Key words: Weld nuts, punch nuts, car body production
A modern car body contains some 300 welded and punched fasteners, such as bolts, nuts and studs. The quality of the attachment of these parts to the stamped body components are of utmost importance in terms of reliability and safety of the final product. Crucial components like front and rear axis are mounted to such fasteners, the seat belts and steering column are anchoraged to them and electrical wirings use some of the nuts for earth grounding purposes.
The welded fasteners could be put in place either by using projection or arc splash welding techniques. The latter is mainly being used for stud and some bolt welding, whereas projection welding is the dominating method for nut and M- or T-thread bolt welding. These nuts and bolts are provided with annular projections or 3-4 separate projections depending upon the application. With an annular projection it is possible to obtain a watertight joint, in some nut types combined with a plastic insert. The annular projection is also preferable for attachments subjected to fatigue stress and high loads. Compared to fasteners with separate projections, the annular projection offers less crack initiation points.