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High-power laser welding for demanding applications (TriLaser) Kalervo Leino and Miikka Karhu

Introduction Laser welding has long been widely used in sheet metal product manufacturing, e.g. the automobile industry. Applications in heavier industries, however, have been much more limited. This is largely due to the strict accuracy requirements that laser welding places on the preparation of the parts to be welded. The development of hybrid laser welding and the introduction of cost-effective highpower fibre and disc lasers have made laser welding a serious alternative to traditional high-quality welding pro-cesses in heavy metal industries and highly demanding applications. Hybrid laser welding is a novel welding process in which a laser beam and an arc welding process are coupled together and directed to a single spot in the weld groove. The arc welding process in hybrid laser welding is usually gas metal arc (MIG/MAG) welding. Hybrid laser welding combines the advantages of laser and arc welding. The welding speed equals that of laser welding, and the melting efficiency that of gas metal arc welding. The heat input and welding distortions are only slightly higher than with laser welding. The accuracy tolerance requirements of weld grooves are much more forgiving than in laser welding.

Methods The welding tests are conducted when: a) preparing thick-walled (multi-pass) austenitic stainless steel joints representing demanding energy equipment applications, and b) fabricating multi-metal joints.

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When welding thick sections, hybrid laser welding is challenging, e.g. narrow gap TIG welding, is the standard welding method in power plant engineering. The benefits of laser hybrid welding in-clude high cost-efficiency and minimal welding distortions. At the first stage, moderate laser power of 3 kW was used, but the acquisition of a more powerful 10–15 kW fibre laser is under way. Plans also include combining the power of three 10+ kW laser power sources to conduct tests with laser power in excess of 30 kW. In multi-metal joints, the attraction of laser welding derives from the narrow weld profile, which means minimal melting of the materials, and the possibility of positioning the weld accurately to control the composition of the weld metal much better than with arc welding processes. The use of hybrid welding further improves the possibilities of weld metal composition control.

Results Welding tests, even with relatively low laser power, have shown that hybrid laser welding is very competitive with the traditional highquality arc welding processes. Laser hybrid welding with a laser power of 3 kW is more than five times faster than narrow-gap TIG welding in the corresponding conditions. With low laser power, hybrid laser welding has drawbacks however. Low laser power results in relatively small penetration depth, which leads to a substantial number of filling passes and the use of filler material. With a low laser power welding parameter, tolerances

VTT Research Highlights 3  

Production matters. VTT in global trends. Kai Häkkinen (ed.)

VTT Research Highlights 3  

Production matters. VTT in global trends. Kai Häkkinen (ed.)