超音波によるスポット溶接部の品質評価

抄録

Weld quality of spot welds was examined by a newly developed ultrasonic testing with a focussed probe. This method is based on the composite effects of convergence of the ultrasonic beam and attenuation of reflected waves due to the multiple reflection, and the back wall echo in the welded region is distinguished from the interface echo in the faying surface. In this study, the weld quality and weld size were evaluated by the parallel line scannings over the spot weld.
In the scanning graphs of sound spot weld, the periphery of spot weld is given by the sharp minimum pattern and the welded region is represented by the protrusive pattern surrounded by the sharp minima. When the spot weld includes the expulsion, crack and shrinkage cavity or blow hole in the welded region, different patterns appear in the scanning graphs. The expulsion gives lower echo height region linearly distributed around the protrusive pattern, and the crack and shrinkage cavity give the depressed and small protrusive pattern in the protrusive one. Besides, irregular shaped nugget and mechanical or solid bonding interspersed around the welded region are evaluated by the irregular and banded shape of minimum pattern, respectively. These patterns were confirmed by the macroscopic observation of fracture surface. The imaging technique was also developed for the twodimensional representation of nugget and shrinkage cavity, from which the diameter and area of nugget were measured, precisely.