Page 26 - Апрель

METALWORKING EQUIPMENT AND TOOLS

of deformations at a depth of less than 100 μm are
intermediate in nature compared to graphs 1 and 2.
The Kf parameter can be used to monitor the effect
of tool wear on the intensity of deformations of the
surface layer, but at constant processing conditions.
When changing machining modes, the Kf values can
change, causing changes in the tool failure criteria.
The search for a diagnostic parameter that would tangential cutting edge geometry
be sensitive to changes in the state of the tool, but
changed little with variations in processing modes is
also an important goal of the research. Practice has shown that VA signals and the Kf parameter
are most dependent on the cutting speed. In fig. 3 shows the dependences of Kf on the cutting
speed for a sharp and worn tool when turning the alloy KhN77TYuR. For a tool with wear, the
Kf values change by a factor of five when the cutting speed changes from 15 to 50 m / min. In
fig. 3 shows a graph of changes in the qf index, defined as the ratio of the Kf value with a sharp
instrument to the Kf value with a blunt instrument. It can be seen that in the entire range of
cutting speed variations, qf varies within 20%. With real variations of the speed relative to its
optimal value (35 m / min) for the KhN77TYuR alloy, the changes in qf are no more than 5%.
Thus, knowing the values of Kf at different cutting conditions for a sharp tool, it is possible
to monitor the value of the qf index in a wide range of variation of cutting conditions, having a
single failure criterion [qf]. For the case shown in Fig. 3, the refusal criterion [qf] = 2, that is,
a decrease in Kf from the initial level by half is allowed. It is important to note that during the
cutting process, when the processing conditions change, intense self-oscillations can occur, in
which the regularities of the Kf behavior can be violated. With high requirements for surface
quality, work with large amplitude self-oscillations should be excluded. The identification of
modes with self-oscillations can be done using the analysis of VA signals [17]. Figure 4 shows
the spectra of the VA signal accompanying the turning of a cylindrical work piece without intense
self-oscillations (Fig.4a) and with intense self-oscillations (Fig.4b). In fig. 4b, the oscillation
amplitudes at the selected frequencies are tens of times larger than those in Fig. 4a.
All processing conditions were identical, but the spectrum in Fig. 4b was formed with
an increased overhang of the cutter, i.e., with a reduced stiffness. Intense self-oscillations are
accompanied by impact interaction of the tool with the work piece surface and partial rupture
of their contact. As a result, the traces from the cutting tool acquire a characteristic periodic
appearance with deteriorated roughness (Fig. 5). In fig. 5a, it can be seen that as a result of
boring with intense self-oscillations, not just waviness is formed on the surface, but traces of
periodic chips that arise after separation of the chips due to the formation of brittle cracks. Brittle
cracks are not limited only to the formation of chip elements, but also create micro cracks in
the surface layer of the treated surface. Figure 5b shows the traces of the cutter on the surface
of a cylindrical steel part in the event of intense self-oscillations. Breaks in the contact between
the tool and the work piece, as well as their impact interaction, sharply deepen the cut from
the cutter and form uneven edges of the track itself. Here, too, chips are formed due to brittle

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