to calculate the stress distribution in the mold and in the molded polymer product. Predicted shear stresses on the micron scale mold features will be correlated with the experimentally observed level of mold wear and 'molded in' stresses. The simulations and experimental results (pressures, temperatures, shear stresses, fill time, and cooling time) will also be used to design a process window as a function of feature size/aspect ratio, mold material, and processing conditions. The goal is to develop an efficient mass production method with cycle time similar to or less than that in conventional injection molding and embossing.