TWI Industrial Member Report Summary 841/2006
By C M Allen
Hybrid laser-arc welding processes were originally suggested as long ago as the late 1970s (1,2), with reported benefits compared to laser welding (3,4,5) including:
- Increased tolerance to joint fit-up.
- Greater welding speed, leading to higher productivity.
- Increased penetration.
- Lower net heat input, leading to reduced distortion.
- Improved weld quality.
- The potential to replace some laser power, for a given depth of penetration, by some cheaper arc power, thereby increasing cost effectiveness.
Interest in and development of the hybrid laser-arc process has become renewed over the past ten years. Industrial application of laser-arc hybrid welding has to date concentrated mainly on laser-MAG welding of C-Mn steels, one example being in shipbuilding panel lines (6). In terms of applications of laser-arc hybrid welding of thin section aluminium, the subject of this report, some examples have been cited from the automotive sector (7,8), with many more for autogenous laser hybrid welding, especially using robot delivered Nd:YAG lasers, as briefly outlined in section 3 of this report.
The material-process combination addressed in this report is thin section (1.2mm thick) 5251-H22 automotive aluminium alloy welded by Nd:YAG laser-AC MIG. AC MIG is a low heat input arc process of interest, with demonstrated capabilities for welding of thin sheet aluminium in terms of penetration control and good gap bridging ability.
The combination of these two processes is foreseen to offer welding speeds and productivity better than that of autogenous laser welding, with a gap bridging ability better than autogenous laser welding and more comparable to the AC MIG process. Introduction of such a hybrid process in to a Nd:YAG laser welding operation would allow relaxation of fit up tolerances, with increases in productivity, with minimal additional capital expenditure being incurred. Different inert gases and filler wires have also been investigated briefly, to see whether choice of gas and/or consumable could offer further improvements in weld quality, penetration, productivity and joint fit-up tolerance for hybrid laser-arc welding.
The objective of this project was:
- To determine the process benefits and limitations, principally welding speed and tolerance to fit up, of hybrid Nd:YAG laser-AC MIG welding for butt and edge lap welding of thin section automotive aluminium alloy.