Page 15 - january

PRODUCTION AUTOMATION

In addition to the breakdown of the CT,
the situation with intense self-oscillations
causes a sharp decrease in the surface
quality. Figure 3 shows a micrograph of the
cone surface obtained on a milling-boring
machine under self-oscillation conditions
(Ra = 0.8 μm). The smallest taper diameter
was 4.8 mm, and the finishing allowance а) frequency, khz
did not exceed 0.3 mm. This emphasizes
the fact that self-oscillation can occur both
at high tool loads and during finishing
operations, when control of the cutting
process by monitoring the active power
consumed by the machine drive becomes
impossible. The power consumed by cutting
practically does not stand out against the b) frequency, khz
natural background noise.
When working with a small-sized tool Fig. 2. An example of the spectra of VA signals obtained during
on multi-operation machines, a difficult normal turning (a) and at turning with intense self-oscillation (b).
situation also arises, since the machine
drive is designed for the entire range of operations, including roughing, consuming the maximum
power value, and finishing, where the power value can hardly be distinguished from the idle
noise background.
The nature and sources of the occurrence of self-oscillations during cutting have been well
studied [9 - 12], which makes it possible to compose algorithms for calculating and controlling
the processing modes.
The experimental study was carried out on a
3-axis milling machine DMG 635eco. Figure 4 shows
the distribution of the energy of the VA signal (a,
b) and the active power (c, d) by the color intensity
during the processing of aluminum (a, c) and tool
steel (b, d) in different modes. In this case, the depth
varied from 0.1 to 2 mm, and the rotational speed of
the cutter - from 1000 to 3000 rpm, the feed did not
change.
As it can be seen from Fig. 4, the active power
signal (c, d) is not very sensitive to small changes in
the depth of cut, and only at depths of 1 mm or more
can we speak of linear dependences of the measured
Fig. 3. Inner conical surface after self-oscillating signal on the depth of cut for both aluminum and steel.
boring. With the vibration signal, the picture is somewhat

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