Study of thin-wall injection molding

Thin-wall injection molding has received increasing attention over the past few years due to economic and environmental concerns. However, due to the difficulties encountered in the thin-wall molding process, systematic investigation is lacking in machine performance, mold design/manufacture requirement, molding characteristics, computer aided engineering (CAE) simulation, part quality and part design criteria. Furthermore, the combination of viscoelastic materials, complex molding geometry and cyclic processing conditions has generated some problems, such as flow marks, polymer degradation, sink marks and warpage, under high-speed and high-pressure injection molding. So it is very important to design, operate, and control thin-wall molding optimally to guarantee part quality as well as reduce cost.; In this study, alternate and synchronous dull and glossy flow marks, two surface quality problems, were studied. For the alternate flow marks, the effect of polymer rheology, mold geometry, operating variables, and mold surface coatings on the appearance of the flow marks was studied. The flow marks occurred above a critical wall shear stress, but disappeared at high injection speeds. Mold geometry and mold temperature were found to affect the wavelength and the width of the flow marks, while melt temperature did not have much effect. Slip was not the cause of the generation of the alternate flow marks. For synchronous dull and glossy flow marks, the effect of operating parameters, mold geometry, and mold surface coatings on the flow marks was studied. The flow marks occurred above a certain flow front velocity, but were less visible as the mold temperature was increased. It was also found that mold surface coatings did not eliminate the flow marks. The generation of these flow marks was explained by an entry viscoelastic flow instability.; Furthermore, thin-wall injection molding with micro-features was investigated. The filling length in microchannels was measured and compared with simulation. The heat transfer coefficient was found to be very sensitive to the filling length prediction. In order to investigate the effect of input properties on the simulation output, mold cavity pressure was studied. The goal was to understand the effect of pressure-dependent viscosity, heat capacity, heat transfer coefficient, juncture pressure loss and pvT-data on cavity pressure and pressure drop prediction, and evaluate the importance of each parameter. The cavity pressure and pressure drop were measured experimentally and compared. Furthermore, the method to improve the prediction accuracy was discussed to help design and predict. (Abstract shortened by UMI.)...