New laser-based process for tribological coatings

A new efficient process for tribological coatings has been developed by an industrial partner network from North Rhine-Westphalia. The laser-based coating process reduces energy consumption by up to 90 percent compared to conventional oven processes.

The new process for tribological coatings achieves not only a reduction in energy consumption but also a sustainable reduction in material loss during coating application and the elimination of chemical cleaning agents and blasting media. It results from the cooperation of the companies Bechem, Cleanlaser, Evonik and Fraunhofer ILT in the conclusion of the research project "ENLAPRO", which is funded by the state government of North Rhine-Westphalia and the European Union.

The overall objective of the project, which was consortium-led by Evonik, was to develop an energy-efficient, laser-based production process for PEEK-based (polyetheretherketone) tribological coatings. This can be used to coat metallic components that are exposed to high mechanical stresses-such as pistons or bearing shells in internal combustion engines or metal components in air-conditioning compressors.

The central innovative content of the new process is the significant improvement in energy efficiency, since only the coating material and a thin edge layer of the component are heated by laser radiation. Initial calculations show energy consumption reduced by up to 90 percent compared with oven processes - depending on the size of the component and the coating area. The new coating process can also sustainably reduce material loss during coating application and eliminate the need for chemical cleaning agents and blasting media thanks to laser pretreatment.

Evonik laid the foundation for the project work by developing new high-performance materials based on Vestakeep PEEK. Bechem then produced a water-based PEEK dispersion as a necessary condition for the use of immersion, pressure and spray processes (excluding electrostatic spraying). Since no company in Germany has been able to produce stable PEEK dispersions in a wide range of viscosities to date, this development is a significant innovation for Bechem and the chemical location of North Rhine-Westphalia.

Using the new laser-based melting process, adhesive-stable PEEK coatings on aluminum and steel can be produced and characterized with both Evonik's Vestakeep PEEK powder and Bechem's dispersions. For this purpose, Fraunhofer ILT implemented a set-up process head including process control and performed extensive heat conduction simulations in parallel to generate process understanding. Finally, an aluminum and a steel demonstrator were successfully coated with PEEK using the new process in the three main process steps - laser pretreatment, coating, laser melting.

For laser-based coating processes, preheating of the component surface is necessary to produce adhesion-resistant coatings. As part of the "ENLAPRO" project, CleanLaser determined suitable parameters for laser pretreatment of steel and aluminum to increase the adhesion strength between the PEEK layer and the component and thus reduce the necessary preheating temperature. The company also developed a new miniaturized optics concept. It not only enables weight to be reduced by 20 percent, but mainly improves the energy efficiency of the pretreatment.

A large number of applications, especially in mechanical and automotive engineering, are characterized by frictional and wear stresses combined with the highest requirements in terms of temperature stress and corrosion resistance. This often requires the use of special coatings. In terms of material properties, high-performance polymers in particular are predestined for such applications.

Conventional coating processes typically involve several steps: chemical component cleaning and pretreatment of the component using blasting media, coating application in powder form with a material loss of up to 70 percent, and a subsequent, energy-intensive oven process. In this, the complete component is heated to typically 400 °C to melt the coating material and thus obtain an adhesion-resistant coating.

Project partners in the project, which is supported by funding from the European Regional Development Fund (ERDF), are the companies Carl Bechem GmbH, Hagen (development of PEEK coatings), Clean-Lasersysteme GmbH, Herzogenrath (laser pretreatment) and the Fraunhofer Institute for Laser Technology ILT, Aachen (laser process development). Funding code: EFRE-0801268 (OM-3/23).