SU1210994A1 - Method of monitoring a cutting process - Google Patents

Description

The invention relates to the structure, in particular to methods for controlling the cutting process, ensuring the efficiency of machining.

The purpose of the invention is improving the accuracy of measurements and expanding the limits of control of cutting modes,

During mechanical processing, acoustic emission signals are recorded that amplitude is divided into 128 128 quantization levels with a width of each level of k 80 mV, maxima in the N f (A) curve are distinguished, where N is the number of pulses of acoustic emission signals; A - the magnitude of the amplitude of the pulses, change the conditions of machining, for example, by varying the cutting conditions, the pairs of instrumental - processed materials, etc. „identify these maxima for friction destruction, plastic deformation of the instrumental and the materials being processed, the process itself; ssa cut.

The method is based on the fact that in the process of cutting, acoustic emission signals (AE) are generated. At the same time, several parallel-sequential processes of different energy intensity take place in the shaping zone: plastic deformation, three processes, destruction of the material being processed and tool materials. Sources of AE signals during plastic deformation are dislocation movement, twinning processes, and during friction - processes of microscopic irregularities impact, adhesion seizure 5 at destruction – nucleation, growth of microcracks “their fusion into macrocracks along shear planes.

Therefore, each process is characterized by its mathematical expectation of the statistical amplitude I J of the generated AE signals,

To register the sources of AE signals, the entire range of amplitudes: divided by 128 levels of quantization. This number of quantization levels is explained by the minimum sample of a random amplitude from the general population of events. The width of each quantization level (channel) should be 80 mV. With a decrease

five

0

3

0

five

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In the case of the width of the quantization level, the transition from the macro level to the micro level occurs when studying the cutting process. For example, at k 80 mV, one source close to the Normal distribution is recorded, which in this case characterizes the cutting process itself, and the area under the curve represents all the energy of AE signals generated in the cutting zone. At k 40 mV, the channels are narrowed, t, e, as if the resolution amplitude scale increases by a factor of 2. In this case, three sources of AE signals are clearly visible: friction, plastic deformation, and destruction. And at k 10 mV, the process of friction in the cutting zone can be divided into three microprocesses: friction of asperities on microroughnesses, plastic deformation of asperities, reduction of asperities. At k 10 mV, it is possible to identify the processes proceeding at micro levels. However, modern equipment, for example, IA-1024-95, allows recording only signals with a channel width of 10 mV k: 80 mV.

Subsequently, the identification of the registered sources is carried out by changing the machining conditions, for example, by varying the cutting modes of the tool pairs — the materials being processed, etc.

Example.

I The studies were carried out on a vertical milling machine FN 20 ZEBRAK (Czechoslovakia).

Four-teeth cutters with a diameter of 12 mm with a tilt angle of teeth ø 40 with a tapered shank were used as a cutting tool. The cutting part was made of high-speed steel R6M5K5.

Geometry sharpening tools:

y- (f 45 °;

(10-15

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S

U- 14, L: 3, J f

R 1 .mm; D 0 °.

The main part of the tests was carried out on samples from ZOHGSA steel under the following cutting conditions: V 0.03-1.2 m / s; S 8 - 80 mm / min; , 01-5 f-iMj B 5 - 25 mm .. A piezoelectric sensor was attached to the samples. In this case, it was assumed that the signals A 9 generated as a result of the processes taking place in the processed material are recorded.

rial, since the AE signals generated in the instrument are significantly weakened when the interface between the instrument and the material being processed passes

A standard set of acoustic emission equipment consisting of a piezoelectric sensor, a preamplifier, a filter unit, a main amplifier, a signal processing unit, a pulse analyzer M-1024-95, and a digitizer were used as measuring equipment.

When conducting experiments at n 128, k 20 mV, sources are recorded that characterize the processes of friction, plastic deformation of the discharge of the material being processed. FIG. I shows the change in the nature of the Nf (A) curve as a function of the change in the milling speed. At low cutting speeds, one source is recorded (Fig. 1, curve 1). Another source appears with increasing cutting speed (Fig., Curve 2). At high cutting speeds, three sources are recorded (Fig. 1, curve 3 AE signals. In this case, both the mode of the sources and the number of pulses that characterize the sources change. With increasing feed and depth of cut, the tendency of the N f (A) curve to change has the same pattern. With increasing plastic properties of the materials being processed, the third source appears on more High cutting speeds: Based on experimental data, it can be assumed that the third source describes the process of destruction of the material being processed.

In this case, AE signals are generated. Due to the formation, growth and merging of microcracks into main cracks along shear planes. When the cutting depth t decreases from 0.5 to 0.01 mm, sources 3 and 2 disappear. Only source 1 remains. After the coolant is introduced into the cutting zone, a decrease in the number of pulses from this source is observed by a factor of 5-10. If we assume that source 1 characterizes the processes of friction of the instrument with the material being processed, and the sources of voltages (HV) are the same 9-i

giving asperities and adhesive setting, then the effect of coolant on a significant reduction in the number of pulses from source 1 becomes. In FIG. Figure 2 shows the effect of coolant on the distribution curve of N f (A) AE signals. Coolant, on the one hand, due to the lubricating effect reduces the coefficient of friction

tool and processing material, as evidenced by the decrease in the number of pulses of the source of friction () FIG. 2), on the other hand, by reducing the temperature of the cutting zone, it increases the work required for plastic deformation and destruction (2 and 3, Fig. 2) of the material being processed. FIG. Figure 3 shows the change in the N f (A) curve when processing three materials of different physical and mechanical properties on the same cutting conditions.

Steel is selected as material

Zohgsa. Three sources crawled: 1 — friction; 2 - plastic deformation; 3 - destruction (curve 2). For copper (curve 1), only friction is characteristic for the same cutting conditions.

and plastic deformation. The source of destruction does not manifest.

Conversely, a brittle material (70 g) is characterized by weak plastic deformation and intense brittle fracture processes (curve 3).

Consequently, the recorded sources can be characterized by the mode of distributions and the area of the source (total number of pulses). At the same time, according to energy intensity, the sources are arranged in the following order: friction, plastic deformation, destruction. Sources of friction include the processes of micro-roughness and adhesion seizure, the sources of plastic deformation — dislocation movement, the sources of fracture — the growth of cracks.

Amplitude analysis of AE signals allows identifying sources of AE signals when processing materials at both macro and micro levels (the macro level is friction, plastic deformation, destruction; the micro level is the separation, i.e., the process of friction on the same components ).

The graphical dependence of Nf (A), a section with clearly pronounced extremes is identified and the dependence of the area change under the indicated sections on the parameters of the cutting process is established, the optimal parameters are those that correspond to the minimum. values of the area under these sites.

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15 10 5

20 30 0 50 BO 70 A FIG.

20 30 40 50 BO 70 A fi & 3

Editor L. Pchelinska

Compiled by G. Barinov

Tehred L. Mikesh Proofreader L. Pilipenko

Order 583/16 Circulation 1000 Subscription,

VNIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5

Branch PPP Patent, Uzhgorod, st. Project, 4

Claims (1)

METHOD OF MONITORING THE CUTTING PROCESS, based on the registration of vibroacoustic signals, which consists in the fact that, in order to increase the control accuracy, acoustic emission signals are recorded during machining, and a graphical dependence N = f (A) is constructed, where N is the number of pulses of acoustic emission signals; And the magnitude of the amplitude of the pulses, in this case, select areas with clearly expressed extrema and establish the dependence of the change in the area under the indicated areas on the parameters of the cutting process, and take optimal parameters _{t to} which correspond to the minimum values of the area under these sections. 5210994