Hybrid Laser Arc Welding

Hybrid laser-arc welding is a joining process whereby arc welding and deep penetration laser welding are carried out simultaneously in the same process. In theory, the beam from any laser source (CO₂, Nd:YAG, diode, Yb fibre, Yb:YAG disk etc) can be combined with any arc welding process (MIG/MAG, TIG, SAW, plasma), although hybrid laser-MIG/MAG and laser-TIG are perhaps the most common combinations. As a consequence of this, the process has the individual advantages of both laser and arc welding combined.

Deep penetration welds comparable with laser welds can be made, at the same time having a tolerance to joint fit-up more comparable with arc welds. Furthermore, arc welding consumables can be used, giving a degree of control over weld quality and properties greater than that possible with autogenous laser welds.

Hybrid welding is already being used, or under consideration, by the following industries:

• Road transport – the high welding speed of hybrid welding is attractive to the high production volume environments found in the automotive industry, especially so as the part fit-up tolerance is greater than that of autogenous laser welding.
• Shipbuilding – the low distortion of hybrid welding when compared with processes such as MAG welding or SAW reduces the amount of, and hence costs associated with, distortion correction and rework. Conventional joining methods have been estimated to take 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.
• Oil and gas – hybrid orbital girth welding and longitudinal welding of pipes has been demonstrated, and with further developments could be of interest in the oil and gas sector as a means of increasing root pass and overall joint completion rates, depending on the pipe steel grades used and operating environment requirements

TWI has over a decade of experience of hybrid laser-arc welding processes and their development. This includes experience of combining a variety of industrial lasers used for metals welding (principally CO₂, Nd:YAG and, most recently, Yb fibre lasers) with 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 used for structural and pipeline applications, conventional (austenitic) and higher strength (duplex and ferritic) stainless steels, as well as a wide range of aluminium alloys.

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 2-3 over laser welding.
• 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.
• Increase in single pass penetration depth: this is controlled by the choice of laser and welding parameters used, but single pass penetrations of up to at least 6-12mm can be achieved using higher power lasers.
• Increase in welding speed: this is dependent on the laser source used and materials being welded, but speeds of up to at least 5m/min are possible in thinner sections.
• The increases in penetration depth and/or welding speed are particularly significant as the net heat input is reduced. This results in lower distortion welding, suitable for long seam welds between plates, box sections, plates and attachments etc

Over the past decade, TWI has been carrying out developments of the hybrid welding process on a range of materials, within the Core Research Programme (CRP) and Group Sponsored Projects, as well as 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 and weld qualities and properties.
• Nd:YAG laser-MAG welding of T joints between C-Mn steels, and resulting properties, for shipbuilding applications.
• High speed, low distortion hybrid welding of aluminium alloys using latest generation fibre lasers.
• Low internal porosity content hybrid welding of aerospace aluminium alloys using fibre-delivered lasers.
• Hybrid welding of higher strength stainless steels.
• Real-time process control when hybrid welding butt joints in steels, stainless steels or aluminium alloys

For more information, please contact us.