JP2604461B2 - Electric discharge machining method and apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an electric discharge machining method and apparatus using machining electrodes having various electrode shapes, and in particular, to a coordinate perpendicular to an electrode feeding operation direction. By oscillating the center of the machining electrode in the plane, the machining area by EDM is progressively increased and increased to the desired machining shape and dimensions. The present invention relates to a high-precision electric discharge machining method and apparatus capable of completing machining at any machining position of an object at the same time within a highly accurate tolerance for the desired machining shape and dimensions.

[Conventional technology]

By utilizing the discharge phenomenon between the EDM electrode and the workpiece having various electrode shapes according to the workpiece shape,
2. Description of the Related Art An electric discharge machining method for forming a concave or convex machining portion having a desired machining shape and dimensions in a workpiece by removing machining chips from the workpiece is well known. Further, in this electric discharge machining method, the machining electrode is gradually fed only in a feed direction toward the inside of the workpiece to form a machining chip removal portion congruent with the shape of the machining electrode in the workpiece. And a swing type in which an operation (oscillating operation) is applied to the machining electrode in the coordinate plane perpendicular to the feed direction together with the feed direction, and the electrical discharge machining progresses gradually. Has been conventionally performed.

A well-known example of the latter oscillating discharge machining method and an apparatus for performing the method is disclosed in, for example, Japanese Patent Publication No. 55-16773. That is, the oscillating electric discharge machining method and apparatus disclosed in Japanese Patent Publication No. 55-16773 discloses that a machining electrode is applied to the machining electrode in a coordinate plane perpendicular to a feed direction approaching the workpiece. In addition, an oscillating motion is given to advance the electric discharge machining, and the speed of the oscillating motion itself is increased and decreased in consideration of the machining gap between the machining contour of the workpiece and the machining electrode. It merely shows the principle technology of the processing method.

On the other hand, in recent electric discharge machining methods which have developed the oscillating electric discharge machining method disclosed in the above-mentioned Japanese Patent Publication No. 55-16773, the speed at which the electrode center of the machining electrode is displaced along the oscillating locus is set to a constant speed. Or a method of monitoring the discharge current value and oscillating the discharge current level so as to keep the discharge current level constant so that the processing amount per unit time (workpiece removal amount) by the processing electrode is constant. Has been adopted.

The principle of such a known oscillating EDM method will be described with reference to a simpler illustrated example. As shown in FIG. 5A, a machining area hole (a machining electrode 4 is For example, a processing electrode 4 having a rectangular shape in a hole formed by feeding operation into the object 2 or a hole previously processed by a milling method or the like is placed in a coordinate plane as shown in FIG. , The electric discharge machining area of the workpiece 2 gradually progresses and increases, and the workpiece 2
Is formed with a rectangular concave processing area 3. In this case, the workpiece 2 and the processing electrode 4 both have a thickness dimension in a direction perpendicular to the paper of FIG. The concave processing areas 3 face to face. That is, the large processing surface on the long side of the concave processing region 3 is different from the large area electrode surfaces 4a and 4c on the long side of the processing electrode 4 and the small area electrode surfaces 4b and 4d on the short side. 3a, 3c and the small work surfaces 3b, 3d on the short side are subjected to electric discharge machining, and a pulse voltage is applied from an electric discharge machining power supply via a discharge gap between the machining electrode 4 and the work 2 The electric discharge machining is progressing.

However, when the electrode shape of the processing electrode 4 includes the long-side electrode surfaces 4a and 4c having a large area and the short-side electrode surfaces 4b and 4d having a small area, such a processing electrode 4
Is rotated once along the oscillating locus C, as described above, the application of the pulse machining voltage from the electric discharge machining power supply causes the small-area electrode surfaces 4b and 4d of the machining electrode 4 to become the small-area workpiece surfaces 3b and 4d. 3d
When machining the electrode, a large-area electrode surface 4a of the machining electrode 4
4c has a higher discharge energy level per unit area than when processing the large-area processed surfaces 3a, 3c,
The amount of machining waste removed increases, and the electric discharge machining progresses deeply when viewed from the center of the electrode. If such an electric discharge machining process is continued, a large area of the work surface 3
Before the workpieces a and 3c reach the required final shape and dimensions, a phenomenon occurs in which the workpiece surfaces 3b and 3d having a small area of the workpiece 2 reach the desired final dimensions.

[Problems to be solved by the invention]

When the above-mentioned phenomenon occurs, the swinging operation of the machining electrode 4 is continued in order to cause the large-area processed surfaces 3a and 3c, which have not reached the final dimensions, to reach the desired final shape and dimension values. While the progress of EDM continues, the machining electrode 4 can be used even on small-area surfaces 3b and 3d that have quickly reached the final shape and dimensions.
There is a problem that the electric discharge machining is continued due to the electric discharge from the electrode and the electric discharge machining progresses, and eventually the electric discharge machining is performed extra. In other words, the work surfaces 3b and 3d having a small area have a dimension value exceeding the desired final dimension, causing problems such as deviating from the allowable tolerance and reaching the limit value of the allowable tolerance, resulting in a decrease in accuracy.

In order to prevent such a decrease in accuracy, if the operator intervenes to correct the swing trajectory of the machining electrode 4 or the like,
There is also a problem that the electric discharge machining efficiency is reduced and the automatic function of the electric discharge machine is limited.

In the above specific example, the shape of the machining electrode has an extreme difference in the EDM working area with respect to the center of the electrode, that is, the final shape is different at each machining surface of the workpiece due to the irregular shape. Although it reaches the dimensions, in addition, the electric discharge machining is started from a position where the electrode center of the machining electrode is shifted from the center of the electric discharge machining area of the workpiece, so that the machining is performed by each part of the machining electrode. The same problem occurs when there is variation in the processing allowance.

Further, when an abnormality such as a short circuit is detected in the discharge gap, the swing path is appropriately changed from a predetermined swing trajectory toward the center, and control is performed to recover from the abnormal state. As a result, a difference occurs in the time required to reach the final dimension value on each of the surfaces to be processed, resulting in the same problem as described above.

Therefore, an object of the present invention is to solve the above-mentioned problems in the swing electric discharge machining method in view of the above-mentioned problems.

Another object of the present invention is to be influenced by the shape of the machining electrode, misalignment between the center of the electrode and the center of the electric discharge machining part of the workpiece, servo operation based on abnormal discharge pressure in the discharge gap, and the like. A high-precision electrical discharge machining method that enables the electrical discharge machining to be completed simultaneously to the desired shape and dimensions at all electrical discharge machining positions on the workpiece and within a high-accuracy allowable dimensional tolerance, and that method can be implemented And a simple electric discharge machining apparatus.

[Means for solving the problem]

The present invention performs relative swinging motion along a predetermined swing trajectory between a workpiece and a processing electrode, and desirably forms an inner surface including a wall surface or a bottom surface of a concave portion or a hole of the workpiece. In the case of electrical discharge machining to the shape and size of the electrical discharge machining, when an abnormality such as a short circuit is detected in the discharge gap, the swing path is temporarily displaced from a predetermined swing trajectory toward the center.
The desired electrical discharge machining shape at any position on the inner surface,
An ideal final oscillating motion path for which machining is completed to the dimensions is determined, the current position of the instantaneous machining electrode in the current oscillating path, and the position of the final oscillating motion path corresponding to the instantaneous machining electrode position And the difference seen in the direction crossing the path is regarded as the remaining machining allowance (hereinafter, simply referred to as the remaining machining allowance), and the remaining machining allowance is used as a parameter to calculate the swing motion speed at the current position. The machining allowance is controlled so that the machining allowance is made uniform so that the remaining machining allowance is eliminated after passing through the final one-turn swing path on all machining surfaces.

That is, according to the present invention, in the electric discharge machining method for machining the inner surface of the concave portion or the hole while relatively swinging the machining electrode and the workpiece with the machining feed direction in a direction perpendicular to the machining feed direction,
The remaining machining allowance is calculated from the difference between the instantaneous position of the machining electrode in the oscillating motion and a position to be passed at the time of the final machining specified in advance, and the calculated instantaneous remaining machining allowance and each rotation of the oscillating motion are calculated. Compare with the reference remaining machining allowance set for each path, and the instantaneous remaining machining allowance is slower at a machining position larger than the reference machining allowance, the swing speed is lower than a preset swing speed, and at a small machining position, An electric discharge machining method for controlling the swing speed to be higher than a preset swing speed is provided.

Further, according to the present invention, in the electric discharge machining apparatus for performing electric discharge machining on the inner surface of the concave portion or the hole while relatively oscillating the machining electrode and the workpiece in a direction perpendicular to the machining feed direction, Position extracting means for extracting the position of the machining electrode every time in the circulating path of the dynamic motion, and the current position of the processing electrode extracted by the position extracting means and the swinging motion to be passed by the machining electrode at the time of the final machining specified in advance. Remaining machining allowance calculating means for calculating a difference between the position on the circuit path and the remaining machining allowance at each position, and the latest remaining machining allowance determined by the remaining machining allowance calculating means and the minimum remaining machining in the immediately preceding circuit The difference between the maximum remaining machining allowance and the minimum remaining machining allowance in the immediately preceding one round obtained by the remaining machining allowance calculating means is set to the denominator side. Calculation means and the quotient obtained by the division means are large A swing speed control unit that controls the swing speed to be lower than a preset swing speed at a machining position and to be higher than a preset swing speed at a small machining position. Electric discharge machining apparatus is provided.

[Action]

According to the above-described electric discharge machining method and apparatus according to the present invention, the machining electrode for performing electric discharge machining on the inner surface of the concave portion or the hole portion of the workpiece, in the course of the relative oscillation motion of both, has the oscillation motion. While moving on the path, at a point where the remaining machining allowance, which is defined as the difference between the path of the oscillating movement that the electrode center passes during the final machining and the current electrode center position, is large, the machine advances at a slow machining speed, At a point where the machining allowance is small, the machining proceeds at a high machining speed, so that the remaining machining allowance on the workpiece side surface of the workpiece is uniform at all positions, and the electric discharge machining proceeds gradually, so that the final swing path traverses. When finishing, the EDM can be ended at any position with the shape and dimensions falling within the desired tight tolerances, and therefore, EDM with high machining accuracy can be achieved. Hereinafter, the present invention will be described in more detail based on examples.

〔Example〕

FIG. 1 is a flowchart showing the operation of the basic action means and the transition of the machining process when the electric discharge machining method according to the present invention is performed, and FIG. 2 is an electrode between the workpiece and the electric discharge machining electrode. FIG. 3 is a plan view for explaining, by way of a representative example, the positional relationship between the two in the course of the progress of the relative swinging motion in a coordinate plane perpendicular to the feed direction. FIG. 4 is a block diagram showing an example of the configuration of a main part of a machining apparatus. FIG.

First, referring to FIG. 2, FIG. 2 is a plan view showing a positional relationship between a workpiece and a machining electrode in the conventional electric discharge machining method shown in FIG.
FIG. 4 is a plan view illustrating a process of performing a relative swinging motion between a workpiece and a machining electrode in the electric discharge machining method according to the present invention.

In FIG. 1, a workpiece 10 has a concave portion or a hole 12
The inner surface of the workpiece 10 is subjected to electric discharge machining by the machining electrode 14. Here, the machining electrode 14 has, for example, a rectangular shape, and therefore, the inner surface of the workpiece 10 to be subjected to electric discharge machining by the machining electrode 14. (Refer to the inward surface including the wall surface and the bottom surface facing the electrode surface of the processing electrode 14.) This indicates that the electrode is also processed into a rectangular shape.

As a premise of the present invention, the workpiece 10 and the processing electrode 14,
The electric discharge machining region is gradually increased to a desired shape and size by placing the electric discharge machining region in a coordinate plane parallel to the paper surface of FIG. 2 and performing a relative swinging motion between the two through a discharge gap. Since the relative swinging motion is performed, the center of the machining electrode 14 (the coordinate plane of the machining electrode) is set in the coordinate plane using an appropriate drive source such as an electric servomotor as an actuator of the machining electrode 14. Refers to the operation center within).
The workpiece 10 is caused to swing along a swing path or a trajectory around the swing center G, or the workpiece 10 is moved with respect to the electrode center of the machining electrode 14 which is stationary in the coordinate plane.
Is applied in two orthogonal directions within the same coordinate plane with respect to the swing center G, and a swinging motion is performed as a result of the combined operation.

Further, in the illustrated example of FIG. 2, in the relative swinging motion, the center of the machining electrode 14 is the same as the swing path or swing locus 16a that is currently passing, and the center of the machining electrode 14 is
Work surface 10 having desired final shape and dimensions of work 10
An ideal oscillating path 16e that finally passes to process and form e (shown by a dashed line) is illustrated. When the electric discharge machining progresses from the oscillating path 16a to the oscillating path 16e, Work surface having the desired final shape and dimensions of the work 10
The electric discharge machining of 10e ends.

At this time, in the present invention, the current position of the center of the processing electrode 14, for example, the point 14a on the swing path 16a and the ideal center of the processing electrode 14 in the ideal swing path 16e that finally passes through should be passed. Connecting both points with the typical passing point 14e, and
The concept of the dimension seen in the direction passing both the swing trajectories 16a and 16e, that is, the machining allowance to be subjected to electric discharge machining from now on is introduced and defined as a residual machining allowance E, and this residual machining allowance E is used as a control parameter. Thus, the control of the electric discharge machining operation described later is performed. Here, since the swing path 16a through which the machining electrode 14 is currently passing is gradually shifted to the final swing path 16e according to the progress of the machining operation, the remaining machining allowance E is, of course, constant. Is not the amount, and the electrode center position of the processing electrode 14 is
When sequentially following various positions on the same swing path 16a, the remaining machining allowance E at each point is defined for each point, and the remaining machining allowance E at the other points coincides with the same amount as a constant value. Not something. However, as shown in FIG.
The value of the remaining machining allowance E due to the difference between the current position and the final position of the center of the machining electrode 14 as viewed on a line passing through a and 16e, and the desired final machining surface 10e of the workpiece 10 and electric discharge machining up to the present. Naturally, the value of the remaining machining allowance, which is the value of the difference from the processed surface 10a, is equal.

Now, an oscillating-type electric discharge machining method and apparatus according to the present invention using the above-mentioned remaining machining allowance E as a control parameter will be described below with reference to FIGS.

Referring to FIG. 1 together with FIG. 2 described above, as a functional means for performing the electric discharge machining method according to the present invention, the remaining machining allowance E is calculated every moment in the electric discharge machining process. Machining allowance calculating means 20, a program for a swing path to be followed by a machining electrode 14 having a predetermined shape, based on a machining program for electric discharge machining of a concave portion or a hole 12 having a desired machining shape and dimensions on the workpiece 10. The swing program storage means 22, which stores the information of the swing trajectory 16e to be finally traced to the remaining machining allowance calculating means 20, and the electrode center of the machining electrode 14 in the process of electric discharge machining passes at the present time. The current electrode position extracting means 24 for extracting the position on the swinging path 16a from the means for executing the swing program or the detector provided in the electrode driving actuator, the detector of the workpiece feeding mechanism, etc .; Arithmetic means The difference between the position 14e of the ideal passing point on the final swing path 16e calculated by 20 and the current electrode position 14a on the electrode swing path 16a at the current time is calculated as the remaining machining allowance E (14e-14a) at the current time. = E) and when the oscillating motion of the machining electrode 14 advances from the current oscillating path 16a to the next oscillating path (not shown), the current electrode position is stored in the immediately preceding oscillating path. Remaining machining allowance storage means 2 capable of supplying data as the value of remaining machining allowance E while passing through the moving path
6, the remaining machining allowance E calculated by the remaining machining allowance calculating means 20;
From the remaining machining allowance E stored in the remaining machining allowance storage means 26 and the stored value of the remaining machining allowance E on the swing path of the immediately preceding revolution, the following division operation is performed: 、 (current remaining machining allowance E) − (previous revolution A division means 28 for performing a minimum remaining machining allowance E ′ _MIN ) {(maximum remaining machining allowance E ′ _MAX during the previous lap) − (minimum remaining machining allowance E ′ _MIN during the previous lap)}; Oscillation speed control for increasing or decreasing the passing speed of the machining electrode 14 in the current oscillating path based on the calculation result of the dividing means 28 so as to adjust the amount of machining waste removed by electric discharge machining to an appropriate level. means
It has 30 means. That is, the various functional means 20 to
The provision of 30 constitutes the electric discharge machining apparatus of the present invention. Here, the technical significance of the quotient of the division performed by the dividing means 28 is that the current remaining machining allowance E is calculated for each electrode position when the machining electrode 14 passes through the immediately preceding swing path. The tendency of the remaining machining allowance E at the current electrode position with respect to the distribution state of the remaining machining allowance E ′ (the significance of the denominator part in the above calculation) is relatively large. In the case of the remaining machining allowance, the machining electrode 14 is made to slowly pass through the swing path 16a in order to reduce the machining allowance, thereby promoting the electric discharge machining action progressing through the electric discharge gap, and conversely, comparing If the remaining machining allowance value is extremely small, the machining electrode 14 is allowed to pass through the machining electrode 14 at a relatively high speed in order to suppress a decrease in machining allowance, and a parameter D for determining to suppress the progress of the electric discharge machining operation is set as a parameter D. It has the significance of calculating. In other words, if the remaining machining allowance is large, the swing speed should be slow, and if the remaining machining allowance is small, the swing speed should be increased. Therefore, for example, by using the parameter D as in the present embodiment as the reference machining allowance set for each of the orbital paths described in Claim 1, the comparison standard of the remaining machining allowance becomes clear, The remaining machining allowance calculated every moment is compared with the reference machining allowance, and the swing speed can be appropriately controlled according to the magnitude of the comparison result.
The reference machining allowance may be a value calculated based on the remaining machining allowance in the immediately preceding one revolution, like the parameter D of the present embodiment, or an appropriate reference machining allowance may be determined in advance in accordance with each orbital route. For example, it may be determined experimentally and set.

Then, based on the judgment parameters obtained by the division operation in this way, if the electric discharge machining action by the machining electrode 14 is controlled so that the remaining machining allowance at each position tends to be equal, the final swing path By passing the processing electrode 16e through the processing electrode 16e, the processing of the final processing surface 10e of the workpiece 10 is completed once at a dimension within a predetermined tolerance without leaving variation in the processing allowance.

FIG. 3 is a block diagram showing the configuration of a specific embodiment of the electric discharge machining apparatus according to the present invention having the above-described various functional units 20 to 30.

The embodiment shown in the figure is an example in which a machining program for a workpiece is automatically supplied from a well-known numerical control device (NC device), and the NC device 40 has a desired shape and dimensions of the workpiece 10. A program unit 41 storing an NC program corresponding to the numerical control data as a numerical control data, an NC execution unit 42 for creating and sending an NC machining program for executing NC control according to the NC program of the program unit 41, and an NC from the NC execution unit 42 A machining servo interpolation unit 43 that creates and sends an interpolation function program in a servo operation when performing NC machining by the machining program.

The electric discharge machine has a structure for controlling the electric discharge machining by imparting a swinging motion to the machining electrode 14 (FIG. 2) based on the machining program supplied from the NC device 40. A swing interpolator 51 for taking out a swing program from the execution unit 42 to create and send a swing path, and applying three machining electrodes 14 according to the outputs of the swing interpolator 51 and the machining servo interpolator 43 of the NC device 40. Driving motor of each axis driven in the dimensional direction (this example is an example in which the machining electrode 14 swings, and the machining electrode 14 is operated by each drive motor in the X-axis, Y-axis, and Z-axis directions). A pulse synthesizing unit 52 for synthesizing a driving pulse for swing driving to be supplied to the output pulse unit 53 for sequentially transmitting a driving pulse of the pulse synthesizing unit 52, Electrode current position extraction unit 54 for extracting the current position, the remaining machining allowance operator described above 20 and an arithmetic unit 57 for performing an arithmetic function of the division unit 28, the swing speed control means
A CPU 55 having a swing speed calculating unit 58 that executes the function of 30 and calculates an increase / decrease adjustment speed of the swing speed from a quotient of the calculation result;
A storage unit 56 including well-known RAM means for storing a remaining machining allowance E and a quotient of division as a calculation result performed by the CPU 55 is provided.

Note that the swing program storage means 22 in the above-described first configuration is provided in the NC device 40 in this example, and the current electrode position extracting means 24 is a swing program determined by the drive pulse generated by the pulse synthesizing section 52. As means for extracting the current electrode position from the movement path, an electrode current position extracting means 54 is provided.

In the electric discharge machining method and apparatus according to the present invention having the above-described configuration, the passing speed of the machining electrode 14 in the swinging path is determined by using the remaining machining allowance E as a control parameter and the determination parameter D (the quotient of the above-described division). ) To control the progress of the EDM action,
For example, as shown in FIG. 4, even if the swing speed is changed stepwise between V _MAX and V _{MIN in accordance} with the value of the determination parameter D, the machining allowance after passing through the final machining path is obtained. In the experimental example, the electric discharge machining of the rectangular concave portion 12 as shown in FIG. 2 shows that the final machining dimension on the long side and the short side was 10 μm to 15 μm between the conventional two. Although present as a variation difference, according to the electric discharge machining method of the present invention, the result was reduced to 2 to 3 microns.

〔The invention's effect〕

As can be understood from the above description, according to the oscillating motion type electric discharge machining method and apparatus according to the present invention, a calculation value on the electric discharge machining action called a residual machining allowance is adopted, and the residual machining allowance is used as a parameter for controlling. Is calculated, and the moving speed of the center of the machining electrode, which shifts the oscillating path or locus, is controlled in accordance with the judgment parameter to control the progress of the electric discharge machining operation, and the remaining machining allowance is determined according to the machining program. When the machining end point is reached after passing through the swing path, the dimensions of the work surface of the workpiece at all positions are within a predetermined tolerance, and the machining is completed. Does not cause over- or under-processing, resulting in uneven dimensions.
Therefore, it is possible to obtain an effect that an electric discharge machining result with extremely high machining accuracy can be obtained.

Further, the present invention starts from a misalignment state in which the electrode center of the machining electrode is not set at the center of the machining region at the start of electric discharge machining, and therefore, the remaining machining allowance greatly varies at each point on the swing path. Even in the state, at the time of final processing,
It is also possible to obtain an effect that there is no variation in the desired size and shape, and that the processing is completed at the same time.

Similarly, since the shape of the processing electrode has a rectangular shape as in the embodiment, even when the processing area facing the processing surface has a large variation in the processing area, the processing surface of the processing object is high at every position. It has the effect that electrical discharge machining can be achieved by machining accuracy.

Furthermore, in the conventional constant-speed rocking-type electric discharge machining, an operator cannot intervene during machining to check machining accuracy and avoid the intervention of human action such as adjusting machining conditions. Then, it becomes possible to eliminate the intervention of such a human action, and therefore, it is possible to further improve the automation rate of electric discharge machining.

Also, conventionally, the remaining machining allowance remains to the end at the corner of the concave portion to be processed of the workpiece, and only the processing of the corner must be performed after the completion of the processing of the other parts. Although it was necessary to additionally perform a useless swinging motion, the present invention is directed to a tendency to gradually eliminate the remaining machining allowance at any machining surface position in the process of gradually shifting the swinging motion path. Since the discharge action is controlled, the disadvantage that the remaining machining allowance remains only at the corners is eliminated, and unnecessary machining of the machining electrode is eliminated, resulting in improved machining accuracy and improved machining efficiency. Improvements are also obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart showing the operation of the basic action means and the transition of the machining process when the electric discharge machining method according to the present invention is performed, and FIG. 2 is an electrode between the workpiece and the electric discharge machining electrode. FIG. 3 is a plan view illustrating the positional relationship between the two in the course of the progress of the relative oscillating movement in a coordinate plane perpendicular to the feed direction by way of a representative example. FIG. FIG. 4 is a block diagram showing an example of the configuration of a main part of an electric discharge machining apparatus. FIG. FIG. 5 (A) and FIG. 5 (B) are plan views for explaining a conventional electric discharge machining operation. 10 Workpiece, 12 recess or hole, 14 working electrode, 16a current swing path, 16e final ideal swing path, 20 remaining machining allowance calculation means, 22: swing program storage means, 24: current electrode position extraction means, 26: remaining machining allowance storage means, 28: division means, 30: swing speed control means, 40: NC device, 55 ... CPU, 56 ... storage unit.

Claims (4)

(57) [Claims] 1. An electric discharge machining method for machining an inner surface of a concave portion or a hole while oscillating a machining electrode and a workpiece relatively in a direction perpendicular to a machining feed direction. The remaining machining allowance is calculated from the difference between the instantaneous position of the machining electrode and the position to be passed at the time of the final machining specified in advance, and is set for each of the calculated instantaneous remaining machining allowance and each of the orbital paths of the oscillating motion. By comparing with a reference remaining machining allowance, the swing speed is lower than a preset swing speed at a machining position where the instantaneous remaining machining allowance is larger than the reference machining allowance, and the swing speed is previously reduced at a small machining position. An electric discharge machining method characterized by controlling the swing speed to be higher than a set swing speed. 2. An electric discharge machine for electric discharge machining of an inner surface of a recess or a hole while relatively oscillating a machining electrode and a workpiece in a direction perpendicular to a machining feed direction. Position extracting means for extracting the position of the machining electrode every time in the orbital path; and the current position of the processing electrode extracted by the position extracting means and the orbital path of the oscillating movement to be passed by the processing electrode at the time of the final processing specified in advance. Remaining machining allowance calculating means for calculating the difference between the remaining machining allowance at each position by calculating the difference with the position of
A predetermined division in which the difference between the minimum remaining machining allowance in the orbit and the minimum remaining machining allowance in the immediately preceding cycle obtained by the remaining machining allowance calculating means is on the denominator side. Dividing means for performing an operation, wherein the swing speed is lower than a preset swing speed at a machining position where the quotient obtained by the dividing means is large, and the swing speed is preset at a small machining position. And an oscillation speed control means for controlling the oscillation speed to be higher than the oscillation speed. 3. The position extracting means for extracting a current position of the processing electrode from a swing path of the processing electrode determined by a processing program of the workpiece and a swinging motion program of the processing electrode. The electric discharge machining device according to claim 2. 4. The reading means for reading a position of the processing electrode at a present time detected by a position detecting means of an operation actuator for moving the processing electrode along the swing path. An electric discharge machining device according to item 1.