JP2012232385A - Numerical control device and machining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a numerical control device and machining method, capable of highly precisely machining a workpiece in a machine tool, and capable of greatly shortening a machining time.SOLUTION: Data showing a relationship between a rotation speed S and a thermal displacement T of a spindle 7 is measured in advance and is stored. With the data, the thermal displacement Tn of the spindle 7 and a standard thermal displacement TO at a contact point Pn of a tool 73 and a workpiece W are found, and a machining error TnO at the contact point Pn is found (Steps 1 to 4). Then, Rotation speeds Sn and SSn of the spindle 7 are decided so that the machining error TnO is within the allowable error An of the workpiece, and the rotation standard speed SO of the spindle 7 commanded in an NC program and the feed standard speed FO of a table 3 are changed (Steps S5 to 9). Because the above treatment is done for each machining portion in a machining step (one machining step) with the same tool 73, the machining time is greatly shorened compared with the past, while the high machining precision for the workpiece is maintained.

Description

  The present invention relates to a numerical control device (hereinafter referred to as an NC device) and a processing method for processing a workpiece by numerically controlling a machine tool, and in particular, processing the rotational speed of a spindle on which a tool is mounted with the same tool. The present invention relates to an NC apparatus and a processing method that are changed depending on a processing site in a process.

  Generally, an NC device of a machine tool processes a workpiece by rotating a spindle on which a tool is mounted at a constant rotational speed. However, for example, the tool diameter at the contact point between the tool and the workpiece when machining the inclined surface of the workpiece with a tool whose rotation axis is oriented in the vertical direction is the same as the tool and the workpiece when machining the vertical surface of the workpiece. It may be smaller than the tool diameter at the point of contact with the object. In this case, the processing speed when processing the inclined surface of the workpiece is lower than the processing speed when processing the vertical surface of the workpiece. Therefore, the machining time of the workpiece can be shortened by setting the machining speed for machining all the surfaces of the workpiece to the machining speed for machining the vertical surface. For this purpose, it is necessary to change the rotational speed of the spindle which is proportional to the machining speed. However, when the rotational speed of the main shaft is changed, the amount of heat generated in the main shaft also changes and the amount of thermal displacement of the main shaft fluctuates, so that the machining accuracy tends to decrease.

  Thus, for example, Japanese Patent Application Laid-Open No. 2002-239882 (Patent Document 1) and Japanese Patent Application Laid-Open No. 5-277894 (Patent Document 2) describe NC devices having a thermal displacement correction function. In the NC apparatus described in Patent Document 1, different thermal displacement coefficients assigned by dividing the spindle rotational speed into a plurality from low speed to high speed are preset. Then, the NC device performs optimal thermal displacement correction by changing the thermal displacement coefficient in accordance with the spindle rotational speed from a numerical control program (hereinafter referred to as NC program). Thereby, highly accurate processing can be performed. Further, the NC device described in Patent Document 2 stores in advance correction values such as the position of each feed shaft corresponding to the main shaft rotation speed (main shaft rotation speed). Then, the NC device corrects the position and the like of each feed shaft based on the correction value corresponding to the commanded spindle rotation speed. Thereby, highly accurate processing can be performed.

Japanese Patent Laid-Open No. 2002-239872 JP-A-5-277894

  In the NC devices described in Patent Documents 1 and 2 described above, in machining a workpiece that is a machining process in which a plurality of machining processes (one machining process) using the same tool are combined, the spindle rotation speed is changed for each machining process. Since the thermal displacement correction is performed, the processing time in all the processing steps can be shortened. However, in recent years, in machining a workpiece, further reduction in machining time is desired.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an NC apparatus and a machining method capable of machining a workpiece with high accuracy in a machine tool and greatly reducing machining time. .

(NC device)
(Claim 1) An NC apparatus according to the present invention is an NC apparatus that changes the rotational speed of a spindle on which a tool is mounted in a machine tool depending on a machining site in a machining process using the same tool, and at least the machine tool. NC program for numerically controlling the machine, data relating to the tool, data relating to the workpiece, and storage means in which data indicating the relationship between the rotational speed of the spindle and the amount of thermal displacement is stored in advance, and the tool Based on the data and the data on the workpiece, contact point calculation means for calculating the contact point between the tool and the workpiece, and on the basis of the data on the tool, the rotation speed of the spindle at the calculated contact point is calculated. Based on the data indicating the relationship between the spindle rotation speed calculation unit to be calculated, the rotation speed of the spindle and the amount of thermal displacement, the calculated Thermal displacement amount calculating means for calculating a thermal displacement amount of the main spindle from a rotation speed of the shaft and a reference rotation speed of the main spindle specified in the NC program; and the workpiece instructed in the NC program. Comparison means for comparing the machining accuracy of the spindle and the calculated thermal displacement amount of the spindle, and the NC program so that at least the thermal displacement amount of the spindle is within the machining accuracy range of the workpiece. Spindle rotation speed changing means for changing the commanded rotation reference speed of the spindle, and the relative reference feed speed of the tool and the workpiece commanded to the NC program based on the changed rotation speed of the spindle The workpiece based on the NC program in which the rotation reference speed of the spindle and the relative reference feed speed of the tool and the workpiece are changed. Comprising a machining control means for numerically controlling the processing, the.

  (Claim 2) The rotation reference speed of the spindle commanded to the NC program is set based on the maximum diameter of the tool used when machining by the NC program and an appropriate machining speed of the tool, The spindle rotation speed calculation unit may calculate the rotation speed of the spindle at the contact point based on the calculated diameter of the tool at the contact point and an appropriate machining speed of the tool.

  (Claim 3) The rotation reference speed of the spindle commanded by the NC program is determined by the maximum diameter in the contact range of the tool that comes into contact with the workpiece when machining by the NC program, and the appropriate tool Based on the machining speed, the spindle rotation speed calculation unit calculates the rotation speed of the spindle at the contact point based on the calculated diameter of the tool at the contact point and the appropriate machining speed of the tool. You may do it.

(Processing method)
(Claim 4) The machining method of the present invention is a machining method in which the rotational speed of a spindle on which a tool in a machine tool is mounted is changed depending on a machining site in a machining process using the same tool, and at least the machining An NC program for numerically controlling the data, data relating to the tool, data relating to the workpiece, and data indicating the relationship between the rotational speed of the spindle and the amount of thermal displacement, data relating to the tool, and A contact point calculation step for calculating a contact point between the tool and the workpiece based on data relating to a workpiece, and a spindle for calculating a rotation speed of the spindle at the calculated contact point based on data relating to the tool Based on the rotation speed calculation step and data indicating the relationship between the rotation speed of the spindle and the amount of thermal displacement, the calculated rotation of the spindle is calculated. A thermal displacement amount calculating step for calculating a thermal displacement amount of the main spindle from the speed and a rotation reference speed of the main spindle specified in the NC program; and a machining accuracy of the workpiece specified in the NC program. And a comparison step that compares the calculated magnitude of the thermal displacement of the spindle with the NC program so that at least the thermal displacement of the spindle is within the machining accuracy range of the workpiece. A spindle rotation speed changing step for changing the rotation reference speed of the spindle, and a relative feed reference speed of the tool and the workpiece commanded by the NC program is changed based on the changed rotation speed of the spindle. Based on the NC program in which the feed speed changing step, the rotation reference speed of the spindle and the relative feed reference speed of the tool and the workpiece are changed, the workpiece is processed. Comprising a processing control step of value control, the.

  (Claim 1) Since the data indicating the relationship between the rotational speed of the spindle and the amount of thermal displacement is stored in advance, by calculating the rotational speed of the spindle at the contact point between the tool and the workpiece, the data at the contact point is calculated. The amount of thermal displacement of the spindle can be determined. On the other hand, since the rotation reference speed of the main shaft is commanded in the NC program, the reference heat displacement amount of the main shaft can be obtained from data indicating the relationship between the rotation speed of the main shaft and the heat displacement amount. The difference between the thermal displacement amount of the main shaft at the contact point and the reference thermal displacement amount of the main shaft represents a processing error at the contact point. Therefore, the rotation speed of the spindle is calculated from the data indicating the relationship between the rotation speed of the spindle and the amount of thermal displacement so that the machining error is within the machining accuracy of the workpiece commanded by the NC program, and the NC program The commanded rotation reference speed of the spindle can be changed. Furthermore, the relative feed reference speed of the tool and the workpiece commanded in the NC program can be changed based on the changed rotation speed of the spindle. And since the above processing is performed for each processing part within the machining process (one machining process) using the same tool, the machining time of the workpiece is maintained at a high accuracy and the machining time is significantly shortened compared to the conventional method. can do.

  (Claim 2) The spindle at the contact point obtained from the rotation diameter of the spindle determined based on the maximum diameter of the tool and the appropriate machining speed of the tool based on the tool diameter and the appropriate machining speed of the tool at the contact point. The rotation speed has been changed. Thereby, in the process (one process) by the same tool, since the process speed of a tool can always be made into an appropriate value, process efficiency can be improved.

  (Claim 3) When machining with the NC program, the rotation reference speed of the spindle determined based on the maximum diameter of the tool in contact with the workpiece and the appropriate machining speed of the tool is determined as the diameter of the tool at the contact point. And the rotation speed of the spindle at the contact point obtained based on the proper machining speed of the tool. Thereby, in the process (one process) by the same tool, since the process speed of a tool can always be made into an appropriate value, process efficiency can be improved. In addition, since the rotation speed of the spindle is adapted to actual machining, machining accuracy can be further increased.

  (Claim 4) According to the processing method of the present invention, the same effects as those of the above-described NC apparatus can be obtained. Further, other characteristic portions in the NC apparatus can be similarly applied to the processing method of the present invention. And the same effect is produced.

It is a front view of a vertical machining center provided with an NC device. It is a functional block diagram of NC device. It is a flowchart for demonstrating the process of NC apparatus. It is a figure which shows the blade diameter of the tool for calculating | requiring the rotation reference speed of the spindle commanded to NC program. It is a figure which shows the data which show the relationship between the rotational speed of a main axis | shaft, and the amount of thermal displacement.

(1. Machine structure of machine tool equipped with NC device)
The NC device is a device that changes the rotation speed of a spindle on which a tool is mounted in a machine tool, depending on the machining site in a machining process (one machining process) using the same tool. As an example of a machine tool, a vertical machining center will be described as an example and described with reference to FIG.

  As shown in FIG. 1, the vertical machining center 1 includes a bed 2, a table 3, a column 4, a slider 5, a spindle head 6, a spindle 7, an automatic tool changer 8, and an NC unit 9. Outlined.

  The bed 2 has a substantially rectangular shape and is arranged on the floor. However, the shape of the bed 2 is not limited to a rectangular shape. A table 3 and an automatic tool changer 8 are provided on the bed 2. A column 4 is erected on the rear side of the bed 2.

  The table 3 has a rectangular shape, and is provided on a guide member 31 provided on the bed 2 and extending in the front-rear direction (Y-axis direction) so as to be slidable in the Y-axis direction. The guide member 31 is provided with a table motor 33 having a ball screw mechanism 32 that slides the table 3 in the Y-axis direction. On the table 3, the workpiece W is placed and magnetically attracted and fixed.

  The column 4 has a substantially gate shape and is erected on the rear side of the bed 2. The leg member 41 of the column 4 is provided with the NC device 9, and the upper member 42 of the column 4 is provided with the slider 5.

  The slider 5 is provided so as to be movable in the left-right direction (X-axis direction) along a guide surface 43 formed on the front surface of the upper member 42 of the column 4. A slider motor 52 having a ball screw mechanism 51 for moving the slider 5 in the X-axis direction is provided on the upper member 42 of the column 4.

  The spindle head 6 is provided so as to be movable in the vertical direction (Z-axis direction) along a guide surface 53 formed on the front surface of the slider 5. The slider 5 is provided with a spindle head motor 62 having a ball screw mechanism 61 that moves the spindle head 6 in the Z-axis direction.

  The main shaft 7 extends in the vertical direction (Z-axis direction) on the main shaft head 6 and is supported so as to be rotatable around the Z-axis. A spindle motor 72 having a gear mechanism 71 that rotates the spindle 7 around the Z axis is built in the spindle head 6. A tool 73 for processing the workpiece W is detachably attached to the lower end of the main shaft 7. That is, the tool 73 is attached to the spindle head 6 so as to be rotatable around the Z axis.

  The automatic tool changer 8 is provided with a plurality of types of tools 73 (not shown). The automatic tool changer 8 is configured so that the tool 73 can be automatically changed with the spindle 7.

  The NC device 9 drives and controls the spindle motor 72 and the like to rotate the tool 73 around the Z axis, and drives and controls the table motor 33, the slider motor 52 and the spindle head motor 62 and the like. The machining of the workpiece W is controlled by relatively moving W and the tool 73 in the X-axis direction, the Y-axis direction, and the Z-axis direction.

(2. Configuration of NC device)
Next, the NC device 9 will be described with reference to the functional block diagram of FIG.
The NC device 9 includes an input unit 91, a storage unit 92, a tool contact point calculation unit 93, a spindle rotation speed calculation unit 94, a thermal displacement amount calculation unit 95, a comparison unit 96, and a spindle rotation speed change unit 97. And a feed speed changing unit 98 and a machining control unit 99.

  The input unit 91 includes input means such as a touch panel and the like, NC program necessary for machining, data on the tool 73, data on the workpiece W, data indicating the relationship between the rotational speed S of the spindle 7 and the thermal displacement amount T, and the like. Is stored in the storage unit 92.

  The tool contact point calculation unit 93 is based on the data on the tool 73 and the data on the workpiece W read from the storage unit 92, and the contact point Pn (n = 1, 2,...) Between the tool 73 and the workpiece W. ) Is calculated. n represents a time when the tool 73 and the workpiece W are relatively moved.

The spindle rotation speed calculation unit 94 calculates the rotation speed Sn (n = 1, 2,...) Of the spindle 7 at the contact point Pn based on the data relating to the tool 73 read from the storage unit 92.
Specifically, the rotational speed Sn (min ⁻¹ ) of the main shaft 7 is determined such that V is the machining speed (m / min) of the tool 73 and Dn (n = 1, 2,...) Is the tool 73 at the contact point Pn. Is expressed by the following formula (1). Note that the processing speed (m / min) of the tool 73 is an appropriate value (upper limit value) defined in advance by the material of the tool 73, and is a fixed value in this example.
Sn = 1000V / πDn (1)

The thermal displacement amount calculation unit 95 stores the rotation speed Sn of the main shaft 7 input from the main shaft rotation speed calculation unit 94, the rotation reference speed S0 of the main shaft 7 instructed by the NC program read from the storage unit 92, and the memory. The reference thermal displacement amount T0 and the thermal displacement amount Tn at the contact point Pn (n = 1, 2) determined based on the data indicating the relationship between the rotational speed S of the main shaft 7 and the thermal displacement amount T read from the unit 92. ,..., A processing error Tn0 (n = 1, 2,...) Of the processing at the contact point Pn is calculated.
Specifically, the machining error Tn0 of the machining at the contact point Pn is represented by the difference between the thermal displacement amount Tn at the contact point Pn and the reference thermal displacement amount T0.

  The comparison unit 96 includes a machining error Tn0 at the contact point Pn input from the thermal displacement amount calculation unit 95 and an allowable error An (n = 1, 1) at the contact point Pn instructed by the NC program read from the storage unit 92. Compare the size with 2,. The machining accuracy is not limited to the allowable error An, and a tolerance or the like may be instructed to the NC program as a comparison target.

  Based on the comparison result input from the comparison unit 96, the main shaft rotation speed changing unit 97 calculates the rotation reference speed S0 of the main shaft 7 commanded by the NC program read from the storage unit 92, and calculates the rotation of the main shaft 7. The speed is changed to Sn or SSn (n = 1, 2,...) Described later.

The feed speed changing unit 98 is based on the changed rotation speed Sn or SSn of the spindle 7 input from the spindle rotation speed changing unit 97, and the feed speed of the table 3 (relative feed speed between the tool 73 and the workpiece W) Fn. (N = 1, 2,...) Is calculated, and the reference feed speed of the table 3 (relative feed reference speed between the tool 73 and the workpiece W) F0 instructed by the NC program read from the storage unit 92. Is changed to the calculated feed speed Fn of Table 3.
Specifically, the feed speed Fn (mm / min) of the table 3 is such that f is the one-blade feed (mm / tooth) of the tool 73, N is the number of blades of the tool 73, Sn is the rotation of the spindle 7 at the contact point Pn. When it is set as speed (min <^-1> ), it represents with following Formula (2). Therefore, the feed speed Fn of the table 3 can be calculated from the rotational speed Sn of the main shaft 7.
Fn = fNSn (2)

  The machining control unit 99 processes the workpiece W by numerically controlling the machine tool 1 in accordance with the NC program in which the changed rotation speed Sn of the spindle 7 and the feed speed Fn of the table 3 are instructed.

(3. Operation of NC device)
Next, the operation of the NC device 9 will be described with reference to FIG. In the storage unit 92, the NC unit necessary for machining, the data related to the tool 73, the data related to the workpiece W, the data indicating the relationship between the rotational speed S of the spindle 7 and the thermal displacement amount T, and the like are input to the input unit 91. Is stored in advance.

  Here, in the NC program, the rotation reference speed S0 of the spindle 7 is commanded for each machining step (one machining step) by the same tool 73. The rotation reference speed S0 of the main shaft 7 is a rotation speed to be changed.

  As shown in FIG. 4, the rotation reference speed S0 of the spindle 7 commanded by the NC program is the maximum blade diameter Damax at the blade 73a of the tool 73 used when machining by the NC program (see FIG. 4A). ) Or the maximum diameter Dbmax (see FIG. 4B) in the contact range e of the blade 73a of the tool 73 that contacts the workpiece W and the material of the tool 73 when machining by the NC program. Based on the machining speed V (m / min), which is an appropriate value (upper limit value), it is set by the above-described equation (1).

  Further, in the NC program, the feed reference speed F0 of the table 3 is instructed for each machining process (one machining process) by the same tool 73. The feed reference speed F0 in this table 3 is the feed rate to be changed. The feed reference speed F0 (mm / min) of the table 3 is set by the above-described equation (2). Therefore, the feed reference speed F0 of the table 3 can be calculated from the rotation reference speed S0 of the spindle 7.

  The data relating to the tool 73 includes, for example, the type of the tool 73, the shape and size such as the diameter and length of the blade 73a, the material, and the machining speed V that is an appropriate value (upper limit) defined in advance by the material of the tool 73. It is data of. The data relating to the workpiece W is, for example, data such as material shape dimensions, material data, and workpiece shape dimensions, processing accuracy (allowable error An, tolerance, surface roughness, etc.). Data indicating the relationship between the rotational speed S of the main shaft 7 and the thermal displacement amount T is, for example, data as shown in FIG. 5 and is measured in advance and stored in a database.

  As shown in FIG. 3, when an NC program necessary for machining is specified from the input unit 91, shape dimension data such as the diameter and length of the blade 73 a of the tool 73 read from the storage unit 92 and the workpiece W A contact point P1 between the tool 73 and the workpiece W is calculated based on the shape dimension of the material and the shape dimension data of the processed product (step S1). Then, based on the shape data such as the diameter and length of the blade 73a of the tool 73 read from the storage unit 92, the rotational speed S1 of the spindle 7 at the contact point P1 is calculated by the above-described formula (1) (step). S2).

  The calculated rotation speed S1 of the spindle 7, the rotation reference speed S0 of the spindle 7 commanded by the NC program read from the storage unit 92, the rotation speed S of the spindle 7 read from the storage unit 92, and the amount of thermal displacement Based on the data indicating the relationship with T, the reference thermal displacement amount T0 and the thermal displacement amount T1 at the contact point P1 are obtained, and the machining error which is the difference between the thermal displacement amount T1 at the contact point P1 and the reference thermal displacement amount T0. T10 is calculated (step S3).

For example, from the data indicating the relationship between the rotational speed S of the main shaft 7 and the thermal displacement amount T shown in FIG. 5, the thermal displacement amount T1 when the calculated rotational speed S1 of the main shaft 7 is 20000 (min ⁻¹ ) is 16 μm. It becomes. Further, the reference thermal displacement amount T0 when the rotation reference speed S0 of the spindle 7 commanded by the NC program is 10,000 (min ⁻¹ ) is 8 μm. Therefore, the machining error T10 at the contact point P1 is a difference of 8 μm between the thermal displacement amount T1 and the reference thermal displacement amount T0.

  Then, the allowable error A1 at the contact point P1 commanded to the NC program is read from the storage unit 92, and the magnitude of the machining error T10 and the allowable error A1 at the contact point P1 is compared (steps S4 and S5). When it is determined that the machining error T10 at the contact point P1 is equal to or less than the allowable error A1, the machining dimension is within the allowable range even if machining is performed at the calculated rotational speed S1 of the main shaft 7, and thus read from the storage unit 92. The rotation reference speed S0 of the spindle 7 commanded by the NC program is changed to the rotation speed S1 (step S6).

  On the other hand, when it is determined in step S4 that the machining error T10 at the contact point P1 exceeds the allowable error A1, the machining error T10 and the data indicating the relationship between the rotational speed S of the main shaft 7 and the thermal displacement amount T are calculated. The rotational speed SS1 of the spindle 7 at which the allowable error A1 is equal is read (step S7). Even if the machining is performed at the read rotation speed SS1 of the main spindle 7, the machining dimension is within the allowable range. Therefore, the rotation reference speed S0 of the main spindle 7 commanded by the NC program read from the storage unit 92 is set to the rotation speed SS1. (Step S8).

  Then, based on the changed rotational speed S1 or SS1 of the spindle 7, the feed speed F1 of the table 3 is calculated by the above-described equation (2), and the feed of the table 3 instructed by the NC program read from the storage unit 92 is performed. The reference speed F0 is changed to the calculated feed speed F1 in Table 3 (step S9). Then, it is determined whether or not the changing process in the machining process (one machining process) by the same tool 73 of the NC program is completed (step S10), and when it is determined that the changing process is not completed, the process proceeds to step S1. It returns and calculates the next contact point P2, and repeats the above-mentioned process. On the other hand, when it is determined in step S9 that the changing process has been completed, the machine tool 1 is numerically controlled in accordance with the NC program in which the changed rotational speed Sn of the spindle 7 and the feed speed Fn of the table 3 are commanded. The workpiece is machined (step S11).

(4. Effect of processing by NC device)
Data indicating the relationship between the rotational speed S of the main shaft 7 and the thermal displacement amount T is measured and stored in advance. Thus, the thermal displacement amount Tn and the reference thermal displacement amount T0 of the main shaft 7 at the contact point Pn between the tool 73 and the workpiece W can be obtained, and the machining error Tn0 at the contact point Pn can be obtained. Then, the rotational speeds Sn and SSn of the spindle 7 are determined so that the obtained machining error Tn0 is within the allowable tolerance An of the workpiece, the rotational reference speed S0 of the spindle 7 commanded by the NC program, and the table 3 The feed reference speed F0 can be changed. And since the above process is performed for every processing part in the processing process (one processing process) by the same tool 73, while maintaining the processing precision of the workpiece W highly accurate, processing time is significantly larger than before. Can be shortened.

1: Vertical machining center, 2: Bed, 3: Table, 4: Column 5: Slider, 6: Spindle head, 7: Spindle, 8: Automatic tool changer 9: NC device, 71: Tool, W: Workpiece 91 : Input unit, 92: storage unit, 93: tool contact point calculation unit, 94: spindle rotation speed calculation unit, 95: thermal displacement amount calculation unit, 96: comparison unit, 97: spindle rotation speed change unit, 98: feed rate change unit 99: Machining control unit

Claims (4)

A numerical control device that changes the rotation speed of a spindle on which a tool in a machine tool is mounted, depending on a machining part in a machining process using the same tool,
Storage means for storing in advance at least a numerical control program for numerically controlling the machine tool, data relating to the tool, data relating to the workpiece, and data indicating the relationship between the rotational speed of the spindle and the amount of thermal displacement; ,
Contact point calculation means for calculating a contact point between the tool and the workpiece based on the data on the tool and the data on the workpiece;
A spindle rotation speed calculation unit that calculates the rotation speed of the spindle at the calculated contact point based on the data relating to the tool;
Based on the data indicating the relationship between the rotation speed of the spindle and the amount of thermal displacement, the calculated spindle rotation speed and the rotation reference speed of the spindle commanded by the numerical control program, the heat of the spindle Thermal displacement amount calculating means for calculating the displacement amount;
Comparison means for comparing the machining accuracy of the workpiece commanded in the numerical control program with the calculated amount of thermal displacement of the spindle,
Spindle rotation speed changing means for changing the rotation reference speed of the spindle commanded to the numerical control program so that at least the amount of thermal displacement of the spindle is within the machining accuracy range of the workpiece;
Based on the changed rotation speed of the spindle, a feed speed changing means for changing the relative reference feed speed of the tool and the workpiece commanded to the numerical control program;
A numerical control device comprising: a processing control means for numerically controlling the processing of the workpiece based on the numerical control program in which the rotation reference speed of the spindle and the relative reference feed speed of the tool and the workpiece are changed. In claim 1,
The rotation reference speed of the spindle commanded in the numerical control program is set based on the maximum diameter of the tool used when machining by the NC program and an appropriate machining speed of the tool,
The spindle rotation speed calculation unit is a numerical control device that calculates the rotation speed of the spindle at the contact point based on the calculated diameter of the tool at the contact point and an appropriate machining speed of the tool. In claim 1,
The rotation reference speed of the spindle commanded in the numerical control program is set to the maximum diameter in the contact range of the tool that comes into contact with the workpiece and an appropriate processing speed of the tool when machining by the numerical control program. Set based on
The spindle rotation speed calculation unit is a numerical control device that calculates the rotation speed of the spindle at the contact point based on the calculated diameter of the tool at the contact point and an appropriate machining speed of the tool. A machining method for changing a rotation speed of a spindle on which a tool in a machine tool is mounted, depending on a machining part in a machining process using the same tool,
A storage step for storing in advance at least a numerical control program for numerically controlling the machine tool, data on the tool, data on the workpiece, and data indicating a relationship between a rotational speed of the spindle and a thermal displacement amount;
A contact point calculation step for calculating a contact point between the tool and the workpiece based on the data on the tool and the data on the workpiece;
A spindle rotation speed calculation step for calculating the rotation speed of the spindle at the calculated contact point based on the data on the tool;
Based on the data indicating the relationship between the rotation speed of the spindle and the amount of thermal displacement, the calculated spindle rotation speed and the rotation reference speed of the spindle commanded by the numerical control program, the heat of the spindle A thermal displacement calculation process for calculating the displacement;
A comparison step of comparing the machining accuracy of the workpiece commanded in the numerical control program with the calculated amount of thermal displacement of the spindle;
A spindle rotation speed changing step for changing the rotation reference speed of the spindle commanded to the numerical control program so that at least the amount of thermal displacement of the spindle is within the machining accuracy range of the workpiece;
Based on the changed rotation speed of the spindle, a feed speed changing step of changing a relative feed reference speed of the tool and the workpiece commanded to the numerical control program;
A machining control step comprising: numerically controlling machining of the workpiece based on the numerical control program in which the rotation reference speed of the spindle and the relative feed reference speed of the tool and the workpiece are changed.

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