| 摘要 |
PROBLEM TO BE SOLVED: To identify a nugget part and a corona bond part quantitatively and securely with improved reproducibility by judging cases where a transversal ultrasonic level is higher and lower than a reference level as the nugget and corona bond parts, respectively. SOLUTION: When an ultrasonic probe 50 enters a welded part, namely when the level of a first reflection wave (a longitudinal wave) of a lower plate 20 is larger than the level of a first reflection wave (a longitudinal wave: S wave) of an upper plate 10, a gate G is applied. The gate G is set with a proper interval such as t2/3 based on a time interval of t2 between the S wave and the first reflection wave of the lower plate 20. Then, the level of the reflection transversal on the bottom surface of the lower plate is measured for each fine scanning displacement of the ultrasonic probe 50. When the level drops temporarily and the increase after that is lower than a reference level, no nugget part 32 is formed although a welded part exists, and all are judged to be a corona bond part 34. When the level drops temporarily and the increase after that is higher than the reference level extremely, it is judged that the nugget part 32 has been formed at the welded part.
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