Page 35 - June

METALWORKING EQUIPMENT AND TOOLS

The stagnant zone is regularly destroyed, its
fragments are carried away by the converging chips
or the cutting surface. Chipping occurs with regular
shifts, traces of which are visible on the chip itself
and on the surface of the workpiece. These and
a number of other processes associated with the
heterogeneity of the workpiece material and the
frictional contact of the surfaces of the tool [8], to one
degree or another, violate the emerging equilibrium.
For example, at the moment of the formation of a
crack in the coming off shavings, its effect on the
front surface sharply decreases in magnitude and
direction, the balance is disturbed, and the tip of
the tool rushes to the EFS. One- the shortest path,
but along a complex trajectory determined by the
characteristics of the vibration modes, the so-called
normal modes, in which the reserves of potential
energy have been concentrated at the moment
of imbalance. In fig. 3 shows an example of the
hodograph of the cutter tip speed (Fig. 3a) directly
Fig. 2. Schematic representation of the forces acting during turning (the central part of the hodograph)
on the tip of the cutter from the side of the rear edge
(Fз), from the side of the chips (Fс) and from the side and when entering the keyway. The arrows show
of the elastic system of the tool (Fy). the direction of motion along the trajectory of the
hodograph in time.
Figure 3b shows an example of recording a vibration signal along two mutually perpendicular
axes when turning a workpiece with a groove. The plane of the hodograph in Fig. 3 is determined
by the vector of cutting speed (Z-axis) and the normal to the cutting surface (X-axis), which
in this case coincides in direction with the axis of rotation of the part. It can be seen that
during cutting the hodograph contour is close to an elliptical shape and occupies a relatively
compact area elongated in the tangential direction in the direction of the cutting speed. This
area significantly increases at the moment the tool enters the groove, when the holding forces
from the chip side disappear, the elastic system is able to free itself from the excess potential
energy and begin to shift towards the EFS.
Simultaneous movement of a variety of vibration modes (vibrations along normal
coordinates) forces the tool tip to move along a complex trajectory [9 - 11]. At the same time,
at the moment of entering the groove, the speed of the tool tip in the direction of the normal to
the cutting surface (X-axis in Fig. 3b) is several times higher than this speed in normal cutting.
It is important that this movement is directed from the cutting surface, although it is known
that during cutting there is a deformation displacement of the tip from the cutting surface, i.e.,
the coordinates of the EFS of the cutter tip are inside the workpiece body. This is due to the fact

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