Projection Welding

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Questions and Answers

Follow up describes the ability of the welding equipment to maintain full force while the projection weld collapses. This is very critical because any variation will change the contact resistance and thus the heat being generated in that projection. Generally this would result in more heat and the projection might overheat and start to expel molten material. If the material expels there may not be anything left to form a nugget. This weld nugget collapse occurs very quickly and some large press welders have excess weight to move causing inertia or a faulty gun cylinder may stick and not be able to follow up properly.

Oversized projections can cause issues in projection welding. All processes are set up based upon design criteria. Meaning projections will be a given size and shape with some tolerance for variation and the process will accommodate this variation. What happens when the stamping tooling wears and the projections go out of specification or a punch breaks and some parts are missing a projection? The process is now out of control.

Undersized projections can cause issues in projection welding. All processes are set up based upon design criteria. Meaning projections will be a given size and shape with some tolerance for variation and the process will accommodate this variation. What happens when the stamping tooling wears and the projections go out of specification or a punch breaks and some parts are missing a projection? The process is now out of control.

Unequal shape or size projections can cause issues in projection welding. If one or more or the projections are not the same shape or size, current will flow through the part differently. The current will flow through all projections making contact at the end of the squeeze portion of the weld cycle. The larger cross section projections will not heat as fast as smaller ones. The smaller mass projections in contact will heat faster and start to collapse sooner than the larger ones in contact. If a projection height is short it may not even be in contact at current initiation. It won’t make contact until the other projections start to collapse. When contact does occur arcing or expulsion is likely from this short projection. Quality could be compromised. Before it makes contact the other projections are carry its current so they are overheated. Again the process is not in control.

Poor electrode alignment or being out of parallel can be a serious problem with projection welding. Generally projection welding involves making several small projections welds with one electrode delivering the force and current to the part. Therefor if the electrode contacts one side of the part first those projections will be in the most intimate contact and carry most of the current. Projections on the other side of the part will have little if any force and could be subject to expulsion when the current initiates. This is both dangerous and bad for weld quality since the projection may be expelled when the current initiates.

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