Spot Welding
Questions and Answers
Cracks appearing in the parent material around the weld nugget can be caused by several issues. They are:
High Weld Force – can fracture the parent material with excessive forging action.
Insufficient Cooling – Over heating can cause excessive stresses from expansion and contraction along with the forging action.
Metallurgy of Material Welded – Some materials become brittle at the temperatures experienced in resistance welding.
Low weld strength can be caused by anything which retards weld nugget growth or formation. It can also be caused by the condition of the materials being welded.
Internal cracks in the weld nugget can lead to decreased strength and need to be prevented or reduced.
Excessive weld indentation can cause rejected product. It is a condition that is specified is some quality plans, AWS D8.7 Recommended Practices for Automotive Weld Quality- Resistance Spot Welding. To reduce indentation one must reduce excessive forces and heat at the surface.
Electrode sticking to the work piece generally is caused by excessive heating between the electrode and the work piece. In the Relative Resistivity Diagram RC has become too large. Any factor which would cause this is an issue that must be addressed to prevent this manufacturing problem. In many cases this condition is accompanied with excessive surface expulsion.
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