RU2320457C2 - Method for evaluating state and position of cutting edges of one-blade, built-up multi-blade and axial tools - Google Patents

Abstract

FIELD: working materials by cutting in NC-machine tools and in automatic lines.

SUBSTANCE: method comprises steps of one-blade and multi-blade working, measuring instantaneous values of electric voltage at output of electric pickup; converting them to digital signal by means of analog-digital converter; comparing both signal one to other; in order to improve efficiency and reliability of monitoring process using as measuring converter high-frequency touch-free eddy-current pickup with power supply frequency of generator winding no less than 250 kHz at frequency of analog-digital converter no less than 100 kHZ and moving cutting edges of tool at fixed gap in range 0.1 - 5 mm and at speed 0.5 - 250 m/min before working and periodically during said working for storing levels of signals corresponding to value of gap between end of pickup and each cutting edge; according to percentage signal values of eddy-current pickup corresponding to each cutting edge evaluating their position, integrity, wear degree, axial and radial beatings.

EFFECT: enhanced efficiency and reliability of evaluation state and position of cutting edges.

3 cl, 8 dwg, 1 tbl

Description

Ensuring the reliability of the automatically performed cutting process on CNC machines and automatic lines using axial, as well as single-blade and multi-blade assembled carbide tools, is directly related to the efficiency and reliability of monitoring its condition, since failures of this type of equipment due to the fault of the tool account for more than 50% of the time forced downtime (see V.K. Starkov. Cutting. Stability and quality management in automated production. M: Mashinostroenie, 1989. - p.113-114).

Known methods for monitoring the state of the cutting tool in terms of thermopower (see V.K. Starkov. Cutting. Stability and quality management in automated production. M .: Mashinostroenie, 1989. - p.119-120), which allow you to control the amount of wear of the tools during cutting with pre-selected cutting conditions.

The disadvantage of these methods is that they only fix the amount of wear of the cutting edges, but do not provide the ability to control the time of their reliable operation, and also that they cannot be used to control the state and position of the cutting edges of a multi-blade assembly tool.

A known method of measuring the position and wear of the cutting edges of the tool using touch sensors (see V. M. Valkov. Control in the HAP. - L.: Engineering, Leningrad. Department., 1986. - p. 151). This control method has a number of significant drawbacks: for control, a machine stop is required, which reduces productivity; special, high-precision, expensive probe probes are required; at contact of the probe to exclude its breakdown, it is necessary to provide a force of not more than 0.15 kg; it is not possible to control a rotating or moving tool.

The closest method (prototype) for the same purpose is a method for monitoring the cutting edges of prefabricated multi-blade tools (see Description of the invention to the patent of the Russian Federation RU 2203778 C2 "Method for monitoring the condition of the cutting edges of prefabricated multi-blade tools" dated 02.06.2003), which provides for the process multi-blade processing measurement of thermopower of each cutting edge and comparing them with each other.

For reasons that impede the achievement of reliability and efficiency of monitoring the condition of the cutting edges of a multi-blade tool when using the known method, it relates to the fact that it does not allow to control a rotating or moving tool during processing.

The analysis of the prior art, including a search by patents and scientific and technical sources of information and identification of sources containing information about analogues of the claimed invention, allowed us to establish that the applicants did not find an analogue characterized by the features of the claimed invention, and the definition from the list of identified analogues of the prototype as the closest on the basis of the totality of the characteristics of the analogue, it was possible to identify the totality of the significant ny signs in the claimed object set forth in the claims.

Therefore, the claimed invention meets the requirement of "inventive step" under applicable law.

Figure 1 is a diagram illustrating the implementation of the control method for the example of an 8-tooth face mill with carbide cutting inserts.

The method is as follows. The high-frequency eddy current sensor 1 is installed outside the processing zone relative to the cutting edges 2 of the face mill 3 with a fixed gap S, selected in the range of 0.1 ... 5 mm. When the cutter rotates, the sensor transmits signals about the position of each cutting edge relative to the end of the sensor through the object communication device (USO), an analog-to-digital converter (ADC) to the microprocessor of the numerical control device (CNC) of the CNC machine. The magnitude of the signals is proportional to the gap between each cutting edge and the end of the sensor. Figure 2 shows the waveform of the output signal U for one revolution of the cutter, depending on the gap S between the vertices of the teeth of the cutter and the end face of the sensor.

The eddy current sensor 1 is made in a cylindrical body (4 mm in diameter), in which two coils are located - a generator and a measuring one. A high-frequency voltage of electric current with a frequency from 10 kilohertz to several megahertz is supplied to the generator coil. The electromagnetic field of this coil induces eddy currents in the conductive surface to be monitored, which affect the characteristics of the measuring coil, changing its complex resistance

Z = R + R _BH + iω (L + L _BH ),

where R is the intrinsic resistance of the measuring coil;

R _BH - additional resistance introduced into the measuring coil due to the interaction with the eddy current circuit;

i is the imaginary unit of a complex number;

ω is the frequency of the electric current;

L is the inductance of the measuring coil;

L _BH is the additional inductance introduced into the measuring coil by eddy current circuits.

Insertion resistance and inductance are calculated by the formulas:

R _BH = (ωμ) ² R _μ / [R _μ + (ωL _μ ) ² ];

L _BH = (ωμ) ² L _μ / [R _μ ² + (ωL _μ ) ² ],

where R _μ and L _μ - equivalent resistance and inductance of the eddy current circuit;

μ is the mutual induction coefficient of the equivalent eddy current circuit with the sensor measuring coil circuit.

The values of R _μ , L _μ and μ depend to a large extent on the electrical and less on the magnetic characteristics of the materials being monitored, in which eddy currents are induced, as well as the size of the sample, its quality and continuity. In relation to tool materials (high-speed steels, hard alloys, cermets, superhard materials, industrial diamonds) having various electrical and magnetic characteristics, such numerical characteristics have not been previously studied. The study of the suitability of these materials as applied to the eddy current method was carried out using eddy current sensors of the Bauman Moscow State Technical University. The research results are given in table. 1. The numerical values shown in the table correspond to the deviation of the oscilloscope beam in millivolts (mV). As can be seen from the table, the studied materials showed good controllability when using the eddy current method.

During processing, to determine the position and condition of the cutting edges, it is enough to only move the cutting tool with the previously set gap S parallel to the end of the sensor, which will give signals about the current state and position of each cutting edge (see figure 1). The difference in the levels of the initial and current signals is used to estimate the wear of the cutting edges. If the maximum permissible level of wear of the cutting edges is exceeded, the control program of the CNC machine is given a command to automatically change the tool, and in case of an emergency (catastrophic wear, chips, chipping, breakage), a command is sent to emergency stop the machine and the alarm device (US) is turned on .

To determine the position of the cutting edges 2 and the amount of wear of the tool 3 (for example, an end mill) relative to three mutually perpendicular coordinate axes, one sensor 1 is installed on each axis (Fig. 3). The amount of wear will be proportional to the difference between the values of the current signals and the signals before processing.

To increase the measurement accuracy when monitoring an axial tool along the horizontal axes X, Y and Z, two diametrically opposite sensors (D ₁ , D ₂ along the X axis, D ₃ , D ₄ along the Y axis, D ₅ and D ₆ along the Z axis) included in the differential circuit (Fig. 5). According to this scheme, it is possible to automatically control during processing the wear, runout, integrity of a large group of tools (face mills, reamers, countersinks, drills, boring mandrels).

Figure 6 shows the control circuit of the sensor 1 turning tools in automatic mode. Monitoring the position and wear of the tool is especially important before the final (finishing) pass. This allows you to increase productivity, processing accuracy and eliminate rejects due to the timely automatic introduction of correction in the control program.

Figure 7 shows the control circuit of the sensor 1 of the cutting edges 2 of the boring mandrel 3.

On Fig is a diagram of the control of wear and runout of an axial tool (countersinks, reamers, drills).

Thus, the above information indicates the fulfillment of the following set of conditions when using the claimed invention:

the tool that performs the claimed invention, when it is implemented, is intended for use in metalworking for automatic or manual control of the condition and position of the cutting edges of single-blade and multi-blade tools, on the basis of which automatic control of the processing process is performed;

for the claimed invention in the form as described in the independent clause of the claims below, the possibility of its implementation using the means and methods described above in the application is confirmed;

means embodying the claimed invention, when implemented, is able to ensure the achievement of the technical result perceived by the applicants.

Therefore, the claimed invention meets the requirement of "industrial applicability" under applicable law.

INFORMATION SOURCES

1. Eddy current transducer. USSR author's certificate No. 568007 of 06/20/1977.

2. Valkov V.M. Control in the gap. - L .: Mechanical engineering. Leningra. Dep., 1986. - p. 232.

Table 1. Controllability of hard alloys, carbon, alloy and high-speed steels Signal value, mV Clearance mm Hard alloy Become T15K6 T5K10 VK6 Steel 45 9XC 25H6VF P18 P6M5 0 59 55 57 43 44 43 42 42 0,085 53 51 52 38 40 38 38 38 0.16 47 44 46 34 35 33 33 33 0.235 41 39 40 thirty 32 29th 29th 29th 0.31 34 29th 34 24 29th 24 24 25 0.39 28 25 26 21 23 22 21 21 0.55 eighteen 16 17 fifteen 17 16 fourteen fourteen

Claims (3)

1. A method for monitoring the condition of the cutting edges of single-blade, prefabricated multi-blade and axial tools during single-blade and multi-blade processing, including measuring the instantaneous voltage values produced by the measuring transducer in the form of an electric sensor, converting them into a digital signal using an analog-to-digital converter and comparing them among themselves, characterized in that a high-frequency non-contact vortex installed outside the processing zone is used as an electric sensor a current sensor with a supply frequency of the generator coil of at least 250 kHz at a sampling frequency of an analog-to-digital converter of at least 100 kHz, while before processing and periodically during processing with a gap relative to the end of the eddy current sensor in the range of 0.1 ... 5 mm at a speed of 0.5 ... 250 m / min by the cutting edges of the instrument with storing signal levels corresponding to the size of the gap between its end and each cutting edge, and according to the relative values of the eddy current sensor signal, corresponds to they each cutting edge, carried out to assess their situation, integrity, wear values of axial and radial runout. 2. The method according to claim 1, characterized in that to determine the position of the tool cutting edges in the direction of three mutually perpendicular coordinate axes, one eddy current sensor is used, the axis of each of which is parallel to the corresponding coordinate axis. 3. The method according to claim 1, characterized in that, in the direction of each of the coordinate axes, two diametrically located sensors are included, which are included in order to increase the sensitivity according to a differential circuit.

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