Thermal analysis of revolution pitch effects on friction stir welding of polypropylene

This study explores the relationship between revolution pitch, heat generation, and flow properties in polypropylene friction stir welding joints. Utilizing a modified computational fluid dynamics method, simulations of polypropylene friction stir welding are conducted to elucidate material flow and thermal history in relation to revolution pitch. The study investigates the impact of revolution pitch on internal defects, hardness, and tensile strength of the polypropylene joint. Simulation results reveal that revolution pitch influences polypropylene strain rate and viscosity, leading to variations in internal voids within the stir zone. A higher revolution pitch results in vertical mixing, while a lower revolution pitch causes horizontal lamellar mixing in the stir zone. Controlling revolution pitch is crucial for producing robust joints, as a very low revolution pitch increases the risk of over-stirring and air tapping, while a very high revolution pitch hinders proper joint formation. The optimal heat range for robust joint formation is identified between ~175 (revolution pitch = 0.0410) and ~210 °C. (at revolution pitch = 0.0107). The study demonstrates that consistent polypropylene joint properties can be achieved with similar revolution pitch, even at different friction stir welding tool velocities.