Application of Laser Cladding on Brake Disc Wear-Resistant Coatings
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2021-04-24
In urban areas, fine particulate pollution consistently reaches levels severe enough to pose health risks. Notably, 25% of these fine particle emissions come from brake pad wear.
The new laser-clad wear-resistant material now enables the application of a durable, anti-corrosion coating on automotive brake discs. This effectively reduces wear, minimizes fine particle contamination, and significantly extends the lifespan of the braking system.
■ Image source: Laserline
Using wear-resistant materials can reduce emissions of fine particles.
According to the latest research, fine particulate matter is the most harmful type of air pollutant to our health. In particular, ultrafine particles—such as soot and dust—are classified as carcinogens. Moreover, these tiny particles can trigger allergies, asthma, and respiratory and cardiovascular diseases. Internal combustion engines, especially diesel engines, are widely recognized as the primary culprits behind urban fine particulate pollution. As a result, countries around the world have been actively discussing practical measures to reduce fine particle emissions from road traffic.
To the frustration of many drivers, the top regulations happen to be driving bans and speed limits. Yet, in the current debate, one point seems consistently overlooked: diesel engines are only part of the problem, as a significant portion of the fine particulates detected in city centers actually comes from wear—and specifically, from the tiny particles generated by brake discs and pads. In fact, aside from tires, these fine particles primarily originate from brakes. And even a widespread shift to electric vehicles wouldn’t change this reality.
Only by controlling brake wear can we significantly reduce particulate pollution. Therefore, Germany is expected to legally define maximum limits for brake-related particulates by mid-2021. Meanwhile, manufacturers and suppliers are already exploring alternative approaches.
A brand-new laser cladding process that helps reduce wear and corrosion.
Wear-resistant overlay coatings are ideal for protecting high-load components from wear. However, they have almost never been used in conventional automotive brake discs. Anti-corrosion overlay coatings, on the other hand, have already found applications on brake discs for some time. In contrast, wear-resistant overlays have so far remained limited to niche markets like high-end sports cars and luxury vehicles—segments where cost is less of a concern. Unfortunately, due to cost considerations, the coating processes currently employed are not yet suitable for large-scale industrial production.
A technological innovation could soon change this scenario: advanced laser cladding—also known as overlay coating—now enables the creation of standardized, high-strength, wear-resistant layers on brake discs, significantly reducing friction, minimizing fine particle emissions, and extending service life. Compared to thermal spraying, a technique commonly used in the sports car industry, laser cladding is more cost-effective, as it consumes less material and energy while also cutting down on preparatory work.
Therefore, the new method is also well-suited for cladding thin wear-resistant layers onto traditional gray cast iron brake rotors, making it affordable even for the mass market. Laser cladding can even be applied to small or micro-sized vehicles. While laser-clad brake discs may have a slightly higher upfront cost, their extended service life ultimately delivers excellent value for money. Moreover, laser-clad coatings are far less sensitive to impacts and collisions compared to heat-treated platings—since thermal spray coatings merely adhere mechanically to the substrate, whereas laser cladding forms a strong metallurgical bond with the gray cast iron base material.
■ Image source: Laserline
Increasing the processing rate is the key to success.
The new process builds on the traditional laser cladding technique, which has already been successfully applied in industrial settings. However, this conventional method is not suitable for cladding brake discs—primarily due to the surface processing rate. Specifically, the cladding speed is too slow for mass-producing wear-resistant components. Therefore, increasing the processing rate is the key factor in developing a cost-effective cladding solution.
The latest process enables single-layer overlaying of brake discs in 30 seconds or less, depending on the thickness of the overlay layer, the material used, and the size of the brake disc. This process relies on minimal energy input and limited melting between the base material and the overlay material. As a result, the entire overlaying procedure can now be completed in just 3 to 5 minutes.
Processing time is achieved by rapidly moving components beneath the laser beam and powder-fed nozzle. The laser and nozzle are positioned from above, directing their energy toward the workpiece—causing the ejected cladding material to melt simultaneously with the base material. As the two materials merge within the molten pool, they form a metallurgically bonded alloy that solidifies into a highly stable coating. Brake disc cladding typically involves two main steps: first, a buffer layer is applied to provide corrosion resistance, followed by the deposition of a wear-resistant coating made from carbide materials.
■ Image source: Laserline
Diode lasers deliver optimal results at a lower investment cost.
To achieve the best cladding results, a uniformly distributed laser beam intensity is essential. At the same time, high-speed cladding requires a relatively large spot diameter. A diode laser with moderate beam quality is ideally suited for this process. By selecting a laser with a beam quality of 110 or 220 mm·mrad, it’s possible to generate spot diameters ranging from 3 mm to 14 mm—or even larger.
By carefully selecting these laser parameters, it’s possible to achieve a large, uniformly distributed spot without causing defocusing or degrading beam quality. This ensures even melting of the gray cast iron layer while enabling minimal fusion between the substrate and the overlay material. Additionally, the powder utilization rate—reaching as high as 80%–90%—is highly impressive: although slightly lower than in wire-fed cladding processes, it still significantly outperforms the material efficiency of thermal spraying techniques.
Finally, under the same beam quality conditions, diode lasers can achieve the highest power output. Thanks to modular stack technology, diode lasers can effortlessly deliver kilowatt-level laser power—up to 10 kW or even higher—in a remarkably compact footprint. This advantage ensures a cost-effective investment in equipment, helping to keep the total cost of ownership (TCO) for diode-laser-based processes competitively low.
■ Image source: Laserline
In summary, laser cladding of the wear-resistant layer on brake discs using diode lasers could pave the way for a reliable, technologically advanced, and economically viable process in the future—significantly reducing fine particle emissions caused by braking. While brake discs coated with the cladding still generate some fine particles, the emissions are substantially lower compared to uncoated discs. This approach preserves the cost-effectiveness advantage of gray cast iron brake discs. Ultimately, the laser-based wear-resistant cladding process is set to become the foundation for the next generation of standardized brake discs.
Source: Xinruida Laser
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