Enhancing real-time ultrasound signatures of molten nugget growth for quality evaluation of resistance spot welds

Abstract

This paper presents an effective means of enhancing weak acoustic reflections in real-time ultrasound signatures of a spot weld, by analyzing the propagation of acoustic waves through the electrodes and heated weld region. A new method of processing the ultrasound data is presented that removes undesired acoustical reflections in the electrode cap and enhances weak reflections at the solid-liquid interface. To facilitate this, frequency and amplitude attenuation resulting from the weld medium and acoustical interfaces of the layered weld structure are examined. Sources of echoes that destructively interfere with the desired reflections are also identified and removed by optimal filter design. Finally, basic image processing techniques are applied to a B-scan representation of the weld to improve visualization of the liquid nugget during cooling. This additionally permits the accurate measurement of the final weld thickness; an important quality control parameter.

Real time monitoring of spot-welded joints under service load using lead zirconate titanate (PZT) transducers

“…Some research work [19,20] employed multiple signals for real-time evaluation of welding quality. Technologies, such as infrared thermography technology [5], sonic emission technology [21] and ultrasound signal technology [22], were also employed to perform non-destructive quality monitoring. Most of the existing nondestructive methods indirectly evaluate the quality of the spot welds based on the monitored data when the joint was not loaded.…”