RU2636209C1 - Method of cooling control of high-speed motor-spindle of metal-cutting machine - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: method includes an adjustable supply of refrigerant to the stator of the motor-spindle and to its front and rear bearing supports while simultaneously measuring their temperature. The refrigerant is supplied with the condition that the temperature of the motor-spindle stator and its bearing supports are equal to a predetermined design value.EFFECT: reducing the vibration of the motor-spindle and increasing its service life.1 cl

Description

The invention relates to mechanical engineering, in particular to the management of high-speed motor spindles of machine tools.

One of the main directions of development of metal cutting machines is the widespread use of mechatronic modules that combine energy, information and control functions in a single structural unit, which provides a coordinated choice of parameters of individual subsystems subordinate to a single task - to achieve the required operational characteristics. Motor spindles most fully illustrate the main problems of mechatronic systems of machine tools and are the most important nodes that determine the quality of equipment.

The prior art methods for controlling high-speed motor spindles of metal cutting machines, including controlled refrigerant supply (V. V. Bushuev and others. High-speed motor spindles of the drives of the main movement of metal cutting machines, Vestnik MGTU Stankin No. 3, 2011, http: // stanoks.com/index.php?catid=49:articles&id=1502:2014-01-28-09-36-49&Itemid=192&option=com_content&view=article).

The disadvantages of analogues include the imbalance of control and the uneven cooling of the stator and bearing bearings, which limit speed and cause a tendency to vibrations in the motor spindle, which leads to a low resource and overall performance of the unit.

The closest technical solution to the claimed object - the prototype - is a method of controlling the cooling of a high-speed motor-spindle of a metal cutting machine, which includes an adjustable supply of refrigerant to the stator, front and rear bearing bearings and simultaneous measurement of their temperature and vibration level (RF Patent No. 2509627, IPC V23V 19 / 02, published on March 20, 2014).

The disadvantages of the prototype include the imbalance of control and uneven cooling of the stator and bearing bearings, limiting speed and causing a tendency to occur in the motor spindle of vibrations, which leads to a low resource and efficiency of the spindle unit (SHU) as a whole.

The objective of the invention is the balanced cooling of the stator and bearing bearings of the motor spindle, which minimizes the vibration of the latter.

The technical result is an increase in the efficiency of a high-speed motor-spindle of a metal cutting machine by increasing its speed and service life, due to thermal and vibration stability.

The problem is solved, and the claimed technical result is achieved by the fact that in the method of controlling the cooling of a high-speed motor-spindle of a metal cutting machine, which includes an adjustable supply of refrigerant to the stator, front and rear bearing bearings and simultaneous measurement of their temperature and vibration level, the supply of refrigerant is carried out so that :

, где

where

T _s , T _1,2 - current measured temperatures of the stator, front and rear spindle bearings;

- приведенная начальная жесткость ШУ при температуре 20°С;

- reduced initial stiffness of ШУ at a temperature of 20 ° С;

k _T = k- а ₁ ζ _T1 ΔT ₁ - а ₂ ζ _T2 ΔT ₂ - reduced stiffness of the spindle unit at measured temperatures T _1,2 ;

a is the distance between the spindle bearings;

b - the length of the console part of the spindle from its end to the front support;

E is the elastic modulus of the spindle material;

J _{a, b} is the geometric moment of inertia (section) of the support and cantilever parts of the spindle;

j ₁ , j ₂ - the stiffness of the front and rear bearings of the spindle;

m is the reduced mass of the spindle;

f _t = r _t / 2π is the frequency of the natural oscillations of the spindle (at measured temperatures T _1,2 );

- приведенное смещение шпинделя (при измеренных температурах Т_1,2);

- reduced spindle displacement (at measured temperatures T _1.2 );

and ₁ = [ a + b) ² / a2 , a ₂ = b ² / a ² - dimensionless coefficients characterizing the design parameters of the control unit;

ζT _1,2 = [(β _kp -β _vn ) d _vn -0,6β _kp d _vn -β _to d _k ] is the relative change in the initial linear deformation (clearance - interference) in the support of the shaft (front, rear) when changing it temperature 1 ° C;

β _kp , β _int , β _k - linear expansion coefficients of the housing, the inner ring of the bearing and rolling elements of the bearing;

d _int, d _nk , d _to - the inner diameter of the outer ring of the bearing, the outer diameter of the bearing housing, the diameter of the rolling elements of the bearing.

The basis of the claimed method is the principle of ensuring maximum rigidity of the spindle assembly, which guarantees a minimum level of vibrations and, consequently, an increase in speed, stability, efficiency and service life of a high-speed motor spindle for metal cutting machines.

It is known that the oscillation of the spindle assembly is described by the equation:

which, transforming to

allows you to get a general solution of spindle oscillation:

It is indicated here:

2g = v / m, p ² = k / m, where m is the reduced mass, v is the reduced characteristic of damping properties, k is the reduced hardness, and ₀ is the initial amplitude of natural vibrations, F is the periodically changing external influence, ω is the circular frequency , t is time;

- динамический коэффициент, характеризует изменение динамических смещений относительно статических;

- dynamic coefficient, characterizes the change in dynamic displacements relative to static;

f = p / 2π is the spindle natural frequency (without heating).

The reduced hardness k is determined by the expression:

a is the distance between the spindle bearings;

b - the distance of the cantilever part: from the front support to the spindle end;

E is the elastic modulus of the spindle material;

J _{a, b} is the geometric moment of inertia (section) of the support and cantilever parts of the spindle;

j _1,2 - rigidity of the spindle bearings.

, внутриобъемный

перепад температур, перепад температуры опоры и корпуса детали ΔT, которые позволяют получить значение максимальной жесткости k_T при увеличении температуры ШУ.Under the well-known laws of thermal and power loads on ШУ - (Q and Р) and using thermoelastic models, the following values are determined: thermal strain value δ _T , absolute temperature excess in the part of ШУ

volumetric

temperature difference, temperature difference of the support and part housing ΔT, which allow us to obtain the maximum stiffness value k _T with increasing temperature of the ШУ.

Regulation or stabilization of temperature in the housing is determined by the uniform distribution of temperature in the volume of the control unit and the minimum excess absolute temperature. It was established that there are criteria that determine the degree of temperature uniformity in the parts of the control unit both in space and in time. The Bi number (Bio) is a criterion for the uniform distribution of the temperature of the part under the condition Bi≤0.1. For SH, the number Bi (Bio), as a rule, is always Bi≤0.1.

The criterion Bi = αL (d) / λ depends and is determined by the heat transfer coefficient (W / m deg), the thermal conductivity coefficient λ (W / m deg) and the size L (d) (m). In relation to metal-cutting machines, the values of α for free convection vary from 2 to 15, and the values of λ for steels from 40 to 50, for cast irons from 50 to 65.

Then the values of the ranges of the Biot criterion can be determined: for parts made of steel Bi = (0.04-0.375) L, for parts made of cast iron Bi = (0.031-0.3) L. Therefore, the size L (d) of parts for which the temperature field can be considered relatively uniform will be within the limits: for steels - less than 2.25 ÷ 0.267 m, for cast irons - less than 3.32 ÷ 0.33 m.

Then, the change in the initial deformation in the bearing support is determined by the expression [p. 225, Details and mechanisms of metal-cutting machines. / Edited by D.N. Reshetova - M.: Mechanical Engineering. 1972. - 520 p.]:

We transform (5) to the form:

There ζ _T = [(β -β _{corolla kn)} d _ext d _ext -0,6β _kn -β _to d _k] - the relative change in the initial linear deformation (gap - preload) in the support SHU when changing its temperature by 1 ° C, where β _kp , β _int , β _k - linear expansion coefficients of the housing, the inner ring of the bearing and rolling elements; d _int , d _nk , d _to - the inner diameter of the outer ring of the bearing, the outer diameter of the bearing housing, the diameter of the rolling elements; T _m , ΔT _p - excess oil and bearing temperatures.

Then substituting (6) in (4) and, after performing the transformation, we obtain the value of reduced stiffness in (1):

Here j _1,2 = 1 / (δ _01,02 -δ _{T1, T2} ) = j _01,02 / (1-δ _{T1, T2} j _01,02 )

- начальная деформация передней и задней опор ШУ;Where

- the initial deformation of the front and rear supports of the ШУ;

or, taking into account the initial rigidity k (4) and transforming (7), we obtain:

k _T = ka ₁ δ _T1 -a ₂ δ _T2 ,

and substituting (6) we have:

, где ζ_Т1, ζ_T2 - относительное изменение начальной линейной деформации (зазор - натяга) и избыточные температуры ΔT₁, ΔТ₂ в опорах 1,2 ШУ.here

, where ζ _T1 , ζ _T2 is the relative change in the initial linear deformation (clearance - interference) and excess temperatures ΔT ₁ , ΔT ₂ in the supports of 1.2 ШУ.

Therefore, the natural frequency of the SHU (with heating) will be equal to:

From (9) we obtain the dependence of the excess temperature and the natural frequency of the spindle (with heating):

Since ΔТ _c = Т _с -20 ° С and ΔT _1,2 - = Т _1,2 -20 ° С, where Т _с , Т _1,2 are the current measured temperatures of the stator, front and rear spindle bearings, respectively, we obtain

Taking into account (11), knowing the measured characteristic of the natural frequency, we determine the required cooling temperature that provides the maximum rigidity of the motor spindle, and, therefore, the speed, stability, efficiency and operating life of the control gear.

Thus, the claimed combination of essential features set forth in the claims makes it possible to balance the cooling of the stator and bearing bearings of the motor spindle to minimize vibration of the latter.

The analysis of the claimed technical solution for compliance with the conditions of patentability showed that the characteristics indicated in the independent claim are essential and interrelated with each other with the formation of a stable, unknown at the priority date, level of the set of necessary features sufficient to obtain the required synergistic (over-total) technical result.

The above information indicates the following conditions are met when using the claimed technical solution:

- an object embodying the claimed technical solution, when implemented, relates to mechanical engineering, in particular to high-speed motor spindles for metal cutting machines;

- for the claimed object in the form described in the independent claim, the possibility of its implementation using the methods and methods described above or known from the prior art on the priority date has been confirmed;

- the object embodying the claimed technical solution, when implemented, is able to ensure the achievement of the technical result perceived by the applicant.

Therefore, the claimed subject matter meets the requirements of the patentability conditions of “novelty”, “inventive step” and “industrial applicability” under applicable law.

Claims (18)

A method of controlling the cooling of a high-speed motor-spindle of a metal-cutting machine, including an adjustable supply of refrigerant to the stator and to its front and rear bearings with simultaneous measurement of their temperature, characterized in that the refrigerant is supplied with the condition T _c = T _1,2 = [k- (2π) ² mf _T ² ] / ( a ₁ ζ _{T 1} + a ₂ ζ _{T 2} ) + 20 ° С, where T _c , T _1,2 - current measured temperatures of the stator, front and rear spindle bearings, respectively;

- reduced initial stiffness of the spindle unit at a temperature of 20 ° C; a is the distance between the spindle bearings; b - length of the cantilevered portion of the spindle from its front end to a support; E is the elastic modulus of the spindle material; Ja, b is the geometric moment of inertia of the cross-section of the support and cantilever parts of the spindle; j ₁ , j ₂ - the stiffness of the front and rear bearings of the spindle; m is the reduced mass of the spindle; f _T = p _T / 2π is the spindle eigenfrequency at measured temperatures T _1.2 ;

- reduced spindle displacement at measured temperatures T _1.2 ; k _T = k - a ₁ ζ _{T 1} ΔT ₁ - a ₂ ζ _{T 2} ΔT ₂ - reduced stiffness of the spindle unit at measured temperatures T _1,2 ; ΔT _1.2 = T _1.2 -20 ° C; and ₁ = ( a + b ) ² / a ² , and ₂ = b ² / a ² - dimensionless coefficients characterizing the design parameters of the spindle unit; ζ _{T 1,2} = [(β _kp - β _vn ) d _vn - 0.6β _kp d _vn - β _to d _k ] - the relative change in the initial linear deformation in the front and rear supports of the spindle unit when their temperature changes by 1 ° C ; β _kp , β _int , β _k - linear expansion coefficients of the housing, the inner ring of the bearing and rolling elements of the bearing bearings; d _int , d _nk , d _to - the inner diameter of the outer ring of the bearing, the outer diameter of the bearing housing, the diameter of the rolling elements of the bearing bearings.