Spot Welding
Questions and Answers
Edge distance is a very important design criteria in resistance welding. Any weld on an edge can expel metal and or result in a partial weld nugget. This type of weld is considered deficient in quality programs. Edge welds should be avoided in all design and set up situations.
Part fit up is very important in determining the quality of resistance welds. All weld schedules call out a force value with the purpose of holding the part together, containing the weld nugget and performing a little forging as the weld cools. If the part does not fit up properly then part of this force is used to force or form the part into place and is not available to contain and forge the weld nugget.
ALIGNMENT, FIT UP & WORN CYLINDERS CAN CASUE PROBLEMS
Burrs on the edges of stampings can cause problems because they prevent the part from seating properly or the burrs can break off and become particles which can be expelled during the welding operation.
Dirt, oil, burrs or scale on the surface of the parts being welded can affect resistance welding. They can cause expulsion from the surface, the interface or cause defects in the weld nugget.
If one alters the weld time from the desired range and exceeds the extreme either too long or short you risk surface expulsion, electrode mushrooming, and excessive indentation. If weld times are short you risk small nuggets and low weld strength or no welds.
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