Friction Stir Welding of Thermoplastics Using Specialized Tool

Abstract

Friction Stir Welding is a novel welding technique in which a non-consumable rotating tool with a profiled pin is plunged into the adjoining surfaces and moved along the welding direction which results in a weld behind. The technique was first applied to metals and alloys while, lately, its use has also been extended to thermoplastic polymers. HDPE thermoplastic polymer was used as a test material with the aim of getting joint properties similar or closer to that of the base material. FSW of thermoplastics is different from metals and alloys because of their bonding nature, hardness, and thermal conductivity and hence conventional FSW technique is not effective in its core form and pose problems. Hence, to address these problems, a specialized heat-assisted welding tool was developed and its heating was controlled at uniform rate. The parameters considered for the welding process were – temperature at the weld seam, rotational speed of tool, and traversing speed of tool. Taguchi technique was employed for the process so as to come at the best welding combination with minimum number of experiments. Welding using the developed tool on CNC was successfully demonstrated. Weld quality was dictated by the resulting defects in the seam region of the weld. It was found out, using S/N ratios and main effects, that temperature is the most significant factor followed by rotational and traversing speeds. Temperature at its highest level while rotational and traversing speeds at their lowest levels give us highest possible strength and percent elongation while also helps in reducing defects. The optimum combination of factors’ levels resulted in almost 96% weld efficiency. This work increases our understanding of the process in terms of temperature control and helps in developing the process to be applied to most of the thermoplastic materials in use.