Despite a significant number of publications and the increasing use of numerical simulation, there is still a debate about the optimum gate design and packing conditions in the molding industry. Shrinkage uniformity for unfilled polymers is dominated by the time dependent pressure distribution in the cavity and the resulting volumetric shrinkage; gate freeze‐off is obviously important and difficult to predict; and pressure gradients during the packing phase, depend on process and design parameters and are also affected by the mold elasticity. Molding trials have been conducted on an instrumented mold (fan gated rectangular slab, 2 mm thick) under a variety of processing conditions and with different gate thicknesses using HDPE (Solvay Eltex A1050). Pressure decay during the molding cycle at different locations along the flow path have been correlated with sample thickness distribution. Overpacking at moderate packing pressure is shown to be a direct consequence of mold elasticity and to be related to both filling flow rate and gate thickness. The decay to a finite residual pressure can be computed by coupling the mold elasticity with the PVT behavior of the polymer. The results highlight the importance of gate design and processing parameters on the dimensional accuracy of the part and low internal stress level. When dealing with thick gates, packing pressure profiling appears to be the best way to avoid gate area overpacking. Mold elastic deformation can play a significant role in the cavity pressure‐time history, even for a seemingly stiff mold construction.

In this study, the aging‐induced embrittlement of three polymer glasses is investigated using a previously developed hybrid experimental–numerical method. The evolution of yield stress of unnotched tensile bars upon aging is coupled to the evolution of embrittlement of notched tensile bars using a numerical model combined with a critical hydrostatic stress criterion that determines the onset of failure. The time‐to‐embrittlement of notched tensile bars with a different notch geometry is predicted and in good agreement with the experimentally determined value. Next to that, the approach is extended to three polysulfone polymers, and it is shown that the value of the critical hydrostatic stress correlates well with the polymers entanglement density: : polymers with a denser entangled network display higher values, that is, a higher resistance against incipient cavitation. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47373.

During the cooling process in injection molding, heat fluxes in the mold are generally lower in inner regious of corners. This asymmetric cooling generates a corner deformation: the part angle is smaller than the mold one. This phenomenon is known to be the main cause of corner warpage in injection molding of thermoplastics.The second phenomenon leading to a corner warpage has firstly been described for thin compression molded SMC parts and is called "spring forward effect". Due to the large fiberlength / part-thickness ratio, most fibers in SMC parts are oriented in the planar direction leading to higher thermal expansion coefficients in the thickness direction as compared to those in the surface direction. When the part cools after polymer curing, a decrease of the enclosed angle in a corner occurs after mold extraction. Because of mold restraints for injection molded thermoplastic parts, the shrinkage in the thickness direction is much larger than the in-plane shrinkage and so the spring forward effect can appear.An experimental study and a two dimensional thermo-viscoelastic calculation of a polymer corner deformation in a mold performed on Abaqus code were carried out. We show that the spring forward effect is generally the major source of corner deformation for injected thermoplastic parts.