INVESTIGATIONS INTO RESISTANCE SPOT WELDING OF Cu AND STRUCTURAL. STEELS

Abstract

The quality of resistance spot weld is affected by various welding parameters viz. welding current, weld time and electrode force. So influence of these parameters has been studied of resistance spot welding of copper and mild steel (structural steel) of lmm thickness. Separate tests were carried out for each of the variable. It has been found that tensile shear strength increases with increase in weld current, weld time and electrode force. Metal expulsion has been observed at excessive weld current, weld time and extremely low electrode force. Metal expulsion weakens the spot welds. That is why, a reduced failure load has been observed at excessive weld current and weld time. A reduced shear strength has also been observed at higher electrode force. Qualitative characteristics of spot welds has been assessed by measuring size of weld nuggets & HAZ, degree of electrode indentation and hardness of weld nugget and HAZ. Weld nugget size, width of HAZ and degree of electrode indentation increase with increase in weld current, weld time and electrode force. Hardness of weld nugget and HAZ decreases with increase in weld current, weld time and electrode force. Metallographic examination reveals columnar structure in weld nugget. Grains in HAZ adjacent to fusion line has been coarsen. Width of recystallized zone of HAZ has been increased with increase in weld current and weld time. Shrinkage cavity has been observed in center of weld nugget at higher weld current.