Laser welding process devised for large-area protective layers

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Hannover, Germany -- A new laser development project in Germany is developing a process to to achieve up to 400% higher process speeds for deposition welding (cladding) of wear and corrosion protective layers on large work pieces.

Current gas metal-arc welding uses a light art to simultaneously melt the wire electrode and workpiece. The materials' mixing rate is 30%, meaning the coating process must be repeated up to three times to ensure sufficient quality of the protective layer. In this method, deposition speeds top out at 5 kg/hr, or roughly 24 hrs to coat a 1 m2 area, which translates to more overhead costs (energy and workers).

Project HoDopp, began in June 2012, funded by the German Federal Ministry of Education and Research (BMBF) within a program for SME innovative production researching, aims to increase throughput by up to 400% -- up to 20kg/hr deposition rate -- as well as reduce welding depth and improve the mixing rate to <5% so that only a single layer is necessary. Participants include laser research association Laser Zentrum Hannover eV (LZH) and three industry firms: MERKLE, G+F Strate GmbH, and Druckguss Service Deutschland GmbH.

The keys to their work are two new processes that separate the melting of the wire and workpiece. The light arc burns between two electrodes but does not contact the workpiece. Adapting the nozzle form and burner position, and reducing the amount of protective gas, eliminates sputter and ensures process stability. A second step utilizes a low-output diode laser (<0.5 kW) to achieve low but homogeneous penetration depth on the workpiece, melting it shortly before the wire contacts the surface (a deflector device controls temperature distribution).

"High energy input is needed to melt the deposition material, and this is provided by the light arc," explains Jörg Hermsdorf, head of LZE's Machines and Controls group. "On the other hand, the laser uses a low output power and can be used for precise, guided control of joining the melted material to the base material."

The HoDopp partners calculate that the process time can be reduced to 6 hr for a 1m2 area, which would make laser deposition welding more attractive for areas larger than 1 × 2 meters. That speed, combined with inexpensive diode laser technology, opens up the process for a range of applications. While automakers have already adopted laser welding for conventional tool and moldmaking, this new process could be used in a number of other applications: protective layers on shafts, rollers, and clamping devices; repairs on transport systems; or adding protective layers onto stressed areas of oil drilling shafts.



Schematic set-up of the combination of the processes. (Source: Laser Zentrum Hannover eV)



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