Expanding head riveting method and system

Claim 1

In combination with a workpiece having a bore, a first counterbore which is substantially cylindrical, and a second counterbore which is frusto-conical and tapers forwardly between the first counterbore and the bore and toward the bore, (a) a rivet having an axially extending shank received in the workpiece and defining an axis, (b) the rivet including a head having an end face, a first section located forwardly of said end face, and a second and forwardly tapered frusto-conical section located forwardly of the first section, (c) the first section having an initial undeformed outer surface of a diameter which is less than but about the same as the initial diameter of the first counterbore, the rivet first section being radially deformed to have peripheral engagement with the first counterbore, (d) said head end face being substantially flush with the work surface, (e) said head end face initially defining an undeformed ring-shaped dome extending about said axis and in substantial axial alignment with the outer surface of the shank, (f) the dome having an annular crest portion in axial alignment with said shank outer surface, and the dome radially outer extent which defines only about half of the dome being located in axially spaced relation to a forward taper defined by said second and forwardly tapered section, said dome crest portion being rearwardly convex in axial radial planes, (g) the head end face forming a concave central recess radially inwardly of said crest portion, the outermost annular extent of said recess located approximately in alignment with the outer surface of the shank.