The new laser cladding method can significantly reduce the formation of fine particles and wear, for example in disc brakes.
Braking is difficult
Most disc brake rotors are made of grey cast iron. This material can withstand the high temperatures that brake components often reach and is relatively inexpensive. However, grey cast iron wears easily, forms particulates and corrodes. The solution is to apply a thin layer of a harder material - such as stainless steel - to the surface of the brake rotor to protect it from both wear and corrosion. However, none of the techniques normally used to produce such coatings are applicable to disc brakes. For example, coatings produced by electroplating and thermal spraying do not bond metallurgically to grey cast iron. This means that they can flake off. In addition, these methods are expensive to implement.
Traditional laser cladding (also called laser material deposition or LMD) is not a solution either. In this technique, powdered stainless steel is applied to the surface of the part and a high-powered diode or fiber laser is used to melt this powder and the part. This re-solidifies and creates a new layer of coating that has a strong metallurgical bond with the base material. However, the laser will also melt some of the grey cast iron so that some of the carbon can migrate from it into the steel coating. This will cause the coating to become brittle or develop cracks or other defects that could shorten the life of the part.
New laser cladding technology
The solution is a new laser material coating process. The method, called Extreme High-Level Laser Material Deposition (or EHLA for short), introduces several key innovations to laser cladding. Like traditional LMD, EHLA deposits powdered metal on the surface of the disc brake and melts both using a high-power diode laser ( HighLight DL series). However, EHLA uses a specially designed nozzle that allows the cladding powder to be melted "on the fly" in the laser beam before it hits the surface of the part. The droplets of molten metal thus hit the part in a very thin layer of molten grey cast iron. All this metal then quickly solidifies to form a thin coating.
The EHLA method does not excessively heat the brake rotor part and thus no significant amount of carbon can migrate from the brake rotor into the coating. Although it avoids problems with changes to the material itself, it produces a solid thin film that is metallurgically bonded to the part. In addition, it is much faster and more efficient in terms of powder consumption than traditional laser cladding.
EHLA is a recipe for success
EHLA is a flexible method that can be adapted to the exact requirements of the application. Sometimes it can be useful to apply two different layers. The EHLA cladding nozzle has been specifically designed to allow more than one powder material to be used at the same time. When creating this layer, the laser power is adjusted so that the harder material does not melt. The small powder particles simply "embed" into the solid steel layer like blueberries when baking a cake. This creates an extremely wear-resistant outer layer. However, this outer layer is fragile and therefore prone to cracking, which can then allow moisture to seep through. Therefore, a base layer of only pure stainless steel is first applied to "seal" the part and prevent moisture from entering.
EHLA is faster and uses metal powder more efficiently than traditional laser cladding, which means it is more cost effective. In addition, it is applicable to many materials other than grey cast iron and stainless steel.
Interested in this article? Read more about the topic in the Laser Cladding and Plating application note.