Influence of material adhered to welding tool in consideration of shape of cutting tools on friction stir spot welds

This paper investigates the influence of the presence or absence of material adhered to the tool in A5052/A6061 lap joints when friction stir spot welding tools with cutting edges and rake angles similar to a cutting tool are used. The main focus was the inflection of material flows by the behaviour of the material adhered to the tool during the friction stir spot welding. The failure load of friction stir spot lap joints made using tools with adhered material was more than 1.5 times higher than those made using tools without adhered material in some welding conditions. At this time, it was clear that the ability of the tool to discharge chips did not change irrespective of whether or not there was adhered material. In addition, the material flows during friction stir spot welding, with or without adhered material, were the material flow made by the chips in the keyhole edge and the material flow made by the cutting edge of the tip of the probe in the keyhole corner. However, when tools with adhered material were used, the material flow in the keyhole corner produced not only a flow of welding material but also a flow of adhered material stirred inside the welding material. From the results, when these tools with adhered material are used, it is clear that the adhered material assists the flows inside of the welding material and can improve the characteristics of friction stir spot welds.