TWI Technical Literature Review 22958
By C C Hughes and C M Allen
A number of industries require welding processes for high quality, high productivity, low distortion welding of thick (>25mm) section metals, eg for pipe joining, pressure vessel manufacture or heavy support structures. To this end, multi-pass narrow gap arc welding techniques have been developed, but the productivity of these techniques can be an issue in some situations. Higher productivity electron beam (EB) welding is capable of thick section welding in a single-pass, but restrictions on use of some materials, and the requirement for welding in a vacuum, can dissuade some potential users from its adoption.
The welding of section thicknesses much beyond 25mm is still outside the capabilities of most laser welding processes. However, high power lasers (defined here as ?10kW), including modern fibre and disk lasers, can be capable of weld penetration depths in a single-pass at or approaching these values. Laser welding in vacuum, or at subatmospheric pressures at least, has also been demonstrated to increase penetration depth, even at more modest power levels. Section thicknesses >25mm have also been welded previously using a third process variant: multi-pass laser melting of a wire consumable in to a narrow gap/narrow groove preparation, in an analogue of narrow gap arc welding.