Modeling and Characterization to Minimize Effects of Melt Flow Fronts on Premolded Component Deformation During In-Mold Assembly of Mesoscale Revolute Joints

In-mold assembly can be used to create mesoscale articulating polymeric joints that enable the miniaturization of devices, reduction in production costs, and increase in throughput. One of the major challenges in miniaturizing devices using the in-mold assembly is to develop appropriate characterization techniques and modeling approaches for the interaction between polymer melt flow fronts and premolded components. When a high speed, high temperature second stage melt comes in contact with a premolded mesoscale component that has similar melting temperatures, the premolded component can experience a significant plastic deformation due to the thermal softening and the force associated with impingement of the melt flow front. In our previous work, we developed methods to inhibit the plastic deformation by supporting the ends of the mesoscale premolded components. In this paper, we present an alternative strategy for controlling premolded component deformations. This involves a mesoscale in-mold assembly strategy that has a multigate mold design for bidirectional filling. This strategy permits in-mold assembly using polymers with comparable melting points. This paper demonstrates the technical feasibility of manufacturing in-mold-assembled mesoscale revolute joints using this bidirectional filling strategy. An experimental technique was developed for characterizing the transient impact force of the melt flow front on premolded components inside of a mold. The experimental data were used to validate a new computational model for predicting the effects of the melt flow front position in order to minimize the plastic deformation of premolded component using the bidirectional filling strategy. This paper also investigates the effects of the flow front position on the force applied on the premolded component and its corresponding plastic deformation.