JPH0227110B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting damage to a cutting tool, and is improved so that damage can be detected accurately.

In recent years, in response to the need for unmanned machining, various methods have been developed to detect damage to cutting tools during machining. One such method is to use an acoustic emission sensor (hereinafter abbreviated as AE sensor) that detects ultrasonic waves (acoustic emission) generated when a substance breaks. In other words, damage to the cutting tool can be detected even during machining by monitoring the acoustic emission signal (hereinafter abbreviated as AE signal) corresponding to the acoustic emission output from the AE sensor.

Next, we will introduce the conventional technology using such a method in the first example.
This will be explained with reference to FIGS. FIG. 1 shows an example of application to a hobbing machine, and FIG. 2 shows its measurement block diagram. In both figures, 1 is the AE sensor, 2
is a hob (gear cutting tool), 3 is a main bearing, 4 is a gear, 5
is the flyhole, 6 is the tip metal (sub-bearing), and AE sensor 1 detects the acoustic emission generated from hob 2 and responds accordingly.
Sends AE signal. This AE signal is transmitted to the AE detector 7
The AE signal is converted into a voltage and input to the counter 8, which counts the number of times the AE signal exceeds a predetermined threshold (see FIG. 3). of course,
The threshold value is set at a voltage higher than the noise level. The life of the gear cutting tool was determined based on the number of counts detected by the counter 8. In addition, during the experiment, a data recorder 9 for memory and an oscilloscope 10 for monitoring are added to collect data.

However, the above-mentioned conventional technology has the following drawbacks.

(i) As long as the AE signal converted to voltage exceeds the threshold, it is counted as one event regardless of the size of the AE signal, so the number of counts and tool life often do not match. Therefore, damage to the tool cannot be accurately determined.

(ii) If the threshold setting level is incorrect, wear cannot be detected. In other words, only phenomena that generate large AE signals, such as tool damage or breakage, can be evaluated. This inability to detect wear has prevented the practical application of high-speed hobbing. The reason for this is that, for example, if there is variation in workpiece hardness and a workpiece with a hardness higher than the expected hardness is processed at high speed, the hob will wear out significantly during processing and become defective. By the way, when hobbing, tools are generally replaced when the hob flank wear V _B reaches 0.4 to 0.5 mm. It is known that when this flank wear V _B exceeds 0.5 mm, wear progresses rapidly, and when V _B exceeds 1 mm, the hob becomes defective. Therefore, when trying to machine a hard workpiece at high speed as mentioned above,
V _B becomes 0.5mm quickly, and wear is 0.5mm
If it exceeds mm, it means high-speed machining.
When V _B exceeds 0.5 mm, the combination of increased wear rate immediately leads to hob failure.

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, an object of the present invention is to provide a damage detection method that can accurately detect the degree of damage such as chipping or breakage, and can also detect the progress of wear. The configuration of the present invention that achieves this object uses a sensor to detect acoustic emission generated from a cutting tool of a machine tool,
In the method of detecting damage to the cutting tool based on the acoustic emission signal sent from the sensor, the acoustic emission signal exceeding a predetermined threshold value is integrated and the cutting tool is detected based on the cumulative value. It is characterized by detecting damage to.

The present invention will be explained below based on examples.

FIG. 4 is a block diagram showing an apparatus for implementing the method of the present invention. In the same figure, 1 is an AE sensor,
2 is a hob, 3 is a main bearing, 4 is a gear, 5 is a flywheel, 6 is a tip metal, 7 is an AE detector, 8 is a counter, 9 is a data recorder, 10 is an oscilloscope, and these are conventional It is the same as the thing. Furthermore, this device is provided with a DC amplifier 11 and an integrator 12. Therefore, of the AE signals converted into voltages, those exceeding the threshold are integrated by the integrator 12. This integral value corresponds to the shaded area in FIG. Each integral value is then accumulated by a counter 8. In other words, this cumulative value corresponds to the sum of the areas of the hatched parts in FIG.

FIG. 6 shows data obtained when a workpiece having a predetermined hardness was hobbed using this device. Also, the cutting speeds at this time were 200rpm, 160rpm, and
It was set to 130 rpm. As can be seen from this figure, there is a correlation between the amount of wear and the cumulative value of the integrated value of the AE signal. Conversely, if you monitor the cumulative value, you can see the progress of wear even during machining. Of course, it is also possible to detect the degree of damage caused by defects, breakage, etc. Furthermore, even though the cutting speed is the same as the data example shown in Figure 6, if the cumulative increase rate of the integral value is large, the workpiece may be too hard or other cutting conditions may be abnormal. This indicates that the hob wear rate is abnormally high. In this case, damage to the hob can be prevented by taking appropriate measures before the hob is damaged. Furthermore, since such an abnormality is detected by detecting the rate of increase in the cumulative value, abnormal wear can be detected at the initial stage of the wear. Therefore, if this method is used, the practical application of high-speed hobbing will be promoted.

It goes without saying that the present invention can be widely applied not only to hobbing machines but also to gear shapers, milling machines, and NC gear cutting machines.

As specifically explained above in conjunction with the embodiments, according to the present invention, damage to the cutting tool is detected based on the cumulative value of the acoustic emission signal by integrating it. Not only can the degree of wear be detected accurately, but also the progress of wear can be detected even during machining.

[Brief explanation of drawings]

Figure 1 is a front view of a hobbing machine using the conventional method, Figure 2 is its measurement block diagram, and Figure 3 is an AE hobbing machine.
A characteristic diagram showing the signal, Fig. 4 is a block diagram showing the measurement block of the device that implements the method of the present invention, Fig. 5 is a characteristic diagram showing the AE signal, and Fig. 6 shows the accumulation of the integral value of the AE signal and flank wear. FIG. In the drawing, 1 is an acoustic emission sensor (AE sensor), 2 is a hob, 8 is a counter, 1
2 is an integrator.

Claims (1)

[Claims] 1. A method for detecting acoustic emission generated from a cutting tool of a machine tool using a sensor, and detecting damage to the cutting tool based on an acoustic emission signal sent from the sensor. A method for detecting damage to a cutting tool, comprising integrating an acoustic emission signal exceeding a value and detecting damage to the cutting tool based on the cumulative value.