Investigation of Weld Forces and Strength of Friction Stir Welded Polypropylene

Abstract

Friction stir welding (FSW) is an advanced joining technology specifically developed for welding materials that are difficult to weld (e.g. polymers). Over the last two decades, more and more research has been published on the applicability and development of the technique on polymeric materials. The aim of the present study is to investigate the applicability of the method for welding polymeric materials and to analyse the effect of the parameters of FSW. In the tests, 4 mm thick polypropylene sheets were welded by varying two welding parameters (tool speed (n) and feed rate (v_f)) in four levels. Thus, a complete experimental design with 16 measurement points was created. During the welding process, the force components on the tool/workpiece were measured, from which the resultant welding force was calculated and the strength of the joints was characterized by tensile testing. The ratio of the tensile strength of the joints and the tensile strength of the material were used to characterise the process in terms of joint efficiency. During welding, the axial force component (F_z) was the dominant force value. The resultant forces (F_e) decreased with increasing n, while they increased with increasing v_f. The tensile strength of the joint, and hence the bonding efficiency, improved with increasing n, while it deteriorated with increasing v_f. The ratio derived from the ratio of n to v_f was also analysed, with an increase in the ratio showing a decreasing trend in the resulting weld strength and an improving trend in the bonding efficiency.