JP2000096105A - Production of electrode for discharge coating and electrode for discharge coating produced by its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sufficiently high quality by filling the powder of a heat resistant coating material into a desired die without blending a binder, applying pressure thereon, energizing it under pressure to generate plasma at the contact points between particles and executing sintering. SOLUTION: Particles P at the inside of a die are applied with voltage from the contact points Pn and Pm between a punch 1A or 2A and the particles P. Namely, as to the sintered body, by being energized under pressure from upper and lower both sides, plasma is generated at these contact points, so that diffusion is swiftly allowed to occur between the particulate bodies, and stable sintering is made possible. In this way, the obtd. electrode has the following characteristics: it is composed of a simple material; in the case the material is a mixture, the characteristics of the coating layer formed by discharge impact coating working are made to be the ones different from those of the original electrode: its thermal conductivity is low as much as possible; at the time of the coating working, the degree of concentration of energy is made high on the discharge point, and the deterioration in the base material hardly occurs; its strength is high: and its hardness is high.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for applying a discharge coating to a surface of a machine component or the like to convert the physical properties of the surface of a base material.
The present invention relates to a method for producing a coating electrode used for giving abrasion resistance, easy generation of electrons, a low coefficient of friction, and the like, and a coating electrode produced by the method.

[0002]

2. Description of the Related Art A technique for obtaining a discharge coating material by spark sintering a powder of a heat-resistant material is known. However, conventionally, the binder was blended into a plurality of base materials and mixed and sintered, so that the desired physical properties could not be obtained in terms of hardness, abrasion resistance, etc. after discharge coating. There was a problem to say.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a discharge electrode material having a sufficiently high quality after discharge coating, and a discharge-coated electrode material produced by the method. It is in. The present invention provides a method of sintering a material that has been conventionally difficult to sinter without using a binder to obtain a discharge coating electrode, and a discharge coating electrode material manufactured by such a method.

[0004]

In order to achieve the above object, the powder of the heat-resistant coating material is filled into a desired mold without blending a binder, and is pressurized. A plasma is generated at the point and sintered to produce an electrode for discharge coating. As the heat-resistant coating material, powder such as WC, which has conventionally been difficult to sinter alone, is used alone and without a binder. During sintering, the pressing force, the discharge current density and the discharge time are controlled in order to give a desired density to the sintered body.

When particles of the material powder are energized in a pressurized state, plasma is generated at a contact portion between the particles, so that the surface is activated by the plasma and diffusion between the particles occurs. The material powder is pressurized, and the contact portions of the particles are further heated by energization and locally fused, so that further diffusion proceeds, and the particles are deformed and bonding between the particles occurs.

Hereinafter, the state where sintering is caused by the method of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a state in which two spherical particles are bonded by sintering, FIG. 2 is a schematic diagram showing a state of particles sintered in a sintering mold, and FIG. FIG. 4 is a front view of a mold used in the apparatus shown in FIG. 3, FIG. 5 is an explanatory view of the first experiment design method when there is no interaction, and FIG. 6 is a second experiment plan. It is explanatory drawing in case there exists a mutual effect of the law. FIG. 1 shows a state in which two spherical particles of the material powder are in contact with each other and are successively pressed. In the figure, in the state of 1, 2
The particles are in contact at point a. The radius of the particles is r, and their center distance L1 is equal to 2r. The state 2 in the figure shows a state in which plasma is generated at the mutual contact portion a, the surface is activated by the plasma, diffusion between particles occurs, and a fused portion b of particles is generated.
The distance between the particle centers is L2. The state of No. 3 shows a state in which the diffusion is further advanced, the particles are deformed, the bonding between the particles occurs, and the neck part d is generated. The distance between the particle centers is L3. The approaching amount of two particles (L1-L
If 3) is α,

(Equation 1) Here, K is a constant and n is the diameter of the neck.

[0007] Eventually, the particles are deformed to fill the spaces between the particles, and the density of the sintered body increases. The distance between the centers of the particles shrinks from the initial L1 to L2 and L3, the sintered body is densified, and simultaneously heated from the side by the mold e.
Sintering will proceed.

[0008] Inside the actual mold, the particles are three-dimensionally and three-dimensionally contacted, but if simplified two-dimensionally, they are as shown in Fig. 2 which is a schematic diagram. A voltage is applied to the particle P from contact points Pn and Pm between the punch 1A or 2A and the particle P. In other words, when the pressurized current is applied to the sintered body from both the upper and lower sides, plasma is generated at these contact points, so that the diffusion is rapidly caused between the granules and stable sintering becomes possible. This characteristic is shown by Equation 1.

Here, assuming that the strength of the formed sintered body is σ,

(Equation 2)

That is, as the strength, the smaller the particle diameter d to be sintered, the higher the strength σ. The porosity p is determined by the strength σ
Indicates that it acts exponentially. The K value according to the method of the present invention is 1.5 times or more higher than the K value according to the known sintering.

[0011] Desirable characteristics of the electrode used for the discharge impact coating include: 1) a simple material. When the material is a mixture, the physical and metallurgical characteristics of the materials are different from each other, so the electrode material is altered during the discharge impact coating process, and the characteristics of the formed coating layer are different from those of the original electrode. Will be different. 2) Thermal conductivity is as low as possible. When applying the discharge impact coating, the concentration of energy at the discharge point increases, and the coating is applied with almost no deterioration of the base material. 3) High strength. It is necessary to sufficiently withstand the mechanical shock at the time of impact discharge coating processing. 4) Hardness should be as high as possible. When abrasion resistance characteristics or easy electron emission characteristics are required, an easy electron generating material is used as an electrode. And it is required to have high hardness.

At the time of performing the electric discharge coating, if the diameter of the crater generated by the sintered electrode is a,

(Equation 3) Can be represented by

Since a discharge current flows through the crater, the temperature rises and diffusion proceeds rapidly. If the temperature is approximately T ° C.,

(Equation 4) It is expressed as

J. Fisher reports that grain boundaries and dislocation diffusion are greatly affected by crystal defects. Assuming that the thickness of the grain boundary is d and the diffusion density after τ time at the positions of x and y is C,

(Equation 5)

Equation (5) shows that diffusion coating can be sufficiently performed by a short-time discharge according to the characteristics of the error function. Further, the base material of the electrode material is not a single substance but a mixture, and the concentration C of each component is C1, C2, C
3,... Cn, each element diffuses individually at the time of diffusion to form a coating, in other words, the components of the discharge coating layer change in a complicated manner depending on the depth, It is difficult to control the industrial and metallurgical conditions according to the purpose.

Therefore, an ideal single substance is selected as an electrode material, which is activated and sintered, molded at a free density, and then the electrode material is formed. The density of the electrode is as low as the strength permits. It becomes effective. That is, it is advantageous that the thermal conductivity of the electrode is lower. This electrode can be used as an effective system when used as an SSD.

[0017]

Embodiment 1 A material having good temperature characteristics, that is, a material having an effective hardness up to a high temperature, and a high hardness material having a high electric conductivity,
WC was selected. SSD processing was performed using a WC material as an electrode. As the SSD conditions, the gap was servo-fed with a discharge time τ 0.5 μsec and a discharge peak value IP30A for SSD processing. Base material drill: TaC15% Co5% Remaining WC diameter 0.8
WC was subjected to SSD processing on a drill having a diameter of mm to test the abrasion resistance.

The work piece is 50% ceramic-filled epoxy P
Electrode material (A), rotation speed (C), feed speed (B),
The step feed (D) and the whole were statistically processed to perform a performance test of the discharge coating process. The workpiece is a 1.6m thick PCB with 3 and 5 layers, and the rotation speed is 30000RPM and 60000RPM.
And the feed rates are 5 m / min and 7 m / min.
Compared to SD processed and non-SD processed, WC SS
D The processing contribution was analyzed for variance.

Table 1 shows the actual measurement conditions, and Table 2 shows the processing contribution ratio and the results of variance analysis. Similarly, in the second example of Table 1, the contribution ratio is 82%, and in the third example, it is 31%. It is known that the SSD effect is improved by the electrode density.

【table 1】

[Table 2] However, here, A: Electrode material for SSD machining of drill B: Drilling feed speed A × B Electrode material and feed speed C Drill speed A × C Electrode material and speed of drill D Step feed e Error column Combination of experiments Level 1 Conditions for estimating the state of factors Level 2 Same as above Total number of data Total number of experimental data Contribution ρ% Percentage that contributed to producing results

[0020]

Example 2 A WC material having a diameter of 4 mm and a length of 6 mm was mounted on the apparatus shown in FIG. 3 and the die 6 shown in FIG. In the drawing, 1a to 1n are movable punches, 2a to 2n are fixed punches, 4 is a cooling water coil, 5 is a sintered body, 5a to 5n are formed between movable punches 1a to 1n and fixed punches 2a to 2n. Is a material powder filled in the cavity, 6 is a die, 7 is a reinforcing cylinder, and 8 and 8 are current-carrying terminals. Center size
Fill the cavities 5a to 5n with 0.6 μm WC powder,
At first, 1a ~ 1n and 2a ~ 2n with upper and lower punches
Pressurize to 50kg / cm, energize at 300A and hold for 1 minute, then increase current to 750A, pressurize to 300kgf / cm2, hold for 4 minutes, control feed position and form WC with 88% density did.

The die 6 is made of graphite and has movable punches 1a to 1n and fixed punches 2a to 2n as shown in FIG.
Has a die hole through which the movable punch 1a is inserted.
1 to 1n. A WC powder having a center particle diameter of 0.6 μm was charged into the cavity and sintered. Electric power was supplied from the power supply terminals 8 to control the amount of feed of the punch to obtain a sintered body having a target density.

According to the present invention, since a sintered body which can be used as an electrode as it is without the need for post-sintering processing is obtained, compared with a case where a large-sized sintered material is processed to produce an SSD electrode, The cost was reduced to about 1/5 or less. That is, the unusable portion becomes zero, and the material can be saved. Material 10
There was an effect that 0% can be used, and the cost of electrode baking time was also reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram when a particle is made into a sphere in a particle sintered state.

FIG. 2 is an overall schematic diagram when particles are made into spheres in a particle sintered state.

FIG. 3 is a vertical cross-sectional view (a cross-sectional view taken along the line XX shown in FIG. 4) showing one embodiment of the sintering apparatus.

FIG. 4 is a sectional view taken along the line YY shown in FIG.

FIG. 5 is a table showing actual measurement conditions, and is an explanatory diagram in the case where there is no effect interaction of the first experimental design method.

FIG. 6 shows a contribution ratio ρ% and a calculation table, and is an explanatory diagram in the case where there is an effective interaction of the second experiment design method.

[Explanation of symbols]

 1A, 1B vertical pressing punch a contact point of particles at the start of sintering b contact point of particles at the start of sintering n width of neck r particle diameter d neck portion 1a-1n movable punch 2a-2n fixed punch 4 cooling water coil Reference Signs List 5 sintered body, 5a to 5n material powder filled in cavity 6 die 7 reinforcing cylinder 8, 8 conducting terminal

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[Procedure amendment]

[Submission date] September 24, 1998 (1998.9.2)
4)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG.

FIG. 4

FIG. 2

FIG. 3

FIG. 5

FIG. 6

Claims (4)

[Claims] 1. A powder of a heat-resistant coating material is filled into a desired mold without blending a binder, pressurized, and a current is applied under the pressure to generate plasma at a contact point between the particles and sinter the powder. Production method for an electrode for discharge coating. 2. The method for producing an electrode for discharge coating according to claim 1, wherein a desired density is imparted to the sintered body by controlling a pressing force, a discharge current density and a discharge time. 3. An electrode for electric discharge coating produced by the method according to claim 1. 4. The electrode for discharge coating according to claim 3, further comprising an easy electron generating material.