JP2000246548A - EDM - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a highly productive electric discharge machining method capable of reducing machining time and maintaining good machining accuracy. SOLUTION: This is an electric discharge machining method in which a small hole is formed in a bottom surface of a large hole formed in a workpiece by electric discharge, and has an outer diameter substantially equal to the diameter of the large hole formed. An insulating guide core provided with a guide hole that penetrates both end surfaces and abuts at a position where a small hole is cut is inserted into the drilled thick hole, and a discharge serving as a counter electrode of the workpiece in the guide hole. An electric discharge machining method characterized by inserting a machining electrode and subjecting a small hole to electric discharge machining.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric discharge machining method, and more particularly, to an electric discharge machining method for continuously drilling holes having different shapes and / or diameters in multiple stages.

[0002]

2. Description of the Related Art In electric discharge machining, a cutting tool and a workpiece are used as electrodes in an insulating liquid such as white kerosene, and spark discharge is repeatedly performed between the electrodes. It is a method for performing processing, and is widely used for die processing such as drawing dies, press dies, forging dies, and plastic molding dies, and for drilling parts having holes with complicated contours.

2 to 4, a large-diameter round hole is drilled vertically from the top surface of a rectangular parallelepiped made of a metal material at a depth Z1, and a small-diameter round hole is coaxially formed from the bottom of the large-diameter round hole. An example of a drilled product in which round holes having different diameters are continuously drilled in two stages, and are drilled at a depth Z2 and the total depth (Z1 + Z2 = Z) is shallower than the height of the metal material. When such a drilled product is machined, a small-diameter round hole is first drilled at a depth Z, and then a large-diameter round hole is drilled at a depth Z1. It was.

[0004] When the drilling is performed in the above-described processing procedure, a small hole having a small diameter is inevitably drilled. However, in the cutting using a drilling machine, the chisel of the drill becomes long. In addition to problems such as an increase in thrust due to difficulty in performing appropriate thinning, torque increase due to friction on the outer periphery, misalignment due to poor biting due to longer chisel, and chip discharge The above-mentioned Z value naturally had a limit (usually several tens of mm) due to the difficulty of smooth operation and breakage of the drill.

In the case where the above-mentioned cutting is performed by electric discharge machining, "illustration: mechanism of electric discharge machining and 100% utilization method"
[Author: Mitsubishi Electric Corporation (Supervision: Nagao Saito), Publisher:
Technical Review Co., Ltd., Publication date: May 25, 1989, first edition, 8th print] Page 48: Item 1 of "Why" of EDM, description of "Why" regarding machining speed and Page 49: Figure 1.2
As shown in Fig. 8, precision machining is required when electric discharge machining of a long hole with a small diameter is required, thereby increasing the number of machining steps, increasing the consumption of electrodes, and frequently interrupting the process for replacement. And reduce productivity.

FIGS. 5 to 7 show, in place of the small-diameter round hole of the drilled product shown in FIG. Another example of a drilled product in which a round hole and a square hole different from each other are continuously drilled in two stages is shown. However, when such a drilled product is machined, the drilling machine cannot be used.

[0007] When machining the above drilled product by electrical discharge machining, the machining procedure is as follows: first, a large diameter round hole is drilled, and then a small hole with a square cross section is formed. When machining a small hole having a second square section from the bottom surface of the hole, the discharge machining accuracy of the hole is reduced due to the occurrence of secondary discharge such as centering and abnormal discharge.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above facts, and has as its object to reduce the processing time and to maintain the processing accuracy well. An object of the present invention is to provide a highly productive electric discharge machining method.

[0009]

According to the first aspect of the present invention, there is provided an electric discharge machining method for forming a small hole in a bottom surface of a large hole formed in a workpiece by electric discharge. An insulating guide core having an outer diameter substantially equal to the diameter of the drilled thick hole and provided with a guide hole penetrating both end surfaces and abutting at a position for cutting the narrow hole is provided in the drilled thick hole. It is characterized in that a small electrode is inserted into the guide hole and a machining electrode serving as a counter electrode of the workpiece is inserted into the guide hole to perform electric discharge machining of the small hole.

The electric discharge machining method according to the second aspect of the present invention is the electric discharge machining method according to the first aspect of the present invention, wherein the shape of the large hole formed in the workpiece and the bottom surface of the large hole are drilled. The shapes and cross-sectional areas of the small holes are different from each other.

According to a third aspect of the present invention, there is provided an electric discharge machining method according to the first aspect of the present invention, wherein a shape of a large hole formed in a workpiece and a bottom surface of the large hole are formed by drilling. The shapes and cross-sectional areas of the small holes are different from each other.

According to a fourth aspect of the present invention, in the electric discharge machining method of the first to third aspects, the insulating guide core is made of polyfluoroethylene.

In the present invention, the workpiece is not particularly limited as long as it has conductivity itself. For example, iron, cast iron, carbon steel, low chromium steel, low nickel-chromium steel, Cast stainless steel, heat-resistant steel, corrosion-resistant cast iron,
Tool steel and other steel materials such as iron and steel are listed.

In the present invention, the shape and size of the fine hole drilled in the bottom surface of the thick hole formed in the workpiece are not particularly limited, and the "thick" of the thick hole is not particularly limited.
And `` thin '' of the small hole represents the relationship between the relative hole size, generally, as described above, the smaller the outer diameter of the two holes, the more difficult the drilling process,
The deeper the two holes are, the more difficult it is to drill.However, the electric discharge machining method of the present invention employs a method in which the outer diameters of the two holes are small or the depth is large. It is preferably used.

In the electric discharge machining method of the present invention, a fine hole may be formed on the bottom surface of the large hole, and a fine hole may be formed by the bottom surface of the small hole. There is no particular limitation. For example, there are two steps of simply forming a small hole on the bottom surface of a thick hole, and three steps of forming a smaller hole with the bottom surface of a small hole,. Can be or,
The number of fine holes drilled on the same bottom surface of the large hole is not particularly limited, and can be set arbitrarily.

The insulative guide core used in the electric discharge machining method of the present invention can withstand the high frequency electric discharge applied and the high temperature generated accompanying the drilling, and
It is not particularly limited as long as it has insulation liquid resistance to the used insulation liquid, and may be made of an insulating inorganic material or may be made of an insulating organic material. However, for example, those made of a fluorine-based resin such as polytetrafluoroethylene can be used.

The guide hole of the insulating guide core allows the electric discharge machining electrode to be inserted smoothly, allows the electrode surface to accurately contact the predetermined position of the small hole to be subjected to electric discharge machining, and for forming the small hole. In order to prevent unnecessary displacement such as misalignment during electric discharge machining, an inner diameter substantially equal to the diameter of the hole to be drilled by electric discharge machining is provided so as to penetrate from one end surface to the other end surface facing the same,
The end face that comes into contact with the bottom surface of the large hole is machined so as to be in close contact with the bottom surface of the large hole.

According to the electric discharge machining method of the present invention, a small hole is drilled in the bottom surface of a thick hole formed in a workpiece by electric discharge. It may be formed by electric discharge machining.

As described above, the electric discharge machining method of the present invention has an outer shape substantially equal to the diameter of a large hole drilled, and guides through both end faces to abut a position where a small hole is drilled. The insulated guide core provided with the hole is inserted into the drilled thick hole, and the narrow hole is subjected to electrical discharge machining. The wall surface of the thick hole of the workpiece serving as one of the electrodes is opposed to this. It is completely insulated and isolated from the working electrode, which is the electrode, and discharges only on the cutting surface,
Since there is no risk of secondary discharge such as abnormal discharge,
The next discharge does not impair the drilling accuracy.

Further, according to the electric discharge machining method of the present invention, it is sufficient to start electric discharge machining of a small hole from the bottom of an existing thick hole, which is smaller than the conventional method using no insulating guide core used in the present invention. Therefore, the processing length of the small hole can be remarkably shortened, so that the number of processing steps can be drastically reduced, and not only the processing cost can be reduced, but also the processing capacity can be dramatically improved.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in further detail with reference to embodiments shown in the drawings.

FIG. 1 shows a thin hole (12) having a hole diameter Ds and a hole depth Z2 on the bottom surface of a large hole having a hole diameter D1 and a hole depth Z1 formed in the workpiece 1 by the electric discharge machining method of the present invention. ) Is an explanatory view of an embodiment in which a hole is drilled. First, a thick hole 11 having a depth D1 and a diameter D1 is formed vertically from the upper surface of the workpiece 1 and a guide hole 21 having a diameter Dc is provided. The insulated guide core 2 is inserted into the large hole 11 in close contact therewith, and has an outer diameter da (da is a guide hole 21 having a diameter Dc provided in the insulative guide core 2 at a position retracted upward. The EDM electrode 3 (which is set to be slidable in the inside) descends, penetrates the guide hole 21, and comes into contact with the bottom surface of the large hole 11.

In this state, while the workpiece 1 is immersed in insulating oil, a high-frequency voltage is applied between the workpiece and the electric discharge machining electrode 3, and the large hole of the workpiece 1 is in close contact with the surface of the machining electrode 3. 11
Spark discharge is repeatedly performed with the bottom surface of the machining electrode 3.
, The bottom of the large hole 11 is sequentially removed,
A thin hole 12 having a depth Z2 and a diameter Ds is formed coaxially with the thick hole 11. FIG. 1 shows a state in which a small hole 12 is formed with the above dimensions, and the electric discharge machining electrode 3 has receded to a standby position.

(Embodiment 1) A rectangular parallelepiped steel ingot having a height of 115 mm and made of carbon tool steel SKD61 was formed into a work to be drilled by the electric discharge machining method of the present invention, and the outer diameter was perpendicular to the center of the upper surface of the rectangular parallelepiped. It is intended to drill a thick round hole having a diameter of 3 mm and a depth (Z1) of 100 mm, and a thin round hole having an outer diameter of 2 mm and a depth (Z2) of 10 mm in the same direction from the bottom surface in the same direction as the thick round hole. is there.

First, an outer diameter of 3 mm and a depth (Z1) of 100 mm are perpendicular to the center of the upper surface of a drilled workpiece according to a conventional method.
A thick round hole is drilled. Next, as shown in FIG. 1, an insulating guide core 2 made of polytetrafluoroethylene having an outer diameter of 3 mm, an inner diameter of 2 mm, and a length of 100 mm is inserted so as to be in close contact with the inner surface of the above-mentioned thick round hole, and the lower end surface is formed. After confirming that it adhered to the bottom of the thick round hole, the outer diameter was 1.8 mm and the length was 1
A 50 mm copper electric discharge machining electrode 3 is inserted into the guide hole 21 of the insulating guide core 2 and is brought into contact with the bottom surface of the thick round hole. Thereafter, in a bath of a discharge treatment liquid (manufactured by Mitsubishi Petroleum Co., trade name "Diamond EDF-K"), using a high frequency power supply (model: M35J-G70) manufactured by Mitsubishi Electric Corporation under the processing conditions shown in Table 1. Cutting was performed to form a small hole of the type shown in FIGS.

[0026]

[Table 1]

(Example 2) FIGS. 5 to 7 are the same as Example 1 except that the small hole of Example 1 was replaced with a square having a cross section of 2 mm and a small hole of 10 mm in depth. A small hole of the type shown in FIG.

(Comparative Example) A rectangular parallelepiped steel ingot identical to that used in Examples 1 and 2 was used as a drilled workpiece, and was vertically cut from the center of the upper surface of the rectangular parallelepiped by a conventional electric discharge machining method. Then, a small round hole having an outer diameter of 2 mm and a depth (Z) of 110 mm is drilled by electric discharge, and again from the center of the upper surface of the rectangular parallelepiped, a diameter of 3 mm and a depth (Z) are coaxial with the small round hole.
1) A 100 mm thick round hole is to be drilled by electric discharge. The electric discharge machining conditions were the same as in the example, and the same two-stage round hole was drilled as in the example.

The processing time required in Examples 1 and 2 and the comparative example and the roughness of the processed surface of the obtained two-step round hole are as shown in Table 1. The roughness of the processed surface is determined by JI
The maximum height (Ry) was measured and evaluated according to SB0601.

[0030]

[Table 2]

As is clear from Table 1, in each of the above-mentioned examples by the electric discharge machining method of the present invention, the machining time was reduced to 1/20 as compared with the comparative example by the conventional method. While exhibiting extremely high productivity, the roughness of the machined surface indicates a cutting accuracy of 4 times or more, and it is recognized that this is an extremely excellent electric discharge machining method.

[0032]

Since the electric discharge machining method of the present invention is configured as described above, the drilling time is extremely short and the electric discharge machining accuracy is at a very high level.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of an embodiment of an electric discharge machining method according to the present invention.

FIG. 2 is a plan view showing an example of a machined product in which a small hole is cut in the bottom surface of a large hole.

FIG. 3 is a sectional view taken along line III-III in FIG.

FIG. 4 is a sectional view taken along line IV-IV in FIG.

FIG. 5 is a plan view showing another example of a machined product in which a small hole is formed in the bottom surface of a large hole.

FIG. 6 is a sectional view taken along line VI-VI in FIG.

FIG. 7 is a sectional view taken along line VII-VII in FIG. 2;

[Explanation of symbols]

 1: Workpiece (steel material, positive electrode) 11: Large hole 12: Fine hole 2: Insulating guide core 21: Guide hole 3: Processing electrode (negative electrode) Dl: Diameter of large hole 11 Ds: Small hole 12 Diameter dc: Outer diameter of insulating guide core 2 Dc: Diameter of guide hole 21 da: Diameter of machining electrode 3 Z1: Depth of large hole 11 Z2: Depth of small hole 12

Claims (4)

[Claims] 1. An electric discharge machining method in which a small hole is formed in a bottom surface of a large hole formed in a workpiece by electric discharge, and has an outer diameter substantially equal to the diameter of the large hole formed. Insert an insulating guide core provided with a guide hole that penetrates both end surfaces and abuts a position where a small hole is to be cut, into the drilled thick hole, and becomes a counter electrode of the workpiece in the guide hole. An electric discharge machining method characterized by inserting a machining electrode and subjecting a small hole to electric discharge machining. 2. The method according to claim 1, wherein the shape of the large hole drilled in the workpiece and the shape of the small hole drilled in the bottom surface of the large hole are the same, and only the cross-sectional area is different. EDM method. 3. The electric discharge machining method according to claim 1, wherein the shape of the large hole drilled in the workpiece and the shape and the cross-sectional area of the small hole drilled in the bottom surface of the large hole are different from each other. . 4. The electric discharge machining method according to claim 1, wherein the insulating guide core is made of polyfluoroethylene.