ENHANCE THE LIFE OF SPOT WELDING ELECTRODES USED FOR WELDING OF ZINC COATED STEELS

Abstract

Resistance spot welding is an important part of the automotive manufacturing industry. Today's automobiles typically contain five-thousand or more spot welds. Spot welding is attractive to the industry for its speed and relative simplicity; however, it is not without its disadvantages. The industry's increased use of coated steel. The chemical reaction of the coating with the electrodes caused greater variation in the electrode life. The electrode wear reduces the electrode life. Between one-half and three-quarters of the cost of a spot weld is the electrode cost. Greater savings would be realized if the electrode's life could be improved. Cryogenic treatment is an inexpensive one time permanent treatment affecting the entire section of the component. Cryogenic treatment and tempering is a one-time permanent process that improves the physical and mechanical properties of various materials such as ferrous and nonferrous metals, copper, aluminum, and their alloys. It uses sub-zero temperatures to dimensionally stabilize, refine and close grain structures, release internal stresses for the life of the material, and produces longer wear life to parts subject to wear and abrasion. The cryogenic treatment improves performance, and increases the life of metal tools. Unlike a coating, it is a through treatment that treats the entire tool, and keeps its benefits even after repeated resharpening, until the tool is completely worn out. Electrode life (Electrode endurance test) is defined as the number of welds made with a pair of electrodes, while maintaining weld button diameters above a specified minimum value. A study was performed to investigate the electrode life in spot welding electrodes used in zinc coated steels. Electrode life was conducted to investigate the effects of electrode degradation on electrode life ii in resistance spot welding of 0.8-mm with coating weight 120 gm/m2 thick sheet zinc-coated steel using a spot welding machine and electrodes with tip-face diameter of 5 mm. A series of spot welds made as per the AWS D8.9 -97 standard norms. The reduction in joint strength occurs because of undersized nugget formation due to increased contact areas of electrodes and hence reduced current density. The electrode degradation may be monitored by the increase in all three areas (nominal tip-face area, and electrode to sheet and sheet to sheet contact areas), but the electrode to sheet contact area is believed.to be the most suitable because a minimum ofextra work is needed to measure it. The button (nugget) diameter, measured from twist testing at regular intervals. A twist test method was performed on spot welds at regular intervals to know the electrode life. Cu-Cr-Zr, Cu-Cr, Cu-W electrodes was used to measure the electrode life.