Diamond grinding wheels are highly effective tools for grinding hard and brittle materials such as carbide, glass, ceramics, and gemstones. In recent years, with the rapid development of high-speed grinding and ultra-precision grinding technology, higher demands have been placed on grinding wheels. Vitrified resin-bonded grinding wheels no longer meet production needs. Metal-bonded grinding wheels, owing to their remarkable properties such as high bond strength, excellent formability, and long service life, have become widely used.
Metal-bonded diamond grinding wheels are primarily divided into two types, sintered and electroplated, depending on their manufacturing method. To fully utilize the superabrasive properties, a new type of grinding wheel, single-layer high-temperature brazed superabrasive grinding wheels, was developed in the early 1990s using a high-temperature brazing process. This type of grinding wheel is still under development in China.
1. Sintered Diamond Grinding Wheels
Sintered metal-bonded grinding wheels are typically manufactured using a high-temperature sintering process using metals such as bronze as a bond. They offer high bond strength, excellent formability, high-temperature resistance, excellent thermal conductivity, wear resistance, long service life, and the ability to withstand heavy loads. Because the grinding wheel inevitably shrinks and deforms during the sintering process, it must be shaped before use. However, dressing is difficult. The current common method of grinding wheel truing, using rollers, is not only time-consuming and labor-intensive, but also results in significant diamond particle shedding during the dressing process, resulting in significant wheel wear and tear, and low truing accuracy.
2. Electroplated Diamond Grinding Wheels. Advantages of Electroplated Diamond Grinding Wheels:
① The electroplating process is simple, requiring minimal investment, and is easy to manufacture.
② No dressing is required, making them easy to use.
③ The single-layer structure enables high operating speeds, currently reaching 250-300 m/s abroad.
④ Despite having only a single layer of diamond, they still have a sufficient lifespan.
⑤ For roller grinding wheels requiring high precision, electroplating is the only manufacturing method. Precisely because of these advantages, electroplated grinding wheels have an undisputed dominant position in high-speed and ultra-high-speed grinding. Electroplated diamond grinding wheels have drawbacks: the coating metal lacks a strong chemical metallurgical bond with the substrate and abrasive surfaces. The abrasive is effectively merely mechanically embedded in the coating metal, resulting in weak holding force. The diamond particles are heavily loaded, easily falling off (or flakes off) during efficient grinding, leading to overall failure. To increase holding force, the coating thickness must be increased, which reduces the exposed abrasive height and chip space, making the grinding wheel susceptible to clogging, poor heat dissipation, and burns on the workpiece surface. Currently, domestic electroplated grinding wheel manufacturing has yet to achieve optimal wheel topography optimized for processing conditions. These inherent drawbacks of single-layer electroplated diamond grinding wheels significantly limit their application in high-efficiency grinding.
3. Single-layer brazed diamond grinding wheels
To maximize the diamond's effectiveness, it is necessary to increase the bond's holding force on the diamond and improve the wheel's bond strength. Single-layer, high-temperature brazed superabrasive grinding wheels overcome the shortcomings of electroplated grinding wheels by achieving a chemical metallurgical bond between the diamond, binder, and metal substrate, resulting in high bond strength. Maintaining the bond layer thickness at only 20% to 30% of the abrasive grain height allows for high-load, high-speed, and efficient grinding. The abrasive grains can be firmly held, allowing brazed wheels to achieve an exposed grain height of 70% to 80%. This increases chip space, reduces wheel clogging, and maximizes abrasive utilization.
Under the same processing conditions as electroplated grinding wheels, single-layer, high-temperature brazed superabrasive wheels offer lower grinding forces, power loss, and grinding temperatures, enabling higher operating speeds. This is particularly significant for ultra-high-speed grinding exceeding 300 to 500 m/s. Single-layer, high-temperature brazed uncoated diamond grinding wheels with Cr-Ag-Cu alloy brazing are brazed using high-frequency induction brazing at 780°C for 35 seconds, followed by natural cooling. This achieves a strong bond between the diamond and the steel substrate. X-ray energy spectrum and X-ray diffraction analysis revealed that Cr3C2 was formed between Cr and diamond, and (FexCry)C was formed between Cr and the steel matrix. Comparative experiments with solder without Cr showed that this was the main factor for achieving high bonding strength between the alloy layer and both the diamond and steel matrix. Grinding experiments also confirmed that diamond does have high holding strength.