Abstract: A 3-25 mm metal plate 22, 27, usually ferrous, is welded by a heavy-duty laser (5-25 kw) which melts through the plate and into a support member 24, 31 below to give a unitary weld. A gas supply to the laser beam focus is provided such that on the one hand the plasma is retained at least partially near the weld pool to give good energy transfer and on the other the plasma does not all escape.

Abstract: Contiguous metal plates are welded together without special edge preparation or bevelling e.g. of cut edges 13 from one side using a focussed high intensity laser beam 7. To ensure maintenance of welding conditions even when the plate edges are spaced apart by cutting imperfections or the like a wire 12 is fed to, or near, the beam focus 10 to intercept the beam and give rise to a plasma. This plasma is kept in place by gas supply means 8, the gas supply through ducting 15, 16 of which (a) prevents plasma building up above the weld zone (which would decrease the beam intensity at the weld) but (b) holds some plasma in the region of the beam impingement on the wire so as to allow energy transfer to the adjacent walls.Butt welds or T welds can be made in this way, even in plate material, in a single pass from one side. The technique thus permits the arrangement of work stations on a production line to be simplified and rationalized when making up multiweld repeat structural units e.g. in shipbuilding.