Online Monitoring the Quality of AC Resistance Spot Welding Using Electrode Vibration Signals

Electrode displacement method has been used to monitor weld quality of traditional AC resistance spot welding (RSW) process for long, and with this method the displacement fluctuation characteristics (e.g. electrode vibration signals) in the displacement curve were always removed as noises. In the current study, the electrode vibration is investigated as a useful signal. The authors used a displacement sensor to measure the transient electrode displacement (Fig.1(a)) in RSW process, and then extracted the electrode vibrations in each cycle (Fig.1(b)) from the displacement curve and found that the electrode vibration is strongly related to the weld nugget growth and is very sensitive to the change of welding current (Fig.1(c)) and thus can be used to online predict the weld quality, such as good weld, sticking weld, small weld and expulsion. In view that displacement sensor is not suitable for industrial applications for its inconvenient installation and high cost. The authors proposed to use accelerometer, which is relatively cheap and very easy to attach to the welding machine without interference with the surroundings±woerkpieces•. The experimental results showed that the electrode vibration signals monitored in the welding phase using accelerometer is consistent with that extracted from the displacement signals, as shown in Fig.1(d).

Fig. 1 Electrode displacement and vibration curves. (a) electrode displacement and welding current signals; (b) electrode vibration extracted from displacement signals; (c) electrode vibration with different welding current; (d) electrode vibration monitored using both accelerometer and displacement sensor.