Torque-Angle Signature Analysis of Weld Stud Tightening

This paper investigates the reliability of tightening automotive weld studs, using experimental techniques. During the nut installation on weld studs, only a small amount of the applied torque is used to produce the required clamp load in the joint. While a large amount of the input torque is lost in overcoming friction between the sliding surfaces. Large scatter in the stud tension often results from the normal friction variations. As a result, the weld stud becomes more susceptible to a pull-through failure mode especially in thin sheet metal applications. The torque-angle signature during stud tightening is analyzed to assess the strength and quality of the weld stud joint. The effect of the weld stud thread type, stud coating, sheet metal thickness and stud material on the torque-tension relationship of weld studs is investigated. An experimental procedure and test set up are proposed to test weld studs. The findings of this study would improve the reliability and safety of weld stud assemblies that are widely used by the automotive industry in the manufacturing of passenger cars and trucks.