Experimental investigation on the weldability of wood-plastic composites by friction stir welding using a self-reacting double-stationary shoulder tool

• Novel double reversed threading tool design for welding wood composite materials (50 % fibers, 50 % LDPE). • Tool traverses specimen thickness between two stationary shoulders, preventing root defects. • Introduced revolutions per distance (RPD) metric to quantify energy per unit length of welding. • Achieved sound weld joints with homogeneous nuggets and relative flexural strength up to 99.18 %. In this study, the weldability of wood–plastic composites (comprising 50 % wood flour and 50 % low-density polyethylene) was examined using an innovative self-reacting friction stir welding tool featuring a double-stationary shoulder design. The tool, made from hardened K340 Isodur tool steel with a hardness of 60 HRc, was tested by varying the tool rotational speed (600 to 2200 rpm) and linear welding speed (0.2 to 0.6 mm/s) across five different Revolutions Per Distance (RPD) values, which measure energy input per unit length. The visual appearance, macrostructure, and mechanical properties of the welded specimens were assessed. A statistical regression equation was developed to relate the RPD and rotational speed to the relative flexural strength of the specimens. The tool design produced high-quality welds with a uniform welding nugget and minimal defects. The relative flexural strength values for the samples ranged from 62.85 % to 99.18 % in the entry region and 66.64 % to 92.14 % in the exit region.