A method for measuring displacement and deformation of electrodes during resistance spot welding

Abstract

A new method for measuring the time-dependent displacement and deformation of electrodes during resistance spot welding (RSW) is described. The method allows assessment of the non-stationary thermal expansion of the electrodes. By measuring the electrode indentation close to the weld-piece surface, the method enables a better estimation of indentation than the present methods that rely on measurement of the displacement of the outside part of the electrodes or their holders. The method is based on using a digital video camera to acquire image sequences of electrode caps in the RSW process. A regular pattern of shallow bores is drilled into the caps to enhance the contrast of the acquired images and facilitate image processing. The distances between the bores are analyzed from the image sequences to determine the temporally and spatially resolved displacement and deformation of the caps. The analysis revealed that the cap deformations in some welding regimes can reach up to 20% of the maximum cap displacements, which are approximately 200 µm. The employed image processing algorithms are presented as well as examples of results that demonstrate the applicability of the method.

Real-time monitoring system for resistance spot welding quality

“…The technology developments of sensing, computer and intelligent monitoring make real time monitoring of RSW quality possible. Various electrical and mechanical variables, such as welding current [6,7], electrode force [8,9], dynamic resistance [10][11][12], electrode voltage [13],electrode displacement [14][15][16] and ultrasonic [17][18][19], have been researched to monitor and evaluate the welding quality. Welding current and electrode force are the most important process parameters and directly affect the welding quality, and classification of electrode force patterns was used to evaluate welding quality in a servo-controlled RSW system [8].…”

A new method for nondestructive quality evaluation of the resistance spot welding based on the radar chart method and the decision tree classifier

“…The dynamic resistance and electrode displacement are the most commonly used parameters or variables for weld quality estimation [5,6]. The electrode displacement is mainly caused by the thermal expansion of the weld nugget, and it can make rapid responses to small changes of any variables affecting the welding quality [7][8][9]. It is believed that the amount of the thermal expansion, melting, expulsion, and electrode wear can be reflected by the slope, magnitude, and fluctuation of the displacement curve [10][11][12].…”

Resistance spot weld strength estimation based on electrode tip displacement/velocity curve obtained by image processing

“…The feedback signal must be a signal whose values are closely correlated with the welding nugget development. The most commonly applied feedback signals are electrical signals (welding voltage, welding current and dynamic resistance), 13 electrode displacement [14][15][16] and ultrasound transmission. 17 Other signals like welding force, acoustic and sonic emission, infrared light emission and thermoelectric voltage are used for various control algorithms as well.…”

“…Farson et al, 22 for example, used electrodes with extremely heavy mushrooming in order to obtain reference points. Kus ˇc ˇer et al 15 drilled small holes in electrode tips for the same purpose. In our previous paper 23 we presented a method for obtaining image processing based electrode displacement which does not need any special features of the electrode tips.…”

“…Kuščer et al . 15 drilled small holes in electrode tips for the same purpose. In our previous paper 23 we presented a method for obtaining image processing based electrode displacement which does not need any special features of the electrode tips.…”