JPS6227932B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrode material for electrical 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 involves placing the workpiece and machining electrode facing each other in an insulating machining fluid with an extremely small gap, and repeating short-term pulsed arc discharge.
This is a method of processing a workpiece. Since it is a non-cutting process, it can easily process even hard and strong materials such as hardened steel and diamonds. It can process complex shapes. The force applied during machining is small, the thermal effect is small, and the machining accuracy is high. While it has advantages such as being easy to automate and being economical, it has disadvantages such as slow processing speed, electrode wear, and the need to precisely control the gap between the workpiece and the electrode. However, today it has been gradually improved and is widely used.

In electrical discharge machining, a short arc discharge of 10 ^-7 to 10 ^-3 s melts and evaporates the workpiece, forming a shape that corresponds to the electrode. This phenomenon occurs and the electrode wears out.
The amount of wear of the electrode is much smaller than that of the workpiece, but it also varies depending on the material of the electrode and the magnitude of the discharge energy. Conventionally, this electrode material was copper,
Pure metals such as aluminum, tungsten, and molybdenum, mild steel, copper alloys, sintered alloys, and graphite are used, but each has advantages and disadvantages. For example, electrodes made of copper, aluminum, etc. have high conductivity and are easy to process into the shape of the electrode, but they are subject to rapid wear and tear, resulting in dimensional changes in deep holes, etc., and the need to replace the electrode midway. or Graphite is also easy to process and has relatively little wear and tear, but because it lacks toughness, it is prone to breakage and may require electrode replacement. On the other hand, sintered alloys such as copper-tungsten and silver-tungsten are less abrasive, but have the drawbacks of low conductivity, which causes biting at the beginning of arc discharge, and poor fitting, which slows machining speed. However, when carving a deep shape with high dimensional accuracy into a mold, conventionally a sintered body of copper-tungsten or the like is used, which is machined into an electrode of a predetermined shape, and then the electrode is machined using an electric discharge machine. In order to attach the machine to the workpiece, a shank material made of a general metal such as hard steel was soldered with silver on the surface opposite to the surface in contact with the workpiece. Electrode materials made of copper-tungsten sintered bodies finished as described above have a slow processing speed, and the joint strength by brazing is not necessarily sufficient, and discharge may occur when the joint area is large or when external force is applied to the joint. During machining, there was a drawback in that localized discharges occurred due to the presence of minute voids due to insufficient compatibility between the brazing filler metal and the sintered material, resulting in the bonding part peeling off and falling off.

The present invention has been made in view of these points, and as an electrode material for electric discharge machining, it particularly improves the biting at the start of machining, increases machining speed, maintains dimensional accuracy, and reduces electrode wear. 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 a simple process. 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.
In other words, the present invention is based on Japanese Patent Application No. 121556/1983 (Japanese Unexamined Patent Application Publication No. 55/1988), which was filed by the present applicant on almost the same day as the patent application.
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 brazing is used for this bonding. This makes it possible to easily bond layers ranging from relatively thick layers (for example, about 2 to 3 mm) to relatively thin layers.

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 infiltrant, and the shape may be powder or lump, but it is used in 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 an alloy layer, 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 contained and 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 body and the outer periphery of the shank material, the surface of the sintered body in contact with the workpiece (hereinafter referred to as the electrode surface) is sintered with a pure copper plate or pure silver plate. Braze the plate pieces cut into a cross-sectional shape. The thickness of the plate depends on the shape to be formed on the workpiece, but it is usually
Approximately 0.5 to 3 mm is sufficient. As the brazing material in this case, for materials containing tungsten, a silver brazing material to which nickel of JIS Z3261 BAg-3 grade is added is suitable for the purpose of improving wettability. but,
When using in a vacuum, it is better to use BAg-8 grade silver brazing filler metal, as it contains zinc and cadmium, which will evaporate in a vacuum atmosphere and cause problems. After brazing, necessary machining is performed to create an electrode for electrical discharge machining.

By the manufacturing method of the present invention, electrode materials for electrical discharge machining are prepared from the electrode surface, such as a copper layer, a brazing layer, a copper-tungsten or copper-molybdenum sintered body, a bonding layer, a shank material or a silver layer, a brazing layer, a silver- A five-layer composite electrode material consisting of a tungsten or silver-molybdenum sintered body, 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 as in the present invention, arc discharge is performed in the highly conductive layer at the start of electrical discharge machining, resulting in smooth discharge, and the workpiece is connected to the electrode. The copper or silver-tungsten or molybdenum sintered body acts as an electrode after it has been processed into the corresponding shape and the copper or silver layer and also the brazing layer have been consumed, but at this point the shape of the sintered body is not covered. It adapts to the shape of the machined surface, arc discharge progresses smoothly, there is less wear on the electrode, it is possible to form precise dimensions on the workpiece, and the overall machining speed increases. It is. 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. By increasing the size and integrating the shank material, there are excellent effects in terms of quality, safety, productivity, etc. Note that if a silver layer or a copper 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 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 at a molding pressure of 4t/cm ² Molded at. 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 a predetermined size so that it can be attached to the electrode attachment part of an electric discharge machine, and the surface to be joined with the electrode material is degreased and cleaned, and a bonding material is applied. This step will be explained below using the cross-sectional view of FIG. 1a and the plan view of FIG. 1b. The bonding material is silver and cobalt in a ratio of 60:40.
The mixed powder mixed in the ratio of 1 is made into a paste with alcohol and applied (Fig. 1, 12). 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 an infiltrant 14 in an amount 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 infiltration, if the excessively adhered infiltrant is removed, a three-layer composite electrode material consisting of a copper-tungsten sintered body 21, a bonding layer 22, and a shank material 23 continuous from the bottom as shown in FIG. 2a can be obtained. . Next, after cleaning the surface of the sintered body 21 that will become the electrode surface, a 3 mm thick copper plate is loaded through BAg-3 silver brazing material, placed in a furnace, and bonded by melting the brazing material. As shown in FIG. 2b, a five-layer composite electrode material consisting of a pure copper layer 24, a silver brazing bonding layer 25, a copper-tungsten sintered body 21, a bonding layer 22, and a shank material 23 is obtained from the electrode surface. Similarly, for the prismatic electrode material, Figure 2c is obtained. If there is any seepage of silver solder, adhesion of infiltration material, or misalignment of the copper plate, sintered body, or shank material, final machining is performed to finish the work.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing steps of an embodiment of the method of the present invention, and FIG. 2 is a diagram showing an embodiment of the method of the present invention. 11... Tungsten skeleton, 12... Bonding material, 13, 23... Shank material, 14... Infiltration material (copper), 15... Graphite container, 21... Approximately 30% copper
Containing tungsten sintered body, 22... bonding layer, 24...
Pure copper layer, 25...brazing layer.

Claims (1)

[Claims] 1. In a method for producing 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 through a bonding material consisting of ~40% by weight, and a process of bonding the electrode surface to a thickness of 0.5 to 3 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 a copper layer or a silver layer by brazing.