Comparison of high power YB-fibre and Nd:YAG lasers when welding Ti-6Al-4V

The beam qualities of modern solid-state laser sources, such as Yb-fibre and Yb:YAG disc lasers, are significantly higher than those available with a Nd:YAG rod laser. As a result, the beam can be focused into a much smaller spot diameter for a given focal length and hence higher power densities become available at the workpiece. In this study, a multi-mode Yb-fibre laser has been compared to a Nd:YAG rod laser in terms of weld quality when welding 3.25mm thickness Ti-6Al-4V. Titanium alloys are increasingly utilised in aerospace structures as a result of their high specific strength, fatigue performance and corrosion resistance, and because of this, the weld qualities achieved in this work are compared with stringent aerospace welding criteria. The generation of porosity in the weld metal was significantly decreased at incident power densities above ~8.0×10⁴W/mm². Furthermore, above this power density, undercut present in the weld profile could also be reduced, whilst still maintaining low levels of weld metal porosity, at certain welding speeds.