ANALYSIS & OPINION

Laser and e-beam welding communities pool expertise

The UK Association for Laser Users (AILU) is launching a Power Beam Processing special interest group at a workshop hosted by TWI near Cambridge on 22 September. The group will aim to pool expertise from the laser and e-beam welding communities, says Dave MacLellan, executive secretary of the AILU

A new special interest group (SIG) is being formed at AILU to focus on power beam processing. Power beam welding differs from arc welding in that the heat source for the welding process is an intense beam of energy (either a laser beam or beam of electrons) as opposed to an electrical arc.

Electron beam (or e-beam) welding shares many characteristics with laser welding and laser hybrid welding (where laser welding is combined with an arc) in terms of techniques, parameters, joint design and other factors. The purpose of the new SIG is to bring together the laser welding and electron beam welding communities, and to share knowledge of the welding processes to enhance the performance of both techniques.

AILU has supported laser beam welding since the beginning of the association, and now in 2015 is looking to engage with specialists in electron beam welding to support them in a mutually beneficial environment (no similar association currently exists for electron beam welding).

The SIG will be launched at the AILU workshop titled ‘Successful industrial welding techniques and applications with laser and electron beam’, which is being held at TWI near Cambridge. The workshop will be chaired by Jon Blackburn of TWI, while the power beam processing SIG will be chaired by Nick Longfield of Rolls Royce. The workshop will hear presentations from researchers, industry experts, service and equipment providers and industrial end-users giving case studies and helpful information to promote the use of power beam processing in industry.

Both laser and e-beam welding are suitable for many applications where difficult materials are to be welded or where the depth-to-width ratio required is a higher aspect ratio than can be achieved with conventional arc welding. The lower heat input from e-beam and laser welding results in reduced distortion and less post-processing. Process speed is typically higher for power beam welding than arc welding which leads to increased productivity.

Often laser beam welding takes place with a shielding gas to prevent contamination by air of the weld metal as it heats up to melting point (or above) and cools to solidification. E-beam welding takes place in a vacuum which eliminates the potential for contamination by air. In some cases, where the material or application demands it, laser beam welding can also take place in a vacuum.

Where a high aspect ratio weld is required, conduction welding (where the heat is transferred from the material surface) is not able to provide a solution. Keyhole welding is instead required, this being achieved by increasing the beam power density beyond that required to melt the metal being welded and raising the temperature to a point of rapid vaporisation where a hole is drilled and traverses the weld line, molten weld metal then back-fills the hole forming a high aspect ratio fusion weld.

Markets which can benefit from the techniques of power beam processing include aerospace, automotive, power generation and nuclear industries. The requirements of these industries for strength coupled with low mass mean there is a requirement for high-integrity joining of titanium, zircaloy, hafnium and nickel, aluminium and stainless alloys – many of these requiring careful shielding or processing in a vacuum owing to the volatile nature of the weld fume and the susceptibility to diffusion of oxygen or nitrogen from the air if not shielded or welded in a vacuum.

Both laser and e-beam have their own strengths and weaknesses in terms of beam delivery, cycle time, ease of automation, complexity and cost of implementation. By combining experts in both technologies in a SIG, it is intended that information can be shared which will enable new developments and cross-fertilisation of ideas between the different communities to further improve results in production and provide new areas for research and development.

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By Dave MacLellan, Executive Director, AILU

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