JPH06198547A - Fracture predicting method for rotary cutting tool - Google Patents

Abstract

PURPOSE:To predict occurrence of a fracture in a cutting tool precisely by detecting individual cutting torque patterns each time multiple works are cut by the cutting tool and comparing this with the predetermined cutting tool fracture critical torque level. CONSTITUTION:When a new cutting tool 12 is used because of a change and the like, a new work 14 is cut by the new cutting tool 12 installed in a tool holder 16 examinationally so that cutting torque of this time is detected by a torque sensor 18 while feeding power is detected by a load cell 24, and the detected results are stored in a storage device 30. A cutting tool fracture critical torque level, which is as high as the torque level nearly meeting the fracture of the cutting tool 12, is set on the basis of the detected cutting torque pattern. Then, a torque pattern detected during actual cutting and the cutting tool fracture critical torque level are compared with each other, and a spindle motor 22 is stopped when the cutting torque pattern becomes larger than the cutting tool fracture critical torque level, so that the fracture of the cutting tool 12 is prevented beforehand.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for predicting breakage of a rotary cutting tool.

[0002]

2. Description of the Related Art A rotary cutting tool such as a drill or a tap is generally attached to an appropriate machine tool for use. Especially when operating such a machine tool unattended, if the blade breaks, the work will be lost,
There is a problem that the time for repair is lost. Therefore, conventionally, in order to detect the breakage of the cutting tool, using a touch sensor to a tool or a blade, optically detecting the breakage, or using acoustic emission technology,
For example, it detects the amount of change in the current and power of the spindle motor that drives the blade to rotate.

[0003]

However, in these conventional techniques, although it is possible to detect after the cutting tool is broken, it is impossible or extremely difficult to predict the breaking. There is. Further, the breakage of the cutting tool often occurs when the cutting power increases as the wear of the cutting tool increases, and in such a case, not only the breaking of the cutting tool but also the finishing accuracy of the workpiece based on the wear of the cutting tool The double problem of deterioration occurs.

Further, recently, a carbide material is often used for the material of the cutting tool, which reduces wear and further greatly improves the life of the cutting tool. However, on the other hand, since the cemented carbide tool breaks with a torque that is not so large, there is a problem that proper cutting torque management is demanded.

Therefore, the present invention solves such a problem, predicts the occurrence of breakage in a rotary cutting tool, and prevents it in advance, and accordingly, does not perform cutting work by a worn cutting tool. The purpose is to be able to. Furthermore, when the cutting tool is made of super hard material,
The purpose is to enable appropriate cutting torque management.

[0006]

In order to achieve the above object, the present invention detects a cutting torque pattern when a test work is cut experimentally with a new cutting tool, and detects the breaking torque of the cutting tool from the detected pattern. Set the cutting tool breakage risk torque level of the size before reaching, detect the cutting torque pattern at each cutting when actually cutting a large number of workpieces with this cutting tool, and determine the cutting torque pattern at the time of actual cutting. The breaking risk of the cutting tool is predicted by comparing with the risk level of the breaking risk of the cutting tool.

[0007]

The breaking torque when a predetermined work is cut by a certain rotary blade is generally 5 to 6 times the cutting torque when the work is cut when the blade is new. Therefore, a level of about 3 to 4 times the cutting torque is set as a level at which there is a risk of breakage, and the breaking torque is predicted by comparing the cutting torque pattern during actual cutting with this cutting tool breakage risk torque level. It becomes possible.

For example, when it is detected that the cutting torque pattern during actual cutting becomes larger than the set level, the motor for rotating the cutting tool is stopped,
Stepping back may be performed or the clutch of the rotary drive system may be disengaged to prevent the cutting torque from increasing further. Therefore, it is possible to perform appropriate cutting torque management when the cutting tool is formed of a cemented carbide material that is likely to break.

The rotary cutting tool mentioned here indicates a broad concept including not only ordinary cutting tools such as drills but also tapping screws and the like. The tool breakage risk torque level may be set by a torque value of a predetermined magnitude,
Alternatively, it may be set based on a cutting torque pattern that changes with the progress of cutting.

[0010]

EXAMPLE FIG. 4 shows an apparatus configuration for detecting and learning a cutting torque pattern during trial cutting. Where 10
Is a machine tool for machining a workpiece 14 with a rotary cutting tool 12 such as a tap or a drill. Cutting tool 12 is a tool holder
16, a torque sensor 18, a clutch 20, and a continuously variable transmission 21 are connected to a spindle motor 22. Torque sensor 18
Is a magnetostriction detection type and can detect the cutting torque of the cutting tool 12 with high accuracy without contact. The spindle motor 22 is connected to the frame 26 via a load cell 24 for detecting cutting feed power. When the frame 26 is moved by the feed motor 28, the blade 12 is fed. The torque sensor 18 and the load cell 24 are connected to a storage device 30 for storing the detected values of cutting torque and feed power.

When a new cutting tool 12 is to be used for replacement or the like in such a structure, the cutting torque pattern is first learned. In that case, a new cutting tool 12 is attached to the tool holder 16 and a new work piece 14 is cut experimentally,
The cutting torque at that time is detected by the torque sensor 18, the feed power is detected by the load cell 24, and the detection results are stored in the storage device 30.

The cutting torque is preferably detected and stored as a cutting torque pattern including a time change as shown in FIG. This is because it is often insufficient to detect and learn only the maximum torque generated. For example, when tightening a tapping screw, a torque peak occurs in two processes, a tap process by the screw itself as a rotary blade and a screw tightening process by a tightening tool, and it is better to detect both by a torque pattern.
Accurate prediction of breakage is possible. Further, in the case of a tap, for example, it is actually impossible to distinguish between the sudden increase in torque due to biting of cutting chips and the increase in torque due to tool wear unless the torque pattern is used. Of course, there are cases where it is sufficient to detect and store only the maximum value of the generated torque.

As shown by the broken line in FIG. 3, the cutting torque pattern often changes somewhat every time it is detected. Therefore, it is desirable to detect this about 10 times and store the averaged cutting torque pattern. Even when only the maximum value of the generated torque is detected, it is desirable to store the average value similarly. In particular, it is desirable to store the average value of the cutting torque pattern together with the cutting time information.

The storage device 30 stores a torque of a magnitude which is considered to cause breakage of the cutting tool 12, that is, a breaking torque of the cutting tool 12 in correspondence with the type, material, diameter and the like of the cutting tool 12. For example, when the cutting tool 12 is a tap, the breaking torque of the cutting tool is 5 to 6 times the above average value when the catch rate between the cutting tool and the work defined by the size of the prepared hole is 100%. . In addition, a value 3 to 4 times the above average value when the catch rate is 100% is the cutting tool breakage risk torque level indicating that there is a risk of breakage, and the storage device
Remembered in 30. The magnitude of the stored value is also shown in FIG.

Table 1 shows specific examples of these values when the cutting tool 12 is a tap. In this case, the work material was JIS SCM440 (H _B 193) and the tap material was JIS SKH3.

[0016]

[Table 1]

FIG. 2 shows a device configuration for an actual cutting operation. Here, 32 is a CPU, which is connected to the torque sensor 18 and the load cell 24, and is also connected to the storage device 30. Reference numeral 34 is a control device, which receives signals from the CPU 32, both motors 22 and 28, the clutch 20, and the continuously variable transmission
21 and can be controlled. Other configurations are the same as those shown in FIG.

During the cutting operation, the torque sensor 18 and the load cell 24 detect the cutting torque and the feed power by the torque sensor 18 and the load cell 24 for each work 14 or for each suitable number of works 14. Then, as shown in FIG. 1, the detected cutting torque pattern is compared by the CPU 32 with the tool breakage risk torque level. When the cutting torque pattern becomes larger than the risk level of breakage of the cutting tool, the cutting torque is prevented from further increasing by stopping the spindle motor 22, stepping back, or disengaging the clutch 20, thereby preventing breakage of the cutting tool 12.

Tool wear is one of the causes of increasing the cutting torque. That is, when the number of processed works 14, that is, the number of times of cutting increases, the cutting edge of the cutting tool 12 wears and the cutting torque increases as shown in FIG. Therefore, the cutting tool 12 is replaced when the cutting torque reaches the cutting tool breakage risk torque level. Alternatively, instead of immediately replacing the cutting tool 12 when the cutting tool breakage risk torque level is reached, if the cutting tool wear becomes severe, the cutting tool breakage danger torque level will often be exceeded. The replacement may be performed when the number of times or the level excess time exceeds a predetermined value.

Incidentally, since the relationship between the number of cutting operations and the increasing characteristic of the cutting torque is usually empirically known, the information on the number of cutting operations and the actually detected cutting torque pattern information are sent to the CPU 32. Therefore, the life of the cutting tool 12 can be predicted.

Alternatively, a second dangerous torque level is set between the blade breakage risk torque level and the blade breakage torque, and the cutting torque pattern at the time of actual cutting is the cutting tool breakage risk torque level and the second dangerous torque level. It is possible to predict whether or not the cutting tool will be broken by detecting whether or not there is a certain time or more between the cutting edge and the cutting edge.

Specifically, taking a tap as an example, for example, when the cutting tool breakage risk torque level is set to 3 times the cutting torque with a catch rate of 100%, and the cutting tool breakage torque is set to 5 times that, The second dangerous torque level can be set to four times that.

[0023]

As described above, according to the present invention, a new
It is detected when a test work is cut with a cutting tool.
From the cutting torque pattern to the breakage of the cutting tool.
Set the tool breakage risk torque level of this size, and
Cutting at each cutting when actually cutting a large number of workpieces
Each torque pattern is detected and this is broken
Predict breakage of the cutting tool by comparing it with the dangerous torque level
By doing so, it is possible to predict breakage of the cutting tool
And breakage of the cutting tool when operating the machine tool unattended
It is possible to prevent work loss and repair time loss.
And when the tool wears, change the cutting tool at an appropriate time.
It is possible to replace it, and processing accuracy based on tool wear
Can be prevented and the work piece finish accuracy can be reliably controlled.
Can be treated.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a cutting torque according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an apparatus for cutting a large number of works.

FIG. 3 is a diagram exemplifying a cutting torque when a trial cutting is performed with a new cutting tool for learning a cutting pattern.

FIG. 4 is a schematic configuration diagram of an apparatus for trial cutting with a new cutting tool.

[Explanation of symbols]

 10 Machine tool 12 Cutting tool 14 Workpiece

Claims (6)

[Claims] 1. A cutting torque pattern when a test work is experimentally cut with a new cutting tool is detected, and a cutting tool breakage risk torque level of a size before the breaking of the cutting tool is set from the detected pattern. , The cutting torque pattern at each cutting when actually cutting a large number of workpieces with this cutting tool is detected, and the cutting torque pattern at the time of actual cutting is compared with the cutting tool danger torque level to break the cutting tool. A method for predicting breakage of a rotary blade, which comprises predicting. 2. A cutting tool breakage risk torque level is set from the average value of a plurality of cutting torque patterns obtained by experimentally cutting a plurality of test works with a new cutting tool. The method of predicting breakage of a rotary blade according to claim 1. 3. The method of predicting breakage of a rotary cutting tool according to claim 1, wherein the cutting torque pattern has cutting time information. 4. The rotation according to claim 1, wherein a magnetostrictive torque sensor is provided between the driving source of the cutting device and the tool holder to detect the cutting torque pattern. Method for predicting breakage of cutting tools. 5. The method of predicting breakage of a rotary cutting tool according to claim 1, wherein the feed power of the cutting tool at the time of cutting is detected. 6. In addition to the cutting tool breakage risk torque level, a cutting tool breakage torque having a size leading to the breaking of the cutting tool is set from the cutting torque pattern detected during the trial cutting, and the cutting tool breakage risk torque is further set. A second dangerous torque level is set between the level and the cutting tool breakage torque, and the cutting torque pattern during actual cutting is at least a certain time between the cutting tool breakage danger torque level and the second dangerous torque level. The method for predicting breakage of a rotary cutting tool according to any one of claims 1 to 5, further comprising detecting whether or not the cutting tool is broken.