A hybrid approach for measurement thickness of complex structural parts using ultrasonic inspection and on-machine probing

A hybrid approach for the thickness measurement of complex structural parts on a CNC machine tool is proposed. On-machine probing is firstly carried out to acquire the actual shape data for a part, after which the normal directions of the measurement points are estimated, and finally on-machine ultrasonic inspection is performed to measure the thickness. Calibrations of the on-machine probe and the ultrasonic thickness sensor are conducted to improve the measurement precision. The motion accuracy of the CNC machine tool is pre-evaluated to ensure reliability of the measurement data, and the measuring error is found to be less than 1 mu m. A case study of a hollow turbine blade is performed, and the results show that the deviation in the thickness measurement at any measurement point is less than 0.02mm.