Effects of Process Parameters and Post-Weld Insulation on Angular Distortion Behavior of HDPE Extrusion-Welded Structures

Unlike conventional fiber-reinforced plastic (FRP), high-density polyethylene (HDPE) is recyclable and has recently attracted attention as an environmentally friendly hull material for small craft. During fabrication of HDPE hull structures, thermal deformation can occur due to the material's high thermal expansion coefficient and the substantial heat introduced during joining, affecting fabrication quality. However, systematic understanding of weld-induced deformation in HDPE extrusion welding remains limited. In this study, the angular distortion of HDPE extrusion-welded fillet specimens was experimentally investigated under various process parameters and post-weld treatment conditions. Specimens 8-20 mm thick were welded using 8, 15, and 20 mm welding shoes, with extrusion conditions corresponding to welding speeds of 0.36-0.72 m/min. Angular distortion generally decreased as plate thickness and welding speed increased. Notably, even under an identical extruded mass per unit length, distortion varied with welding speed, indicating that the thermal exposure time of the base material acts as an independent governing factor. Post-weld insulation, in which the weld region was covered to delay cooling, showed thickness-dependent tendencies. For thin plates (8 and 12 mm), insulation increased distortion by up to 38%, whereas for thicker plates (15 and 20 mm), distortion decreased. These results suggest that the deformation behavior of HDPE extrusion welding may differ from that of conventional steel welding, highlighting the need for further analysis and modeling approaches that consider HDPE's material characteristics.