JPS6059099B2 - Electrical discharge machining method and device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to electric discharge machining in which an electrode and a workpiece are opposed to each other via a non-insulating liquid and a spark discharge is generated in the gap between the electrodes. In addition to the main machining direction, a predetermined electrical discharge machining gap is maintained between the electrode and the workpiece while changing the relative position of the electrode and the workpiece in a plane perpendicular to this direction, and electrical discharge in the non-opposed gap is maintained. The present invention relates to a controlled method and apparatus for actively inhibiting erosion.

As is well known in the art, electrical discharge machining methods that use water as a machining fluid have many characteristics.

That is, ・1) There is no need to worry about fire.

(2) Do not generate toxic or flammable hydrocarbon gases.

(3) Since there is no carbon, even if an abnormal arc occurs,
No tar or carbon is generated and arc marks do not grow.

etc. On the other hand, the disadvantages are (1) electrolytic action.

(2) Rust occurs on the workpiece.

(3) Due to poor insulation, the side clearance is wide (this is due to the fact that discharge occurs even over a considerable distance).

), the accuracy is poor. etc. By the way, water is used as a machining fluid in wire-cut electrical discharge machining, but this is because the electrode is a thin wire of about 0.2 wnφ, and the part facing the workpiece changes one after another, and the part of the workpiece that faces the workpiece changes one after another. Because they do not face each other while staying close to the point for a long time, the electrolytic effect described above and long-distance discharge due to the low withstand voltage (several 10 to several 100
Up to μml.

), this is thought to be because the gap between the poles does not expand. Therefore, even in general electric discharge machining that processes according to the shape of the electrode, as in the wire-cut electric discharge machining described above, as long as there is a sufficient distance between the electrode and the workpiece, except for the opposing gap where the discharge occurs. It can be understood that unnecessary erosion is not caused to the workpiece. Here, let us consider the discharge erosion effect when a machining fluid that is not highly insulating, such as water, is introduced into the gap between the poles.

Figure 1 shows the relationship between the electrode and the workpiece in electrical discharge die carving when water is used as the machining fluid. Electrode 1 is connected to the main axis (Z
The figure shows a workpiece 2 being machined in the axial direction. The gap G1 between the electrode 1 and the workpiece 2 on the bottom surface is
In an insulating machining fluid? It can be narrowed down to the point where there is no significant difference. This means that the gap between the poles and the average machining voltage Vg are the gap length. This is due to faithfulness to the basic principle of electrical discharge machining, which is theoretically possible to control the gap to a point on the verge of a short circuit, since the relationship is almost linear when the gap is narrow. Note that the above-mentioned average machining voltage Vg is the voltage obtained by smoothing the machining voltage of the machining power source 3. Ru. A high-frequency pulse power source consisting of a DC power source 4, a switching element 5, and a current-limiting resistor 6 is normally used as the power source 3 for machining. Machining is performed while randomly selecting states, and the comparator 7 compares whether the average voltage Vg is higher or lower than the reference setting voltage Vr. This error voltage ε is amplified by the amplifier 8, and Z The Z-axis feed is controlled by the axial drive motor 9, so that the gap between the poles is such that the average voltage [EVg''.Reference setting voltage Vr is achieved.In FIG. 1, 10 is a resistor, and 11 is a capacitor, 12 is a processing fluid,
13 indicates a processing liquid tank. Next, the gap G on the side
Focusing on 2, G, , G4, and G5, since these gaps are not controlled in any way artificially, they increase in the order of G2 → G3 → G4 as a function of the facing time with the electrode 1.

The reason for the increase is that the probability that a discharge will occur after the pulse voltage is applied by the machining power supply 3 is higher in the narrower the gap and lower in the wider gap, but if the number of repetitions of the discharge is 1
Since the number of discharges is approximately 1000 to 100,000 times per second, over time, even if only a few percent of the discharges occur on the sides, the number of discharges becomes considerable. In particular, when water is used as a machining fluid, the insulating properties are low, so the probability of electrical discharge is high even if there is a considerable distance, and the gap G2~
It is clear that the spread of G is remarkable. By the way, the inventors have confirmed through experiments that the probability of discharge is inversely proportional to the gap length within a narrow gap length range.

Also, the expansion amount ΔG of the gap G during the time Δt is:
Therefore, if we substitute equation (1) into equation (2), we get
If we solve this, we will find G as a function of t, (when the initial value t=o, G=G1), and the gap length increases in proportion to the time k east. I can see it going on.

However, in reality, as the gap length increases, A in equation (1) above begins to decrease significantly, so after a certain time or a certain gap, the increase in the gap becomes negligible ( G4:G5). However, when water is used as the machining fluid, the gap length reaches as much as 0.1 to 0.3wn, and the conventional wisdom is that the difference from the electrode dimensions is too large to be of any use. This was a fatal drawback when water was used as a machining fluid in normal electrical discharge machining.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and it is possible to maintain a critical gap (gap length beyond which the gap does not increase) in a plane perpendicular to the main processing direction of the electrode and the workpiece. An electrode that applies a displacement that exceeds the relative position of the electrode and the workpiece, divides the electrode into a plurality of parts within the above-mentioned plane, and approaches the workpiece with the above-mentioned relative displacement while insulating them from each other. By energizing and machining, a controlled micro-gap is maintained in the opposing side gaps, and no electrical discharge is caused in the non-opposing side gaps, preventing an increase in the gap length and shaping the workpiece into the desired shape. It is an object of the present invention to provide a method capable of accurately processing a shape and an apparatus for carrying out the method.

An embodiment of the method of the present invention will be described below with reference to FIGS. 2 and 3, which are embodiments of the apparatus of the present invention.

In the figure, 20 is an X-Y control table, 21 is an X-axis direction drive motor that drives the table 20 in the X-axis direction,
22 is a Y-axis direction drive motor that drives the table 20 in the Y-axis direction; 23 is a numerical control device that controls the motors 21 and 22; 13 is a machining fluid tank placed on the table 20; 2 is the A workpiece 1 placed in the machining liquid tank 13 is an electrode that faces the workpiece 2 with the machining liquid 12 interposed therebetween.
The electrode structures 1A, 1B, 1C, and 1D are electrically insulated from each other by an insulator 1E.

Further, as the processing fluid 12, a liquid with low insulation properties such as water is used. Note that the workpiece 2 is moved in the X-axis direction or the Y-axis direction by drive motors 21 and 22.
A relative displacement occurs between the electrode 1 and the electrode 1 on a plane perpendicular to the Z-axis direction of the electrode 1. Drive and control in the z-axis direction are omitted in this figure. Further, 24 is an amplifier for amplifying the output of the numerical control device 23, and 25A to 2
5D is a switching element that transmits the output of the numerical control device 23 to each of the electrode structures 1A to 1D via the amplifier 24, and 26A to 26D are the switching elements 25.
Current limiting resistors A to 25D, 4 being a DC power source, form a discharge between the electrode 1 and the workpiece 2 via the switching elements 25A to 25D, respectively. The switching elements 25A to 25D are controlled by a numerical control device 23 via a switching control amplifier (hereinafter simply referred to as an amplifier) described later. Further, 3 indicates a processing power source. FIG. 3 is a detailed circuit diagram of the amplifier 24, which is composed of a NAND gate 27, a switching control oscillator 28, and an average voltage detection circuit 29, each of which is controlled by a numerical controller 23. It is something that will be done.

In addition, in this FIG. 3, 29A to 29D are the above NANs.
The NAND elements constituting the D gate 27 control the switching elements 25A to 25D, respectively. 30A
~30D are analog switches controlled by the numerical control device 23, and 31A~31D are the analog switches 30 described above.
A diode connected in series with each of A to 30D, 32 to
34 is a resistor, 35 is a capacitor, and 36 is a diode.

Note that other parts are the same as those in FIG. 2, and therefore are designated by the same reference numerals. Next, the operation of the device shown in FIG. 3 will be explained.

Now, when the electrode 1 in FIG. 2 is driven by the motors 21 and 22 and the X-axis direction drive moke 21 drives the table 20 in the plus X direction, the output power from the numerical control device 23 becomes 1. 27, NAND element 2
Since the gate of 9D is opened, a pulsed switching signal is output from NAND element 29D, and switching element 25D performs switching. Also, at this time, among the analog switches 30A to 30D, the switch 30D corresponding to plus
Of these, the voltage is taken out as a reduced signal (2) via the diodes 36 and 31D and further via the voltage dividing resistors 32 and 33, smoothed by the capacitor 35, and sent to the numerical controller 23.
and is given as a speed control signal. Therefore, when the electrode that is currently discharging comes too close to the workpiece 2, the feeding is stopped or reversed to prevent short circuits. Also, in the case of simultaneous two-axis feed, the gate of the corresponding NAND element is similarly opened, the analog switch is also turned on, and the two axes can move simultaneously. The above analog AND circuit operates according to the lower voltage, so the lower voltage in either the X-axis direction or the Y-axis direction
In other words, since control is performed based on the signal from the side that is too close, there is little possibility that the electrode 1 will be damaged. According to the above control method, since only the electrodes in the direction of machining are energized, there is no discharge or electrolytic action in the electrodes in other directions, and a desired shape can be precisely machined. Note that in the above embodiment, the case where the electrode 1 is divided into four pieces has been illustrated and explained;
plus X1 minus Y), (plus X1 minus Y),
(minus X1 plus Y), (minus X, plus Y)
It is also possible to make such connections.

Another method is to apply an alternating current or low-voltage current voltage to each electrode to detect proximity to the workpiece, and then apply a unipolar machining current only to the electrodes for which proximity has been confirmed to perform machining. The method of doing so also has similar effects.

In this case, the amplifier 24 in FIG. 2 is provided with a proximity sensing circuit to determine which electrode has reached the dischargeable distance 2. As explained above, according to the present invention, the displacement between the electrode and the workpiece in a plane perpendicular to the main machining direction of the electrode and the workpiece exceeds the critical gap (gap length at which the gap does not increase further). In addition to applying current to the relative position of the workpiece, the electrodes are divided into a plurality of parts within the above-mentioned plane and are insulated from each other, and the electrodes that are close to the workpiece are energized to perform machining. By doing this, it is possible to maintain a controlled minute gap in the opposing side gaps, prevent electrical discharge in the non-opposing side gaps, prevent the gap length from increasing, and accurately machine the workpiece shape into the desired shape. An excellent electrical discharge machining method and an apparatus for carrying out the method can be provided.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the state of the discharge gap between a tool electrode and a workpiece in underwater electrical discharge machining, and FIG. 2 is a diagram illustrating an embodiment of the apparatus according to the present invention for explaining an embodiment of the method according to the present invention. , FIG. 3 is a detailed explanatory diagram of the switching control amplifier in FIG. 2. In the figure, 1 is an electrode, 2 is a workpiece, 20 is an X-Y control table, 3 is a processing power source, and 23 is a numerical control device.

Claims (1)

[Claims] 1. A plurality of insulated and divided electrodes and a workpiece are placed opposite to each other via a liquid with low insulating properties, and the direction in which the electrodes and the workpiece face each other is defined as the main processing direction. A method in which machining is performed by applying a relative displacement between the electrode and the workpiece in the plane, in which the relative displacement between the electrode and the workpiece causes electrical discharge. 1. An electrical discharge machining method characterized in that, when displacement occurs in a direction, electrodes located in the direction are selectively energized to cause discharge, and electrodes not located in the direction are not energized. 2. The electrode and the workpiece are opposed to each other via a liquid with low insulation, and the opposing direction of the electrode and the workpiece is divided into a main processing direction and a direction in a plane substantially perpendicular to the main processing direction, In the device that performs processing by applying a relative displacement between the electrode and the workpiece in the plane, the electrode is divided into a plurality of pieces via an insulator, and a driving device that applies the relative displacement, a device for energizing the workpiece, the drive device changes the relative position with respect to the workpiece;
An electric discharge machining device that processes the workpiece by applying electricity to an electrode that generates an electric discharge between the workpiece and the workpiece. 3. The electrical discharge machining apparatus according to claim 2, wherein the device for selectively supplying current to the electrode is operated by a drive signal from a drive device that provides relative displacement between the electrode and the workpiece. 4. Electrical discharge machining according to claim 2, characterized in that the device for selectively energizing the electrode is operated by a proximity sensing voltage consisting of alternating current or low voltage direct current applied between the electrode and the workpiece. Device.