Assessment of laser weld width based on time and frequency domains of ultrasonic testing signals

The ultrasonic test is used for evaluating the laser weld width and the direction perpendicular to the laser weld is adopted for the scan. In the frequency domain analysis, the frequency spectrum characteristic curve shows that the change of the main frequency is in good agreement with the position of the probe. The boundary of the weld width is evaluated using amplitude changes of the main frequency in the base metal and fusion zones. The tested values have larger errors compared to the actual values when the weld width is small. A mathematical model of calculating small weld widths is established based on the time domain signal. The results after correction fit the actual values well, and most of the relative errors are within 0.1 mm. From an analysis of the error statistics, the accuracy and stability after correction meet the requirements of engineering applications and provide an important basis for the quality evaluation of laser welds.