The last issue of Schweißzeit reported on adaptive controls for resistance welding. Such an adaptive system is, for example, the IQR control for the Genius inverter series, which, based on the proven constant current control, takes up these possibilities of adaptive control in order to compensate for the known weaknesses of pure constant control. The IQR control is a process control. The aim of process control is to maintain an optimised, controlled and thus quality-capable process of the current production in this state. IQR is a rule-based, discrete-time real-time system.
The rules are stored as artificial intelligence (AI) and take into account material behaviour and disturbance variables. IQR includes rules that guide the welding process for different materials. The aim of the rules is to achieve rapid melting and avoid splashing. Current and voltage measurement and the calculation of resistance and power are used. The resistance curve must be dependent on the heat development in the welding lens and must be reproducible in terms of its curve in order to be able to use the resistance curve as a reference variable. The basic IQR welding process is divided into 4 areas:
IQR phase 1, pre-run (minimum 30ms) with detection of the resistance curve, then IQR phase 2, heating until the lens starts to melt and then IQR phase 3, lens formation without overheating with power reduction to prevent splashing. This is followed by IQR phase 4, the metallurgical microstructure formation depending on the material and fracture strain. IQR is a control method with tools that can be used for all resistance curves that occur in spot welding.
In summary, the IQR control is a process stabilisation for the resistance welding process. It is the “small control loop” for ensuring spot welding quality.