FEATURE / THERMOPLASTIC COMPOSITE BRACKET Observations from the initial trials of various cutouts led to the following conclusions: * Multiple interlocks had minimal effect on load capability * Simulation using re-melt function (temperature profiles due to heating on the composite inserts) provided a good indicator of bond quality * Simulation predicted voids, flow hesitations and weld line development A more uniform wall thickness is required to reduce voids and improve bond. Uniform walls can be achieved by coring out the base. Topology Figure 8. Topology optimization load path. Figure 9. Process simulation temperature gradients. optimization provides a map of where we can core the part and still maintain strength. The blue volumes shown in Figure 8 illustrate the main load paths, all the load cases are considered in the topology simulations. Working within the constraints of topology map, injection mold process simulation iterations are used to investigate core designs. The effect on filling, packing and cooling cycles in the injection mold process are studied. Filling simulations study flow patterns and weld line development. Packing and cooling simulations monitor melt temperatures and melt volumes. Investigation of the temperature history on the composite inserts during the molding process is studied. Figure 9 shows how the temperature on the insert develops during the injection and packing process. The process to determine bond quality was developed by reverse engineering the simulation results to the bond in the initial design iteration. Simulations of the new design show much improved bond using the criteria developed. The simulation of the melt volumes, as shown in Figure 10, during the packing phase of the injection molding show melt continuity through the part during cooling. The revised design maintains continuity to the gate during cooling. The melt continuity allows pack pressure to be maintained 20 | SAMPE JOURNAL | Figure 10. Melt volume of molten polymer prior to gate freeze. throughout the part resulting in less void potential and molded in residual stress. Using the results of the simulations the as a guide, the following modifications are made in design iteration 2: * Additional coring - used topology optimization and process simulation to locate area where coring would be beneficial for processing and not hurt strength * Increased wall thickness along the top of the inserts to eliminate flow hesitation * Used filling simulation to modify insert cutouts for improved flow and bonding The changes made are shown in Figure 11. M A R C H /A P R I L 2 0 2 0 w w w. s a m p e . o r ghttp://www.sampe.org