JPH04189419A - Finish electric discharge machining method - Google Patents

Abstract

PURPOSE:To realize stable machining, by running a large electric discharge current from an electric discharge starting time point to a later certain time point, and changing this electric discharge current into a small one after the period. CONSTITUTION:An electric discharge circuit is made to be ON at a time point t0, and voltage impression is started between a machining electrode and a workpiece. And bath voltage Vg and a bath current Ig are observed, and a time point when the bath voltage Vg drops to the level of electric discharge start detection reference voltage Va, or a time point t1 when the bath current Ig drops to the level of an electric discharge start detection reference electric current Ia, is defined an electric discharge start time point. And, the growth of electric discharge plasma is judged by the voltage Vg dropping to the level of voltage Vb or the current Ig rising to the level of an electric current Ib, and at its time point t2, for example, an electric discharge electric current value is changed into a small one suitable for finish working, by changing the electric current limit resistance value of an electric discharge power supply device. Finish electric discharge is completed at a time point t3 when a fixed time T2 has passed from the electric discharge start time point t1.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention temporally controls the discharge energy by controlling the discharge current, and improves the relationship between machining speed and finished surface accuracy. The present invention relates to a 1-1-ge electrical discharge machining method.

[Prior Art] In finishing machining by electric discharge machining, in order to reduce the surface roughness of the machined surface, the electric discharge energy for one time is small, thereby reducing the amount of machining and removal.

As a means for this purpose, for example, the on-time width of the switching element is reduced to shorten the discharge duration, or the limiting resistance is increased to reduce the discharge current.

[Problem to be solved by the invention] In order to improve the precision of the machined surface, it is necessary to reduce the energy of one discharge as much as possible, or because the discharge plasma is cooled by the surrounding machining fluid,
More energy is lost through this cooling than the electrical energy supplied, increasing instability and causing the discharge to disappear midway. For this reason, it is difficult to obtain an effective discharge during finishing machining, and machining efficiency cannot be improved. On the other hand, if the discharge current is increased in an attempt to improve the efficiency of electrical discharge machining, the amount of soil removed per discharge increases, which has the disadvantage of worsening the roughness of the discharge machining process3. As shown in Fig. 11, it was not possible to improve accuracy and improve machining efficiency at the same time.

Another method has been used in which a capacitor is added between the electrode and the workpiece, and the energy lost by the discharge plasma due to cooling is replenished by the electrical energy stored in the capacitor, thereby preventing the discharge from disappearing. However, in this method, the amount of replenishment energy is controlled by the capacitor capacity and the discharge starting voltage, and there is a problem that depending on the discharge state, the replenishment energy may be excessive, worsening the roughness of the machined surface.

[Means for solving the problem] From the start of discharge to a certain point thereafter, a large voltage is applied between the electrode and the workpiece, or a current limiting resistor is made small to allow a large discharge current to flow, and cooling is performed. After that period, the discharge current is changed to a smaller value to reduce the energy applied to the leather workpiece.This state is continued until the end of the discharge. The switching point is the point detected from a drop in the voltage between the machining electrode and the liquid application] or the increase in the discharge current, or the point at which a certain period of time has elapsed from the start of the discharge, or both. Whichever of these two points is reached first shall be the point in time.

[I'I　　　　　　　　　　　 The present invention will be explained in detail using FIGS. 1 and 2.

FIG. 1 explains the invention set forth in claim 1. In this figure, (a) represents the temporal change in the voltage between the machining electrode and the workpiece (interelectrode voltage; Vg), and (b) represents the change in the voltage between the machining electrode and the workpiece under the above applied voltage. It represents the temporal change in the current generated between the electrodes (interelectrode current, 1 g). Then, at time point to, the discharge circuit is turned on and voltage starts to be applied between the machining electrode and the workpiece. Then, by observing the inter-electrode voltage Vg and the inter-electrode current 1g, the time t1 when the inter-electrode voltage Vg drops to the level of Va or the time t1 when the inter-electrode current 1g rises to the level Ia is determined to be the time to start discharge. Since the discharge current continues to decrease by 4 from this point t1, discharge plasma grows. The growth of this discharge plasma is caused by the drop of the electrode gap voltage Vg to the level of Vb or by the electrode gap current I.
Judgment is made when g rises to the level of Ib. At the time t2, for example, by changing the value of the current limiting resistor included in the discharge power supply equipment, the discharge current value is switched to a small value suitable for finishing machining, as shown by the solid line in FIG.

At this time, the discharge plasma grows, the gasified region is wide, and the temperature is rising, so the discharge is difficult to disappear even by the cooling effect of the machining fluid, and thus the discharge remains stable and continues even with a small discharge current value. It's getting easier. This discharge,
In other words, the final discharge ends at time t3, which is a certain period of time 1'1 elapsed from time t1 when the start of discharge was detected.

Fig. 2 explains the invention claimed in claim 2, and the difference from the invention claimed in claim 1 (Fig. 1) is that the switching point of the discharge current is determined by the voltage value or the discharge current value. Rather, the point is set at a time t2- after a certain period of time 1゛1 has elapsed from the discharge start time [1]. If the discharge growth is poor, as shown in Figure 2 (a) and (b), if the electrode gap voltage Vg does not drop to a predetermined level (■b; discharge growth detection reference voltage) or if the electrode gap Since it takes too much time for the current 1g to rise to a predetermined level (Ib, the discharge current detection reference current), in such a case, the discharge current is switched as in the invention described in claim 1. This will occur after a very large amount of discharge current has flowed, leaving large machining marks on the workpiece. In order to prevent such a situation from occurring, the present invention switches the current after a certain period of time T1 has elapsed, regardless of the values of the inter-electrode voltage Vg and the inter-electrode current 1 g after the start of discharge.

According to the third aspect of the invention, the discharge current is switched at the earliest of the switching point according to the first aspect of the invention and the switching point according to the second aspect of the invention.

[Example] FIG. 3 shows an example of a power supply device used in the method according to claim 1. The processing electrode P and the workpiece W are provided with a discharge circuit 10 consisting of a main power source 11, a switching element 12, and a current limiting resistor 13, and a discharge circuit 20 consisting of a main power source 21, a switching element 22, and a current limiting resistor 23. connected in parallel. The two switching elements 12 and 22 are connected to the discharge current control circuit 3 which provides gate signals to each of the switching elements 12 and 22. Further, the discharge circuit is provided with a discharge current detector 4 and a voltage detector 5 between electrodes, both of which are connected to a discharge start detection circuit 6 and a discharge growth detection circuit 7. The discharge start detection circuit 6 is connected to a discharge duration timer 81. This discharge duration timer 81 is connected to a rest time timer 83. Also,
This rest time timer 83 is connected to the discharge current control circuit 3. Furthermore, the output of this pause time timer 8 is sent to the discharge start detection circuit 6 and the discharge growth detection circuit 7,
The signals from both number detection circuits 6 and 7 are output only when the voltage application signal S1 is being issued from the timer 83. On the other hand, the discharge growth detection circuit 7 is connected to the discharge current control circuit 3. The initial operation of this power supply device is performed according to the timing shown in FIG. That is, at time point 10, a voltage application signal is issued to the discharge current control circuit 3 due to the time-up of the body II-time timer, thereby turning on the gate signal G1. After applying a voltage between the machining electrode P and the workpiece W, when the inter-electrode voltage Vg becomes equal to or lower than the set discharge start detection reference voltage Va, or when the inter-electrode current Ig is set as the discharge start detection reference current 1a.
At the time point t1 above, the discharge start detection circuit 6 outputs a discharge start signal, sets the discharge duration timer 81, and starts timing. As a result, the timer 81 outputs the discharge raw signal S2. Then, when the inter-electrode voltage section Vg becomes equal to or less than the set discharge growth detection reference voltage Vb, or when the inter-electrode current 1g becomes the set discharge growth detection reference current 1g (time t2), the discharge growth detection circuit 7 The current switching signal S3 is output to the discharge control circuit 3, and the above gate signal G
1 is turned off and the gate signal G2 is turned on from off.

Then, at time t3, when the discharge duration timer 81 reaches the set discharge duration '2'2, the gate signal G2 is turned off, the pause time timer 83 is set, and the pause time begins.

Next, FIG. 4 shows a power supply device used to carry out the method according to claim 2. The difference from the apparatus shown in FIG. 3 is that there is no discharge growth detection circuit, and a workpiece protection timer 82 is connected to the discharge start detection circuit 6. This workpiece protection timer 82 is connected to the discharge current control circuit 3.

The operation of this power supply device is performed at the timing shown in FIG. 2(c). The current switching here occurs at a time t2- when the workpiece protection timer 82 has counted a certain period of time T1 from the time t1 when the start of discharge was detected.

In other words, the current switching signal S3 is issued from this timer 82 at time t2-.

Further, FIG. 5 shows a power supply device used to carry out the method according to claim 3. This device corresponds to a combination of the rain sounds shown in Figs. 3 and 4, and the output of the discharge detection circuit 6 and the output of the workpiece protection timer 82 are led to the OR circuit 9, and the output here is connected to the current IJJ. It is manually input to the discharge current control circuit as a switching signal.

In addition, in the power supply apparatus shown in FIGS. 3 to 5, main power supplies 11 and 12 are provided for each of the two discharge circuits 10.20, but instead of this, a common power supply is provided for the two discharge circuits 10.20. It is also possible to use one main power source.

Furthermore, a specific example of the discharge current control circuit 3 in the power supply device shown in FIGS. 3 to 5 is shown in FIG. The first flip-flop 31 has its set terminal S connected to the pause time timer 9, and is set by the rise of the voltage application signal S1 from there, and also reset O:! 1: R is connected to the discharge duration timer 81, and the discharge raw signal S is sent from there.
It is reset by the falling edge of 2. On the other hand, the second flip-flop 32 has a current of 1 uJ at its set end S.
The switching signal S3 is input and set by its rising edge, and the reset terminal R is set by the manual input to the reset terminal R of the first flip-flop 31. It is designed to be reset at the falling edge. And the first. A
One of the outputs of the ND circuit 33 is the output from the output Q of the first flip-flop 31, and the other is the output from the output port of the second flip-flop 32. Also, the second A
Nl) The circuit 34 has one output from the output Q of the first flip-flop 31 and the other output from the output Q of the second flip-flop 32. The output of the first A N I) circuit 33 is the switching element 1.
2, and the output of the second AND circuit 34 provides a gate signal G2 to the switching element 22.

[Effects of the Invention] In the present invention, the discharge current is increased only for a predetermined period immediately after the start of the discharge when the discharge tends to become unstable, thereby growing the discharge plasma and supplying sufficient energy to stabilize the discharge.
As soon as that period ends, the discharge current is changed to a low one suitable for finishing discharge machining, so the energy contributing to the addition becomes smaller, and the discharge almost disappears during the work. It is possible to perform extremely stable finishing electrical discharge machining with high efficiency.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating temporal changes in inter-electrode voltage and inter-electrode current regarding the first invention of the present application. FIG. 2 is a diagram illustrating temporal changes in inter-electrode voltage and inter-electrode current regarding the second invention of the present application. FIG. 3 shows a power supply device according to the method of the first invention of the present application. FIG. 4 shows a power supply device according to the method of the second invention of the present application. FIG. 5 shows a power supply device according to the method of the second invention of the present application. FIG. 6 shows a specific example of the discharge current control circuit of the power supply device shown in FIGS. 3-5. 1.0.20...discharge circuit, 11. ．． 21... Main power supply 1.2.22 Switching element, 1.3.23.
・Current limiting resistor, 3], 32...Flip-flop,
33.34...AND circuit, 4...Current detector, 5
... Electrode voltage detector, 6. Discharge start detection circuit, 7.
・・Discharge growth detection circuit, 81・Discharge duration timer,
82... Workpiece protection timer, 83 Body 11 hour timer, 9... OR circuit.

Claims (3)

[Claims] (1) (a) Set the discharge current to be larger than that during the finishing discharge and apply a voltage between the machining electrode and the workpiece to start the discharge; (b) set the above-mentioned discharge start time t1. Detected by observing the voltage or discharge current between the machining electrode and the workpiece, (c) After the discharge start time t1, the voltage between the pressurizing electrode and the workpiece drops or the discharge current The time point t when Vb increases and reaches a predetermined reference value Vb at which it can be determined that the discharge has grown.
2, the discharge current is switched to the finishing discharge current, (d) the voltage application between the machining electrode and the workpiece is stopped at time t3 when a predetermined time T2 has elapsed from the discharge start time t1, and (e) the above (f) A finishing electrical discharge machining method in which a voltage is applied again between the machining electrode and the workpiece after a predetermined time has elapsed from the time when the electrical discharge was stopped. (2) In the finishing electric discharge machining method according to claim 1,
The time point at which the discharge current is switched to the finishing discharge current is set to a predetermined reference value at which it can be determined that the voltage between the machining electrode and the workpiece has dropped or the discharge current has increased and the discharge has grown after the discharge start time t1. A finishing electric discharge machining method characterized in that instead of setting the time t2 at which the electric discharge has been reached, the time t2' is set at the time when a predetermined time T1 has elapsed from the point at which the electric discharge starts. (3) In the finishing electric discharge machining method according to claim 1,
The time point at which the discharge current is switched to the finishing discharge current is set to a predetermined reference value at which it can be determined that the voltage between the machining electrode and the workpiece has dropped or the discharge current has increased and the discharge has grown after the discharge start time t1. Instead of reaching the point t2, the voltage between the machining electrode and the workpiece decreases after the discharge start point t1, or the discharge current increases, reaching a predetermined reference value at which it can be determined that the discharge has grown. A finishing electric discharge machining method characterized in that the finishing electric discharge machining method is characterized in that the finishing electric discharge machining method is carried out at the earliest of a time point t1 and a time point t2' when a predetermined time T1 has elapsed from the time of discharge start.