Method of making closed cavity pistons

A method of securing a cap on a piston body, comprising, forming a first annular contact surface at an open end of a cylindrical piston body,

• forming a second annular contact surface on an annular surface of an oil conduit in the interior center of the piston body,
• forming a cap to close the open end of the piston body and forming a pair of annular surfaces thereon which are in engagement with the first and second annular surfaces on the piston body,
• placing the cap over the open end of the piston body and thereby placing the annular surface on the cap and the body in close intimate engaging relation, to form two pairs of mating annular surfaces,
• making at least one annular surface of the annular surfaces in each pair of mating annular surfaces in the shape of a V,
• and simultaneously welding the respective engaged annular surface of the cap and the piston body together by subjecting the cap and body to an extreme high current density to fuse the respective engaged annular surfaces together.