When Selecting Superabrasive Grains

Selecting the right diamond and CBN abrasives is a very challenging task. In this section, we will explain the factors to consider when making this selection, including the characteristics of the superabrasives, whether or not they are coated, the bonding agents used, and their size (grain size).

• Whether the workpiece contains ferrous materials
• Temperature during tool use

Furthermore, over the past decade or so, the prices of diamond and CBN abrasives have fallen significantly. While the price difference between the two is not as great as it once was, diamond abrasives are generally considered to be less expensive than CBN.

There are many types of diamond and CBN abrasives that differ in shape, hardness, and color depending on their synthesis methods and sorting processes. This is because altering the catalyst or synthesis conditions changes the amount of impurities within the crystal, the porosity of the abrasive grain, and the presence or absence of grain boundaries, which in turn affects the grain’s toughness (hardness).

They are broadly categorized into products such as single crystals, which have no voids or grain boundaries, and polycrystals, which contain internal impurities, voids, and grain boundaries within the grains.

Generally, polycrystalline abrasives have good friability and thus offer superior cutting performance, while single crystals with few internal impurities offer excellent heat resistance and wear resistance. Since each diamond and CBN abrasive product has specific toughness data and geometric characteristics, the selection process typically begins by narrowing down the options based on past adoption and machining records. The optimal product is then selected after conducting grinding tests that include both higher and lower grades.

Coated abrasives are abrasives in which metals such as nickel, copper, or titanium are coated onto the surface of the abrasive grains. They are selected to improve mechanical retention with resin-based binders or to achieve a chemical bond with metal bonds. Additionally, they help prevent the graphitization of the diamond substrate by transferring the heat generated during machining to the metal coating.

In superabrasive grinding wheels, the bonding agent serves to bind and hold the abrasive grains in place. While the bonding method is selected and tools are developed based on the workpiece material and application, the bonding method also influences the selection of abrasive grains.

• Vitrified bonds are porous bonding agents composed primarily of glass. Since the sintering temperature is high—around 1,200°C—abrasive grains with low impurity levels and high heat resistance are selected.
• Resin bonds are bonding agents made from resins such as phenolic resin. Because they are soft and elastic, coated abrasive grains are used to increase the surface area, and measures are taken to prevent grain loss from the grinding wheel.
• from the grinding wheel. Metal bonds use metals such as cobalt, copper, tungsten, nickel, and iron as the bonding material. Since they are sintered at temperatures of approximately 600–700°C, heat-resistant, uncoated abrasive grains capable of withstanding high sintering temperatures are the mainstream choice. However, in some cases, Ti-coated grains with high heat resistance are used to enhance bonding with the metal bond.
• Electroplating is a method in which an electric current is applied to a metal shank in an electroplating bath, using nickel plating to fix one or two layers of abrasive grains to the surface of the substrate. Since manufacturing precision depends on how well the abrasive grains interact with the plating solution, the cleanliness of the abrasive grains themselves and their metal content are critical requirements.

Grit size refers to the size (particle diameter) of diamond or CBN abrasive grains. The notation and classification methods for grit size are defined by international standards.
（See the Mesh Size Standards Table）

However, since these standards do not specify grit sizes finer than 500/600 Mesh (#500, 500-grit), superabrasive suppliers have established their own standards; consequently, the grit sizes of products from different tool manufacturers are not uniform.
（See our reference standards：Micron Designations and Grit Size Standards）

Generally, grit size is selected based on the depth of cut relative to the machined surface, surface roughness, and machining efficiency. Similar to selecting the grit number for sandpaper, coarser grits remove more material in a single pass, while finer grits remove less but produce a smoother surface, making them suitable for finishing.