Jing Yang

Research Projects

Analysis of a Process for Rapid Replication of Electroforming Micromolds

Electroforming is an important step in the fabrication of microparts using the LIGA (an acronym for the German words for lithography, electroplating and molding) process. This research considers a novel process for rapid replication of thermoplastic electroforming LIGA micromolds incorporating metallic microscreens. During the process, the walls of the microfeatures on the mold stamp are subject to the pressure forces imparted by the flowing thermoplastic melt. The pressure forces on the two sides of the mold feature walls are often unbalanced because of the non-uniform distribution of fluid flow or the different sizes of the cavities adjacent to the mold walls. The unbalanced pressure distribution results in bending stresses on the mold walls, which might lead to a catastrophic breakage of the mold features. To improve the mold life, the effects of mold temperature, inlet polymer melt temperature, flow rate, and cavity width on the mold stress are investigated in this thesis. A computational simulation model is implemented for the process, which forms the basis for a systematic parametric exploration. The parametric studies are used to obtain operating range of the injection molding parameters as well as design guidelines on the mold feature layout so as to eliminate catastrophic mold failures.

Replication of Microscreen-based Electroforming Micromolds by Resin Transfer Molding

During resin transfer molding process for the replication of microscreen-based electroforming molds, the development of residual stress can result in the deformation of thermoset composite structures. It is desired to predict residual stress and deformation in the resin transfer molding process to improve the dimensional accuracy for manufacturing thermoset composite structures. A thermo-chemo-viscoelastic model is developed to simulate the heat transfer and curing for the resin transfer molding process, the residual stress and deformation induced in the process was investigated in this work. The effect of various process parameters, such as cure temperature, cooling rate, geometry, and porosity of porous foam, on the residual stress and deformation is presented. Three types of mold geometry were considered in this study, and design windows for these types of geometries were also suggested for choosing process parameters of resin transfer molding process to minimize the residual stress and deformation.

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