JPS6227933B2 - - 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 machine hard and strong materials such as hardened steel and diamond, it can machine complex shapes, the force applied during machining is small, the thermal effect is small, and the machining accuracy is high. While this method has advantages such as high productivity, ease of automation, and economy, it has disadvantages such as slow processing speed, electrode wear, and the need to precisely control the gap between the workpiece and 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 also occurs on the electrode side, causing wear and tear on the electrode. . Although the amount of wear of the electrode is much smaller than that of the workpiece, it also varies depending on the material of the electrode 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, 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 through the process. do.
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 are less abrasive, but have the drawbacks of low conductivity, which causes biting in the early stages 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 then finished into an electrode of a predetermined shape, and then the electrode is mounted on an electric discharge machine. 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 to increase machining speed, and from the viewpoint of maintaining dimensional accuracy, there is little wear on the electrode. Another object of the present invention is 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 by a mechanical bonding method, 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 the patent application filed in 1973, which was filed by the present applicant on approximately the same date as the present patent.
-121556 (JP-A-55-48537 hereinafter referred to as the "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 to utilize mechanical bonding. This results in a relatively wide layer (if the electrode has a large surface area, it will be difficult to bond).
can be reliably joined. In addition, in the present invention, copper,
In addition to silver, it also includes aluminum or its alloys. Although this is not as effective as pure copper or pure silver, it was added because it was found to significantly improve the biting properties. Therefore, in the present invention, the thickness of the layer is set to 0.5 to 5 mm in consideration of aluminum and its alloy, but the essence thereof is not different from that of the A invention.

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 3 μm to tungsten or molybdenum powder with an average particle size of 3 μm 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 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 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 material and the outer periphery of the shank material, the surface of the sintered body that is in contact with the workpiece (hereinafter referred to as the electrode surface) is coated with highly conductive copper or silver. Alternatively, plate pieces cut into the cross-sectional shape of a sintered body from aluminum or its alloy plates are joined. Although the thickness of the plate depends on the shape formed on the workpiece and the joining method, it is usually about 0.5 to 5 mm. The first joining method is
As shown in the cross-sectional view in Figure a and the plan view in Figure b, a copper plate 14 with high conductivity is fixed with screws 15 to an electrode material in which a shank material 13 is integrated with a copper-tungsten sintered body 11 via a bonding layer 12, for example. There is a way.
The material of the screw 15 is preferably copper or copper alloy. When joining, the electrode surface of the sintered body 11 and the joint surface of the copper plate 14 are kept clean and smooth and screwed to prevent gaps from forming. Further, as shown in the cross-sectional view of FIG. 2a and the plan view of FIG. There is also a method of press-fitting. In this case, the electrode surface of the sintered body 21 is finished by machining in advance according to the ring size of the collar into which the electrode surface is press-fitted, or a mold of this size is used when making the skeleton molded body. On the other hand, the silver plate 24 may be made from a plate by machining, or may be made by casting or powder metallurgy. In addition, when press-fitting, clean the electrode surface of the sintered body and the surface of the silver plate in contact with the sintered body, stack the silver plate on the integrated electrode material, and press-fit by applying compressive force in the longitudinal axis direction of the electrode material. do. In this case, use a jig if necessary, and make sure that the silver plate is in close contact with the sintered body so that there are no gaps. Also, if the silver plate is soft and deformed, it is repaired to the shape of the electrode in post-processing.

The sintered body may be joined to the sintered body by screws as shown in the cross-sectional view of FIG. 3a and the plan view of FIG. 3b, instead of press-fitting. For example, in an electrode material in which a shank material 33 is integrated with a copper-tungsten sintered body 31 via a bonding layer 32, a thread is cut into a copper block with high conductivity, and a thread is also cut into the electrode surface of the sintered body and screwed. 35
Join by. In this case too, clean the joint surface and
Avoid creating gaps. Further, as shown in the cross-sectional view of FIG. 4a and the plan view of FIG. There is also a method of joining by driving 45. In this case, the material of the pin 45 is preferably copper or a copper alloy in view of deformation by driving to bring the sintered body and the copper plate into close contact, as well as electrical conductivity and corrosion resistance. The dimensions, number, etc. of the pins vary depending on the shape of the electrode and the thickness of the copper plate, but usually a small number is sufficient. Note that the electrode surface of the sintered body and the bonding surface of the copper plate should of course be made smooth and clean, and should also be closely attached by pin bonding so that there are no gaps. There are other mechanical joining methods, but they can be used depending on the purpose of use.

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 copper-molybdenum sintered body. A four-layer composite electrode material consisting of , a bonding layer, and a shank material is obtained. As in the present invention, by providing a layer with high conductivity such as a copper layer, silver layer or aluminum layer on the electrode surface in contact with the workpiece, arc discharge is performed in the layer with high conductivity at the start of electrical discharge machining, thereby making it smooth. After the copper, silver, or aluminum layer is consumed, the copper or silver-tungsten or molybdenum sintered body acts as the electrode, but at this point In this case, the shape of the sintered body adapts to the shape of the workpiece surface, arc discharge progresses smoothly, there is less wear on the electrode, and precise dimensions can be formed on the workpiece. The overall machining speed increases.
The method of mechanically joining layers with high conductivity as in the present invention has the advantage that the thickness of the layer can be set arbitrarily, and also layers different from the infiltration material of the sintered body can be joined. Since it is different from brazing, there is no difficulty in selecting the brazing material.

In addition, by integrally joining the shank material in the infiltration process using a bonding material as in the present invention, the brazing process between the shank material and the electrode material can be omitted, the strength is increased, and the electrode material does not peel off or fall from the shank material. In addition to increasing the processing speed due to the composite body having the high conductivity layer, the integration of the sink material has 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 forming the electrode surface, 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. 5th below
This step will be explained using the cross-sectional view in Figure a and the plan view in Figure b. 60:40 silver and cobalt as bonding materials
The mixed powder mixed in the ratio of 1 is made into a paste with alcohol and applied (Fig. 5, 52). In FIG. 5a, a tungsten skeleton 51 is placed at the center of the bottom of a graphite container 55, a shank material 53 is loaded through a bonding material 52, and the amount of the bonding material is dissolved and soaked into the skeleton in the gap between it and the graphite container 55. Copper powder is filled in as an infiltrant material 54 with a certain amount surplus to the amount required to form the alloy and the bonding layer. Next, this graphite container 55 is charged into a continuous hydrogen furnace and passed through the furnace at 1200°C for 30 minutes as the infiltration condition to melt the infiltrant and uniformly soak it into the skeleton, and at the same time form a bonding layer. Form. After infiltration, if the excessively adhered infiltrant is removed, a copper-tungsten sintered body 11 and a bonding layer 1 are formed on the upper part as shown in Fig. 1a.
2. A three-layer composite electrode material continuous with the shank material 13 is obtained. Next, cut a 20 mm diameter disk from a 3 mm thick copper plate, make a hole in the center for passing a 4 mm diameter screw, and countersink the head of the screw on the plate surface that is in contact with the workpiece surface. Clean the hole and flatten the board surface. On the other hand, in order to fasten a screw to the electrode surface of the composite electrode material, a screw that matches the diameter of the screw is cut and cleaned, and the electrode surface is flattened and cleaned. Next, the copper plate is placed on the electrode surface of the composite electrode material and screwed using screws.
By this manufacturing method, a four-layer composite electrode material consisting of a copper layer 14, a copper-tungsten sintered body 11, a bonding layer 12, and a shank material 13 as shown in FIG. 1 is obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the method of the present invention, and FIG.
The figure shows an embodiment of the method of the present invention, FIG. 3 shows an embodiment of the method of the present invention, FIG. 4 shows an embodiment of the method of the present invention, and FIG. 5 shows a method of the present invention. It is a figure which shows the process of one Example. 11,21,31,41...Tungsten sintered body containing about 30% copper, 12,22,32,42...Joining layer, 13,23,33,43,53...Shank material, 14,24,34,44... Pure copper layer, 15... Screw, 35... Threaded portion, 45... Pin, 51... Tungsten skeleton, 52... Bonding material, 54... Infiltration material (copper), 55... Graphite container.

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. The process of bonding the iron-based metal body to a predetermined surface via a bonding material consisting of ~40% by weight, and the process of bonding the electrode surface to a thickness of 0.5 to 5 mm after infiltration.
1. A method for producing a composite electrode material for electric discharge machining in which a copper, silver, aluminum or aluminum alloy-tungsten or molybdenum layered electrode material is formed by a mechanical bonding method.