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20.11.2017 | Manufacturing | News | Onlineartikel

Coating Hydraulic Cylinder Rods More Efficiently

Nadine Winkelmann

Fraunhofer Institute for Material Beam Technology IWS Dresden has upgraded an existing powder plasma welding machine at Bosch Rexroth’s Boxtel-based plant in order to coat large hydraulic piston rods significantly more quickly.

In close collaboration with Bosch Rexroth, Fraunhofer IWS Dresden has developed a process for efficient high-performance laser powder coating. A system for coating large cylinder rods up to a length of 19 metres and 600 millimetres diameter has been upgraded in Boxtel, the Netherlands. According to Fraunhofer IWS, the new process will increase system productivity many times over by enabling deposition rates of up to 15 kilograms per hour. Researchers have optimised the systems technology for laser power values of up to 20 kilowatts and also prepared the technology for Industry 4.0 applications. Ideas for further potential developments are to be worked out in the coming months. Closed digital control loops, process management simulation, as well as connecting self-monitoring components for automatic fault monitoring and minimisation, are planned for quality control purposes.

Reliable metallurgical adhesion

In comparison to earlier configurations, the new procedure should process considerably higher powder quantities in a significantly shorter time. The aim of the development has been to fuse weld metal in order to create a more hard-wearing and corrosion-resistant coating. While alternative thermal spraying methods yield only metallic clamping between the applied powder and the base material to be coated, this new solution creates a metallurgically fused joint on the cylinder rod surface with minimal mixing in of low-alloy iron base material into the top layer. In contrast to plasma powder cladding, the laser powder cladding process has already allowed mixing degrees of under three percent for single-layer coating.

To machine the hydraulic rods, the rods to be coated are clamped in the system and turned while a laser is fed along these rods at a constant feed, thereby forming a spiral coating bead with low porosity and a uniform layer height. The laser power should not only significantly accelerate the welding process but also introduce less heat into the base component, thereby keeping the component’s structure and form intact. Depending on the application and the conditions, different types of powder materials with specially adapted properties, such as wear resistance, hardness, corrosion resistance or specific frictional properties, can be deposited. In addition, Fraunhofer IWS has equipped Bosch Rexrodt’s system with a specially developed inductive heating process. A specific heat conduction process is hence made possible, which allows also fault-free welding of coatings that are highly sensitive to cracks and are difficult to weld.

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