Shunt and spacing of spot welds
Very often, so-called shunts lead to faults in resistance welding. Either caused by welding spots being too close to each other or by contact of the components, the components with the welding fixture or the components with the electrode away from the contact surface. Part of the welding current then flows over these already welded points or contact points described above. Of course, this part cannot then contribute to the actual welding. The point with the shunt is smaller than the one without. In case of shunts caused by already welded spots, this can be counteracted by selecting a second welding programme with higher current.
As a rule of thumb for a point spacing with virtually no shunt effect, the point spacing should be greater than 10 * total sheet thickness if the quality requirements are low. The distances are also described in DIN 1912 Part 6. Considering these reference values for the arrangement and spacing of the spot welds definitely helps to achieve a design that is suitable for welding. See also DVS leaflet 2903 Part 3 and DIN 8528 Part 1.
For dynamic loading of single-cut joints, a maximum in shear strength is achieved with a point spacing greater than or equal to 4 times the point diameter. For multi-row connections, an optimal point spacing of approx. 5 times the point diameter applies. These are only examples for a construction suitable for welding, furthermore overlapping and edge distance are important. The distance of a spot weld to the edge of the sheet should always be at least equal to the spot diameter. In practice, these basic points are often not realised, the welding system manufacturer and especially the operator then have to deal with unnecessary difficulties.