After starting the welding production with systematically optimized process parameters well planned in the process window, some irregular problems could still arise due to process tolerances and unintended changes in welding process conditions, for example electrode degradation, electrode misalignment, gap between sheets and possible errors from preceding processes such as variation of temperature in hot pressing resulted in changes in sheet surface conditions.
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 used as an indication of welding problems and criterion for improving the welding process conditions.
SORPAS can simulate and predict splash and 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 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. It can be done by prolonging the squeeze time, slightly increase the electrode force during squeeze time, or by using a preheating pulse with 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 may be 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.
Numerous automotive parts, especially for the safety components are produced by hot stamping technology today. The high strength at the final stage and the good plastic formability after heating is the main benefits of this technology.
But welding on hot stamped parts can be tricky, since heat treatment process effects the properties of base material and surface coating.
For example, intermetallic alloying reaction between the Al-Si coating and the iron of the sheet material takes place during heating process in the furnace. As a result the electrical resistance of AlSi coating increases after heat treatment. 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 is achieved.