An assessment of the welding performance of high-brightness lasers and a comparison with in-vacuum electron beams

A unique experiment carried out at TWI a few years ago compared the welding performance of a number of fibre-delivered lasers with beam qualities ranging between 4 and 23mm.mrad, under identical processing conditions, and demonstrated the effect of laser beam brightness, together with beam quality and spot diameter, on the welding performance on both steel and aluminium. This paper describes a continuation of this earlier study, carrying out welding under identical processing conditions and comparing, against these initial results, the welding performances of laser beams with even higher beam qualities (higher brightness) and of an in-vacuum electron beam. This investigation demonstrates that the welding performance of a high-brightness laser set-up is highly dependent on the conditions of the metal vapour column forming between the processing point and the focusing lens. The effective removal of this metal vapour column, which scatters and/or absorbs some of the incident laser power, is essential in maximising the welding performance that is achievable with high-brightness lasers. By using an argon side-jet shielding and a series of argon cross-jets along the beam path between the focusing lens and the processing point, it was shown that the welding performance of high-brightness lasers could be improved considerably, and matching, or possibly surpassing, that of an equivalent beam quality in-vacuum electron beam used under similar conditions of power, spot size and welding speed.