Shunt – Error during resistance welding
A common problem is the occurrence of shunts during resistance welding. Shunt means that part of the current does not flow through the lens to be welded, but bypasses it in a variety of ways.
In some cases, the shunt may be negligible, but in other cases it may severely affect the strength of the weld.
Some causes of shunt are:
- Distance between the welding spots too small in relation to the material and thickness
- Intensive contact of the parts to be welded close to the weld
- Contact of the workpieces with live parts (electrodes/holders/arms)
- Indirect welding, especially if the position of the sheet thicknesses is not observed
- Contact of the workpieces with electrically conductive guides or insertion aids
The amount of shunt current depends, among other things, on point spacing, sheet thickness(es), conductivity of the material and surface coatings.
In practice, shunt is compensated for in automated systems by selecting a different programme with a correspondingly larger welding current. Of course, this is not possible with manual systems. But this is one of the reasons why Harms & Wende developed the IQR welding system, which detects and regulates shunts by means of voltage measurement.