Bosch Rexroth expands laser cladding capabilities for cylinder rods

Prof. Dr. Eckhard Beyer, head of the Fraunhofer-Institute for Material and Beam Technology IWS in Dresden together with Bernd Bodenstedt Technical Plant Manager Bosch Rexroth Boxtel, officially released the enhanced laser cladding process at Bosch Rexroth’s cylinder plant in the Netherlands. To develop and install this process, Bosch Rexroth and the Fraunhofer-Institute have closely worked together. The result: a unique machine which is able to coat cylinder rods with an economically laser-applied Enduroq coating, serving as a cost efficient and reliable alternative for the known nickel-chromium layers.

In the latest development in laser cladding, an overlay welding application techniques, a high performance laser applies corrosion and/or wear resistant layers on the surface of cylinder rods. Specially formulated powders are fed into the welding zone of the coating process, melted by the laser source and adhered to the melted top layer of the rod. This results in a highly reliable cylinder rod coating based on metallic compound of the materials, at Bosch Rexroth also known as Enduroq cylinder rod coating.

The laser machine at Bosch Rexroth was developed in close cooperation with the Fraunhofer-Institute in Dresden and can be considered as a unique process development. The heavy duty diode-laser that is used, decreases the cycle times of this process enormously compared to other coating techniques. As a result of this high speed process and the typical characteristics of the laser, the heath influence on the cylinder rod is as limited as possible, making sure that the characteristics and dimensions of the basic material remain in an optimal shape. Depending on the desired result, such as improved corrosion resistance chemical resistance or better protection against wear (erosion), special formulated powders and optimized parameter settings can be applied.

Unique machinery

According to Bernd Bodenstedt, we can speak of a unique development. “This machine is not even commercially available on the market. Our goal of already further developing this machinery and technology was not only to expand our technical capabilities and the range of coatings, but also to improve efficiency of our coating process in general. Two key factors have contributed to this result. Firstly we have increased the power density of the laser source, resulting in a considerably wider melting pool than other coating processes. Secondly the production capacity has increased by enabling higher powder feeding speeds in both the radial and the axial direction.”

“The laser cladding process has been put in operation late 2016, and results have been promising ever since. This is why we immediately searched for further expansion possibilities. Together with the Fraunhofer-Institute we have been able to do so, and both deepened as widened our so called process-window, resulting in a less critical and more stable process – an enormous quality improvements. Furthermore, we have specifically addressed the challenge of realizing an economical alternative for the known nickel-chromium based coatings. One important pre-requisite for example was the installation of a pre-heating induction system.

Induction pre-heating

Arthur Brussaard, Product Unit Director Cylinder for Bosch Rexroth, explains what the recent expansion implies. “Until now, we used laser cladding exclusively for applying very wear resistant layers or the advanced and ultra-corrosion resistant Enduroq 3 layer, which is most suitable for application in the offshore market. However, as the process and used materials remained quite costly, we could not yet substitute the economically viable nickel-chromium coating. To realize this, the process needed to be upgraded and extended with an induction-based heating system. To obtain a solid compound in the welding process of some selected powders, it is required to pre-heat the cylinder rod.”

“Also together with the Fraunhofer Institute, we have developed a number of new coating materials and powders, therewith significantly expanding our portfolio of applied coatings – one of which being the economical alternative for nickel-chromium coating. Some coatings with the by Bosch Rexroth developed unique CIMS measuring system! 

These developments enables us to apply our extended range of Enduroq coatings onto rods with dimensions of up to 19 meters length and 600mm in diameter. Together with the optimal selection of seals and guiding strips and the right fluid, we will again be able to manufacture the highest quality cylinders, ensuring the longest possible lifetime.”