Friction stir welding of thick high-density polyethylene plates

This study investigates the influence of critical process parameters: pin diameter, welding speed, rotational speed, and plunge force on the joint quality of friction stir butt-welding of thick high-density polyethylene (HDPE). A new stationary shoulder friction stir welding tool was utilized to butt-weld 14 mm-thick pipe-grade HDPE plates. A numerical heat conduction model was developed to predict thermal profiles and the material’s physical state. Experimental validation was achieved by comparing thermocouple data from the tool shank and HDPE mid-thickness with simulation results. The validated model was subsequently employed to correlate temperature distributions with joint morphology and mechanical performance. Results indicate that optimized parameters yield high-quality joints, achieving weld strengths exceeding 100% of the base material and a maximum elongation of approximately 50%. Conversely, the study identifies a critical thermal threshold beyond which bubble formation occurs, significantly degrading joint strength. These findings provide a predictive framework for optimizing thermal cycles in thick-section polymer friction stir welding to ensure superior mechanical properties.