JP3231567B2 - Wire electric discharge machining method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wire electric discharge machining method,
In particular, finishing from the rough machining (first cut machining) by wire electric discharge machining to the desired finishing machining, and with excellent machined surface roughness (smaller machined surface roughness), or even with the specified dimensions and shape accuracy The present invention relates to a machining method capable of performing the machining method, a machining feed servo control method suitable for carrying out the machining method, and a switching use thereof.

[0002]

In order to improve the machining efficiency of a series of wire electric discharge machining operations from rough machining to finishing machining, the present inventors have, as a power source for finishing machining in particular, a specific high-frequency AC as described later. For the finishing work after roughing (first cut processing) using a voltage source, the second cut processing, or the second cut and third cut processing, to obtain the dimensional and shape accuracy of the workpiece and improve the predetermined surface roughness In the machining of a desired plurality of stages, the machining feed servo control method is a so-called zero method servo control in which the feed speed is zero and the feed direction is reversed when the deviation of the discharge gap voltage with respect to the servo reference voltage is zero in the first cut machining process. On the other hand, in the machining process including the finish machining after the second cut machining process, the feed rate is set to the electric discharge machining gap voltage. In the deceleration servo control method, when the voltage deviation of the discharge gap with respect to the servo reference voltage is zero, the machining feed rate is set to an experimental value that matches the machining speed according to the set machining conditions (mainly conditions such as machining voltage or discharge pulse). It is proposed in the following patent application to perform processing by switching selection. [Application Date] March 23, 1994 [Application Number] 1994 Patent Application No. 92828 [Title of Invention] Wire electric discharge machining method and power supply circuit for wire electric discharge machining

[0003]

However, after the above invention,
Although the setting and adjustment of the power supply and the servo feed and the processing method have been repeatedly improved, the second cut after the first cut processing step adopts the deceleration servo control method described in detail later as the control method of the processing feed. A machining step in which an intermittent voltage pulse with a pause time obtained by turning on and off a switch element of a DC power supply for obtaining the size / shape accuracy and processing surface roughness of the processing power is used as a processing power source; In the finishing or final finishing by high-frequency AC voltage source to achieve the desired shape accuracy and the finished surface roughness,
Even if the same deceleration servo control method is used as the processing feed servo control method, the processing conditions, especially the characteristics of the aqueous processing fluid, do not match if they change, and a predetermined shape is obtained until the processing step such as the second cut.・ Even if the dimensional accuracy and the roughness of the machined surface were obtained, the dimensional and shape accuracy was often impaired by the next finishing or final finishing.

In particular, in the above-mentioned aqueous machining fluid commonly used for the wire electric discharge machining, for example, a change in water quality (particularly, specific resistance value or conductivity) due to the life of the ion exchange resin or the like, and a machining fluid in a machining gap portion. When a partial change in the concentration of machining chips due to irregular flow or the like acts as a partial change in the specific resistance of the machining fluid in the machining gap, the no-load voltage in the discharge gap due to the output of the machining power supply, that is, the high-frequency AC voltage source. And the detected servo data or signal from the detection circuit connected to the discharge gap deviates from the data or signal corresponding to the set experimental value. There is a disadvantage that shape accuracy is greatly impaired.

For example, when the specific resistance value of the machining fluid changes below a predetermined value at the time of finishing with the high-frequency AC voltage source, the voltage of the discharge gap apparently decreases. As the servo control method, the above-mentioned feed rate used in the semi-finishing processing for obtaining the dimensional and shape accuracy such as the second cut processing in the previous stage is proportional to the discharge gap voltage, and the voltage deviation of the discharge gap with respect to the servo reference voltage is zero. When using the deceleration servo control method in which the processing feed speed of the experimental value almost matches the processing speed according to the set processing conditions is used as it is, the processing feed speed decreases extremely, while the processing amount (processing speed Or the processing power of the processing power supply) does not decrease so much,
In punch punching, the dimensions and shape are smaller than specified values,
Conversely, the size and shape of the hole of the die are processed to be larger than a predetermined value, resulting in a result that the desired finish is not obtained.

[0006] Instead of the deceleration servo control method in the second cut processing step in the above case, a conventional constant speed servo control method which has been conventionally used in finishing processing (corresponding to the set processing conditions in the case of the above deceleration servo control method). As a constant feed rate of the processing feed rate of the experimental value, the gap voltage is less than or equal to a predetermined value sufficiently lower than the servo voltage, or with a gap short circuit,
When the servo control method that performs the retraction operation of the short circuit or the gap recovery) is adopted, the machining feed rate is constant,
Since the ratio of the discharge energy supplied by the high-frequency AC voltage source supplied to the discharge gap to be diverted to a portion other than the discharge portion of the discharge gap is large, the machining amount is too small, and the size and shape of the punch cutout have a predetermined value. In the case of die processing, on the contrary, the size and shape of the hole in the die are processed to be smaller than a predetermined value, so that a desired finish cannot be obtained.

Accordingly, the present invention provides a method of fabricating an object which is capable of accepting a certain degree of property change such as a specific resistance of a machining fluid during finishing or final finishing with a high-frequency AC voltage source. It is an object of the present invention to develop a servo control method capable of achieving a finished machining, and to provide a series of wire electric discharge machining methods for switching to the developed servo control method at the time of finishing processing using a high-frequency AC voltage source.

[0008]

Means for Solving the Problems A wire electrode stretched in a predetermined state between a pair of spaced guides is renewed and moved in the axial direction while moving the workpiece from a direction substantially perpendicular to the axial direction. Work is performed by a discharge pulse generated by applying an intermittent voltage pulse between the two in a state in which a machining liquid is interposed between the wire electrode and the workpiece while the machining liquid supply is interposed between the wire electrodes and the workpiece, and In wire electric discharge machining for providing relative machining feed along a predetermined contour to be formed on a plane in a perpendicular direction, the wire electric discharge machining is connected in series to a DC voltage source as (a) the voltage pulse. Using intermittent voltage pulses with pauses obtained by turning on and off the switched electronic switch elements, the working fluid to be used, the electrodes, the material combination of the workpiece, the plate thickness, and the processing Under the machining conditions set according to the purpose and the like, and the servo control method of the machining feed, the feed rate is proportional to the discharge gap voltage, and the feed rate becomes zero when the gap voltage deviation with respect to the set servo reference voltage is zero. A first-cut machining step of first machining and forming the contour-shaped machining groove as a zero-method servo control method in which a feed direction is reversed; and (b) after the first-cut machining, the set machining conditions are second-cut and third-cut. Etc. 1
Or, while sequentially switching to the machining conditions of a plurality of machining steps, the servo control method of the machining feed is set so that the feed rate is proportional to the discharge gap voltage, and the voltage deviation of the discharge gap with respect to the set servo reference voltage is zero. A semi-finishing processing step of switching to a deceleration servo control method in which a feed rate corresponding to the machining speed is set and performing processing of obtaining predetermined dimensions and shape accuracy and surface roughness; and (c) the voltage after the semi-finishing processing. A pulse is switched from a current pulse by a high-frequency coupling transformer inserted between the voltage pulse supply source and the discharge gap to a high-frequency AC voltage source under predetermined processing conditions obtained by AC voltage conversion, and the servo control method is the deceleration servo control method. And the proportional gain of the servo control is switched to a lower value than the proportional gain at the time of the above-mentioned semi-finishing, and the predetermined dimension and shape accuracy are And a finish machining step for performing surface roughness processing are sequentially performed by a series of wire electric discharge machining methods. (2) In the machining method according to the above (1), An intermittent voltage pulse source having a pause time obtained by turning on and off a DC power supply by a switch element in a cutting process and a semi-finishing process forms a voltage pulse by turning a DC voltage source on and off by a switch element. A normal type voltage pulse supply circuit in which a predetermined current limiting resistor is inserted in a series circuit, and a current limiting resistor is inserted in a series circuit in which a DC voltage source forms a current pulse by turning on / off a switching element. And a non-resistive current pulse supply circuit in which no current limiting resistor other than a small resistor for current detection or the like is inserted. The switch element is a discharge machining method using a voltage pulse source that is turned on for a predetermined time width by detecting that discharge is started by a discharge gap applied voltage pulse of the normal type voltage pulse supply circuit, and (3) In the processing method according to (2), a high-frequency AC voltage is output and supplied from the secondary winding of the high-frequency coupling transformer to the discharge gap in the finishing step. For this purpose, a high-frequency AC voltage source that is switched and controlled so that an intermittent current pulse having a pause time supplied to the primary winding of the transformer is supplied from the resistance-less current pulse supply circuit is used. By using the electric discharge machining method, it is possible to achieve better.

[0009]

Since the wire electric discharge machining method of the present invention is carried out by the above-described configuration and method, it is not necessary to use a high-frequency AC voltage source as a power source for machining, such as a machining process to obtain a roughened surface. The reproducible state can be surely achieved without being affected by the property change of the working fluid such as the specific resistance, that is, without impairing the dimension and shape accuracy.

[0010]

1 and 2 are explanatory views of the overall structure of an apparatus for carrying out the machining method of the present invention. FIG. 1 mainly shows a servo control circuit for machining feed, and FIG. 1 mainly shows a processing power supply circuit, and 1 is a wire electrode that can be axially updated and fed while a predetermined tension is applied between a pair of positioning guides 2A and 2B arranged at a distance. Is a workpiece mounted on a work stand 4 mounted on an xy cross table (not shown) and opposed to each other via a minute discharge gap from a direction substantially perpendicular to the axial direction of the wire electrode. Machining is performed by generating an electric discharge by a machining voltage such as an intermittent voltage pulse applied between the two under the supply intervention. Then, the first cut processing step (first processing step) of the rough processing and the semi-finishing (second processing) including at least the second cut for obtaining the dimensional accuracy are performed.
A) The machining voltage for machining in the machining process, that is, the intermittent voltage pulse, is supplied from the voltage pulse source 5 for wire electric discharge machining in the illustrated embodiment to the coaxial or shield wire as the power supply connection lines 11A and 11B. Switching switch 14 for switching between a voltage pulse source 5 and a high-frequency AC voltage source 30 to be described later.
Or further, to the lead wire near the discharge gap, the wire is supplied between the wire electrode 1 and the workpiece 3 preferably by using a twisted wire.

A plurality of voltage pulse sources 5 are connected in parallel with a DC voltage source 6A according to the current capacity.
The most usual conventional intermittent voltage pulse generation / supply circuit 6 comprising a series circuit of an electronic switch element 6B such as a T transistor, a current limiting resistor 6C, and a reverse voltage prevention rectifier 6D is arranged in parallel with the discharge gap. Power supply connection line 11A,
11B, the intermittent voltage pulse is generated as desired by the control of the switch element 6B by the pulse control device 7. That is, the control device portion of the switch device 6B of the control device 7 includes a predetermined ON time signal τ _ON and OFF which is selected and set in advance, except when the switch device 6B is changed and controlled by the discharge state detection signal of the discharge gap. The time signal τ _OFF is regularly and alternately repeated to control the supply of the voltage pulse, and the ON time signal of the switching element 6B is applied to the discharge gap from the start of application of the voltage pulse to the start of discharge in the discharge gap. The measurement of the on-time signal is started from the start of the discharge in the discharge gap after the start of the application of the voltage pulse so that the discharge duration increases as a function of the discharge start delay period, that is, the discharge duration of each discharge pulse is set to a fixed value, and the measurement is started. There is a control for turning off the switch element 6B upon completion and shifting to the off time. In the following description, mainly the latter case will be described. Obtain, but the present invention is not construed as being limited thereto.

The voltage pulse source 5 includes, in addition to a machining voltage pulse supply circuit 6 for turning on and off the switch element 6B, a discharge current amplitude Ip of a discharge pulse from the circuit 6
And a pulse current amplification circuit or current pulse supply circuit 8 for further increasing the processing speed by increasing the processing average current, comprises a variable DC voltage source 8A, a switch element 8B, and a reverse voltage prevention rectifier 8C. And is provided in parallel with the circuit 6. The current pulse supply circuit 8 outputs a steep rising high current when the control device 7 turns on the switch element 8B so that a so-called resistance-free circuit having no so-called current limiting resistor in the series circuit or the switch element 8B. A circuit 8 in which a current limiting resistor is not inserted in addition to a minute detection resistor for operating a current controller 7A of a switch element 8B provided in a control device 7 for preventing damage, In the wire electric discharge machining, the on-time signal of 6B or the on-time signal from the start of the discharge is within several tens μS at most, and usually several μS.
Since it is within S, even if the switch element 8B is turned on during the on-time signal that operates by detecting the start of discharge in the gap by the voltage pulse applied by the circuit 6, even if the switch element 8B or at least the circuit 8 is saturated. Although the circuit 8 may not be damaged even if the current limiting resistor is not provided in the circuit 8 due to the transition time to the region operation or the like, the operation region of the switch element 8B is referred to as an unsaturated region or at least the circuit 8. Is set such that the range in which the current is sufficiently smaller than the saturation current value of the switching element 8B (usually a fraction) is the operating region, there is no problem of damage to the switching element 8B and the switching element 8B This is preferable because the current off-off characteristic of the circuit 8 becomes sharp and steep.

The above-mentioned current pulse supply circuit 8 serves as the voltage pulse source 5 together with the voltage pulse supply circuit 6 as the workpiece 3
Semi-finishing of one or more processing steps such as rough processing for forming a processing groove first, that is, a first cut processing step, and a second cut processing step for performing processing for obtaining dimensional and shape precision of the processing after the first cut processing step An intermittent voltage pulse is used as a processing voltage until the processing step, that is, up to the first and second processing steps, and the gate input is connected to the control device 7 by the changeover switch 8E. The control related to the circuit 6 is performed, but after the completion of the semi-finishing processing step, one or more times of finishing of a processing surface roughness processing using a high-frequency AC voltage as a third processing step When moving to the machining process,
The voltage pulse supply circuit 6 is separated by an open / close switch 49 if necessary, and the changeover switch 8E is switched to the high-frequency intermittent pulse gate signal circuit 8D side so that the current pulse supply circuit 8 functions as a high-frequency current pulse generation circuit. It is.

A predetermined dimension comprising a first cut processing step using the above-described voltage pulse source 5 as a processing power source and one or more processing steps such as a second cut and a third cut after the first cut processing. When executing the machining step of the semi-finishing processing for obtaining the shape accuracy and the surface roughness, all the changeover switches 8E, 1 in FIG. 1 and FIG.
The circuits 4, 48, and 49 are operated in the connection state opposite to that shown in the figure, and the circuits 31 to 37 that detect and supply the discharge state of the discharge gap to the servo feed control circuit for machining operate.

That is, 31 is a voltage dividing circuit for detecting a discharge gap voltage, 32 is an inverting amplifying circuit comprising an operational amplifier for amplifying the detected divided voltage by half-wave or full-wave as required, and 33 is rectifying and integrating the amplified voltage. An integrating circuit, 34 is an inverting amplifying circuit for an integrated voltage, a gain adjusting circuit for adjusting a servo gain (gain) by adjusting a variable resistor 34A, 35 is a sample-hold amplifier for an amplified voltage whose gain has been adjusted, and 36 is a sample-hold amplifier. A / D to convert amplified voltage to digital signal
A converter 37 is an input / output circuit of the converted digital signal to the NC device at the next stage, and a photocoupler for circuit insulation composed of a light emitting element and a light receiving element, and 38 is a 4-axis or 3-axis having two or more axes simultaneously Is an NC controller for electric discharge machining or a control device incorporating a microcomputer or the like capable of controlling the motor, 39 is a motor driver, and 40 is a servo motor for XY 2-axis, Z-axis, or further UV 2-axis for taper machining.

[0016] Thus, the above-mentioned finishing processing, the first rough processing or first cut processing leading to the finishing processing, the second cutting processing of the next stage, or the third finishing processing, etc. There are various types of discharge state detection circuits or detection adjustment circuits in the discharge gap of the servo feed control for machining in the above-mentioned example, and one example thereof has a configuration as shown in FIG. The detected discharge gap voltage is supplied from the voltage dividing circuit 31 to the A / D conversion circuit 3.
Up to 6, it is converted into a digital signal according to the desired gain,
A desired setting voltage or a servo reference voltage input by an operator according to the purpose of processing and the like is sent to the NC device in the control device 38 by the input setting means 38A, where the desired setting voltage or servo reference voltage is sent to the control device 38 via the photocoupler 37 and calculated. Normally, a zero method servo control system in which the deviation is zero in the first cut processing step, the feed speed is zero, and the feed direction is reversed in the first cut processing step, and the zero deviation servo processing method is set in the semi-finishing processing step. A drive control signal is supplied to the driver 39 of the servomotor 40 by switching so as to be each processing feed of a predetermined deceleration servo servo control method in which a feed rate according to the processing speed of the processing condition is set.

In the finishing processing using such a high-frequency AC voltage source, a high-frequency coupling transformer 13 provided between the high-frequency current pulse supply circuit 8 and the discharge gap, and a semi-finishing processing step for obtaining the dimensional and shape accuracy are performed. A high-frequency AC voltage source 30 constituted by a circuit device 12 housed in a box-shaped box comprising
Are used and switched as described below. The high-frequency coupling transformer 13 includes one intermittent high-frequency current pulse output from the high-frequency current pulse supply circuit 8,
One is converted into one cycle of high-frequency AC voltage,
High permeability ring core 1 made of high frequency ferrite etc.
3A, the primary winding 13B and the secondary winding 13C have a turn ratio of 1: 1 to 3, preferably 1: 1 to 2, and the number of turns is 1 to 5 turns of the primary winding, preferably 1 to 3. 2 turns, secondary winding 1
For the purpose of obtaining a high-frequency AC voltage for finishing processing, which has a small number of turns for enabling high-frequency response such as 12 turns, preferably 1 to 4 turns, and is rather high in voltage and small in current, the primary winding The secondary winding is wound so that the number of turns of the secondary winding is equal to or greater than that of the wire.

Next, the output of the high-frequency current pulse supply circuit 8, the connection between the power supply connection lines 11A and 11B between the discharge gap formed by the wire electrode 1 and the workpiece 3, and the circuit device 12 are switched. Explaining this, an open / close switch that connects / disconnects the primary winding 13B to / from the output of the high-frequency current pulse supply circuit 8 and an open / close switch that connects / disconnects the secondary winding 13C to / from the discharge gap are output from the high-frequency current pulse supply circuit 8. The power supply circuit on / off switches 14A and 14B provided in the circuit portions of the power supply connection lines 11A and 11B connected between the wire electrode 1 and the workpiece 3 at both ends and the discharge gap, respectively, and the input ends of the primary winding are connected to each other. The primary winding on / off switch 1 inserted in one or both connection circuits during connection to both of its output lines on the high frequency current pulse generation circuit 8 side of the power supply circuit on / off switches 14A and 14B C, and both ends of the output of the secondary winding are connected to one or both of the connection circuits during connection to both the wire electrode 1 and the workpiece 3 on the discharge gap side of the power supply circuit on / off switches 14A and 14B. And a secondary winding on / off switch 14D.
4A, 14B, primary and secondary winding on / off switch 1
4C and 14D are the former open / close switches 14A and 14B
Is turned on, the latter on / off switches 14C and 14D are opened and closed in opposite directions so as to be turned off, and the power supply circuit on / off switches 14A and 14B are off and the primary and When the secondary winding on / off switches 14C and 14D are turned on, a power supply circuit for finishing by the high-frequency AC voltage, which is an object of the present invention, is formed. It should be noted that the drawing shows a case in which one open / close switch is provided for each of the primary winding and the secondary winding, and a case where the number of changeover switches provided is the smallest. It goes without saying that various switching circuit configurations can be achieved depending on the number of switches.

FIG. 3 shows the processing power supply circuit of FIG. 2 as the above-mentioned power supply circuit for finishing processing, that is, the open / close switch 49 is turned off, the gate signal circuit 8D is turned on by the changeover switch 8E, and the high-frequency current pulse supply circuit 8 is turned on. The timing chart when the power supply circuit on / off switches 14A and 14B are turned off and the transformer primary and secondary winding on / off switches 14C and 14D are respectively turned on is shown as an almost ideal waveform for two cycles. A is a high-frequency gate signal output from the intermittent pulse gate signal circuit 8D to turn on / off the switch element 8B; b is output from the high-frequency current pulse supply circuit 8 based on the gate signal; The current pulse c supplied to the primary winding 13B is induced in the secondary winding 13C based on the pulse current and is generated in the discharge gap. Discharge gap voltage waveform when the discharge occurs in the discharge gap based on the high-frequency AC voltage and said high-frequency AC voltage applying to be pressurized, d is an example of the discharge current of the discharge gap. Then, the waveform shaping of the generated high-frequency AC voltage by the combination of the current pulse supply circuit 8 and the coupling transformer 13 (usually, a sharp and smooth sinusoidal waveform, or A
It is effective to insert a desired inductance in series with the secondary winding 13C and the discharge circuit in the discharge gap in order to form a continuous wave of T _OFF = 0). Are connected in series, a magnetic core having high magnetic permeability may be provided so as to surround the wire electrode 1 in the electrode 1 or the guides 2A and 2B.

In the finishing processing of the present invention, the gate signal of the intermittent pulse output from the gate signal circuit 8D is T _ON = 100 ns and T _OFF = 1.0 in the drawing.
In μS, T _{ON is} about 50 nS to about 1000 nS or less, on the order of μS, and T _OFF is about 500 nS to 10 μs or about several tens of μS, and it is preferable that AT _OFF ≧ 0 as long as the AC voltage of c is mutually connected. The condition is set so that Further, the output current pulse waveform b of the high-frequency current pulse generation circuit 10 has a switch element 8B or at least a current of the circuit 8
It is shown that the gate signal a is turned off before the saturation region operation state in which the rising current is sufficiently smaller than the saturation current value of B and the switching element 8B or the circuit 8 is cut off at high speed.

According to a recent test, the high-frequency AC voltage of the secondary winding 13C shown in FIG.
Ferrite toroidal core such as high permeability Mn-Zn ferrite or Ni-Zn ferrite having an inner diameter of about 30 mmφ (for example, PC50 [or PC30] T40 manufactured by TDK)
× 16 × 24) on the core 13A which is a double product of about 3.
A 5 mm ² Teflon-based resin-coated conductor is connected to the primary winding 13 </ ^b > B:
When one turn and the secondary winding 13C are set to two turns, the output of the DC voltage source 8A is about 60V and the output is about 150 to 17
0 V, the output of the voltage source 8A is about 25 V,
At 65 V, a suitably high-frequency high-frequency AC voltage that can be applied to the finishing process for improving the above-described machined surface roughness can be obtained, and a discharge occurs in the first half wave of one cycle of the AC voltage as shown in a discharge current waveform d. Then, in the next half-wave of the opposite polarity, electric discharge occurs continuously. However, the finish machining can be advanced with an average machining current smaller than about 1 A.

By the way, in finishing with such a high-frequency AC voltage source, the value of the discharge gap and the floating capacitance of the structure around the discharge gap and the power supply circuit portion for machining is determined by the purpose of the finishing. If the discharge is not made correspondingly small, a discharge of a high discharge peak current due to the charging and discharging of the floating capacity will be mixed, and if the discharge of the high peak is mixed, the processed surface will be roughened, and the target processed surface roughness (about 3. 5-1 μmRma
x or more). Also, as described above, if the stray capacitance is not sufficiently small, the applied high-frequency AC voltage is attenuated, otherwise the processing efficiency is poor or the processing efficiency is easily reduced significantly. The processing efficiency of the finishing processing for improving the surface roughness is reduced.

For this reason, the finishing circuit provided with the discharge state detecting circuits 31 to 37 of the servo feed control of the conventional example shown in FIG. 1 employs a discharge gap between the electrode and the workpiece and its surroundings.
Even if the stray capacitance of the high-frequency AC voltage source 30 and the power supply circuit from the voltage source 30 to the discharge gap can be reduced as desired by devising, etc., the discharge gap has servo control for machining feed. As a discharge state detecting circuit for use, an electronic circuit in a box of a normal power supply unit from the voltage dividing circuit 31 to the A / D conversion circuit 36 is connected, and not only the electronic circuit but also its circuit configuration and structure are used. Approximately 10
The detection circuit portion has a stray capacitance of about 0 to 1000 PF, and the stray capacitance of the detection circuit portion corresponds to the high-frequency AC voltage source 30 described above.
This is an obstacle to the finish processing for improving the roughness of the machined surface.

Therefore, when finishing with the high-frequency AC voltage source 30 described above, it is essential to reduce the stray capacitance of the machining circuit portion as much as possible. The source 5 or the voltage pulse supply circuit 6 needs to be separated by an open / close switch 49, and the discharge state detection circuits 31 to 37 of the discharge gap 9, which are used as signals for controlling a machining power supply and controlling servo feed of machining, It is necessary to switch to the discharge state detection circuits 41 to 47 having a small capacitance by using the open / close switch 48. FIG. 1 illustrates an example of the discharge state detection circuits 41 to 47. Reference numeral 41 denotes a light emitting element 41 such as various light emitting diodes.
A and a photosensor, a photocoupler, or a photoelectric conversion element including a light-receiving element 41B such as a photoconductive element, a photodiode, or a phototransistor.
A and the light receiving element 41B are electrically insulated, and the light emitting element 41A is connected in series with a resistor 41C such as a non-inductive resistor and is directly connected to a discharge gap, of course, via a lead wire or the like. Connected to. 43A is an integrating circuit for the output of the photocoupler 41, 42 is an inverting amplifier circuit, 44 is a gain adjusting circuit for further inverting and amplifying and adjusting the servo gain by adjusting the variable resistor 44A, 43B is an integrating circuit, and 45 is a sample and hold amplifier. The circuit, 46 is an A / D converter, and 47 is an input / output circuit. Although there is a slight difference in configuration between the circuits 43A to 47 and the conventional detection circuits 32 to 37 described above, they are substantially the same. The detected and adjusted digital signal is input to a control device 38 having an NC control device and the like, is subjected to predetermined processing such as an input setting signal of an input means 38A, and is subjected to a drive control signal to a driver 39 of a servo motor 40. Control signal 38B for controlling processing conditions such as processing power supply and pulse conditions or supply conditions of the processing liquid supply device in accordance with the detection signal, if necessary. To output.

In the drawing, an element 41D connected in parallel to the light emitting element 41A is a rectifying element,
When A is a light-emitting diode, a similar light-emitting diode may be used. In order to protect the light-emitting element 41A against withstand voltage against reverse voltage and to use a high-frequency AC voltage source as a processing power supply, This is because the light emission characteristics are kept good in the same manner as the positive and negative voltage drops.

According to the above configuration, only the high-frequency AC voltage source 30 as a power source for finishing is connected to the discharge gap formed by the electrode 1 and the workpiece 3 during finishing. A voltage pulse source 5 for intermittently supplying a voltage pulse with an idle time by controlling on / off of a normal type electronic switch element used up to a stage such as a semi-finishing process before the finishing process is mechanically opened and closed. Only a discharge state detection circuit having a small capacitance is connected by a mechanical open / close switch 48 to a discharge state detection circuit which is completely separated from the discharge gap by a switch 49 and which is usually provided with one or more plural circuits. Only the series circuit of the resistor 41C and the light emitting element 41A is connected in parallel to the discharge gap. This means that the floating capacitance due to the floating capacitance due to the network around the discharge gap and the discharge energy per discharge will not be greater than the predetermined value. Therefore, the processing surface is not roughened, and conversely, the stray capacitance is present, without saying that the high-frequency AC voltage or the finishing processing pulse is unexpectedly attenuated or the like, thereby lowering the processing efficiency, On the other hand, if the discharge state can be detected without increasing the stray capacitance and the feed of the finishing processing can be suitably or desirably controlled and processed, the drum characteristics of the processed surface of the workpiece 3 and the pre-processing step It is possible to carry out processing while controlling the variation of the processing shape due to the above, etc., and it is possible to carry out the desired surface roughness finish of about 3.5 to 1 μm Rmax. Should be.

In the conventional processing circuit of FIG.
When the discharge state detection circuits 31 to 37 are used, not only the processing efficiency is poor, but also the processing surface roughness cannot be 3.5 to 1 μmRmax or more due to the presence of the stray capacitance. Conventionally, in order to finish the surface roughness of about 3.5 to 1 μm Rmax or more, the discharge state detection circuits 31 to 37 are separated from the discharge gap by a mechanical switch or the like, and are set in the NC device of the control device 38. The machining is performed at a speed (normally, a feed speed corresponding to the machining speed according to the set machining conditions when the voltage deviation of the discharge gap with respect to the servo reference voltage to be set is zero). In the processing of the processing feed of the above, it was not possible to perform processing for controlling the drum characteristics and the variation in shape of the processed surface of the workpiece 3 as desired, which was a problem.

Therefore, the machining feed servo control method, which is the object of the present invention, and the dimensional / shape accuracy including one or more machining steps such as a first cut machining step and a second cut, and an improvement in the roughness of the machined surface. The machining feed servo control method for each processing step of the medium processing or the medium finishing processing step will be examined. First, the workpiece 3
This is the first cut (usually rough machining) machining step in which a machining groove with a desired contour shape is formed in the first step. However, since this is the largest machining amount in all machining steps, the machining surface roughness and dimensions /
It is desirable to increase the machining speed as much as possible within a range in which the shape accuracy can be corrected in the machining process after the next process. In such a machining servo control method, the feed speed is set to the discharge gap (average). A so-called zero-method servo control system in which the feed speed becomes zero and the feed direction is reversed when the deviation of the gap voltage from the set servo reference voltage is zero in proportion to the voltage is suitable.

FIG. 4 is an explanatory view of a characteristic curve of the embodiment of the zero-method servo control system.
m / min), the gap voltage (average processing voltage) V on the horizontal axis
_G (V) is taken, the set servo reference voltage SV under certain set processing conditions, and the maximum speed of forward and backward reversing feeds ±
As F _P, the gain characteristic shows a different A, B2 type of characteristic curve the magnitude of the difference between the gap voltage, curve A, but the feed rate as a whole and also B is proportional to the gap voltage, setting servo reference When the deviation of the gap voltage from the voltage SV is zero, the feed speed becomes zero, and the servo reference voltage SV
When the gap voltage is high, the feed direction is reversed so that forward feed is performed when the gap voltage is high, and conversely, reverse feed is performed when the gap voltage is low.

By the way, FIG. 5 is the machining speed on the vertical axis (machining feed rate per time) MS, the characteristic curve of the working speed to the average machining voltage in the horizontal axis took discharge gap voltage (average machining voltage) V _G view the The maximum machining speed when the gap voltage V _GO is equal to the predetermined set pause time τ _{OFF in the} discharge gap.
The discharge is started without any delay at the same time as the start of the application of the voltage pulse having the pulse width τ _ON , which is supplied with a delay, and the discharge according to the set processing pulse condition is performed one after another without any discharge. It is shown. According to the conventional setting method of processing conditions, the gap voltage is set to the voltage V _GO.
The lower region is a region where the gap is short-circuited, and this voltage V
_In the area before and after _GO , the gap is in an arc discharge state, and the servo reference voltage SV is set to a voltage value at which the gap length at which the voltage pulse supplied to the discharge gap averages, for example, about 70% is discharged is maintained. That is, the SV is set. Thus,
In order to increase the machining speed, the servo reference voltage SV is lowered to approach the voltage V _GO , and the discharge gap length is reduced to perform machining. However, the set servo reference voltage SV is close to the voltage V _GO . If you increase the servo gain in the settings,
Since the short circuit or hunting occurs easily unstable partly like too feed due to inertia, the zero method servo control feed rate becomes zero when the deviation zero discharge gap voltage (average machining voltage) V _G is to servo reference voltage SV The method is
This is compatible with the servo control method of the first cut processing step.

Next, in one or a plurality of processing steps such as second cut and third cut processing, the dimensional / shape precision is obtained, and in the middle processing or semi-finishing processing for improving the roughness of the processed surface,
Since it is a kind of chamfering for one of the processing surfaces formed by the first cut processing, the amount of processing is small and the electrical conditions set are different, but the same model used in the first cut processing step When a power supply for processing, that is, a power supply of an intermittent voltage pulse generation and supply method having a pause time is used, the processing energy and the processing capacity under the processing conditions set by the processing power supply with respect to the required processing amount of the second cut processing step. However, there is room for the processing speed.

In the meantime, the semi-finishing process such as the second cut process is not only a process for improving the surface roughness, but also a process for obtaining dimensional and shape accuracy including adjustment and correction of the drum amount. It is necessary to ensure a processing state in which the average voltage is always constant. In other words, the processing surface formed by the front and rear fart-cut processing steps partially has a random size and shape error, and therefore, the amount of processing at the processing portion of the processing path changes. However, in order to keep the average machining voltage (= discharge repetition frequency) constant even if the machining amount changes, it is necessary to have a servo control characteristic that can change the feed rate.

Therefore, in general, there is a margin in machining energy, and unless there is a margin, the machining feed speed does not become zero or the backward feed does not occur, and a certain speed (usually set at a predetermined value) is not obtained. In semi-finishing and finishing of surface processing, in which the processing proceeds while continuing to feed at a feed rate according to the processing speed of the electrical processing conditions, the feed rate is changed to the discharge gap voltage in place of the zero method servo control method as the servo control method. In order to improve machining accuracy, it is necessary to adopt a deceleration servo control method in which a feed rate corresponding to the machining feed rate of the set machining condition is set when the voltage deviation of the discharge gap voltage with respect to the set servo reference voltage is zero in proportion to the set servo reference voltage, As a characteristic of the servo control, the feed rate changes according to the machining amount,
It is desirable and necessary to operate so that the average machining voltage is constant.

FIG. 6 is an explanatory diagram showing deceleration servo characteristic curves C and E of certain characteristics and a characteristic curve diagram D for constant speed feed in a coordinate diagram similar to that of FIG. When the deviation of the gap voltage with respect to the voltage SV is zero, a processing speed corresponding to the set processing conditions at the time of semi-finishing or finishing processing to be processed and a feed speed FS corresponding to a processing amount in the processing are set, and the deceleration servo is performed. characteristic curves C and E of the control system in the working feeding characteristics rightward up through the intersection between the set feed speed FS this servo reference voltage SV, i.e. the feed rate is proportional to the gap voltage (average machining voltage) V _G, the The upward-sloping angle or the proportionality constant is a servo gain (or gain) that can be adjusted or selected and set. And in the case of the deceleration servo control system, feed rate machining feed is stopped becomes zero when the gap voltage is lower than a certain degree than the servo reference voltage SV, and further the gap short or advance reduces the gap voltage V _G feed direction reaches the backward voltage V _B that defines is one that retracts inverted. Then, in the semi-finishing step of one or more processing steps for improving the dimension and shape accuracy after the first cut processing step such as the second cut processing, and the improvement of the processing surface roughness, the servo control of the deceleration feed is performed. Even if the machining amount changes to a certain extent, it is necessary that the feed rate changes quickly and the average machining voltage must be constant, so that the angle of rising to the right is large and the proportional constant is large. By selectively setting the deceleration servo control characteristic curve C having a large gain characteristic and executing the semi-finishing processing, the size and shape accuracy of the workpiece can be quickly and reliably finished.

On the other hand, in the finishing process for obtaining a roughened surface mainly by using the high-frequency AC voltage source 30 after the above-mentioned semi-finishing processing as a power source for processing, the power source for processing comprising the high-frequency AC voltage source 30 is used. In general, there is not much margin in terms of machining energy and machining capacity, and it is set to just about the same. As described above, the machining voltage pulse circuit is separated so that the stray capacitance of the machining circuit portion is sufficiently small, and the discharge gap is set. It is not the length required to switch the state detection circuit, etc., but is affected greatly by the processing conditions, in particular, changes in gap conditions such as changes in the characteristics of the aqueous processing fluid. As described above, if the specific resistance of the machining fluid drops below a predetermined value due to malfunction of the machining fluid supply system, or a change in the resistance of the machining gap due to irregularity in the concentration of machining chips, as described above. ,
The voltage of the discharge gap to which the high-frequency AC voltage is applied apparently decreases, and therefore, as a servo control method for machining feed, a curve C suitable for the semi-finishing process such as the second cut described above is used.
When the deceleration servo control is adopted, the machining feed speed becomes too slow or stops, and the machining amount becomes excessive.For example, in punch punching, the machining surface roughness is almost finished, but the dimensions and shape are smaller than predetermined values. In many cases, the dimensional accuracy is impaired.

[0036]

[Table 1]

To further explain this point, Table 1 shows that the machining fluids having different specific resistance values are used, and the servo control method of the machining feed and the characteristics such as the gain thereof are suitable for the semi-finishing of FIG. Each processing of the deceleration servo control method C having a characteristic, the servo control method D having a constant speed which has been often used in the finishing processing, and the deceleration servo control method E having a gain characteristic adopted in the present invention described later. A dimensional error in which the finishing process is performed using the high-frequency AC voltage source 30 by the feeding method (each value is an error of 10% with respect to a predetermined dimensional value).
Point average). According to the processing data in Table 1,
In the case of the deceleration servo control method C, the dimensional error in machining due to the difference in the resistivity of the machining fluid as described above is large, and especially when the machining amount is excessive when the resistivity is lowered, the dimension is too large. In contrast, according to the constant speed servo control method of D, the dimensional accuracy is large although the tendency is generally similar, but the processing amount is too small when the specific resistance value decreases. As a result, the processing accuracy is considerably reduced.

The servo gain of the constant speed servo control method D is regarded as zero for the moment, and the servo gain of the deceleration servo control method C is set to a certain gap voltage with respect to the maximum dimensional difference of about 5 μm. a difference l ₁ feed speed when the, compared to the maximum size difference of about 24μm at that time, the ratio of the dimensional difference 5:24 =
Servo gain l of deceleration servo control method from 1: 5 to C
₁ (= 41 mm / min) about 1/5 servo gain l ₂
(= 8 mm / min), the machining was performed by setting the deceleration servo control method E, and as shown in Table 1, even if the specific resistance value of the machining fluid changed or decreased to some extent, the dimensions were reduced. High-precision machining has come to be performed with little change in accuracy. Incidentally, greater than often above or for the servo gain l ₂ of the deceleration servo control system of the E according to the experiments in which the ratio described above with reference to the constant rate of gain zero (l _1: l ₂ = 4: 1) was better for the processed data.

FIG. 7 is a partial view of an embodiment of a discharge state detecting circuit for executing the machining feed of the aforementioned deceleration servo control method. In FIG. 7, the changeover switches 48 and 49 in FIG. 30 and discharge detection circuits 41 to 47
And the servo control circuits 41 to 41 when the finishing process is performed on the semi-finished processing surface to obtain the surface roughness.
47 is an enlarged view of a gain adjustment circuit 44 for inverting amplification and servo gain adjustment in the volume variable resistor 4.
4A, resistors 44B-1 to 44B-n and switches 44C-1 to 44C for switching and selecting the resistors are provided to switch the degree of amplification so that a desired gain characteristic can be easily selected and set. Note that the plurality of voltage sources 44D-1 to 44-n and the selection changeover switches 44E-1 to 44E-n show an example in which the servo reference voltage data can be switched and set in the operational amplifier portion of the gain switching setting. .

FIG. 8 shows the servo control for executing the machining feed of the deceleration servo control method having the characteristic E described above in FIG.
FIG. 4 is an explanatory diagram of a block diagram configured to be performed by a control device 38 having an NC control device and the like therein. The control device 38 controls a zero-method servo control method used by selection setting in the above-described first cut processing step. A zero method / calculator 38C- which calculates a signal from the input servo reference voltage data 38A and the discharge gap data from the discharge state detection circuits 31 to 37 and outputs a control signal.
1. Similarly, in a semi-finishing step of one or more processing steps such as a second cut, etc., a high gain characteristic is obtained by calculating from the servo reference voltage data 38A and the discharge gap detection data by the discharge state detection circuits 31 to 37, or A deceleration servo calculator 38C-2 that outputs a control signal of a deceleration servo control method having a large gain, and servo reference voltage data 38A and discharge state detection circuits 41 to 4 in the finishing process.
And a deceleration servo computing unit 38C-3 which outputs a control signal of a deceleration servo control method having a low gain characteristic or a low servo gain by calculating from the discharge gap detection data obtained by the computation unit 7C. Reference numeral 3 denotes switching means 3 together with the open / close switches 8E, 14, 48, and 49 for each of the processing steps.
Switching is selected by 8D, and a predetermined control signal is output to the motor driver 39.

As described above, the electric discharge machining apparatus of the present invention has been described with reference to the illustrated embodiment. However, the present invention is not limited to the above-described embodiments, and various modifications may be made to each part without departing from the spirit of the present invention. In addition, it can be implemented. For example, in FIG. 2, in the case of a power supply circuit for wire electric discharge machining in which the current pulse supply circuit 8 is not provided, a resistance reduction circuit for short-circuiting the current limiting resistor 6D of the intermittent voltage pulse generation circuit 6 is provided. Alternatively, the gate signal circuit 8D may be switched and connected to the gate signal circuit of the switch element 6B. The gate signal circuit 8D can be provided not only as a part of the pulse control device 7 but also internally. Further, in the control device 7, the stored switching control data can be read out or the like to perform the switching operation by software,
Furthermore, in order to further increase the high-frequency AC voltage for finishing processing, for example, to 2 MHz, two sets of current pulse supply circuits 8 are provided in parallel, for example, each having τ _ON = 10.
At 0 ns, two sets of 1 MHz high frequency (current) pulse generating circuits of τ _OFF = 900 ns have a phase difference of about 180 ° (π), and one cycle of the high frequency AC voltage is about 50
It may be adjusted so as to be completed within 0 ns. Further, as the high-frequency AC voltage source, a normal, for example, transistor-inverter-type high-frequency AC voltage source is used, and this is connected to the discharge gap via a matching circuit. In the case where rough machining or medium machining is used by switching the machining power supply to the intermittent voltage pulse source 5 by switching with the open / close switch 49, the voltage pulse source may be used. In this case, the discharge state detection circuit is switched to the conventional detection circuits 31 to 37 by the open / close switch 48 as shown in the drawing, but the discharge state detection circuits 41 to 47 are used as they are. Alternatively, since the circuits 41 to 47 do not become an obstacle to processing such as roughing, the circuits 41 to 47 are kept connected as they are and the conventional detection circuit is not used. Even better this configuration change as a connection structure to run a 31 to 37 is capable at the respective portions of the present invention.

[0042]

Since the wire electric discharge machining method of the present invention has the above-described configuration, when finishing using a high-frequency AC voltage source as a machining power supply, a discharge state detection circuit such as a servo control is used together with the machining power supply. And the machining feed rate is proportional to the gap voltage detection signal by the detection circuit, and when the voltage deviation of the discharge gap with respect to the set servo reference voltage is zero, the feed rate corresponding to the machining speed of the set machining condition is set. The control method is used, and the proportional gain of the servo control is switched to a value lower than that of the semi-finishing processing step, so that the dimensions are not affected by changes in properties such as the specific resistance of the machining fluid.・ The finishing process to achieve the desired surface roughness can be performed reliably without impairing the shape accuracy.

[Brief description of the drawings]

FIG. 1 is an electric discharge machining circuit diagram of an embodiment mainly showing a discharge state detection circuit portion used in each machining step of the wire electric discharge machining method of the present invention.

FIG. 2 is an electric discharge machining circuit diagram of an embodiment mainly showing a power supply circuit portion for machining used in each machining step of the wire electric discharge machining method of the present invention.

FIG. 3 is a timing chart of a high-frequency AC voltage for processing when the circuit in FIG. 2 is operated as a power supply circuit for finishing processing.

FIG. 4 is a characteristic curve diagram for explaining servo control feed characteristics of a zero method method.

FIG. 5 is a characteristic curve diagram of a processing speed for explaining a servo reference voltage setting for zero method servo control.

FIG. 6 is a characteristic curve diagram for explaining characteristics of servo control feed of a deceleration servo control method.

FIG. 7 is a circuit partial view of an embodiment in which the switching setting of the servo gain in the deceleration servo control method is performed in the discharge state detection circuit portion.

FIG. 8 is a partial block diagram of an embodiment in which the switching setting of the servo gain of the deceleration servo control method is performed together with the switching setting of the servo control method.

[Description of sign]

 1, wire electrode, machining electrode 2A, 2B, positioning guide 3, workpiece 4, work stand 5, voltage pulse source for wire electric discharge machining 6, voltage pulse generation and supply circuit 6A, DC voltage source 6B, electronic switch Element 6C, current limiting resistor 6D, reverse voltage prevention rectifier 7, pulse control device 8, current pulse supply circuit 8A, variable DC voltage source 8B, electronic switch element 8C, reverse voltage prevention rectifier 8D, gate signal circuit 8E, changeover switch 11A , 11B, power supply connection line 12, circuit device 13, high-frequency coupling transformer 13A, ring core 13B, primary winding 13C, secondary winding 14A, 14B, 14C, 14D, on / off switch 30, finishing power supply 31, discharge gap Voltage detecting voltage dividing circuits 32 and 42, inverting amplifying circuits 33, 43A and 43B, integrating circuits 34 and 44, gain adjustment Circuits 35 and 45, sample and hold amplifiers 36 and 46, A / D converters 37, 41 and 47, photocouplers 38, control devices 38C-1 to 38C, servo calculators 38D, switching means 39, motor drivers 40, servo motors 41A, light emitting element 41B, light receiving element 41C, resistor 41D, rectifier 44B-1 to n, gain resistor 44C-1 to n, gain selection switch 44D-1 to n, servo reference data voltage source 44E-1 to n, reference data Changeover switch 48, 49, open / close switch

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B23H 7/06 B23H 7/02 B23H 1/02

Claims (3)

(57) [Claims] 1. A workpiece which is stretched in a predetermined state between a pair of guides spaced apart from each other and is reciprocated in an axial direction while moving the workpiece from a direction substantially perpendicular to the axial direction via a minute gap. In the state where a machining fluid is supplied and interposed between the gaps, machining is performed by applying an intermittent voltage pulse between the two to perform machining with a discharge pulse generated, and the wire electrode and the workpiece are cut in the perpendicular direction. In a wire electric discharge machining for providing a relative machining feed along a predetermined contour to be formed on a plane, (a) an electronic switch in which the wire electric discharge machining is connected in series to a DC voltage source as the voltage pulse. The intermittent voltage pulse having a pause time obtained by turning on and off the element is used to meet the machining fluid, electrode, material combination of workpiece, plate thickness, and the purpose of machining. The feed rate is proportional to the discharge gap voltage and the feed rate is zero when the gap voltage deviation from the set servo reference voltage is zero. A first cut processing step of first forming the processing groove having the contour line shape as a zero method servo control method, and (b) setting the processing conditions after the first cut processing to one or more of a second cut and a third cut. While sequentially switching to the machining conditions of a plurality of machining steps, machining of the machining control is performed when the feed rate is proportional to the discharge gap voltage and the voltage deviation of the discharge gap with respect to the set servo reference voltage is zero. Switching to the deceleration servo control method in which the feed rate is set according to the speed, while processing to obtain the specified dimensions, shape accuracy, and surface roughness A finishing processing step, and (c) after the intermediate finishing processing, a predetermined processing condition obtained by current pulse → AC voltage conversion by a high frequency coupling transformer inserted between the voltage pulse supply source and the discharge gap after the intermediate finishing processing. Switching to a high-frequency AC voltage source and selecting the servo control method as the deceleration servo control method, and switching the proportional gain of the servo control to be lower than the proportional gain at the time of the semi-finishing processing to obtain a predetermined dimensional / shape accuracy and A wire electric discharge machining method characterized by sequentially performing a finishing process step of performing surface roughness processing. 2. An intermittent voltage pulse source having a downtime obtained by turning on and off a DC power supply by a switch element in the first cut processing step and the semi-finishing processing step, and switches the DC voltage source to an on / off state of the switch element. A normal voltage pulse supply circuit in which a predetermined current limiting resistor is inserted in a series circuit that forms a voltage pulse when turned off,
No current limiting resistor is inserted in the DC voltage source in a series circuit that forms a current pulse by turning on / off the switching element, or no current limiting resistor other than a small resistor for current detection is inserted. A resistor current pulse supply circuit is juxtaposed, and the switch element of the current pulse supply circuit detects that discharge has started by the discharge gap application voltage pulse of the normal type voltage pulse supply circuit, and turns on for a predetermined time width. 2. The method according to claim 1, wherein the control is performed.
2. The wire electric discharge machining method according to 1. 3. An intermittent current pulse having a pause time supplied to a primary winding of the transformer to supply a high-frequency AC voltage from a secondary winding of the high-frequency coupling transformer to a discharge gap. 3. The wire electric discharge machining method according to claim 2, wherein the connection is switched and controlled so as to be supplied from a resistance-less current pulse supply circuit.