Nondestructive testing method and application for internal defect of metal balls

Nondestructive testing for internal defects is necessary owing to the extensive application of metal balls in different industrial fields. The flat-bottom holes (FBHs) are used as the reference standards for the detection of internal defects. An ultrasonic measurement model with spherical-focused transducer based on multi-Gaussian beam is proposed to describe the detection of FBHs inside the metal ball. The comparison between the predicted signals and the pulse-echo responses of FBHs is given to certify the accuracy of the model. The distance-amplitude-correction (DAC) curves are provided to evaluate the equivalent size and depth magnitude of the defects inside the balls. The experimental results indicate that the model can predict and evaluate the internal defects accurately and efficiently. Finally, the method of spiral fully unfolding of ball surface based on orthogonal clamping is developed and successfully applied to the automatic ultrasonic testing system for internal defects of bearing balls combining with the model-based DAC curves.