With respect to their material characterisation, ceramics are subdivided into oxide, non-oxide and silicate ceramics. In the case of oxide ceramics, aluminium oxide and zirconium oxide or zirconia (ZrO2) represent the industrially most important
materials. Oxide ceramics have mostly ionic bonds (> 60 %), exhibit favourable sintering properties and are disadvantageous compared to other ceramics with respect to their heat resistance.
Carbides (boron carbide B4C, silicon carbide SiC), nitrides (silicon nitride Si3N4), borides and silicides are included first and foremost with the non-oxidic ceramics. They have a high percentage of covalent bonds (5 — 40 %), which, in combination with the small inter-atomic distance, leads to high chemical and thermal stability. This brings about high strength and hardness, but also limited ductility.
Finally, silicate ceramics are first separated into coarse ceramics and fine ceramics. The coarse ceramics include magnesite, mullite, silica or zircon stones. The silicate ceramics which fall into the fine-ceramic category are glass ceramics, steatite and cordierite.
As opposed to metal machining, when processing ceramics, the process forces are higher as a rule, especially in the normal direction [KOEN88, TIO90, WECK90a]. It is imperative that these forces be absorbed by correspondingly rigid machines and spindle systems. Otherwise, excessively soft, resilient systems lead to decreased dimensional and formal accuracy in the functional surface. Furthermore, ceramic-machining is more demanding on machine protection. Grinding sludges have a highly abrasive effect due to the hardness of the removed particles.
There is a lot of research available pertaining to the use of diamond grinding wheels for grinding ceramics [CART93, JUCH90, NAGA86, SPU87, SUBR88, WARN92, WIMM95, WOBK91, among others]. Since diamond reacts sensitively to strong thermal loads, increased demands are placed on cooling lubricant supply.
Concerning the type of bond, tools bonded with synthetic resin and metal are the most often used in ceramic grinding. Grinding wheels bonded with synthetic resin exhibit more wear during the process, but lower process forces, and therefore result as a rule in better surface quality and formal accuracy. The size of the diamond grains used varies between D7 and D252, whereby grain sizes between D91 and D181 are selected for most machining operations. Grain concentrations in ceramic machining are usually between C75 and C100 [VERL94].
With respect to the maximum obtainable specific material removal rates, values up to 50 mm3/mms are cited for machining high-performance ceramics with external grinding. Higher specific material removal rates are realisable with other grinding kinematics, such as surface grinding, but these cannot be considered representative methods. In ceramic chip removal, increasing machining performance is accompanied by concurrently increasing process forces.