This chapter discusses factors affecting the grinding of the new generation of hard engineering ceramics. Particular attention is drawn to effects on predressing time and surface quality. Electrolytic in-Process Dressing (ELID) grinding is introduced as an exciting new process used for machining a range of very hard materials and, in particular, for machining ceramics.
14.1.1 Use of Ceramic Materials
Ceramic materials are used in engineering where there are demanding requirements for particular material properties. These may include requirements such as unusually high heat resistance, unusually high wear and corrosion resistance, low specific weight, or unusual electrical properties. Noticeable examples include ceramic bearings for high speeds in the machine tool industry and electronic components for the computer industry.
It is possible to engineer ceramic materials for high density and high strength. Developments in ceramic materials have greatly increased the range of engineering applications in recent decades. Zirconia, for example, is a modern material that is very tough and, apart from the obvious use for jewelry, is finding increasing engineering use for wear resistance. Hard silicon nitride ceramics also offer a way to overcome the greatest disadvantage of traditional ceramics: that being their brittleness. Ceramic-ceramic composites have further increased the range of properties that can be achieved.
14.1.2 Machining Hard Ceramics
Abrasive machining is practically the only successful method for machining these hard and brittle materials. Superabrasive grinding wheels with diamonds are generally employed due to the extreme hardness of some ceramics. The combination of high hardness and strength, however, causes considerable wear on the diamond abrasive itself with effect on the geometric accuracy of the grinding wheel, the protrusion height of individual grains (cutting edges), and the distribution pattern of active cutting edges. Therefore, careful preparation of the wheel prior to grinding is essential.