Page 23 - Апрель

METALWORKING EQUIPMENT AND TOOLS

distortion of the spectrum shape, expressed in the change in the ratio of the effective amplitudes
for different frequency ranges. That is, the distortion of the shape of the spectrum of VA signals
can be used as a diagnostic sign of a change in the state of the cutting tool [9, 10]. An increase
in heat generation in the contact zone of the surfaces of the tool and the work piece material
leads to a change in the mechanical properties in the friction pair, for example, to a decrease
in the hardness of the work piece material. In works [17 - 19] it is shown that the amplitude of
the high-frequency VA signal in the frictional contact in the first approximation with an increase
in the hardness of the softer element of the friction pair increases almost linearly. Thus, with
an increase in temperature (and a decrease in the mechanical characteristics of the processed
material) in frictional contact under conditions of adhesive friction [16, 17], the high-frequency
components in the spectrum of the VA signal should decrease.
On the other hand, an increase in the load in the contact of the tool with the machined
surface causes additional deformations of the entire technological system and increases its
potential energy [18 - 20], making it less stable when separating the chips. The situation can be
aggravated by a decrease in the bearing capacity of
the cutting surface with an excessive increase in the
contact temperature, which forms surface waviness
and instability of the properties of the surface layer,
noted in [5]. When separating the elements of the
shavings, the balance of forces in the technological
system is disturbed, leading to the release of potential
energy, relaxation of elastic deformations with the
occurrence of oscillations at the natural frequencies
of the technological system. If, at the same time, the
contact of the surfaces of the tool with the material of
the part is maintained, then as the cutting ability of
the tool decreases and the pressure in the frictional
contact increases, the damping of high-frequency
oscillations grows at a faster pace than low-frequency
ones.
It follows from what has been said that with an
increase in the potential energy determined by the
cutting forces, oscillations in the technological system
in the region of relatively low frequencies, which are
most actively involved in the accumulation of potential
energy, will also increase. These provisions made it
possible to use the ratio of the effective amplitudes (Kf) of the vibration signal in the high and
low frequencies as a diagnostic feature [9, 10]. In fig. 1 shows examples of the spectra of VA
signals from the accelerometer accompanying the turning of a 45 steel bead with a depth of
0.5 mm, feed 0.15 mm / rev, with a cutting speed of 47 m / min. The spectra are presented to
illustrate the extreme situations in the experiment carried out: for cutting with a sharp plate

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