Investigation of thermal contact resistance at a plastic-metal interface in injection molding

Thermal contact resistance (TCR) at the plastic-metal interface is one of the parameters required for the simulation of plastic processing techniques such as injection molding. However, the available data is both unreliable and insufficient due to the difficulties involved in measuring this parameter. The effects of thermal contact resistance on the heat transfer in plastics processing with particular reference to injection molding of thermoplastics is investigated using combined experimental measurement techniques, parametric studies and numerical analysis.; TCR under steady state conditions has been determined experimentally at typical thermoplastic-mold metal interfaces for an amorphous and a semi-crystalline polymer using a one-dimensional heat meter type apparatus. However, a parametric study established that TCR in injection molding is a time and space (location on the part surface) dependent parameter. The analysis shows that the thickness direction shrinkage is the cause of the disparity between the steady state experimental data and data from an injection molding experiment available in literature. The gap at any location on the part surface is a function of the thickness direction shrinkage and the deformation due to unbalanced cooling and non-uniform shrinkage. A finite element analysis was used to study the heat flow across a typical interface in injection molding, and to establish the basis for an analytical solution to the heat equation. This solution was used to develop a model for an effective time dependent TCR which can be utilized to improve the simulation of injection molding. An improvement of up to 20% in the cooling time predictions is expected with the use of the improved model of TCR.; The parametric study, using computer simulation of the injection molding process, was also undertaken to analyze the effect of TCR on the simulation and to determine the effect of injection molding processing parameters, such as hold pressure, on the physical mechanism affecting TCR.; An inverse method was developed and tested with simulated data for the determination of thermal conductivity and TCR from transient temperature measurements.