explained considering the amplitude of the ultrasonic
vibration. It can be clearly seen from the Fig. 4 that the normal
grinding force increases with the increase of cutting depth. In
the depth of cuts lower than 5.2μm, when the workpiece is
ultrasonically vibrated, the diamond grits are not continuously
in contact with the workpiece. In this stage of ultrasonic
grinding, the only factor that affects the normal grinding force
will be the normal contact force between the workpiece and
wheel resulting from the non-continues contact between them
or in other words, will be the force resulting from the
ultrasonic vibration. The effect of that force will increase with
the increasing of cutting depth. With raising the cutting depth
more than 5.2μm the initial pressure, resulting from
penetration of abrasive particles into the surface of the
workpiece, increases. Therefore an initial static force, which is
added to the resulting force of ultrasonic vibration, will be
produced. The sum of the two discussed forces (initial static
force and ultrasonic vibration force) cause the normal force to
increase in the ultrasonic grinding process.