JP2020146776A - Tool service life detector and tool service life detection method - Google Patents

Abstract

To provide a tool service life detector and a tool service life detection method capable of accurately detecting a service life of a processing tool including chipping.SOLUTION: As shown in the figure (a), a vibration sensor 13 is attached to a main shaft 12 along a feeding direction of a processing tool 21. Vibration information acquired on the vibration sensor 13 is amplified on an amplifier 14 and is fed to a calculation part 15. The calculation part 15 calculates a distance of Mahalanobis on the basis of the vibration information. In the calculation, a sample line parallel to a processing time axis is drawn to a wave form curve acquired from the vibration information, the number of intersections where the wave form curve and the sample line cross is set to a change amount, a sum of segments of the sample line partitioned by the wave form curve is set to an existence amount, then the change amount and the existence amount are used for calculation of the distance of the Mahalanobis. As the result, a figure (b) is acquired.EFFECT: As an effect, in the figure (b), an MD value on a boundary region is significantly large to a normal region, abnormality (service life) can be detected at a preferable timing.SELECTED DRAWING: Figure 12

Description

The present invention relates to a tool life detection device and a tool life detection method that are attached to a machine tool and detect the life of a machining tool during machining work.

In metal machining, in order to maintain a certain level of machining quality, it is necessary to accurately grasp the life of the machining tool and replace the machining tool at an appropriate time.
Conventionally, the number of times of machining until the machined surface roughness of the object to be machined (hereinafter referred to as a workpiece) becomes out of the standard is investigated, and the number of times in which a safety factor is expected is used as a guideline for tool replacement.

The safety factor is empirically determined in consideration of the chipping of the machining tool and the variation of the machining tool. Chipping is a so-called blade spill. Abrasion occurs gradually in proportion to the number of times of machining, but chipping occurs suddenly. Variations occur due to the success and failure of machining tools.
Therefore, the safety factor is expected to be about 10%.

I checked the machining tools that were replaced at the number of times that the safety factor was expected. Then, I found something that could still be used to a considerable extent. That is, the machining tool whose machined surface roughness should be within the standard was replaced before the end of its life.
If the machining tool is used for the entire life, productivity can be improved by increasing the number of machining times and the procurement cost of the machining tool can be reduced.
Therefore, a technique capable of detecting the life of a machining tool with high accuracy is required.

Therefore, some techniques for detecting the life of the machining tool have been proposed (see, for example, Patent Document 1 (FIG. 5)).

In Patent Document 1, the Mahalanobis distance (hereinafter referred to as MD value) is obtained by the Mahalanobis Taguchi method (hereinafter referred to as MT method) based on the data obtained during processing, and the milling cutter (multi-blade tool) is obtained by this MD value. It is to detect the life of the.

The data obtained during machining are the spindle torque command value in the machine tool, the vibration amplitude in the X-axis direction, the vibration amplitude in the Y-axis direction, the vibration amplitude in the Z-axis direction, the strain in the X-axis direction, and the strain in the Y-axis direction.
Conventional techniques will be described with reference to FIG.
FIG. 15A is a graph for explaining the identification of the flank wear amount, and FIG. 15B is a graph for explaining the identification of chipping. In each case, the number of processes (number of passes) is on the horizontal axis, and the Mahalanobis distance is on the vertical axis.

In FIG. 15A, for example, 8000 (vertical axis) is set as a criterion, and when the upward-sloping curve reaches 8000, the tool is replaced (Patent Document 1, paragraph 0033).
In FIG. 15B, when a new multi-blade tool is artificially chipped, an MD value of about 2000 is obtained, and when the multi-blade tool after 830 passes is artificially chipped, a MD value of about 2000 is obtained. An MD value of about 18,000 can be obtained.
Abnormality can be determined by separating the amount of wear and chipping (Patent Document 1, paragraph 0047).

Then, in Patent Document 1, when the Mahalanobis distance during processing is displayed at a position isolated above by a predetermined distance with respect to the Mahalanobis distance during processing corresponding to the flank wear amount, it is determined that chipping has occurred. It is said to detect (Patent Document 1, paragraph 0046).
However, the distance displayed at the isolation location varies. Since it is complicated and complicated to judge by the changing distance, the effectiveness of Patent Document 1 for chipping remains questionable.
That is, the technique of Patent Document 1 is recognized to be effective against wear, but the effectiveness remains questionable against chipping.
However, while effective use of machining tools including multi-blade tools is required, it is required that abnormalities including chipping can be detected correctly.

JP-A-2017-226027

An object of the present invention is to provide a tool life detection device and a tool life detection method capable of detecting the life of a machining tool including chipping with high accuracy.

The present inventors paid attention to the following two points in the technique of Patent Document 1.
The first point is that the torque command value, vibration amplitude, and strain are selected as data.
The second point is the method of processing the vibration amplitude.

Regarding the torque command value, vibration amplitude, and strain at the first point, the processing load of data processing by a computer increases in proportion to the number of data. If there are three types of data, it is difficult to acquire the data.
As a result of conducting experiments and studies, the present inventor has found that the number of acquired data can be reduced by focusing on chipping among wear and chipping. That is, chippyin has a large effect on vibration and a small effect on torque command value and strain. From this idea, I came up with the idea that the acquired data should be limited to vibration.

Regarding the vibration amplitude at the second point, Patent Document 1 pays attention to the magnitude of the vibration wave.
If there is a first wave and a second wave of the same size, the width of the first wave in the time axis direction (time axis length) is wide, and the width of the second wave is narrow, the width of this wave Is thought to affect the life of the machining tool. This point is missing in Patent Document 1.
We have come to the conclusion that it is necessary to add the width of the wave to the amplitude of the vibration.

The present inventors limited the acquired data to vibration, and proceeded with experiments and verifications based on analyzing the obtained vibration by amplitude and wave width (time axis length), and completed the present invention. It was.

The invention according to claim 1 is a tool life detecting device attached to a machine tool that performs machining on the work by a relative motion between the machining tool and the work, and detects the life of the machining tool during the machining work.
This tool life detection device is obtained by a vibration sensor attached to a component of the machine tool to detect vibration, a calculation unit that calculates the Mahalanobis distance based on vibration information from the vibration sensor, and this calculation unit. It is equipped with a determination unit that determines whether or not the Mahalanobis distance is greater than or equal to the determination value, and an abnormality display unit that displays an abnormality when the determination unit determines that the Mahalanobis distance is greater than or equal to the determination value.
In the calculation unit, a sample line parallel to the processing time axis is drawn on the waveform curve obtained from the vibration information, the number of intersections where the waveform curve and the sample line intersect is used as the amount of change, and the waveform curve is divided by the waveform curve. The sum of the line segments of the sample line is used as the abundance amount, and the change amount and the abundance amount are used for calculating the Mahalanobis distance.

The invention according to claim 2 is the tool life detection device according to claim 1.
The component of the machine tool is the spindle of the machine tool to which the machining tool is attached.
The vibration sensor is characterized in that it is attached to the spindle and along the feed direction of the machining tool.

The invention according to claim 3 is the tool life detection device according to claim 1 or 2.
The calculation unit is characterized in that the distance of the Mahalanobis is calculated by using a part of the vibration information obtained when the machining tool makes one pass relative to the work. To do.

The invention according to claim 4 is the tool life detection device according to any one of claims 1 to 3.
In the calculation unit, the frequency at which the blade of the machining tool hits the work is set as the fundamental frequency.
This fundamental frequency is set as the primary frequency, and the frequency of the secondary or higher is determined based on this primary frequency.
It is characterized in that vibration information at least in the vicinity of the primary frequency is filtered from a part of the vibration information, and the distance of the Mahalanobis is calculated using the filtered vibration information.

The invention according to claim 5 is a tool life detection method that is attached to a machine tool that performs machining on the work by a relative motion between the machine tool and the work and detects the life of the machine tool during the machining work.
The process of detecting vibration generated in the components of the machine tool and
The process of calculating the Mahalanobis distance based on the detected vibration information,
It consists of a process of detecting an abnormality when the distance of Mahalanobis obtained by calculation is equal to or greater than the judgment value.
In the step of calculating the Mahalanobis distance, a sample line parallel to the processing time axis is drawn on the waveform curve obtained from the vibration information, and the number of intersections where the waveform curve and the sample line intersect is used as the amount of change. It is characterized in that the sum of the line segments of the sample lines separated by a waveform curve is used as the abundance amount, and the change amount and the abundant amount are used for calculating the Mahalanobis distance.

The invention according to claim 6 is the tool life detection method according to claim 5.
In the step of calculating the Mahalanobis distance, the Mahalanobis distance is calculated using a part of the vibration information obtained when the machining tool makes one pass relative to the work. It is characterized by doing.

The invention according to claim 7 is the tool life detection method according to claim 5 or 6.
In the process of calculating the Mahalanobis distance, the frequency at which the blade of the machining tool hits the work is set as the fundamental frequency, this fundamental frequency is set as the primary frequency, and the second or higher frequency is determined based on this primary frequency.
It is characterized in that vibration information at least in the vicinity of the primary frequency is filtered from a part of the vibration information, and the distance of the Mahalanobis is calculated using the filtered vibration information.

In the invention according to claim 1, a sample line parallel to the processing time axis is drawn on the waveform curve obtained from the vibration information, the number of intersections where the waveform curve and the sample line intersect is used as the amount of change, and the waveform curve is separated. The sum of the line segments of the sample line is taken as the abundance amount, and the amount of change and the abundance amount are used to calculate the Mahalanobis distance.
The line segment of the sample line separated by the waveform curve corresponds to the width of the wave.

That is, in the present invention, only vibration information is selected as the primary information from a large number of data (primary information). As a result, the burden on the calculation unit could be significantly reduced.
Then, the number of intersections where the waveform curve and the sample line intersect is used as the amount of change, the sum of the line segments of the sample line separated by the waveform curve is used as the abundance amount, and the amount of change and the abundance amount are used for the calculation of the Mahalanobis distance. As a result, the accuracy of life detection can be improved, and the machining tool can be used to the limit.
Therefore, the present invention provides a tool life detection device capable of detecting the life of a machining tool including chipping with high accuracy.

In the invention according to claim 2, the vibration sensor is attached to the spindle and along the feeding direction of the machining tool.
If the axial direction of the spindle is the z-axis direction, the direction perpendicular to the z-axis and the feed direction of the machining tool is the y-axis direction, and the direction orthogonal to both the y-axis and the z-axis is the x-axis direction, the vibration sensor is installed. It was confirmed that the tool life can be detected in any of the x-axis direction, the y-axis direction, and the z-axis direction.
However, it was found that the life determination is more reliable in the y-axis direction than in the x-axis direction and the z-axis direction. Therefore, it is recommended that the vibration sensor be mounted along the feed direction of the machining tool.

In the invention according to claim 3, a part of the vibration information obtained when the machining tool makes one pass relative to the work is used. The burden on the calculation unit can be reduced and the cost of the calculation unit can be reduced by performing the calculation using a part of the vibration information as compared with the calculation using all the vibration information.

In the invention according to claim 4, the calculation is performed using vibration information filtered based on at least the fundamental frequency. Since filtering is performed based on at least the fundamental frequency, only the vibration information when the blade hits the work can be used for the calculation, and the reliability of the life determination can be further improved.

In the invention according to claim 5, similarly to claim 1, a sample line parallel to the processing time axis is drawn on the waveform curve obtained from the vibration information, and the number of intersections where the waveform curve and the sample line intersect is used as the amount of change. , The sum of the line segments of the sample lines separated by the waveform curve is used as the abundance amount, and the amount of change and the abundance amount are used for the calculation of the distance of Maharanobis.

That is, in the present invention, only vibration information is selected as the primary information from a large number of data (primary information). As a result, the burden on the calculation unit could be significantly reduced.
Then, the number of intersections where the waveform curve and the sample line intersect is used as the amount of change, the sum of the line segments of the sample line separated by the waveform curve is used as the abundance amount, and the amount of change and the abundance amount are used for the calculation of the Mahalanobis distance. As a result, the accuracy of life detection can be improved, and the machining tool can be used to the limit.
Therefore, the present invention provides a tool life detection method capable of detecting the life of a machining tool including chipping with high accuracy.

In the invention according to claim 6, as in claim 3, a part of the vibration information obtained when the machining tool makes one pass relative to the work is used. The burden on the calculation unit can be reduced and the cost of the calculation unit can be reduced by performing the calculation using a part of the vibration information as compared with the calculation using all the vibration information.

In the invention according to claim 7, the calculation is performed using vibration information filtered based on at least the fundamental frequency, as in claim 4. Since filtering is performed based on at least the fundamental frequency, only the vibration information when the blade hits the work can be used for the calculation, and the reliability of the life determination can be further improved.

It is a principle diagram of the experimental apparatus which concerns on this invention. It is a graph of the machined surface roughness and the vibration wave obtained in the experiment. It is a figure explaining the amount of change and the amount of existence used when calculating an MD value. It is a figure explaining that a part of vibration information is used. It is a graph of MD value created based on the vibration information of a work. It is a figure explaining the effectiveness of this invention. It is a principle diagram of the experimental apparatus provided with the vibration sensor in the x-axis direction of the main axis. It is a graph of the MD value created based on the vibration information in the x-axis direction. It is a figure explaining filtering. It is a graph of the MD value created based on the vibration information in the x-axis direction after filtering. It is a graph of the MD value created based on the vibration information of the main axis in the z-axis direction. It is a graph of the MD value created based on the vibration information of the main axis in the y-axis direction. It is a basic block diagram of the tool life detection apparatus which concerns on this invention. It is a flow figure explaining the operation of the tool life detection apparatus which concerns on this invention. It is a figure explaining the prior art.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

The tool life detection device 31 according to the present invention will be described with reference to FIG. 13, but the basic principle of the present invention as a premise thereof will be described with reference to FIGS. 1 to 12.
As shown in FIG. 1, the experimental device 10 includes a table 11, a spindle 12, a vibration sensor 13, an amplifier 14 that amplifies the vibration information from the vibration sensor 13, and an MD value based on the amplified vibration information. It is provided with a calculation unit 15 for calculating.
As the vibration sensor 13, a small uniaxial acceleration pickup was used in the experiment, but the type and type may be arbitrarily selected.

The lower plate 16 is placed on the table 11, the work 17 is placed on the lower plate 16, and the upper plate 18 is placed on the work 17. Then, a plurality of (4 bolts in this example) bolts 19 are passed through the upper plate 18, the work 17, and the lower plate 16 and then screwed into the table 11. It is permissible to fix the lower plate 16 to the table 11 and fix the work 17 and the upper plate 18 to the lower plate 16 with bolts 19.

An end mill 21 as a cutting tool is attached to the spindle 12. One side of the work 17 is cut by relatively moving the end mill 21 and the work 17 in the x-axis, y-axis, and z-axis directions and rotating the end mill 21.

Experimental conditions:
-Work material: SKD11 baked to the center
-Work dimensions: 5 mm x 100 mm x 100 mm

・ Number of end mill blades: 6 ・ Spindle speed: 3170 rpm ・ Cutting: 0.1 mm
・ Feed speed: 5.3 mm / sec ・ 1 pass time: Approximately 20 seconds (time to cut 100 mm length once with an end mill)
-Work exchange: Work is exchanged in about 200 passes. Because the cutting allowance disappears in about 200 passes.

-Sampling frequency: 6.4 kHz
・ Measurement items: Machined surface roughness, cutting vibration, presence or absence of chipping:
・ ・ For cutting vibration, the vibration data is set to the absolute value for each pass, and the average value of the absolute values is used.
・ ・ For chipping, check with a microscope every 25 passes (2.5 m).
-Calculation item: MD value (details will be described in FIG. 3)

As shown in FIG. 2A, when the cutting distance (m) is taken on the horizontal axis and the machined surface roughness (Ra (μm)) is taken on the vertical axis, the machined surface gradually becomes rough. This is because the end mill gradually wears.
The workpiece is exchanged when the horizontal axis exceeds 20 m and when it exceeds 40 m, and when the third workpiece is being cut, that is, when the cutting distance is around 70 m, the roughness jumps to 1.5 μm. It was. When the blade of the end mill was observed with a microscope, chipping (chip of the blade) was observed.

In this way, chipping can be detected by monitoring the roughness of the machined surface. However, it is difficult to measure the roughness of the machined surface during actual operation.
On the other hand, vibration can be measured during cutting work. Therefore, it is examined whether or not chipping can be detected by vibration.

As shown in FIG. 2B, the vibration gradually increased. There is a large turbulence before 40 m on the horizontal axis, but this turbulence is the boundary between the first and second days, and is the turbulence that occurs when the cutting work is stopped or started.
It is predicted from FIG. 2A that chipping occurs when the cutting distance is around 70 m. However, the change in vibration is not remarkable before and after the cutting distance is 70 m. Therefore, it is difficult to detect chipping.

To overcome this difficulty, the MD value (Mahalanobis distance) is used in the present invention.
The MD value can be obtained by calculating the amount of change or the existence value by the MT method calculation formula. The amount of change and the existence value will be described with reference to FIG. Since the MT method calculation formula is well known, the description of the formula and the calculation will be omitted.

A comparative example is shown in FIG. 3 (a).
In FIG. 3A, the vibration value 23 is plotted after the cutting time is plotted on the horizontal axis and the vibration is plotted on the vertical axis. The vibration value 23 is a digital value. In MT (Mahalanobis Taguchi method), an appropriate sample line 24 is drawn parallel to the horizontal axis (machining time axis). Then, in the standard method, the number of vibration values 23 existing above the sample line 24 is used as the abundance amount. The number of points in the first mountain 25 is 6, the number of points in the second mountain 26 is 5, and the number of points in the third mountain 27 is 3. By the calculation of 6 + 5 + 3 = 14, the abundance is 14.

The sample line 24 drawn parallel to the processing time axis is separated by a first mountain 25, a second mountain 26, and a third mountain 27.
Let the line segment of the sample line 24 separated by the first mountain 25 be m1. A line segment is a line of finite length and is different from a line of infinite length. The unit of the line segment m1 is the cutting time.

The length of this line segment m1 is expected to have a great influence on the damage given to the end mill. However, in the comparative example described in FIG. 3A, only the magnitude of vibration is considered, and the line segment m1 is not considered at all. The present inventors paid attention to this point.

Therefore, the present inventors have found that the reliability of the MD value can be improved by considering the line segment m1.
FIG. 3B is an example.
By connecting the vibration values (FIGS. 3 (a) and 23) given at the points with a smooth curve, the waveform curve 28 shown in FIG. 3 (b) was obtained. Then, the number of intersections 29 (6 in this example) where the waveform curve 28 and the sample line 24 intersect was used as the amount of change.
In addition, the sum (m1 + m2 + m3) of the line segment m1 of the first mountain 25, the line segment m2 of the second mountain 26, and the line segment m3 of the third mountain 27 was taken as the abundance amount.
In the present invention, the MD value is calculated based on the amount of change and the amount of abundance.

The sample line 27 and the waveform curve 28 have been described graphically to facilitate understanding, but it goes without saying that they are virtual lines in a computer. The intersection 29 and the line segments m1 to m3 are also virtual points and lines.

The MD value is calculated for each pass, but in order to reduce the burden on the calculation unit, the following measures are preferably taken.
As shown in FIG. 4, of the vibration data of 20 seconds (1 pass), 2 seconds from the 1st to the 3rd seconds of the stable period is set as the MT method calculation area. By performing the calculation for only 2 seconds out of 20 seconds, the burden on the calculation unit can be reduced to 1/10.
The MT method calculation area may be set at an arbitrary location, such as changing to 2 seconds from the 9th second to the 11th second.

The MD value calculated based on FIGS. 3 (b) and 4 will be described with reference to FIG. 5 (b).
FIG. 5A is the same diagram as FIG. 2B.
The area between 0 and 67.5 m on the horizontal axis of FIG. 5 (a) is shown in a packed manner in FIG. 5 (b), and the area between 67.5 and 69.9 m on the horizontal axis of FIG. 5 (a) is shown in FIG. In 5 (b), it is expanded and shown.

On the horizontal axis, the MD value between 0 and 67.5 m was 5 or less as shown in FIG. 5 (b). This period is called the normal range for convenience.
On the horizontal axis, the MD value between 67.5 and 69.9 m varied between 0 and 249, as shown in FIG. 5 (b). This period is called the boundary area for convenience.
On the horizontal axis, the MD value at 70 m and above exceeded 100 as shown in FIG. 5 (b). This period is called an abnormal area for convenience.

For example, when the determination value is set to "50", the MD value becomes equal to or greater than the determination value at (68.6) in the middle of the boundary region, and it is possible to determine that it is abnormal at this point.
This possibility was confirmed in another demonstration experiment. The result will be described with reference to FIG.

In this demonstration experiment, the workpiece was cut with a turret lathe.
As shown in FIG. 6A, the MD value was small and stable while grinding up to 160 workpieces. The skilled worker in charge of the lathe noticed an abnormality at point A. The number of production at point A is 184.

As shown in FIG. 6B, when a determination value is given, the MD value becomes equal to or greater than the determination value at the time point B. The number of production at point B is 171.

It is assumed that the 171st to 184th workpieces are "defective".
According to FIG. 6B to which the present invention is applied, the number of defective products is limited to one.
On the other hand, in FIG. 6A to which the present invention is not applied, the number of defective products reaches 17 by the calculation of 187-170 = 17.

By applying the present invention, a special effect that the occurrence of defective products can be minimized is exhibited. That is, according to the present invention, it is possible to continue using the cutting tool to the very limit while minimizing the occurrence of defective products.

By the way, the vibration sensor 13 is attached to the upper plate 18 in FIG. In this mounting, it is necessary to attach / detach the vibration sensor 13 when the work 17 is replaced, which increases the man-hours for attachment / detachment.
Since it is required to reduce the man-hours, it is considered to attach the vibration sensor 13 to the spindle 12.

As shown in FIG. 7, the vibration sensor 13 was attached to the main shaft 12 and along the x-axis direction, an experiment was performed, and the MD value was calculated. As a result, it is shown in FIG.
As shown in FIG. 8, the MD values in the boundary region and the abnormal region were not significantly different from the MD values in the normal region. With this, it is difficult to give a judgment value, and even if it is given, there is a risk that an erroneous judgment will be made, and countermeasures are required.

In FIG. 1, since the vibration sensor 13 was attached to the work 17 side, the present inventors could directly detect the vibration by the vibration sensor 13, but in FIG. 7, the vibration sensor 13 is attached to the spindle 12. ing. It was considered that a bearing was interposed between the spindle 12 and the end mill 21 and the vibration was damped by the gap between the bearings. It is necessary to take measures to compensate for this attenuation.

It was noted that the end mill 21 has six blades per circumference at a pitch of 60 °, and there is a difference in vibration between when the blades hit the work 17 and when the blades do not hit the work 17. That is, we focused on the fact that the vibration data when the blade is not in contact reduces the reliability.

FIG. 9A is the same diagram as in FIG.
The vibration information in the MT method calculation region of FIG. 9 (a) was frequency-analyzed as shown in FIG. 9 (b). Since the 6-flute end mill is rotated 3170 rpm, 317 Hz is the fundamental frequency for cutting by the calculation of 6 × 3170 ÷ 60 = 317.
In FIG. 9 (b), horizontal lines are added to 317 Hz (primary), 634 Hz (secondary), 951 Hz (third), 1268 Hz (fourth), and 1585 Hz (fifth).
Then, as shown in FIG. 9C, filtering is performed so that each frequency has a width of about 10 Hz, and the filtered waveform is used as a new MT method calculation area.

The result of recalculating the MD value based on this new MT method calculation area is shown in FIG.
Compared with FIG. 8, in FIG. 10, the MD value in the boundary region is significantly different from the MD value in the normal region. Therefore, in FIG. 10, abnormality detection becomes easy and accurate.

In FIG. 9 (c), only 317 Hz (fundamental frequency) was used as the new MT method calculation region, and when the calculation was performed, a difference was observed between the normal region, the boundary region, and the abnormal region, although not as much as in FIG.
Next, when two frequencies consisting of 317 Hz (primary frequency) and 634 Hz (secondary frequency) were set as the new MT method calculation area and calculated, they approached FIG. 10 a little.
That is, when calculating based on the primary frequency to the nth frequency (n is an integer of 2 or more), the larger n is, the clearer the difference between the normal region and the boundary region or the abnormal region.

In the embodiment, n is set to 5, but n may be appropriately set according to the situation. Depending on the situation, the nth frequency may not be necessary.
Therefore, the fundamental frequency is set as the primary frequency, the frequency of the secondary or higher is determined based on this primary frequency, the vibration information in the vicinity of at least the primary frequency is filtered from a part of the vibration information, and the filtered vibration information is used. Then, the distance of Maharanobis should be calculated.

As shown in FIG. 11A, the vibration sensor 13 was attached to the spindle 12 and along the z-axis direction.
The MD value as shown in FIG. 11B was obtained. This MD value depends on the new MT method calculation area.

As shown in FIG. 12A, the vibration sensor 13 was attached to the spindle 12 and along the y-axis direction. “Along the y-axis direction” means that the axis of the vibration sensor 13 is arranged parallel to the y-axis. The same applies to the x-axis direction and the z-axis direction.
The MD value as shown in FIG. 12B was obtained. This MD value depends on the new MT method calculation area.

10 (x-axis direction), FIG. 11 (b) (z-axis direction), and FIG. 12 (b) (y-axis direction) are compared.
Focusing on the boundary region, FIGS. 10 (x-axis direction) and 12 (b) (y-axis direction) are excellent in terms of abnormality detection.
Further, paying attention to the abnormal region, FIG. 12B (y-axis direction) is excellent.

Therefore, although the vibration sensor 13 can detect an abnormality no matter where it is attached to the main shaft 12, it is preferably arranged in the x-axis direction or the y-axis direction, and further preferably in the y-axis direction.

Next, the tool life detection device 31 according to the present invention will be described with reference to FIGS. 13 and 14.
As shown in FIG. 13, the machine tool 30 includes a table 11 that supports the work 17 and a spindle 12 to which the machining tool 21 is detachably attached as main elements, and includes a tool life detecting device 31.

The tool life detection device 31 includes a vibration sensor 13 attached to a component of the machine tool 30 (for example, a work 17 or a spindle 12), an amplifier 14 that amplifies the vibration information obtained by the vibration sensor 13, and an amplified vibration. A calculation unit 15 that calculates an MD value based on information, a judgment unit 32 that compares the calculated MD value with a judgment value, and an abnormality display unit that notifies the surroundings of an abnormality when the judgment unit 32 determines an abnormality. It consists of 33. Anomalies are signaled by the sound of a buzzer or bell, the light of a lamp or revolver, a graphic or text display on a display, or a combination of these.

The machine tool 30 may be provided with a table 11 for supporting the work 17, and may be a milling machine, a drilling machine, a boring machine, or a lathe. If the machining tool 21 is a cutting tool, the cutting tool may be a milling cutter, an end mill, a drill, or a tool bit.

At ST (step number) 01 in FIG. 14, a vibration sensor is attached to the machine tool.
In ST02, the determination value MDb is read.
Next, machining is started (ST03), an MD value is calculated for each pass (ST04), and it is determined whether or not the MDcal obtained by the calculation is equal to or greater than the determination value MDb (ST05).

If MDcal is less than the determination value MDb, the process returns to ST04 and processing is continued. When the work is interrupted due to a break or when the work is artificially finished, this flow is finished by ST06.

When MDcal is determined to be equal to or higher than the determination value MDb in ST05, an abnormality display is performed (ST07).
It is permissible to stop the processing together with the abnormality display, but preferably, wait until the path is completed (ST08).
When the pass is completed, machining is stopped (ST09), the machining tool is replaced (ST10), and when the work is continued, the process returns to ST03 (ST11).

That is, the tool life detection method according to the present invention comprises the following steps.
The determination value is the process of detecting the vibration generated in the component of the machine tool (ST01 to ST03), the process of calculating the Mahalanobis distance based on the detected vibration information (ST04), and the calculated Mahalanobis distance. It comprises a step (ST05) of detecting an abnormality at the above time.

Then, in the process of calculating the Mahalanobis distance, a sample line parallel to the processing time axis is drawn on the waveform curve obtained from the vibration information, and the number of intersections where the waveform curve and the sample line intersect is used as the amount of change, and the waveform curve is used. The sum of the line segments of the delimited sample lines is taken as the abundance amount, and the amount of change and the abundance amount are used to calculate the Mahalanobis distance.

It should be noted that this flow describes a preferable example, and may be changed as appropriate.

Further, in the embodiment, the machining tool 21 is a cutting tool (end mill, etc.), but the machining tool 21 may be a grinding tool, a polishing tool, or a drilling tool, and any type of tool can be used as long as it is used for machining. Absent.
Further, in the embodiment, the component of the machine tool to which the vibration sensor is attached is a work or a spindle, but the component of the machine tool may be a machining tool, a base of a turret, or a stage for fixing the work. Any element may be used as long as it is a part where vibration generated by machining is transmitted.

The present invention is suitable for a tool life detection device and a tool life detection method attached to a machine tool.

12 ... Spindle, 13 ... Vibration sensor, 15 ... Calculation unit, 17 ... Work, 21 ... Machining tool (cutting tool, end mill), 24 ... Sample line, 28 ... Wave curve, 29 ... Intersection, 30 ... Machine tool, 31 ... Tool life detection device, 32 ... Judgment unit, 33 ... Abnormality display unit, m1 to m3 ... Line segment.

Claims (7)

A tool life detection device that is attached to a machine tool that performs machining on the work by the relative movement of the machine tool and the work, and detects the life of the machine tool during the machining work.
This tool life detection device is obtained by a vibration sensor attached to a component of the machine tool to detect vibration, a calculation unit that calculates the Mahalanobis distance based on vibration information from the vibration sensor, and this calculation unit. It is equipped with a determination unit that determines whether or not the Mahalanobis distance is greater than or equal to the determination value, and an abnormality display unit that displays an abnormality when the determination unit determines that the Mahalanobis distance is greater than or equal to the determination value.
In the calculation unit, a sample line parallel to the processing time axis is drawn on the waveform curve obtained from the vibration information, the number of intersections where the waveform curve and the sample line intersect is used as the amount of change, and the waveform curve is divided by the waveform curve. A tool life detection device, wherein the sum of the line segments of the sample line is used as the abundance amount, and the change amount and the abundant amount are used for calculating the distance of the maharanobis. The tool life detection device according to claim 1.
The component of the machine tool is the spindle of the machine tool to which the machining tool is attached.
The vibration sensor is a tool life detecting device characterized in that it is attached to the spindle and along the feeding direction of the machining tool. The tool life detection device according to claim 1 or 2.
The calculation unit is characterized in that the distance of the Mahalanobis is calculated by using a part of the vibration information obtained when the machining tool makes one pass relative to the work. Tool life detector. The tool life detection device according to any one of claims 1 to 3.
In the calculation unit, the frequency at which the blade of the machining tool hits the work is set as the fundamental frequency.
This fundamental frequency is set as the primary frequency, and the frequency of the secondary or higher is determined based on this primary frequency.
A tool life detection device characterized in that vibration information at least in the vicinity of the primary frequency is filtered from a part of the vibration information, and the distance of the Mahalanobis is calculated using the filtered vibration information. It is a tool life detection method that is attached to a machine tool that performs machining on the work by the relative movement of the machining tool and the work, and detects the life of the machining tool during the machining work.
The process of detecting vibration generated in the components of the machine tool and
The process of calculating the Mahalanobis distance based on the detected vibration information,
It consists of a process of detecting an abnormality when the distance of Mahalanobis obtained by calculation is equal to or greater than the judgment value.
In the step of calculating the Mahalanobis distance, a sample line parallel to the processing time axis is drawn on the waveform curve obtained from the vibration information, and the number of intersections where the waveform curve and the sample line intersect is used as the amount of change. A tool life detection method, characterized in that the sum of the line segments of the sample lines separated by a waveform curve is used as the abundance amount, and the change amount and the abundant amount are used for calculating the Mahalanobis distance. The tool life detection method according to claim 5.
In the step of calculating the Mahalanobis distance, the Mahalanobis distance is calculated using a part of the vibration information obtained when the machining tool makes one pass relative to the work. A tool life detection method characterized by The tool life detection method according to claim 5 or 6.
In the process of calculating the Mahalanobis distance, the frequency at which the blade of the machining tool hits the work is set as the fundamental frequency, this fundamental frequency is set as the primary frequency, and the second or higher frequency is determined based on this primary frequency.
A tool life detection method characterized in that vibration information at least in the vicinity of the primary frequency is filtered from a part of the vibration information, and the distance of the Mahalanobis is calculated using the filtered vibration information.

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