TIG spot and plug welding
By overlapping two plates a spot weld can be achieved by using the DCEN TIG process to fuse through the top plate and melt into the lower plate. Initial use of the process was carried out without a filler wire but hot cracking problems with the alloys meant that it was confined to pure aluminium up to 2 mm thick. The development of automatic wire feeding systems capable of feeding wire into the weld pool as the weld is terminated has helped in extending the range of alloys that could be welded. Even with this improvement, however, it has been found that the critical nature of the surface condition causes welding defects such as oxide films. This means that the process does not find general use because of low strength and poor quality.
Further work has taken place using fully automated equipment and helium shield gas and with low-frequency AC. These improvements have resulted in a wider use of the process but MIG spot welding tends to be preferred as providing better and more consistent quality.