In the welding process of the intermediate frequency spot welder, the resistance is composed of the contact resistance between welds, the contact resistance between electrodes and welds and the resistance of the welds themselves. As the temperature increases, the size of the resistance is constantly changing.
During welding, the difference of electrode pressure, current and material to be welded all affect the dynamic resistance change. When different metal materials are welded, the dynamic resistance changes differently. At the beginning of welding, the metal in the welding area is not melted but is preheated, and the contact resistance drops rapidly. As the temperature increases, the resistivity increases, while the resistance decreases due to the increase in the contact area caused by heating, where the increase in resistivity is dominant, so the curve rises.
When the temperature reaches a critical value, the resistivity growth decreases and the solid becomes liquid. Due to the increase of the contact area due to heating softening, the resistance decreases, so the curve decreases again. Finally, because the temperature field and current field basically enter the steady state, the dynamic resistance tends to be stable.
From the point of view of the resistance data, the change from about 180μΩ at the beginning of the welding to about 100μΩ at the end is quite large. In theory, the dynamic resistance curve is only related to the material, and has universal properties. However, in the actual control, because the resistance is difficult to detect, it is difficult to control according to the resistance change. The detection of welding current is relatively easy, if the dynamic resistance curve is converted into a dynamic current curve, it is very convenient to implement. Although the dynamic current curve is related to the power and load characteristics of the intermediate frequency spot welder, when the hardware conditions (intermediate frequency spot welder) are certain, the dynamic current curve and the dynamic resistance curve have corresponding rules.
Post time: Dec-04-2023