Investigation on the effects of tool geometry on the microstructure and the mechanical properties of dissimilar friction stir welded polyethylene and polypropylene sheets

The extensive usage of polymers in numerous industries has agitated the researchers to promote their joining and assembling processes. Nowadays, friction stir welding was introduced as an alternative method to the conventional joining processes. The aim of this study is to investigate the effects of tool geometry on dissimilar friction stir welding of polyethylene-polypropylene. Four different pin profiles, including threaded cylindrical, squared, triangular and straight cylindrical were considered. The interaction effects of welding variables, including rotational speed and traverse speed were also studied. In order to control the material flow, the used tools were equipped with a stationary shoulder. Tensile test and durometer hardness tests were carried out and microstructure analysis was conducted for all the welded joints. It was observed that the threaded cylindrical pin profile had the best performance for each welding process condition. The SEM observations showed that using the threaded cylindrical tool, provide more laminar and the uniform material flow regime during welding than the other tool pin shapes. In the optimum joining condition, welded joint with defect-free uniform microstructure, with strength equal to 98% of polyethylene and with higher elongation and hardness than the polyethylene was obtained. The optimum rotational speed equal to 1860 rpm with the highest travel speed equal to 12.5 mm/min provides the welded joints with best mechanical properties. (C) 2017 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.