JPH0457449B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a wire cut electric discharge machining apparatus.

In particular, the present invention is characterized in that when current is passed through electric wires installed in parallel, the parallel electric wires repel or attract each other depending on the direction of the current flowing through each wire.
Utilizing the so-called Fleming's law, the electromagnetic force generated by the excitation current supplied to the workpiece and the discharge current for machining flowing between the wire electrode and the workpiece attracts each other to the wire electrode. By applying a force that approaches the workpiece, the wire electrode deflects in the direction away from the workpiece during electrical discharge machining, and by straightening it, it improves machining accuracy. This is the purpose.

In a wire-cut electrical discharge machining device that uses a wire electrode, the wire electrode is usually pulled out from one storage reel, moved while applying a predetermined tension to the processing section having a pair of positioning guides, and then wound onto the other reel. and between the pair of positioning guides, the workpiece is opposed from a direction substantially perpendicular to the axis of the wire electrode that is updated in the axial direction of the wire electrode to form an electrical discharge machining gap,
A machining fluid such as water or oil is supplied to this gap, and intermittent voltage pulses are repeatedly supplied to generate a discharge pulse. By repeating this discharge, the workpiece is machined. At this time, the wire electrode or workpiece is machined. By applying processing feed such as a predetermined contour shape relatively to the workpiece on the plane in the perpendicular direction, cutting and punching into various shapes can be performed.

However, in this wire cut electric discharge machining, the wire electrode is bent due to the discharge pressure generated during the discharge, and the electrode is bent in a so-called arched shape as the machining progresses.

Particularly before and after the portion where the feeding direction of machining changes, this arcuate electrode bending directly deteriorates machining accuracy. Let's assume that the distance between the pair of positioning guides, or the so-called span of the wire electrode, is 10 cm, and that a discharge pressure of 20 g is applied to the center of the span, then 800 g will be applied to the wire electrode made of 0.2 mmφ brass wire.
When electrical discharge machining is performed with a tension of , the center of the wire electrode will be deflected by approximately 0.62 mm from its original position at the center, resulting in poor machining accuracy.

The present invention, which achieves the above object while eliminating the drawback that the machining accuracy of the corner portion is reduced, will be explained based on the drawings illustrating the present invention.

FIG. 1 schematically shows an embodiment of a wire-cut electrical discharge machining apparatus according to the present invention. An upper arm 3 and a lower arm 4 protrude from a column 2 provided on a bed 1 to the side of the table. A head 5 that can move up and down is supported at the tip of the upper arm 3, and a guide holder 6 is mounted at the bottom of the head 5 using a numerical control device (not shown) to move XY and Y at right angles to each other on a horizontal plane. It is supported so that it can be moved in any direction. The wire electrode 7 that can be wound around the storage drum 8 is interposed between a number of guide rollers 9 and 10, and a pinch roller 11 that applies brake control to drive the wire electrode to apply a predetermined tension to the wire electrode 7. The part sandwiched between the brake rollers 12 is opposed to the workpiece 14 through a positioning guide 13 such as a ship shape or a die shape for positioning the processing part. This workpiece 14 is fixed to a stand 16 fixed to a table 15 by a clamp plate 17. The table 15 is supported by the bed 1, and is moved on a horizontal plane in X and Y axes directions perpendicular to each other by a numerical control device (not shown). A processing voltage pulse from a pulse power source 29, which will be described later, is applied between the wire electrode 7 and the workpiece 14,
Machining is performed under the injection of machining fluid 18. The wire electrode 7 used for the electrical discharge machining action between the workpiece 14 and the workpiece 14 is provided between the other positioning guide 19 such as a boat shape or die shape, and a plurality of guide rollers 20 and 21. Pinch roller 22 and capstan 23 for updating the wire electrode 7
The paper passes through the sandwiched portion and is collected by the winding drum 24.

Thus, the wire electrode 7 may be approximately 0.05 to 0.5
Thin wire of about mmφ, tungsten, molybdenum,
Although fine wires made of copper or alloys of these wires are sometimes used, usually copper-based alloy wires such as copper or brass are used, and when the above tungsten wires are used, they are thinner wires of about 0.05 mmφ. It is a thin line.
The wire electrode 7 is placed between the positioning guides 13 and 19 for positioning the electrical discharge machining part by the wire electrode 7.
requires applying a tension of around several kilograms or less. Since the wire electrode 7 is exposed to intermittent electric discharge of high frequency (approximately several tens of kHz or more) between the workpiece 14 and the workpiece 14 due to the current flowing through the wire electrode 7, the wire electrode 7 is In the machining groove of the workpiece 14, machining is progressing in a direction opposite to the direction in which machining is progressing, usually in an arcuate state toward the rear of the machining groove. In order to reduce this curvature, it is sufficient to increase the tension applied to the wire electrode, but
If strong tension is applied to a thin wire electrode, it will break. That is, in order to prevent the wire electrode 7 from being cut, there is a limit to the tension that can be applied, and since the wire electrode 7 also stretches in response to the applied tension or force, as described above, the wire electrode 7 is attached to the workpiece 14. Or, it is unavoidable that the machining groove has a certain degree of arc shape, and the positioning guide 1
As the distance between the positioning guides 3 and 19 increases, the radius of curvature of the arc increases, and the position of the processed portion is displaced more greatly from the position between the positioning guides.

FIG. 2 is an enlarged view of the main part of the embodiment of the present invention, and the upper and lower cases 30 to which the positioning guides 13 and 19 on both the upper and lower sides of the workpiece 14 are fixed are not shown. The structure is such that the position of the wire electrode 7 can be adjusted by fine movement in the vertical direction and in the direction perpendicular to the plane of the paper, and the case 30 is attached to the guide holder 6 with bolts or the like.
and the lower arm 4, respectively. Cap 31 for injecting machining fluid 18 into this case 30
is removably attached, and its ends, together with the case 30, form upper and lower nozzles 32. Next, the excitation current energization means for the front and back directions of the workpiece, which is provided in each of the 30 cases so as to sandwich the workpiece 14 in the front and back directions, will be described. A support member 33 made of an insulating material is fixed, and a support plate 34 also made of an insulating material is fixed to the support member with screws or the like. A gear 35 made of a conductive material is rotatably supported between the support member 33 made of an insulating material and the support plate 34.

A leaf spring 3 with a contact 36 attached to this gear 35
6A is attached with screws 37, and the tips of the contacts 36 are adapted to come into elastic contact with the front and back surfaces of the workpiece 14. A leaf spring 36A that holds this contact 36
The gear 35 to which is attached is the gear 3 made of insulating material etc.
8A meshing, the gear 38 is fixed to the shaft of a servo motor 39 fixed to the guide holder 6 and the lower arm 4, respectively. A brush 44 is inserted into the brush insertion hole 43 of the bracket 42 attached to the guide holder 6 and the lower arm 4 against the elasticity of the spring 45.
Two nuts 46 are tightened and fixed at the rear end of the brush 44, and the tip of the brush 44 is attached to the spring 4.
It is always in contact with the gear 35 which rotates with the elastic force of 5. Each brush 44 is connected via a nut 46 to both outputs of an excitation power source 40 having a polarity via a polarity changeover switch 17.
The excitation current is made to flow through 4.

As shown in FIG. 3, the cross-sectional contour line 14B of the machining surface or machining gap surface of the workpiece 14 tends to have an arcuate convex shape or the like in the direction of machining feed, as shown in the figure. This is because the wire electrode 7 is pushed and renewed in a curved state by the pressure generated in the machining gap due to the action of the working fluid flowing through the wire in addition to the pressure caused by the pulse discharge. In FIG. 3, reference numeral 14A indicates a portion of the workpiece 14 that has been completely machined with the wire electrode 7, which is one cut surface of the processing groove of the workpiece 14 corresponding to the processing feed direction. 18A,
18B indicates the flow direction of the machining fluid 18 after it is coaxially jetted from the opening of the jet nozzle 32 along the wire electrode 7, and the machining fluid 18 flows along the contour line 14B of the machining gap. The figure shows the jet flow directed within the machined groove under the influence of

On the other hand, if two conductive wires l ₁ and l ₂ are placed in parallel at an appropriate interval as shown in Fig. 4a, and current is passed in both from the upper + side to the lower - side, that is, in the same direction,
As shown in Fig. 4b, a magnetic field line pattern is formed according to the right-handed screw rule, and an attractive electromagnetic force F is generated between the two conducting wires l ₁ and l ₂ , so that a restraining tension, etc. is applied to the conducting wires l ₁ and l ₂ . It is well known that if they are not provided, the two will approach each other.

Taking these points into consideration, the present invention has been developed through various trial production and experiments, and as a result, when a discharge current flows through the workpiece 14 and the wire electrode 7 due to discharge for machining, an excitation current is applied to the workpiece 14. The electromagnetic attraction force in the machining feed direction is generated between the wire electrode 7 and the workpiece 14 by the discharge current and excitation current, as shown in FIG. This is intended to correct the bending of the wire electrode 7 toward the rear side of the processed groove and straighten the wire electrode 7 in the processed portion between the guides 13 and 19. A pulse power supply 29 is connected to the wire electrode 7 to supply voltage pulses to the current-carrying pins 25 and 26 through which discharge current flows. It is connected to the negative electrode of the pulse power source 29 so that voltage pulses are supplied from either one or both simultaneously, and the positive electrode of the workpiece 14 is connected. Workpiece 1
4 and the wire electrode 7 is not fixed in one place, but is approximately 120 degrees to the left and right in the axial direction of the wire electrode 7 and around the wire electrode 7, especially in the forward direction of machining. Randomness occurs over time within a certain angular range, and therefore, at that time, the machining discharge current is caused to flow through both current-carrying pins of the wire electrode 7 or rollers 25 and 26, i.e. It is necessary to switch whether the power is supplied from the upper or lower current-carrying pin, and in consideration of this point, the excitation current supplied to the workpiece is also switched between the contacts 36 and 36 by the switch 27. The direction of the excitation current flowing in the front and back directions of the workpiece 14 is configured to be switched depending on the position of the discharge generation point, particularly in the thickness direction of the workpiece, and further in synchronization with the output voltage pulse of the pulse power source for machining. It is desirable that the configuration be such that it can be switched at high speed. In this way, in the present invention, a pair of contacts 36 are provided on the workpiece 14.
An excitation current different from the discharge current for machining is passed from the excitation DC power supply 40 through the wire electrode 7 as a current in the same direction almost parallel to the discharge current for machining. By alternately switching the voltage polarity of the excitation current applied to the workpiece 14 through the contact point 36 using the switch 41, the electromagnetic force acting on the wire electrode 7 due to the excitation current flowing through the workpiece 14 can be changed to the wire electrode 7. The excitation current is designed to eliminate deviation in the axial direction or the thickness direction of the workpiece 14, and the excitation current is applied to a predetermined direction from side to side centering on a part of the workpiece 14, that is, the part immediately in front of the workpiece 14 in the direction of progress of machining. By intensively flowing a current in the same direction that is substantially parallel to the axis of the wire electrode 7 within the angle, a mutually attractive force is generated between the discharge current flowing through the wire electrode 7 and the wire electrode 7 The deflection can be reduced by pulling it forward in the direction of progress of processing. In this way, the wire electrode 7 is pulled out from the storage drum 8, runs in tension between the guides of the processing section, and then runs toward the winding drum 24 to maintain a minute gap with the workpiece 14. Then, apply the voltage pulse to the pulse power supply 29.
The current is applied to one or both of the energizing pins 25 and 26 via the switch, and the workpiece 1
A pair of contacts 36 that elastically contact 4 from both sides are
It is rotated via gears 38 and 35 by a servo motor 39 controlled and rotated by a numerical control device (not shown), and the position in contact with the workpiece 14 is on the planned machining line of the workpiece 14. That is, it is controlled so that it is located at a portion immediately before the front in the direction of progress of processing, or at a portion near the said portion within a predetermined angle to the left and right with respect to the front in the direction of processing.

The voltage of the excitation DC power source 40 is applied to the pair of gears 35 made of this conductive material by the switch 4.
1 and the brush 44, the positive and negative polarities of which are switched between each other as necessary, are applied,
This applied voltage is applied to the workpiece 14 through a contact 36 attached to the gear 35, and an excitation current parallel to the wire electrode 7 flows in said portion. Then, by intensively passing an excitation current from the DC power source 40 to the desired position of the workpiece 14, the excitation current flowing through the workpiece 14 and the electric discharge cause the wire electrode to pass through the gap from the workpiece 14. An electromagnetic force as explained in FIG. 4 can be generated between the pulsed discharge current flowing through the electrode 7, and this electromagnetic force can be made into a force that attracts each other by matching the directions of the flowing currents.
Moreover, since the workpiece 14 has a larger mass than the wire electrode 7 and is fixed to the table 16, the wire electrode 7 is eventually drawn into the machining groove of the workpiece 14 in the direction of machining progress. As a result, the above-mentioned deflection is canceled out and the object is straightened.
In other words, if it is pulled in the direction of progress of machining, the machining gap in that part narrows and machining is performed.
The purpose can be achieved by approximately balancing the cause and degree of arcuate deflection of the wire electrode 7 with the degree of the corrective action by the electromagnetic force.

The negative electrode of one terminal of the processing pulse power supply 29 is
energizing pins or rollers 25 on both sides of the workpiece 14;
Usually, it is always connected to the wire electrode 7 via the wire 26, and in the illustrated embodiment, it is configured to be switched and connected to either one of the energizing pins or rollers 25 or 26 via the changeover switch 27. For example, if the excitation DC power source 40 is connected to the contacts 36, 36 without going through the changeover switch 41, and an excitation current always flows through the workpiece 14 from the top surface to the bottom surface, In the machining gap, an electromagnetic attractive force is generated in the wire electrode portion below the discharge point in the axial direction of the wire electrode 7, as described above, whereas an electromagnetic repulsion force is generated in the wire electrode portion above the discharge point. This state may be switched to the energizing pin or roller 25 or 26 by a switch 27, or by providing a changeover switch 41, which was assumed not to be provided above, and turning the switch 41 on. Therefore, the direction of the excitation current remains constant unless the direction is switched from the lower surface to the upper surface of the workpiece 14, and as the position of the discharge point moves in the wire electrode axis direction, that is, in the workpiece thickness direction. If the direction of the excitation current can be changed by the changeover switch 41 at a predetermined frequency, for example about 2KHz, switching between the current-carrying pins or rollers 25 and 26 is not necessarily necessary, and both sides of the workpiece 14 From wire electrode 7
However, in order to more reliably obtain the average linearity of the wire electrode 7 as a state of more random attraction and repulsion, the switch 27 and the switch 41 may be configured to conduct various different It is preferable to configure the switching state so that the state switching progresses randomly.

In the above case, in the illustrated embodiment, the changeover switches 27 and 41 are shown as mechanical switches, but if it is desired to switch at a high speed of several KHz or higher, as described above, electronic switches such as transistors or the like may be used. It is necessary to use a switch element, and in any case, not only at such high speeds but also at low speeds on the order of seconds or milliseconds, the switching is performed by stopping the supply voltage pulse from the processing pulse power source 29. It is desirable that the power supply 29 is synchronized with the time or during the rest period, and the power supply 29 is
It is preferable that the high-frequency voltage pulse train for machining is intermittent at a relatively low frequency, as described in Publication No. 13196, and the excitation power source 40 is not a direct current, but a voltage pulse train that is a part or more of the voltage pulses of the pulse power source 29 for machining. As a pulse power source that is almost synchronized with the voltage pulse, it is possible to reduce the loss of excitation current and to reduce the heating of the workpiece 14 due to the current, and the power source 40 supplies pulse currents with different polarities of equal positive and negative polarity. If so, the output section changeover switch 41 can be omitted. Further, the positions of the pair of contacts 36, 36 for supplying the excitation current to the workpiece 14 are set so that the motor 36 is controlled by numerically controlled machining commands, etc., so that they are located almost immediately before the front in the machining direction. As explained above, the machining gap is within a range of about 180 degrees in the direction of machining progress, and the main area is, for example, spread over a range of 70 degrees to 120 degrees, so the contact point The position 36 is also controlled to move at a faster speed on both ends than in the center (the part immediately in front of the machining direction) in the above-mentioned angular range.
Control such as performing processing while reciprocating at a frequency of around Hz or lower is also effective.

The outline of the present invention has already been explained above, and the specific device configurations of the second and third embodiments of the present invention will be described as follows.

First, if the excitation power supply 40 is a DC power supply whose current value can be adjusted and set as described in the embodiment, the voltage pulses from the processing pulse power supply to the wire electrode are supplied to one of the pair of power supply means. (preferably from the feeding side of the wire electrode), the excitation current applied to the workpiece from the DC excitation power source 40 through the pair of contacts may be applied from one fixed direction. Needless to say, feeding voltage pulses to the wire electrode only from one side is extremely disadvantageous in increasing the machining current and machining speed, and also causes many wire electrode breakages, as well as concentrated discharge. The frequency of occurrence of this will increase, the discharge state will become unstable, and the machining speed will eventually decrease. Therefore, the voltage pulses are supplied to the wire electrode from power supply means provided on both sides of the workpiece, or For example, it is preferable to perform machining by stabilizing the discharge state by alternating a desired plurality of discharge pulses, by switching alternately at every predetermined period, or by combining the two.

A high-speed switching means is required for simultaneous power supply to the pair of power supply means and for switching to select one of the power supply means. A drive control circuit that inserts switching elements such as FETs between the power supply means 25 and 26 according to the discharge current capacity, and supplies an on/off control signal between the element drain and source between the gate and source of the switching element. The control circuit supplies a desired drive signal, for example, a drive signal to the switching element on one side to perform processing, and causes a current in the same direction as the excitation current flowing through the workpiece to flow through the wire electrode. discharge pulse
When counting 50, the on-drive signal is switched and supplied to the other switching element, and when 20 discharge pulses in the opposite direction are counted in this state, the switch is switched to generate the discharge pulse in the same direction again. Do you want to repeat this from now on?
Alternatively, a mode may be provided in which a drive signal is simultaneously applied to both switching elements during switching of the pair of switching elements or after switching a predetermined number of times, and power is supplied from both power supply means while a desired number of discharge pulses are generated. Also good.

Further, in order to switch the conduction polarity from the excitation power source 40 to the contacts of the pair of current supply means at high speed,
The configuration can be implemented by, for example, the power source 40 having a configuration similar to that of the power source that supplies pulse currents with different polarities of positive and negative, and specifically includes a DC power source, a switching element, and a safety resistor. and preferably a rectifier, connected in opposite directions between the pair of current-carrying means, and for each switching element of each series circuit, the control circuit or a control circuit similar to the control circuit. From the desired drive signal, for example, during the rest period of the machining voltage pulse or the rest period set for switching, after turning off one switching element that is in drive, the other switching element is turned off for a predetermined period set for the switching element. Alternatively, it is possible to output a signal that is turned on and driven for a period of counting a desired number of discharge pulses, and to switch the direction of flow of the excitation current.

In addition, if the excitation power source 43 can switch the conductivity of the contacts of the pair of current-carrying means at a relatively high speed, in this type of wire-cut discharge, the discharge between the wire electrode and the workpiece can be changed at a relatively high speed. How far away the wire electrode was from both the upper and lower power supply means or from either one of them, that is, at what position in the thickness direction of the workpiece was the discharge performed, the so-called discharge position. Detection and discrimination are possible as is well known, and on the other hand, in this type of wire cut electrical discharge machining,
When a discharge occurs between the wire electrode and the workpiece at a certain position in the thickness direction of the workpiece, the discharge may be said to be in the vicinity of the two, but due to the occurrence of the discharge, the discharge position Since machining debris from the workpiece and electrode consumable debris are present in the vicinity of the circumference, several or more voltage pulses that are subsequently supplied in the interval may be discharged one after another near the discharge position. This is normal, and the fact that the remachining process is performed using multiple electrical discharges, and the distance between the parts due to the discharge pressure and intervening gas pressure, causes the discharge generation position to be located in a direction other than the thickness direction of the workpiece. Since the machining progresses in such a manner that the machining progresses from one point to another, for example, by detecting the position where the discharge occurs,
There is also a control mode in which the direction of excitation current flow is switched if necessary, the switched state is maintained during the generation period of the subsequent desired discharge pulse, and then the discharge generation position is detected for the next discharge pulse and the direction is switched if necessary. It is possible.

According to experiments, when machining a workpiece 14 with a thickness of 100 mm, the discharge pulse width (gate signal) was set to 2 μs, the pause width between voltage pulses was set to 8 μs, and an average machining current of 22 μs was applied to the wire electrode 7. When amperage is applied, a pressure of approximately 16 g is generated in a direction perpendicular to the axial direction of the wire electrode 7, and the amount of deflection of the wire electrode 7 at approximately the center of the workpiece 14 is 0.2 mm. Summer. On the other hand, while an average current of 20 amperes is applied to the workpiece 14 through the contact 36 in the same phase as the machining current,
The amount of deflection of the wire electrode 7 when processed at a processing speed of ² /min was only about 0.03 mm, and the amount of deflection could be reduced. Moreover, the workpiece 14
Since a current is applied to reduce the deflection of the wire electrode 7, the wire electrode 7 does not generate heat, and wire cut electrical discharge machining can be continued for a long time while correcting the deflection of the wire electrode 7. It is effective.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, and FIG. 2 is an enlarged view of the main parts of the present invention.
b is a partial diagram for explanation. 7 is a wire electrode, 14 is a workpiece, 18 is a machining liquid, 25 and 26 are energizing pins, 27 is a switch, 2
9 is a pulse power supply, 36 is a contact, 40 is an exciting current,
41 is a switch, 44 is a brush.

Claims (1)

[Claims] 1. While a wire electrode is renewedly moved in the axial direction between a pair of positioning guides arranged at a predetermined interval, a workpiece is moved a minute distance from a direction perpendicular to the axial direction of the electrode. A voltage pulse supplied from a pulse power source is applied between the workpiece and the wire electrode with a machining fluid interposed therebetween to generate a pulse discharge, and the wire electrode and the workpiece In a wire-cut electrical discharge machine that provides a relative machining feed on the perpendicular plane between the workpiece and the workpiece, wires are connected to each side of the workpiece as a power supply connection between the pulse power source and the wire electrode. a pair of power supply means connected to the electrodes to supply power; a connection means connectable so that power can be supplied from the pair of power supply means simultaneously or from either one; A pair of energizing means each having a contact point that can be brought into contact with the electrode under pressure and rotatable around the electrode axis, and each of the energizing means can be moved to the left and right from the front in the direction of machining. A drive device that rotates and moves at the same time by a predetermined angle in substantially synchronization; and an excitation power source that is connected across the pair of current supply means and that supplies an excitation current in a predetermined direction to a portion of the workpiece between the pair of contacts. The excitation current flowing through the workpiece can flow through the workpiece when the discharge current due to the pulse discharge flows through the wire electrode, and the direction of the excitation current flowing through the workpiece switching means for the connection means for switching the power supply connection from the pulse power source to the pair of power supply means to select one of the power supply means so as to match the direction of the discharge current flowing through the wire electrode; and the excitation. A wire-cut electrical discharge machining apparatus characterized in that it is provided with both or either one of polarity switching means for switching the polarity of conduction from a power source to the contacts of the pair of current-carrying means. 2. The wire cut electric discharge machining according to claim 1, wherein the excitation power source is a DC power source, and is connected to the pair of energizing means via a polarity switching means that can be switched and controlled. Device. 3. The method according to claim 1, wherein the negative output terminal of the processing pulse power source is configured to be switched and connected to one of the pair of power supply means via a power supply switching means. Wire cut electrical discharge machining equipment. 4. A conventional wire cut electric discharge machining is performed by applying a voltage pulse between the wire electrode and the workpiece while the excitation current from the excitation power supply is supplied to and flowing through the workpiece. A wire cut electric discharge machining apparatus according to claim 1. 5. The excitation current in the workpiece by the excitation power source is supplied and distributed in synchronization with voltage pulses repeatedly applied between the wire electrode and the workpiece. 1
The wire cut electric discharge machining apparatus described in 2. 6. The excitation power source is a DC power source and is connected to the pair of energizing means via a polarity switching means that can be switched and controlled, and the direction of the excitation current flowing through the workpiece is set during wire cut electrical discharge machining. 2. The wire-cut electric discharge machining apparatus according to claim 1, characterized in that the polarity can be switched at a predetermined cycle by switching control of a polarity switching means. 7. The wire-cut electric discharge machining apparatus according to claim 1, wherein the excitation power source is a pulse power source that alternately outputs positive and negative electrode pulses.