The effect of top surface lubrication on the friction stir welding of polycarbonate sheets

In this work, top surface lubrication during friction stir welding of polycarbonate sheets was applied. A homogenous layer of Paraffin wax has been placed on the top surface of the joint area with a width that ensures to cover the shoulder diameter. Then FSW was applied using conventional FSW tool with rotating pin and shoulder at different FSW parameters (Rotation speeds of 1000, 1500, 2000 min^–1 and welding speeds of 25, 50, 75,100 mm/min). The main objective of using the wax is to act as a lubricant that reduces the friction between the shoulder and the polycarbonate surface. The joints produced were investigated in terms of surface quality, internal defects, and mechanical properties. During FSW the wax is melted and played as lubricant between the tool shoulder and the polycarbonate surface and resulted in defect-free surface with no thickness reduction of the original plate. The transverse cross-section showed defect-free joints for the majority of the FSW parameters investigated. Tensile testing results showed a reduction of the tensile strength after FSW, and an enhancement in the tensile strength with the increase of welding speed or rotation speed. The fracture occurs at the joint zone and the fracture surface investigation using SEM showed the existence of spherulitic structure in the weld joint.