Experimental study of CO_2 laser welding inside a groove-Application to high thickness laser welding

摘要

Laser welding inside a groove has to be considered when a high thickness material is welded. The use of a groove shape allows the access of the laser beam to the lower part of the groove. The choice of the groove geometry (groove width, depth, or aperture angle), as well as the assist gas setup (leading, trailing or backside protection) are then significant operating parameters for the process control. In this study, U- and V-shaped groove welding with a CO_2 laser was investigated. The U-shaped groove welding generates an increase in penetration depth, a very strong reduction of the process noise and of the plasma plume volume, compared to a bead on plate or a V-shaped groove welding. Also, the penetration depth for a U-groove welding is 20% greater than for a V groove. The groove geometry and the surface tension effects are determinant for these improvements. The influence of shielding gas shows that a trailing protection (gas flow emitted from the nozzle towards the welding direction) should be adopted in order to better control the oxidation of the weld bead seams.