Grinding is a material removal and surface generation process used to shape and
finish components made of metals and other materials. The precision and surface
finish obtained through grinding can be up to ten times better than with either
turning or milling.
Grinding employs an abrasive product, usually a rotating wheel brought into
controlled contact with a work surface. The grinding wheel is composed of
abrasive grains held together in a binder. These abrasive grains act as cutting
tools, removing tiny chips of material from the work. As these abrasive grains
wear and become dull, the added resistance leads to fracture of the grains or
weakening of their bond. The dull pieces break away, revealing sharp new grains
that continue cutting.
The requirements for efficient grinding include:
• abrasive components which are harder than the work
• shock- and heat-resistant abrasive wheels
• abrasives that are friable. That is, they are capable of controlled
Most abrasives used in industry are synthetic. Aluminum oxide is used in three
quarters of all grinding operations, and is primarily used to grind ferrous
metals. Next is silicon carbide, which is used for grinding softer, non-ferrous
metals and high density materials, such as cemented carbide or ceramics.
Superabrasives, namely cubic boron nitride or "CBN" and diamond, are used in
about five percent of grinding. Hard ferrous materials are ground with "CBN",
while non-ferrous materials and non-metals are best ground with diamond.
The grain size of abrasive materials is important to the process. Large, coarse
grains remove material faster, while smaller grains produce a finer finish.
The binders that hold these abrasive grains together include:
• vitrified bonds, a glass-like bond formed of fused clay or feldspar
• organic bonds, from synthetic resins, rubber, or shellac
• metal or single-layer bond systems for superabrasives
Wheels are graded according their strength and wear resistance. A "hard" wheel
is one that resists the separation of its individual grains. One that is too
hard will wear slowly and present dulled grains to the work and overheat,
affecting the final finish. If too soft a wheel is used, it will deteriorate
quickly, requiring frequent replacement.