Joining of Bar and Nut to Die-Quenched Steel Sheet by Punching

Abstract

A mechanical joining process of a bar and nut to a hard hot-stamped steel sheet was developed, because the resistance projection welding generally used for joining of bolts and nuts to hot-stamped sheets has low joinability. In this process, a slightly smaller hole than a bar and nut was made in the sheet with the bar and nut having a small round or chamfer at the bottom corner, and then the bar and nut were inserted into the hole. The punched hole was ironed with the bar and nut during the insertion, and thus the joint strength became high. No pre-punching is required for the sheet, whereas higher strength than that for the sheet is necessary for the bar and nut. For the bar and nut having a radius of 1.0 mm at the bottom corner, the ironed surface was the largest, and thus the maximum joint strength was obtained.