THE QUALITY OF FLASH WELDED-JOINTS IN MILD-STEEL - A STUDY ON THE EFFECTS OF WELDING PARAMETERS

This paper discusses the results obtained in a detailed experimental study on the effects of various welding parameters on the quality of flash welded mild steel sheets and plates used for wheel rims. Only welding parameters were varied in the case of sheets, whereas for plates, pre- and postwelding parameters also were varied. The effect of secondary voltage on the steel sheets was also studied. The quality was assessed by metallographic examination, hardness profiles across the weld, macro etch, geometry of flash, and tensile tests. Freedom from defects, smoother hardness profiles with a minimum increase in hardness at the weld, increased flash height and upset slope, and wider heat-affected zone (HAZ) were considered as criteria of acceptable quality. The results indicated that though flashing is the main and important stage of the flash welding (FW) process, pre- and postwelding stages significantly control the quality of welds. For example, an increase in preflashing energy (either by increase in preflashing current and length) and preheating energy (by increase in number of impulses) improve the quality significantly. Increasing the number of postheating impulses also was found to improve the quality, while an increase in current-off time had an adverse effect. Generally, higher upsetting forces are considered better for the quality. However, the present study showed that upset current-on time is more significant, which helps in easy removal of plastic material even with less upsetting force. Overall, the study indicated the quality of flash welds can be effectively controlled only when a comprehensive study is made taking into account all the stages.