Hybrid laser-arc welding is a joining process simultaneously combining arc and laser welding in the same weld pool. In theory, the beam from any welding laser source (CO2 , Nd:YAG, diode, Yb fibre, Yb:YAG disk etc) can be combined with any arc process (MIG/MAG, TIG, SAW, plasma). Typically, however, hybrid laser-MIG/MAG and laser-TIG are the most common process combinations.
The hybrid process has the individual advantages of both welding processes. Deep penetration hybrid welds can be made, comparable with the penetration depths achieved by laser welds, but at the same time having a tolerance to joint fit-up and a weld cap profile more comparable with arc welds. Furthermore, arc welding consumables (and gas mixtures) can be used, offering a degree of control over weld quality and properties than is possible with autogenous laser welding.
Hybrid welding is already being used, or under consideration, by the following industries:
- Road transport – the high welding speed of the hybrid process is attractive to the high production volume environments found in the automotive industry, especially given the greater part fit-up tolerance than that of autogenous laser welding.
- Shipbuilding – the lower heat input and distortion introduced when hybrid welding, when compared with MAG welding or SAW, reduces the costs associated with distortion correction and rework. By contrast, conventional arc welding methods and their associated re-work have been estimated to constitute up to 20-30% of overall manufacturing costs.
- Rail transport – as in shipbuilding, the low distortion that can result from hybrid railcar seam welding, compared with conventional arc welding processes, is of interest as a means of reducing fabrication costs, as well as the higher welding speeds reducing overall welding time.
- Oil and gas – the hybrid welding of pipes has been well demonstrated, and with continuing developments in laser sources and pipe steels, continues to be of interest as a future means of increasing overall joint completion rates, depending on steel grades used and operating environment requirements.
The chief benefits of hybrid laser-arc welding can be summarised as:
- Improved tolerance to joint fit-up: for example, hybrid welding can extend the tolerance to joint gap by a factor of at least 2-3 times over laser welding, or greater, if real-time adaptive control of hybrid welding parameters is carried out.
- Improved weld quality: hot cracking (e.g. in some higher strength Al alloys) can be avoided, and internal porosity content reduced, with respect to laser welds.
- Increases in single pass penetration depth: this is controlled principally by the choice of laser and welding parameters used, but single pass penetrations >6-12mm can be achieved using higher power (≥5kW) lasers.
- Increases in welding speed: this is also dependent on the laser used and materials being welded, but speeds of >5m/min can be possible in thinner materials.
- The increases in penetration depth and/or welding speed, when compared with arc welding, are particularly significant: the net heat input can be reduced, resulting in lower distortion, rendering hybrid welding of particular interest for the making of long seam welds between plates or between sections, the welding on of attachments etc
TWI has nearly 15 years of experience of hybrid laser-arc welding processes and their development. This includes combining a variety of industrial welding laser sources (including CO2, Nd:YAG and, since their advent at the beginning of the last decade, Yb fibre lasers) with both MIG/MAG and TIG arc welding.
Furthermore, TWI’s research and development in this area has covered a broad base of engineering alloys, including C-Mn steels for both structural and pipeline applications, conventional (austenitic) and higher strength (duplex and ferritic) stainless steels, and a wide range of aluminium alloys used for light engineering, road transport and aerospace applications.
Over this time, TWI has been carried out a number of hybrid welding development and implementation projects, funded through its own Core Research Programme (CRP), Joint Industry/Group Sponsored Projects, and European-funded Collaborative Projects, as well as confidential evaluative or developmental work for its Industrial Members.
Examples of TWI’s work in hybrid welding include:
- CO2 laser-MAG welding of butt joints between C-Mn steel plates, including assessments of joint gap bridging ability, weld qualities and properties, for shipbuilding application.
- Robotic Nd:YAG laser-MAG welding of T joints between C-Mn steels, and their resulting properties, also for shipbuilding applications.
- High speed, low distortion hybrid welding of aluminium alloys using Yb fibre lasers, for rail transport application.
- The development of low internal porosity content hybrid welding methods for aerospace aluminium alloys.
- The development of hybrid welding for conventional and higher strength stainless steels.
- The development and demonstration of real-time joint monitoring and process control when hybrid welding butt joints in steels, stainless steels and aluminium alloys.
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