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Aluminum has a tendency to form voids or cracks in the weld nugget as it solidifies. These voids are generally not desirable. In many cases this condition can be improved with good force follow up or application of a secondary forging force near the end of the weld cycle.
Squeeze is the first segment of the weld schedule. It’s function is to apply force on the work pieces to bring them together. This pressure under the face of the electrode in turn makes good electrical contact and controls and contains the resultant weld nugget during the weld and hold portion of the weld cycle. If current is applied prematurely before the proper force has been reached these functions will be compromised and expulsion and poor nuggets should be expected.
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.
Internal cracks in the weld nugget can lead to decreased strength and need to be prevented or reduced.
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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