Discharge machining method

Abstract

To provide an electric discharge machining method which makes it difficult for cracks or chips to occur in through holes even if the shortest distance between the through holes is short, and which can shorten the machining time by increasing the machining speed. [Solution] This is an electric discharge machining method for simultaneously forming five or more through holes, the shortest distance between which is less than 0.5 mm, in a plate-shaped workpiece 2 made of a brittle material, using an electric discharge machine 1. The electric discharge machine 1 has five or more pipe electrodes 11 corresponding to the five or more through holes, and a substrate 12 for holding these pipe electrodes 11, and forms the five or more through holes simultaneously while independently flowing machining fluid through each of the five or more pipe electrodes 11 and oscillating the substrate 12 in a horizontal plane without rotating it.

Description

[Technical Field]

[0001] The present invention relates to an electric discharge machining method for simultaneously forming a plurality of through holes in a workpiece. [Background technology]

[0002] As an example of such an electric discharge machining method, Patent Document 1 discloses "a method for drilling through holes in an amorphous carbon substrate, characterized in that electric discharge machining is performed using an electrode formed by fixing, via resistors, a plurality of conductive rods whose dimensions are smaller than the final dimensions of the through holes by a predetermined finishing amount, thereby simultaneously drilling a large number of through holes with a diameter of 2.0 mm or less in the amorphous carbon substrate." [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-118852 Summary of the Invention [Problem to be solved by the invention]

[0004] When multiple through holes are formed simultaneously by electrical discharge machining, if the distance (shortest distance) between the through holes becomes short, there is a problem that the through holes are more likely to crack or chip. This is not a significant problem with the amorphous carbon substrate that Patent Document 1 targets, but the problem becomes more pronounced with materials that are even harder and more brittle, such as conductive ceramics.

[0005] The problem to be solved by the present invention is to provide an electric discharge machining method that is less likely to cause cracks or chips in through holes even if the shortest distance between the through holes is short, and that can increase the machining speed and shorten the machining time. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided the following electric discharge machining method. An electric discharge machining method for simultaneously forming five or more through holes, each having a shortest distance between adjacent through holes of less than 0.5 mm, in a plate-shaped workpiece made of a brittle material by an electric discharge machine, comprising: the electric discharge machine has five or more pipe electrodes corresponding to the five or more through holes, and a base material for holding these pipe electrodes; An electric discharge machining method in which machining fluid is independently passed through each of the five or more pipe electrodes, and the five or more through holes are formed simultaneously and in parallel while the substrate is oscillated in a horizontal plane without being rotated. [Effects of the Invention]

[0007] The electric discharge machining method of the present invention is a method for simultaneously forming five or more through holes in a plate-shaped workpiece made of a brittle material, with the shortest distance between the through holes being less than 0.5 mm.With the electric discharge machining method of the present invention, even if the shortest distance between the through holes is short, cracks and chips are less likely to occur in the through holes, and the machining speed can be increased to shorten the machining time. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a conceptual diagram showing the configuration of an electric discharge machine used in an embodiment of the present invention. [Figure 2] 3 is a schematic plan view showing an example of an arrangement of through holes formed in a plate-shaped workpiece in an embodiment of the present invention. FIG. [Figure 3] FIG. 3 is a cross-sectional view showing an example of a pipe electrode used in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] In an embodiment of the present invention, an electric discharge machine is used to simultaneously and in parallel form five or more through holes, each having a shortest distance between adjacent through holes of less than 0.5 mm, in a plate-shaped workpiece made of a brittle material. Figure 1 conceptually shows the configuration of the electric discharge machine used in this embodiment of the present invention. The electric discharge machine 1 shown in the figure has five or more pipe electrodes 11 corresponding to the five or more through holes to be simultaneously and in parallel formed, and a substrate 12 that holds these pipe electrodes 11. In this embodiment, the substrate 12 is made of a conductive material, particularly aluminum or iron. In this embodiment, although not shown, the workpiece 2 and the substrate 12 are electrically connected to an electric discharge machine current applying device, with one pole acting as a positive pole and the other as a negative pole. Although eight pipe electrodes 11 are shown in Fig. 1, the number of pipe electrodes 11 may be five or more, for example, ten or even one hundred or more. The arrangement of five or more pipe electrodes 11 is not limited to the linear arrangement shown in Fig. 1, and may be, for example, a simple lattice or a lattice with phase shifts. In short, it is sufficient that the arrangement corresponds to an arrangement of five or more through holes in which the shortest distance between the through holes is less than 0.5 mm. As will be described in more detail in the examples below, the greater the number of pipe electrodes 11, i.e., the greater the number of through holes formed simultaneously, the more significantly the effect of improving the machining speed compared to conventional small hole electrical discharge machining methods is manifested.

[0010] 2 shows a schematic example of an arrangement of through holes 21 formed in a plate-shaped workpiece 2. For convenience, the figure shows three through holes 21. Here, the shortest distances between the through holes in the arrangement in the figure are L1, L2, and L3, and in this embodiment, L1, L2, and L3 are all less than 0.5 mm.

[0011] In this embodiment, the machining fluid is passed through each of the pipe electrodes 11 independently, and five or more through-holes 21 are formed simultaneously in parallel while the substrate 12 is oscillated in a horizontal plane without being rotated. Specifically, in this embodiment, as shown in Fig. 1, a machining fluid collection section 13 is provided to cover the top of the pipe electrodes 11, and machining fluid is circulated independently through this machining fluid collection section 13 to each of the pipe electrodes 11. Here, in this embodiment, the machining fluid circulates between the machining tank 15 and the machining fluid collection section 13 through a machining fluid circulation path 14. Note that in this embodiment, the machining fluid is circulated from the upper end to the lower end of the pipe electrode 11. However, the machining fluid may alternatively be circulated from the lower end to the upper end of the pipe electrode 11. In this embodiment, when five or more through holes 21 are formed simultaneously, the substrate 12 is oscillated in a horizontal plane without rotating. As a result, five or more pipe electrodes 11 corresponding to the five or more through holes 21 oscillate in a horizontal plane together with the substrate 12. In this embodiment, since the pipe electrodes 11 oscillate in a horizontal plane, the diameter of the through holes 21 is larger than the diameter of the pipe electrodes 11. For example, by using a pipe electrode with a diameter of 1.8 mm and setting the oscillation width to 0.09 mm on one side, for a total of 0.18 mm, a through hole with a diameter of 2 mm can be formed. The remaining 0.02 mm is the discharge gap (the gap between the electrode and the workpiece). This discharge gap width varies depending on the machining conditions, but is generally approximately 0.005 to 0.05 mm on one side.

[0012] In this embodiment, when five or more through holes 21 are formed simultaneously, machining fluid is independently circulated through each pipe electrode 11, and the substrate 12 is oscillated in a horizontal plane without rotating. This is an electric discharge machining method devised by the inventors as a result of extensive testing and investigation, with the aim of suppressing cracking and chipping in the through holes and increasing the machining speed when the shortest distance between the through holes formed simultaneously is less than 0.5 mm. Specifically, when electric discharge machining is performed without oscillating the pipe electrode when the shortest distance between the through holes formed simultaneously is less than 0.5 mm, electric discharges tend to occur simultaneously from both walls of the through holes, resulting in cracking and chipping in the through holes and increased clogging of the pipe electrode. Furthermore, when electric discharge machining is performed without independently circulating machining fluid through each pipe electrode, it is difficult to remove machining debris, which can lead to abnormal discharges and machining stalls at depths of approximately 5 mm or more. To prevent cracking or chipping of the through holes, it is necessary to lower the machining current, which would result in a decrease in machining speed. In contrast, in this embodiment, by independently flowing machining fluid through each pipe electrode 11 and oscillating the substrate 12 in a horizontal plane without rotating it, cracking or chipping of the through holes and clogging of the pipe electrodes can be prevented without lowering the machining current, even under conditions where the shortest distance between simultaneously formed through holes is short (less than 0.5 mm). Specifically, in this embodiment, the machining current (peak value of discharge current) can be set to, for example, 3 to 6 A (when the main power supply voltage is 240 V). In the example of Patent Document 1, the machining current is set to 2 A. In comparison, in this embodiment, electric discharge machining can be performed under conditions of a higher machining current.

[0013] In this embodiment, the workpiece 2 is made of a brittle material. Examples of brittle materials include conductive ceramics, cemented carbide, cermet, and amorphous carbon, as described in Patent Document 1. However, the effects of the present invention are particularly pronounced when a plate-shaped conductive ceramic body, which is a hard and brittle material, is used as the workpiece. Note that conductive ceramics are ceramic materials in which conductive ceramic particles are finely dispersed in an insulating material such as alumina or zirconia, and amorphous carbon does not fall under the category of conductive ceramics.

[0014] In this embodiment, the thickness of the workpiece 2 can be 5 mm or more, and can also be more than 6 mm. When the thickness of the workpiece 2 is 5 mm or more, clogging of the pipe electrode 11 is likely to occur, and the effect of this embodiment achieved by oscillating the pipe electrode 11 is significantly exhibited. Furthermore, when the thickness of the workpiece 2 is more than 6 mm, the effect is even more significantly exhibited.

[0015] In this embodiment, the pipe electrode 11 can be cylindrical, i.e., a simple pipe shape, or it can be a so-called "coreless" electrode, which has a non-concentric wall inside along its length. Figure 3 shows an example of a cross section of a coreless pipe electrode 11. This coreless pipe electrode 11 has a straight wall 111 inside. In addition, such coreless pipe electrodes have traditionally been used in small-hole electrical discharge machining (EDM) to prevent cores (remnants of the workpiece) from remaining in the through-hole by rotating the pipe electrode on its axis. In this embodiment, however, a coreless pipe electrode is used in an EDM process in which the pipe electrode 11 oscillates horizontally without rotating. In this embodiment, since the pipe electrode 11 oscillates, the use of a coreless pipe electrode is not necessarily required to prevent cores from remaining in the through-hole. However, the use of a coreless pipe electrode is preferable, particularly from the perspective of preventing clogging of the pipe electrode 11. That is, when a coreless pipe electrode is used, even if a core remains (remnants of the workpiece), its shape is not cylindrical and is not similar to the inner diameter of the pipe electrode, thereby preventing clogging of the pipe electrode 11. Furthermore, even if clogging occurs in the pipe electrode 11, the multiple holes allow the machining fluid to continue to be supplied to the holes, preventing a decrease in machining speed. The preferred range of oscillation is 0.01 to 0.25 mm. If it is smaller than this, the core may remain, and if it is larger than this, the pipe needs to be made relatively thinner, which may make it difficult to handle and prone to deformation.

[0016] In this embodiment, current can be applied to each pipe electrode 11 through the substrate 12. However, when the number of pipe electrodes 11 is large, applying current to each pipe electrode 11 from the substrate 12 may result in partial disconnection or poor electrical continuity, resulting in poor discharge, depending on the method of joining the pipe electrodes 11. Therefore, in this embodiment, as conceptually shown in FIG. 1 , each pipe electrode 11 is electrically joined to the top or bottom surface of the substrate 12 (the bottom surface in FIG. 1 ) by electrical joining means 16. The electrical joining means 16 may be any of mechanical joining (fastening, clamping, etc.) using a beam or the like, joining using wire bonding, joining using a conductive adhesive, joining using solder or brazing, etc. Note that, although the electrical joining means 16 is provided on the bottom surface of the substrate 12 in FIG. 1 , it may also be provided on the top surface of the substrate 12, or on both the top and bottom surfaces. [Example]

[0017] As an example, a test was conducted to form a through hole in a workpiece made of conductive ceramics and having a thickness of 10 mm using the electrical discharge machining method according to the present invention (hereinafter referred to as "the machining method of the present invention") as well as the conventional small-hole electrical discharge machining method and the conventional die-sinking electrical discharge machining method as comparative examples, and the machining time was measured. The results are shown in Tables 1 and 2.

[0018] [Table 1]

[0019] [Table 2]

[0020] The test results shown in Table 1 are the results of forming through holes with a diameter of 1 mm, and when there were two or more holes, the shortest distance between the through holes was set to 0.2 mm. Note that although the machining method of the present invention is intended for five or more holes, the through holes were formed in accordance with the machining method of the present invention in order to compare the machining time with the small-hole EDM method and the die-sinking EDM method. As for the processing conditions, the processing current and the like were adjusted for each processing method, on the premise that no cracks or chips would occur in the through-holes. For the discharge electrode, a coreless pipe electrode with a diameter of 0.9 mm was used, oscillating 0.04 mm on one side for the present invention machining method and the small-hole EDM method, while an electrode with a tip diameter of 0.97 mm was used for the die-sinking EDM method. Note that for the small-hole EDM method, the EDM was performed while the coreless pipe electrode was rotated. Small hole EDM required a long processing time when machining multiple holes. Since cracks were less likely to occur in the first hole, the machining conditions could be strengthened and the hole could be machined quickly. However, when machining the second hole close to the first hole, cracks were more likely to occur, so the machining conditions had to be significantly lowered.

[0021] On the other hand, the test results shown in Table 2 are for the formation of through holes with a diameter of 2 mm, and when there were two or more holes, the shortest distance between the through holes was set to 0.2 mm. The machining conditions were the same as when forming through holes with a diameter of 1 mm, except for the shape of the discharge electrode used. For the present invention machining method and the small-hole EDM method, a coreless pipe electrode with a diameter of 1.8 mm was used, oscillating 0.09 mm on one side, and for the die-sinking EDM method, an electrode with a tip shape of 1.97 mm diameter was used.

[0022] As shown in Tables 1 and 2, the machining method of the present invention was able to shorten the machining time compared to the conventional small hole electrical discharge machining method when the number of holes was five or more. In other words, with the small hole electrical discharge machining method, cracks are less likely to occur in the first hole, so the machining conditions can be strengthened and the hole can be machined quickly.However, when machining the second hole close to the first hole, cracks are very likely to occur, so the machining conditions must be significantly lowered.As a result, when the number of holes is five or more, the machining time is longer than with the machining method of the present invention. The reason why the machining speed can be relatively increased in small-hole EDM is because a high current is applied (this becomes the rate-limiting factor if the chips are discharged properly). On the other hand, applying a high current makes cracks more likely to occur (cracks occur when there is a further area to advance). This becomes more pronounced when the current is concentrated in a smaller area (for example, a single coreless electrode). Because the next discharge occurs before the area is cooled by the machining fluid, the temperature tends to rise locally, making it more likely to cause cracks. Therefore, when machining points are close to each other, it is necessary to keep the current low to prevent cracks. In contrast, with the machining method of the present invention, even if the machining current is set to the same level as that which causes cracks in small-hole electrical discharge machining, the machining range is wide, so there is little local temperature rise and cracks are unlikely to occur. [Explanation of symbols]

[0023] 1 Electric discharge machine 11 Pipe electrode 111 Wall 12 Base material 13 Machining fluid collection part 14 Processing fluid circulation route 15 Processing tank 16 Electrical bonding methods 2 Workpiece 21 through hole

Claims

1. An electric discharge machining method for simultaneously forming five or more through holes, each having a shortest distance between adjacent through holes of less than 0.5 mm, in a plate-shaped workpiece made of a brittle material by an electric discharge machine, the method comprising: the electric discharge machine has five or more pipe electrodes corresponding to the five or more through holes, and a base material for holding these pipe electrodes; The electrical discharge machining method comprises flowing machining fluid independently through each of the five or more pipe electrodes, and simultaneously forming the five or more through holes in parallel while oscillating the substrate in a horizontal plane without rotating it.

2. The electric discharge machining method according to claim 1 , wherein the brittle material is a conductive ceramic.

3. 3. The electric discharge machining method according to claim 1, wherein the workpiece has a thickness of 5 mm or more.

4. 3. The electric discharge machining method according to claim 1, wherein the pipe electrode has a non-concentric wall therein.

5. 3. The electric discharge machining method according to claim 1, wherein the five or more pipe electrodes are electrically connected to the upper surface or the lower surface of the base material in the electric discharge machine.

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