Investigation of welding defects in friction stir spot welding of plastics

In friction stir spot welding applications, there are some factors that provide welding strength, welding performance and the formation of defects that may occur in welding. Among these factors, machine parameters and welding tool design should be compatible with each other. If these factors are not chosen appropriately, the welding will not be of the desired quality. In this study, high density polyethylene sheets were joined using friction stir spot welding technique. It has been determined that some of the joints made have low weld strength, defects on the weld surface and around the stir zone. By investigating the causes of these defects, suggestions were made to prevent these defecs It has been observed that these defects are not repeated in the welds made with the suggestions made and it has been determined that high weld strength can be obtained. The highest weld strength and performance were obtained by 0.2–0.4 mm plunge depth, 45–60 s stirring time, 700–900 tool rotation speed and 30 mm shoulder diameters. In order to obtain a perfect weld in friction stir spot welding, it was determined that a homogeneous mixture should be formed between the stirring zone and the thermo-mechanically affected zone. Low weld strength was obtained in all joints with defects detected in these regions. Low weld strengths and weld defects were detected at dwell times of less than 30 s, at all tool rotational speeds with a stirring time of less than 45 s, at a plunge depth greater than 0.4 mm, and at low tool rotation speeds.