JP2019000945A - Workpiece machining method of machine tool - Google Patents

Abstract

To correct a machining error caused by a time delay before a temperature change in a machine is detected by a temperature sensor provided in a machine due to heat transfer delay, concerning a machining method capable of correcting a machining error based on heat deformation of a machine tool more accurately.SOLUTION: A main shaft 1 is fixed in a predetermined phase when a tool for finish machining of a workpiece is indexed or in a predetermined timing, and a cutting edge of a tool T is brought into contact with a peripheral surface of a spindle chuck 2 or the workpiece w. Preferably, the detection of the contact may be detected by the change of a servo current value of a feed motor 4x of a tool post 3, the load fluctuation of the feed motor 4x is detected by the force (number N) not damaging a tool cutting edge, and the coordinate of the tool post 3 at the time when detecting the contact is stored. The coordinate of the tool post 3 at the time when detecting the contact is corrected by being compared with the coordinate obtained when corrected only by conventional means or the coordinate obtained when measured last time, and thereby a correction value is updated automatically.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for machining a workpiece by correcting a machining error caused by thermal deformation of a machine tool, and in particular, a machining method capable of more accurately correcting a machining error based on thermal deformation on the headstock side. It is about.

  When the machine tool is operated, the machine temperature rises due to the processing heat, the heat generation of the motor and the bearing part, the temperature rise of the hydraulic oil and the cutting fluid, and the thermal deformation of each part of the machine tool accompanying it decreases the machining accuracy of the workpiece. Therefore, by measuring the temperature of each part of the machine tool and measuring the machining error of the workpiece that was machined at that time, the relationship between the temperature of each part of the machine and the machining error is obtained, and an arithmetic expression or correction for correcting the command value of the machining program An arithmetic table is created, registered in the controller, and the machining program command value is corrected to prevent machining errors.

Since the amount of thermal deformation of the machine tool may be considered to be proportional to the temperature, generally, as shown in FIG. s1, s2,..., sn are attached, and coefficients α1, α2,..., αn and constant β are multiplied by the detected values t1, t2,. (Hereafter referred to as “conventional”)
δ = α1t1 + α2t2 ++ αntn + β
The method of calculating with is adopted.

  Since the machine tool processes the workpiece into a three-dimensional shape, the correction value δ is also calculated as a three-dimensional correction value in each axial direction. For example, in the case of a lathe, correction values in the Z-axis direction that is the main axis direction and the X-axis direction that is the cutting feed direction of the tool are calculated, and in a lathe that moves the rotary tool in the Y-axis direction, the correction value in the Y-axis direction Is also computed. In addition, the coefficient α and the constant β in the above arithmetic expression are different values depending on the position of the tool rest. For example, in a lathe, the coefficient α and the constant β are set as a function of the position of the tool rest, or a plurality of positions A correction value corresponding to the position of the tool post is determined in such a manner that the correction value at the intermediate position is obtained and the correction value at the intermediate position is obtained by interpolation calculation from the correction values on both sides.

  As a means for improving the accuracy of the correction value by the above calculation, for example, in Patent Document 1, the difference between the correction value δ calculated every predetermined time interval and the previous correction value δf is registered in advance. When the set value is exceeded, the value obtained by adding the adjacent set value to the previous correction value δf is used as the correction value, the maximum value δmax and the minimum value δmin are registered, and the calculated correction value δ is the maximum value. When the value is larger than the minimum value or smaller than the minimum value, it has been proposed to use the maximum value or the minimum value as a correction value.

  In Patent Document 2, a coefficient for calculating a correction amount based on a change in the environmental temperature and a time difference when the environmental temperature affects a workpiece machining error are registered in a controller in advance, and measured during machining. It has been proposed to calculate a correction value from the temperature of each part of the machine and the ambient temperature at a time separated from the time of machining by a time difference.

Japanese Patent Laid-Open No. 2005-014109 JP 2006-055919 A

  Main heat sources for thermally deforming the machine are motors and bearings of main shafts and rotary tool shafts, hydraulic devices such as hydraulic cylinders, and workpiece processing parts. The heat generated in the workpiece processing part is transferred to the bed or table by the cutting oil flowing down from the processing part. The position of the main heat source varies depending on the type of machine tool. For example, in the case of a lathe, it is a spindle motor, a tool motor mounted on a tool post, a hydraulic device, and a machining unit. The cutting oil that flows down from the processing portion normally flows down on a cover provided on the upper surface of the bed, and the upper surface of the bed inside is indirectly heated by heating the cover.

  A sensor provided for measuring thermal deformation of a machine is attached to the surface of a machine member such as a headstock, a bed, or a tool post. On the other hand, the heat of the hydraulic device provided in the index device of the spindle bearing or the turret tool post is generated inside the machine. Therefore, there is a time delay until the heat generated in the machine is detected by the sensor on the machine surface. Even if a temperature change inside the machine is not detected by the sensor due to a delay in heat transfer, thermal deformation occurs inside the machine, and the deformation affects the entire machine without causing a time delay. With the conventional method as described above, it is not possible to correct an error in thermal deformation due to a time delay until a change in heat generation in the machine is detected by a sensor.

  In a lathe that performs only turning with the main spindle rotating at all times, it is considered that there is no significant fluctuation in the temperature rise of the main spindle bearing. However, in a so-called compound lathe that can machine a workpiece with a rotary tool attached to the tool post while the spindle is stopped, the spindle rotates or stops during machining of one workpiece. Frequently, the heat generated in the bearing fluctuates rapidly. Therefore, in a compound lathe with a rotating tool mounted on the tool post, the conventional means cannot sufficiently correct the thermal deformation error that causes the main shaft bearing to be a heat source and thermally deforms the main head.

  It is an object of the present invention to provide a workpiece machining method capable of correcting a machining error caused by a time delay until a temperature change in a machine is detected by a temperature sensor provided in the machine due to a heat transfer delay. It is said.

  When the tool for finishing the workpiece is determined or at a predetermined timing, the spindle 1 is fixed at a predetermined arbitrary phase, and the chuck 2 mounted on the spindle or the tool T on the peripheral surface of the workpiece w is fixed. Touch the cutting edge. The tool T to be contacted is a tool determined for performing the next machining, and is preferably a finishing tool.

  The contact is preferably detected by a change in the servo current value of the feed motor 4x of the tool post 3 on which the tool T is mounted, and the feed motor 4x with a force (several N) that does not damage the cutting edge of the tool T to be contacted. And the coordinates of the tool post 3 when the contact is detected (X coordinate or XY coordinate on a lathe) are stored. The positions in the Z-axis direction with which the cutting edge is brought into contact are two predetermined positions A and B.

  Correct the thermal deformation by correcting the coordinates of the tool post 3 when contact is detected by correcting the coordinates of the tool post 3 only with the conventional means, and more practically compared with the coordinates of the last measurement. The correction value is automatically updated by registering the operation for measurement in the controller 6 in advance.

For example, the thermal deformation correction value δ in the present invention is
δ = α1t1 + α2t2 + α3t3 +... + αntn + β + γ + εS Here, γ is a correction term set by measuring the displacement of the spindle, ε is a correction coefficient set by measuring the tilt angle of the spindle, and S is a Z from the measurement position (A or B) to the machining position P. Axial distance. γ and ε are sequentially updated at a predetermined timing during workpiece machining.

  In addition to the conventional method of measuring the temperature of each part of the machine with temperature sensors s1, s2,..., Sn and indirectly measuring and correcting the thermal deformation of the machine, the workpiece machining method of the present invention directly measures the displacement of the machine. The correction value is corrected by obtaining a difference (deviation) between the actual displacement and the actual displacement measured and corrected.

  The positions where the cutting edge of the tool T is brought into contact are two positions A and B that are separated by a predetermined distance in the main axis direction, so that it is possible to detect positional deviation and inclination deviation. The correction value can be corrected more accurately when the position P is away from the position P. In the method of obtaining the correction value by bringing the tool edge into contact with the peripheral surface of the work w, the work w is damaged due to the difference in hardness between the work and the tool edge, but the deviation is detected before finishing the work w. Therefore, the scratch can be removed by finishing. When high-precision machining is specified for a part of the workpiece, it is only necessary to detect the deviation at the specified position.

  In the present invention, not only the thermal deformation is indirectly corrected using the temperature of the machine surface, but also the corrected thermal deformation is further corrected by adding a correction based on an actual deformation that is sequentially updated at predetermined intervals. Therefore, correction corresponding to a sudden temperature change in the machine is possible. The correction value is sequentially corrected by using the cutting tool to contact the position of the cutting edge with the chuck or workpiece, so there is no need to use a tool setter, no need to stop the machine, and accurate machining dimension correction even during continuous machining. Is possible.

  Furthermore, since it is not necessary to prepare a new measuring device and the measurement can be performed automatically in a short time, the influence on the machining cycle is small, and necessary corrections can be sequentially performed even during unmanned operation.

Example block diagram Schematic side view of slant type lathe Diagram showing an example of measurement on the chuck surface Explanatory drawing which shows the relationship between the correction value and correction value in FIG. Diagram showing an example of measuring on the peripheral surface of a workpiece Explanatory drawing which shows the relationship between the correction value and correction value in FIG. Figure similar to Figure 1 in a more practical embodiment

  The present invention will be further described below with reference to the drawings. 1 and 2 are views schematically showing a slant turret lathe having the simplest structure. The slant type lathe includes a bed 11 whose upper surface is inclined. The headstock 12 stands vertically from the bed 11, and the main shaft 1 is pivotally supported by a main shaft bearing 13 indicated by a dotted line in the drawing. A chuck 2 is attached to the front end of the main shaft 1, and a chuck opening / closing cylinder 14 is attached to the rear end. A spindle motor 15 that rotates the spindle is attached to the spindle stock 12, and the rotating shaft of the spindle motor 15 and the spindle 1 are connected by a synchronous belt device 16.

  The spindle 1 of the slant lathe tends to be displaced in the X-axis direction due to the difference between the left and right rising heights in FIG. 2 from the bed 11 of the headstock 12 and the heat generated by the spindle motor 15, and the temperature of the Z-axis lathe Due to thermal deformation due to imbalance, it may become oblique with respect to the X-axis (see the one-dot chain line d1 and the two-dot chain line d2 in FIGS. 4 and 6).

  The tool post 3 is provided on a bed 11 so as to be movable in the X-axis direction (cutting feed direction of the tool) on a lateral movement table 21 that is movable in the Z-axis direction (spindle axis direction). The lateral movement table 21 is screwed to a Z-axis feed screw 26z that is rotated forward and backward by a Z-axis feed motor 4z. The tool post 3 is screwed to an X-axis feed screw 26 x that is rotated forward and backward by an X-axis motor 4 x mounted on the lateral movement table 21. A turret 23 is mounted on the tool post 3 via an indexing device 22. The indexing device 22 has a built-in hydraulic device that fixes the indexing position of the turret 23, and includes a motor 24 for indexing rotation of the turret and a tool motor 25 that drives a rotary tool attached to the turret. Yes.

  The Z-axis feed motor 4z and the X-axis feed motor 4x are controlled by the controller 6 via servo amplifiers 5z and 5x. The controller 6 outputs position commands ez and ex for the respective motors to the servo amplifiers 5z and 5x based on the machining program 31. On the other hand, feedback signals fz and fx are returned from the feed motors 4z and 4x to the servo amplifiers 5z and 5x. A position deviation c, which is a difference signal between the command signal ex of the X-axis feed motor 4x and the feedback signal fx, is given to the contact detector 7. The contact detector 7 sends a contact signal h to the controller 6 when the position deviation c exceeds a preset set value. When receiving the contact signal h, the controller 6 sends a stop command i to the X-axis feed motor 4x and immediately stops it. As the servo amplifier 5x for detecting the position deviation c, it is desirable to use a servo amplifier that can detect the position deviation at a time interval of 0.1 millisecond.

  Temperature sensors s1, s2,... Sn are attached to appropriate portions of the bed 11, the spindle stock 12 and the tool post 3, and the controller 6 detects the detected values t1, t2,. The correction means 32 which calculates a correction value based on this is provided.

When the machine is operated, the machine is thermally deformed by the heat from the heat source of each part. The temperature of each part of the machine is detected by temperature sensors s1, s2,... Sn, and an arithmetic expression of a thermal deformation correction value δ based on the detected temperature of these temperature sensors is registered in the correction means 32. In order to facilitate understanding, in FIG. 1, the correction means 32 has an arithmetic expression similar to that in the prior art: δx = αx1t1 + αx2t2 + αx3t3 +.
Will be described as being registered. For machining and rough machining of workpieces that do not require high accuracy, the specified values specified in the machining program 31 are corrected with correction values δz and δx calculated based on the above formula, and the position commands ez of the motors 4z and 4x are corrected. , Ex.

  The positions of the head stock 12, the chuck 2 and the workpiece w as viewed from the tool post 3 after being corrected by the correcting means 32 in FIG. 1, that is, after being corrected by the conventional method, are shown in FIG. As shown in That is, the position of the tool edge after being corrected by the conventional method when machining the machining point p of the workpiece w becomes the position of the point p1, and the machining of the point p of the workpiece can be performed by setting the tool edge to the point p1. Is going to be done. Note that the position of the point p1 in FIG. 6 is the position before the next process is performed. The outer periphery of the product is a position cut from this position, for example, by a finishing allowance. Moreover, the diameter of the workpiece | work in measurement position A and B does not need to be the same.

  However, for the reasons described above, the thermal deformation cannot be completely corrected only by the correction calculation of the correction means 32 using the conventional calculation formula. That is, the actual positions of the headstock, chuck, and workpiece as viewed from the tool post are deviated from the one-dot chain line d1 calculated by the correcting means 32 as shown by a two-dot chain line d2 in FIGS. . The deviations Δa and Δb are deviations that should be further corrected (corrected) in the X-axis direction from the values corrected by the correction means 32. 4 and 6, Δa, Δb and δa, δb are shown at substantially equal intervals, but in reality, Δa, Δb are smaller than δa, δb.

  The controller 6 is configured to set a predetermined spindle phase, for example, an origin phase, and two predetermined Z-axis positions A and B (see FIGS. 3 and 5) on the peripheral surface of the chuck 2 or the workpiece w. Measurement operation setting means 33 provided with a measuring device, and correction means 34 for further correcting (correcting) the correction value corrected by the correction means 32.

  It is during finishing that it is necessary to more accurately correct the thermal deformation of the machine. The measuring operation setting means 33 fixes the spindle 1 to the set phase when the finishing tool T is indexed or at a predetermined timing during machining, and the tool that is indexed at that time is fixed. The cutting edge is moved to one of the set Z-axis positions A and B, and the tool cutting edge is approached at a low speed toward the outer periphery of the chuck 2 or the workpiece w at the position. When the position deviation c exceeds the set value during this low speed approach, the contact detector 7 outputs a contact signal. The position of the tool post detected at this time is deviated by Δa and Δb from the position where the tool edge after being corrected by the correcting means 32 should be in contact with the chuck 2 or the workpiece w. Upon receiving the contact signal h, the measurement operation setting means 33 stops the X feed motor 4x, and the X coordinate (X coordinate of the point a2) of the tool post 3 at that time and the measurement position after correction by the correction means 32. The difference Δxa from the X coordinate command value (the X coordinate of the point a1) is calculated and stored.

  The measurement operation setting means 33 next retracts the tool blade edge in the X-axis direction and then moves to the other measurement position B, and the X coordinate of the tool post 3 (X coordinate of the point b2) and the correction means by the same operation. The difference Δxb from the X coordinate command value (the X coordinate of the point b 1) after correction at 32 is calculated and stored.

The correction means 34 detects from the detected position γ = Δxa in the X-axis direction and the measurement position (position A in the example in the figure) from the tilt angle (Δxa−Δxb) / L of the spindle to the machining position P of the workpiece. The correction value in the x-axis direction at the machining position P is obtained by multiplying the distance S by γ + εS = Δxa + (Δxa−Δxb) S / L
Calculate with.

  In the above operation, the direction in which the tool edge approaches the chuck peripheral surface is best in the horizontal direction, but in the case of the slant type, the tool blade tip is moved from the upper side to the lower side. This is because contact between the tool blade edge and the chuck peripheral surface is detected more quickly based on the relationship between the feed load acting on the X-axis motor 4x and the weight of the tool post.

  In the subsequent machining, the specified value of the machining program is corrected with the arithmetic expression set in the correction means 32 and the correction value set in the correction means 34 to obtain a position command ex to be given to the x-axis feed motor 4x. When the finishing tool is next determined or when the set timing comes, the set value of the correction means 34 is changed by the same operation to perform automatic continuous machining of the workpiece.

In the above description, for the sake of easy understanding, the correction means 32 calculates the correction value according to the conventional method, the correction means 34 calculates the correction value according to the present invention, and adds both to correct the command value. However, it is more practical to register an arithmetic expression with a correction value added to the correction means 32. In this case, the arithmetic expression to be registered in the correction means 32 is
δx = αx1t1 + αx2t2 + αx3t3 + ... + αxntn + βx + Δx + (Δxa−Δxb) × S / L
It becomes. In this case, δa and δb in FIGS. 4 and 6 are the values of δ calculated by the above equation, and Δa and Δb are the values of Δaf and Δbf at the previous measurement as shown in parentheses in FIGS. Since this is the difference between the value and the values of Δag and Δbg at the time of the current measurement, the correction means 34 calculates the difference and updates γ and ε in the calculation formula for obtaining δ registered in the correction means 32. Operation is performed (see FIG. 7).

  The above equation is a correction value based on a geometric calculation when it is assumed that the thermal deformation error on the tool post 3 side is correctly corrected with the correction value calculated by the correction means 32. It should be possible to perform more accurate correction by multiplying γ and ε by the necessary coefficient by measuring the dimensional error when the workpiece is actually machined based on such a concept. .

  If the tool post 3 is a lathe that also moves in the Y-axis direction, the inspection similar to the detection operation in the X-axis direction described above is also performed in the Y-axis direction, and a correction value in the Y-axis direction is calculated. Further, when the lathe is a two-spindle opposed lathe and grips both ends of a long workpiece with opposing chucks, a deviation γL from the position after correction by the correction means 32 of the left and right L-R spindles, γR, εL, and εR are detected respectively, and the deviation in the X-axis direction is an amount obtained by interpolating the deviations ΔxL and ΔxR in the X direction at both ends at the position of the machining point. It is only necessary to calculate and correct the amount of deflection at the machining point of the workpiece from the positional deviation of both ends and the deviation of the inclination angle by a well-known calculation formula for both-end support beams.

1 Spindle 2 Chuck 3 Tool post 4x Feed motor 6 Controller T Tool w Workpiece

Claims (4)

In a workpiece machining method of a machine tool provided with a means for correcting a machining error caused by thermal deformation accompanying a temperature change,
When a highly accurate machining process such as a finishing process is started or at a predetermined timing registered in the controller in advance, the spindle is stopped at a predetermined phase, and the cutting edge of the tool mounted on the tool post of the machine is determined in advance. Feeds at a low speed toward the peripheral surface of the main spindle chuck or the peripheral surface of the workpiece gripped by the main spindle chuck at the measured position, and stops the feed motor when the load of the feed motor reaches the set load. The correction value is corrected with a correction value based on the difference between the coordinates of the tool post at the time and the position of the tool post when the tool edge is located at the measurement position, and the correction is made until the next measurement timing. A workpiece machining method for a machine tool, wherein machining is performed by correcting the position of the tool post with the corrected value.   The measurement positions are two positions separated by a predetermined distance in the spindle axis direction, and the coordinates of the tool post detected at the two positions and the position where the tool post should be when the tool edge is located at the measurement position. The workpiece machining method for a machine tool according to claim 1, wherein the correction value is calculated based on a difference.   A work machining method for a machine tool, wherein a position where the tool post should be when the tool cutting edge is located at the measurement position is a position of the tool post corrected with a correction value corrected based on a previous measurement.   Detects the load fluctuation of the tool post feed motor based on the position deviation that is the difference signal between the position command given to the tool post feed motor, which is a servo motor, and the position feedback signal. Machine tool work machining method from bottom to bottom or horizontal.

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