PSI - Issue 77

6

Andreas Fezer et al. / Procedia Structural Integrity 77 (2026) 229–236 Andreas Fezer / Structural Integrity Procedia 00 (2026) 000–000

234

Figure 5. Influence of the BETAMATE™ 1640 adhesive on the spot diameter

3.3. Influence of Sheet thickness The influence of sheet thickness is shown in Figure 6. Each bar consists of data from four sheet pairs, representing 120 weld spots, as the average values from the electrode forces of 5, 6, 7 and 8 kN are shown here. It can be seen that the spot diameters of the 2 mm thick sheets are always larger than those of the 1 mm thick sheets. This is because the bulk resistance of the base material is twice as high for the 2 mm thick sheets. Remarkably, the spot diameter does not increase further at a sheet thickness of 3 mm, but is actually slightly smaller than the spot diameter at a sheet thickness of 2 mm. This shows that the spots do not continue to grow steadily with thicker sheets, but rather reach their peak at some point. There are several possible reasons for this. For one thing, the probability of weld spatter increases with thicker sheets, and for another, it could be due to the less concentrated current flow. Furthermore, the contact resistances of this sheet sample could differ greatly from the others. However, this was not investigated in more detail. In (Fezer et al. 2025), it was shown that contact resistances constitute the main resistance at the beginning of the weld. However, the extent to which initial contact resistances influence the weld result and thus the spot diameters was not investigated.