The hybrid laser-arc welding process is characterised by the simultaneous application of a focused laser beam and an electric arc in a single process zone.
This combination provides several benefits one of which is to provide a much increased gap-bridging capability compared to that available when welding with the laser source alone. The process operates such that consumables provide the appropriate amount of molten material to bridge gaps or fill grooves, while the laser enables deep penetration at high speed.
Consequently the hybrid process significantly increases tolerance to joint fit-up variation and edge preparation quality.
TWI has recently conducted pioneering work on hybrid Nd:YAG laser-MIG/MAG welding with adaptive control.
An integrated hybrid welding system was developed, based on a Trumpf 4kW Nd:YAG laser, a Servo Robot sensing and joint tracking system, a Kawasaki robot and a Lincoln MIG/MAG welding machine. In this system, the sensing and joint tracking device, located ahead of the welding head, detected the joint position and gap. Real-time information was returned to the control system and compared with pre-determined sets of weld parameters.
Joint gap variations were automatically compensated for by the real-time control of the laser beam travel speed along the seam.
Welding has been successfully demonstrated on butt joints with variable gaps (0 to 1.5mm) in 8mm thickness steel plate.
Acceptable weld quality (level B in BS EN ISO 13919-1:1997) was achieved with joint gap variations outside those normally tolerated by hybrid laser-MAG welding without on-line adaptive control.
The welding torch stand-off distance and orientation with respect to the seam can also be controlled if necessary. This could further increase the tolerance to variation in fit-up and enhance the capability to maintain weld quality.
In production adaptive control should allow consistent and reliable automatic weld completion, leading to an increase in the quality of manufactured parts, and at reduced cost.
For further information, please contact Steve Shi at TWI.