Material extrusion 3D printing and friction stir welding: an insight into the weldability of polylactic acid plates based on a full factorial design

In this work, material extrusion (MEX) 3D-printed polylactic acid (PLA) thin workpieces were joined via the friction stir welding (FSW) process to evaluate the feasibility and the key features of the process. To ensure the reliability of the process, a special fixture was designed and manufactured. Three critical parameters were investigated, i.e., the welding tool geometry, the travel speed, and the tool rotational speed. Two different tool geometries were manufactured and tested. Specimens were welded with various welding parameters values, to calibrate the experimental ranges of the subsequent full factorial course. The results were recorded and evaluated with an optical microscope, a stereoscope, and scanning electron microscopy (SEM). The thermal field and the mechanical performance of the joints were measured and evaluated. In the majority of the welding scenarios, the welded specimens' mechanical performance was increased compared to the identical not welded 3D-printed samples. The travel speed proved to be the most critical parameter affecting the mechanical strength of the parts. The highest tensile strength is reported for a specimen welded with 6 mm/min travel speed, 1400 rpm rotational speed, and weld tool with the cylindrical pin. The results were analyzed and optimized with statistical modeling tools, to evaluate and document the impact of each parameter studied herein. Herewith, a cost-effective and efficient FSW joining process of MEX-made polymeric pieces enables a new possibility to permanently assemble 3D-printed parts of limited size to larger assemblies, with the aid of simple tools and a milling machine.