| Abstrakt: |
In resistance spot welding (RSW), initial resistance between electrodes (RBE) determines heat input (according to Joule's law) and greatly affects the quality of joints. In turn, RBE values are characterized by substantial uncertainty and vary during the RSW processes. To reduce their dispersions, preliminary low-current pulses are applied. In some cases, the quality of the formed RSW joints are controlled using dynamic resistances obtained by feedback from advanced power sources. In these studies, the effect of four preheating current diagrams on the stabilization of the RBE values was investigated for a wide range of parts made of copper, brass, bronze, austenitic stainless steel, as well as aluminum, titanium and zirconium alloys with thicknesses from 0.2 to 1.0 mm in various combinations. Also, the RSW process control capabilities were assessed using feedback from an up-to-date digital synthesizer of unipolar current pulses. As a result, the RBE values were stabilized in all studied cases. Ranges of the variations between the maximum and minimum RBE values decreased from about 5–11 down to 2–5 times. However, the applied algorithms of the preheating current pulses had no effect on the RBE dispersions. It was found that dynamic electrical processes in a welding gun cause distortion of actual RBE curves, which makes it difficult to control heat input and, respectively, the formation of weld nuggets. [ABSTRACT FROM AUTHOR] |
