The superabrasive grits cBN and diamond are a great deal more expensive than the conventional abrasives already mentioned. Thus, the construction of superabrasive grinding wheels is also different from that of conventional ones. A further reason for the altered construction has to do with the fact that such grinding wheels exhibit a higher wear resistance. Furthermore, in order to reach higher material removal rates, which is what makes such grinding wheels economical, much higher burst resistance values and grinding wheel speeds are necessary than in the use of conventional grinding wheels. Therefore, grinding wheels with diamond or cBN have bodies applied only with a thin abrasive coating. Basic requirements of the body material are:
• a high heat conductivity,
• high mechanical strength,
• good vibration dampening.
These property requirements are partially in contrast to each other and thus necessitate compromises. Not all combinations between the body and the grinding wheel layerare possible and technically sensible. Some frequently used body materials are:
• aluminium, steel, bronze,
• synthetic resin with metallic or non-metallic fillers,
• fibre-reinforced synthetic resin,
• ceramics.
Aluminium and Steel Bodies
Metallic bodies are distinguished by their high strength. Theoretically, for a body design without a central hole and with an approximately constant tension curve across the cross-section, rotational speeds of 500 m/s can be reached. The highest practically feasible rotational speed is 280 m/s. Since the ratio of elastic modulus to density for steel and aluminium as a function of their compositions differs only minimally, strain levels are nearly identical at any given rotational speed.
Bronze Bodies
These bodies are manufactured in both cast and sintered form. Of the two, sintered bronze reaches the highest burst resistance value [FRAN88].
Synthetic Resin Bodies with Metallic or Non-Metallic Fillers
Bodies made of synthetic resin do not reach the strengths of those of steel or aluminium. However, their improved damping properties are advantageous. Synthetic resin bodies filled with metal have better heat conductivity than those with nonmetal fillers. Copper and aluminium are examples of metallic fillers used in this context.
Synthetic Resin Bodies with Reinforcing Fibres
This type of body makes use of the strength of non-metallic fibres (glass fibres, carbon fibres) in a plastic matrix. The small density of fibres in connection with their high strength makes it possible to use them at maximum rotational speeds.
Ceramic Bodies
These bodies correspond in their construction to conventional vitrified grinding wheels. The prerequisite for their use is a coordination of the bonds of the body and the grinding wheel layerwith respect to their strength and strain.