JPH0475819A - Composite electrode for electric discharge machining - Google Patents

Abstract

PURPOSE:To improve a machining speed and coarseness of a machined surface by using a carbon fiber-reinforced carbon sintered substance, utilizing conductivity provided by carbon fibers and having specified density or more, for a composite electrode for electric discharge machining used for a resin molding tool. CONSTITUTION:A composite electrode for electric discharge machining has a texture wherein carbon fibers and inorganic microsubstance are integrally embedded in a carbon matrix. The carbon matrix has mosaic structure wherein optical anisotropic particles are uniformly crowded, as seen by using a polarizing microscope. The composite electrode is formed of a carbon fiber-reinforced carbon sintered substance wherein a ratio of an interface peeled at an interface between the carbon fibers and the carbon matrix is 10% or less of that of a total interface and density is 1.65% or more. A sintered substance produced by sintering a composite substance formed of carbonic powder, having self- sintering property, where uncarbonized carbonic fibers or uncarbonized carbon fibers and an inorganic microsubstance are embedded can be employed as the carbon fiber-reinforced carbon sintered substance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a composite electrode for electric discharge machining used for electric discharge machining of metals such as resin molding molds.

[Prior art] Conventionally, the materials used for electrical discharge machining electrodes are metals such as copper, silver, and their tungsten alloys, or graphite-based materials made by kneading coke powder and pitch, forming, and sintering. ing.

With these conventional electrodes for electric discharge machining, whether the electrode is made of metal or graphite, when the speed of electric discharge machining is increased, the roughness of the machined surface deteriorates and smoothness cannot be obtained. Therefore, it is known that if electrical discharge machining is performed under conditions that increase the smoothness of the machined surface, the machining speed must be slowed down, resulting in contradictory results, and this problem has not yet been fully resolved. .

In order to solve these problems, for example,
Publication No. 5731 discloses an electrical discharge machining electrode material in which 5 to 70% by weight of ceramic fine powder is mixed with semi-formed coke fine powder, pressure molded, and then sintered at 2000° C. or higher. Further, JP-A-1-97523 discloses a graphite-based electrical discharge machining electrode made of specific mesocarbon microbeads as a raw material, pressure-molded and sintered.

[Problem to be Solved by the Invention 1] However, the above-mentioned electrode has a comparatively low electrical resistivity for increasing the machining speed, and the roughness of the formed machined surface has not yet been sufficiently improved.

The present invention has been made in view of the above-mentioned circumstances ([C] The purpose is to provide excellent composite electrodes for electrical discharge machining.

[Means for Solving the Problems 1-1] The joint electrode for electrical discharge machining of the present invention has a structure in which (ζ carbon fibers or carbon fibers and inorganic microscopic bodies are integrally embedded in a carbon matrix, The carbon 71-trix has a mosaic structure in which optically stable fine particles are uniformly densely packed (~) when seen under a priority microscope, and the interface between the carbon fiber and the carbon 71-trix is separated at the interface. It is characterized by being constructed of a wood fiber reinforced carbon sintered body having a ratio of 10% to the total interface [J] and a density of 1.65L.

The composite electrode for electrical discharge machining of the present invention is made of a carbon fiber-reinforced carbon sintered body.

This carbon fiber-reinforced carbon sintered body can be used as an electrode material to lower the electrical resistivity, improve the machining speed, and make the surface to be machined less uneven. Furthermore, by adding KERAMIX, which is made up of inorganic microscopic particles, the electrical resistivity is further reduced (and the roughness of the machined surface can be further reduced).

The carbon fibers that make up this carbon fiber-reinforced carbon sintered body ensure the strength of the sintered body.
It may be one that exhibits anisotropy or one that exhibits isotropy. #N navy blue may be cut short fibers or long fibers. Further, the carbon fibers may be oriented in a fixed direction in the matrix or may be oriented randomly.

The blending ratio of carbon fiber in the carbon fiber-reinforced carbon sintered body is 2~
50 weight 91'3, more preferably 10=40% by weight.

The inorganic microscopic bodies that can be a component of the carbon fiber-reinforced carbon sintered body can be composed of microscopic metals and ceramics.

The shape of these inorganic microscopic bodies may be a powder, a fiber such as a whisker, a hot flake, or the like. The blending ratio of the inorganic fine carbon fibers and carbon sintered bodies is preferably 3 to 30% by weight, preferably 1) or 5 to 10% by weight.

Component part τ゛ of carbon fiber reinforced carbon sintered body 71-
Rix has a mosaic structure in which optically anisotropic fine particles are uniformly densely packed when viewed under a polarizing microscope.

Having optical anisotropy when viewed with a polarizing microscope is considered to have fibers in which carbon is regularly arranged in a certain direction.

Naturally, this carbon matrix is in a state in which carbon particles with optical anisotropy are tightly packed together. Uniformly densely packed means that the carbon particles flow and patterns such as chairs and flow lines are silent. It is preferable that the carbon particles have a mosaic pattern (grains of about 30 .mu.m) observed under a polarizing microscope.

The peeled area of the interface between the carbon fibers and the carbon matrix constituting the carbon fiber-reinforced carbon sintered body of the present invention is determined by setting the peeled interface area to 10% or less (necessarily) to the total interface area. Carbon fibers are separated from carbon fibers (2), but the reinforcing effect of carbon fibers is not fully exerted.For this reason, the area of delamination at the interface is preferably 3% or less than 10% of the total interface. It is better to do so.

This separation between the carbon fiber and the carbon 7 trix can be observed and measured using a scanning electron microscope (hereinafter referred to as SEX).

Further, the porosity of this carbon fiber-reinforced carbon sintered body is preferably 10% or less. The pores in this sintered body appear as black dots when observed with a polarizing microscope. Therefore, the porosity can be calculated from the area of the black dots that occupies the observed area.

The density of the carbon fiber reinforced carbon sintered body according to the present invention is 1.65
The above characteristics are a combination of the denseness of carbon 71-ricks, few pores, and no peeling at the interface between carbon fibers and carbon matrix.I) Therefore, the denseness of these matrices is If the porosity is too high or there is a lot of separation between the fiber and matrix, the specific gravity will be 1.
．． It will be 65 or less.

The mechanical strength of this carbon fiber-reinforced carbon sintered body is directly influenced by the blending ratio of the constituent carbon fibers, the material and blending ratio of the inorganic particles, the peeling area ratio between the carbon fibers and the carbon matrix, and the porosity. do.

When the mechanical properties of this carbon fiber-reinforced carbon sintered body are defined by bending strength, the bending strength of this sintered body is preferably 600 Ky/~ or more.

The carbon fiber-reinforced carbon sintered body of the present invention is a sintered composite consisting of a self-sintering carbonaceous powder in which uncarbonized carbonaceous fibers or uncarbonized carbonaceous fibers and inorganic microscopic bodies are embedded. A sintered body obtained by

Here, the uncarbonized carbonaceous fiber refers to a carbonaceous fiber that has not been subjected to normal carbonization treatment. In other words, it refers to carbonaceous fibers that can be carbonized by rough heat treatment. Specifically, when pitch is used as a raw material, the as-spun fiber or the spun fiber is
Refers to fibers that are infusible at temperatures not exceeding 0°C. PAN(
For polymeric fibers such as polyacrylonitrile and rayon, it refers to fibers that have undergone the decomposition process and have not yet been graphitized. Examples of this type of carbonaceous fiber include pitch fibers obtained by spinning coal-based or petroleum-based raw material pitch, and infusible fibers obtained by infusibleizing the same.

The spinning and infusibility of this raw material pitch may be carried out according to conventional methods, and the conditions are not particularly limited. Normally, pitch fibers are produced by supplying raw material pitch to a spinning machine and producing 300 to 400
It can be obtained by heating it to about 0° C. and extruding it from a nozzle under pressure with an inert gas. Further, such pitch fibers can be image-held at about 150 to 500 DEG C. for 0 DEG to 5 hours in a roughly oxidizing atmosphere to make them infusible to 11ffl. Note that this raw material pitch may be optically isotropic or optically anisotropic.

The fiber length of the uncarbonized carbonaceous fibers is not particularly limited to short fibers or long fibers. However, in the case of short fibers, 0
．． 01 to 50 m can be used. especially,
A length of 0.03 to 10 m+ is preferable in terms of ease of mixing and aspect ratio. If the length is too long, the fibers will become entangled with each other, resulting in poor dispersibility, which in turn will result in poor isotropy of product properties.
Moreover, if it is shorter than 0°01 m+, the strength of the product will drop rapidly, which is not preferable. In addition, the fiber diameter is 5 to 25μ
It is preferable to have a diameter of about m. In addition, these fibers can also be used as nonwoven fabrics or coated fabrics.

It is preferable that the uncarbonized carbonaceous fibers be further surface-treated with a material containing a caking component such as tar, pitch, or organic polymer to improve compatibility with the binder. This surface treatment can be carried out by adding about 100 to 1000 parts by weight of a material containing a viscous component to $1100 parts by weight of carbon fibers, stirring the mixture, washing with an organic solvent, and drying.

The tar and pitch used for this surface treatment may be either coal-based or petroleum-based. When pitch is used, heating to about 140 to 170°C is required during stirring, so tar is more preferable as a treatment material, and also because of the carbonization yield in the subsequent carbonization and graphitization steps. Among them, coal-based ones are more preferable.

Examples of organic polymers used for this surface treatment include phenol resin, polyvinyl chloride, and polyvinyl alcohol.

As the organic solvent used for cleaning in the above-mentioned surface treatment, aromatic solvents such as toluene and xylene can be used. Approximately 100 to 1000 parts by weight of the organic solvent is added to 100 parts by weight of the mixture of uncarbonized carbon fibers and the material containing the adhesive component, and the mixture is stirred and washed. This washing removes light oils containing many volatile components. The uncarbonized carbonaceous fibers that have been washed are dried under conditions such as heating and/or reduced pressure in a non-oxidizing atmosphere such as nitrogen or argon. The drying process is not limited to these methods.

Generally, the uncarbonized carbonaceous fibers that have been dried and surface-treated are subjected to a dispersion treatment, if necessary. That is, the dried fibers may be lumped or agglomerated, so in such cases, it is necessary to use a regular powder mill, i-mizer,
The inorganic microparticles, which are dispersed by any means such as a bulbarizer, serve as raw materials for the carbon fiber-reinforced carbon sintered body of the present invention, together with the uncarbonized carbonaceous fibers. This aa microscopic body is
It is added to further reduce the electrical resistivity of the composite electrode for electric discharge machining, and to obtain a machined surface with high smoothness as well as machining speed. And it forms a dense sintered body1
, this R-free microscopic body is one that does not react with carbon at a melting point of 1000° C. or higher, more preferably 1. :H\/1000
The following are good.

Examples of such inorganic substances include those having electrical conductivity such as inorganic borides, inorganic carbides, and inorganic nitrides. Examples of inorganic borides include TiB5, TaB2, ZrB2
, B4 C, N i B, CoB, BN, etc. Examples of inorganic carbides include TiC, T
Examples include aC1ZrC. Examples of inorganic nitrides include BN, dinitride, Cr2N, Ta
N, AJ) N, 7 [3 who can name N, etc.
, furthermore, Fe, Mn, Mo, Ni, Nb, Si, V
, Ti, W, and other inorganic materials can also be used. Note that these inorganic substances can also be added in the form of metals.

Furthermore, inorganic microscopic bodies include whiskers and ceramic fibers in addition to fine particles.

By selecting an appropriate one from among the above L) microscopic particles, the characteristics of the composite electrode for electrical discharge machining can be controlled in a suitable state. When used, particles with a particle size of 0.1 to 5 μm are preferable, more preferably 0.1 to 5 μm, considering compatibility with the matrix material, dispersibility, and strength and wear resistance of the finished sintered body. It is 0.2 to 4 μm.

In addition, when non-m fibers are used as the inorganic microscopic bodies, the diameter Q, 7~ 40/,! m, length O501 to -8
Preferably, the diameter is 1 to 15 μm.
m, and the length is 0.05 to 3 mm.

The carbonaceous powder constitutes the binding material of the carbon fiber-reinforced carbon sintered body of the present invention. This carbonaceous powder has self-sintering properties and is uncarbonized or not completely carbonized. This self-sintering carbonaceous powder can be made of either petroleum-based or coal-based powders, specifically Menker 7 Bonn microbeads, bulk mesophase pulverized products, and low-temperature sintering. Among these, petroleum-based and coal-based carbon microbeads are preferred from the viewpoint of uniformity of particle size and composition, and stability. From the point of view of ′:E
J charcoal type is more preferable 1. Self-sintering carbonaceous powder () has a particle size of 30 um or less, β-, resin amount 3-
About 50% is preferable. The amount of β-resin is more preferably 6 = -30%, and still more preferably 8 to 25%.

The sintered body of the present invention can be produced by simply mixing, for example, uncarbonized carbon fibers, inorganic powder or inorganic fibers, and self-sintering carbonaceous powder in a dry process, and then press-molding and firing the mixture. It can be manufactured using a simple process. Then-C is required [machining is performed as required, and it is made into a finished product.

The uncarbonized carbonaceous fiber, the inorganic powder or the inorganic fiber, and the self-sintering carbonaceous powder are combined and molded to form a composite. Although the mixing means at this time is not particularly limited, it is preferable to mix the above-mentioned raw materials uniformly in order to achieve uniformity. The blending ratio of the self-sintering carbonaceous powder and the uncarbonized carbonaceous fiber is about 2 to 70 parts by weight to 100 parts by weight of the former, and more preferably 1 part by weight to 1 part by weight of the former. :', the latter is about 10 to 50 parts by weight. Also, regarding the addition of inorganic particles, the total
The binding content is preferably 3-30% by weight, more preferably 5-10% by weight.

Molding of the sintered body according to the present invention can be carried out by a conventional method, and usually takes about 7JO of 1 H-101 on/c.
It is sufficient to form the blade into a predetermined shape under pressure. Or C.I.P.
Molding may be performed by a method such as a method, a HIP method, a bot press method, or the like. Molding is carried out at room temperature or under an inert atmosphere.
It can be carried out under heating to about ℃.

The molded body is sintered to become a sintered body according to the present invention.

Note that sintering here refers to carbonizing and solidifying the uncarbonized carbonaceous fibers and the self-sintering carbonaceous powder by firing at a temperature of about 700 to 2000° C. under normal pressure. Note that, if necessary, this carbonized composite may be heated to a temperature higher than the sintering temperature in a graphitization furnace to graphitize it. The carbonization conditions are not particularly limited, but usually the temperature is raised from room temperature to about 1,500°C at a heating rate of about 0.1 to b in a non-oxidizing atmosphere, and then waited for about 0.5 to 10 hours. Bye. Hey,
During sintering, by sintering at a higher temperature, a part of the composite is carbonized and then graphitized.

Further, the conditions for graphitization are not particularly limited, and the temperature is raised from the temperature during sintering in a non-oxidizing atmosphere to a temperature of 0.1-b or higher to a temperature at which the added inorganic fine particles do not dissolve. 5-1
All you have to do is wait for about 0 hours. When graphitized,
Graphite crystals further improve the density of the product.

This special carbon fiber-reinforced carbon sintered body consists of a composite before sintering of uncarbonized carbonaceous powder with self-sintering properties in which unsettled carbonaceous lithium and inorganic powder or inorganic fibers are embedded. It is. Therefore, when sintering the composite,
Since the carbonaceous fibers used as reinforcing materials are uncarbonized or not completely carbonized, the uncarbonized carbonaceous fibers and the uncarbonized carbonaceous fibers that have self-sintering properties are the same when carbonized. It has certain physical properties (strength, shrinkage rate, etc.).

Therefore, the interfacial adhesion between these carbonaceous fibers and the carbonaceous powder is improved, and high strength and excellent wear resistance can be obtained. In short, when a composite is sintered, the uncarbonized carbon fibers and carbon powder shrink to the same degree and bond together, which increases their interfacial adhesion and improves the strength of the composite electrode for electrical discharge machining. do.

In addition, parts made of carbon fiber-reinforced carbon sintered bodies containing inorganic powder or inorganic l1i1 have increased conductivity, lower specific resistance, are denser, increase machining speed, and have smoother and less ugly surfaces to be machined. It is possible to create an electrode with increased .

Furthermore, as described above, the self-sintering carbonaceous powder as a binder eliminates the need for conventional binders made of liquid carbonaceous materials. Therefore, there is no need to repeat impregnation and firing in order to fill the pores caused by the use of a liquid binder. The special carbon fiber reinforced carbon sintered body according to the present invention is
As described above, it can be manufactured at low cost through the simple steps of dry mixing, pressure molding, and firing.

In general, when uncarbonized carbon fibers are surface-treated with a material containing a caking component such as tar, pitch, or organic polymer, the wettability of the carbon fiber interface increases, which makes it difficult to use as a binder. Since the compatibility with the carbonaceous powder is improved, the interfacial adhesion between these carbonaceous fibers and the carbonaceous powder is further improved.

[Example] Hereinafter, this will be explained in detail with reference to Examples.

(Example 1) Uncarbonized carbonaceous fibers made of infusible fibers with a diameter of 15 μm and a length of 0.3M obtained by spinning coal-based optically isotropic pitch using a conventional method are prepared. . 130% by weight of this uncarbonized carbonaceous fiber and 70% by weight of self-sintering carbon powder consisting of coal tar-based mesocarbon microbeads with a center particle size of 7 μm were blended and then uniformly mixed to obtain a mixture. molded at a molding pressure of 2 tons/cm to a diameter of 40
N + A columnar composite with a height of 50 m.

Next, this composite was heated to 1000°C at a heating rate of 150°C/hour in a non-oxidizing atmosphere, and held at the same temperature for 1 hour to sinter, forming uncarbonized carbon fibers and self-sintering. The carbonaceous powder was carbonized and consolidated.

Then, in a non-oxidizing atmosphere, the temperature was raised to 2000°C at a heating rate of 500°C/hour and held for 20 minutes to graphitize, resulting in a bulk density of 1.80! iF/CIt3 bending strength 9
50Kg/CI! A carbon V & fiber reinforced carbon sintered composite of t2 was obtained.

A portion of this carbon fiber-reinforced carbon sintered body was used for surface observation using a polarizing microscope and observation of the matrix and interface state using SEM. When observed using a polarizing microscope, the carbon particles formed by the sintered matrix adhere to each other in a t-saic pattern, with each particle shining in a different color pattern, and the fibers have a uniform color scattered throughout this 71-rix. It was observed as an island.

The area of these black dots was approximately 3% by area when the total area was 100% by area. SFMT: Observed 71~
The interfacial state between the 71-Rix and the reinforcing fibers was such that they were integrally bonded, and no separation of the 71-Rix and the reinforcing fibers was observed.

(Example 2) 30% by weight of the same infusible unsettled carbon fiber as in Example 1, etc.
95% of 1 ton of coal tar-based Men Carbon Micro 1 with a center particle size of 7I1m as a self-sintering carbonaceous powder mixed with 1% by weight of titanium boride with a particle size of 1.0μm 5% by weight was added and molded into a columnar composite with a diameter of 40 m and a height of 50 #11 in the same manner as in Example 1 [-2].

Next, this composite is heated to '1000'C in a non-oxidizing atmosphere at a rate of 150C/hour and sintered by keeping it at the same humidity for 1 hour to form uncarbonized carbon fibers and self-sintering. The carbonaceous powder was carbonized and consolidated. Then, in a non-oxidizing atmosphere, the temperature was raised to 2000°C at a gas flow rate of 500'C2' hours and held for 20 minutes for sintering.

By the way, using a part of this carbon fiber-reinforced carbon sintered body, the surface observation using a polarizing microscope #J was carried out in the same manner as in Example No. 1.
The interfacial state between the matrix and the reinforced mM was observed using SEM, and the density and bending strength were measured. When observed using a polarizing microscope, 71 helices were observed to be sintered carbon particles or individual particles in close contact with each other in a colored pattern (shining L-saic pattern), and NM was dotted within this 71-1 sock. The butanium boride particles were observed as islands with a uniform color, and the butanium boride particles were observed as white dots.The area of the black dots indicating pores was approximately 3 It was %. The state of the interface between the 71-trix and the reinforcing fibers observed by SEX was such that they were both integrally bonded, and no separation of the 71-trix and the reinforcing fibers was observed. In addition, the carbon fiber-reinforced carbon sintered body has a density of 1.83 g/an'' and a bending strength of 115
To 0! It was J/an2.

As a comparative example, the bulk density is 1 and 99. A commercially available graphite electrical discharge machining electrode for precision finishing with a bending strength of 100 ONS'/cm2 and a bending strength of 100 ONS'/cm2 was used.The electrode for evaluation was machined to a diameter of 20mm, a height of 35Mff1, and a 5M diameter electrode in the center. I made a hole and used it.

The electrodes of the above examples and comparative examples were set in an electric discharge machine (), and the roughness of the machined surface and machining speed were evaluated under the following conditions.The conditions were: current value = 1OA,
5A, time 5 minutes, on time = 10μs, 30μS
1 Working fluid: white kerosene (jet flow 0035Ny/CIA), workpiece: hot work tool steel.

The results are shown in Table 1.

In both Examples 1 and 2, compared to the conventional material of the comparative example, the machining roughness was small and the smoothness was excellent, and the machining speed was fast. Furthermore, in the examples, Example 2, in which inorganic microparticles were added, was slightly better. This composite electrode for electrical discharge machining has improved performance compared to conventional graphite-based electrodes.

[Effects of Hatsumachi] Table 1 (Private T Kamishiro) The composite electrode for electric discharge machining of the present invention is made of a special carbon fiber-reinforced carbon sintered body. This carbon fiber reinforced carbon sintered body has high density and high strength. It is possible to improve both machining speed and machined surface roughness, which are difficult to improve because of conflicting results in normal electric discharge machining.

Patent applicant: Toyota Motor Corporation Patent applicant: Osaka Gas Co., Ltd.

Claims (2)

[Claims] (1) It has a structure in which carbon fibers or carbon fibers and inorganic microparticles are embedded integrally in a carbon matrix, and the carbon matrix has a uniform density of optically anisotropic fine particles when seen with a polarizing microscope. It has a mosaic structure, the ratio of peeled interfaces between the carbon fibers and the carbon matrix is 10% or less of the total interfaces, and the density is 1.
．． A composite electrode for electrical discharge machining, characterized in that it is made of a carbon fiber-reinforced carbon sintered body having a carbon fiber strength of 65 or more. (2) Carbon fiber-reinforced carbon sinter obtained by sintering a composite consisting of carbonaceous powder having a self-sintered body in which uncarbonized carbonaceous fibers or uncarbonized carbonaceous fibers and inorganic microscopic bodies are embedded. A composite electrode for electric discharge machining characterized by being composed of a body.