High strength injection molding welding and interface crystal phase changes in polyamide 6

Injection molding is a widely used method for production of plastic components, offering both simplicity and high strength. In this study, secondary injection molding was utilized to weld polyamide 6 (PA6). The welded samples were evaluated for the welding strength via a shear tensile test. Three process parameters of mold temperature, injection temperature, and injection speed were varied to determine the optimal conditions for welding. A polarizing microscope analysis of the welding interface revealed formation of a shish kebab layer (SKL) structure, which significantly contributed to the welding strength. A differential scanning calorimetry analysis of the welded samples showed that changes in the crystallinity at the interface were closely related to the welding strength under different injection molding conditions. To analyze the crystal phase of the interface after welding, we propose the use of Fourier-transform infrared spectroscopy area scanning to obtain the relationship between the phase transformation and welding strength. Additionally, microhardness testing is proposed as a means of evaluation of the welding effect. Overall, this study highlights the importance of optimization of process parameters in secondary injection molding to achieve strong welds in PA6, where the SKL structure and crystallinity changes at the interface have crucial roles. Highlights * The high welding shear strength reaches 80% of the base material. * The interfacial crystalline structure has a significant impact on the strength. * The crystalline changes were analyzed using FTIR region scanning. * The relationship between microhardness and welding strength was obtained. * The wide-ranging conditions have reference value for industrial production. KEYWORDS crystalline phase, Fourier-transform infrared, injection molding, interface, microhardness, polyamide 6, welding strength
1 | INTRODUCTION Plastics have a significant economic value. Injection molding is used to process more than 33% of all plastics. (1) Thermoplastic resins may be effectively melted and joined [...]