Monitoring Resistance Spot Nugget Size by Electrode Displacement

Abstract

A high-speed video imaging system was employed to directly measure the electrode displacement of the small scale resistance spot welding (SSRSW) process. This measurement technique was chosen because it eliminates a number of potential error sources inherent in other electrode displacement measuring techniques. Careful observation of the heating and cooling portions of the electrode displacement curves revealed that each is comprised of two identifiable segments. Distinct high-velocity segments of the displacement curves were thought to correspond to solid-liquid phase transitions in the weld nugget, while lower-velocity portions corresponded to thermal expansion or contraction of solid material. It was found that the magnitudes of the high speed portions of the electrode displacement were more closely correlated with the weld nugget thickness than was the overall magnitude of the electrode displacement. Furthermore, all measures of electrode displacement were more closely correlated to weld nugget thickness than to nugget diameter.

Analytical modeling of heat conduction for small scale resistance spot welding process

“…Except near the edge of the electrode, the isothermal lines are almost flat, extending from the center of the faying interface to 1/3 of the electrode diameter. Compared to experimental results [11], the model predicted weld nuggets with larger diameter and smaller thickness. This error could be caused by incorrect modeling of heat generation in the bulk material and at the sheet/sheet faying interface.…”

“…For example, the ratio is 4.69 for the welding conditions and samples used in some prior work [10,11]. Consequently, a one-dimension simplification of the process is reasonable initial assumption for the analytical modeling.…”

Modeling small-scale resistance spot welding machine dynamics for process control

“…After frame-by-frame processing of images, the electrode displacement was obtained. Previous reports [8,9] provide detailed discussions of the accuracy of this technique and comparisons to alternative methods for displacement measurement in small-scale RSW. The welding current and time were varied so as to produce welds over a range of heat inputs that had different nugget sizes and extents of expulsion of molten metal during welding, as shown in Table 1.…”

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

“…Therefore, nondestructive quality evaluation methods based on the feature analysis of the dynamic signals during RSW process attract special attentions [1][2][3][4]. 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].…”