JP6982291B2 - Machine tool work processing method - Google Patents

Description

The present invention relates to a method of 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 of the headstock side. It is about.

When a machine tool is operated, the machine temperature rises due to machining heat, heat generation of motors and bearings, temperature rise of hydraulic oil and cutting fluid, etc., and the accompanying thermal deformation of each part of the machine tool lowers 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 machined at that time, the relationship between the temperature of each part of the machine and the machining error is obtained, and the command value of the machining program is corrected. By creating a calculation table, registering it in the controller, and correcting the command value of the machining program, machining errors are prevented from occurring.

Since the amount of thermal deformation of the machine tool can be considered to be proportional to the temperature, generally, as shown in FIG. 1, temperature sensors are placed at key points of the machine tool bed 11, the spindle base 12, and the tool post 3. With s1, s2 ... sn attached, the coefficients α1, α2 ... αn and the constant β that are multiplied by the detection values t1, t2 ... tn of each sensor are determined by test processing, and the correction value δ is calculated by the following equation. (Hereinafter referred to as "conventional type")
δ ＝ α1t1 ＋ α2t2 ＋ ・ ・ ・ αntn ＋ β
A method such as calculating with is adopted.

Since the machine tool processes the work into a three-dimensional shape, the above-mentioned correction value δ is also calculated as a correction value in each of the three-dimensional axial directions. For example, in the case of a lathe, the correction value in the Z-axis direction, which is the main axis direction, and the correction value in the X-axis direction, which is the cutting feed direction of the tool, are calculated. Is also calculated. Further, since the coefficient α and the constant β in the above calculation formula have different values depending on the position of the tool post, for example, in the case of a lathe, the coefficient α and the constant β are set as a function of the position of the tool post, or at a plurality of locations. The correction value at the intermediate position is determined by the interpolation calculation from the correction values on both sides, and the correction value according to the position of the tool post is determined.

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 at a predetermined time interval and the previous correction value δf is registered in advance adjacent to each other. When the set value is exceeded, the value obtained by adding the adjacent set value to the previous correction value δf is set as the correction value, the maximum value δmax and the minimum value δmin are registered, and the calculated correction value δ is the maximum. When it is larger than the value or smaller than the minimum value, it is proposed to use the maximum value or the minimum value as the correction value.

Further, 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 the machining error of the work are registered in advance in the controller and measured at the time of machining. It has been proposed to calculate the correction value based on the temperature of each part of the machine and the environmental temperature at a time separated by a time difference from the time of processing.

Japanese Unexamined Patent Publication No. 2005-014109 Japanese Unexamined Patent Publication No. 2006-055919

The main heat sources that thermally deform machines are the machining parts of hydraulic equipment and workpieces such as motors and bearings for spindles and rotary tool shafts, and hydraulic cylinders. The heat generated in the machined part of the work is transferred to the bed or table by the cutting oil flowing down from the machined part. The position of the main heat source differs depending on the type of machine tool. For example, in the case of a lathe, it is a spindle bearing, a tool motor mounted on a tool post, a hydraulic device, and a machining part. The cutting oil flowing down from the processed portion usually flows down onto a cover provided on the upper surface of the bed, and by heating this cover, the upper surface of the bed inside the cover is indirectly heated.

A sensor provided for measuring thermal deformation of a machine is attached to the surface of a mechanical member such as a headstock, a bed, and a tool post. On the other hand, the heat of the hydraulic device provided in the index device of the spindle bearing and the turret tool post is generated inside the machine. Therefore, there is a time delay before the heat generated inside the machine is detected by the sensor on the surface of the machine. Even if the temperature change inside the machine is not detected by the sensor due to the 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 the error of thermal deformation due to the time delay until the change in heat generation inside the machine is detected by the sensor.

It is considered that there is no significant change in the temperature rise of the spindle bearing in a lathe that only performs turning in which the spindle is constantly rotating. However, in a so-called compound lathe that can machine a workpiece with a rotary tool attached to the tool post with the spindle stopped, the spindle rotates or stops during the machining of one workpiece, so the spindle Frequently, the heat generated by the bearings fluctuates rapidly. Therefore, in a compound lathe in which a rotary tool is mounted on a tool post, the conventional means cannot sufficiently correct the correction of the thermal deformation error in which the spindle bearing serves as a heat source and the spindle is thermally deformed.

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

When the tool for finishing the work is indexed or at a predetermined timing, the spindle 1 is fixed in a predetermined arbitrary phase, and the tool T is placed on the peripheral surface of the chuck 2 or the work w mounted on the spindle. Bring the cutting edge into contact. The tool T to be brought into contact is a tool indexed for performing the next machining, and is preferably a finishing tool.

The contact is preferably detected by the 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 is used with a force (several N) that does not damage the cutting edge of the tool T to be contacted. The load fluctuation is detected, and the coordinates of the tool post 3 (X coordinates or XY coordinates on a lathe) when contact is detected are stored. The positions in the Z-axis direction in which the cutting edge is brought into contact are two predetermined positions A and B.

Accurately correct the thermal deformation by correcting the coordinates of the tool post 3 when contact is detected by comparing with the coordinates when corrected only by the conventional means, and more practically, the coordinates when measured last time. By registering the operation at the time of measurement in the controller 6 in advance, the correction value is automatically updated.

For example, the correction value δ for thermal deformation in the present invention is
It is calculated by an expression such as 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 inclination angle of the spindle, and S is Z from the measurement position (A or B) to the machining position P. Axial distance. γ and ε are sequentially updated at predetermined timings during workpiece processing.

The work processing method of the present invention directly measures the displacement of the machine 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. Correct the correction value by finding the difference (deviation) from the actual displacement when measured and corrected by the conventional method.

By setting the positions where the cutting edge of the tool T comes into contact with the two positions A and B separated by a predetermined distance in the spindle direction, it is possible to detect the positional deviation and the tilt deviation, and the positions A and B where the positions are detected are processed. It is possible to more accurately correct the correction value when the position P is far from the position P. In the method of contacting the cutting edge of the tool with the peripheral surface of the work w to obtain the correction value, the work w is damaged due to the difference in hardness between the work and the cutting edge of the tool, but the deviation is detected before the finishing process of the work w. The scratches can be removed by finishing. When high-precision machining is specified for a part of the work, the deviation may be detected at the specified position.

In the present invention, not only the temperature of the machine surface is used to indirectly correct the thermal deformation, but also the indirectly corrected thermal deformation is further corrected by making corrections based on the actual deformations that are sequentially updated at predetermined intervals. Therefore, it is possible to make corrections corresponding to sudden temperature changes inside the machine. Then, using a cutting tool, the position of the cutting edge is contacted with the chuck or workpiece to sequentially correct the correction value, so there is no need to use a toolsetter, there is no need to stop the machine, and accurate machining dimension correction is performed even during continuous machining. Will be possible.

Further, 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 the necessary correction can be sequentially performed even during unmanned operation.

Block diagram of an embodiment Schematic side view of a slant type lathe The figure which showed the example of measurement on the peripheral surface of a chuck Explanatory diagram showing the relationship between the correction value and the correction value in FIG. The figure which showed the example of measuring on the peripheral surface of a work Explanatory diagram showing the relationship between the correction value and the correction value in FIG. A diagram similar to FIG. 1 in a more practical embodiment

Hereinafter, the present invention will be further described with reference to the drawings. 1 and 2 are diagrams schematically showing a slant-type turret lathe having the simplest structure. The slant-type lathe comprises a bed 11 with a slanted top surface. The headstock 12 rises vertically from the bed 11, and the spindle 1 is pivotally supported above the headstock 12 by a headstock bearing 13 shown by a dotted line in the figure. A chuck 2 is attached to the tip of the main shaft 1, and a chuck opening / closing cylinder 14 is attached to the rear end. The spindle motor 15 that rotates the spindle is attached to the headstock 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 type lathe tends to be displaced in the X-axis direction due to the difference in the rising height between the left and right sides of the headstock 12 from the bed 11 and the heat generated by the spindle motor 15, and the temperature in the Z-axis direction is high. Due to thermal deformation due to imbalance, it may be slanted with respect to the X-axis (see one-dot chain line d1 and two-dot chain line d2 in FIGS. 4 and 6).

The tool post 3 is provided on the bed 11 on a lateral moving table 21 that is movable in the Z-axis direction (main axis axis direction) so as to be movable in the X-axis direction (tool cutting feed direction). The lateral moving table 21 is screwed into a Z-axis feed screw 26z that rotates forward and reverse with the Z-axis feed motor 4z. The tool post 3 is screwed into an X-axis lead screw 26x that is rotated forward and reverse by an X-axis motor 4x mounted on a lateral moving 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 for fixing the indexing position of the turret 23, and includes a motor 24 for indexing rotation of the turret and a tool motor 25 for driving a rotary tool attached to the turret. There is.

The Z-axis feed motor 4z and the X-axis feed motor 4x are controlled by the controller 6 via the servo amplifiers 5z and 5x. The controller 6 outputs position commands ez and ex for each motor to the servo amplifiers 5z and 5x based on the machining program 31. On the other hand, the feedback signals fz and fx are returned to the servo amplifiers 5z and 5x from the feed motors 4z and 4x. 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. Upon receiving the contact signal h, the controller 6 sends a stop command i to the X-axis feed motor 4x to immediately stop the contact signal h. It is desirable to use a servo amplifier 5x that can detect the position deviation c at a time interval of 0.1 milliseconds.

Temperature sensors s1, s2 ... Sn are attached to the bed 11, the headstock 12 and the tool post 3 at appropriate positions, and the controller 6 has detected values t1, t2 ... Tn of these temperature sensors. A correction means 32 for calculating a correction value based on the above is provided.

When the machine is operated, the heat from the heat source of each part causes thermal deformation of the machine. The temperature of each part of the machine is detected by the temperature sensors s1, s2 ... Sn, and the calculation formula of the 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 the same arithmetic expression as the conventional one δx ＝ αx1t1 ＋ αx2t2 ＋ αx3t3 ＋ ・ ・ ・ ＋ αxntn ＋ βx
Is explained 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 by the correction values δz and δx calculated based on the above equation, and the position commands ez of each motor 4z and 4x are corrected. , Ex.

The positions of the spindle 12, the chuck 2, and the work w as seen from the tool post 3 after being corrected by the correction means 32 of FIG. 1, that is, after being corrected by the conventional method, are shown in FIGS. 4 and 6, for example, the alternate long and short dash line d1. Will be shown by. That is, the position of the tool cutting edge after being corrected by the conventional method when machining the machining point p of the work w becomes the position of the point p1, and by setting the tool cutting edge to the point p1, the machining of the point p of the work can be performed. It is supposed to be done. The position of the point p1 in FIG. 6 is the position before the processing of the next step is performed. The outer circumference of the product is a position where, for example, only the finishing allowance is cut off from this position. Further, the diameters of the workpieces at the measurement positions A and B do not have to be the same.

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

The controller 6 is set 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 work w. It includes a measurement operation setting means 33 provided with a device, and a 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 measurement operation setting means 33 fixes the spindle 1 to a set phase when the finishing tool T is indexed or at a predetermined timing during machining, and the measuring operation setting means 33 of the tool indexed at that time. The cutting edge is moved to one of the set Z-axis positions A and B, and the tool cutting edge is brought close to the outer periphery of the chuck 2 or the work w at that position at a low speed. 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 cutting edge corrected by the correction means 32 should come into contact with the chuck 2 or the work w. Upon receiving the contact signal h, the measurement operation setting means 33 stops the X feed motor 4x, and at the measurement position after correcting with the X coordinate (X coordinate of the point a2) of the tool post 3 at that time and the correction means 32. The difference Δxa from the command value of the X coordinate (X coordinate of the point a1) is calculated and stored.

The measurement operation setting means 33 then retracts the tool cutting edge in the X-axis direction, then moves to the other measurement position B, and performs the same operation as the X coordinate of the tool post 3 (X coordinate of the point b2) and the correction means. The difference Δxb from the command value of the X coordinate (X coordinate of the point b1) after the correction in 32 is calculated and stored.

The correction means 34 is from the detected deviation γ = Δxa in the X-axis direction and the measurement position (position A in the example of the figure) where the inclination angle of the main axis (Δxa−Δxb) / L is γ to the machining position P of the work. With the value multiplied by the distance S, the correction value in the x-axis direction at the machining position P is γ + εS = Δxa + (Δxa−Δxb) S / L.
Calculate with.

In the above operation, the direction in which the tool cutting edge is brought closer to the peripheral surface of the chuck is best in the horizontal direction, but in the case of the slant type, the tool cutting edge is moved from above to below. This is because the contact between the tool cutting edge and the peripheral surface of the chuck is detected more quickly due to 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 designated value of the machining program is corrected by the arithmetic expression set in the correction means 32 and the correction value set in the correction means 34, and the position command ex is given to the x-axis feed motor 4x. Then, when the finishing tool is indexed or 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 work.

In the above description, in order to facilitate understanding, it is described that the correction means 32 calculates the correction value by the conventional method, the correction means 34 calculates the correction value according to the present invention, and the correction means 34 adds both to correct the command value. However, it is more practical to register the arithmetic expression with the correction value added to the correction means 32. The arithmetic expression registered in the correction means 32 in this case is
δx ＝ αx1t1 ＋ αx2t2 ＋ αx3t3 ＋ ・ ・ ・ ＋ αxntn ＋ βx ＋ Δx ＋ (Δxa−Δxb) × S / L
Will be. 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 time of the previous measurement as shown in parentheses in FIGS. 4 and 6. Since it is the difference between the value and the values of Δag and Δbg at the time of this measurement, the correction means 34 calculates this difference and updates γ and ε of the calculation formula for obtaining δ registered in the correction means 32. It works (see Fig. 7).

The above equation is a correction value based on a geometric calculation assuming that the thermal deformation error on the tool post 3 side is correctly corrected by the correction value calculated by the correction means 32, but in reality, it is the above-mentioned correction value. By measuring the dimensional error when the workpiece is actually machined based on such an idea, it should be possible to make more accurate correction by multiplying γ and ε by the required coefficients. ..

If the tool post 3 is a lathe that also moves in the Y-axis direction, the same inspection as the detection operation in the X-axis direction described above is performed in the Y-axis direction as well, and the correction value in the Y-axis direction is calculated. Further, when the lathe is a two-spindle facing lathe and both ends of a long work are gripped by facing chucks for processing, the deviation γL from the position after correction by the correction means 32 of the left and right LR spindles, γR, εL, and εR are detected, respectively, and the deviation in the X-axis direction is the amount obtained by interpolating the deviations ΔxL and ΔxR in the X-direction at both ends at the position of the machining point. The amount of bending at the machining point of the work may be calculated and corrected from the positional deviation of both ends and the deviation of the inclination angle by the calculation formula of the support beam at both ends, which is well known in the above.

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

Claims (2)

In the work machining method of a machine tool equipped with a means for correcting machining errors due to thermal deformation due to temperature changes.
At a predetermined timing registered when or pre controller precise machining process, such as the finishing step is started, to stop the main shaft at a predetermined phase, advance a cutting edge of the tool attached to the tool rest of the machine tool It feeds at low speed toward the peripheral surface of the spindle chuck or the peripheral surface of the work gripped by the spindle chuck at two measurement positions separated by a predetermined distance in the specified spindle axis direction, and the load of the feed motor is applied at each measurement position. When the set load is reached, the feed motor is stopped and the correction value is based on the difference between the coordinates of the turret at that time and the position where the turret should be when the tool cutting edge is located at the measurement position. A machine tool work machining method characterized in that the correction value is corrected and the position of the tool post is corrected by the corrected correction value until the next measurement timing. The work of the machine tool according to claim 1 , wherein the position where the tool post should be when the tool cutting edge is located at the measurement position is the position of the tool post corrected by the correction value corrected based on the previous measurement. Processing method.

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