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.
EXCESSIVE WELD INDENTATION
Conditions to consider are:
Long Weld Times – This permits the weld to heat excessively and nuggets to grown too large allowing electrode penetration. Reduce weld times.
High Weld Force – The force is too high and the forging action is driving the electrode into the part. Back the force down.
High Weld Current – Currents are too high encouraging excessive heat and nugget growth. This leads to the part becoming very plastic and indenting. Reduce the current.
Poor Fit Up – If the alignment or fit up is poor improper pressure is being used for the weld and the acting electrode face is not correct for the current which will lead to excessive heat in a small area and in turn indentation. Correct the root problem.
Electrode Impact on Part – Welders have been set up to close so quickly that the electrodes literally impact the work piece like a hammer. This can in fact indent the part and it can also mushroom the electrode face.
Other factors that can play a part but are less prevalent are low weld force, small electrode face area, insufficient cooling, insufficient edge distance, metallurgy of the work piece and poor head/electrode follow up.