Fraunhofer Institute for Production Technology IPTResearch project "CoilCladding"
Plain bearings are critical components in the automotive, aerospace, and power generation industries. High-performance applications require bearings that combine high structural rigidity with excellent tribological properties. Bimetal bearings – consisting of a steel substrate with a bronze coating – meet these requirements.
Challenges in the bronze casting process: improving efficiency and avoiding lead
Today, manufacturers typically produce bimetal bearings by casting bronze onto a prepared steel substrate. This process involves extensive material preparation, manual handling, and subsequent post-processing – the total process time is approximately three days. Material efficiency is correspondingly low, at less than ten percent. In addition, the bronze alloys commonly used in the casting process typically contain lead, which does not comply with European RoHS2 guidelines. These limitations create a clear need for a lead-free and resource-efficient alternative process.
Lead-free bronze coating with Express Wire Coil Cladding (EW2C)
In the CoilCladding research project, the project team is developing a new method for manufacturing bimetal bearings that is both industrially scalable and environmentally sustainable.
The method used here is called Express Wire Coil Cladding (EW2C), which was developed and patented at Fraunhofer IPT. This process builds on wire-based laser metal deposition (LMD-w), specially designed for coating rotationally symmetrical components.
The key innovation of EW2C lies in decoupling the wire feed from the actual welding process: The wire is first wound into spring coils and positioned directly on the shaft to be coated. During welding, the shaft rotates around its own axis while a high-power laser welds the coils onto the surface. This decoupling ensures higher process stability and significantly increased deposition rates – up to 14 kg/h when using a 35 kW laser – without being limited by the wire feed speed.
Research focus in the CoilCladding project: wire, shielding gas, build-up welding
Previous work at Fraunhofer IPT has successfully demonstrated the EW2C process with steel and nickel-based alloys. However, bronze presents new challenges – particularly since bronze tends to oxidize quickly and is difficult to handle in wire form. The project focuses on three closely related areas of research to qualify the process for industrial bronze cladding.
- Wire handling. The team is systematically investigating various bronze alloy compositions and wire geometries. Key material properties such as springback are being characterized and used to design and validate the winding process. Moreover, the researchers are developing a concept for automating wire handling.
- Protective gas system. Without a suitable inert gas atmosphere, oxidation during the coating process degrades coating quality. The two-part protective gas enclosure currently used requires manual assembly and is therefore unsuitable for industrial use. The researchers are developing concepts for automated protective gas supply and experimentally investigating how different gas atmospheres influence coating quality.
- Bronze deposition welding. The project is systematically establishing process parameter space – including laser power, spot size, and shaft rotation speed –for bronze wires. The influence of coil geometry and machining strategy is then examined using metallographic and mechanical tests. Suitable parameters and strategies are then selected based on the resulting coating properties.
Validation and industrial implementation of the EW2C process
The researchers are producing several demonstrators with different coil geometries in order to validate the entire process chain. They characterize the coating properties using metallographic analysis and mechanical tests, and evaluate the economic viability of the process in comparison to the conventional casting process. At the end of the project, a fully industrially viable process chain for the bronze coating of rotationally symmetrical components will be available, bringing EW2C to an industry-ready level of technological maturity.
Market potential and areas of application for bimetal bearings with bronze coating
Plain bearings are used across a wide range of industries – in both stable and rapidly growing markets, from aviation to wind energy. Beyond the bearing industry, the new process can be transferred to any area of application that requires high-quality tribological or thermal coatings on rotationally symmetrical components.
Project partners
- Kugler Bimetal SA, Le Lignon, Schweiz (Coordination)
- Fraunhofer Institute for Production Technology IPT, Aachen
- Hans Achenbach - Techn. Federn GmbH, Bad Berleburg
Funding
This project is funded by the Federal Ministry for Economic Affairs and Energy (BMWE) on the basis of a resolution of the German Bundestag as part of the “Central Innovation Program for SMEs (ZIM)” program.
Funding code: KK5271505JN4
Project management agency: AiF Projekt GmbH