Thermal contact resistances (TCR) play an im portant role in heat transfer. TCR is therefore of significance in the simulation of injection mold ing processes where one of the factors determin ing productivity is the cooling time. Simulation software packages either consider TCR as negli gible or use a constant value based on steady- state conduction, whereas in injection molding, TCR is time-dependent. We use simulation of the injection molding process to show that using TCR values within the range obtained from steady state experiments may lead to underpre dicting cooling times by up to 15% and, hence, there is a need to use time-dependent TCR in the heat transfer simulations. Our simulation result indicates that the value of TCR also affects the frozen layer fraction in the early postfilling period.

Thermal contact resistance (TCR) plays an important role in the heat transfer during injection molding. However, there is no consensus on the magnitude of TCR to be used in simulation as most of the reported results are based on steady state experiments. A numerical simulation of the heat transfer in injection molding is used in studying its effect and significance. The TCR is shown to attain its maximum magnitude in the postfilling period, and more accurate values than those available in literature are required for a better simulation of the postfilling stage. The effect of interface gap formation between the plastic and the mold on the contact resistance is also studied. This shows that the gap may have contributed to the high magnitude of TCR reported from the one experimental study of TCR in injection molding. However, the gap formation is shown to be dependent on the part geometry as well as processing conditions—in terms of shrinkage and warpage effects. The gap is both a function of time and space (location on the part surface) and this makes any experimental determination of the gap and TCR difficult. [S1087-1357(00)01404-0]

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Heat transfer in polymer processing by injection molding is affected by the thermal contact conductance at the interface between the polymer and the metal mold. The modeling of thermal contact conductance at such interfaces is simplified by the assumption of an isothermal condition at the two contacting surfaces. In this study we examine the validity of such an assumption for the case of an interface involving plastic (a low thermal conductivity material) and metal (a high thermal conductivity material). The study shows that at such an interface between materials of widely varying thermal conductivity, the conditions at the interface depart from the isothermal assumption, with the heat flux becoming more uniform and the temperature difference varying by a larger magnitude across the contact plane. This effect is more pronounced as the width of the gaps increases for the same area of contact. This suggests that the modeling of the contact conductance should be based on average temperatures for the contacting surfaces.