Joining of Taper Nut and Bolt to Ultra-high Strength Steel Sheet by Punching

Abstract

A mechanical joining process of taper nuts and bolts to ultra-high strength steel sheets by punching was developed, because resistance projection welding generally used for joining of nuts and bolts has low joinability for the ultra-high strength sheets. In this process, the sheet is punched with the taper nut and bolt, and the nut and bolt are joined by ironing and expanding the punched hole. The upper surfaces of the nut and sheet are aligned by controlling the stroke in order to attach other parts. No pre-punching is required for the sheet, whereas higher strength than the sheets is necessary for the nuts and bolts. For the die-quenched steel sheet having a tensile strength about 1500 MPa, the joint strength was about two times higher than that specified in the Japanese Industrial Standard of weld nuts. For the sheets above 780 MPa in tensile strength and above 1.6 mm in thickness, sufficient joint strength was obtained.