JPS6227934B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrode material for electric discharge machining, and more particularly to a method for manufacturing a composite electrode material having a conductive layer formed by sintering and infiltration using a powder metallurgy method.

Electrical discharge machining is a non-cutting process, so it can easily process hard and strong materials such as hardened steel and diamonds, and it can also process complex shapes.The force applied during machining is small, and the thermal effect is small. It has advantages such as high processing accuracy, easy automation, and economical. However, it has drawbacks such as slow processing speed, electrode wear, and the need to precisely control the gap between the workpiece and the electrode. In electric discharge machining, the workpiece is melted and evaporated by a short arc discharge, forming a shape that corresponds to the electrode, but a similar phenomenon occurs on the electrode side, and the amount of wear is small, but the electrode wears out. becomes. The degree of electrode wear varies depending on the material of the electrode material and the magnitude of the discharge energy.

Conventionally, pure metals such as copper, aluminum, tungsten, and molybdenum, mild steel, copper alloys, sintered alloys, and graphite have been used as electrode materials, but each has advantages and disadvantages. For example, when copper, aluminum, etc. are used, the conductivity is high and it is easy to process the shape of the electrode, but it is subject to heavy wear, resulting in dimensional changes when drilling deep holes, requiring the electrode to be replaced during processing. There is also. Graphite is also easy to process and has relatively little wear and tear, but it lacks toughness and is prone to breakage, which may require electrode replacement. On the other hand, sintered alloys such as copper-tungsten and silver-tungsten have low wear, but have the drawbacks of low conductivity, biting in the early stages of arc discharge, and poor fitting, resulting in slow machining speed. However, when carving a deep shape with high dimensional accuracy into a mold,
A sintered body such as copper-tungsten is used to finish the electrode into a specified shape, and a shank material made of a general metal body such as hard steel is soldered with silver on the opposite side to the side that contacts the workpiece in order to attach it to the electrical discharge machine. I was using it with it attached.

Brazed electrode materials do not necessarily have sufficient joint strength due to brazing, and when the joint area is large or external force is applied to the joint, insufficient compatibility between the brazing material and the sintered material may occur during electrical discharge machining. Another disadvantage was that the presence of minute voids caused local discharges and the like, causing the joints to peel off and fall off.

The present invention uses a sintered body such as copper-tungsten and improves the machining speed by improving the biting especially at the start of machining, considering the fact that the machining speed is slow but the electrode wear is low and the dimensional accuracy is high. It is an object of the present invention to provide a manufacturing method for forming an electrode material mainly made of a high-melting point metal sintered body, which can firmly integrate even the shank portion through an increase in size and a simple process.

In order to increase the processing speed by combining the slow processing speed of high melting point metal sintered bodies with the fast processing speed of copper or silver, a copper layer or a silver layer is placed on the surface of the workpiece. Depending on the shape to be carved into the workpiece, the conductive layer, such as a copper layer or a silver layer, may be a thin layer of 1 mm or less. In this case, the conductive layer can be provided by a surface treatment method such as plating. The present invention is characterized in that a highly conductive layer is provided on the electrode surface of the electrode material, and that a shank material is joined and integrated with the electrode material at the same time as infiltration.
That is, the present invention is based on Japanese Patent Application No. 53-121556 (Japanese Unexamined Patent Publication No. 1983-12155), which was filed by the present applicant on almost the same day as the present patent.
48537 hereinafter referred to as "A Invention". ) is an invention related to a manufacturing method.

Specifically, in the invention A, a copper layer or a silver layer is bonded to the electrode surface, and this bonding is devised by using plating or vapor deposition. This makes it possible to easily bond relatively thin and wide layers (eg, about 0.5 to 1 mm thick).

The present invention adds 1 to 10% by weight of one or both of thorium oxide (ThO ₂ ) and zirconium oxide (ZrO ₂ ) powders with an average particle size of 3μ to tungsten or molybdenum powder with an average particle size of 3μ as a high melting point metal. The mixed powder is then molded into an electrode shape using a mold at a molding pressure of 1 to 4 t/cm ² . After forming, it is sintered in a hydrogen atmosphere at 1000° to 1300°C for 30 minutes to 3 hours to create a skeleton (fired product) mainly made of tungsten or molybdenum. The purpose of adding thorium oxide and zirconium oxide is to improve processing speed. Next, the skeleton is infiltrated with copper or silver as an infiltrant, and at the same time a shank material is joined. For this purpose, a general metal body to be used as a shank material is processed into a predetermined shape in advance, the bonding surfaces are cleaned, and a bonding material is applied. The bonding material is usually 40 to 60% by weight of silver and one or both of cobalt and nickel for a total of 60 to 60% by weight.
Mix well and use 40% by weight. The finer the powder mixture is, the better the dispersion becomes. The amount of mixed powder is
The amount may be about 0.1 to 0.2 g/cm ² , and the mixed powder may be used as it is, or may be made into a paste with water, alcohol, etc., or may be used in a mesh plate. By regulating the alloy components, powder size, and powder amount in this way, the bonding strength can be improved.

The skeleton is placed on the bottom of a graphite container that matches the electrode dimensions, and a shank material is placed on top of it via a bonding material so that it matches the shape of the electrode material, and the shank material is melted into the gap between the graphite container, the skeleton, and the shank material. Fill with soaking material. Copper or silver is used as the infiltration material, and it may be in the form of a powder or a lump, but it is used in the form of small pieces. The amount of infiltration material may be the required amount to soak into the skeleton and the amount to melt the bonding material to form a composite metal, but there is a gap between the graphite container, skeleton, and shank material, so take this into consideration and add a slightly larger amount by weight. . Next, this graphite container was charged into a continuous hydrogen furnace, and the infiltration conditions were
Pass through the furnace at 1300° to 1000°C for 30 minutes to 3 hours. Through this infiltration, 20 to 35% by weight of copper or silver is uniformly distributed in the skeleton, and there are no voids in the tungsten or molybdenum skeleton, resulting in a copper or silver-tungsten or molybdenum sintered body. A portion of the infiltration material dissolves the bonding material and forms a bonding layer.

Furthermore, after removing the infiltration material adhering to the copper or silver-tungsten or molybdenum sintered material and the outer periphery of the shank material, the surface of the sintered body that contacts the workpiece (hereinafter referred to as the electrode surface) is degreased and cleaned, and then the specified copper Electroplating is performed using a plating solution or a silver plating solution. In this case, since a plating layer on the side surface of the sintered body is not required, an organic insulating film that is not eroded by the plating solution is formed in advance. When using a plating solution, consider the adhesion between the plating layer to be generated and the sintered body, the degree of completeness of the plating layer, plating solution management, working time, etc. In addition to electroplating, chemical plating and vacuum deposition can also be used, but the latter two produce thin films and can only be used in special cases. As the electroplating, ordinary copper sulfate plating, copper pyrophosphate plating, copper cyanide plating, silver cyanide plating, silver nitrate plating, etc. can be used.

The manufacturing method of the present invention can be used as an electrode material for electrical discharge machining from the electrode surface, including a copper layer, a copper-tungsten or copper-molybdenum sintered body, a bonding layer, a shank material or a silver layer, and a silver-tungsten or silver-molybdenum sintered body. A four-layer composite electrode material consisting of , a bonding layer, and a shank material is obtained. By providing a copper layer or a silver layer on the electrode surface in contact with the workpiece according to the manufacturing method of the present invention, arc discharge is performed at the high conductivity layer of copper or silver at the start of electrical discharge machining, resulting in smooth discharge and machining speed. Even after the layer disappears, the electrode shape of the copper or silver-tungsten or molybdenum sintered body corresponds to the melting surface of the workpiece, so arc discharge progresses smoothly and electrode wear is minimal, allowing precise dimensions to be formed. They can be formed on the workpiece, increasing the overall processing speed. In addition, by integrally joining the shank material using the bonding material in the infiltration process as in the present invention, the brazing process can be omitted, the strength is increased, and the electrode material does not peel off or fall from the shank material, and the processing speed using the composite material can be reduced. increase,
Integration of shank materials has excellent effects in terms of quality, safety, productivity, etc. Note that if a copper layer or a silver layer is provided on the shank joint surface of the electrode material at the same time as the electrode surface is formed, the shank material can be soldered and joined, which may be preferable in terms of work efficiency.

Examples of the present invention will be described below.

Example 1 5% by weight of thorium oxide with an average particle size of 3μ was added to 95% by weight of tungsten powder with an average particle size of 3μ, mixed well, and placed in a cylindrical mold with a diameter of 20mm and a height of 20mm under a molding pressure of 4t/cm. Mold in ^{step 2} . After molding, it is sintered at 1000℃ for 1 hour in a hydrogen atmosphere to create a tungsten skeleton. On the other hand, hard steel (S45C) is machined as a shank material to the specified dimensions so that it can be attached to the electrode mounting part of an electrical discharge machine, and the surface that connects to the electrode is degreased and cleaned, and a 60:40 ratio of silver and cobalt is used. Make the mixed powder into a paste with alcohol and apply. This process will be explained below using the cross-sectional view of FIG. 1a and the plan view of FIG. 1b. In FIG. 1a, the tungsten skeleton 11 is placed at the center of the bottom of the graphite container 15, the shank material 13 is loaded through the bonding material 12, and the amount of the bonding material that is soaked into the skeleton and the bonding material is dissolved in the gap between the graphite container 15 and the graphite container 15. Copper powder is added as the infiltrant material 14, taking into consideration the amount that is slightly surplus to the amount required to form the alloy and the bonding layer. Next, this graphite container 15 is placed in a continuous hydrogen furnace and passed through the furnace at 1200°C for 30 minutes as infiltration conditions to melt the infiltrant and uniformly soak it into the skeleton, while at the same time forming a bonding layer. do. After the infiltration, if the excessively adhered infiltrant is removed, the copper-tungsten sintered body 21, the bonding layer 22, and the shank material 23 are continuous from the electrode surface as shown in the cross-sectional view of FIG. 2a and the plan view of FIG. 2b. A three-layer composite electrode material can be obtained.

Next, a clear coat is applied to the outer circumference of the electrode material except for the surface that will become the electrode surface of the sintered body 21, and after forming an insulating film, the electrode surface is buffed, degreased and cleaned, and placed in a copper sulfate plating bath, and the electrode material is used as a cathode and a copper plate. Copper plating is performed on the electrode surface using the electrode as an anode. The plating bath is copper sulfate ( _CuSO4 .
5H ₂ O) 210g/, sulfuric acid 50g/, chlorine ion 50
mg/, thiourea 0.01g/, dextrin 0.01
plating at a cathode current density of 5 A/dm ² and a bath temperature of 30° C. for 20 minutes. This will cause the electrode surface to
A copper plating layer (24 in Figure 2a) with a thickness of 0.7 mm was obtained. After copper plating, the required parts are buffed to the specified dimensions. Note that the clear coat to prevent electrodeposition is removed as necessary. By the method of the present invention, as shown in FIG.
A four-layer composite electrode material of No. 3 is obtained. Note that the entire surface of the electrode material may be plated in advance and then machined into a predetermined shape.

Example 2 Using the same raw material as in Example 1, it was placed in an E-shaped mold as shown in the plan view of Figure 3b and molded at a molding pressure of 4t/cm ² .After molding, it was heated at 1000°C in a hydrogen atmosphere. Sinter for 30 minutes to create a tungsten skeleton. On the other hand, we machined hard steel (S45C) as a shank material to the specified dimensions so that it could be attached to the electrode attachment part of the electrical discharge machine.
The joint surface with the electrode surface was degreased and cleaned, and a mixed powder of silver and cobalt mixed at a ratio of 60:40 was made into a paste with alcohol and applied. A composite electrode material having a three-layer structure including a shaped copper-tungsten sintered body 31, a bonding layer 32, and a shank material 33 is obtained.

Next, a clear coat is applied to the outer periphery of the electrode material except for the surface that will become the electrode surface of the sintered body 31, and after forming an insulating film, the electrode surface is buffed, degreased and cleaned, and placed in a silver nitrate plating bath.
Silver plating is performed on the electrode surface using the electrode material as a cathode and the silver plate as an anode. The plating bath consists of silver nitrate 50g/, sodium carbonate 50g/, sodium nitrate 60g/, potassium cyanide 50g/, and the cathode current density
Plating was carried out for 20 minutes at 1.5 A/dm ² and a bath temperature of 20°C. This results in a silver plating layer approximately 0.5 mm thick (Fig. 3 a, b).
34) was obtained. After silver plating, the required areas are buffed to the desired dimensions. The clear coat to prevent eyelid electrodeposition should be removed if necessary. By the method of the present invention, a pure silver layer 3 is formed from the electrode surface as shown in FIG. 3a.
4, copper-tungsten sintered body 31, bonding layer 32,
A four-layer composite electrode material of the shank material 33 is obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the steps of an embodiment of the method of the present invention, FIG. 2 is a diagram showing an embodiment of the method of the present invention, and FIG. 3 is a diagram showing an embodiment of the method of the present invention. 11... Tungsten skeleton, 12... Bonding material, 13, 23, 33... Shank material, 14... Infiltration material (copper), 15... Graphite container, 21, 31
...Copper-tungsten sintered body, 22, 32...Joining layer, 24...Copper plating layer, 34...Silver plating layer.

Claims (1)

[Claims] 1. In a method for manufacturing an electrode material for electrical discharge machining by infiltrating high melting point metal tungsten or molybdenum with copper or silver, a total of 60% of silver and one or two of cobalt and nickel are added during infiltration. A process of bonding a ferrous metal body to a predetermined surface via a bonding material consisting of ~40% by weight, and a process of bonding the electrode surface to a thickness of 0.5 to 1 mm after infiltration.
1. A method for producing a copper or silver-tungsten or molybdenum layered composite electrode material for electrical discharge machining, comprising the step of forming copper or silver by plating or vapor deposition.