Effects of injection molding parameters and welding sequence on the interfacial strength of glass fiber-reinforced polypropylene

Lightweighting is a key trend in the development of the modern automotive industry. Two-component injection molding and welding technology show significant potential for advancing automotive lightweighting. In this study, polypropylene (PP) and 30% glass fiber-reinforced polypropylene (30% GF/PP) were selected as welding materials. The effects of injection molding parameters (mold temperature, injection temperature, and injection speed) and welding sequences (PP-30% GF/PP, 30% GF/PP-PP, and 30% GF/PP (2)-30% GF/PP (1)) on welding strength were investigated. Results indicate that the 30% GF/PP-PP configuration achieved the highest tensile strength among the three methods, reaching a maximum of 28.1 MPa. The distribution of glass fibers at the interface and the cross-sectional morphology of the damage were observed under a microscope, and the welding mechanisms of the three welding sequences were analyzed. Optimal injection molding parameters were determined using the response surface model (RSM), identifying a mold temperature of 120 degrees C, an injection temperature of 255 degrees C, and an injection speed of 84 mm/s. The maximum predicted welding strength was 28.3 MPa, with mold temperature exerting the greatest influence on welding strength. Additionally, for the production of large and complex parts, using the fiber-containing material as the second melt in injection welding is more effective.