Effect of tool rotational speed on friction stir welding of polymer using self-heated tool

With the growing development in industrial applications of commodity plastics, demand for quick and reliable welding methods has increased. Friction stir welding (FSW), a newly developed technique, is widely used for joining polymer materials. In the present study, friction stir welding is carried out on a 3 mm polypropylene (PP) sheet by a novel self-Heated FSW tool in which external force creates additional frictional heat. Tool rotational speed is varied with fixed tool traverse speed and tool tilt angle. This investigation is aimed to study the forces and torque engendered on the tool during the welding and their effect on the joint quality. The microstructural morphologies of the weldments are analysed by two different microscopes such as cross-polarized light microscope and scanning electron microscope. To evaluate the mechanical characteristics of the welded joints; microhardness test, tensile test and flexural tests are performed. The tool forces and spindle torque decreased with the increment of tool rotational speed owing to greater softening of the material. This reduced forces and torque leading to better mixing of materials at the interface of the butt joint. Though the proper bonding is achieved by this novel tool, a few micropores are observed in the stir zones. Although, with the increase of tool rpm, the microhardness is reduced due to a high-level at material softening, owing to better material mixing at higher rpm, tensile strength and flexure strength are increased with rise of tool rpm up to 1600 rpm.