Resistance Welding of Steel Sheets
Welding of High-Strength Steels
The increased application of high-strength steels in the car industry causes a big problem in welding of sheet metals. Differences in the steel elasticity and the hardening of the sheets which has been caused by cold forming, result in poor fit-up and thus in increased sheet bulging which differ from part to part and occur even inside the parts; a determination before welding is not possible. Since, in most cases, sheet bulging is not compensated by fixing with clamps and pressure pads or similar tools, the welding gun is to provide the necessary force.
Without adaptive welding current control, the compensation of the disturbance "sheet bulging" is, for all welding spots, managed through an extraordinary increase of the gun force only. However, the diameters of the welding spots which are located in the areas without sheet bulging are too small because the electrode force has been set too high. Instead of the electrode force increase, therefore, the application of an adaptive current control (adaptation of welding current and welding time) is the better solution of this problem.