The Laser Zentrum Hannover e.V. (LZH) and three industrial partners have set a goal to achieve up to 400 percent higher process speeds for deposition welding of wear and corrosion protection layers on large work pieces. An absolutely new process combination of a non-transmitted light arc and laser-based warming of the work piece will be developed within the project HoDopp, which is for small and medium sized enterprises. The welded material has a very high purity level, and should provide work piece protection with the very first layer applied.

In the gas metal-arc welding process currently in use, a light arc melts the wire electrode and the work piece simultaneously. The mixing rate for the materials is 30%, meaning that the coating process must be repeated up to three times to ensure sufficient quality of the protective layer. Using this process, with maximum deposition speeds of 5 kg/h, it can take up to 24 hours to coat a square meter area, and energy and personnel costs are high.
 
The project HoDopp, which started in June 2012, aims at reaching a four times higher deposition rate at up to 20 kg/h. At the same time, the welding depth should be reduced and mixing rates of <5% achieved, so that only a single layer is necessary. This can be done by strictly separating the process for melting the wire and the work piece and results in a high increase in both productivity and welding process quality.
 
This can be achieved by combining two separate processes in a completely new way. In the southern German company MERKLE, a modified gas metal-arc deposition welding process is currently being optimized, in which the light arc burns between two electrodes, but does not come into contact with the work piece. By adapting the nozzle form and the burner position, and by reducing amount of the protective gas, a stable and sputter-free process is possible.
 
A second process step is being developed in the Materials and Processes Department at the LZH. A diode laser of the newest generation with a low output level of under 0.5 kW is used to achieve a low but homogeneous penetration depth on the work piece. The laser focusses on and melts work piece shortly before the melted wire meets the surface. A deflector device is used to the control temperature distribution.
For Jörg Hermsdorf, Head of the Machines and Controls group, this combination of the individual processes is ideal. “This combination can be used to exploit the advantages of both tools. High energy input is needed to melt the deposition material, and this is provided by the light arc. 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.“
 
By combining this innovative light arc process with inexpensive diode laser technology, the project partners have calculated that process time can be reduced to only 6 hrs. for one square meter, making deposition welding highly attractive for areas larger than 1 x 2 meters. Being inexpensive and faster and at the same time with higher quality, this innovative process is interesting for many applications. Apart from the conventional tool and mold making applications in the automotive industry, this process can also be used for protective layers on shafts, rollers and clamping devices, for repairs on damaged transport systems, or for protective layers on the stressed areas of oil drilling shafts.
 
The project HoDopp is financed by the German Federal Ministry of Education and Research (BMBF) within a program for SME innovative production researching. Apart from the LZH and MERKLE, the firms G+F Strate GmbH and Druckguss Service Deutschland GmbH are taking part in the project, and are responsible for testing and quality assurance.

More information at http://www.lzh.de/