Warpage Behavior and Its Restrain Method in CF/PP Pultruded Wire Grid Structure Insert Injection Molding Process

Recently, advanced CFRTPs have begun to be used as lightweight structural materials in aircraft and some mobility products due to their high mechanical properties and productivity. However, it is not widely used in general products due to the high intermediate material and manufacturing costs. Therefore, it is necessary to develop an innovative technology to manufacture CFRTP products at low cost. As an effective way to meet this challenge, a hybrid insert injection molding technology was developed in this study. This method achieves complex shape formability by combining injection molding and pultrusion methods. When six CF/PP pultruded wires were arranged in a grid structure and inserted into a mold to over-mold PP, the molded product showed significant warpage. In this study, warpage deformation mechanism was investigated by experiments and finite elemental simulation, and some restrain methods were tried, thus realized by experiment. As a result, it was found that the difference in thermal shrinkage rate between CF/PP and PP was the cause of the deformation. It was also found that this manufacturing method required inserting a flat lattice structure in the center of a symmetrically shaped product to restrain the deformation. To meet this requirement, a symmetrical shaped mold for injection molding and a locally heating compression forming method for intersection of the wires to manufacture a flat grid structure were developed. As a result, using the mold and pre-forming method, the deformation was reduced by 79.2%. Finally, a stable insert injection molding process was established.