Cutting speed influences the power required for the cutting process and the tool life. It does not influence the forces acting on the cutting tool. The forces acting on the cutting tool depend solely upon the properties of the workpiece material, the cutting-tool geometry, and the depth of cut and rate of feed. Example 2.22 shows how increasing the cutting speed affects the power required for a given process. The upper limit is set by the rigidity of the machine tool being used and the power available at its spindle.
The cutting speed also influences the tool life. It has just been shown that increasing the cutting speed increases the power required. Since power can be defined as the rate of doing work or using energy, increasing the cutting speed increases the rate at which energy is dissipated at the cutting zone. Since energy cannot be created or destroyed (law of conservation of energy), the mechanical energy of cutting is converted into heat energy in the cutting zone. This increases the temperature at the tool tip and reduces the tool life. The relationship between cutting speed and tool life is logarithmic; an empirical relationship has been derived experimentally:
(V * t)^n = C
where:
V...cutting speed in m/min
t...tool life in minutes
n...tool life index
C...a constant for a given set of cutting conditions
