Abstract: A friction joining element for mechanically joining a sheet set prepared by stacking two or more metal sheets including a high strength steel sheet as an upper sheet. The friction joining element includes a mandrel having an overall length adjusted to be equal to or less than the total thickness of the sheet set, and a collar disposed at an upper portion of the mandrel. The friction joining element has a screw thread on a side surface of a head-side portion of the mandrel.

Abstract: In performing friction element welding of a sheet set constituted by two or more metal sheets, an element is press penetrated into the sheet set. The element may include a round columnar mandrel; a disc-shaped collar provided at an upper end face of the mandrel; and a conical pin extending from a lower end face of the mandrel. The element has a plurality of fluidized-metal discharge grooves arranged spirally in a flat area of the lower end face of the mandrel, the flat area excluding the pin. Alternatively, the element may include a round columnar mandrel having a lower end face that forms a conical face with an apical angle ?m, the conical face having one or more pairs of chippings discharge grooves or having a plurality of cutting edges, the chippings discharge grooves each extending in a curved manner from an apex of the conical face.

Abstract: An element, a friction element welding method, and a method for producing a friction element welded joint. The element is for performing friction element welding on a sheet stack of two or more stacked metal sheets by pressing the element into the sheet stack while the element is rotated. The element includes a circular columnar mandrel that is to enter the sheet stack, a circular collar disposed at an upper end portion of the mandrel, a first conical body extending from a lower end surface of the mandrel, and a second conical body disposed on the lower side of the first conical body. The vertical angle ? of the second conical body and the vertical angle ? of the first conical body satisfy the relation ?<?.