Characterization of an electrical melting point using a focusing transducer

The thickness resonances of an elastic plate normally insonified by an ultrasonic plane wave are well known. From these resonance frequencies, the plate thickness can be easily deduced. In this paper, we use a focusing ultrasonic transducer with a large bandpass to characterize an electrical melting point between two steel plane shells. This solder type is abundantly used in the manufacturing of cars. The solder is placed in the focal spot of the beam. The transducer can be parallely moved to the surface of the sheet steel. A number of time signals are recorded along a diametrical line of the melting point with a small step. For each time signal, two spectra are computed: the magnitude spectrum also called backscattered spectrum and the phase spectrum. The results are processed with graphic software. The different images allow the evaluation of the quality of an electrical melting point.