RU2585917C1 - Method of determining temperature in metal cutting zone - Google Patents

Abstract

FIELD: metallurgy; measurement technology.

SUBSTANCE: invention relates to metal forming and may be used when measuring temperature in cutting zone. Main machine electric drive power consumed for process of cutting is determined by signals of current and voltage sensors. Signal proportional to main power of electric drive of machine, passed through dynamic link, simulating dynamic properties of thermal model of cutting process and converted to type of transfer function, binding signals which characterise said power and heating of part of chips deformed in cutting. Sum of signal proportional to temperature of cooling medium, and output signal of said dynamic unit determines temperature in cutting zone.

EFFECT: invention usage allows to increase efficiency and providing high accuracy of measuring temperature in cutting zone using already available information system of machine.

1 cl, 1 dwg

Description

The invention relates to the field of engineering, in particular to the field of measuring temperatures in the cutting zone during blade processing of metals.

A known method of measuring the temperature in the cutting zone using the built-in thermocouple installed in the workpiece material [patent for invention RU No. 2445588 C1, IPC G01K 7/02, 03/20/2012], in which the hot junction of the thermocouples are rolled in shape in the form of a plate to a thickness much smaller than the thickness of the removed chips, they are buried into the part to the thickness of the plate and welded to the part so that at the time of cutting with a milling cutter, the hot junction of the thermocouple becomes a chip element and heats up to the maximum temperature, which is realized in chip not slide on the front surface of the instrument, the thermal wave temperature recorded with a sampling frequency of at least 10,000 Hz, including repeatedly recorded the thermocouple hot junction temperature at the time of its cutting element until the moment of its complete destruction.

Also known is a method of determining the magnitude of the temperature field, the temperature in the cutting zone and the nature of its distribution in the material being processed using an artificial thermocouple [patent application RU No. 2005110736 A, IPC G01K 7/04, 10/20/2006], which consists in its oscillography the output voltage, in which during cutting the tool is continuously fed until it touches the thermocouple installed in the material being processed, the preliminary value of the temperature field is determined from the oscillogram, which is then increased by Dimensions junction thermocouple and approximates the temperature distribution in the treated material character function, and for determining the temperature in the cutting zone function is extrapolated from the tool contact point of the thermocouple to the point in the transition thermoelectrodes junction.

The disadvantages of such methods are:

- the need to embed a thermocouple in the body of the part, which makes it impossible to carry out continuous temperature control during metal cutting during the shaping of the surface of the part;

- the impossibility of using these methods in the system of automatic regulation of cutting conditions.

A known method of non-contact determination of temperature in the cutting zone during machining [patent for invention RU No. 2398659 C1, IPC B23B 25/06, G01N 3/58, 09/10/2010], which consists in the fact that the cutting zone of the part is isolated from the external air, and using a gas analyzer, the probe of which is placed near the cutting zone, measure the concentration of carbon-containing gases formed in the cutting zone, the value of which is used to judge the temperature of the cutting process.

The disadvantage of this method is the difficulty of its application in the process of cutting metal during the shaping of the surface of the part, since it requires the installation of additional special structural devices.

Closest to the proposed method is a method for determining the temperature of contact interaction during friction and cutting [patent for invention RU No. 2124707 C1, IPC G01K 7/02, G01K 13/04 dated 01/10/1999], which allows to measure the temperature in the metal cutting zone, using electrical parameters characterizing the process of metal cutting.

The disadvantages of this method are:

- the need for constructive refinement of the machine in order to isolate the thermocouple elements;

- the temperature is measured discretely by switching resistors, which does not allow continuous measurement of the temperature in the metal cutting zone during the formation of the surface of the part.

The objective of the invention is the expansion of the functionality of the method for determining the temperature in the zone of metal cutting, in particular, to build a system of automatic control of cutting conditions in a production environment.

The technical result of the invention:

- the ability to measure temperature in the zone of metal cutting during the shaping of the surface of the part;

- ensuring speed, continuity, high accuracy of temperature measurement using the existing information system of the machine without installing additional structural devices.

The problem is solved, and the technical result is achieved by the fact that in the method for determining the temperature in the metal cutting zone during shaping of the surface of the part, including measuring the magnitude of the electrical signals associated with the parameters characterizing the metal cutting process, according to the invention, the current and voltage of the main electric drive of the machine are measured and determined power of the aforementioned electric drive, form a dynamic link with a transfer function in the form of:

W _PR (p) = τ (p) / N _res (p) = K / (T · p + 1),

where K = 1 / F _T · K _T is the transmission coefficient of the dynamic link,

T = s · m / F _T · K _T - time constant of the dynamic link,

N _rez - the power of the main drive spent on the cutting process,

C is the specific heat of deformable during the cutting part of the chip,

m is the mass of the chip being deformed during the cutting process,

τ is the temperature difference of the part of the chip deformable during the cutting process and the cooling medium,

τ = θ-θ _OS ,

θ - temperature deformable during the cutting part of the chip, equal to the temperature in the cutting zone of the part,

θ _OS - the temperature of the cooling medium,

F _T - heat transfer area deformable during the cutting part of the chip,

K _T - heat transfer coefficient deformable during the cutting part of the chip,

and the temperature in the metal cutting zone is determined by applying a power signal of the aforementioned electric drive to the generated dynamic link and summing the output signal of the said link with a signal proportional to the temperature of the cooling medium.

The method of determining the temperature in the metal cutting zone is implemented as follows.

1. Make a model of the relationship between engine power and temperature in the cutting zone (thermal model of the cutting process). The temperature in the cutting zone is determined by overheating of the heated body. The heated body is a part of the chip deformable during cutting. Overheating of the heated body is the temperature difference of the heated body and the cooling medium. The model is composed on the basis of the equation of thermal equilibrium, converted into the transfer function of the connection between the power of the electric drive of the main movement and the overheating of the heated body.

2. Determine the power of the main drive electric drive by the product of the current and the motor voltage. For this, standard equipment devices are used: a current sensor and a voltage sensor, or a current sensor and a tachogenerator, which allow continuous measurement of the power of the main drive electric drive. Measurement accuracy is characterized by a class of accuracy of devices.

3. A signal proportional to the power of the main drive electric drive is passed through a dynamic link based on a thermal model of the cutting process. Receive a signal proportional to the overheating of the heated body.

4. A signal proportional to the overheating of the heated body is summed with a signal proportional to the temperature of the cooling medium. This amount is a characteristic of the temperature in the metal cutting zone.

High speed measurement of temperature in the metal cutting zone is ensured by the fact that standard equipment devices directly record the response of the main drive to a change in cutting conditions.

Continuous measurement of the cutting temperature, high accuracy of its measurement, high speed and the absence of the need to change the design of the machine and the use of constructive devices for measuring the temperature in the cutting zone make it possible to build a system for automatically controlling the cutting conditions using the method for determining the temperature in the cutting zone of metal from the energy parameters of the main electric drive machine movements and its application on an industrial scale.

The invention is illustrated by the drawing, which shows a flowchart of a method for determining the temperature in the zone of metal cutting.

The conversion of power to cutting temperature is as follows.

The electric drive of the main movement of the machine 1 creates the engine torque M _LW and the engine speed ω _LW , which are converted through the reducer 2 at the moment of the spindle M _ШП and the speed of rotation of the spindle of the machine ω _ШП . The product of M _PS by ω _PS is the power N _Res consumed by the cutting process 3. This power enters the heated body. In accordance with the equation of thermal equilibrium (1), the power is converted to overheating of the heated body.

where N _rez · dt is the heat entering the heated body;

N _rez - power spent on overheating of the heated body;

t is the current time;

c · m · dτ is the heat entering the heated body;

C is the specific heat of the heated body;

m is the mass of the heated body;

τ - overheating of the heated body;

τ = θ-θ _os ;

θ is the temperature in the zone of metal cutting;

θ _OS - the temperature of the cooling medium;

F _T · K _T · τ · dt - heat entering the cooling medium from the heated body;

F _T is the heat transfer area of the heated body;

K _T is the heat transfer coefficient of the heated body;

Based on equation (1), the transfer function of the cutting power and the overheating of the heated body is compiled:

where K = 1 / F _T · K _T is the transfer coefficient of the dynamic link model;

T = c · m / F _T · K _T is the time constant of the dynamic link;

p is the Laplace operator.

The temperature in the cutting zone is the sum of the temperature of the cooling medium θ _os and the overheating of the heated body τ. The circuit is implemented by the adder 4.

The determination of temperature in the zone of metal cutting is as follows. In the process of forming the surface of the part, the energy state of the electric drive is characterized by current I and voltage U. Voltage sensor 5 and current sensor 6 determine the voltage and current of the motor, respectively. Using the multiplication unit 7, the output signals of the current sensors U _ДТ and voltage U _{ДН are} multiplied, forming an analog of the power spent on the cutting process U _N. The voltage signal U _{N is} passed through a dynamic link W _PR (p) 8, which is a model for converting cutting power into overheating of a heated body, according to equation (1).

The result is a voltage U _τ proportional to the overheating of the heated body τ. This voltage is summed by the adder 9 with a voltage U _θos proportional to the voltage of the cooling medium. At the output of the adder, a voltage U _{θ is} generated proportional to the temperature in the metal cutting zone.

The voltage U _θ can be used in the feedback of the automatic control system of cutting conditions.

An example of a specific implementation of the method

When cutting KhN77TYuR material with a VK6M cutter, the power spent on the cutting process, N _res = 7000 watts. When the motor voltage U = 440 V, the current consumption I = 15.9 A. The voltage sensor 5 converts the motor voltage U = 440 V to U _DN = 5 V. Current sensor 6 converts the current I = 15.9 A to U _DT = 1 V The product of the signals from the current and voltage sensors is carried out by the multiplication unit 7 and is U _N = 5 B, which is proportional to the power N _rez = 7000 W. When this signal passes through the W _PR 8 link, a voltage U _τ = 3 V is created, which is proportional to the overheating of the heated body, which is τ = 700 ° C. The voltage U _θос = 0.086 V is proportional to it, proportional to the temperature of the cooling medium. The sum of the stresses U _τ = 3 B and U _θс = 0.086 B is proportional to the temperature in the cutting zone θ = 720 ° С.

So, the claimed invention allows to measure the temperature in the metal cutting zone during the shaping of the surface of the part, provides speed, continuity, high accuracy of temperature measurement using the existing information system of the machine without installing additional structural devices, allows you to solve the problem of constructing a system for automatic control of cutting conditions in production conditions.

Claims (1)

A method for determining the temperature in the metal cutting zone during shaping of the surface of the part, including measuring the magnitude of electrical signals associated with parameters characterizing the metal cutting process, characterized in that the current and voltage of the main electric drive of the machine are measured and the power of the said electric drive is determined, a dynamic link with a transfer function is formed as:
W _PR (p) = τ (p) / N _rez (p) = K / (T p + 1),
where K = 1 / F _T K _T is the transmission coefficient of the dynamic link,
T = c m / F _T K _T - time constant of the dynamic link,
N _pez is the power of the main electric drive spent on the cutting process,
C is the specific heat of deformable during the cutting part of the chip,
m is the mass of the chip being deformed during the cutting process,
τ is the overheating of the part of the chip deformable during cutting,
τ = θ-θ _OS ,
θ - temperature deformable during the cutting part of the chip, equal to the temperature in the cutting zone of the part,
θ _OS - the temperature of the cooling medium,
F _T - heat transfer area deformable during the cutting part of the chip,
K _T is the heat transfer coefficient of the part of the chip deformable during cutting,
and the temperature in the metal cutting zone is determined by applying a power signal of the aforementioned electric drive to the generated dynamic link and summing the output signal of the said link with a signal proportional to the temperature of the cooling medium.

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