Preparation and welding of zinc coated steel

Citation

(2002), "Preparation and welding of zinc coated steel", Industrial Robot, Vol. 29 No. 2. https://doi.org/10.1108/ir.2002.04929bad.008

Preparation and welding of zinc coated steel

Keywords: Welding, Patents, Robotics

Applicant: British Aerospace, UKPatent number: GB2274257Publication date: 20 July 1994Title: Method of Preparing and Welding Zinc Coated Steel

This patent describes a method of preparing a zinc coated steel work piece for welding and a method of welding such a prepared work piece. Welding of zinc coated steel (galvanised steel) by laser is made difficult by the presence of the zinc coating. The high vapour pressure and low vaporisation temperature of zinc means that when welding is attempted by laser the zinc vaporises rather than melts which gives rise to the problems of highly porous welds and instability of the melt pool due to the escaping vapours when this boils.

The zinc coated steel work piece is prepared for welding by scanning with laser radiation, to remove the zinc coating layer. The laser is preferably an excimer laser and has a wavelength in the range of 150 nanometres to 20 micrometres, at a fluence of 0.1 to 100 Joules per square centimetre. The laser is pulsed, with a pulse length in the range of 1 nanosecond to 10 microseconds, onto the surface of the work piece with a minimum of 1 pulse, preferably 10 pulses, impacting at each point. The prepared surface of the work piece can then be welded to a further work piece by resistance spot welding, arc welding, friction welding or laser welding. For laser welding a laser is used, preferably operating at a power of substantially 750 watts at a scan rate of substantially 240 millimetres per minute in an atmosphere of nitrogen.