JPH0694085B2 - Machine tool equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a machine tool device suitable for use in machine tools widely used for machining, particularly when high precision machining is required. is there.

[Conventional technology]

There are some machine tools such as conventional lathes whose main parts are made of stone or concrete in order to improve the machining accuracy, but it is difficult to finish the main parts themselves with high accuracy, and chipping or cracking occurs. There was a drawback that the strength was low, such as easy occurrence. Therefore, it is common to use a metal material mainly composed of a steel material.

However, with machine tools made of metal materials, the relatively large coefficient of thermal expansion of metals (11 to 13 × 10 ^-6 / ° C for steel materials)
Affected). As a result, when sub-micron unit (1μm or less) ultra-precision processing is required,
A special tool for operating the entire machine tool equipment in an environment where the temperature and humidity are tightly controlled, or for warming up the machine tool before starting the machining operation and for operating the machine tool under stable conditions. It is necessary to add various structures and devices, and there is the inconvenience that expensive machine tools can be used only under extremely limited operating conditions, and stable, high-quality, high-precision workpieces. Was difficult to obtain.

On the other hand, with the recent development of science and technology, especially electronics-related technology, various optical instruments, precision measuring instruments, electrical appliances, optical communication equipment, and various mechanical devices have become extremely high with miniaturization. Precision is being sought, and there is a growing demand year after year for the precision of various parts used in the manufacturing process of products, with the aim of significantly improving precision, quality, and durability. There are many demanded examples.

[Problems to be Solved by the Present Invention]

As mentioned above, as the machining accuracy of various parts is required to be even higher, in the conventional lathes that use a metal headstock, the sliding motion between the bearing and the bearing is affected by the rotational movement of the main spindle during operation. Due to the heat generated, the temperature of the headstock, spindle, front bearings, rear bearings, thrust seats, etc. rises, resulting in thermal expansion of these headstocks, spindles, etc., resulting in slight dimensional changes in each component. This occurs or the clearance between the members slightly changes, which adversely affects the rotation accuracy of the spindle, and as a result, the accuracy of the workpiece attached to the tip of the spindle decreases.

Further, even when the operation operation is temporarily interrupted, a difference in contraction occurs between the respective members when the headstock is cooled, so that the accuracy change of the work piece is likely to occur even when the operation is restarted after the temporary operation is stopped,
There is a drawback in that machining that requires ultra-precision accuracy of 1 μm or less is extremely inconvenient, and high-precision machining is difficult, and ceramic materials are drawing attention as materials that replace conventional metal materials. However, for the various components that are the main components of machine tools, it has not been possible to specify a ceramic material that can satisfy the various properties required for them, and therefore, up to now, there are no component parts for machine tools made of ceramics. The situation was complete.

[Means for solving problems]

In view of the above circumstances, the inventors of the present invention form at least a spindle and a bearing of a spindle forming a headstock in a machine tool, a front bearing, a rear bearing, a thrust seat, and a headstock frame with a silicon nitride ceramic material. It is possible to realize with a machine tool equipped with a conventional metal headstock, with a simple structure and a short warm-up time, without using tightly controlled operating environment conditions, expensive control equipment and complicated structures. This makes it possible to perform difficult ultra-precision machining.

〔Example〕

Next, taking a machine tool device according to the present invention as an example of a lathe,
The details will be described.

In FIG. 2, reference numeral 1 denotes a base forming a base of a lathe, and a bed 2 is placed on the top of the base 1, and a ceramic material supporting a spindle 3 made of a ceramic material is also mounted on the bed 2. The spindle headstock 4 formed in 1. is fixed by fixing means such as accumulating, and the spindle 3 is connected via a V belt 5 so as to rotate by a spindle driving motor 6 installed in the lower portion. ing. A work piece (not shown) supported by the tip of the main shaft 3 is a tool rest (not shown) fixed on a saddle 7 and a slider 8 movably installed on the upper surface of the bed 2 so as to be movable left and right and front and back. ), It is designed to be cut into an arbitrary shape with a blade.

Of these, in the headstock 4, the spindle 3 that supports the workpiece is, as shown in FIG.
The other end is supported by the front bearing 42, and the driving force is transmitted from the V belt 5 engaged with the pulley P via the coupling C. The axial thrust acting on the spindle 3 during rotation is regulated by the front thrust seat 43 and the rear thrust seat 44, and the front bearing 42, the headstock 4, and the front thrust seat are also regulated. 43 and the rear thrust seat 44 are fixed to the main shaft 3 by a separate metal fitting (not shown).

In addition, it is extremely difficult to finish the machining accuracy of the combination of the inner diameters of the front bearing 42 and the rear bearing 43 and the outer diameter of the main shaft 3 supported by these bearings to a high precision of a micron unit. There is a problem that the clearance increases due to the minute wear caused by the continuous use, and the rotation accuracy is disturbed. Since it is impossible for the ceramic main shaft 3 and the bearings 41 and 42 to correct the clearance due to the wear that has once occurred, the main shaft 3 is tapered as shown in FIGS. 3 and 4. Surfaces A and B are formed in advance, and A and B are formed on these tapered surfaces.
Since B is received by the tapered surfaces formed on the front bearing 42 and the rear bearing 41, respectively, the main shaft 3 can be supported with high precision at a minimum and optimum clearance. The axial thrust that acts further is the front thrust seat 43 and the rear thrust seat.
44, and the front bearing
42, headstock 4, front thrust seat 43, and rear thrust seat 44
Are fixed to the main shaft 3 by a separate metal fitting (not shown).

In the device configured as described above, the main shaft 3, the front bearing 42 that supports the main shaft 3, the rear bearing 41, the headstock 4, the front thrust seat 43, the rear thrust seat 44, etc. are formed of a ceramic material. However, the ceramic material forming the constituent parts of the machine tool device of the present invention is required to have a combination of the following characteristics.

High mechanical strength.

Great wear resistance.

The coefficient of thermal expansion is small and suitable.

It should be easy to combine and bond with metal and be able to perform it properly.

Not susceptible to vibration.

However, although it was extremely difficult to develop and select a ceramic material having these characteristics, the present inventors
It has been found that, out of many ceramic materials that have existed in the past, a silicon nitride ceramic material is most suitable for the configuration of the main shaft, bearing, etc. that form the main element of a machine tool. Moreover, among the silicon nitride ceramic materials, the coefficient of thermal expansion is particularly 3 to 5 × 10.
It is in the range of ^-6 / ° C. It is a silicon nitride ceramic that is sintered after adding a sintering aid whose main component is yttrium oxide (Y ₂ O ₃ ) or magnesium oxide (MgO). It is necessary to have a strength of 50 kg / mm ² (JIS 3-point bending test) or more.

Next, the fine crystal structures of various ceramic materials and their characteristics will be described.

FIG. 1 (A) schematically shows the crystal structure of a silicon nitride ceramic, and the crystal grains have a needle-like or long columnar fine structure, and a glass layer exists as a grain boundary layer. It has higher toughness than other ceramic materials.

On the other hand, of the oxide-based ceramic materials, the typical alumina ceramic material has a relatively large crystal structure with an average grain size of 10 μm, as shown in FIG. The bending strength at 30 kg / mm ² is not only insufficient, but the coefficient of thermal expansion is 6-8 × 10 ^-6 /
It is as large as ℃ and is unsuitable as a component such as the main shaft and bearing which are the main parts of machine tools. However, alumina ceramic materials are suitable for the production of large-sized products, and the intermediate thermal expansion between the silicon nitride ceramic materials that make up the spindle and various accessories such as metal flanges and retainers that make up the headstock related parts. Since it has a coefficient, it was the most suitable material for forming the spindle stock that holds the shaft and bearings.

Further, as shown in FIG. 2C, the silicon carbide ceramic material generally has a crystal grain size of about 3 to 7 μm, has a high degree of sintering, and can obtain a high-density sintered body at room temperature. The flexural strength at about 50 kg / mm ² is relatively large, and the sliding characteristics are excellent, but it has poor toughness and low resistance to mechanical shock, so it is suitable as a ceramic material for shafts and bearings. Not a thing.

Further, as shown in FIG. 1 (D), the crystal structure of the zirconia ceramic material, this zirconia ceramic material has a fine crystal structure, has a high degree of sintering, and is a high-density sintered body. . Also, although the ceramic material called partially stabilized zirconia has a crystal grain size of about 0.2 to 1.0 μ and a bending strength at room temperature of about 80 kg / mm ² or more,
The coefficient of thermal expansion, which is an important item when configuring the main part of a machine tool, is close to the coefficient of thermal expansion of metal materials, which is 8 to 11 × 10 ^-6 / ° C. It is unsuitable as a material for the bearing.

It is also an essential condition that a ceramic material that constitutes a machine tool that performs so-called sub-micron precision machining with an accuracy of 1 μ or less is not easily affected by various vibrations. Damping is an important factor. Therefore, the typical damping factors for vibration of alumina, silicon nitride, silicon carbide, cermet, and steel materials used as comparative materials are 20 mm in diameter.
× A comparative analysis was performed using a rod-shaped sample having a length of 20 mm. The test method is as follows: Table 1 shows the results of the impact rate of the shock wave transmitted through the sample measured and compared with the sensor attached to the sample in advance by impacting the sample with a hammer.

As is clear from this table, among the four types of ceramic materials and five types of iron and steel materials for comparison, a total of five types, silicon nitride and silicon nitride have a large damping ability against vibration, and it is understood that silicon nitride is the most excellent. This indicates that the silicon nitride main shaft and bearing are extremely effective against chatter vibrations generated during machining.

In addition, a sliding characteristic comparison test was carried out when a lubricating oil was used in order to evaluate the optimum ceramic material used for the spindle and bearing.

As an evaluation method, an annular test piece with a diameter of 30 mm and a thickness of 8 mm was used, and one of the two test pieces was fixed and the other was pressed in a rotational motion state, and a comparative evaluation of sliding wear was performed. Was carried out. The wear volume and wear coefficient of the fixed piece and the rotating piece were measured, and the wear volume (Vmm) for each test piece,
Pressing load (P kg) and the specific wear amount (V / P x L) defined by the slip travel distance (L mm), and further into the comprehensive evaluation value (specific wear amount of fixed piece x wear coefficient x specific wear amount of rotating piece) Comparative evaluation was performed. The evaluation results are shown in Table 2.

Silicon nitride, silicon carbide, and cermet showed a marked difference in sliding characteristics compared to alumina, and silicon nitride was the best among the above three types. Silicon carbide and cermet can be considered as candidate materials for wear resistant parts because they have relatively excellent sliding characteristics, but mechanical strength, toughness, sliding characteristics and manufacturing of large parts such as spindles and bearings of machine tools. When considering the overall difficulty level, etc.,
It turned out that silicon nitride is the best.

Further, even silicon nitride materials have different crystal structures and characteristics depending on the manufacturing method. A comparative test of various silicon nitride materials is performed, and it is necessary that the silicon nitride material applicable for machine tools has the following characteristics. I found something.

The crystal structure should be needle-like or long columnar.

The coefficient of thermal expansion should be 3.0 to 5.0 × 10 ^-6 / ° C.

The bending strength at room temperature shall be 50kg / mm ² (3-point bending method according to JIS 1601-1981) or more.

Fracture toughness value (KIC), which represents the toughness of a material, is 5.0 (IND method)
That is all.

Weibull coefficient (m), which represents the variation in material strength, is 12
That is all.

Porosity is less than 0.1%.

Young's modulus (E) representing the elasticity of the material is 3.0 × 10 ⁶ kg / cm ² or more, and Poisson's ratio (μ) is 0.25 or more. The silicon nitride material having these characteristics is the same as the method for producing alumina, and Y ₂ as a sintering aid is added to silicon nitride.
An oxide of a rare earth element such as O ₃ and alumina are mixed and crushed by a ball mill to prepare a primary raw material. Then, after filling and pressing this primary raw material in a pressing machine, the firing temperature was set to 1700.
It can be obtained by firing at about 1800 ° C for about 2 to 3 hours.

It has been found that a silicon nitride material having the above-mentioned characteristics is optimal as a ceramic material for machine tool parts. That is, it effectively exerts effects such as a mechanical shock and a damping method against vibration when used as a machine tool part, wear resistance, sliding characteristics, and minimizing dimensional changes during heat generation.

〔The invention's effect〕

As described above, according to the present invention, at least the main shaft, the front bearing, the rear bearing, the headstock, the front thrust seat, the rear thrust seat, and the like have at least a main shaft, a front bearing, and a rear bearing that have a low heat resistance among the above-mentioned ceramic materials. Since it is made of a silicon nitride ceramic material with an expansion coefficient, the clearance with the bearing can be stably maintained at the minimum and optimum values, and the rotational driving force is transmitted from the rear of the main shaft via the coupling. Due to this structure, excessive bending stress is not generated on the ceramic spindle.

Thus, stable and highly accurate rotation can be obtained without applying a special structure.

Further, according to the above-mentioned embodiment, the driving force is applied on the extension line of the central axis as compared with the method of transmitting the driving force between the front and rear bearings, so that stable rotation can be given, resulting in a special operating environment and a long operating time. It is possible to provide a machine tool device that does not require warm-up operation and has ultra-precision machining accuracy.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a crystal state of a silicon nitride ceramic material and another ceramic material which constitute a main part of the machine tool device of the present invention, and FIG. 2 is a lathe as an embodiment of the machine tool device of the present invention. FIG. 3 is a vertical sectional view of only the headstock 4 in FIG. 2, and FIG. 4 is a vertical sectional view of another embodiment of the headstock 4 only in FIG. 1: Frame, 2: Bed 3: Spindle, 4: Spindle base 7: Saddle, 8: Slider

Claims (1)

[Claims] 1. In a machine tool such as a lathe having a main shaft supported by bearings arranged at both ends, a taper surface is formed at least at the end of the main shaft on which a workpiece is machined, and a bearing corresponding to the taper surface is formed. In addition to supporting the main shaft, headstock, and bearing, at least the entire main shaft and bearing have a needle-like or columnar crystal structure, a porosity of 0.1% or less, and a thermal expansion coefficient of 3.0 to 5.0 × 10 ^-6. / ° C and logarithmic decay rate 2.40 × 10 ^-2
A machine tool device comprising the above silicon nitride ceramics.