KR20090121001A - A rigidity measurement of the main spindle which uses magnetic force - Google Patents

Abstract

PURPOSE: A rigidity measuring device of a main shaft using magnetic force is provided to measure the change of rigidity due to the change of contact rate during the rotation of a main shaft using induction effect and repulsive power effect of a magnet. CONSTITUTION: A rigidity measuring device of a main shaft using magnetic force comprises a fixed block(10), a force measuring device(11), and a bracket. The force measuring device is formed on the fixed block. The bracket is installed on the top of the force measuring device. A magnet generating force pulling a main spindle system(14) is formed on the upper side of the bracket.

Description

A rigidity measurement of the main spindle which uses magnetic force

The present invention relates to a stiffness measuring device of the spindle that can consider the effect of the contact rate change due to the centrifugal force when the spindle system rotates at high speed by using the magnet suction, repulsive force effect and the magnetic induction effect of the ferromagnetic material.

The machine tool industry is a core infrastructure that leads the development of the entire machine industry, and is an essential area that affects product quality improvement, productivity improvement and technology development in related industries.

Recently, the direction of machine tool technology development is aimed at high precision, high speed, and high performance, and research of various tooling technologies is required to satisfy these needs during high-speed cutting using a machining center.

Tooling in the machining center deals with the interface between the machine body and the cutting tool, which is applied to high speed, high precision, intelligent, multifunctional and unmanned.

For high-speed cutting, a good spindle structure through vibration reduction should be designed to increase the rigidity of the tooling system, and the problem of heat suppression by high-speed rotational friction should be solved.

Problems with tooling systems for high speed machining include the problem of tool holder shank geometry and the clamping of the spindle and the tool.

In other words, how precisely the tool is attached to the machine tool and how long can it be maintained during machining?

To this end, various backing tooling systems and clamping methods such as HSK, KM and BBT shanks have been researched and developed.

In addition, the diameter of the end of the spindle is slightly smaller than the standard dimension when the spindle is manufactured, so that the initial contact surface pressure is increased to maintain the mating surface pressure during high-speed rotation, thereby increasing the contact rigidity. To increase the binding force.

However, if an inappropriate tool holder shank, machining margin and coupling force are selected, the coupling accuracy and bending stiffness may be deteriorated, which may adversely affect the machining accuracy and may directly damage the spindle such as the bearing part. The choice of binding force is very important.

For this purpose, it is important to understand the change in the rigidity of the spindle interface of the machine tool during cutting and the factors influencing it.

In general, the axial deformation according to the bending load is shown in the figure below. When the bending load F 때 is applied, the displacement δ of the load point is shown in equation (1).

δ = δ₁ + δ₂ + δ₃ (1)

Here, δ₁ is the radial displacement of the tapered shaft core at the reference plane, δ₂ is the displacement due to the inclination of the tapered shaft core at the reference plane, and δ₃ is the displacement due to the elastic deformation of the tool cylinder portion.

In general, δ₃ is determined by the geometry and material of the tool.

Therefore, δ₁ + δ₂ can be regarded as the displacement caused by the presence of the bond, and δ₁ is a negligible value in many cases, so the maximum effect of the presence of the bond is represented by δ₂.

Currently, it is not possible to quantitatively grasp the change in the rigidity characteristics of the spindle interface of the machine tool during cutting, and the selection of the machining margin, the coupling force, etc. is mostly made by the experience of the designer and the operator.

The stiffness evaluation of the main shaft by the experimental method using the current test bar and plug taper gauge is impossible to consider the effect of the centrifugal force, the problem is that the error becomes larger and the actual behavior characteristics can not be properly grasped as the spindle speeds up.

An object of the present invention is to provide a stiffness measuring device of the main shaft that can measure the change in stiffness due to the change of taper contact rate when the main shaft rotates at high speed by using the magnet attraction, repulsive force effect and the magnetic induction effect of the ferromagnetic material. .

The present invention is coupled to the force measuring device to the fixing block, the upper portion of the force measuring device to configure a bracket for the magnet, the upper surface of the bracket is installed a magnet for generating a force to pull the main shaft system.

The present invention can measure the stiffness in consideration of the change in the contact rate of the spindle interface according to the change in the spindle speed, so that the stiffness characteristic evaluation of the main shaft is made in a similar environment to the actual machining situation, the stiffness characteristics evaluation with less error than the prior art is made This has the effect of improving precision and productivity.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a state diagram when the spindle system rotates at low speed, and FIG. 2 is a state diagram when the spindle system rotates at high speed.

As shown in the figure, the force measuring device 11 is coupled to the fixing block 10.

As the force measuring device 11, a load cell, a transgauge, or the like may be used.

The upper portion of the force measuring device 11 is provided with a bracket 12 for magnet installation, and the magnet 13 for generating a force is installed on the upper surface of the bracket 12.

In general, the contact rate is maintained above a certain rate at a low speed of less than 20000rpm, so the displacement δ₂, which is the displacement of the tapered shaft core, does not increase significantly.However, at a high speed of 25000rpm or more, the contact rate of the spindle interface 15 decreases rapidly, so The large increase is a fact identified by experiment.

Coulomb's law is the basic law of the force acting between two charged objects. It is a force inversely proportional to the square of distance, like universal gravitational force, but attraction or repulsive force is applied depending on the polarity of the charge.

The magnetic force (F) acting between two charges m₁, m₂ by Coulomb's law is expressed as

F (N) = S (m₁m₂) / r² ----- Equation (1)

Where m₁, m₂: stimulus intensity, r: distance between positive stimuli, S: proportional constant

In Eq. (1), S, m₁, m₂ are given values, so the force F is obtained by finding the distance r between both magnetic poles.

Equation to find the stiffness on the constant bending load used for the evaluation of machine tool stiffness

κ = F / δ (kN / μm) ----- Formula (2)

The rigidity can be obtained by.

Due to the small increase of δ₂, which is the displacement of the tapered shaft core at the inclination of the spindle system 14 at low speed rotation, the distance between the magnet and the spindle system is reduced to r₁, and when the magnetic force F₁ is obtained by the force measuring device, F₁ in equation (1) R r is obtained by substituting ,, and stiffness κ 의 of the main shaft system is obtained by substituting these forces F ₁ and r 에 in equation (2).

κ₁ = F₁ / (r-r₁)

During high speed rotation of the main shaft system 14, the contact ratio of the main shaft interface unit 15 decreases rapidly, so that δ 2 is greatly increased, and the value of r 2 is greatly reduced, and consequently, the magnetic force F 2 is increased.

Substituting the F 2 and r 2 values obtained by the force measuring device into Eq.

κ₂ = F₂ / (r-r₂)

As described above, the present invention can measure the stiffness of the main shaft in consideration of the effect of changing the contact ratio of the main spindle interface unit 15 by the centrifugal force, so that the existing main shaft is in an environment similar to the actual processing situation rather than the stiffness evaluation in the stationary state. Rigidity measurements can be made to improve the precision and productivity of machined parts.

1 is a state diagram when the main shaft system rotates at a low speed

2 is a state diagram when the main shaft system rotates at a high speed;

※ Explanation of code for main part of drawing

10. Block for fixing 11. Force measuring device

12. Bracket 13. Magnet

14. Spindle System 15. Interface

Claims (2)

In the rigidity measuring device of the machine tool spindle, The force measuring device 11 is coupled to the fixing block 10, and a bracket 12 for magnet installation is provided on the upper part of the force measuring device 11, and a main shaft system is provided on the upper surface of the bracket 12. Stiffness measurement apparatus of the main shaft using a magnetic force, characterized in that it comprises a magnet (13) for generating a pulling force. The distance between the magnet 13 and the main shaft system 14 is the force {F (N)} = proportionality constant (S) {intensity of stimulus (m₁) and intensity of stimulus (m2)} / magnet A stiffness measuring device of a main shaft using a magnetic force, characterized in that obtained by the square of the distance between the main axis system (r²).

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