JP2006035395A - Wire cut electric discharge machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce degradation of machining shape accuracy by correcting an error in a taper angle generated by a cause for a clearance of a wire guide without conducting test processing. <P>SOLUTION: A composite movement vector UV is obtained from command movement vectors U and V of each taper axis. A taper-direction angle α is calculated from the command movement vector U in a U axial direction orthogonal to a V axial direction where a conductor pushes out a wire electrode, and the composite movement vector UV. A position shifted in a direction opposite to an offset direction V- of the conductor by a clearance quantity L of the wire guide is as the position of the center of the axis of the wire electrode, then a correction quantity is calculated by the taper-direction angle α and the clearance quantity L. A positioning error of the wire electrode generated by a cause for the clearance is corrected by applying correction movement vectors x, y, u, and v to each of the command movement vectors X, Y, U and V of a machining axis or the taper axis. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wire-cut electric discharge machining that prevents a reduction in machining shape accuracy caused by a positioning error of a wire electrode caused by a clearance of a wire guide during machining by correcting a horizontal position of the wire guide. In particular, the present invention relates to wire-cut electric discharge machining that corrects the horizontal position of the wire guide so that the inclination angle of the actual wire electrode during machining becomes a set taper angle during taper machining.

  A wire electrode, which is a tool electrode, is stretched between a pair of wire guides with a predetermined tension applied, and a machining voltage is applied to the machining gap formed between the wire electrode and the workpiece to discharge the wire electrode. A wire-cut electric discharge machining is known in which a wire electrode and a workpiece are moved relative to each other and the workpiece is machined into a desired shape by electric discharge energy. In a wire-cut electric discharge machining apparatus having a general configuration, wire guides are provided above and below with a workpiece interposed therebetween. An electrical conductor is provided near the wire guide and feeds power from the electrical conductor to the wire electrode. During electric discharge machining, the wire electrode runs from the direction of one wire guide to the direction of the other wire guide.

  In order to obtain a desired machining shape, it is required to move the wire electrode with respect to the workpiece along a required relative movement locus on an arbitrary plane orthogonal to the plate thickness direction of the workpiece. In a wire cut electric discharge machining apparatus provided with a numerical control device, the relative movement trajectory of a wire electrode drawn on a program plane is represented by a machining program such as an NC program based on a desired machining shape trajectory. The control device decodes the machining program, analyzes the program data (NC data), and outputs the movement data to the movement control device. The movement control device controls the positioning of each moving body so that the wire electrode actually moves relative to the workpiece along the relative movement locus programmed.

  The wire guide not only guides the travel of the wire electrode, but also positions the wire electrode relative to the workpiece. The wire guide used in the wire-cut electric discharge machining apparatus can be divided into several types depending on the configuration, material, etc., one of which is a die guide. A material having wear resistance such as diamond and sapphire is used for the guide body of the die guide. The die guide has an advantage that the positioning accuracy can be maintained.

  In many wire guides, a slight gap (clearance) of several μm to several tens of μm is provided between the wire electrode and the wire electrode so that the wire electrode can be easily inserted into the wire guide and run smoothly. Therefore, an error in the position of the wire electrode in the wire guide occurs within the clearance range. In wire-cut electrical discharge machining, which requires machining shape accuracy of several μm or less, as in the case of finishing machining of precision parts and molds, satisfactory error in machining shape accuracy cannot be obtained due to this error. There is. In order to eliminate the machining shape error caused by the clearance of the wire guide, it is considered to improve by moving the wire guide to a position that supports the discharge reaction force received by the wire electrode and the pressure of the machining fluid jet (patent) Reference 1 and Patent Reference 2).

  However, when taper processing is performed, the direction in which an error occurs differs depending on the direction in which the wire electrode is inclined. In view of this, the present applicant has invented and has applied for a patent on a wire-cut electric discharge machining method that eliminates a machining shape error caused by clearance in taper machining (see Patent Document 3).

  By the way, many wire-cut electric discharge machining apparatuses employ a guide assembly that integrally accommodates a wire guide, a current-carrying member, and a machining liquid jet nozzle as a configuration advantageous for wire-cut electric discharge machining. The nozzle opening is provided on the surface of the workpiece with a slight gap so that the machining liquid jet is stably supplied. The wire guide is provided near the workpiece for reasons such as reducing the positioning error, vibration, and deflection of the wire electrode. In order to reduce the power loss by reducing the resistance value, it is desirable to provide the energizer as close to the workpiece as possible. In addition, it is required that the energizing body is always in contact with the wire electrode reliably. Therefore, the wire guide and the electrical conductor are provided close to the wire axis direction. As a result, the axis center of the wire electrode at the position where the wire electrode is pushed out is offset with respect to the axis center of the wire electrode passing through the wire guide.

  Since the wire electrode is vertically aligned with respect to each axial direction in the setup operation before processing, no positioning error of the wire electrode occurs when the vertical alignment is performed (see Patent Document 4). FIG. 4 shows a state of the wire electrode immediately after vertical ejection in a certain wire cut electric discharge machining apparatus. For example, in the case of the wire-cut electric discharge machining apparatus shown in FIG. 4, the contact position between the wire electrode and the guide portion of the wire guide in the horizontal uniaxial direction in which the current conductor presses the wire electrode is Is in the direction of pressing. Since the control device recognizes the initial position of the wire guide immediately after the vertical projection as the origin, the state in which the positioning error of the wire electrode occurs due to the clearance when the wire electrode is tilted is different. Therefore, even if an error is uniformly corrected in each axial direction, the wire electrode may not be accurately positioned.

The positioning error of the wire electrode due to the clearance in the taper processing causes an error in the taper angle, and often causes an unacceptable machining shape error. Specifically, for example, there is a problem that the blade thickness dimension is not obtained in the cutting blade processing. Therefore, it is necessary to ensure sufficient processing accuracy before processing. For this reason, when taper machining is performed, error is actually measured by performing test machining in advance, and machining is performed after the numerical values are corrected (see Patent Document 5 and Patent Document 6).
Japanese Utility Model Publication No. 56-67923 (pages 5 to 6) Japanese Examined Patent Publication No. 4-78411 (page 3, Fig. 4) Japanese Patent Application No. 2004-4909 JP 2003-71636 A (pages 3 to 4) JP 2000-24839 A (page 4) JP-A-2-279220 (page 3)

  Thus, when performing taper processing, some test processing is required, and the setup time tends to be long. Records recorded by test processing are accumulated to create a database, and an appropriate value of the distance between the wire guides with respect to the set taper angle is read from the data table stored in the storage device, and taper processing is performed at the correct taper angle. It is possible. However, the data obtained by test machining is low in reliability other than machining performed under the same conditions as the test machining on the same machine, and is sufficient for changes in the diameter of the wire electrode at each unit taper angle. Since it is necessary to prepare measurement data in each axial direction that can be handled, a huge amount of measurement data is required, and test machining for that is a heavy burden on the operator. In the case of machining in which the taper angle is gradually changed, machining data cannot be obtained, and it is practically difficult to remove the taper angle error.

  The present invention provides a wire-cut electric discharge machining method that does not require such test machining and that can correct the taper angle error caused by the clearance of the wire guide and reduce the reduction in machining shape accuracy. Objective.

  The wire-cut electric discharge machining method of the present invention obtains the combined movement direction and the combined movement amount of each axis from the command movement direction and the command movement amount of each axis of the taper shaft, and is orthogonal to the axial direction in which the energizer pushes the wire electrode. The taper direction angle formed by one axial direction of the taper shaft and the combined moving direction is calculated, and the taper direction angle is determined by setting the position where the clearance amount of the wire guide is shifted in the direction opposite to the offset direction of the current-carrying member as the center position of the wire electrode. And a relative movement between the wire electrode and the workpiece based on the movement command value obtained by calculating the correction amount from the clearance amount and adding the correction amount to the command movement amount of the machining axis or the taper axis. It is characterized by controlling.

  The control device calculates a command movement vector for each axis of the taper axis from the NC data to obtain a combined movement vector. Then, the taper direction angle formed by the axial direction and the combined movement direction is obtained from the command movement vector and the combined movement vector of the taper axis orthogonal to the axial direction in which the electric current body presses the wire electrode. Since the clearance amount is known, the correction movement vector can be obtained by calculating the taper direction angle and the clearance amount.

  At this time, at the initial position of the wire guide immediately after the vertical projection, the position of the axis center of the wire electrode is already pushed by the energizing body and is shifted from the center position of the wire guide by the clearance amount. In other words, the combined movement direction is a taper direction in which the wire electrode is inclined, so that the position where the current-carrying body is shifted in the direction opposite to the direction in which the current-carrying electrode is pressed (offset direction of the current-carrying body) When the position is set, the positioning error of the wire electrode can be calculated in consideration of the contact position between the wire electrode and the guide portion of the wire guide due to the current-carrying member being pressed against the wire electrode.

  Accordingly, by calculating the sum of the obtained corrected movement vector and the combined movement vector of each axis of the machining axis or the taper axis, the combined movement vector of the taper axis to which the correction value is added is obtained. Then, the movement command value of each axis in which the error due to the clearance is corrected is obtained by distributing the combined movement vector added with the correction value to each axis. Alternatively, the corrected movement vector for each axis can be obtained by first distributing the corrected movement vector to each axis, calculating the corrected movement vector in the direction of each axis, and adding it to the command movement vector for each axis. .

  As described above, the wire-cut electric discharge machining method of the present invention is a wire electrode positioning error caused by the clearance in consideration of the deviation of the center position of the wire guide from the position of the axis center of the wire electrode immediately after the vertical feeding. Therefore, the taper angle error can be corrected without performing test processing. As a result, it is possible to reduce the deterioration of the machining shape accuracy, shorten the setup time, reduce the burden on the operator, and improve the work efficiency.

  FIG. 1 shows a preferred embodiment of the wire cut electric discharge machining method of the present invention. The case of the wire cut electric discharge machine shown in FIG. 4 will be described below. The wire-cut electric discharge machining apparatus shown in FIG. 4 includes a computer numerical control device, and at least simultaneously performs four-axis control of a machining axis (X axis, Y axis) and a taper axis (U axis, V axis). . Further, the lower wire guide is fixed and the upper wire guide is moved, and the upper electrode guide is moved with respect to the lower wire guide so that the wire electrode is inclined. Accordingly, the taper angle is determined by the distance between the upper wire guide and the lower wire guide (hereinafter referred to as the inter-guide distance) and the position of the upper wire guide.

  The wire electrode 1 is stretched between an upper wire guide 2 and a lower wire guide 3 which are die guides. The upper wire guide 2 and the energizing body 4 are housed in a guide assembly attached to the tip of the upper arm that is suspended from a taper device composed of two linearly moving bodies that move in the taper axis direction. The lower wire guide 3 and the current-carrying body 5 are housed in a guide assembly that is fixed to the column, passes through the processing tank, and is attached to the tip of the lower arm that protrudes below the workpiece. The workpiece is moved by two linear moving bodies that move in the direction of the machining axis. Since the above-described configuration is a general configuration as a 4-axis control wire-cut electric discharge machining apparatus, detailed description of illustrations will be omitted except for necessary members.

First, a clearance amount is set (S1). The clearance amount L is directly input by the operator and stored in the storage device of the control device. When the clearance is different between the pair of upper and lower wire guides, the respective clearance amounts L _U and L _B are set. The diameter of the wire electrode to be used and the inner diameter (guide part) of the wire guide are input data, the wire electrode diameter is d, the inner diameter of the wire guide is D, and the controller calculates the clearance amount by (D−d) / 2. L can be set. If the inner diameter of the pair of upper and lower wire guides are different, give each having an inner diameter D _U, the D _B. When using a wire guide with the same wire electrode diameter and the same inner diameter continuously, use the previous setting value as it is, and set it when the diameter is different from the wire electrode used before or when the inner diameter of the wire guide is different. Overwrite the value.

Next, the axial direction in which the wire electrode is pushed out by the energizing body is set (S2). “Axial direction data” indicating the axial direction may be recognized by the control device. Specifically, for example, “V−” is used. When the offset direction of the current conducting body is different between the upper current conducting body and the lower current conducting body, the respective axial direction data is set. Since the axial data itself is data that does not change inherent to the machine, it is stored in the storage device as internal data. In the embodiment, the current-carrying member offset amount indicating how much the current-carrying member has offset the wire electrode from the axial center or the current-carrying member offset angle indicating how much the wire electrode is inclined from when it is stretched vertically. By setting, the axial direction is set at the same time. Therefore, it is preferably set every time the values of the upper and lower electrification element offset amounts ε _U and ε _B or the electrification element offset angles β _U and β _B are changed.

Then, vector data in the offset direction of the current-carrying member is obtained from the current-carrying member offset amount (S3). The current-carrying body offset amounts ε _U and ε _B may be read by the operator by marking the means for sliding the current-carrying body. In addition, when the current-carrying member offset angles β _U and β _B are used as axial direction data, the angles are assumed to be mechanically known values. At this time, the distance CZ between the electrical conductor and the wire guide is unique to the machine and does not change. Therefore, if the distance CZ between the current-carrying member and the wire guide is known, if one of the current-carrying member offset amount and the current-carrying member offset angle is set, the other can be obtained by calculation. Examples of vectors in the offset direction of the current-carrying body are shown in FIGS. FIG. 2 shows the case of the lower wire guide in FIG. 4 and the required vector is the vector −v.

  At the time of taper machining (S4), the control device obtains a combined movement direction and a combined movement amount of each axis of the taper shaft for each predetermined unit movement command value (S5). The predetermined unit movement command value is arbitrary within a range of values that can be positioned by the driving device that moves the moving body of each axis. When not specified by the operator, the minimum drive unit possible with the control device is assumed. Generally, the smaller the unit movement command value is, the higher the compensation accuracy of the correction is. Therefore, it is preferable that the unit movement command value is set to a small value within a range that does not impose a burden on the arithmetic device to the extent that it affects control. The combined movement amount and the combined movement direction are obtained by calculation from the combined movement vector UV of the command movement vectors U and V of each axis of the taper axis. The combined movement vector UV is shown in FIG.

  Prior to the actual movement of the moving body, the NC program is sequentially analyzed to obtain NC data. Taper machining is programmed in the NC program with a taper angle or a taper shaft movement command value (movement amount or position coordinate value). When the taper angle is programmed, it can be recognized from the taper angle θ that the taper machining is performed, and the command movement direction and command movement amount of each axis of the taper axis are determined from the taper angle θ and the known guide distance T. Can be obtained. When the movement command value of the taper shaft is programmed, it can be recognized from the data of the movement command value that the taper machining is performed, and the taper angle is calculated from the command movement direction and command movement amount of each axis of the taper shaft and the distance T between the guides. θ can be obtained. Therefore, the combined movement vector UV can be obtained from the sum of the command movement vectors for each axis of the taper axis. Then, by analyzing and calculating the component of the combined movement vector UV, the combined movement direction and the combined movement amount can be obtained.

  Next, the control device calculates the taper direction angle formed by the command movement direction in the axial direction orthogonal to the axial direction in which the electric current body presses the wire electrode on the taper plane and the previously obtained combined movement direction (S7). ). The taper direction angle α can be obtained from, for example, a command movement vector in the axial direction orthogonal to the direction in which the current-carrying member presses the wire electrode, and a combined movement vector of the command movement vectors of each axis of the taper axis. In the case of the lower wire guide in the configuration of the wire-cut electric discharge machining apparatus shown in FIG. 4, it can be calculated from the command movement vector U and the combined movement vector UV as shown in FIG.

  Subsequently, the control device calculates the correction amount of the taper axis from the taper direction angle and the clearance amount. The correction amount is calculated for each of the upper wire guide and the lower wire guide. At this time, the correction amount is calculated with the position shifted by the clearance amount of the wire guide in the direction opposite to the offset direction of the current-carrying member as the position of the axis center of the wire electrode. The correction amount is represented by a corrected movement vector uv or a corrected movement vector u, v in each axial direction. The correction amount in each axial direction can be obtained from two corrected movement vectors u and v in each axial direction obtained by distributing the combined corrected movement vector uv to each axis of the taper axis. FIG. 3 shows a guide plan view when the clearance amount of the wire guide is shifted in the case of the lower wire guide.

  As can be seen from FIG. 3, the contact position between the wire electrode and the guide portion of the wire guide is on the guide circle of the wire guide, and the correction amount is within the range of the positioning error due to the clearance. The wire electrode is already pressed against the guide portion of the wire guide by the electric current body in the state immediately after the vertical delivery, and the control device recognizes the initial position of the wire guide immediately after the vertical delivery as the origin (0, 0). Therefore, the correction amount is a maximum of the clearance on both sides, in other words, not more than twice the clearance, and is 0 at the minimum.

If the lower wire guide of FIG. 3, the offset direction of the energizing member is the direction of the vector -v, outside the wire electrode in the guide circle which is the amount of clearance L _B shift in the V + direction can not exist. Therefore, when the combined movement vector UV is in the V-direction (U = 0), the contact position between the wire electrode and the guide portion of the wire guide does not change even if the wire electrode is inclined in that direction. 0. Conversely, when the synthetic movement vector UV is V + (U = 0), the correction value is 2 × L _B, the wire electrode even more that direction be inclined wire electrode is inclined wire electrode It can be seen that the contact position between the wire guide and the guide portion of the wire guide does not change. For example, when the combined movement vector UV is shown in FIG. 3, the contact position where the wire electrode contacts the lower wire guide may be at a point (L × cos α, L + L × sin α) shifted from the taper direction. Recognize.

  As described above, since the calculation method differs depending on the direction of the combined movement vector UV, in other words, the taper direction, when calculating the correction amount, as shown in FIG. The correction amount is calculated from the taper direction angle and the clearance amount with the guide clearance amount shifted position as the center position of the wire electrode, and the correction amount is obtained corresponding to the taper angle. The control process is calculated for each case (S6 to S9, S12 to S18).

  Then, the control device calculates the corrected movement command value by adding the obtained correction amount to the movement amount of the machining axis or the taper axis (S10). A specific calculation method of the correction amount and whether the correction axis is a machining axis or a taper axis depends on the configuration of the wire cut electric discharge machining apparatus. In the case of the 4-axis control wire-cut electric discharge machining device shown in FIG. 4, when correcting the position of the lower wire guide, the correction amount is added to the movement command values of the X axis and the Y axis to correct the position of the machining axis. Then, when correcting the position of the upper wire guide, the correction amount is added to the movement command values of the U axis and the V axis to correct the position of the taper axis.

  When calculating the corrected movement command value for each axis, a combined vector obtained by summing the combined movement vector UV of the previously calculated movement command value and the combined corrected movement vector uv is calculated. It can be obtained by distributing to each axis, or can be obtained by adding the corrected movement vectors u and v in the direction of each axis to the command movement vectors U and V of each axis obtained from the NC data.

  The above process is sequentially repeated from the machining start point to the machining end point of the NC program to correct the positioning error due to the clearance between the upper wire guide and the lower wire guide (S11). When the clearance amount value is not set or 0 is given, the correction value of the wire guide is not calculated. Further, it is possible to prevent the wire guide correction control. This is effective, for example, when at least one of the wire guides does not have a clearance, or when the desired machining shape accuracy does not require correction of the wire guide due to the clearance. is there.

  In the wire-cut electric discharge machining method of the embodiment, as already described, the current-carrying member offset amount ε or the current-carrying member offset angle β is set and the taper angle θ is obtained. Therefore, in particular, it is possible to correct the positioning error of the wire electrode in consideration of the influence of the current-carrying member more accurately even in a taper angle range where the wire electrode and the guide portion of the wire guide do not contact each other. Hereinafter, the case where the amount of movement in the direction orthogonal to the axial direction in which the wire electrode is pushed out by the energizer is 0 will be described more specifically (S6).

  In the configuration of the wire-cut electric discharge machining apparatus of FIG. 4, the specific correction amount calculation when the movement amount in the U-axis direction is 0 is as follows. First, since the movement amount in the U-axis direction is 0, the correction amount in the U-axis direction is 0 (S12). When the movement amount in the V-axis direction is 0 or less (S13), the contact position between the wire electrode and the wire guide does not change, so that each axis correction amount is set to 0 (S14).

When the movement amount in the V-axis direction is positive (S13), the wire electrode moves away from the contact position of the wire guide immediately after the vertical projection. Then, until the contact portion of the wire guide on the opposite side comes into contact, the wire electrode does not contact the guide portion of the wire guide (S15). In this case, in the wire electrode, since the taper angle θ and the current-carrying member offset angles β _U , β _B have a front-back relationship, the current-carrying member offset angle β _U , β _B is adjusted so as to match the change in the current-carrying member offset angles β _U , β _B. The correction amount can be calculated by linear interpolation with the angles β _U and β _B (S16).

When the wire electrode comes into contact with the guide portion on the opposite side of the wire guide, in other words, when the taper angle θ is equal to or greater than the current-carrying member offset angles β _U and β _B (S17), It is shifted in the V-axis direction by the amount. After that, since the contact position between the wire electrode and the guide portion of the wire guide does not change, the error of the shifted position is maintained as it is. Therefore, only in this case, the clearance amount on both sides is set as the correction amount (S18).

  The wire cut electric discharge machining method according to the embodiment described above shows a correction amount calculation process using the wire cut electric discharge machining apparatus having the configuration shown in FIG. 4 as a specific example. Therefore, when the configuration of the moving body and the offset direction of the current-carrying body are different, it is necessary to make appropriate changes to the calculation process specifically shown in the embodiment, but this is a 4-axis control wire-cut electric discharge machining apparatus. If so, it can be similarly implemented.

  The wire cut electric discharge machining method of the present invention can be combined with other wire cut electric discharge machining methods as long as the effects of the present invention can be exhibited. For example, a correction value can be obtained in combination with a method of correcting a taper angle error caused by a change in posture caused by a deviation of a bending point of a wire electrode in a wire guide by correcting the position of the wire guide. . Or it can comprise so that correction amount may be calculated, changing a setting value according to consumption of an electrically-conductive body.

  INDUSTRIAL APPLICABILITY The present invention can be used in a wire-cut electric discharge machining apparatus having a configuration in which at least one of a pair of upper and lower wire guides has a clearance, and the pair of wire guides are relatively moved to incline the wire electrode with respect to the workpiece. . The present invention contributes to suppression of a reduction in machining shape accuracy of a wire cut electric discharge machining apparatus and improvement in workability.

It is a flowchart which shows the calculation process in preferable embodiment of the wire cut electric discharge machining method of this invention. It is a taper top view explaining the calculation system in the wire cut electric discharge machining method of the present invention. It is a guide top view of the lower wire guide explaining the calculation system in the wire cut electric discharge machining method of the present invention. It is the side view and guide top view which show schematic structure of the wire cut electric discharge machining apparatus in preferable embodiment of the wire cut electric discharge machining method of this invention.

Explanation of symbols

1 Wire Electrode 2 Upper Wire Guide 3 Lower Wire Guide 4 Upper Conductor 5 Lower Conductor

Claims (1)

  The combined movement direction and the combined movement amount of each axis are obtained from the command movement direction and the command movement amount of each axis of the taper shaft, and the one-axis direction of the taper shaft and the combined movement perpendicular to the axial direction in which the energizer pushes the wire electrode. The taper direction angle formed by the direction is calculated, and the correction amount is calculated from the taper direction angle and the clearance amount with the position where the clearance amount of the wire guide is shifted in the direction opposite to the offset direction of the current conductor as the center position of the wire electrode And controlling the relative movement between the wire electrode and the workpiece based on a movement command value obtained by adding the correction amount to the command movement amount of the machining axis or the taper axis. Processing method.

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