JPS6158256B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric discharge machining apparatus, and particularly to an improvement of a finishing control apparatus thereof.

In a typical electrical discharge machining apparatus, a workpiece and an electrode are relatively fed in the machining direction, and the feed amount is controlled by a servo system so that the gap between the two is constant. In this type of electrical discharge machining, rough machining is normally performed at high machining speeds, followed by finishing machining at low speeds, but the electrodes used for both machining are separate electrodes with similar shapes and slightly different sizes. was used. In other words, the discharge voltage in finishing machining is lower than that in rough machining, so the discharge gap between the workpiece and the electrode in finishing machining is narrower, and for this reason, the shape of the electrode itself is made slightly larger than in rough machining. Conventionally, it was necessary to use electrodes of different shapes during both machining operations.

As a conventional improved electric discharge machining device, there is a device that can perform rough machining and finishing machining in an integrated manner using a single electrode. Electric discharge machining is performed while applying a relative feed in the finishing direction in a plane perpendicular to the machining direction, and apparently the same effect as finishing machining using a predetermined amount of larger electrode is obtained. Conventional finishing feed consists of, for example, revolving circular motion.

FIG. 1 shows a conventional electric discharge machining apparatus that performs finish feeding, in which a workpiece 10 and an electrode 12 are placed facing each other in an insulating machining fluid. A pulse current of a predetermined frequency is supplied between the two from a pulse current supply circuit 14, and the workpiece 10 is subjected to electric discharge machining along the shape of the electrode 12 by applying pulse current to the machining gap. The electrode 12 is fed in the processing direction Z by a hydraulic cylinder 16, and the electrode 12 is fixed to a piston 20 via an XY cross table 18. Hydraulic servo valve 22 of hydraulic cylinder 16
A control signal is supplied from a machining gap servo circuit consisting of a voltage differential circuit 24 and an amplifier 26 to form a hydraulic servo system. Voltage differential circuit 24
The electrical discharge machining voltage Vd and the reference value Vs are supplied to
The feed of the electrode 12 in the machining direction is controlled so that the machining voltage Vd matches the reference value Vs on average, and the desired electrical discharge machining progresses.

After rough machining, in which the machining feed reaches a point slightly short of the final desired depth, pulse current supply circuit 1
The discharge energy of 4 is controlled to decrease for finishing machining,
At the same time, the finish feed control circuit 28 gives the electrode 12 a finish feed in a plane perpendicular to the processing feed.
In the figure, an X-axis servo motor 30 and a Y-axis servo motor 32 are connected to the XY cross table 18, and a sine wave having a phase difference of π/2 is applied to both motors 30 and 32 from a control circuit 28, and the amplitude of the sine wave is By setting the voltage to correspond to the side gap difference between rough machining and finishing machining, the electrode 12 has a voltage corresponding to the side gap difference between rough machining and finishing machining.
A relative orbital circular motion is applied between the two ends and 0, and in this state finishing processing is performed to a desired depth.

According to the conventional device shown in FIG. 1, processing is performed that is equivalent to expanding the shape of the electrode 12 by a dimension corresponding to the diameter of the orbital circular motion of the electrode 12, and the rough machined surface due to rough processing is removed, resulting in a good finish. A rough finished surface can be obtained.

However, in the conventional device, uniform revolving motion is applied to the complex-shaped electrode 12, so during finishing machining, the amount of machining or machining speed varies for each part of the electrode, and uniform finishing machining is not possible. The drawback was that it could not be done. FIG. 2 shows the state of drilling a hole in the workpiece 10 using the electrode 12 having an elliptical cross section, and the revolution circle in finishing processing is indicated by the reference numeral 100. In such a non-circular electrode 12, the amount of workpiece to be removed in each part of the trajectory of the orbital circular motion is much larger in parts with a large radius of curvature than in parts with a small curvature, and as a result, the finish As the machining progresses, as shown in FIG.
The depth is larger than that at 0, and the large radius of curvature part 3
There was a problem that the amount of processed residual meat in 00 increased. As a result, the conventional apparatus has the disadvantage that rough-machined surfaces are left unfinished, and the depth at which the electrode reaches during finishing varies from part to part depending on the shape of the electrode.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to provide an improved electric discharge machining apparatus that can obtain a uniform finished surface during finishing machining.

In order to achieve the above object, the electrical discharge machining apparatus according to the present invention includes a feed position detection circuit that electrically detects that the feed amount in the machining direction has reached a predetermined value;
A residual metal detection circuit that electrically detects that residual metal from a workpiece has been removed by comparing electric discharge machining voltage during machining with a feed that includes a component perpendicular to the machining direction with a reference value; It includes a timing circuit that detects that the remaining metal removal detection output of the detection circuit continues for a predetermined period, and is characterized in that it controls the stoppage of electrical discharge machining by outputting both detection outputs of the feed position detection circuit and the timing circuit. shall be.

Preferred embodiments of the present invention will be described below based on the drawings.

FIG. 4 shows a preferred embodiment of the electrical discharge machining apparatus according to the present invention, and the same members as those in the conventional apparatus shown in FIG.

In FIG. 4, a movable iron core 34 is fixed to the piston 20 in order to detect the electrode feed amount in the processing direction Z, and the iron core 34 is installed in correspondence with a coil portion of a differential transformer 35. The coil portion of the differential transformer 35 is fixed to the base of the device, and as a result, the electrode 1
The machining feed amount of 2 is detected as the movement amount of the movable iron core 34. The output V ₁ of the differential transformer 35 is supplied together with the output of the voltage differential circuit 24 to the amplifier 26 via a comparison selection circuit 36, and in the embodiment, the comparison selection circuit 36 preferentially selects the lower input value of both input signals. select. The fixed position of the differential transformer 35 is used for setting the final machining position, etc., and before the electrode 12, that is, the movable core 34 has descended to this final position, the output V ₁ of the differential transformer 35 is greater than the output of the circuit 24. As a result, the comparison selection circuit 36 outputs the differential voltage Vd−Vs, which is the output of the circuit 24, to the amplifier 2.
6 and set the voltage Vd at the machining gap to the reference value.
The feed amount of the electrode 12 is controlled to match Vs. Then, as the machining progresses, the electrode 12, that is, the iron core 3
4 reaches the predetermined final position determined by the differential transformer 35, the output V ₁ of the differential transformer 35
supplies a significantly lower voltage to the comparison selection circuit 36;
As a result, the low voltage V ₁ is selectively supplied to the amplifier 26, stopping the lowering of the hydraulic cylinder 16,
Complete electrode feeding in the processing direction.

In the present invention, the output V ₁ of the differential transformer 35 mentioned above is used as a signal for detecting that the feed amount in the processing direction has reached a predetermined value, and the output V ₁ is used as a signal for detecting that the feed amount in the processing direction has reached a predetermined value. supplied to one input. A reference value V _B is supplied to the other input of the comparator 38 , and when the feed amount in the processing direction reaches a predetermined value, the output V ₁ of the differential transformer 35 becomes smaller than the reference value V _B , and the comparator 38 "1" is output from.

Further, in the present invention, a remaining metal detection circuit is provided to electrically detect the remaining processed material (i.e., processing progress state) of the workpiece 10, and in the embodiment, the remaining metal detection circuit includes a comparator 40, The output Vd-Vs of the voltage differential circuit 24 is supplied to one input, and the reference value Vc is supplied to the other input. That is, in a normal machining progress state where there is sufficient machining remaining metal, the output Vd-Vs of the voltage differential circuit 24 is controlled to be almost zero by the electrode feed of the servo system, and the reference value Vc is determined by this difference. Since the voltage is set sufficiently higher than the voltage, the output of the comparator 40 is "0". However, as the machining progresses and the electrode 12 reaches a predetermined machining depth,
Since the feeding of the electrode 12 is stopped, the voltage Vd in the machining gap gradually rises, and when a predetermined amount of machining residual metal is removed, the output Vd-Vs of the voltage differential circuit 24 exceeds the reference value Vc, and the comparison The device 40 outputs "1".

The outputs of both comparators 38 and 40 are connected to an AND gate 42
The output of gate 42 is applied directly to AND gate 46 of clock circuit 44 and also to AND gate 46 via monostable multivibrator 48 and inverter 50. The clock circuit 44 functions to detect that both input signals to the AND gate 42, especially the output of the comparator 40 forming the remaining meat detection circuit, have continued for a predetermined period, and the multivibrator 48 is activated by the output of the gate 42. After a predetermined period of time, the output of the AND gate 42 is still “1”
A control signal is output from the gate 46 only when this is the case. In the embodiment, the output of the clock circuit 44 is applied to the pulse current supply circuit 14, and the circuit 1 is activated under the above-mentioned conditions, that is, when the feed amount of the electrode 12 reaches a predetermined value and the remaining processed material remains below a predetermined value for a certain period of time.
4, and a series of electrical discharge machining is completed.

The embodiment of the present invention has the above configuration, and its operation will be explained below.

During finishing, the electrode 12 is fed with feed in the working and finishing directions from the hydraulic cylinder 16 and the control circuit 28, and the finishing pulse from the pulse current supply circuit 14 performs finishing with good surface roughness. The differential transformer 35 is positioned and fixed at the final processing position, and when the electrode 12 descends to the final position, the comparator 38 of the feed position detection circuit outputs "1".
A signal is supplied to the AND gate 42 and at the same time the downward movement of the electrode 12 is stopped. At this time, electrode 1
2 is the workpiece 10 due to the orbital circular motion on the XY plane.
The opposing position of the two changes with time, and as a result, the machining remaining thickness also changes depending on the opposing position of the two, so the gap voltage Vd and the output Vd of the voltage differential circuit 24
-Vs will also change over time. Therefore, during this process, the output of the comparator 40 forming the remaining meat detection circuit is "1" and "0".
The output will be generated alternately, and in this transient state, the output will continue for a certain period during the finish feeding period of the electrode 12, that is, the period set by the monostable multivibrator 48 of the timing circuit 44, until the remaining thickness becomes less than a predetermined value. During this time, the desired remaining meat removal action is performed without any control output being generated from the timing circuit 44. When the remaining meat on the workpiece 10 is uniformly removed, the comparator 40 outputs a "1" signal that continues for a predetermined period of time, and at this time, the timing circuit 44 outputs an end signal to the pulse current supply circuit 14. processing is completed.

As described above, the machining is completed after the machining feed reaches a predetermined value and the remaining thickness of the workpiece 10 is completely removed, so that according to the present invention, no rough machined surface remains during finishing machining. In addition, finishing accuracy can be significantly improved.

In the embodiment, the fixed position of the differential transformer 35 is set at the final processing position, but it is also possible to move and fix the differential transformer 35 stepwise to any position during processing. , the output of the clock circuit 44 is used as a processing end signal for each stage.

Further, in the embodiment, the finishing feed is a revolving circular motion, but it is possible to apply the present invention to any other arbitrary revolving motion.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing an example of a conventional electric discharge machining device that performs finishing feed, Figs. 2 and 3 are explanatory diagrams showing the machining state with an elliptical electrode in the conventional device of Fig. 1, and Fig. 4 is 1 is a schematic configuration diagram showing a preferred embodiment of an electric discharge machining apparatus according to the present invention. The same members in each figure are given the same reference numerals, 10 is the workpiece, 12 is the electrode, 14 is the pulse current supply circuit, 1
6 is a hydraulic cylinder, 28 is a finishing feed control circuit, 3
8 and 40 are comparators, 44 is a timing circuit, and 48 is a monostable multivibrator.

Claims (1)

[Claims] 1. In an electrical discharge machining device that has an electrode arranged opposite to a workpiece and can provide a relative feed in the machining direction and a relative feed including a component in a direction perpendicular to this between the workpiece and the electrode. , a feed position detection circuit that electrically detects when the feed amount in the machining direction has reached a predetermined value, and a feed position detection circuit that electrically detects when the feed amount in the machining direction has reached a predetermined value, and a discharge machining voltage that is compared with a reference value during machining using a feed that includes a component in a direction perpendicular to the machining direction. It includes a remaining meat detection circuit that electrically detects that the remaining meat of the workpiece has been removed, and a timing circuit that detects that the remaining meat removal detection output of this remaining meat detection circuit continues for a predetermined period. An electric discharge machining apparatus characterized in that stop control of electric discharge machining is performed by outputting detection outputs from both a detection circuit and a timing circuit.