Friction stir spot welding of similar and dissimilar high density polyethylene and polypropylene sheets

Development and modernization in joining and welding techniques of plastic materials have attracted much attention in the field of scientific research and industry. Friction stir welding and friction stir spot welding, nowadays, have gained a significant advantage over other joining techniques due to the ease of operation, with no need for any adhesives or external heaters, and the use of non-consumable tools. In this research, the friction stir spot welding process of similar and dissimilar polymeric materials (polypropylene and high density polyethylene) was investigated experimentally. The effect of tool rotational speed and dwell time on the lap shear strength was studied, while the tool plunging rate, plunging depth, and tool geometry were kept constant during all tests. The welding of dissimilar polypropylene to high density polyethylene was successfully performed within the range of 1400-3500 rpm rotational speeds; however, it was unsuccessful with 800 rpm. Moreover, the friction stir spot welding of similar polyethylene and polypropylene was studied, and the optimum welding conditions were 3500 rpm with a dwell time of 40 s, and 800 rpm with a dwell time of 120 s for polypropylene and polyethylene respectively.