JPH04322911A - Graphite material for electrode, suitable for wire electric discharge machining - Google Patents

Abstract

PURPOSE:To provide a graphite material which can prevent occurrence of pores, cracks and chips, which have been problems caused during wire electric discharge machining for an electric discharge graphite electrode, and which can carry out wire electric discharge machining in a short time and with satisfactory dimensional accuracy and surface roughness. CONSTITUTION:A graphite suitable for an electrode which is formed by a wire electric discharge machining process, has a total volume of pores of 0.090cc/g measured by a mercury press-charge process, and an average pore size is <=1.3mum. Further, a rate of pores having diameters in a range of + or -20% of the average pore size exceeds 50% of the total volume.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a graphite material for forming graphite electrodes used in die-sinking electric discharge machines, and in particular to a graphite material suitable for electrode machining by wire electric discharge machining. It is.

0002

[Prior Art] Such graphite electrodes are formed by cutting or other processing of graphite material, but in recent years electrodes have become more complex in their structure and have advanced dimensions. Accuracy is also increasingly required. In order to meet such demands, it has become necessary to process graphite materials with high precision, and it has also become necessary to process them in a short time.

[0003] One method that meets the demands for higher accuracy and higher speed machining is the wire-cut electrical discharge machining method. As shown in Figure 1, this electric discharge machining method involves applying a constant voltage between the workpiece (graphite material) and a wire electrode inserted through it, and then moving the wire electrode from the top to the bottom in the diagram. The wire electrode is moved in the processing direction while maintaining a certain distance from the workpiece, and the workpiece is cut by electric discharge generated between the wire electrode and the workpiece. Note that during this machining, machining fluid is poured into the machining location in order to remove generated hydrogen, oxygen, machining waste, etc. and to improve electrical discharge. According to such a wire electric discharge machining method, the work of forming electrodes using graphite material can be performed quickly and accurately, which is very advantageous.

However, although the wire electrical discharge machining method has such advantages, it has the following difficulties in producing electrode products with precision and excellent surface roughness.

[0005] Small holes may be formed on the surface of the machined electrode, and chips and cracks may occur near the edges. The finish tended to be rough.

[0006] When the discharge becomes unstable, the discharge concentrates in the same place, causing abnormal local wear of the wire electrode, lowering the tensile strength, increasing the number of wire breaks, and prolonging the time required for machining. Ta.

[0007] The inventors of the present invention have studied various causes of the above-mentioned difficulties and found that (1) the smaller the total amount of pores, the more stable the electric discharge and the less likely the formation of pores in the workpiece. The number tends to decrease. Moreover, disconnection of wire electrodes is also reduced. (2) The smaller the average pore radius, the fewer pores will occur in the workpiece. (3) The more uniform the size of the pores, the more stable the discharge will be, and the less disconnection of the wire electrode will occur. Having obtained the above knowledge, the present invention was completed.

[0008]

[Problems to be Solved by the Invention] The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to improve the suitability of a graphite material for forming electrodes for wire electrical discharge machining. This is an improvement in

An object of the present invention is to stabilize wire electric discharge machining by uniformly distributing electric discharge points, and as a result, to improve machining accuracy and machined surface roughness. It is an object of the present invention to provide a graphite material for electrodes that can be processed in a short time by reducing the incidence of wire electrode breakage.

0010

[Means for Solving the Problems] In order to solve the above problems, the means taken by the present invention is to provide a material for forming an electrode, which is processed by a wire electrical discharge machining method to form the electrode. A graphite material suitable for use in which the total amount of pores measured by mercury intrusion method is 0.090 cc/g or less, the average pore radius is 1.3 μm or less, and ±20% of the average pore radius. A graphite material for an electrode, characterized in that the proportion of pores having a pore radius in the range of 50% or more of the total pore volume is 50% or more. Measurement by mercury intrusion method shows that the surface tension of mercury is 480 dyne/cm and the contact angle is 140.
The test was carried out under conditions of 100°C and a maximum pressure of 100 MPa. Further, the average pore radius was determined based on the 50% pore diameter.

[0011] The total amount of pores in this graphite material is 0.090c.
The reason why it needs to be less than c/g is that stable and uniform discharge cannot be expected during wire electrical discharge machining.

[0012] Further, among the pores in this graphite material, the average pore radius measured by mercury intrusion method is 1.3 μm or less,
The reason why it is necessary for the proportion of pores with a pore radius within ±20% of the average pore radius to be 50% or more of the total pore volume is to achieve uniform electrical discharge during wire electrical discharge machining. This is because the uniformity of the pore size throughout the graphite material plays an important role. however,
Since it is technically impossible to leave only pores with such a specific radius in the graphite material, the above-mentioned range is determined as the tolerance range so that the pores fall within a certain tolerance range.

[0013]

Effects of the Invention When the graphite material according to the present invention constructed as described above is subjected to wire electrical discharge machining, the electrical discharge is generated uniformly over the entire wire electrode, and stable machining can be performed.

[0014] Therefore, the surface of the electrode formed of this graphite material is extremely smooth, making this electrode an excellent product. In particular, electrodes formed by electric discharge machining have no holes on the electrode surface, and no local chips or cracks at all.

On the other hand, regarding the wire electrode, as mentioned above, the electric discharge during electrical discharge machining occurs throughout the wire electrode, so the electric discharge concentrates locally on the wire electrode, resulting in abnormal wear and a decrease in tensile strength. There is no wire breakage caused by cutting, and problems such as longer machining time do not occur.

[0016]

[Example] Petroleum coke was pulverized to an average flow diameter of 5 μm and placed in a kneader. 90 parts by weight of medium pitch was added as a binder to 100 parts by weight of coke powder, and the mixture was kneaded at 200° C. for 1 hour. Further, the lid of the kneader was opened at 200° C. for 1 hour, and the generated gas was exhausted by a blower to remove the gas and obtain a kneaded mixture. After cooling, this kneaded mixture was pulverized and molded using a rubber press at a surface pressure of 1 t/cm2, and the raw product thus obtained was fired at about 1000°C and then graphitized at about 3000°C. In this way, the graphite material shown in Example 1 was obtained.

Petroleum coke was pulverized to an average particle size of 7 μm and placed in a kneader, and 110 parts by weight of medium pitch was added as a binder to 100 parts by weight of the coke powder.
Knead for 1 hour at ℃. Thereafter, the same operations as in Example 1 were repeated to obtain the graphite material shown in Example 2.

[0018] Wire electrical discharge machine DW manufactured by Mitsubishi Electric Corporation
A graphite block of the present invention having a thickness of 100 mm was processed using C-110H and a brass wire having a diameter of 0.2 mm under certain conditions. The results are shown in Table 1.

[0019]

[Table 1]

[0020]

[Effects of the Invention] As detailed above, in the present invention,
"A graphite material that is a material for forming an electrode and is suitable for processing by wire electrical discharge machining to form the electrode has a total pore volume of 0.
090cc/g or less and the average pore radius is 1.090cc/g or less.
The proportion of pores that are 3 μm or less and have a pore radius within ±20% of the average pore radius to the total pore volume is 50
% or more, and as a result, in wire electrical discharge machining, the machining is stabilized by evenly distributing the discharge points, and as a result, machining accuracy and machined surface roughness are improved. In addition, it is possible to provide a graphite material for electrodes that can be processed in a short time with a low incidence of wire electrode breakage.

[Brief explanation of drawings]

FIG. 1 is a partial cross-sectional view showing a graphite material according to the present invention being machined into an electrode by employing a wire electrical discharge machining method.

Claims (1)

[Claims] Claim 1: A material for forming an electrode, comprising:
A graphite material suitable for forming the electrode by processing by wire electrical discharge machining, the total amount of pores measured by mercury intrusion method is 0.090 cc/g or less, and the average pore radius is 1.3 μm or less. A graphite material for an electrode, characterized in that the ratio of pores having a pore radius in the range of ±20% of the average pore radius to the total pore volume is 50% or more.