According to different work piece materials and processing requirements, it is necessary to choose different grinding wheels. Even for the same work piece material, there may also exist 2-5 times difference in grinding ratio among the different models, so it is of great significance to choose the appropriate grinding wheels.
The diamond grinding wheel is the optimal abrasive tool for grinding the non-metallic materials featured with high hardness and brittleness, such as tungsten carbide, optical glass, ceramics, gems and stone material . However, due to the carbonization character of diamond in 700 ℃ ~ 800 ℃, so it is not suitable for grinding steel material. The hardness of CBN is slightly inferior to diamond, but its thermal stability performance is good, which can withstand temperatures up to 1300 ℃ ~ 1400 ℃. Unlike the decomposition of diamond in the high temperature, that is to say, it is unlikely to get oxidation and graphitization and it is also inert to most chemical elements of iron group. Besides, it is of high thermal conductivity, which is 46 times than that of corundum. As a result, grinding wheel made of CBN is of longer life (up to several dozen or one hundred times than the corundum grinding wheel). Consequently, it is a good alternative of corundum grinding wheel grinding of metal materials of high hardness and brittleness, such as hardened steel, high-speed tool steel, bearing steel, stainless steel, heat-resistant steel and titanium alloys.
The bond types of the super abrasive grinding wheels include resin, metal, vitrified and electroplate and vacuum brazed. The resin bond diamond grinding wheels are mainly applied to the sharpening of the cutting and measuring tool, boring, cylindrical grinding and surface grinding; the metal bond can be used to the cut-in grinding, optical contour grinder shaping, single-point cutters edging, spiral grooving of the small drill bits and electrolytic grinding; the vitrified grinding wheels are characterized by the high efficiency, excellent form holding, high durability, easy dressing and long work life. Additionally, due to its chemical stability and heat-resistance, oil-resistance and erosion-resistant of acid and alkali, which is suitable for the high speed fine grinding and high efficiently wet bore grinding, it is also can be on the jig grinder. And the vacuum brazed grinding wheel are good for the super high speed grinding.
Attention should be paid to that due to different manufacturing techniques of the different abrasives, correspondingly, their crystal forms and shapes are different. And thus they are of different intensity, heat stability and Bursting properties. So we are supposed to choose different abrasives, according to bond types and work pieces material and grinding methods. If the vitrified grinding wheel are used for the high proficient and high-precision grinding, we can choose the high-strength and sharp abrasives .
The super-hard abrasives can be classified into metal uncoated and coated ones. The metal coatings can play a important role in the reinforcement of strength and toughness, retard of thermal impact, and bridge the abrasives and bond to improve the performance of the grinding wheel. According to the bond types, work pieces materials and the processing conditions ( wet or dry), we can choose to different grinding wheels. The abrasives for dry grinding are commonly decided to coat the coppers, such as VD-Cu, CBN-Cu; while the abrasives for wet grinding are commonly decided to coat nickles, such as RVD-Ni, CBN-Ni. At present, the metal-coating are developed to Titanium, tungsten carbide, non-metal ceramics etc form the nickles and coppers. At the same time, the coating also developed to the composite coatings from the single layer coating. The abrasive-coated technology has reformed to the powder-coated.
In the beginning, for the hard grinding wheel, we cannot choose a rather low concentration, because higher concentrations can lead to higher grinding ratio. The 200% concentration of super abrasive grinding wheel, in fact, is a kind of universal grinding wheel accessorized with hard abrasives, So it is generally not recommended. At present, for the high speed and high efficiency grinding, we commonly choose higher concentration, and the ceramic bond CBN grinding wheel usually selects concentration more than 125%. For example, the imported ceramic CBN grinding wheels are with the concentration range from 175% to 175%.
The hardness levels of grinding wheel present the holding force of bond for the abrasives. The uniform and stable hardness, and the rational selection of the hardness, are the important premise to ensure the grinding quality. The hardness of superhard abrasive grinding wheels can be chosen from level 3 ~ 7. However, superhard grinding whee;s made in China are not labeled with hardness level.