Expanding head riveting method and system

Claim 1

In combination with a workpiece having a bore, a first substantially cylindrical counterbore of substantial length, 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 workbore and defining an axis, one end of said shank projecting beyond said bore and being adapted to be upset, b. the rivet including a head having a rearwardly protruding dome and defining an end face, a first section located forwardly of said end face and dome, and a second and forwardly tapered frusto-conical section located forwardly of the first section and engaging said second counterbore throughout substantially the frusto-conical extent of said second section, c. the first section having an undeformed substantially cylindrical outer surface of substantial length which interrupts the second section forward taper and extends at an angle thereto and which is of a diameter less than but about the same as the diameter of the first counterbore to provide clearance therebetween, said clearance having substantially the same radial dimension along the length of the first section, the length of the first section and of the first counterbore being approximately equal, the rivet first section being radially expandable into peripheral engagement with the first counterbore, d. the dome adapted to be flattened so as to cause said radial expansion of the rivet first section so that said head end face becomes substantially flush with the work surface and said first section expands into said peripheral engagement with said first counterbore.