The grinding energy to remove a volume of material is a measure of the efficiency of material removal. The specific energy is given by
P
ec = Q (19.11)
Specific energy is a measure of the difficulty of grinding a work material under particular grinding conditions. Hard materials give rise to higher specific energy than soft materials. Typical values of specific energy range from 10 to 200 J/mm3 of material removed. Lower and higher values than these are possible. A value of 10 J/mm3 represents an easy-to-grind material with very efficient grinding conditions. A value of 200 J/mm3 is typical of many finishing operations at lower process efficiency.
The process engineer, having established a database for particular materials and grinding wheels, uses specific energy to determine machine power requirements and machining rates.
19.3.5 Contact Length
The total contact length is due to contact force and grinding geometry. Geometric contact length must be added to dynamic contact length according to:
l2 = l2 +12 (19.12)
c g f 2
19.3.5.1 Geometric Contact Length
The geometric contact length, based on the undeformed shape of the grinding wheel, depends on the depth of cut.
ig=^a~de (19.13)
where the effective grinding wheel diameter is given in Section 19.3.6.