Two reasons can be stated for reduction in the normal
grinding forces in ultrasonic grinding:
1. Ultrasonic vibration provides a self-sharpening action
to the diamond grinding wheel and always causes to
keep it sharp, therefore tool pressure and thereby the
normal grinding force will be reduced.
2. Besides the tangential relative motion between the
workpiece and diamond wheel, a vertical motion will
also be produced between them when ultrasonic
vibration is applied. Ultrasonic vibration makes it easier
for the diamond grits to penetrate into the surface of the
workpieces and promotes much more brittle fracture-
mode machining and this is why a significant reduction
of normal grinding force could be achieved.
The effect of variations of the cutting depth on the normal
grinding force has been plotted in Fig. 4. As it can be inferred
from the diagram, although the normal grinding force
variation follows the same trend with raising the cutting depth
in both the operations, ultrasonic vibration causes to fall the
normal grinding force at any particular depth of cut.