1989 Volume 7 Issue 3 Pages 396-400
This study proposes a ultrasonic measurement of nugget geometry in resistance spot welding of twoplate lap joint of thin plate below 1 mm in thickness. This measurement is immersion method with point focussed probe and is based on the composite effects of convergence of ultrasonic beam and attenuation due to the multiple reflection. Under the condition which the focus of ultrasonic beam places beneath the backwall, there appears a echo from the backwall within the weld region or from the faying surface with an observable time delay behind the surface echo. Since the time delay of backwall echo is as same as that of interface echo but these two echoes provide different amplitude, the weld region is distinguished from unbonded zones. According to the line scanning, three distinct patterns appear; the flat pattern peculiar to the faying surface, decreasing pattern at the vicinity of nugget boundary and increasing or flat pattern at weld region. The nugget size is determined by the distance between two points changing from the decreasing pattern to increasing or flat one, from which the measurement of nugget size is performed with the accuracy of 0.3 mm. A series of parallel line scanning with aid of personal computer provide the configuration of nugget, which is displayed on the CRT with two methods, that is, colour mode and white-black mode evaluated by the amplitude and gradient of amplitude, respectively.