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

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.