The car brake disc of the future will be coated – this is the only way to meet the tighter particulate matter limits set by the Euro 7 standard. The coated surface also protects against corrosion and wear. But which machining process can reliably deliver this quality on a large scale? EMAG has the ideal solution with its VLC 450 DG machine, which combines laser cladding with double-sided face grinding. The grinding step is especially important, as the coating requires a highly precise process. So, what makes the VLC 450 DG stand out?
The Euro 7 standard is coming and with it very strict limits for tire and brake system wear. From 2035, cars will only be allowed to emit around three milligrams of particulate matter per kilometer, which amounts to a radical reduction, as this value is currently up to 40 milligrams depending on the vehicle! But how can this be achieved technologically? “Coating brake discs with hard material” is the answer from automotive designers and developers. EMAG’s laser cladding in particular opens up many possibilities: Matrix material and hard material carbide are fed into a laser tool and welded to the preheated surface. In this way, first an adhesive layer and then the overlying wear protection layer are applied – at least in the case of so-called two-layer systems. There are also developers who rely on a one-layer solution, e.g. for the rear axles in compact vehicles.
But one question is obvious: How can this approach be integrated into a holistic and high-volume production solution – including the subsequent grinding processes that give the wheel its final surface? “This question is our top priority,” explains Jannik Röttger, Head of Grinding Technology at EMAG. “Our unique selling point is that, on the one hand, we can control and influence the turning process and the entire laser welding process on EMAG machines if the customer so wishes. On the other hand, we keep an eye on the subsequent grinding process right from the start. After all, the turning process and central coating parameters should be configured in such a way that the surface produced results in the shortest possible grinding cycle times and low grinding wheel wear with the highest component quality. Isolated solutions for just one of the two processes generate problematic performance figures.”
Perfecting grinding processes
A closer look at the VLC 450 DG grinding machine—a specialised solution for brake discs developed by EMAG experts—shows what this means in practical terms for mechanical engineering. The machine is tailored precisely to the specific coating system and production requirements. At the heart of it all is double-sided face-grinding, a process that is both efficient and reliable. It produces a cross-ground surface on the component, which offers excellent tribological properties. In addition, cross-grinding allows for immediate quality control, as the visible pattern of the grain entering and exiting the surface confirms that all axis angles are correctly set.
Double-sided face-grinding also offers several additional process advantages. The symmetrical application of force allows for maximum feed rates during machining. The large contact area between the grinding wheels and the brake discs ensures excellent component support, which is especially important given the axial instability of brake discs. This results in high-quality finished components. The process uses water as a coolant instead of mineral oil-based emulsions, making it easier to filter out fine grinding particles. In this area, EMAG works closely with cutting fluid and filtration system manufacturers to ensure optimal performance. “Incidentally, this is where users benefit from the vertical arrangement in the VLC 450 DG, as the grinding sludge contains high-strength abrasive particles. With a horizontal tool arrangement, this can quickly lead to problems on the guideways. We have this challenge under control with our machine,” says Jannik Röttger.
Overall, the EMAG machine concept is built for maximum productivity and long-term durability to meet the high demands of batch production. For instance, a robust cooling system ensures strong thermal stability, while the Mineralit machine base reduces vibrations. A shuttle system positioned outside the work area serves as an ideal link to downstream automation. The pick-up spindle transfers components from the shuttle into the work zone, significantly reducing chip-to-chip times.
The VLC 450 DG’s grinding tool also sets a new benchmark in brake disc machining. Designed as a lightweight interchangeable ring weighing under five kilograms, it allows for tool changes in less than ten minutes—a notably short time. The vertical layout, combined with a spacious and accessible work area, makes the machine especially user-friendly during setup. All changeover parts are easy for operators to access.
A holistic approach
Finally, it’s crucial to take a comprehensive view of the entire process chain for hard coating brake discs, as both the coating and grinding steps significantly influence each other. While laser cladding generally results in a similar surface roughness (Rz up to 100 micrometers), the hardness of the surface can vary widely depending on the coating system used. As a result, single-layer and two-layer systems require different grinding approaches: single-layer coatings allow for high cutting speeds, while two-layer systems demand lower motor speeds combined with high torque. Simply put, monolayers behave like hardened steel during machining, whereas the wear-resistant layers in duo-layer systems cut more like carbide. EMAG’s specially developed grinding spindles are tailored to meet these distinct requirements, ensuring efficient processing for both types.
There are also other parameters, such as the choice of abrasive, which are crucial for the productivity of the grinding process. “A direct exchange of information between the development departments of the machine manufacturer, grinding wheel manufacturer and grit material supplier is essential here. Only if there is a continuous exchange of knowledge can the optimum grinding wheel be jointly developed for each coating specification,” says Jannik Röttger.
“Overall, it is crucial that grinding, coating and laser experts work closely together and establish the best possible overall solution on this basis, so that the coating has optimum properties in the braking system and is easy to machine at the same time,” emphasizes Jannik Röttger. “We offer this complete package of mechanical engineering and application knowledge to our customers, including in the context of prototyping – and this naturally also applies when EMAG only develops the grinding technology. In any case, with the VLC 450 DG, customers benefit from a machine that has been specially developed for this application and at the same time has all the typical qualities and decades of experience of EMAG mechanical engineering.”
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