Nd-YAG laser welding of bare and galvanised steels 890887

Until recently, one of the problems that has held back the introduction of lasers into car body fabrication has been the difficulty of integrating the lasers with robots. Flexible beam transmission systems for CO₂lasers require a large number of heavy optics that must be kept accurately aligned and mounted on a robust, heavy robot, that may not have the positional accuracy necessary for laser welding. Nd-YAG laser beams can be transmitted through fibre optics which, as well as being considerably easier to manipulate than a mirror system, can be mounted on more lightweight accurate robots. Although previously only available at low powers, recent developments in Nd-YAG laser technology mean that lasers of up to 1kW average power will soon be available, coupled to a fibre optic beam delivery system. The increasing usage of zinc coated steels in vehicle bodies has led to welding problems using conventional resistance welding as well as CO; laser welding. The use of Nd-YAG lasers may be able to overcome these problems.

This paper outlines work carried out at The Welding Institute on a prototype Lumonics 800W pulsed Rd-YAG laser to investigate its welding characteristics on bare and zinc coated car body steels. Lap welds were made in 0.7mm thick materials at a range of welding speeds, pulse energies, repetition rates and pulse widths, using conventional focusing optics without a fibre. Full penetration welds were made at speeds up to 0.5m/min, which were visually good in the bare steels. Welds in the coated steels were slightly undercut but did not contain any of the surface blowholes that are often found in CO; laser welds in coated steels. These early results show that an 800W pulsed Nd-YAG laser can be used for welding car body steels and that, although the welding speeds are much lower than those achievable with a CO₂laser, the consistency of welds in zinc coated steels is considerably higher.