JP5307696B2 - Wire cut electric discharge machining method and wire cut electric discharge machining apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that a machining surface is formed into a curvature when a machining allowance is varied. <P>SOLUTION: A memory device 40 stores an initial proper average machining voltage V<SB>0</SB>and a proper machining speed F<SB>0</SB>in which an electro-static suction force CF<SB>0</SB>applied to a wire electrode EL in a direction perpendicular to a machining advancement direction X+ in a scheduled machining allowance d<SB>0</SB>and a discharge repulsion force EF<SB>0</SB>are balanced. An operation device 50 determines a proper average machining voltage V<SB>i</SB>and a proper machining speed F<SB>i</SB>in which the electro-static suction force CF<SB>i</SB>and the discharge repulsion force EF<SB>i</SB>are balanced in each machining allowance d<SB>i</SB>based on the initial proper average machining voltage V<SB>0</SB>and the proper machining speed F<SB>0</SB>. A servo-condition setting device 60 sets a servo-curve indicating variation of the machining speed relative to the average machining voltage to be relatively moved at the proper machining speed F<SB>i</SB>in each proper average machining voltage V<SB>i</SB>. During machining, an inter-polar voltage detection device 7 detects the average machining voltage of a machining clearance in each predetermined unit period, and a servo device 8 performs machining at the proper machining speed while responding to the average machining voltage according to a servo curve. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a wire cut electric discharge machining method and a wire cut electric discharge machining apparatus for suppressing the bending of a wire electrode. In particular, the present invention relates to a wire-cut electric discharge machining method and a wire-cut electric discharge machining apparatus for machining at a machining speed that reduces the bending of a wire electrode.

  Wire cut electric discharge machining is an electric discharge machining method in which a material is removed from a workpiece by electric discharge energy using a thin wire wire of less than 1 mm as a tool electrode. The wire electrode is disposed to face the workpiece with a predetermined processing gap. Then, by applying a voltage intermittently to the machining gap and repeatedly generating a discharge, the wire electrode is machined relative to the workpiece along a predetermined relative movement trajectory, thereby moving the workpiece to a desired level. Cut into a machined shape.

  When a voltage is applied to the machining gap, an electrostatic force is generated in the machining gap due to the capacitance. A thin and low-rigidity wire electrode is bent by being attracted in the direction of the processed surface of the workpiece by electrostatic force. Hereinafter, the force that attracts the wire electrode in the direction orthogonal to the processing progress direction is referred to as electrostatic attraction force. On the other hand, when a discharge occurs, a discharge impact force is generated in the discharge gap. The wire electrode is pushed and bent in a direction opposite to the direction of the processed surface by the discharge impact force. Hereinafter, the force that pushes the wire electrode in a direction orthogonal to the processing progress direction is referred to as a discharge repulsion force.

  A voltage is intermittently applied to the machining gap and repeated discharges are generated, so that the wire electrode is vibrated at a high frequency by repeatedly being attracted to the machining surface and being pushed out of the machining surface. It becomes a state. Since the discharge point varies, the behavior of the wire electrode due to vibration is complicated. However, since the wire electrode is supported by a pair of wire guides in a dotted manner and is stretched with a predetermined tension, it can be regarded as a state of vibrating in a drum shape when viewed macroscopically.

  During the first cut, which is a rough machining process that roughly removes material from the work piece and cuts it, the wire electrode vibrates in the machining groove width direction because the wire electrode is sandwiched between the machining grooves. It is suppressed to some extent. In the finishing process after the second cut in which the remaining margin left in the roughing process is removed, one side of the wire electrode is opened, and the vibration of the wire electrode is not suppressed. As a result, the bending of the wire electrode is transferred, and the processed surface is formed into a curved shape with an unacceptable size.

  Even if the machined surface is curved in the roughing process, it is possible to correct the machined surface in several shaping steps in the finishing process by leaving sufficient machining allowance. . However, in the chamfering process that reduces the machined surface roughness that is performed after the shaping process, a sufficient machining allowance that can eliminate the machining shape error due to the curvature formed in the shaping process remains. However, depending on the required machining shape accuracy, satisfactory machining results cannot be obtained.

  Since the electrostatic capacity depends on the average machining voltage, regardless of the magnitude of the discharge energy, when the electrostatic attraction force becomes larger than the discharge repulsive force, the machined surface is formed in an indented state. In contrast, when the electrostatic attraction force is reduced, the processed surface is formed in a state of swelling outward. For this reason, even if the discharge energy is reduced or the tension applied to the wire electrode is only increased, the vibration amplitude of the wire electrode can be suppressed to a small level, but the processed surface is prevented from being curved. Can not.

  In view of this, there has been considered a processing method for reducing the deflection of the wire electrode by balancing the electrostatic attractive force acting on the wire electrode and the discharge repulsive force in a predetermined unit period. The invention of Patent Document 1 is a servo system in which the machining gap is kept constant by relatively moving at a feed speed proportional to the average machining voltage or average machining current, and the change in the feed speed with the fluctuation of the average machining voltage or the average machining current. By changing the ratio of the voltage pulse application time to the voltage pulse non-application time correspondingly, the electrostatic attraction force and the discharge repulsion force are offset to maintain the balance between the electrostatic attraction force and the discharge repulsion force. I have to.

  The electric discharge machining apparatus disclosed in Patent Document 2 measures the no-load time by comparing the machining gap voltage with a reference voltage, and feed speed so that the no-load time becomes a predetermined optimum reference time. Is changed so that the electrostatic attraction force and the discharge repulsion force are balanced. Further, the invention of Patent Document 3 attempts a more accurate simulation of the vibration of the wire electrode due to the electrostatic attractive force and the discharge repulsive force. Patent Literature 3 calculates a machining feed amount at which a discharge gap becomes constant by estimating a no-load time from a discharge gap based on an analysis result of a simulation, and changes the feed speed in accordance with increase / decrease in the machining feed amount. A method is disclosed.

  Non-Patent Document 1 discloses a machining method in which an average machining voltage is varied by manipulating a discharge rest time that does not affect the discharge energy so that the electrostatic attractive force is balanced with the discharge repulsive force. Non-Patent Document 1 discloses that the servo reference voltage is changed so that the no-load voltage becomes constant when the pause time is manipulated because the no-load time fluctuates with the allowance without depending on the pause time. doing.

  The basic concept of the prior art is essentially the same in that a specific type of processing condition is initially set or changed so that the electrostatic attractive force and the discharge repulsive force are balanced. As long as the electrostatic attractive force and the discharge repulsive force are accurately analyzed, a specific type of machining that reduces the machining shape error due to the curvature formed on the work surface by balancing the electrostatic attractive force and the discharge repulsive force. Setting conditions is easy.

Japanese Patent No. 2722867 (paragraphs 0012-0025) Japanese Patent No. 3571293 (paragraphs 0032-0035) Japanese Patent No. 3875052 (paragraphs 0014-0015)

Journal of Electrical Machining, Vol.36, No.81 “Fundamental Study on Machining Accuracy of Wire Electrical Discharge Machining (6th Report)” Ohara Haruki et al. (Pp.15-23)

  By the way, the machining allowance in the finishing process is not always constant due to the swell remaining in the previous process. Assuming that the electrostatic force and the discharge impact force in a given unit period act on the entire surface of the wire electrode facing the workpiece, the region where the electrostatic force is generated differs depending on the size of the machining allowance and the direction in which the discharge impact force acts Different. Therefore, the electrostatic attraction force and the discharge repulsive force acting on the wire electrode in the direction orthogonal to the processing progress direction in the horizontal plane always fluctuate during processing.

  Therefore, the balance between electrostatic attraction force and discharge repulsive force is set by changing the initial processing conditions so that the electrostatic attraction force and discharge repulsion force calculated with the planned allowance according to the set offset value are balanced. However, the electrostatic attractive force and the discharge repulsive force that are recalculated by changing the machining allowance are not accurate, so the electrostatic attractive force and the discharge repulsive force are not balanced. As a result, although the size of the curvature formed on the machining surface is reduced, it is not sufficient for the machining surface to be flat, and further reduction of machining shape error due to the curvature is desired, and there is room for improvement. There is.

  In view of the above problems, the present invention substantially eliminates bending of the wire electrode by constantly balancing the electrostatic attraction force acting on the wire electrode and the discharge repulsion force in response to changes in the machining allowance during processing. An object of the present invention is to provide an improved wire-cut electric discharge machining method capable of forming a machined surface more flatly. The advantages of the wire cut electric discharge machining method of the present invention will be described in detail in the description of the embodiments.

  In order to solve the above problems, the wire-cut electric discharge machining method of the present invention has an appropriate average in which the electrostatic attractive force acting on the wire electrode and the electric discharge repulsive force are balanced in a direction orthogonal to the machining progress direction for each of the machining allowances. Obtain an appropriate machining speed that balances the electrostatic attraction force corresponding to the machining voltage and the appropriate average machining voltage and the discharge repulsion force, and performs machining at an appropriate machining speed in response to the average machining voltage detected every predetermined unit period. Like that.

  Specifically, the wire-cut electric discharge machining method of the present invention balances the electrostatic attraction force acting on the wire electrode and the electric discharge repulsion force in a direction orthogonal to the machining progress direction at the scheduled machining allowance under the set machining conditions. Calculate the electrostatic attraction force and the discharge repulsive force for each of multiple machining allowances based on the initial appropriate average machining voltage and the appropriate machining speed, and the initial appropriate average machining voltage and the appropriate machining speed. To obtain an appropriate average machining voltage that balances electrostatic attraction force and discharge repulsive force for each machining allowance, and an appropriate machining speed corresponding to the appropriate average machining voltage, and to move relative to each other at an appropriate machining speed. To set a servo curve representing the change in machining speed with respect to the average machining voltage, to detect the average machining voltage every predetermined unit period, and to respond appropriately to the average machining voltage detected according to the servo curve So that comprise the step of processing at a factory speed, the.

  The wire-cut electric discharge machining apparatus of the present invention includes an inter-electrode voltage detection device that detects an average machining voltage of a machining gap every predetermined unit period, and an average detected according to a predetermined servo curve that represents a change in machining speed with respect to the average machining voltage. Servo device that outputs a servo signal to process at an appropriate processing speed in response to the processing voltage, and electrostatic attraction acting on the wire electrode in the direction perpendicular to the processing progress direction at the scheduled machining allowance under the set processing conditions A storage device that stores an initial appropriate average machining voltage and an appropriate machining speed in which force and electric discharge repulsive force are balanced, and electrostatic attraction for each of a plurality of machining allowances based on the initial appropriate average machining voltage and the appropriate machining speed Calculation of the force and the discharge repulsive force to obtain the appropriate average machining voltage that balances the electrostatic attraction force and the discharge repulsive force for each machining allowance and the appropriate machining speed corresponding to the appropriate average machining voltage And device, so as comprising a servo condition setting device for setting the servo curve for relative movement at a reasonable processing rate for each proper average machining voltage.

  In servo systems where the machining speed is determined when the average machining voltage is given, when the machining conditions are constant, when the average machining voltage fluctuates and the machining speed increases or decreases, the fluctuation in the average machining voltage becomes a change in the machining allowance. It can be said that it is caused. Since the electrostatic attraction force and discharge repulsion force corresponding to the machining allowance can be calculated from the model, an appropriate average machining voltage and an appropriate machining speed at which the electrostatic attraction force and the discharge repulsion force balance each other are obtained. be able to.

  The present invention obtains an appropriate average machining voltage and an appropriate machining speed at which the electrostatic attraction force and the discharge repulsive force are balanced for a plurality of machining allowances, and the average machining voltage fluctuates corresponding to changes in machining allowances every predetermined unit period. , And at an appropriate machining speed that balances the electrostatic attraction force and the discharge repulsion force with respect to the detected average machining voltage, the electrostatic attraction force and the discharge always remain even if the machining allowance changes during machining. Balance with repulsion is maintained. As a result, the deflection of the wire electrode can be substantially eliminated stably, the processing surface is not formed in a curved shape, and the processing shape accuracy is further improved.

  In particular, during machining, a servo curve that represents the relationship between machining speed and average machining voltage is set so that it moves relative to the average machining voltage for each appropriate average machining voltage that balances electrostatic attraction force and discharge repulsion. In accordance with changes in machining allowance, machining can be performed at an appropriate machining speed that always balances the electrostatic attractive force and the discharge repulsive force. As a result, it is possible to perform machining with no bending of the wire electrode stably during machining simply by setting a servo curve, so that the machining shape accuracy is further improved and the burden on the operator is not increased. .

It is a block diagram which shows the wire cut electric discharge machining apparatus of this invention. It is a top view which shows typically an electrostatic force and an electrostatic attraction force. It is another top view which shows an electrostatic force and an electrostatic attraction force typically. It is a top view which shows typically a discharge impact force and a discharge repulsion force. It is a graph which shows an example of the servo characteristic of the servo apparatus applied to this invention.

  FIG. 1 shows a typical configuration of a wire cut electric discharge machining apparatus according to the present invention as a preferred embodiment. However, components that are not necessary for explaining the present invention are not shown. In the following description, a computer numerical control device and a motor control device may be referred to as a control device. Further, the machining power supply device includes a machining control device and an electric discharge machining circuit.

  As shown in FIG. 1, the wire cut electric discharge machining apparatus of the present invention includes a computer numerical control device 1, a motor control device 2, a moving device 3, a position detection device 4, a machining condition setting device 5, and a machining. A power supply device 6, an interelectrode voltage detection device 7, and a servo device 8 are provided. The computer control device 1 includes an input device 10, a decoding device 20, a command device 30, a storage device 40, an arithmetic device 50, and a servo condition setting device 60.

  The computer numerical control device 1 outputs at least movement command data and machining condition data. The motor control device 2 outputs a control current based on the movement command data to the plurality of movement devices 3 in the control axis direction. The moving device 3 includes a plurality of moving bodies in the control axis direction and a servo motor that moves each moving body. The moving device 3 moves each moving body to move the wire electrode relative to the workpiece along a predetermined relative movement locus defined in the NC program. The position detection device 4 detects the position of the moving body and outputs current position data to the motor control device 2. The motor control device 2 controls the positioning of the moving device 3 according to the current position data.

  The machining condition setting device 5 sets machining conditions based on the machining condition data output from the computer control device 1. The machining power supply device 6 operates each circuit element of the electric discharge machining circuit based on the machining conditions set in the machining condition setting device 5 and applies a predetermined discharge current pulse according to the set machining conditions to a predetermined repetition cycle. To supply the machining gap. The inter-electrode voltage detection device 7 detects the average machining voltage of the machining gap every predetermined unit period. The inter-electrode voltage detection device 7 smoothes and amplifies the inter-electrode voltage acquired from the machining gap, and outputs a digitally converted detection signal.

  The servo device 8 outputs a servo signal to the motor control device 2 so as to perform machining at an appropriate machining speed in response to the average machining voltage detected by the interelectrode voltage detection device 7 in accordance with a predetermined servo curve that has been set. The servo curve is a curve representing a change in machining speed with respect to the average machining voltage in the servo system in which the servo speed is determined when the average machining voltage is determined. Hereinafter, the servo curve including a linear change is simply referred to as a servo curve. Unless otherwise specified, the appropriate machining speed indicates a machining speed at which the electrostatic attraction force and the discharge repulsion force at a predetermined machining allowance are balanced.

  The servo device 8 has, for example, a servo characteristic that provides the servo curve shown in FIG. Therefore, the motor control device 2 moves the wire electrode relative to the workpiece in accordance with a predetermined relative movement trajectory defined by the NC program, and moves the wire electrode at a higher processing speed as the average processing voltage departs from the servo reference voltage. The machining gap is kept constant by relative movement.

  The input device 10 of the computer control device 1 is a means for an operator to input an NC program including a plurality of types of initial setting values. The decrypting device 20 decrypts the NC program and outputs NC data. The command device 30 calculates a movement direction and a movement amount based on the NC data, and outputs the movement command data to the motor control device 2. Further, the command device 30 outputs the machining condition data to the machining condition setting device 5.

  The storage device 40 of the computer control device 1 has electrostatic attraction force and discharge repulsion acting on the wire electrode EL in the direction orthogonal to the processing progress direction in the planned machining allowance under the processing conditions initially set in the processing condition setting device 5. The initial appropriate average machining voltage and the appropriate machining speed that balance the force are stored. The appropriate average machining voltage indicates an average machining voltage in which the electrostatic attraction force and the discharge repulsion force are balanced when electric discharge machining is performed under the set machining conditions.

  In the wire cut electric discharge machining apparatus according to the embodiment, the initial appropriate average machining voltage and the appropriate machining speed obtained in advance by test machining are stored in the storage device 40. Although the initial appropriate average machining voltage and the appropriate machining speed can be obtained by calculation, the proper average machining voltage and the appropriate machining speed obtained in the test machining have actually been confirmed to be straight. Since the data is reliable and reliable, it is advantageous in that the error when calculating the appropriate average machining voltage and the appropriate machining speed for each of the plurality of machining allowances that change thereafter can be made as small as possible.

  The arithmetic unit 50 calculates the electrostatic attraction force and the discharge repulsive force for each of a plurality of machining allowances based on the initial appropriate average machining voltage and the appropriate machining speed, and the electrostatic attraction force and the discharge for each of the plurality of machining allowances. An appropriate average machining voltage that balances the repulsive force and an appropriate machining speed corresponding to the appropriate average machining voltage are obtained. The computing device 50 performs appropriate machining for each appropriate average machining voltage from the initial appropriate average machining voltage and the appropriate machining speed stored in the storage device 40 and the appropriate average machining voltage and the appropriate machining speed corresponding to the obtained plural machining allowances. Servo curves are calculated so that they move relative to each other at speed.

  The servo condition setting device 60 sets a servo reference voltage and a servo gain. Then, the servo condition setting device 60 sets the servo curve calculated by the calculation device 50. In the servo condition setting device 60 in the embodiment, since the servo device 8 has the servo characteristics as shown in FIG. 5, the “servo speed” indicating the inclination of the servo curve provided as a specific parameter is set. Set the servo curve by setting it to an appropriate value.

  The wire cut electric discharge machining method of the present invention basically has an appropriate average machining voltage in which the electrostatic attractive force acting on the wire electrode and the electric discharge repulsive force are balanced in a direction orthogonal to the machining progress direction for each of the machining allowances. An appropriate machining speed is obtained, and machining is always performed at an appropriate machining speed in response to an average machining voltage detected during machining.

  The parameter of the machining speed used in the wire cut electric discharge machining method of the embodiment is a speed represented by a machining removal area per unit time. However, if the feed rate is a servo method other than the constant-speed feed servo method that does not depend on the machining gap, the speed expressed by the machining removal distance per unit time or the relative movement distance per unit time when viewed as a whole machining Therefore, for example, a method of constantly making an appropriate feed rate in response to the detected average machining voltage that fluctuates due to a change in machining allowance to eliminate the bending of the wire electrode is as follows. It is included in the technical idea of the invention.

  Specifically, the wire-cut electric discharge machining method of the embodiment calculates the electrostatic attraction force and the discharge repulsive force at the planned machining allowance based on the offset value by a combination of machining conditions set in the finishing machining process after the second cut. First, an appropriate average machining voltage and an appropriate machining speed at which the electrostatic attractive force and the discharge repulsive force are balanced are obtained. The electrostatic attraction force and the discharge repulsive force at each machining allowance are calculated from the electrostatic attraction force and the discharge repulsive force at the planned machining allowance for each plurality of machining allowances. An appropriate average machining voltage and an appropriate machining speed that balance the discharge repulsive force are obtained.

  A servo curve representing a change in machining speed with respect to the average machining voltage is set based on the relationship between the appropriate average machining voltage and the appropriate machining speed at which the electrostatic attraction force and the discharge repulsive force for each of the machining allowances are balanced. The servo device applicable to the wire-cut electric discharge machining method of the present invention is not limited as long as it is a servo device having a servo characteristic that determines the machining speed when an average machining voltage is given, but at least the average machining voltage is given within a specific range. A servo device having a servo characteristic in which the machining speed increases or decreases in proportion to the average machining voltage is desirable.

  During machining, the average machining voltage that fluctuates as the machining allowance changes for each predetermined unit period is detected, and the machining speed is adjusted so that the electrostatic attractive force and the discharge repulsive force balance in response to the detected average machining voltage. Change and adjust to an appropriate machining speed. In the wire cut electric discharge machining method of the embodiment, the predetermined unit time is a servo cycle determined according to the time required for the operation of the control device and the moving device (drive device), unless there are special circumstances. To do.

  2 and 3 are plan views of the upper surface (program plane) of the workpiece WP when the wire electrode EL and the workpiece WP are viewed from above. 2 and 3 show the electrostatic force generated in the machining gap formed between the wire electrode EL and the workpiece WP. FIG. 2 shows a case where an electrostatic force is generated only between a side surface (hereinafter, referred to as a discharge exposed surface) that is exposed to discharge including the processed side surface SP and the processed removal surface SQ of the wire electrode EL and the workpiece WP. is there. FIG. 3 shows a side surface (hereinafter referred to as a discharge non-exposed surface) where the electrostatic force is not directly exposed to the discharge corresponding to the pre-processing side surface SR formed in the pre-processing step in the wire electrode EL and the workpiece WP. This is also the case.

  When obtaining the electrostatic attraction force CF acting on the wire electrode EL in the direction orthogonal to the machining progress direction, the overall electrostatic force ω is determined from the geometrical difference in the region where the electrostatic force is generated due to the difference in the size of the machining allowance d. The calculation method is different. Therefore, it is necessary to calculate the electrostatic attraction force CF by dividing the case depending on whether the electrostatic force is generated only between the wire electrode EL and the discharge exposed surface or between the discharge non-exposed surface. At this time, in FIG. 2 and FIG. 3, the electrostatic force ω is shown projected onto the horizontal plane on the upper surface of the workpiece WP, and the electrostatic attraction force CF acts only on the upper surface of the workpiece WP. Does not mean.

  Assuming that the relative movement trajectory (offset trajectory) OP of the wire electrode EL is on the X-axis, the wire electrode EL is lowered to the relative movement trajectory OP from the branch point DP between the discharge exposed surface and the discharge non-exposed surface when the machining allowance is d. If the intersection (hereinafter referred to as a “branch point corresponding point”) XD between the vertical line and the relative movement locus OP is on the near side of the machining progress direction X + with respect to the branch point corresponding point when the predetermined allowance dr is present, In this case, the force is generated only between the discharge-exposed surface, and when it is on the far side, the electrostatic force is generated between the discharge-exposed surface. Accordingly, the calculation method of the electrostatic attractive force CF can be divided by comparing the machining allowance dr with the machining allowance d as a reference machining allowance.

  Here, assuming that the radius of the wire electrode EL is r and the discharge gap according to the set processing conditions is g, the distance from the branch point DP to the branch point corresponding point XD is calculated from the sum of the radius r and the discharge gap g. The value obtained by subtracting the allowance d. Therefore, the length x from the center position XO of the wire electrode EL to the branch point corresponding point XD in the machining process with the machining allowance d is obtained by Equation 1.

  When the machining allowance d is equal to the reference machining allowance dr, the length x matches the radius r of the wire electrode EL. This indicates that the reference allowance dr is closely related to the radius r of the wire electrode EL and the discharge gap g. Since the offset value in the machining plan is the sum of the radius r of the wire electrode EL, the discharge gap g, the machining allowance d, and the remaining margin, if the discharge gap g is specified based on the set machining conditions, The reference allowance dr can be obtained by 2.

In the case of a servo system in which the machining speed is determined when an average machining voltage is given, the average machining voltage varies in accordance with the change in machining allowance when the set electrical machining conditions do not change. Therefore, based on the relationship between the proper average machining voltage V ₀ and take cash d ₀ when the discharge repulsive force EF ₀ and electrostatic attraction CF ₀ when a cash d ₀ take appointment at the processing conditions of the initial setting are balanced The machining allowance di when the appropriate average machining voltage in the i-th predetermined unit period is Vi is estimated.

  When the machining allowance d at the appropriate average machining voltage V is equal to or greater than the reference machining allowance dr, the wire electrode EL and the workpiece WP are in the positional relationship shown in FIG. The electrostatic force ω generated between the wire electrode EL and the workpiece WP at this time can be obtained geometrically. Therefore, the electrostatic force in each region is calculated by dividing the region α and the region β from the entire shape of the region where the electrostatic force shown in FIG. 2 is generated.

  The vertical distance from the surface of the wire electrode EL on which the electrostatic force ωα acts in the region α to the processed side surface SP of the workpiece WP is the processing progress direction X + between the rear end position XS and the center position XO of the wire electrode EL. As the distance xi increases, the distance yi gradually decreases from the sum of the radius r of the wire electrode EL and the discharge gap g, and becomes equal to the discharge gap g at the center position XO where the distance xi is equal to the radius r of the wire electrode EL. Therefore, the electrostatic force ωα in the region α can be expressed by Equation 3. However, the position coordinate value of the center position XO of the wire electrode EL is set to zero. Further, it is assumed that the appropriate average machining voltage at this time is V.

  The vertical distance from the surface of the wire electrode EL on which the electrostatic force acts in the region β to the processing removal surface SQ of the workpiece WP is a distance in the processing progress direction X + between the center position XO and the tip position XE of the wire electrode EL. The distance r-yi-di gradually increases from the discharge gap g as the distance from xi increases. The machining allowance di can be obtained by the three-square theorem, as in Equation 2. Therefore, the electrostatic force ωβ in the region β can be expressed by Equation 4. However, the position coordinate value of the center position XO of the wire electrode EL is set to zero. Further, it is assumed that the appropriate average machining voltage at this time is V.

The sum of the electrostatic force ωα in the region α and the electrostatic force ωβ in the region β is the electrostatic force ω, and the electrostatic attraction force CF corresponds to a component (vertical component) in a direction orthogonal to the machining progress direction X + of the electrostatic force ω. To do. The wire-cut electric discharge machining method of the embodiment, the electrostatic attraction force in the cash di takes varies based on the premise that the electrostatic attraction force CF ₀ and the discharge repulsive force EF ₀ is balanced in cash d ₀ takes scheduled CFi Therefore, here, as represented by Equation 5, the electrostatic force ω is assumed to be the electrostatic attractive force CF.

  When the machining allowance extends to both sides of the wire electrode EL with respect to the machining progress direction X +, the wire electrode EL is sandwiched between the machining grooves. Therefore, it is necessary to calculate the electrostatic attraction force CF so as to cancel the electrostatic force generated on the processing surface opposite to the processing surface on one side. However, the processing in which the wire electrode EL is sandwiched between the processing grooves essentially corresponds to the roughing process, and therefore does not actually exist in the finishing process after the second cut. Therefore, the case where the wire electrode EL is sandwiched between the processing grooves is provided as a preliminary calculation step for practically preventing the calculation process in the electronic computer from being interrupted, and need not be considered substantially.

  When the machining allowance d at the appropriate average machining voltage V is smaller than the reference machining allowance dr, the wire electrode EL and the workpiece WP are in the positional relationship shown in FIG. The electrostatic force ω generated between the wire electrode EL and the workpiece WP at this time can be obtained geometrically. Therefore, the electrostatic force in each region is calculated by dividing the region α, the region β, and the region γ from the overall shape of the region where the electrostatic force shown in FIG. 3 is generated.

  3 is the same as the region α shown in FIG. 2, the electrostatic force ωα in the region α can be obtained by Equation 3. Also, the electrostatic force ωβ in the region β in FIG. 3 changes in the vertical distance from the center position XO of the wire electrode EL to the branch point corresponding point XD in the same way as the region β in FIG. The range in the machining progress direction X + to be performed can be replaced with the length x and can be obtained by applying Formula 4. However, the position coordinate value of the center position XO of the wire electrode EL is set to zero. Further, it is assumed that the appropriate average machining voltage at this time is V.

  The vertical distance from the surface of the wire electrode EL on which the electrostatic force acts in the region γ to the pre-processing side surface SR of the workpiece WP corresponding to the non-discharge exposed surface is from the branch point corresponding point XD to the tip position XE of the wire electrode EL. The distance r-yi gradually increases from the distance g-d as the distance xi-x increases in the machining progress direction X +, and is calculated from the sum of the radius r of the wire electrode EL and the discharge gap g at the tip position XE of the wire electrode EL. The distance obtained by subtracting the allowance d. Therefore, the electrostatic force ωγ in the region γ can be expressed by Equation 6. However, the position coordinate value of the center position XO of the wire electrode EL is set to zero. Further, it is assumed that the appropriate average machining voltage at this time is V.

The sum of the electrostatic force ωα in the region α, the electrostatic force ωβ in the region β, and the electrostatic force ωγ in the region γ is the electrostatic force ω, and the electrostatic attractive force CF corresponds to a vertical component of the electrostatic force ω. The wire-cut electric discharge machining method of the embodiment, the electrostatic attraction force in the cash di takes varies based on the premise that the electrostatic attraction force CF ₀ and the discharge repulsive force EF ₀ is balanced in cash d ₀ takes scheduled CFi Here, as expressed by Equation 7, the electrostatic force ω is assumed to be the electrostatic attractive force CF.

  FIG. 4 is a plan view of the upper surface of the workpiece WP when the wire electrode EL and the workpiece WP are viewed from above. FIG. 4 shows the discharge impact force generated with the discharge generated in the machining gap formed between the wire electrode EL and the workpiece WP. The discharge repulsive force EF acting on the wire electrode EL in the direction orthogonal to the machining progress direction is the machining progress direction X + of the combined impact force υ expressed by combining the components of the discharge impact force generated by a plurality of discharges generated in a predetermined unit period. Corresponds to a component in a direction orthogonal to (vertical component).

The discharge impact force is generated in the machining gap where the discharge gap g can exist. The machining gap is the machining between the intersection point (hereinafter referred to as the center point corresponding point) MO and the branch point DP with the perpendicular line dropped from the center position XO of the wire electrode EL to the machining shape trajectory MP in the machining process having a machining allowance d. It is formed between removal surface SQ and wire electrode EL. Therefore, although the discharge point for each discharge is indefinite, the combined impact force υ of the impact force caused by a plurality of discharges in a predetermined unit period is caused by the discharge generated at the center point corresponding point MO on the machining removal surface SQ. The discharge impact force υ ₀ and the discharge impact force ν ₁ due to the discharge generated at the branch point DP can be regarded as an average.

Therefore, it is assumed that the combined impact force υ acts at the position DH where the removal area on the processing removal surface SQ is halved. The position DH at which the removal area is halved corresponds to the position at which the machining allowance is about half of the machining allowance d. Since the discharge repulsive force EF acting on the wire electrode EL in the direction orthogonal to the machining progress direction X + is a vertical component of the combined impact force υ, the vertical component and the branch point of the discharge impact force υ ₀ generated at the center point corresponding point MO. It is equal to half the sum of the vertical component of the discharge impact force υ ₁ generated by DP.

Here, since the distance x from the center position XO of the wire electrode EL to the branch point corresponding point XD is calculated by Equation 1, it occurs at the center point corresponding point MO when the amount of deflection of the wire electrode EL is substantially zero. The angle θ formed by the component of the discharge impact force υ _{0 and} the component of the discharge impact force υ ₁ generated at the branch point DP can be obtained by Expression 8. Further, the components of the discharge impact force generated at the center point corresponding point MO and the discharge impact force generated at the branch point DP when the deflection amount of the wire electrode EL at the planned machining allowance d ₀ is _{0 under} the initial machining conditions and the discharge impact force generated at the branch point DP. Similarly, the angle θ ₀ formed by the component is also obtained by Equation 8.

In actual machining, a machining condition is set that gives discharge energy that generates a discharge repulsive force EF ₀ that is balanced with the electrostatic attraction force CF ₀ that makes the deflection amount of the wire electrode EL substantially zero at the planned allowance d ₀ . Therefore, the machining allowance is changed during machining to become machining allowance di, and the discharge repulsive force EFi that is balanced with the electrostatic attractive force CFi when the direction of the combined impact force υ is changed is generated under the set machining conditions. It can be calculated at the rate of the discharge repulsive force EFi for the elements of the discharge repulsive force EF ₀ to. Therefore, the discharge repulsive force EFi when the planned machining allowance d ₀ changes to the machining allowance di can be obtained by Equation 9.

In the servo system in which the machining speed is determined when an average machining voltage is given, the electrostatic attraction force CFi and the electric discharge corresponding to the appropriate average machining voltage Vi fluctuating with the changing machining allowance di under the set machining conditions. The repulsive force EFi can be obtained. Therefore, an appropriate average machining voltage V ₀ and an appropriate machining speed F ₀ that balance the electrostatic attraction force CF ₀ and the discharge repulsive force EF ₀ when machining the planned machining allowance d ₀ with the set machining conditions are set. As a reference, it is possible to obtain the appropriate average machining voltage Vi and the appropriate machining speed Fi in the changing machining allowance di.

Therefore, the initial appropriate average machining voltage V ₀ and the appropriate machining speed that serve as a reference for balancing the electrostatic attraction force CF ₀ and the discharge repulsive force EF ₀ at the planned machining allowance d ₀ with a combination of the set machining conditions. It is necessary to obtain F ₀ in advance. In the wire cut electric discharge machining method of the embodiment, even if the initial appropriate average machining voltage V ₀ and the appropriate machining speed F ₀ are obtained by calculation, it is verified whether or not the deflection amount of the wire electrode EL is actually zero. Therefore, test machining is performed from the beginning to obtain an accurate appropriate average machining voltage V ₀ and an appropriate machining speed F _{0 in} which the deflection amount of the wire electrode EL is substantially zero.

  FIG. 5 shows an example of servo characteristics of a servo device applied to the wire cut electric discharge machining method of the present invention. In order to relatively move the wire electrode EL at an appropriate processing speed Fi in which the electrostatic attraction force CFi and the discharge repulsive force EFi are balanced in accordance with the machining allowance di, an average that fluctuates by changing the machining allowance d every predetermined unit period. A servo device having a servo characteristic capable of detecting the machining voltage Vi and setting the proper machining speed Fi in response to the detected average machining voltage Vi is applied.

  The optimum servo device that can be applied in the wire-cut electric discharge machining method of the present invention has an appropriate machining speed that balances electrostatic attraction force and electric discharge repulsion force with respect to the detected average machining voltage as shown by the dotted line in FIG. Servo characteristics for obtaining an ideal servo curve. However, it is extremely difficult for a skilled operator to change and set the servo curve that provides the appropriate machining speed F in response to the appropriate average machining voltage V.

  Therefore, in the wire cut electric discharge machining method of the embodiment, a servo device having a servo characteristic capable of obtaining a servo curve as shown by a solid line in FIG. 5 is applied. The range of the appropriate average machining voltage that can be taken corresponding to the change in machining allowance in actual machining is limited to a specific range Vk on the servo curve shown in FIG. In the specific range Vk, the difference between the ideal servo curve indicated by the dotted line and the servo curve indicated by the solid line is slight, and if the maximum allowable error is about 1 μm, there is no problem in terms of machining shape accuracy. It turns out.

  Here, in the case of an electric discharge machining circuit in which the time width of the discharge current pulse is constant (hereinafter referred to as an on-clamp circuit), the average machining voltage V that is the average of the machining gap voltages in a predetermined unit period is The sum of the no-load voltage Vp at the no-load time TW and the machining voltage Vg at the discharge time ON can be obtained by dividing the sum of the no-load time TW, the discharge time ON, and the rest time OF by the discharge cycle.

Value for money the average machining voltage V ₀ early in the die d ₀ takes scheduled at the processing conditions of the initial settings have been obtained by the test processing. Further, the no-load voltage Vp is equal to the voltage of the DC power supply, and a normal discharge that contributes to machining is generated under a predetermined machining condition in the combination of the material of the wire electrode EL and the workpiece WP, and a discharge current is supplied. The discharge voltage Vg at that time is substantially constant. For example, the discharge voltage Vg when the material of the wire electrode EL is brass and the material of the workpiece WP is iron or cemented carbide is about 20V. Therefore, unloading time TW ₀ when the electrostatic attraction force CF ₀ and the discharge repulsive force EF ₀ in cash d ₀ take appointment at the processing conditions of the initial setting is balanced is determined by the number 11.

Since the discharge time ON for each discharge in the finishing process of wire-cut electric discharge machining is an extremely short time that can be ignored in the entire discharge cycle, the electrostatic attraction force CFi and the discharge repulsion force EFi are equal in the machining allowance di. unloading time TWi upon as being the discharge repulsive force EP ₀ is substituted to the electrostatic attraction force CF ₀ since the electrostatic attractive force CF ₀ and the discharge repulsive force EF ₀ in cash d ₀ take is equal And can be calculated by Equation 12. However, it does not deny calculating the no-load time TWi in consideration of the discharge time ON.

  As described above, the average machining voltage V can be obtained by Equation 10. Since the no-load voltage TWi when the electrostatic attraction force CFi and the discharge repulsive force EFi are balanced when the average machining voltage V fluctuates in the predetermined unit period is obtained in Formula 12, therefore, the static voltage in the predetermined unit period is An appropriate average machining voltage Vi in which the electrosuction force CFi and the discharge repulsive force EFi are balanced is obtained by Expression 13.

In the case of a servo characteristic that provides a servo curve as shown by the solid line in FIG. 5, the machining speed F changes proportionally in response to the average machining voltage V in a specific range Vk effective in actual machining. from the time is appropriate processing speed F ₀ at the die d ₀ for the proper average machining voltage V ₀ is taken of plans, and were to be changed by the proper average machining voltage Vi changes to the die di taken by the allowance, proper processing speed Fi Can be calculated by Equation 14.

Since the initial appropriate machining speed F ₀ corresponding to the initial appropriate average machining voltage V ₀ where the deflection amount of the wire electrode EL is substantially 0 at the machining allowance d ₀ obtained by the test machining is reliable data, As shown in FIG. 5, by plotting a plurality of data of the appropriate average machining voltage Vi and the appropriate average machining voltage Vi corresponding to the appropriate average machining voltage Vi obtained by the equations 13 and 14 for each plurality of machining allowances, the appropriate average machining is performed. required servo curve as when connecting each data data mainly, to relative movement proper machining speed Fi for each proper average machining voltage Vi at a proper processing rate F ₀ by a voltage V ₀ (including an approximate curve) Can be obtained.

  In the wire-cut electric discharge machining method of the embodiment, a servo curve for obtaining an appropriate machining speed F corresponding to an appropriate average machining voltage V in which the electrostatic attractive force CF and the electric discharge repulsive force EF are always balanced is used as a parameter for a specific type of machining condition. By setting, you can change and adjust the settings. Specifically, a servo speed that changes the value of the machining speed with respect to the average machining voltage is provided as a parameter for the machining conditions. Changing the machining speed relative to the average machining voltage by setting the servo speed is synonymous with changing the rate of change (speed ratio) of the servo curve. In particular, when the servo curve is a straight line, this corresponds to substantially changing the inclination of the servo curve.

Accordingly, when the machining allowance is set to d _{0 under} the set machining conditions, a plurality of cuttings are performed based on the appropriate average machining voltage V ₀ and the appropriate machining speed F ₀ in which the electrostatic attractive force CF ₀ and the discharge repulsive force EF ₀ are balanced. The electrostatic attraction force CFi and the discharge repulsive force EFi are calculated for each allowance di, and an appropriate average machining voltage Vi and an appropriate machining speed Fi that balance the electrostatic attraction force CFi and the discharge repulsive force EFi are obtained. ) Is set to a servo curve that provides an appropriate machining speed Fi with respect to an appropriate average machining voltage Vi.

  Therefore, when the average machining voltage V is detected every predetermined unit time during machining, and the wire electrode EL is machined at a machining speed F determined by the average machining voltage V in response to the detected average machining voltage V, In response to the average machining voltage Vi detected according to the set servo curve for obtaining the appropriate machining speed Fi with respect to the appropriate average machining voltage Vi, the machining is fed at the appropriate machining speed Fi.

For this reason, when the planned machining allowance d ₀ is changed to the machining allowance di, the initial average machining voltage V ₀ of the machining gap is changed to the appropriate average machining voltage Vi, and the inter-electrode voltage detection device 7 is activated after a predetermined unit period. An appropriate average machining voltage Vi is detected. The servo device 8, in response to a proper average machining voltage Vi changes the appropriate machining speed F ₀ to a proper processing speed Fi accordance servo curves that have been set, the wire electrode EL is electrostatic attraction CFi and the discharge repulsive force EFi Are balanced and are fed at an appropriate machining speed Fi at which the bending amount of the wire electrode EL is substantially zero. As a result, the machining surface is not formed to be curved regardless of the change in machining allowance in the finishing machining process, and the machining shape accuracy is further improved.

  Further, in the wire cut electric discharge machining method of the embodiment, since the operator only sets the servo curve by setting the servo speed, there is an advantage that the burden on the operator does not increase. In addition, an operator of a manufacturer who provides an electrical discharge machine performs some test machining and gives the storage device a combination of multiple types of machining conditions, an appropriate average machining voltage for each machining allowance, and an appropriate machining speed. Therefore, it is possible to carry out the machining so that the bending amount of the wire electrode can be substantially zero, which is advantageous in that the burden on the worker of the manufacturer is reduced. In addition, since the machining is performed at an appropriate machining speed according to the servo curve, the electrical machining conditions are not affected, and the target machining is not hindered.

  In the case of an electric discharge machining circuit (hereinafter referred to as a multi-oscillation circuit) in which the time width of the discharge current pulse is not constant, the no-load time TW in a predetermined unit period cannot be obtained from the discharge cycle. However, since the multi-oscillation circuit is an electric discharge machining circuit used when supplying a discharge current pulse having an extremely short time width, the ratio of the discharge time ON, which is the ON time of the discharge current pulse, to the entire discharge cycle time Since the discharge voltage Vg is as low as about 20 V with respect to the no-load voltage Vp of 80 V or higher, the appropriate average machining voltage V that balances the electrostatic attractive force CF and the discharge repulsive force EF is almost zero. It can be said that it depends on the no-load voltage Vp in the load time TW.

Therefore, if the planned allowance d ₀ is changed to the allowance di and the electrostatic attractive force CF ₀ is changed to the electrostatic attractive force CFi and the discharge repulsive force EF ₀ is changed to the discharge repulsive force EFi and balanced. For example, even if the no-load time TWi is not known, the appropriate average machining voltage Vi at that time can be determined according to the ratio of the no-load voltage Vp in the predetermined unit period. Therefore, when the ratio of the appropriate average machining voltage V to the no-load voltage Vp in the predetermined unit period is the “no-discharge ratio” P, and the no-discharge ratio Pi at the machining allowance di, it can be obtained by Equation 15.

Here, the no-load voltage Vp when the planned machining allowance d ₀ is constant under the set machining conditions, and the appropriate average machining voltage V ₀ in which the electrostatic attractive force CF ₀ and the discharge repulsive force EF ₀ are balanced. , since known reliable numerical, such as by testing process, no discharge ratio P ₀ when the take cash d ₀ is obtained by the number 16.

Since the initial appropriate average machining voltage V ₀ changes to the appropriate average machining voltage Vi and the electrostatic attractive force CFi and the discharge repulsive force EFi are still balanced, the no-discharge ratio Pi at the changing allowance di is As shown in Equation 17, the non-discharge ratio P ₀ at the planned allowance d ₀ can be obtained by multiplying the ratio of the electrostatic attraction force CF ₀ and the discharge repulsion force EP ₀ .

The machining speed F increases or decreases in proportion to the average machining voltage V according to the set servo curve. No discharge ratio P is average machining since voltage is the ratio and V, varies proper average machining voltage Vi changes in cash di take the cash d ₀ take the scheduled free discharge from the no-discharge ratio P ₀ for no-load voltage Vp when the change in specific Pi, proper machining speed Fi, as number 18, the rate of change in the percentage of no-load voltage Vp corresponding to the change in the take cash d when changing the appropriate machining speed Fi from the appropriate machining speed F ₀ Can be obtained at

  If the data of the appropriate machining speed Fi corresponding to a plurality of average machining voltages Vi can be obtained in a combination of a plurality of machining conditions to be set, as in the case of the on-clamp circuit, for each of a plurality of machining allowances di. By calculating the electrostatic attraction force CFi and the discharge repulsion force EFi, obtaining the appropriate average machining voltage Vi and the appropriate machining speed Fi that balance the electrostatic attraction force CFi and the discharge repulsion force EFi, and setting the servo speed at all times. A servo curve capable of obtaining an appropriate machining speed Fi with respect to the average machining voltage Vi is set.

  In the wire-cut electric discharge machining method of the embodiment, a servo device having a servo characteristic that specifically obtains the servo curve shown in FIG. 5 is applied. As already described, in a specific period Vk, If the servo device has a servo characteristic that obtains a servo curve having an appropriate machining speed Fi in which the electrostatic attractive force CFi and the discharge repulsive force EFi are balanced when the average machining voltage Vi is applied, the servo device having other servo characteristics. Even can be applied. Further, it is possible to obtain a proper average machining voltage Vi and a proper machining speed Fi during machining, change and set the servo speed, and proceed with machining while setting a servo curve.

  The wire-cut electric discharge machining method and the wire-cut electric discharge machining apparatus according to the embodiments described above do not depart from the technical idea of the present invention and, as already described, some modified examples, function of the present invention. The present invention can be appropriately modified within a range where the effect can be obtained, or can be applied in combination with other inventions.

  The present invention is useful for precision machining of metal products such as die machining by electric discharge machining, parts machining, and tool electrode machining. The present invention greatly reduces the number of times of test processing, is easy to operate, further improves the processing shape accuracy of metal products, and contributes to the development of metal processing technology.

DESCRIPTION OF SYMBOLS 1 Computer numerical control apparatus 2 Motor control apparatus 3 Movement apparatus 4 Position detection apparatus 5 Processing condition setting apparatus 6 Processing power supply apparatus 7 Electrode voltage detection apparatus 8 Servo apparatus 10 Input apparatus 20 Decoding apparatus 30 Command apparatus 40 Storage apparatus 50 Arithmetic apparatus 60 Servo condition setting device EL Wire electrode WP Work piece CF Electrostatic attraction force EF Discharge repulsion force r Radius of wire electrode g Discharge gap d Removal allowance x Distance from center position of wire electrode to corresponding point of branch point

Claims (3)

  The appropriate average machining voltage in which the electrostatic attraction force acting on the wire electrode and the discharge repulsion force are balanced in a direction orthogonal to the machining progress direction for each of the machining allowances, the electrostatic attraction force corresponding to the appropriate average machining voltage, and the A wire-cut electric discharge machining method for obtaining an appropriate machining speed that balances the electric discharge repulsive force and machining at the appropriate machining speed in response to an average machining voltage detected every predetermined unit period.   Obtaining an initial appropriate average machining voltage and an appropriate machining speed in which the electrostatic attractive force acting on the wire electrode and the discharge repulsion force are balanced in a direction orthogonal to the machining progress direction at the scheduled machining allowance under the set machining conditions; The electrostatic attraction force and the discharge repulsive force are calculated for each plurality of machining allowances based on the initial appropriate average machining voltage and the appropriate machining speed, and the electrostatic attraction forces are calculated for each of the plurality of machining allowances. And calculating the appropriate average machining voltage that balances the discharge repulsive force and the appropriate machining speed corresponding to the appropriate average machining voltage, and the average machining voltage so as to move relative to each other at the appropriate machining speed. A step of setting a servo curve representing a change in machining speed with respect to the above, a step of detecting an average machining voltage every predetermined unit period, and in response to the detected average machining voltage according to the servo curve Wire-cut electric discharge machining method comprising the step of processing at a positive working speed, a.   An inter-electrode voltage detection device for detecting an average machining voltage of a machining gap every predetermined unit period, and an appropriate machining speed in response to the detected average machining voltage according to a predetermined servo curve representing a change in machining speed with respect to the average machining voltage The servo device that outputs the servo signal so as to process with the initial stage where the electrostatic attractive force acting on the wire electrode and the discharge repulsive force are balanced in the direction perpendicular to the machining progress direction at the scheduled machining allowance under the set machining conditions A storage device that stores the appropriate average machining voltage and the appropriate machining speed, and the electrostatic attraction force and the discharge repulsive force for each of a plurality of machining allowances based on the initial appropriate average machining voltage and the appropriate machining speed. And calculating an appropriate average machining voltage in which the electrostatic attraction force and the discharge repulsive force are balanced and an appropriate machining speed corresponding to the appropriate average machining voltage for each of the plurality of machining allowances When the proper average machining voltage the appropriate machining speed in the wire cut electric discharge machining apparatus comprising a servo condition setting apparatus, a setting the servo curve for relative movement to each.

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