Determining Weld Quality in Pulsed Nd:YAG Laser Spot Welds

Abstract

For pulsed Nd:YAG laser spot welding applications, the development of optimum welding procedures ought to include various measures of weld size and quality, such as weld diameter, depth, surface contour and porosity. A split-specimen technique has been developed that, despite the small size of the welds, allows such measurements to be made faster and more accurately than the traditional metallurgical technique involving sectioning, polishing and etching. In the split-specimen technique, spot welds are made along a carefully prepared butt joint, cooled in liquid nitrogen and then fractured rapidly by an impact load. The accuracy and precision of this technique, relative to sectioned welds, were examined using welds on austenitic stainless steel. The influence of the roughness of the butting joint surfaces on measured weld dimensions was determined. It was found that measurements could be made more easily and with less error using the split-specimen technique, provided that the surface center-line average (CLA) roughness was less than about 1 μm. A number of examples illustrating the application of the technique are described in this paper. They include results from studies of pool shape development with increasing power intensity or pulse time, and the influence of welding conditions on porosity type and severity.