Shape optimization of square weld nut in projection welding

This study provides an optimal shape of square nut for better projection welding performance. Both experimental design method and electrical-thermal-mechanical finite element analysis (FEA) are used to investigate the effects of nut shape parameters on the height decrease of nut leg, called setdown. The relationship between the setdown and weld strength is then analyzed. Also, welding time to reach 50% of setdown tset is introduced as another objective function for better welding performance. The optimal nut shape parameters are determined to maximize the setdown, and minimize the tset at the same time via Taguchi method. The difference of setdown values between experiments and FEA is within 12%, which verify the reliability of the FE model. The gap between DIN928 standard for nut leg geometry and the optimized nut leg shape is less than 0.2 mm. The differences of setdown and tset values for two nut shapes are 6% and 9%, respectively.