Good feedback of resin diamond grinding wheel for grinding tungsten carbide coating

What is thermal spray technology?

Thermal spraying technology refers to the use of heat sources (such as electric arcs, plasma arcs, combustion flames, etc.) to melt or semi-melt filamentary or powdered non-metallic and metallic materials at high temperatures, and then atomize them into particles with the help of the power of the heat source itself or high-speed and high-pressure airflow to form a beam of particle spray, which is sprayed at a specific speed onto the surface of the pre-treated substrate, and combines with the substrate material to form a coating with strong adhesion that is no less than the adhesion of the substrate material itself. Depending on the spraying material, it can form a surface coating with various functions such as wear resistance and corrosion resistance.

There are about 6 common spraying processes, namely plasma spraying, Arc Spraying,Flame Powder Spraying, Flame Wire Spraying, HVOF spraying, and Low-Temperature Supersonic Flame Spraying.

High speed oxygen fuel flame

High speed oxygen fuel flame (HVOF) (spraying) technology is a technology based on high-speed particles to obtain coatings. Using a special combustion chamber or a special nozzle, the ignition gas or liquid fuel is sprayed to form a high-speed, high-pressure, and high-temperature combustion flame flow. The metal powder is sent into the flame flow through an inert gas for heating. The molten metal powder is accelerated to hit the surface of the substrate and solidifies rapidly, and is continuously deposited to form a coating.

The WC-10Co4Cr coating prepared by the HVOF process has a dense coating and a porosity of <1%; the coating and the substrate are mechanically and semi-metallurgically bonded, with a high bonding strength of >70MPa; the hardness can reach 1100~1300HV, and high wear resistance can be obtained. Tungsten carbide coatings have been widely used in aircraft landing gear shaft parts with wear resistance requirements, size and precision repair, but due to the constraints of process and coating properties, the surface roughness of the original coating of supersonic flame spraying is generally > Ra3.2μm, which cannot meet the design requirements (<Ra0.2μm). The coating thickness and surface roughness must ultimately be guaranteed by grinding.

Grinding tungsten carbide coating is the use of high-speed rotating diamond grinding wheels to achieve a surface roughness of Ra0.4~Ra0.6μm through rough grinding and fine grinding of the processed parts. The surface roughness can reach Ra0.1~Ra0.2μm after polishing.

For coating grinding, reasonable control of grinding parameters can effectively prevent surface burns and thermal stress deformation of parts, and prevent defects such as surface cracks and coating collapse. During the grinding process, due to the effect of grinding stress, cracks first occur at the junction with the substrate. After the coating is pulled apart, it expands in a direction perpendicular to the main grinding stress. In order to reduce the probability of cracks, the grinding parameters should be optimized to reduce the grinding stress, while increasing the surface roughness of the substrate material and increasing the bonding force between the coating and the interface.

If the grinding wheel is found to be passivated during semi-finishing grinding, it should be trimmed in time, and the minimum grinding amount for fine grinding is at least 0.025 mm per side.

Control of grinding temperature

Experiments show that the grinding temperature increases with the increase of grinding depth. The reasons are as follows: 1) As the grinding depth increases, the normal grinding force also increases, so the energy consumed in the grinding process increases, and the energy converted into heat energy also increases; 2) As the grinding depth increases, the contact arc length between the grinding wheel and the workpiece increases, and the scratching effect between the grinding wheel and the workpiece increases, causing the grinding temperature to increase. The faster the worktable speed, the higher the average temperature of the coating-substrate interface and the grinding surface. This is because the faster the worktable speed, the greater the thickness of the undeformed cutting, the more energy is consumed to cut the same depth, and the greater the heat generated. After further increasing the worktable speed, the grinding temperature of the coating-substrate interface tends to decrease. This is because after increasing the worktable speed, the time that the grinding heat stays in the workpiece becomes shorter, and the heat quickly passes through the surface of the grinding workpiece, reducing the depth of heat penetration on the workpiece surface; at the same time, a large amount of grinding heat can be taken away by the grinding chips and grinding fluid, which reduces the surface temperature of the workpiece. Therefore, the grinding temperature control measures are as follows: 1) The feed amount is less than 0.005mm; 2) The speed of the worktable is 0.3-0.5m/min.

Recently Moresuperhard have one customer who inquiry about resin diamond grinding wheel for  tungsten carbide coating. And he use angle grinder for manual grinding tungsten carbide coating, and grinding on brazed Tungsten Composite Brazed Rod overlay.  They are used on Makita Angle Grinders that have between 2,800 and 11,500 RPM capabilities.

—-EDITOR: Doris Hu, Jason Guo

—POST: Doris Hu