Page 40 - June

METALWORKING EQUIPMENT AND TOOLS

In Fig. 6b, horizontal traces of periodic shifts of small elements of the shavings with a steps.
It is interesting that at each new revolution, the phases of the shifts persist for many revolutions.
This suggests that at the moments of shift of elements on the current turn, microcracks appear,
affecting the material of the future turn. The resulting defects synchronize the moments of
shear from turn to turn. This fact can make the step s stable as the cutting speed changes. At
the initial moment, the chip elements are formed with frequency close to one of the natural
frequencies of the instrumental unit. If subsequently the cutting speed changes smoothly, then
the step s is retained, and the frequency of chip formation changes. This can continue until the
transition of the dynamic system to another natural frequency, which is closer to the frequency
of formation of chip elements, more favorable from the energy point of view [18].
It is not possible to control the occurrence of intense self-oscillations during finishing
using force parameters (cutting forces, torques, drive power). The power parameters in this
situation are small in themselves and it is difficult to distinguish them against the background
of interference. The emergence of intense self-oscillations does not always lead to an increase
in cutting forces, more often on the contrary [16, 17]. However, the emergence of intense
self-oscillations inevitably entails an increase in the amplitude of oscillations at one or several
natural frequencies. In finishing, these are usually high frequencies, which are reliably recorded
against the background of interference using an accelerometer mounted on the elastic system
of the machine. The occurrence of intense self-oscillations can be monitored with the help of
information-measuring systems based on the control of vibration signals [19 - 21] to diagnose
the state of the cutting tool. It is possible to identify the moment of transition of the cutting
process to intense self-oscillations by a sharp increase in the amplitude of the vibration signal
in the frequency range, including the natural frequencies of the tool. The emergence of intense
self-oscillations during processing can be associated with a change in the state of the cutting
tool, a decrease in the rigidity of the workpiece in the processing area, with a change in cutting
conditions. To switch to the technical stability mode, it is necessary to replace the cutting tool,
change the cutting modes or create additional devices that increase the rigidity and damping of
the workpiece section.

Findings
1. During cutting, the elastic system of the
machine is deformed and acquires an excess
of potential energy. According to Lagrange's
theorem, when cutting, the equilibrium position
of the tool tip becomes unstable. Despite
the high dynamic quality of technological
equipment, the process of separating chips
is accompanied by self-oscillations of varying
intensity, supplemented by forced resonant
vibrations. If the attractor corresponding to
these oscillations elongated in the tangential

40 Stanochniy park