Though you use the optimized process parameters in the process window, some irregular problems could still arise. There could be some irregular problems and unintended changes in the welding process. For example, electrode degradation, electrode misalignment, gap between sheets, and possible errors from preceding processes such as variation of temperature in hot pressing can cause problems.
It is important to understand the causes of welding problems and predict the tolerances and limits for the possible causes. One of the common issues in welding production is splash (spatter or expulsion). It is often an indication of welding problems and a criterion for improving the welding process conditions.
SORPAS can simulate and predict splash. It can also evaluate the effects and consequences in welding results due to different process conditions by electrode degradation, gap between sheets, different surface conditions after hot pressing, etc. This will help to quickly find useful solutions and improve production maintenance for increasing consistency of weld quality, stability of production, and productivity.
Gap between workpieces
It is quite common during the welding production, there may be a gap between sheets before starting spot welding, mainly due to the process tolerances in the preceding stamping process, stamping, or sheet forming. This will need special process parameter settings to close the gap between sheets before starting the weld current. Common solutions to close the gaps are:
- prolong the squeeze time
- slightly increase the electrode force during squeeze time
- use a preheating pulse with a lower current before the weld current
Due to mounting errors or elastic deflection of the weld gun during spot welding, the electrodes are quite often not perfectly aligned to each other. The electrodes may be tilted with a small angle to each other or maybe offside with a small distance between the contacting centers of the two electrodes. The electrode alignment may produce irregular weld nuggets or cause severe expulsions (spatter, splash). SORPAS 3D.welding can simulate the effect of electrode misalignment in all situations.
Today many manufactures produce numerous automotive parts, especially for the safety components by hot stamping technology. The high strength at the final stage and the good plastic formability after heating are the main benefits of this technology.
But welding on hot stamped parts can be tricky since the heat treatment process affects the properties of base material and surface coating.
For example, the electrical resistance of AlSi coating increases after heat treatment. Because the intermetallic alloying reaction between the Al-Si coating and the iron of the sheet material happens during the heating process in the furnace. The higher resistance influences the current and nugget formation in the welding process.
In case of projection welding of fasteners, the huge hardness gap between the fasteners and the hot stamped base material causes the projections to collapse before a good weld forms.