Ultrasonic on-machine scanning for thickness measurement of thin-walled parts: modeling and experiments

Abstract

The thickness measurement of large thin-walled part has become increasingly important to inspect the machining quality and compensate the machining errors. So far, commercial hand-held ultrasonic thickness gauges have been widely used in the wall thickness inspection of large thin-walled parts. However, the manual operation has some disadvantages such as insufficient measurement efficiency, intensive labor, and limited accuracy. To tackle these problems, an automatic thickness measuring method is supposed to be an effective approach. In this article, an ultrasonic on-machine scanning technique for thickness measurement of large thin-walled parts is proposed. First, a multi-function integrated ultrasonic thickness on-machine measuring device is innovatively designed, which enables the posture of an ultrasonic sensor to adapt to the measured surface orientation automatically. Second, the on-machine measurement model of the thickness distribution is established, which includes a measuring point coordinate extraction model and a precise thickness assessing model. Then, a scanning motion control strategy for contact ultrasonic measurement is proposed to maintain a constant pressure between the ultrasonic transducer and the workpiece during the scanning process. Finally, taking the arched part, inclined plate, and S-shaped thin-walled part as typical objects, the experimental study has been conducted using the proposed method. The experimental results show that the ultrasonic thickness on-machine measurement accuracy can be controlled within 0.04 mm, which validates the feasibility of the ultrasonic thickness on-machine scanning technique on thickness measurement of complex surface thin-walled parts.