A New Characterization Approach of Weld Nugget Growth by Real-Time Input Electrical Impedance

Abstract

The in-process changes of weld nugget growth during the Resistance Spot Welding were investigated based on the resistance of input electrical impedance. To compute the time varying resistance of input electrical impedance, the welding voltage and current signals are measured simultaneously and then converted into complex-valued signals by using Hilbert transform. Comparing with the dynamic contact resistance as reported in literature, it showed that the time varying resistance of input electrical impedance can be accurately correlated with the physical changes of weld nugget growth. Therefore, it can be used to characterize the in-process changes of weld nugget growth. Several new findings were reported based on the investigation of spot welds under no weld, with and without weld expulsion conditions.

A novel real-time measurement method for dynamic resistance signal in medium-frequency DC resistance spot welding

“…Garza and Das et al [6,7] used a recursive least square (RLS) method to iteratively calculate the resistance and inductance, which improved the sampling resolution of the signal. Ling and Wong et al [8,9] used the Hilbert transform to monitor the time-varying input impedance signal. Hongjie Zhang and Lijing Wang et al [10,11] proposed a new measurement method to obtain the complex electrical impedance, the real part of which reflects the DR changes, and provided more details over time.…”

“…Traditional direct RSW quality inspection methods, such as sampling inspection based on destructive or non-destructive techniques, are inefficient and cannot inspect 100% of the welds on a car body. As a result, reliable nondestructive techniques of RSW quality monitoring by measuring various dynamic signals are generally proposed, such as dynamic resistance (DR) [3][4][5][6][7][8][9][10][11], electrode force [12][13][14], electrode vibration signals [15], ultrasonic signal [16][17][18] and electrode displacement [19][20][21][22][23], to reflect the nugget…”

Electric Resistance Welding of Austenitic and Galvanized Steel Sheets

“…This increases resistance between the electrodes and sheets. The ratio in resistance change leads to a reduction of electric resistance between the metal sheets at the connection point and this could create substandard welded joints [10]. Adhesion and zinc diffusion create an overheating of electrodes and this leads to a shortened lifetime.…”

A new measurement method for the dynamic resistance signal during the resistance spot welding process

“…Luo et al [31] obtained the continuous DR curve by calculating the quotient of the voltage signal and current signal, and the phase shift between these two signals induced by the leakage reactance of the transformer coil was ignored. Another interesting method was reported by Wong and Pang [32], in which the time varying input impedance signal was monitored.…”