JPH0929546A - Electrical discharge machining method of low consumption electrode type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve the electrical discharge machining of low consumption electrode type for finishing the hard-cutting material such as cemented carbide and hardened steel. SOLUTION: A copper tool electrode is cathode, and a work 6 made of hard-cutting material such as cemented carbide and hardened steel is anode, and the work 6 is electrical discharge machined in the insulating machining fluid by the electronic impact by the unipolar high current density spark discharge in which the discharge time is so short for the cathodic iron is difficult to reach the tool electrode 8 and the peak value of the discharge current is increased to the discharge time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-consumer electric discharge machining method for electric discharge machining of a workpiece made of a hard-to-cut material such as cemented carbide or hardened steel with extremely low electrode consumption.

[0002]

2. Description of the Related Art Conventionally, in low electric discharge machining of electrodes,
The tool electrode is anodic and the workpiece is cathodic, and unipolar transient arc discharge is repeated in an insulating machining fluid, and the workpiece is electro-discharge machined by using the impact of cations.

At this time, in order to suppress the consumption of the electrodes as much as possible,
Than the discharge current peak value i _p (A) to extend the discharge time Td of each one to be substantially i _p /Td<0.2(A/μs), for example, when i _p = 20A Td = 100 ~
It is set to 200 μs.

[0004]

In the case of the conventional low-consumable electric discharge machining method for electrodes, for a workpiece made of a difficult-to-cut material such as cemented carbide or hardened steel, the cathode current density is the same as that of general electric discharge machining. ⁴ to 10 ⁶ A / cm ² and the discharge time Td is long, so the surface roughness is 10 μm R
It is not possible to perform electric discharge machining with a finish of max or less, and the electrode wear rate is 12% in weight consumption rate and 20% in volume consumption rate, which is far from 1% which is a target for low consumption electric discharge machining. There is a problem that low consumption electrical discharge machining for finishing cannot be performed.

An object of the present invention is to realize an electrode low consumption electric discharge machining for finishing a difficult-to-cut material such as cemented carbide or hardened steel, which has been impossible in the past.

[0006]

In order to achieve the above-mentioned object, in the electrode low-consumption electric discharge machining method of the present invention, the tool electrode of the copper electrode is made cathodic, and hard-to-cut materials such as cemented carbide and hardened steel are difficult to cut. A unipolar high current density spark whose material work piece is made anodically and the discharge time is short in the insulating working fluid to make it difficult for cations to reach the tool electrode and the discharge current peak value is increased with respect to the discharge time. The electric discharge causes the electric discharge to machine the work piece by electron impact.

Therefore, in the case of the low-consumption electric discharge machining method of the present invention, the polarities of the tool electrode and the workpiece are opposite to those of the conventional method, and the unipolar spark discharge in the insulating machining liquid causes
The workpiece is electro-discharge machined using the impact of electrons.

At this time, the shorter the discharge time is, the larger the cathode current density becomes, and most of the discharge current becomes an electron current, and the power of the discharge is locally concentrated on the workpiece.

Then, by setting the discharge time to an extremely short time in which cations hardly reach the tool electrode, the power of the discharge current density of a strong discharge current density of the order of 10 ⁷ A / cm ² or more is changed in the radial direction. It is added to an instant work piece while suppressing expansion, and by repeating this, it is possible to perform electrical discharge machining of difficult-to-cut materials such as cemented carbide and hardened steel without the consumption of tool electrodes. Achieves low electrode consumption EDM.

[0010] Then, to the discharge time Td below the dischargeable current peak value i _p (A) / Td to (.mu.s) 10 above 1μs are most suitably realistic.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Next, one embodiment of the present invention will be described with reference to FIG. FIG. 1 shows an electric discharge machining circuit to which the present invention is applied. Positive and negative power supply terminals 1p, 1
A DC power supply of 100 to 400 V is applied between n and
When the electronic switch 2 such as is turned on, a current flows from the power supply terminal 1p to the power supply terminal 1n via the electronic switch 2, the processing capacitor 3 and the charging resistor 4, and the processing capacitor 3 has one end 3p positive and the other end 3n positive. It is charged to the negative polarity.

A workpiece 6 made of a hard-to-cut material such as cemented carbide or hardened steel is connected to one end 3p of the processing capacitor 3 via a vibration suppressing resistor 5, and a circuit inductance ( A tool electrode 8 of a copper electrode is connected via a self-inductance 7 and the work 6 and the tool electrode 8 are conventionally separated by a predetermined gap length of about 5 μm in an insulating machining liquid such as white kerosene or pure water. The opposite polarity, that is, the work piece 6 is made anodic and the tool electrode 8 is made cathodic.

When the machining capacitor 3 is charged, a spark discharge is generated between the tool electrode 8 and the workpiece 6 due to the voltage between the terminals, and an electron impact from the tool electrode 8 is applied to the workpiece 6. To be

At this time, the processing capacitor 3 has one end 3p.
Is discharged to the other end 3n through the vibration suppressing resistor 5, the workpiece 6, the tool electrode 8, and the circuit inductance 7, and the voltage between the terminals decreases.

Then, a change in the voltage between the terminals of the machining capacitor 3 is detected by a discharge detection circuit 9 composed of a differentiating circuit or the like, and the detection output of this detection circuit 9 turns off the electronic switch 2 during the electric discharge machining. Inflow of an unnecessary continuous current, which will be described later, from the power supply into the discharge gap between the tool electrode 8 and the workpiece 6 is blocked and blocked.

In addition, according to the circuit inductance 7, 10
Vibration caused by the machining capacitor 3 and the circuit inductance 7 is blocked by the vibration suppressing resistance 5 of about Ω, and spark discharge of the tool electrode 8 and the workpiece 6 is performed by using the tool electrode 8 as the cathode and the workpiece 6 as the anode. It becomes a polar discharge.

By repeating the charging of the machining capacitor 3 by the DC power source and the discharging of this capacitor 3, a unipolar spark discharge is repeatedly generated between the tool electrode 8 and the workpiece 6, and the workpiece 6 is required. Electrical discharge machining is performed.

By the way, according to the theoretical calculation of the positive and negative power distribution by discharge, when the tool electrode 8 is cathodic and the workpiece 6 is anodic, the discharge time Td of each spark discharge can be kept to 1 μs or less. Shorten tool electrode 8, work piece 6
Suppressing radial expansion of the discharge path between (diffusion), the discharge current peak value i _p for the discharge time Td is increased to be a cathode current density in the order of ^{10 7 ~10 8 A / cm 2} , discharge Most of the electric current becomes an electron current, and by repeating this instantaneous unipolar spark discharge, it is possible to perform electric discharge machining with a surface roughness of 10 μm Rmax or less of difficult-to-cut materials such as cemented carbide and hardened steel.

That is, the electric discharge generated between the tool electrode 8 and the workpiece 6 at an instant of 10 ^-6 to 10 ^-7 seconds can be treated as something close to a transient arc from the waveform of the discharge gap voltage. F Theory and McKeon (Mack
eown) formula can be applied.

Based on this theory and formula, the cathode current density is 5 × 10 ⁶ A / with respect to the electrode material such as the tool electrode 8 which can be treated with the work function of the cathode electrode of 4 eV and the cathode temperature of 3000K.
cm ² , 1 × 10 ⁷ A / cm ² , 5 × 10 ⁷ A / cm ² , 5 ×
The electron current density (A / cm ² ) / cathode current density (A / cm ² ) at 10 ⁸ A / cm ² is obtained as shown in Table 1 below.

[0021]

[Table 1]

As is clear from Table 1, when the cathode current density is on the order of 10 ⁷ to 10 ⁸ A / cm ² , preferably 5 × 10 ⁷ A / cm ² or more, the tool electrode 8 and the workpiece 6 Most of the discharge current during this period becomes an electron current.

At this time, the discharge time is 10 ⁻⁶ to 10 ⁻⁷ μs
Since the electric discharge between the tool electrode 8 and the workpiece 6 does not spread in the radial direction, the workpiece 6 of anodism has a high electron current density even if it is a difficult-to-cut material such as cemented carbide or hardened steel. It is processed by the local impact of high temperature electrons.

Since the machining range of the workpiece 6 by one spark discharge is very small, the surface roughness of the workpiece 6 after machining becomes 10 μm Rmax or less, and the electric discharge machining for finishing can be performed.

Further, most of the discharge gap power is consumed by the work piece 6 on the anode side. At this time, the cation current density is very small, the impact of the cations on the tool electrode 8 is very small, and the discharge gap power is very small. The distributed consumption on the cathode side of is very low.

Moreover, the discharge time is 1 μs (1 × 10 ⁻⁶ s
) The following, that is, at the moment when cations hardly reach the cathode tool electrode 8, the tool electrode 8 is not impacted by cations and is not consumed.

Therefore, in the electric discharge machining circuit of FIG. 1, the electric discharge circuit of the machining capacitor 3, the vibration suppressing resistor 5, etc. is considered in consideration of the circuit conditions such as the gap length between the tool electrode 8 and the workpiece 6, the circuit inductance 7, etc. adjust the constant, the discharge time Td and 1μs or less (preferably 0.5μs or less), the discharge current peak value i _p (a) / discharge time Td (.mu.s
) To 10 or more to increase the cathode current density to 5 × 10 ⁷
A / cm ² or higher to realize low electrical discharge machining of difficult-to-cut materials such as cemented carbide and hardened steel.

Next, in the electric discharge machining circuit of the so-called laser circuit configuration (RC circuit) shown in FIG. 1, the current from the DC power source is one of the important factors for electrode consumption, and during the discharge time, the DC power source changes the tool. It is necessary to prevent the continuous current from flowing into the discharge gap between the electrode 8 and the workpiece 6.

That is, as shown in FIG. 2, the electronic switch 2 and the discharge detection circuit 9 are omitted from the configuration of FIG.
By forming an electrical discharge machining circuit having a lathe recon circuit configuration in which one end of the machining capacitor 3 is directly connected to p, the machining capacitor 3 of this circuit is 500 pF, the vibration suppressing resistor 5 is 10Ω, and the charging resistor 4 is in the range of 3 to 30 KΩ. Power terminal 1 while changing
As a result of repeating the electric discharge machining by applying the DC power supply 10 of 100 to 400 V between p and 1n and measuring the electrode wear rate, as shown in FIG. 3, the larger the resistance value of the charging resistor 4 is,
The electrode wear rate has decreased.

In the case of the electric discharge machining circuit shown in FIG. 2, this means that while a unipolar spark discharge is generated between the tool electrode 8 and the workpiece 6 (during spark discharge), the workpiece 6, from one end of the machining capacitor 3 is discharged. A discharge current of the capacitor 3 flows to the other end of the machining capacitor 3 via the tool electrode 8, and the power source terminal 1p directly supplies power to the power source terminal 1n via the tool 6 and the tool electrode 8 from the DC power source. This is because a current also flows, and the amount of cations, which is a cause of wear of the tool electrode 8, also changes due to this sustaining current, and as the charging resistance 4 increases, the sustaining current decreases and the number of cations lessens. .

Therefore, the electric discharge machining circuit of FIG. 1 is provided with the electronic switch 2 and the electric discharge detection circuit 9, and during the spark discharge, the electronic switch 2 is turned off to prevent the continuous current from flowing into the discharge gap to maintain the electric current. Prevents electrode consumption due to electric current.

In the discharge circuit of FIG. 1, the discharge current peak value i _p is fixed at 5 A and the discharge time Td is 0.5.
Repeat the electric discharge machining of the workpiece 6 by changing to μs and 1 μs,
As a result of measuring the weight electrode wear rate (%), as shown in Table 2 below, the values were 1% and 3%, respectively, and the surface roughness of hard-to-cut materials such as cemented carbide and hardened steel, which was impossible in the past, was 10 μmR.
We were able to perform low-consumer electric discharge machining with max.

[0033]

[Table 2]

In the case of this low-consumer electric discharge machining of electrodes, the finishing machining of the workpiece 6 can be performed only by this machining, so that it is not necessary to repeat machining from rough machining to finishing machining unlike the conventional electric discharge machining. The processing time and labor can be greatly reduced, and the processing accuracy is also greatly improved.

The circuit configuration and the like are not limited to those shown in FIG. 1. For example, the sizes of the processing capacitor 3, the charging resistor 4 and the vibration suppressing resistor 5 can be set according to the workpiece 6 or the like. Good.

[0036]

The present invention has the following effects. The polarities of the tool electrode 8 and the work piece 6 are opposite to those of the conventional method, and the work piece 6 is electro-discharge machined by utilizing the impact of electrons by the unipolar spark discharge in the insulating working liquid. The discharge time is set to an extremely short time in which cations are unlikely to reach the tool electrode 8, and the cathode current density is increased so that a powerful discharge power density power is applied to the instantaneous workpiece 6 while suppressing radial expansion. By this repetition, it is possible to perform the electric discharge machining for finishing difficult-to-cut materials such as cemented carbide and hardened steel, which was not possible in the past, without the tool electrodes 8 being consumed by cations, and the electrode wear of the hard-to-cut materials is low. Electric discharge machining can be realized.

[0037] A discharge by time Td to in the 1μs or less discharge current peak value i _p (A) / Td to (.mu.s) to 10 or more, can be performed most practical preferred electrode low consumable discharge machining in line.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of one embodiment of the present invention.

FIG. 2 is a circuit block diagram for explaining the influence of the current of the DC power supply of FIG.

FIG. 3 is a characteristic diagram of the electrode wear rate of FIG.

[Explanation of symbols]

 6 Workpiece 8 Tool electrode

Claims (2)

[Claims] 1. A tool electrode of a copper electrode has a cathodic property, and a workpiece made of a hard-to-cut material such as cemented carbide or hardened steel has an anodic property, and in an insulating working fluid, a cation has a discharge time of the above-mentioned tool. Electrode low-consumption electrical discharge machining characterized in that the workpiece is subjected to electrical discharge machining by electron impact by unipolar high current density spark discharge in which the discharge current peak value for the discharge time is increased in a short time that is difficult to reach the electrode. Method. Wherein the discharge time in the 1μs than the discharge current peak value i _p (A) / discharge time Td (.mu.s) an electrode low consumable discharge machining method according to claim 1, characterized in that more than 10.