JPH09192931A - Surface layer forming method by electrical discharge machining - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform surface treatment having high corrosion resistance and high degree of adhesion by performing electric discharge while stirring powder after making a material for forming a front surface layer of a work piece into the powder state in working fluid and interposing it between poles. SOLUTION: Silicon powder 9 is mixed in working fluid 8 and filled in a processing tank 6, air is fed from an air pump 11 to the processing tank 6, and precipitation of silicon powder is prevented by applying the stirring action. Working fluid decomposition material and processing powder to be formed by electric discharge through a process of automatically, intermittently and vertically moving an electrode 4 is diffused without being accumulated between poles 7. When silicon powder is interposed, the formation of a smooth silicon coating film can be obtained. When silicon powder is interposed between the poles 7, a finishing surface roughness is made minute.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a surface layer by electric discharge machining, and more particularly, it realizes a finely machined surface by promoting electric discharge dispersion on the surface of a material having conductivity, or has a high corrosion resistance and wear resistance. A method of forming a coating.

[0002]

2. Description of the Related Art As known from Japanese Patent Laid-Open No. 62-24916, the inventors of the present invention have been able to apply aqua regia by electric discharge machining using a metal electrode called a semimetal such as a silicon electrode. It proposes a method of forming a tough surface layer that is not corroded and is resistant to damage such as peeling and cracking even when subjected to permanent deformation of several tens of percent. In this conventional method, a normal electric discharge machine is used, a semimetal such as a silicon electrode is used as an electrode material, and SUS304 (18Cr-8Ni) is used as a material to be processed.
Stainless steel), 13Cr steel, or high-speed steel is subjected to electric discharge machining, and a machined surface of SUS304 to 13Cr steel or high-speed steel with strong corrosion resistance is obtained by machining for several tens of minutes to several hours. It is a thing.

An example of the electrode structure in this case is shown in FIG. 13 and explained. Reference numeral 1 is a silicon plate, for example, which is a structure in which the copper round bar 2 is attached to the copper round bar 2 by a conductive adhesive 3. Of course, the electrodes can also be formed by machining or electric discharge machining a silicon material. In something like this,
In order to process the mold etc. by electric discharge machining and to perform the surface treatment of corrosion resistance and abrasion resistance on the surface by the above method, first, rough machining of the shape using copper or graphite electrode with low electrode consumption characteristics After that, processing with a silicon electrode is performed. The reason for processing in two steps is that the silicon material is expensive and the electrode consumption during electrical discharge machining is extremely large, so it is difficult to use it for shape processing with a large amount of processing removal (about 10 times the processing amount is exhaust).

[0004]

That is, in the present situation, it is a two-step process that requires a silicon electrode in addition to the copper or graphite electrode for shape processing. In other words, it is necessary to make a silicon electrode in addition to the shape-processing electrode (copper, graphite), and it is necessary to replace the electrode. Therefore, if it is possible to form a surface layer similar to that using a silicon electrode or the like on the surface of a workpiece only with a copper or graphite electrode for shape processing, it will have great industrial significance. is there.

The present invention has been made in order to solve the above-mentioned problems. By interposing a powder of a material to be surface-treated, and agitating the intervening material with the powder. A method for forming a surface layer by electric discharge machining, which can make the surface of a material to be processed finer or form a coating film on the surface of the material to be processed by an electrode that is usually used for electric discharge machining such as copper for shape machining, graphite, etc. Is to provide.

[0006]

A method of forming a surface layer by electric discharge machining according to the present invention comprises a material for forming a surface layer of a work piece, which is formed between electrodes and a work piece.
The surface layer of the workpiece is formed by discharging the powder while stirring the powder with a stirring means after the powder is interposed in the processing liquid.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1. An embodiment of the method of the present invention will be described below with reference to the drawings. First, the principle of the present invention will be described. FIG.
Indicates a normal discharge state, starting from discharge generation, scattering of molten metal, discharge traces, generation of processed powder, and restoration of insulation. Further, FIG. 1 shows a case where there is a silicon powder as a material for forming the surface layer between the electrodes. The discharge is likely to occur due to the presence of the silicon powder. This is because there is apparently the same effect as that between the gaps is narrowed. The silicon powder is evaporated and melted by the occurrence of electric discharge, and collides with the electrode surface in a high temperature and high pressure state and is firmly pressed.
The mating electrode material (for example, copper or graphite) also acts in the same manner, but since silicon powder is interposed between the electrodes in the first embodiment, there is more silicon powder between the electrodes,
Since the distance to the processing point is shorter than that of the counter electrode, most of the silicon will be pressure bonded.

The above is a description of the principle of the present invention, which will be described in more detail with reference to the schematic diagram of FIG. 3A shows a non-processed state, and FIG. 3B shows a processed state.
Is an electrode, 5 is a work piece installed in the processing tank 6, and a gap 7 is formed between the work piece 5 and the electrode 4. 8 is a working fluid in the working tank 6, 9 is a silicon powder mixed in the working fluid 8, 10 is a power supply device for supplying working energy to the gap 7, 11 is an air pump which is a stirring means, By feeding air into the working fluid 6, the working fluid 8 is stirred. Reference numeral 12 is a hydraulic cylinder device that moves the electrode 4 up and down with respect to the workpiece 5, 13 is a piston rod thereof, and 14 is a servo device that controls the hydraulic cylinder device 12.

The method of the present invention is carried out by the apparatus of the above-mentioned embodiment. The processing liquid 8 contains silicon powder 9 (average particle size 2
0-40 μm, mixing ratio of silicon powder and working liquid 20 g
/ L) was mixed and filled in the processing tank 6, and air was sent to the processing tank 6 from the air pump 11 to give a stirring action to prevent precipitation of the silicon powder. Further, as shown in the figure, the electrode 4 is automatically and intermittently moved up and down so that the processing liquid decomposition product and the processing powder generated by the electric discharge can diffuse without accumulating in the gap 7. A machining liquid circulating pump may be used instead of the air pump 11 which is a stirring means. The electrode material was composed of copper and graphite.

FIGS. 4 and 5 are micrographs showing the metal structure for explaining the effect of the method of the present invention. In FIG. 4, copper is used as the material of the electrode 4 and SKH-5 is used as the workpiece.
1 was used, and a current peak value of 10 A, a pulse width of 16 μs, and a rest width of 16 μs were set as electrical conditions.
In FIG. 4A, kerosene was used as the working liquid, and its surface roughness was 9 μmRmax. On the other hand, FIG.
In (b), kerosene is used as a working liquid, and 20 g of silicon powder is added to 1 L of this kerosene (however, the average particle size is 20 to 40 μm).
φ), the surface roughness is 4 μmRmax
It is.

In FIG. 5, silicon is used as the material of the electrode 4 and SKH-51 is used as the work piece, and the electrical condition is a current peak value of 1 A, a pulse width of 2 μs, and a rest width of 2 μs.
Is set. FIG. 5 (a) shows kerosene as a working fluid, and FIG. 5 (b) shows kerosene as a working fluid, in which silicon powder is interposed. In addition to the above conditions, the results shown in FIGS. 4 and 5 are 0 to 2 in addition to the main power supply voltage of 80 V in order to increase the distance between the electrodes.
A 20V auxiliary power supply was used. FIG. 6 shows a high voltage superimposing circuit used at this time. In the figure, R1, R2 are resistors,
D is a diode, TR1 and TR2 are transistors, 10
Reference numeral a indicates a main power source and 10b indicates an auxiliary power source. FIG. 7 shows the experimental result of the stability of processing obtained by changing the voltage of the auxiliary power supply by such a high voltage superposition circuit.

The following is a summary of what has been obtained by the first embodiment. The higher the voltage is, the more stable it is. That is, when the silicon powder is interposed between the electrodes, the discharge easily occurs at a large distance between the electrodes even with the same voltage, but it is still understood that the processing is more stable when the high voltage is applied. The test piece obtained in this experiment was immersed in aqua regia for 50 minutes, but was not corroded. FIG.
The micrograph of FIG. 5 shows the state of the surface structure of the test piece at this time. As shown in FIG. 4A, the silicon coating film is not formed only by the copper electrode, and the finished surface roughness is also rough. The formation of a smooth silicon coating film can be seen when silicon powder is interposed (FIG. 4 (b)). From FIG. 5, it can be observed that the molten silicon is impacted and collides with the processed surface. Further, if silicon powder is interposed between the poles, the finished surface roughness becomes fine (see FIG. 5 (b)). According to the processing example that was tested, when a silicon electrode was used, the processing liquid used was ordinary mineral oil (kerosene), which required about 30 minutes, but was achieved in about 3 to 5 minutes.

By the way, the electrodes are electrically divided under the condition that the machining speed of the electric discharge machining is the fineness of the finished surface roughness, and
There is a multi-divided processing circuit that processes the connection from the power supply to each electrode through a resistor. FIG. 8 shows another embodiment of the method of the present invention using this multi-division processing circuit.
Reference numeral 15 is a resistor group, 16 is an oscillator, 17 is an amplifier, 18 is a transistor switching circuit, 4a, 4b, ... 4
n is a divided electrode. It has already been revealed by the present inventors that, when an electrode is made of a material having electric resistance instead of being divided in this way, it is an integrated electrode, but is divided every time a discharge occurs and a large number of discharges are generated at the same time. Crab has announced that its typical electrode material is a silicon electrode. In this embodiment as well, by interposing silicon powder between the electrodes, the same effect as that of the above-described embodiment can be obtained.

Also, when electric discharge machining is performed with silicon powder interposed between the electrodes, an electrode made of silicon or a graphite surface is reacted with silicon to form a SiC surface, or silicon powder and zinc are mixed. It is the same when electrical discharge machining is performed with electrodes with resistance such as a mixture, a mixture of silicon powder and copper, a mixture of silicon and water glass, a mixture of silicon, zinc and water glass, etc. The result is that the finished surface becomes finer even under the electrical conditions of. As described above, according to the present invention, the silicon forming the surface layer of the workpiece is interposed between the electrode and the electrode formed by the workpiece in the working liquid in the form of powder, and the discharge is performed. The surface layer of the workpiece is formed by carrying out the above.However, even in such a case, it is not always necessary to prevent the silicon powders to be surface-treated from sticking to each other. Not perfect.

9 to 12 are for preventing the silicon powders to be surface-treated from sticking to each other.
It shows another invention of the present invention to which an oscillating motion mechanism is added. More specifically, 20 is a table on which a workpiece (not shown) is placed, 4 is an electrode facing the workpiece, 4A to 4D are replacement electrodes, and 12 is a hydraulic pressure for servo controlling the electrode 4. Cylinder device, 21 is a hydraulic cylinder device 12
Numerical control device for controlling the servo control of the table 22 is a table 20
X-axis motor for driving the table in the X-axis direction, 23 is the table 20
Is a Y-axis motor for driving in the Y-axis direction, and 24 is an electrode exchanging device, which has a function of automatically exchanging the electrodes 4A to 4D at the stages of rough machining, intermediate machining, and finishing machining as described above. . In addition, 10 is a machining power supply that supplies machining energy between the electrode 4 and the workpiece, and 13 is a hydraulic cylinder device 12.
This is a piston rod of which the electrode 4 is attached to the tip.

In such a structure, a machining layer (not shown) for accommodating the machining fluid is placed on the table 20, the movements of the X-axis motor 22 and the Y-axis motor 23 in the respective directions, and the electrode exchange device 24. The operation and electric conditions of the machining power source 10 are controlled by the numerical controller 21 as with the hydraulic cylinder device 12. A swing motion having a pattern as shown in FIG. 10 is applied between the electrode 4 and the workpiece.

FIG. 11 shows an example of an experiment conducted under the following processing conditions in order to explain the effect of the above-mentioned embodiment in which the swinging motion mechanism is added. Processing conditions are: 1 electrode: copper 2 work piece: high speed steel (SKH-51) 3 working fluid: kerosene mixed with silicon powder 20 g / L 4 electrical condition: current peak value 1ρ = 1A pulse width τp = 2μs pause Width τs = 2 μs 5 Electrode polarity: electrode (−) That is, in FIG. 11, FIG. 11 (a) shows the surface roughness in the case of processing only with the working liquid, and FIG. 11 (b) shows the silicon powder in the working liquid. FIG. 11 (c) shows the surface roughness in the case where the metal powder is mixed and the rocking motion is not applied between the electrode 4 and the workpiece. The surface roughness when motion (rocking speed 96 mm / min) is applied is shown.

FIG. 12 is a photomicrograph showing a metallographic structure for explaining the effect of the above embodiment in which a swinging motion mechanism is added. In FIG. 12 (a), silicon powder is contained in the working liquid. FIG. 12B shows the state of the metallographic structure in the case where the metal structure is mixed and no oscillating motion is applied between the electrode 4 and the work piece. The state of the metal structure when a dynamic motion is given,
Each is shown. In FIG. 12 (a), it can be seen that silicon is fixed and the finished surface roughness is rather rough. FIG. 12 in which a swinging motion is applied between the electrode 4 and the workpiece.
In (b), it looks gentle. The reason for this is considered to be that the phase of the unevenness between the electrode 4 and the surface of the workpiece is changed in position and smoothed.

Although the embodiments of the method of the present invention have been described above, it goes without saying that the present invention also includes the following modifications. B) Not only silicon powder but also other metal powders such as tungsten carbide (WC) and zirconium boride (Z)
It can also be used to form surface layers of semi-metallic or carbides or borides, ie fine ceramic materials, such as rB2). B) Further, the working fluid is not limited to a mineral oil, and silicon oil or water (distilled water) can be used as long as electric discharge machining is performed. C) When coating a non-conductive ceramic or the like, the surface of the ceramic can be formed by making the surface of the ceramic a conductor only by electroless plating, silver mirror reaction, or the like. D) When it is desired to use a non-conductive material as the coating substance, it may be possible to use the finest powder as possible and mix the conductive powder therein to perform the above.
In this case, the non-conductive substance is, for example, alumina (Al2
O3).

In any of the above-mentioned embodiments, what is important is to sufficiently interpose the silicon forming the surface layer such as silicon powder between the electrodes.
That is, in order to make the silicon powder exist near the discharge point in excess of the amount that is machined and removed by one electric discharge, the distance between the electrodes is made wider than in normal electric discharge machining.

[0021]

As described above, according to the present invention, the material for forming the surface layer is interspersed in the working liquid in the form of powder, and the powder is discharged by the stirring means while stirring the powder. By performing the machining, the powder in the machining fluid is not fixed and the electric discharge is evenly dispersed, so that the machining speed can be improved, and the corrosion resistance is large even by the electrode used for the electric discharge machining, Surface treatment with high adhesion is possible. Generally known high temperature nitriding, CVD, etc.
Since the material is processed at a high temperature of around 900 ° C., the material is likely to be distorted or softened, and when the temperature is lowered, the material is easily peeled off. .

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of the present invention, and is an explanatory diagram when a silicon powder is present between electrodes.

FIG. 2 is a diagram for explaining the principle of the present invention and is an explanatory diagram of a normal discharge state.

3 (a) and 3 (b) are each a schematic configuration diagram for explaining one embodiment of the present invention.

4 (a) and 4 (b) are each a micrograph showing a metal structure for explaining the effect of the present invention.

FIG. 5 is a micrograph showing a metal structure for explaining the effect of the present invention.

6 is a principle diagram showing an example of the power supply unit of FIG. 3 by a high voltage superposition circuit in which an auxiliary power supply is superposed on a main power supply.

7 (a), (b), and (c) are explanatory views showing the stability of machining with respect to the discharge start voltage.

FIG. 8 is a principle diagram of a multi-division processing circuit showing another example of the power supply unit.

FIG. 9 is a view corresponding to FIG. 3 for explaining another invention of the present invention.

FIG. 10 is an explanatory diagram showing the pattern of the swing motion of FIG.

11 (a), (b), and (c) are explanatory views showing a comparison of finished surface roughness with and without swinging motion.

12 is a micrograph showing a metal structure for explaining the effect of FIG.

FIG. 13 is a configuration diagram of electrodes for explaining a conventional example.

[Explanation of symbols]

4 electrodes, 5 workpieces, 7 contacts, 8 working fluid, 9
Silicon powder, 10 power supplies, 11 air pump. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A material for forming a surface layer of the workpiece is placed between the electrode and the workpiece in a working liquid in a powder state, and then the powder is stirred by a stirring means. A method for forming a surface layer by electric discharge machining, wherein a surface layer of a workpiece is formed by performing electric discharge while stirring.