If routine test welds indicate a weld quality problem in a batch of spot welded components, repair welds may be needed to recover the batch. The ability to repair or over-weld the components by new spot welds will depend on the design of the component and the quality requirement.
If a weld is made over an existing weld, the surface and interface conditions would be different from the original material. The surfaces may be misshapen and oxidised, and the contact resistance will have changed. Thus, different welding parameters may be required to achieve acceptable weld quality.
A new welding condition could be set up to give acceptable quality and confirmed by destructive tests, but there is a risk of variable weld quality. If the original combination was relatively easy to weld, and the quality requirement was not critical, then acceptable repair welds may be achievable. Such repairs would not be recommended if the weld quality requirement was high.
Welds between original spots
Re-welding components by placing welds between the original spots may be an option, depending on the component design and the space available. If the surface condition at the electrode contact and the interface is consistent, and the materials are in close contact, then it should be possible to set a new welding condition for the additional welds. This must take account of the distance of the new welds from the originals, a higher current may be needed to compensate for current shunting (some of the welding current short circuiting through the nearby weld). Destructive tests on samples of the actual components are needed to confirm the quality of the repair welds.
Arc welded repairs may be necessary if the quality of spot weld repairs prove unreliable. Plug welds or edge fillet welds may be suitable, depending on the component. A design concession may be required. This would have to be agreed between the contracting parties.
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