After actual spot welding, projection welding is the most widely used process in resistance welding. It offers several economic and plant-specific advantages. According to the classification of resistance welding processes, a distinction is made between single-sided and double-sided projection welding (abbreviation RB). In principle, projection welding can be described as a multi-spot welding with a corresponding number of electrodes. The necessary current density is not generated by a narrowed current path through electrodes, but by the shape or cross-section of the projections (also called weld warts).
In the case of multiple projection welds, which is the rule, the projections form a parallel connection. If many projections are welded at the same time for economic reasons, this requires equal resistances of all projections to be welded. This places high demands on the projection geometry, such as cross-section and height, as well as on a uniform contact resistance between the electrode and the projection, which can be realised by a flat contact of the workpieces and a uniform electrode force. Furthermore, it must be ensured that a symmetrical current feed of all projections is given. Since, as mentioned, the projections are welded in parallel, the necessary welding current increases with the number of projections.
Thus, a high connected load of the machine becomes necessary. Today, medium-frequency technology is being used more and more for projection welding machines. In addition to the symmetrical and low mains load compared to AC technology, this technology also offers the advantage of better current distribution to the individual projections.
In modern medium-frequency machines for projection applications, control stroke monitoring is increasingly used for quality assurance. This can be realised with the GeniusHWI control series. Our process monitoring system PQS is also finding more and more applications in projection welding.
The main applications of projection welding are nut welding and ring projection joints. Cross wire welding is also classified as projection welding.