Blind fastener assembly

Abstract

A blind fastener assembly includes a pin, an expander and a sleeve. The pin and expander may include, in one configuration, mating threads for drawing the sleeve axially over the expander toward the blind side of a workpiece, or the pin may be a pull-type wherein the portion of the pin opposite from the blind side end has pull grooves which are adapted to be gripped by a conventional pull gun. The expander extends through aligned holes in the workpiece and has a tapered nose surface at the blind side end adjacent a reduced thickness cylindrical portion which extends axially to a stop shoulder. The shoulder provides a transition to a normal thickness cylindrical portion which extends through the workpiece holes. The sleeve is a tubular member with a portion of its length having a normal radial thickness and a portion having a reduced radial thickness. In a preferred embodiment, the reduced radial thickness portion comprises a reduced outer diameter over a portion of its axial length and a corresponding counter-bore along the same portion of axial length adjacent the end of the sleeve proximate the tapered nose surface on the expander. When an axial force is exerted on the pin, the reduced thickness portion of the sleeve is forced over the tapered nose surface on the expander and expanded in diameter until it contacts the shoulder on the expander. Continued axial force on the pin causes an outwardly extending bulb to form in the reduced thickness portion of the sleeve at the shoulder. Further axial pulling causes a portion of the sleeve to shear off and remain lodged between the reduced thickness surface of the expander and the shoulder while the formed bulb is further expanded and pulled over the normal thickness surface of the expander outer diameter until it clamps against the surface of the workpiece material.