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

Abstract 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°C, an injection temperature of 255°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. Highlights Investigated the effects of injection molding parameters and injection sequences on welding strength. Analyzed the welding mechanisms for different injection sequences. Determined optimal welding parameters using RSM. Identified fiber‐containing melt as the preferred material for the second injection in welding processes.