Keyhole laser welding is now an established joining technique in many sectors of industry, and is being investigated actively in others. Most of the principles of keyhole formation are understood, and the formation and properties of the weld bead and HAZ can be established by adapting predictive methods that have been developed for conventional fusion welding processes. Most materials that can be welded by conventional fusion techniques are suitable for keyhole welding. Low alloy steels are particularly suitable – welds can be made rapidly in thin sections, and full penetration can be achieved in thicker sections in a single pass.

Keyhole laser welding is established joining technique in many sectors of industry

Many variations of keyhole welding have been developed – hybrid arc–beam processes; multiple spot sources; filler wire welding – all of which exploit the advantages inherent in the individual techniques. The process can be modelled by using relatively simple analytical methods to obtain initial estimates for parameter selection in procedure development. To achieve the highest level of detail for practical use, models may be calibrated to known data points to produce a practical processing diagram.

The main benefits of laser keyhole welding become evident when it is used at the limits of its capability: high speed welding of sheet materials, or deep penetration joining in thick sections. As with all laser-based processes, the low energy input is the origin of many of the advantages over competing fusion joining processes, since distortion is low, productivity is high, quality is superior, and new materials may be considered. The accessibility of the beam enables new joints to be designed into products.

The controllability of the beam allows dissimilar materials to be joined. Low distortion reduces the total number of manufacturing steps by removing post-weld straightening. However, the process is often not used to its fullest advantage because of a lack of understanding of the opportunities available at the design stage of a component. In addition, procedures for keyhole welding and quality standards must be generated and approved by classification societies, particularly for thick section materials.

Both are currently obstacles to greater application. Equipment for on-line process monitoring and quality control is continually being sophisticated. This will enable rugged systems to be made, which will increase process automation, and make the process more attractive to a wider range of industry sectors.

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