||Flemming Ove Olsen
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Since the beginning of the 1980s, the industrial applications of high power lasers have been increasing and today lasers are a well established high technology industrial tool. Welding is one of the main applications of high power lasers. The potential of high brightness energy sources such as lasers and electron beams to perform high-quality narrow welds at high production rates is outstanding and many welding applications of these two processes have been developed through the years. Starting from spot welding and fine pulsed welding, which mainly use Nd-YAG lasers, seam welding using continuous-wave СO2 lasers also became an industrial process in the 1980s. The major problem|in using laser (and electron beam) welding was often the stringent joint tolerances these two processes demanded. Laser beams heat only the seam and a small area around it, creating a narrow weld. If a wide gap is used, a weld with an underfill or an undercut results or, in some cases, part of the beam is transmitted through the gap rather than welding the metal. For many years it was considered impossible to use these techniques in heavy industry with its use of relatively coarse components. However. as the output of high-power lasers increased to a level high enough to produce welds 5 mm wide, the process became viable for heavy industrial applications. It was at this point that a research paper from the late 1970s came into the mind of some scientists and engineers involved in laser welding. The paper was one of two dealing with combining an arc process with a laser beam: one paper on arc-augmented laser cutting and one on arc-augmented laser welding. Both papers were part of the steady stream of innovative papers from the team around Professor William M. Steen. at that time working at Imperial College in London. He applied his 2-kW British Oxygen Company (BOC) lasers in many different experiments, including those reviewed in these two studies. At that time, others in the laser welding community were busy concentrating on making narrow cut and keyhole welds, and the idea of combining this fine and precise heat source with an old fashioned arc source was not considered mainstream research at that time. However, when bridging the gap in heavy section welding or when reducing the hardness in steel by reducing the cooling rate became topical in laser welding, this old research paper came into our minds, and a number of my colleagues started to study this process more carefully. By this time we had larger and more reliable laser sources than the two 2-kW laboratory lasers at Imperial College. As a result, promising results came out of the first research into laser hybrid welding. Large heavy-industry projects with potential laser welding applications, such as the shipbuilding projects in Europe and Japan, stimulated this development, and soon many research groups around the world took up the challenge of bringing the two heat sources together. The laser hybrid process that emerged from this research is not a simple process and the equipment is not cheap. However, laser hybrid welding has now found its way into a range of industrial applications. In this book, a summary is presented of recent research on the hybrid laser-arc welding process and its applications. This provides a snapshot of this advanced technology at a particular point in time but developments will continue. New types of laser, the disc laser and the high-power fibre laser, will certainly improve this technology in the future. The results of research using these new laser sources are included in this book, but much more will certainly follow in the near future as a result of the many research teams throughout the world that are active in developing this important process.