JP2650771B2 - Electric discharge machining method and equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to electric discharge machining by oscillating a center of a machining electrode having various electrode shapes in a plane independent of an electrode feeding operation direction. In the electrode swing type EDM that gradually increases and increases the machining area to the desired machining shape and dimensions by machining, if the machining allowance is not uniform in one round of oscillation such as under machining by machining, or machining The present invention relates to a high-precision electric discharge machining method and apparatus for controlling a relative operation between a machining electrode and a workpiece so as to improve machining efficiency when the dust removal method is difficult.

[Conventional technology]

By utilizing the discharge phenomenon between the EDM electrode and the workpiece having various electrode shapes according to the workpiece shape,
In 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 debris from the workpiece, a machining electrode is provided inside the workpiece. 2. Description of the Related Art A swing-type electric discharge machining method in which an operation (oscillating operation) is applied in a coordinate plane perpendicular to the feed direction together with the forward feed direction and the electric discharge machining is gradually advanced has been conventionally performed.

A well-known example of the oscillating electric discharge machining method and an apparatus for performing the method are disclosed, for example, in Japanese Patent Publication No. 55-16773. That is, the oscillating-type electric discharge machining method and apparatus disclosed in Japanese Patent Publication No. 55-16773 discloses a method of applying a machining electrode to a machining electrode in a coordinate plane perpendicular to an electrode feeding direction approaching a workpiece. Further, a swinging motion is given to advance the electric discharge machining, and the speed of the swinging motion itself is increased and decreased in consideration of the size of a machining gap between a machining contour of a workpiece and a machining electrode. 1 shows the principle technology of a mold electric discharge machining method.

In addition to the swing speed control method, recent swing type electric discharge machining methods mainly employ two types of speeds in which the electrode center of the machining electrode is displaced along a swing locus, that is, a method in which the swing speed is constant. Have been.

The principle of such a known oscillating-type EDM method will be described more simply with reference to an illustrated example. As shown in FIG. 5A, a machining area hole of the workpiece 2 (the machining electrode 4 is connected to the workpiece 2).
In the example shown in FIG. 5B, a machining electrode 4 having a rectangular shape in a hole formed by feeding operation or a hole previously machined by a milling method or the like is moved to a locus C ₀ in a coordinate plane as shown in FIG. 5B. When the workpiece 2 is swung, the electric discharge machining area of the workpiece 2 gradually increases, and a short concave workpiece region 3 is formed inside the workpiece 2.

In such a conventional electric discharge machining principle, as shown in FIG. 6, chips (machining chips) 5 are mixed in a discharge gap between the workpiece 2 and the machining electrode 4 during the swing of the machining electrode 4. The main cause of this is that an electrical short circuit occurs due to abnormal approach between the machining electrode 4 and the workpiece 2 due to external disturbances, and in some cases, an abnormal machining state occurs in the electric discharge machining area. Sometimes. When such an abnormal machining state occurs, the feed of the machining electrode 4 is stopped independently of the oscillating motion in any of the above-described oscillating speed constant system and the oscillating speed control system based on the machining gap, The retracting operation is performed relatively from the machining stop position 6 toward the feed axis direction or the swing center C of the electrode, or toward the combined direction of the two, and the shortened state is eliminated by removing the chip 5 or disturbance. A correction operation for eliminating the abnormal machining state is performed. That is, an abnormal machining state is detected from abnormal discharge currents in the discharge gap G, and a retreat operation is relatively provided between the work table on which the workpiece is mounted and the main spindle holding the machining electrode according to the detection signal. Had been adopted.

[Problems to be solved by the invention]

However, in these conventional electric discharge machining methods and apparatuses, when the abnormal machining state is eliminated and the machining state returns to the normal machining state, the machining electrode 4 and the workpiece 2 return to the machining position where they face each other. Since the oscillating motion continues, there is a problem that it is impossible to accurately return to the machining position where the abnormal machining state has previously occurred. In other words, since the retreating motion and the oscillating motion of the machining electrode are independent motions, the oscillating speed control method based on the machining gap mainly returns after retreating during the retreating motion of the machining electrode in the constant oscillating speed method. During the operation, the rocking motion was performed, and as a result, there was a great deviation between the machining stop position 6 and the electric discharge machining restart position 7 after the return operation. When such a shift occurs, a remaining portion of the processing occurs between the processing stop position 6 and the processing restart position 7. Therefore, in order to eliminate such unprocessed portions and secure high machining accuracy of the workpiece, it is necessary to replenish the swing operation amount of the machining electrode 4, and accordingly, it is There was a problem that the processing efficiency was reduced.

Accordingly, an object of the present invention is to relatively retract the processing electrode from the processing stop position when the above-described abnormal processing state occurs and to process the processing electrode forward from the retracted position when returning from the abnormal state to the normal state. The present invention is to provide an electric discharge machining method and an electric discharge machining method for returning the electric discharge machining operation to a stopped position and restarting the electric discharge machining operation.

[Means for solving the problem]

The present invention relates to a discharge state in a discharge gap between a machining electrode and a workpiece, whether an electric discharge machining operation is normally performed normally, an abnormal state due to machining chips entering the discharge gap, or an abnormal state. On the desired processing shape of the workpiece in advance,
Judgment is made as to whether it is in the area where machining is required, and when the occurrence of an abnormal state is detected, the machining is stopped and the machining stop position is stored at the same time, in order to eliminate the abnormal state such as removal of machining waste. The gap between the machining electrode and the workpiece is enlarged, and then the machining electrode is relatively moved back to the stored previous machining stop position, so that the normal state in the approaching discharge gap is restored. The swing machining is restarted when it is detected or when it returns to the machining stop position.

That is, according to the present invention, in the electric discharge machining method for controlling the swing machining operation of the machining electrode according to a discharge state of a gap between the machining electrode and the workpiece, the machining electrode and the workpiece are processed during machining. Detecting a momentary discharge state in the gap, detecting an abnormal discharge state in the gap, stopping the swing of the machining electrode, storing a swing center stop position of the machining electrode at the time of stopping the swing, The processing electrode is caused to retreat from the swing center stop position to the retreat position so as to widen the gap width between the processing electrode and the workpiece, and then the processing electrode is moved from the retreat position to the stored swing center stop. An electric discharge machining method is provided, in which the operation of approaching a position is performed, and when a normal discharge state in the gap is detected during the operation of approaching the machining electrode, the swing of the machining electrode is restarted.

Further, according to the present invention, in an electric discharge machining apparatus for controlling a swing machining operation of the machining electrode according to a discharge state of a gap between the machining electrode and the workpiece, Discharge state detection means for detecting an instantaneous discharge state in the gap; axis feed control means for instructing the swinging and retreating / approaching operation of the machining electrode based on a detection result of the discharge state detection means; While the means detects an abnormal discharge state, a swing speed generating means for stopping the swing of the machining electrode, and a storage means for storing a swing center stop position of the machining electrode when the swing is stopped, At the same time, the swing center stop position is stored in the storage means, and at the same time, a retreat operation for widening a gap width between the processing electrode and the workpiece is performed in accordance with a command from the axis feed control means, and thereafter, the storage operation is stored in the storage means. Servo speed generating means for performing an approach operation between the machining electrode and the workpiece to a moving center stop position, and when the discharge state detecting means re-detects a normal discharge state during the approach operation, stopping the approach operation. An electric discharge machine characterized by comprising:

(Operation)

According to the above-described electric discharge machining method and apparatus according to the present invention, an abnormal electric discharge state due to mixing of machining chips into an electric discharge gap inevitable in an electric discharge machining step, that is, with the occurrence of a short circuit, between the machining electrode and the workpiece. The swing operation of the machining electrode is stopped, and the width of the discharge gap is widened so that machining dust that causes an abnormal state is removed, and then the machining electrode and the workpiece are brought closer to each other again. In the process of forming an electric discharge gap, the machining electrode is positioned by returning to the position where the swing was previously stopped, so that the electric discharge machining should be resumed when the normal state is restored. Is restarted from the position where it stopped. Therefore, unlike the conventional electric discharge machining process, since there is no machining residual portion due to the occurrence of an abnormal state, the necessity of recycling the machining electrode is eliminated, and ultimately, in the swing machining process. Processing efficiency is significantly improved. Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the accompanying drawings.

〔Example〕

FIG. 1 is a block diagram showing a system configuration of an electric discharge machining apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart of a process of performing an electric discharge machining method according to the present invention with the configuration shown in FIG. FIG. 4 is a schematic explanatory view for explaining the operations of the machining electrode performed in accordance with the detection of the abnormal state in the electric discharge gap, such as the stoppage of the swing of the machining electrode, the retreating operation, the reversing operation, etc. in the electric discharge machining method according to the present invention; FIG. 4 is a schematic explanatory view for explaining a blank machining state in a process.

In the embodiment of the present invention shown in FIG. 1, the electric discharge machining apparatus has a well-known electrical connection configuration for supplying a machining current from a machining power supply 10 to a machining electrode 12 and a workpiece (hereinafter, simply referred to as a workpiece) 14. The machining electrode 12 is provided in the electrode feeding direction with respect to the machine frame of the electric discharge machine (not shown), that is, usually in the vertical axis direction (Z axis direction) by the rotational driving force of the driving motor Mz. It is provided with a configuration that can be fed and moved via a feed mechanism (not shown).

On the other hand, the work 14 is mounted on a work table 16 via a clamp or the like, and the machining electrode 12
It is also configured to be moved in the axial direction (X axis, Y axis) by a rotational driving force of the drive motors Mx and My via a feed mechanism (not shown) such as a feed screw. Processing electrode 12
A moving amount detector 18 such as a linear scale similar to that used for a main shaft of a well-known machine tool or a work table (as an example, provided on a feed mechanism for the X-axis). The moving amount detector is also provided for other Y and Z axes.) The moving amount can be detected via the moving amount detector, and therefore, the movement by the drive motors Mz, Mx, and My is precisely controlled. It is possible. In the present invention, the detection amount of the above-described movement amount detector 18 (including the movement detector of another feed axis) is read by the movement amount reading unit 34, detected by the later-described axis feed control unit 22, and The read value is stored as position information in the storage means 22a in the axis feed control unit 22 in accordance with the above.

Now, the system of the electric discharge machine according to the embodiment of the present invention has a configuration in which the electric discharge machining process is controlled by the NC program 20, and the NC program discharges a desired electric discharge machining shape to the work 14 by the machining electrode 12. Built-in processing program. The NC program 20 sends program command data to the servo speed generator 24 to feed the machining electrode 12 detachably held on the spindle in the respective feed axis directions to the servo speed generating unit 24, and causes the machining electrode 12 to move inside the electrode. Is connected so as to send program data for moving and displacing (this is referred to as oscillation) around a predetermined center (hereinafter referred to as the oscillation center) along a predetermined trajectory to the oscillation speed generator 28. I have.

When both the servo speed generator 24 and the oscillating speed generator 28 receive a feed operation command signal from the axis feed controller 22, the feed operation and machining are performed in accordance with the feed program command data and the oscillating program data described above. The swinging operation of the electrode 12 is performed. Here, the axis feed control unit
A detection signal from a discharge state detection unit 36 that constantly detects a discharge state in a discharge gap between the machining electrode 12 and the workpiece 14 is input to 22. According to the discharge state detection signal, a command signal for the above-described feeding operation is provided. Is sent from the axis feed control unit 22.

The servo speed generating unit 24 and the oscillating speed generating unit 28 include a servo axis interpolating unit 26 for path interpolation on each feed axis and an oscillating interpolating unit 30 for trajectory interpolation of the oscillating motion of the machining electrode 12, respectively. Connected to the pulse synthesizer 32 via the
At 32, the movement displacement in the feed axis direction is matched with the swinging motion of the machining electrode 12, and the drive current is supplied to each of the D / A converted drive motors Mz, Mx, and My as necessary. It has become.

In addition, the above-described discharge state detection unit 36 has a discharge state generated in the discharge gap between the machining electrode 12 and the workpiece 14 during the electric discharge machining operation, which is a discharge state appropriate for performing the electric discharge machining, that is, a normal state. Either the machining waste (chip) or the like is mixed in the electric discharge machining gap, or there is an abnormal electric discharge state in which a short circuit state has occurred. Whether the electrode surface of the processing electrode 12 faces the processing unnecessary area (this is defined as an empty processing state in the present specification and will be described in more detail later with reference to FIG. 4), For example, the detection is performed by detecting the average voltage between the poles, and the detection result is fed back to the axis feed control unit 22 described above. Note that, in the above-described system of the electric discharge machine, the axis feed control unit 22 having the storage unit 22a
Is constituted by a microcomputer or a personal computer.On the other hand, a servo speed generator 24, a servo axis interpolator 26, a swing speed generator 28, a swing interpolator 30, a pulse synthesizer 32, etc. It should be understood that the servo mechanism for servo-controlling My and Mz is configured in the same manner as a servo mechanism used in a normal NC machine tool.

In the electric discharge machining apparatus according to the embodiment of the present invention having the above-described system configuration, the machining electrode 12 performs oscillating electric discharge machining in which the machining electrode 12 oscillates about the oscillation center in accordance with the NC program 20. When an abnormal state is detected by the discharge state detecting unit 36 in the discharge gap between the workpiece 12 and the workpiece 14, the swinging of the machining electrode 12 is stopped, as described in detail below, to eliminate the abnormal state. The working electrode 12 is retracted relative to the work 14 so as to widen the gap width of the discharge gap.
2. The workpiece 14 is relatively close to form the EDM gap, and when a normal state is detected in the EDM, the oscillating EDM is restarted. The operation steps of the electric discharge machining including the normal state and the above-mentioned blank machining state will be described below with reference to the flowchart shown in FIG. 2 together with FIG. 1 and the explanatory diagrams of FIG. 3 and FIG.

Now, it is immediately possible that the electric discharge machining process is performed according to the NC data of the NC program 20, but when the electric discharge machining is started and performed between the machining electrode 12 and the work 14 according to the NC program 20. (Start), discharge state detector
Numeral 36 constantly detects a discharge state generated between the machining electrode 12 and the work 14 in accordance with a discharge voltage supplied from the machining power supply 10 (step). That is, the machining electrode 12 and the work 14
The average voltage flowing through the current circuit including the discharge gap between the two is detected to detect a change in the discharge state. In addition, the detected discharge state includes a proper discharge machining between the machining electrode 12 and the work 14 (1) a normal state and a swing trajectory of the machining electrode 12 as shown in FIG. In the process of swinging along S, the electrode surface 12a is in a swing path away from the work surface 14a of the opposed work 14, and the opposite electrode surface 12b is not involved in the electric discharge machining of the work 14 at all. State, that is, the previously described (2) empty machining state,
As shown in FIG. 3, the machining gap 15 between the machining electrode 12 and the workpiece 14 is mixed and interposed with the machining dust 15, thereby causing an electrical shortened state. is there.
Therefore, these three discharge states are sent to the axis feed control unit 22 as detected discharge states.

At this time, the axis feed control unit 22 identifies and determines these three types of discharge states (step).

In the identification and determination, when the idle machining state is detected, a command signal for swinging the machining electrode 12 at a preset maximum swing speed value is issued (step). That is, since the blank machining state is in a region where the machining electrode 12 is not involved in machining, it is necessary to release the machining electrode 12 from this blank machining state as soon as possible. Upon receiving this, the swing speed generating section 28 gives the machining electrode 12 the maximum swing speed. Thus, the machining electrode
12 oscillates at the set maximum oscillating speed, but also during this period, the discharge state is always detected, so long as the idle machining state is detected, the oscillating of the machining electrode 12 at the same maximum oscillating speed Followed by

Further, when it is detected that the discharge state is normal, the axis feed control unit 22 sends the machining electrode 12 at the normal swing speed.
Is issued (step). That is, since the machining electrode 12 and the work 14 maintain the electric discharge gap and continue the electric discharge machining, the command is issued to continue the electric discharge machining as it is. Therefore, the swing speed generator
28 is to give a normal swing speed to the machining electrode 12 to continue the current electric discharge machining process. Incidentally, the normal swing speed in this case is not always limited to a constant swing speed, and in the process where the machining electrode 12 passes through the orbital swing locus, a point where the machining allowance is relatively large is determined. The swing speed is changed according to the difference between the case where the vehicle passes through and the case where the vehicle passes through a point where the machining allowance is small. For example, Japanese Patent Application No. 1-2760 by the present applicant.
It should be understood that the swing speed adjustment disclosed in No. 7 is always being performed.

Further, when it is detected that the discharge state is abnormal, the axis feed control unit 22 issues a command to stop the swing speed of the machining electrode 12 (the swing speed is zero) (step). At the same time, the axis feed control unit 22 reads the relative position between the processing electrode 12 and the work 14 when the swing speed is stopped from the movement amount reading unit 34 and stores it in the storage unit 22a. Thus, the swing speed generating unit 28 immediately stops the swing operation of the machining electrode 12. On the other hand, in accordance with a command from the axis feed control unit 22, the servo speed generating unit 24 causes the machining electrode 12 to retreat relative to the work 14 so as to widen the discharge gap width between the machining electrode 12 and the work 14 ( Process). This saving operation, as shown in Figure 3, is performed the swing center of the working electrode 12 as the displacement from the position C ₁ when swinging stop to a position C ₂ with wider discharge gap G, the machining electrode 12 This is achieved by moving and displacing relative to the work 14. Of course, the retreat operation in the Z-axis direction may be applied to the machining electrode 12 as needed. Then, when the discharge gap G is widened by the retreat operation, the machining debris interposed in the gap is removed with the flow of the machining fluid and the like, so that the discharge state detected by the discharge state detection unit 36 changes from the abnormal state. Move to detection of another state. Accordingly, in response to the transition of the discharge state, the axis feed control unit 22 sends a command signal to the servo speed detection unit 24 to make the machining electrode 12 relatively approach the work 14 again (step). At this time, as a feature of the present invention, the approach operation is
As shown in FIG. 3, the trajectory of the previously performed evacuation operation is performed in reverse. That is, performing the position C ₁ performing the oscillating stop in a storage unit 22a of the shaft feed control unit 22 is stored, the return operation following the trajectory of the back by the action of the feed axis with the aim of this position C ₁ is It is done. When the approach operation is performed in this way, a discharge gap G is formed again between the machining electrode 12 and the work 14. Discharge state detecting portion 36 in this state, when it detects a normal state of detection of the discharge state from being continued (step) resumes discharge machining from a position C ₁ returned along the opposite return path. Until a normal state is detected, the approaching operation is continued assuming that the discharge gap is too large. If the abnormal state is not resolved, the retreat operation and the approach operation are repeated. here,
In the present invention, the evacuation operation and the proximity operation in the event of abnormal state as described above, to retreat toward from its stop position stores the swing stop position C ₁ to the retracted position C _2, then the evacuation since approaching operation aims to stop position C ₁ which is back and stores the trajectory, when the subsequent discharge machining normal state is restored to resume the position in which to stop the swing by detecting the abnormal state before the In effect, they can be deployed from the same location. Therefore, as in the conventional electric discharge machining method,
There is no large deviation between the stop position and the restart position. Therefore, even if an abnormal state occurs during the electric discharge machining process, the machining allowance does not remain, and the electric discharge machining of a desired shape is always performed according to the NC program.

As described above, according to the present invention, in the electric discharge machining process, the discharge state in the discharge gap between the machining electrode 12 and the work 14 is always detected, and from this discharge state, the empty machining state,
The electric discharge machining process is performed while discriminating and judging three kinds of states, a normal state and an abnormal state. When an abnormal state is detected, the retreating and approaching operation steps of the machining electrode 12 for immediately resolving the abnormal state are performed. It is done. Then, when the return from the abnormal state to the normal state is confirmed, the electric discharge machining is advanced again according to the NC program.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, in the oscillation type electric discharge machining, when an abnormality such as a short circuit is detected due to mixing of machining chips in the discharge gap between the machining electrode and the workpiece, Abnormality elimination measures such as removal of machining waste are taken between the machining electrode and the workpiece by widening the discharge gap width.
Evacuation operation to widen the discharge gap An approaching operation that reverses the trajectory to reverse the trajectory is performed between the machining electrode and the work to form the discharge gap again, and when the normal state is restored, the abnormal state is detected and evacuated. Since the electric discharge machining is resumed by returning to the position where the operation started, even if an abnormal state occurs in the electric discharge machining process of the work, if the abnormal state is resolved, the electric discharge machining can be developed from the same position. It is. As a result, the work always has no remaining machining allowance, and the machining efficiency can be maintained at a high level. In particular, abnormalities occur when the machining depth is relatively large with respect to the machining area, machining conditions with relatively small discharge gaps are used, or there is a discontinuous part without machining allowance (empty machining) during one rotation. Machining is likely to occur. In this case, efficient execution of the swing as described above increases the machining speed of electric discharge machining and greatly contributes to shortening of the electric discharge machining process.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a system configuration of an electric discharge machining apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart of a process of performing an electric discharge machining method according to the present invention with the configuration shown in FIG. FIG. 4 is a schematic explanatory view for explaining the operations of the machining electrode performed in accordance with the detection of the abnormal state in the electric discharge gap, such as the stoppage of the swing of the machining electrode, the retreating operation, the reversing operation, etc. in the electric discharge machining method according to the present invention; 5 (A) and 5 (B) are schematic plan views for explaining the principle of the oscillating electric discharge machining method, and FIG. Explanatory drawing explaining the evacuation action at the time of occurrence of an abnormal state in electrical discharge machining. 12 ... machining electrode, 14 ... work, 20 ... NC program, 22 ... axis feed control unit, 22a ... storage means, 24 ... servo speed generation unit, 28 ... swing speed generation unit, 32 ... … Pulse synthesis unit, 34… Moving amount reading unit, 36 …… Discharge state detection unit.

Claims (2)

(57) [Claims] An electric discharge machining method for controlling a swing machining operation of the machining electrode according to a discharge state of a gap between the machining electrode and the workpiece. Detecting the abnormal discharge state in the gap, stopping the oscillation of the machining electrode, storing the oscillation center stop position of the machining electrode when the oscillation is stopped, Moving the machining electrode from the swing center stop position to the retreat position so as to widen the gap width between the machining electrode and the workpiece, and then moving the machining electrode from the retreat position to the stored swing center stop position. An electric discharge machining method, wherein when the normal discharge state in the gap is detected during the approaching operation of the machining electrode, the swing of the machining electrode is restarted. 2. An electric discharge machining apparatus for controlling a swing machining operation of the machining electrode according to a discharge state of a gap between the machining electrode and the workpiece. Discharge state detecting means for detecting a discharge state of the motor, axis feed control means for instructing the swinging and retreating / approaching operation of the machining electrode based on the detection result of the discharge state detecting means, and the discharge state detecting means is abnormal. A swing speed generating means for stopping the swing of the machining electrode while detecting a discharge state; a storage means for storing a swing center stop position of the machining electrode when the swing is stopped; and the storage means. The swing center stop position is stored at the same time, and at the same time, a retreat operation for widening the gap width between the machining electrode and the workpiece is performed in accordance with a command from the axis feed control means, and thereafter, the swing center stored in the storage means is stored. stop A servo speed generating means for performing an approach operation between the machining electrode and the workpiece to a position, and stopping the approach operation when the discharge state detecting means re-detects a normal discharge state during the approach operation. An electric discharge machine characterized by the following.