Functional principle:
In spot welding, the heat required to fuse the weldments is determined by the current, the
current flow time and the pressure of the closing force that form the weld nugget. Figure 2
shows the process and the formation of the weld nugget. Due to the constant interaction of
heat and pressure, the working surface geometry of the electrode cap changes and the work
surface increases in addition to the formation of a burr at the periphery. As the working area
increases in size the current per mm2 of work surface decreases, resulting in the deterioration
of the weld quality.
Welding quality degradation can also be associated with the properties of copper and zinc.
For example, in the automotive industry for reasons of corrosion protection, galvanized steel
sheets is being used more often. Through the welding process there is a formation of
contaminant material (buildup of zinc layers) on the electrode work surfaces resulting in an
increase of resistance to the work area, resulting in a loss of energy at the electrode working
surface, which is needed for heating the weld metal. This result in a lack of repetitiveness of
the expected welding result.
In order to achieve a reproducible welding result, the specific current intensity can be adjusted
proportionally to the work area magnification and the loss resistance via a stepper function.
Electrode management systems are used to repair and replace worn tips of welding electrodes
(ISO 5821). The welding robot brings the electrode caps or tips to the closed position in the
rotating cutter tool where both electrodes are brought to an acceptable shape at the same
time, free of impurities and deformed material.
Figure 2 Spot welding time cycle
