Hybrid/laser welding technique can process thick metal sheets quickly

Hannover, Germany - Welding of thick pipelines and metal sheets made of aluminum alloys or steel at high speeds of 6 m/min and 1.5 m/min, respectively, is accomplished with a hybrid welding process developed at the Laser Zentrum Hannover eV (LZH). In the future, the laser-based process can be used to shorten processing times and, thus, significantly reduce the processing costs of liquid gas tanks and pipelines.

Scientists in the Joining and Cutting of Metals Group at LZH have developed a process that can be used to make single-sided, zero-defect welds in aluminum sheets up to a thickness of 12mm by combining a laser beam with two gas metal arc welding (GMAW) torches. A scanner mirror can be used to oscillate the laser beam lengthwise or crosswise to the feed direction. The joining process can reach feed speeds of 5 to 6m/min, and gaps of up to 0.5mm and edge misalignment of up to 2mm can be bridged. The engineers have also been able to weld steel sheets with a thickness up to 23mm at a speed of 1.5m/min for single-layer welds.

The innovative process is extremely fast and, when compared to conventional, multiple-layer GMAW processes, the seam geometry is very narrow and filler material consumption is considerably lower. At the same time, the quality of the weld seam is very good: Welds for 12mm-thick metal sheets made of the aluminum alloy EN AW 6082 T6 can reach the highest evaluation group B for welding seam impurities, according to DIN EN ISO 12932 and DIN EN ISO 13919 2.

Compared to conventional processes, a further advantage of the combined processes is reduced thermal input and, thus, reduced component distortion. A solid-state disk laser with an output power of 16kW is used for the hybrid welding process.

This hybrid/laser process is 12 times faster than GMAW. To join steel sheets with a thickness of 30mm, conventional GMAW requires a tack weld and around six filler layers. The hybrid process only needs two to three filler layers. The first layer is made using the laser-GMAW hybrid process. It also replaces the tack welds and the first four layers of the conventional GMAW. Subsequently, the sheets are subject to one or two backing runs with the GMAW process. Thus, the hybrid welding process can be used to weld a component with a length of 1.5m in 1 min, whereas conventional processes need 12 min.
The main advantages of hybrid welding are the synergy effects between the arc of the GMAW process and the laser beam. In the combined process, the laser is coupled into the melt pool of the filler material of the GMAW process: The filler material is melted by the arc and in the molten state, it absorbs the energy of the laser beam and transfers the energy to the weld area between the sheets. The laser beam and the arc process stabilize each other, making relatively high welding speeds for arc processes possible and for high gap widths.

The joint project "HYBRILAS: Welding of thick metal sheets using brilliant laser beam sources" was part of the "MABRILAS initiative: Material processing with brilliant laser beam sources," and was supported by the German Federal Ministry of Education and Research (BMBF) and the Association of German Engineers (VDI-TZ).

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