High Efficiency Gas Assisted Cutting (HEGAC) with Yb-fibre laser

The arrival of Yb fibre laser technology provides an opportunity to further reduce the optical energy requirements for thick-section oxygen assisted laser cutting of low carbon mild steel. The high wall plug efficiencies of 25%, coupled with the ability to shape the spatial intensity profile of the beam combined with efficient gas delivery systems, provide the opportunity to further reduce laser power usage. Given the requirement to raise the surface of the mild steel to the ignition point, ∼ 900°C, it is possible to envisage a fibre laser configuration that provides a ring of laser light rather than a spot; since the central region of the spot does not contribute to the ignition process during oxygen assisted cutting. The ring must contain sufficient power to overcome the effects of heat loss through conduction and convection whilst maintaining the substrate surface at the periphery of the cutting oxygen gas-jet, above the ignition temperature. This paper presents the capability of such a system to efficiently cut a grade 43A, 20mm thick mild steel with a maximum laser power of only 400W. The cutting results indicate that a particular optical and gas jet configuration is required to establish a stable cutting condition for a given laser power