JP2001293642A - Tool cutting-edge projection-amount measuring method, tool abrasion-amount measuring method, and numerical control machine tool using them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure only abrasion of a tool by removing thermal displacement of a machine and an effect of vibration of the tool from variation of a cutting-edge position of the rotating tool. SOLUTION: The cutting-edge 102 of the tool shields a laser beam 35 to vary a light receiving amount, and a projection amount of the cutting-edge is measured using the tool cutting- edge position detector for detecting a tool's cutting-edge position based on the variation of the light receiving amount. The tool is moved from a state I where the tool does not cross the laser beam 35 to a state II where the cutting-edge 102 intermittently shields the laser beam 35, and a tool position when the light receiving amount varies, namely a first detection coordinate Zc, is detected. Next, the tool is moved from a state I' where the tool core 103 perfectly shields the laser beam 35 to a state II' where the cutting-edge 102 intermittently shields the laser beam 35, and a tool position when the light receiving amount varies, namely a second detection coordinate Zb, is detected. The projection amount of the cutting- edge is calculated based on a difference between the first detection coordinate Zc and the second detection coordinate Zb. The projection amounts of the cutting-edge are measured before and after machining by the tool, and a tool abrasion amount is calculated based on a difference between them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the amount of protrusion of a cutting edge of a rotary tool mounted on a spindle, a method for measuring a tool wear amount, and a numerically controlled machine tool using the method.

[0002]

2. Description of the Related Art In order to improve machining efficiency, the spindle speed of a current machine tool is greatly increased. When the spindle is rotated at high speed (tens of thousands of revolutions), centrifugal expansion occurs due to centrifugal force, and the position of the blade edge of the tool provided at the tip of the spindle is displaced due to thermal expansion due to heat generation, and further, high-speed machining The position of the cutting edge is displaced by the wear of the tool cutting edge due to the above. For this reason, it is desired to grasp the position of the cutting edge of the rotary tool. JP-A-8-310135 has been proposed as one of the methods for obtaining the position of the cutting edge of a rotating tool.

[0003]

According to the method for detecting the position of a cutting edge disclosed in Japanese Patent Application Laid-Open No. 8-310135, the position of the cutting edge of a rotating tool can be known, but the amount of wear of the tool edge cannot be measured. That is, even if a change in the cutting edge position is obtained by this cutting edge position detection method, the amount of change includes not only the wear amount of the tool cutting edge but also the effect of the thermal displacement amount of the machine. It is not possible to detect only the wear amount separately. Furthermore, if the run-out state changes by removing the tool from the holder or removing the tool holder from the spindle, the amount of change in the cutting edge position includes the effect of the run-out, so It is not possible to detect only the wear amount by separating the change.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to use a tool edge position detecting device capable of detecting the edge position of a rotating tool. Is to measure the amount. Another object of the present invention is to detect the amount of tool wear from the amount of change in the amount of protrusion of the tool edge, and further to provide a numerically controlled machine tool using this tool wear amount measuring method.

[0005]

In order to achieve the above object, a method for measuring the amount of protrusion of a tool edge according to the first aspect uses the following means. When a rotating tool is moved between a light emitter serving as a light source and a light receiver that receives the light, the light reception amount of the light receiver changes because the cutting edge of the tool blocks light. Using a tool edge position detection device that measures the position of the tool edge based on this change in the amount of received light, the tool first approaches the light from a state where the tool and the light do not intersect, and the tool edge intermittently blocks the light and The first detection coordinate which is the relative position of the tool with respect to the cutting edge position detecting device when is changed. Next, the rotary tool is moved from a state in which light is continuously interrupted by the tool core to a state in which light is intermittently interrupted by the tool edge, and the tool is moved relative to the edge position detecting device when the amount of received light changes. A second detection coordinate, which is a relative position, is detected. The amount of protrusion of the tool edge is calculated from the difference between the first detected coordinates and the second detected coordinates.

When measuring the amount of protrusion of the cutting edge in the direction of the rotation axis of the tool, the tool is moved in the direction in which the rotating tool and the light of the cutting edge position detecting device move closer to each other by relative movement in the Z-axis direction (front-back direction). Then, the first detection coordinates are measured, and the second detection coordinates are measured by moving them in the direction in which they are separated from each other.
On the other hand, when measuring the tool tip protrusion amount in the radial direction of the tool,
The first detection coordinate is measured by moving the rotating tool and the light of the blade position detecting device in the Y-axis direction (vertical direction) in a direction in which they approach each other, and the two are moved in a direction away from each other. Thus, the second detection coordinates are measured.

According to a second aspect of the present invention, there is provided a method for measuring a tool wear amount, wherein the first and second tool edge protrusion amounts are measured before and after machining by a tool, and the difference between the measured values is used. A technical feature is to calculate a tool wear amount.

[0008] Claim 3 for achieving the method of claim 2
The numerical control machine tool described in the above, comprises a spindle provided with a rotary tool, a work table for mounting and fixing a workpiece, and a drive means for relatively moving the spindle and the work table, the work table has a tool edge position Is provided with a tool edge position detecting device for measuring the tool edge position. Then, the protrusion amount of the tool blade tip is calculated from the difference between the first detection coordinates and the second detection coordinates by the protrusion amount measurement means, and the protrusion amount before use stored in the storage means by the wear amount calculation means and the current measurement time. A technical feature is to calculate the wear amount of the blade tip from the protrusion amount.

In the above-described method of measuring the protrusion of the blade edge, the second detection coordinates may not be detected properly depending on the shape of the tool. In such a case, the means described in claim 4 can be adopted.

[0010] In the numerical control machine tool according to claim 4,
A through hole is formed in advance at a predetermined distance from the tool core or the tool edge of the shank so that light can pass therethrough. Then, the protrusion amount measuring means moves the rotating tool from a state where light is continuously blocked by the core of the tool to a state where light is intermittently blocked by the passage hole. A third detection coordinate, which is a relative position of the tool with respect to the cutting edge position detection device when the amount of received light changes due to the passage hole, is detected, and a tool protrusion amount is calculated from a difference between the first detection coordinate and the third detection coordinate.

According to a fifth aspect of the present invention, there is provided an alarming means for giving an alarm to an operator when a wear amount calculated by the wear amount calculating means exceeds a limit wear amount of a tool previously input for each tool. Is a technical feature.

According to a sixth aspect of the present invention, there is provided a tool changer for automatically changing a tool when a wear amount calculated by the wear amount calculating means exceeds a limit wear amount of a tool previously input for each tool. It is a technical feature to have means.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a numerically controlled machine tool 10 including a tool edge position detecting device according to an embodiment of the present invention. The numerically controlled machine tool 10 includes a work table 12 movable on the bed 14 in the X direction (lateral direction) and a column 16 movable on the bed 14 in the Z direction (front and rear direction). A work W is placed on the work table 12, and a detector 30 is arranged at a known position on the work table 12 that does not interfere with the work W. On the other hand, the column 16 includes a saddle 18 that can move in the Y direction (up and down direction). The saddle 18 is provided with a spindle 22 that grips and rotates a tool 20.

The detector 30 is formed in a concave shape as shown in FIG. 1, and a laser oscillator 32 and a photodiode 3 receiving light 35 from the laser oscillator 32 are provided on the inner wall of the concave shape.
4 are provided. The configuration of the detector 30 will be described in more detail with reference to FIG. FIG.
(a), (b) is a plan view of the detector 30 shown in FIG. 1 as viewed from the arrow A, that is, a plan view as viewed from above, and a view as viewed from the arrow B, that is, as viewed from the front. FIG. 2A shows an axial edge position 2 of the tool 20.
When detecting 0a, FIG. 2B shows a state in which the cutting edge position 20b in the radial direction of the tool 20 is detected. The laser light 35 from the laser oscillator 32 is received by the photodiode 34, and the laser light 35 is blocked by the tool 20, whereby the cutting edge of the tool 20 is detected as described later.

FIG. 3 is a block diagram showing the configuration of a control device 50 for controlling the numerically controlled machine tool 10 and a photodetector 80 for receiving the light from the laser oscillator 32 and detecting the cutting edge of the tool. The control device 50 includes a central control device (CPU) 56 that manages the entire device, a memory 52 that holds various controls, programs, data on the cutting edge position of the tool, the cutting edge protrusion amount, the tool protrusion amount, and the like, and an interface 54. , 58, 59. The control device 50 is configured such that various data is input via an input device 70 and various data is output via an output device 72. The input device 70 is provided with a keyboard for inputting data, and the output device 72 is provided with a display device such as a CRT for displaying data.

The controller 50 sends a drive signal to a first servo motor 68 for driving a ball screw (not shown) for moving the column 16 via a first motor drive circuit (DUZ) 66. The first encoder 67 attached to the first servo motor 68
, Ie, the cutting edge position of the tool 20 is sent to the control device 50. Further, the control device 50
To a second servo motor 62 for feeding the work table 12 in the horizontal direction (X direction) by a ball screw (not shown).
A drive signal is sent via a second motor drive circuit (DUX) 60. The second encoder 61 attached to the second servomotor 62 sends the rotation position of the second servomotor 62, that is, the position of the work table 12, to the control device 50.
Similarly, the control device 50 sends a drive signal via a third motor drive circuit (DUY) 63 to a third servomotor 65 for sending the saddle 18 in the vertical direction (Y direction) by a ball screw (not shown). . The third encoder 64 attached to the third servo motor 65 is configured to send the position of the saddle 18 to the control device 50.

On the other hand, the photodetector 80 includes an photodiode 90 described above with reference to FIG. 2 and an amplifier 90 for detecting that the cutting edge portion 102 has blocked the laser beam 35 from the output of the photodiode 34, and an output of the amplifier 90. To the control device 50. The amplifier 90
Detects that the cutting edge 102 has reached the laser beam 35 based on a change in the output of the photodiode 34.

FIG. 4A is a view taken in the direction of arrow D in FIG. 2A, that is, a view of the side surface of the tool 20 as viewed from the horizontal direction, and FIG. FIG. The tool 20 includes a blade portion 106 and a shank 104, and the blade portion 106
5 and a tool core 103. The cutting edge portion 102 includes a cutting edge tip portion 101 having no tool core portion 103 in the axial direction, that is, on the opposite side of the shank 104. The difference in the amount of light received by the photodiode 34 when the laser beam 35 in the direction of the paper plane of FIG. 4 is irradiated so as to intersect with the blade 106 of the rotating tool 20 will be described with reference to FIG. The laser beam 35 is applied to the rotating tool 20 by the tool core 103.
Irradiates the shaded portion 108 with the laser light 35
When the laser beam 35 is applied to a portion 107 of the blade portion 106 where the tool core portion 103 does not exist, the laser beam 35 is intermittently blocked by the cutting edge 105.

FIG. 5 shows a method for measuring the amount of protrusion of the blade edge based on the difference in the amount of light received by the photodiode 35 described above.
This will be described with reference to FIG. FIGS. 5A and 5B are views as viewed from an arrow D in FIG. 2A, that is, a view of the side surface of the tool 20 viewed from the horizontal direction.

In FIG. 5A, the tool 20 approaches the laser beam 35 from a position I where the rotating tool 20 and the laser beam 35 do not intersect. In a state where the laser light 35 does not intersect, the laser light 35 is not interrupted, so that the laser light 35 is applied to the photodiode 34.
When 1 reaches the position II where the laser light 35 is reached {107 in FIG. 4 (c)}, the transmitted laser light 35 is intermittently blocked, and the amount of light applied to the photodiode 34 changes. The coordinates of the tool reference position 111 with respect to the reference position 110 when the irradiation light amount changes are defined as first detection coordinates (Zc).

In FIG. 5B, the tool core 103 of the rotating tool 20 and the laser beam 35 intersect and the laser beam 35 is completely blocked by the tool core 103 {FIG. The tool is moved so that the intersection moves from the position I ′ where the laser light 35 does not irradiate to the tool tip end 101 to the position II ′ where the laser light 35 reaches the tool tip end 101. When it comes {1 in Fig. 4 (c)
07}, the amount of light applied to the photodiode 34 changes. The coordinates of the tool reference position 111 with respect to the reference position 110 when the irradiation light amount changes are defined as second detection coordinates (Zb).

The coordinates Z obtained from FIGS. 5A and 5B
b, the cutting edge protruding amount Z ₁ from Zc is expressed by the following equation 1.
[Refer to FIG. 6] Blade edge protrusion amount Z ₁ = Zb−Zc (1) The blade edge protrusion amount Z ₁ obtained by equation (1) is compared with the blade edge protrusion amount Z ₁ ′ at the previous measurement. Calculate the amount of tool wear. When the tool edge position is detected, the position data of the tool is corrected based on the position of the tool.

The amount of wear of the cutting edge portion 102 in the radial direction can be measured in the same manner as described above.

Next, the correction processing of the tool tip position by the control device 50 will be described with reference to FIGS. 7 and 8 which are flowcharts of the processing. In FIG. 7, the tool wear amount measurement processing is executed before the work W is processed or during the processing cycle as needed. The CPU 56 controls the tool 20
Is a predetermined rotation number, that is, whether a predetermined measurement period has been reached (S101). When the measurement cycle is reached (S10
1 is Yes), the tool 20 is positioned at a predetermined measurement start position near the detector 30 as shown by a broken line in FIGS. 2A and 2B by moving the work table 12, the column 16, and the saddle 18. (S102). Thereafter, the tool 20 is advanced toward the laser beam 35 along the Z-axis direction, ie, the Z-axis in FIG. 2A, or toward the laser beam 35 side along the Y-axis direction, ie, the Y-axis in FIG. 2B. It is lowered (S103). Then, the blade edge portion 102 of the tool reaches the laser beam 35, and it is determined whether the amplifier 80 has detected a change in the amount of received laser beam 35 as described above (S104). The tool first detection coordinates Yc or Zc (Y coordinate or Z coordinate) when S104 is Yes are represented by a third servomotor 65 for Y-axis feed or a first servomotor 68 for Z-axis feed shown in FIG. (S105) based on a signal from the third encoder 64 or the first encoder 67 attached to each of them.

Then, the tool core 103 of the tool 20 is completely blocked from the laser beam 35 (108 in FIG. 4C).
Is positioned (S106). Then, the tool 20 is moved to the position shown in FIG.
The tool is moved along the middle Z-axis or the Y-axis in FIG. 2B (S107), and a location that intersects with the laser beam 35 reaches the cutting edge 102 from the tool core 103 of the tool 20. As described above, it is determined whether the amplifier 80 has detected a change in the amount of light received by the laser beam 35 (S108). When S108 becomes Yes, the tool second detection coordinate Yb or Zb (Y coordinate or Z coordinate) is converted to the third servo motor 65 for Y axis feed or the first servo motor 68 for Z axis feed shown in FIG. (S109) based on a signal from the third encoder 64 or the first encoder 67 attached to each of them.

The cutting edge protruding amount Z ₁ is obtained from the detected the first detection coordinate and the second detection coordinate (S110). The resulting blade edge protruding amount Z ₁ is stored in the memory 52 shown in FIG. 3 (S111). Compared to the cutting edge portion protruding amount Z ₁ of the previous measurement stored in the memory 52 and calculates the tool wear amount (S1
12) In comparison with the limit wear amount of the tool previously input to the memory 52 (S113), when the tool wear amount exceeds the limit value (Yes in S113), a warning is transmitted to the operator. Or the tool is automatically replaced (S114). When the tool wear amount does not exceed the limit value (No in S113), since the position of the detector 30, that is, the position of the laser beam 35 in the Y-axis direction and the Z-axis direction is known, the laser beam 3
Based on the position of No. 5 and signals from the third encoder 64 and the first encoder 67, the cutting edge position data stored in the memory 52 is corrected (S115). Perform the above processing,
The operation of measuring the amount of protrusion of the tool edge is completed, and machining is started or restarted based on the corrected edge position data.

In the above-described method for measuring the amount of protrusion of the blade edge, the second detection coordinate (Zb) may not be detected properly depending on the shape of the tool. In such a case, the following can be performed as another embodiment. FIGS. 9A and 9B are views similar to FIG. 5 as viewed from an arrow D in FIG. 2A, that is, a view of the side surface of the tool 20 viewed from the horizontal direction. The tool to be used is provided with a passage hole 112 penetrating therethrough at a fixed distance from the tool core portion 103 or the tool edge portion 102 of the shank 104 so that the laser light 35 can pass therethrough.

FIG. 9A shows the first detected coordinates similarly to FIG. 5A.
(Zc) is determined. FIG. 9B shows that the tool core 103 of the rotating tool 20 and the laser beam 35 intersect and the laser beam 35 is blocked by the tool core 103 {108 in FIG. Moves the tool 20 from the position I ′ where the laser beam 35 is not irradiated,
At the position II 'that has passed through the photodiode 34, the amount of light applied to the photodiode 34 changes. The coordinates of the tool reference position 111 with respect to the reference position 110 at the time when the irradiation light amount changes are defined as third detection coordinates (Zd).

The coordinates Z obtained from FIGS. 9A and 9B
From c and Zd, the tool protrusion amount Z ₂ is expressed by the following equation 2.
[See FIG. 10] Tool protrusion amount Z ₂ = Zd−Zc (2) The tool protrusion amount Z ₂ obtained by the equation (2) is compared with the tool protrusion amount Z ₂ ′ at the previous measurement, and Calculate the amount of wear. When the position of the tool edge is detected, the position of the tool 2 is determined based on the position of the tool.
The position data of 0 is corrected.

The amount of tool protrusion in the radial direction of the tool edge portion 102 can be measured in the same manner as described above.

The processing operation of the tool wear amount detection processing of FIGS. 11 and 12 is basically the same as the processing operation of FIGS. 7 and 8. Instead of the second detection coordinate detection of S107, S108, and S109 of FIG. 7, in FIG. 11, S207, S208, and S2
At 09, the third detection coordinates are detected, the tool protrusion amount is calculated instead of the blade tip protrusion amount (S210), and the tool protrusion amount is stored.
(S211), and the rest is the same as the processing operation of FIGS.

[0032]

According to the first aspect of the present invention, it is possible to measure the amount of protrusion of the cutting edge of the rotary tool without being affected by the amount of thermal displacement of the machine or the change in the state of the runout of the tool. According to the second aspect of the present invention, since the tool wear amount is calculated based on the change in the blade tip protrusion amount of the rotary tool according to the first aspect, the influence of the thermal displacement amount of the machine or the change in the state of the tool runout is reduced. Excluded, only the tool wear can be measured. According to the third aspect of the present invention, tool wear can be managed using a relatively inexpensive apparatus without using a large-scale apparatus such as an expensive CCD camera and an image processing apparatus, so that the cost merit is excellent. According to the fourth aspect of the invention, in addition to the above effects, the tool wear amount can be measured regardless of the shape of the tool.
According to the fifth and sixth aspects of the present invention, by measuring the amount of tool wear, it is possible to prevent the deterioration of product accuracy due to the life of the tool, and to always perform high-precision machining.

[Brief description of the drawings]

FIG. 1 is a perspective view of a numerically controlled machine tool provided with a tool edge position detecting device according to an embodiment of the present invention.

FIG. 2A is a view of the detector shown in FIG.
FIG. 2B is a view of the detector shown in FIG.

FIG. 3 is a block diagram illustrating a configuration of a numerical control device according to an embodiment of the present invention.

4 (a) is a view taken in the direction of arrow D in FIG. 2 (a), FIG. 4 (b) is a sectional view taken along line AA of FIG. 4 (a), and FIG. FIG. 3 is a diagram for explaining a transmission range of FIG.

FIG. 5 is a plan view showing a tool edge position detecting operation.

FIG. 6 is a plan view for explaining a tool blade tip projecting amount.

FIG. 7 is a part of a flowchart according to the embodiment of the present invention.

FIG. 8 is a part of a flowchart according to the embodiment of the present invention.

FIG. 9 is a plan view showing an operation of detecting a tool protrusion position.

FIG. 10 is a plan view for explaining a tool protrusion amount.

FIG. 11 is a part of a flowchart according to another embodiment of the present invention.

FIG. 12 is a part of a flowchart according to another embodiment of the present invention.

[Explanation of symbols]

10 Numerically controlled machine tools, 20 tools, 20a
Axial cutting edge, 20b Radial cutting edge, 30 detector, 32 laser oscillator (light source), 34 photodiode (light receiver), 35 laser beam, 50 numerical controller, 102 cutting edge, 103 tool core, 112 through hole

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3C001 KA02 KB09 TA02 TB02 3C029 DD08 DD20 3C036 BB02 LL09

Claims (6)

[Claims] 1. A rotating tool is moved between a light emitter serving as a light source and a light receiver receiving the light, and a change in the amount of light received by the light receiver due to the cutting edge of the tool blocking the light. A measurement method using a tool edge position detection device that measures a tool edge position, wherein the tool approaches the light from a state where the tool and the light do not intersect, and the tool edge portion intermittently blocks the light. Detecting first detection coordinates that are relative positions of the tool with respect to the blade edge position detection device when the amount of light received by the light receiver changes, and the light intersects the core of the tool and the light is continuously blocked. Move the tool so that the intersection of the light moves from the state to the tool blade edge portion, the tool changes with respect to the blade edge position detection device when the received light changes when the light changes intermittently and the received light amount changes. Second relative position Out to detect coordinates, the tool cutting edge projecting amount measuring method characterized in that the difference between the first detection coordinate and the second detection coordinate measuring the amount of protrusion of the tool cutting edge. 2. The method according to claim 1, wherein the amount of protrusion of the tool edge before and after machining by the tool is measured, and the amount of tool wear is calculated from the difference. Tool wear measurement method. 3. A machine tool comprising: a spindle provided with a rotary tool; a work table for mounting and fixing a workpiece; and driving means for relatively moving the spindle and the work table. A tool edge position for measuring a tool edge position by changing a light receiving amount of the light receiver by moving a rotating tool between a light emitter and a light receiver for receiving the light, and a cutting edge of the tool intercepting the light. For the detection device, the tool is approached to the light from a state where the tool and the light do not intersect, the tool edge portion intermittently intercepts the light, and the light reception amount of the light receiver changes with respect to the edge position detection device. A first detection coordinate which is a relative position of the tool is detected, and the intersection moves from a state where the core of the tool and the light intersect and the light is continuously interrupted to the tool edge. Moving the tool so that, the light detects the second detection coordinate the relative position of the tool relative to the blade position detecting apparatus when the amount received changes to a state which is blocked intermittently changes,
A protrusion amount measuring means for calculating a protrusion amount of the tool blade tip from a difference between the first detection coordinates and the second detection coordinates, and a protrusion amount measured by the protrusion amount measurement means before use of the tool, for each of the tools. And a wear amount calculating means for calculating the wear amount of the tool edge by comparing the protrusion amount before use stored in the storage means with the protrusion amount at the time of the current measurement. Numerically controlled machine tool. 4. A machine tool comprising: a spindle provided with a rotary tool; a work table for mounting and fixing a workpiece; and drive means for relatively moving the spindle and the work table; and a light source provided on the work table. A tool edge position for measuring a tool edge position by changing a light receiving amount of the light receiver by moving a rotating tool between a light emitter and a light receiver for receiving the light, and a cutting edge of the tool intercepting the light. For the detection device, the tool is approached to the light from a state where the tool and the light do not intersect, the tool edge portion intermittently intercepts the light, and the light reception amount of the light receiver changes with respect to the edge position detection device. A first detection coordinate, which is a relative position of the tool, is detected, and the light is provided on the tool from a state where the core of the tool intersects with the light and the light is continuously blocked. Move the tool toward the passing hole to detect the third detection coordinates that is the relative position of the tool with respect to the blade edge position detection device when the light changes intermittently and the amount of received light changes A tool protrusion amount measuring means for calculating a tool protrusion amount from a difference between the first detection coordinates and the third outgoing coordinates; and a tool protrusion amount measured by the tool protrusion amount measuring means before use of the tool. Storage means for storing the tool protrusion amount before use stored in the storage means and wear amount calculation means for calculating the wear amount of the tool blade tip portion by comparing the tool protrusion amount at the time of the current measurement. Numerically controlled machine tool characterized in that: 5. An apparatus according to claim 3, further comprising alarm means for outputting an alarm when a wear amount calculated by said wear amount calculation means exceeds a limit wear amount of a tool stored in advance for each tool. Or the numerically controlled machine tool according to 4. 6. A tool changing means for automatically changing a tool when a wear amount calculated by said wear amount calculating means exceeds a limit wear amount of a tool stored in advance for each tool. The numerically controlled machine tool according to claim 3 or 4, wherein