SU1748995A1 - Method of controlling cutter state - Google Patents

Abstract

Use: control of the state of the cutting tool. Essence: register the signal of acoustic emission in the process of processing the part with the tool. The analysis is carried out on the time variation of the characteristics of the acoustic emission signal. 2 Il.

Description

The invention relates to the field of machine tools and can be used to determine the wear of the cutting tool and the machinability of materials in the conditions of an automated machining process.

The known method of monitoring the state of the cutting tool is based on the dependence of the vibration increase of the tool on its wear, providing for determining the wear by the frequency component of the vibration signal (1-10 kHz), and the achievement of the allowable wear value is determined by exceeding the value of the high frequency component.

The disadvantage of this method is the low accuracy of monitoring the state of the cutting tool, since exceeding a predetermined value of the vibration signal component in the low frequency range may be due to the noise of the tool's technological system.

Closest to the present invention is a method for monitoring the state of the cutting tool, consisting in determining the degree of wear of the cutting tool.

tool edges in amplitude and frequency of vibrations detected by the vibration sensor by integrating the amplified signals and comparing them in the comparator of the device implementing the method. The total energy of vibrations for a certain time interval is compared with a set value, and the excess of the latter by a certain amount registers the allowable amount of wear.

The disadvantage of this method is also the low accuracy of control of the tool state during the cutting process.

The purpose of the invention is to improve the accuracy of monitoring the state of the cutting tool.

Figure 1 is a block diagram of the device implementation method; Fig. 2 shows plots of the dependence of the cepstrum of the acoustic emission signal on the state of the cutting process.

The method of controlling the state of the cutting tool is carried out according to the scheme shown in Fig. 1. Acoustic emission transducer 1, which uses wideband non-resonant

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A piezoelectric transducer is installed, for example, on the tool holder of the tool 2, which contacts the workpiece 3. The acoustic emission signal arising in the cutting bar and propagating in the tool 2. is amplified by a complex consisting of the preamplifier 4 and amplifier 5. The recorded frequency range 0 5-1.5 MHz is the most informative for determining the state of the cutting tool, since it characterizes the physical processes that occur as a result of cutting at macro- and microstructural changes in the crystal lattices of the instrument-part-pair materials. The filtering of the amplified signal of the wideband converter 1 is performed using a combination of 6.1, 6., 6.N bandpass filters, which allow the signal to be studied in different frequency bands. In this case, it is possible to study both individual bands and the entire broadband spectrum of the vibration signal. A set of 6.1, ... 6.N filters is connected to the Fast Fourier Transform (FFT) block 7, and the connection method can be double: parallel or serial with a switch installed on the RXO block 7 for serial polling of the block channels

filtration 6.16. Block 7 implements

decomposition of incoming signals in different frequency ranges into spectral components. Analysis of spectral components is not sufficiently effective in diagnosing the state of the cutting edge of the instrument, since recording the change in the width of the spectrum, the amplitudes of the components depending on the change in the state of the cutting process leads to errors in the device, implementing control of the state of the cutting tool. Therefore, the accuracy of the work increases the analysis of the parameters of the acoustic emission signal function. The kepsgr is a function of the logarithm of the power spectrum of the signal under study.

To determine the parameters of the cepstrum of the acoustic emission signal of the mechanical processing process, the FFT unit 7 is connected to the logarithm unit 8. The output of block 8 is the cap signal of the signal under study, which is fed for subsequent changes in cutting modes to the CNC rack of the cutting machine. Since a change in the state of the machining process entails a change in the parameters of the acoustic emission signal,

This component of the cepstrum signal, represented by the peak of the function (FIG. 2), changes its parameters in accordance with the increase in wear of the cutting edge of the tool, the characteristics of the workability of the workpiece material, the presence of chipping and breaks of the cutting edge of the tool. Since the increase in tool wear characterizes the expansion of the acoustic emission spectrum

0 towards the low frequencies, the peak of the function of the cepstra along the time axis is mixed, ms to the left (Fig. 2b), whereas at the beginning of the cutting until the end of the burn-in of the cutting tool the peak of the cepstrum

5 is shifted to the right (Fig. 2a) as compared with the period of normal wear of the cutting edge (Fig. 2b). The state of breakage of the cutting edge of the tool is characterized by a sharp increase in the peak of the function immediately before chipping the cutting edge, which characterizes the stresses in the cutting wedge. At the moment of breakage, the peak of the cepstrum function disappears (Fig. 2d). Thus, the function of the cepstrum of the acoustic emission signal allows determining the state of the cutting tool during the cutting process.

PRI me R. For example, a DUNEGAN / ENDEVCO Р807В sensor can be used as a broadband piezoelectric transducer for acoustic emission 1. As an amplifier complex, you can use, for example, a broadband amplifier of high-frequency signals UZ-29, or a preamplifier being developed with an amplifier with a complex gain of 60 dB. The combination of bandpass filters 6.1 ... 6.N can be implemented, for example, on the basis of Chebyshev filters. The functions of block 7 FFT and block 8 of logarithm can be implemented on the basis of programmable computers, for example, you can use a computer like Electronics - 60 M. When

5 this, at the input of the computer, a device must be provided for interfacing unit 7 with a system for recording analog electrical signals characterizing the parameters of acoustic emission of the instrument.

Thus, the interface device is included in block 7 FFTs; its execution can be carried out on the basis of ADCs (analog-to-digital converters).

5 At the same time, the number of channels of the interface corresponds to the number of filters 6.N (in the case of parallel input of subbands of the recorded acoustic emission signal). The outputs of block 8 of logarithm in case of using the system in an automated machining process are connected to the CNC rack of a cutting machine

Fig. 2 shows the diagrams of the cepstrum of the acoustic emission signal, corresponding to the state of the cutting edge of the bite cutter, reflected by the cost characteristic Wear, bz Time, t, where hs is the amount of wear on a given face.

The experiments were carried out on the machine TPK-125 VM

Geometry of the turning turning tool: о.-у -8 °, the material of the cutting plate T15K6. The workpiece material, St, 45, diameter 50 mm, Spindle rotation frequency n 800 rpm; feed rate 5–8 mm / min; depth of cut t Oh, 3 mm. Cutting was carried out in the absence of a coolant cooling system (smzsochio-cooling technological medium).

The peak position of the cepstrum function (Fig. 2a) (ha 0, corresponding to the start of cutting) is taken as the reference. The stage of normal wear of the tool (Fig. 26) is characterized by a displacement along the abscissa from the reference position by A by 15%.

Upon reaching the maximum permissible wear (From 0.8-0.85 mm), the peak of the cepstrum is shifted by almost 60% towards the zero response of the system (Fig. 2b). The condition of the tool breakage (Fig. 2d) is characterized by a sharp increase in the peak of the cepstrum function just before chipping the cutting edge, at the moment of the break the peak of the cepstrum disappears. The advantage of the proposed method of controlling the state of the cutting tool compared to the known method is to increase the accuracy of controlling the breakage, the maximum allowable wear, the end of the burn-in time of the cutting tool 1.4 times in terms of automated production.

Claims (1)

The invention of the method of monitoring the state of the cutting tool, including the registration and analysis of the acoustic emission signal during the machining of the part with the tool, is made so that, in order to increase the accuracy of control, the analysis is performed by change) time characteristics of the cepstrum of the acoustic emission signal. I about 4J s but $ №2