The industrial research center Laser Zentrum Hannover e.V. (LZH) and three industrial partners have set a goal to achieve up to 400% higher process speeds for deposition welding of wear and corrosion protection layers on large workpieces. An new process combination of a non-transmitted light arc and laser-based warming of the workpiece will be developed via the HoDopp project, for small and medium-sized enterprises.

LZH conducts R&D in the field of laser technology and is supported by the Ministry of Economic Affairs, Labour and Transport of the State of Lower Saxony.

The welded material will have a very high purity level, and should provide workpiece protection with the very first layer applied.

In the gas metal-arc welding (GMAW) process, which is used now for comparable fabricating tasks, a light arc melts the wire electrode and the workpiece 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. Obviously, energy and personnel costs are high.

The HoDopp project, which started in June, aims to achieve 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 workpiece and results in a high increase in both productivity and welding process quality.

This can be achieved by combining two separate processes in an entirely new way. At the hydraulic cylinder manufacturer AHP Merkle GmbH, a modified gas metal-arc deposition welding process is being optimized in which the light arc burns between two electrodes but does not come into contact with the workpiece. 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 LZH. A new-generation diode laser with a low output level (under 0.5 kW) is used to achieve a low but homogeneous penetration depth on the workpiece. The laser focuses on and melts the workpiece 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 grouping of 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 the light arc provides this. On the other hand, the laser uses low-output power and can be used for precise, guided control of joining the melted material to the base material.”

By combining the innovative light arc process with inexpensive diode laser technology, the project partners calculate that process time can be reduced to just 6 hours for one square meter, making deposition welding very attractive for areas larger than 1x2 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 toolmaking and moldmaking applications in the automotive industry, this process can 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 HoDopp project 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.