TWI Industrial Member Report Summary 203/1983
By M N Watson and C J Dawes
The limitations arising from absorption of the laser beam in the plasma above laser welds and control of the plasma, by directing a jet of helium at it , are described. Experiments were carried out to optimise the angle of the control jet to the laser beam (in the range 25-90°), the intersection point of the jet with the laser beam, and the helium flow rate required for laser welding Types 316 and 321 austenitic stainless steel of 6, 9.5 and 13mm thickness with The Welding Institute's 5kW fast axial flow laser. Improvements in welding speed and penetration of up to 30% were obtained when the laser beam/plasma interaction was the limiting factor. Plasma control is also useful to control weld bead shape to reduce distortion, and to allow low welding speeds which may be necessary to avoid cracking with certain materials. However, an assessment of the suitability of the technique for production use indicated that it was difficult to use in its present form because of blockage of the jet, difficulty in setting up the equipment reproducibly, and the careful control of gas flow needed.