JPS6222744B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a device that automatically detects damage to cutting tools, mainly thermal cracks. In recent years, unmanned operation of various machine tools has become extremely popular, and more recently, technological development has been actively carried out to improve efficiency and precision. In parallel with such technological development, there is a strong demand for effective countermeasures against variations in life span, damage, etc. of cutting tools for machine tools. Particularly, in machining such as milling and gear cutting that repeatedly involves cutting and non-cutting, thermal cracks often occur in the tool, resulting in tool breakage, significantly shortening tool life and increasing variation. Therefore, various methods and devices have been proposed that automatically measure and detect tool damage during cutting and issue an alarm or stop machine operation if the detected value exceeds a limit value. Damage due to thermal cracks,
I can't find anything that focuses on lifespan. An object of the present invention is to provide a device that can accurately and easily detect thermal cracks in cutting tools. Acoustic emission signals (hereinafter simply referred to as AE signals) generated from tools, workpieces, and/or machine tools during cutting include AE signals generated during cutting and AE signals generated during non-cutting, as shown in Figure 1.
AE signal is observed. Generally, tool damage (chips, wear, etc.) occurs when the cutting tool is cutting the workpiece, and tool damage can be detected accurately by detecting the cutting force, vibration of the tool, cutting noise, etc. A method is proposed. However, since damage to the cutting tool due to thermal cracking progresses during non-cutting processes, no means of detecting it has currently been found. Regarding thermal cracks in cutting tools, many years of research by the inventors revealed that when the tool is cooled during non-cutting, the tool surface receives large tensile stress and thermal cracks occur, and as machining continues, thermal cracks occur. I know it will progress. Therefore, we investigated the relationship between the total output of AE signals generated during non-cutting steps in interrupted machining and the thermal crack damage rate of tools. FIG. 6 is a diagram showing an outline of an apparatus for investigating the relationship between the sum of AE signal outputs and tool damage rate in the above-mentioned interrupted machining. In the figure, 1 is an AE signal detector, 2 is an amplifier, 3 is a frequency discriminator, 4 is an integrator, 7 is a gate through which the AE signal passes only when not cutting, 8
is the work material, 9 is the cutting process, 10 is the non-cutting process, 1
Reference numeral 1 indicates an arrow indicating the direction of rotation of the workpiece 8, and reference numeral 12 indicates a cutting tool. In the above device, when the workpiece 8 is rotated in the direction of the arrow 11 and intermittent cutting is performed using the cutting tool 12 (cutting and non-cutting steps are repeated twice during one rotation of the workpiece 8), the cutting tool 12 is A signal obtained through an AE signal detector 1 attached to the rear end with a magnet is amplified by an amplifier 2 and input to a frequency discriminator 4. The above AE signal input to the integrator 4 is integrated over time, and its value is taken out as the output 5. Note that the gate 7 detects whether the cutting tool 12 is cutting or not, and allows the signal from the AE signal detector 1 to pass through only when the cutting tool 12 is not cutting. In the first experiment, the frequency range of the frequency discriminator 3 was set to 0 to 2 MHz (wide), and the integrator 4 summed up all outputs in the above frequency range. The data obtained from this experiment are shown in Table 1.

[Table] The workpiece material in this experiment was alloy steel with an outer diameter of 170 mm, and its material was JIS SCM 430 and hardness HB 290. The tools used were based on JIS P 20. Cutting conditions: cutting speed 100m/min, depth of cut 1.5
mm, feed 0.5 mm/rotation, cutting time 10 minutes.
In Table 1, the output is expressed as a count value that is proportional to the value obtained by integrating the output of the signal over time. If the relationship between the output and the tool damage rate is graphically displayed from the data in Table 1, it will be as shown in Figure 2, and no correlation between the above output and the tool damage rate was observed. In the second experiment, the frequency range of the frequency discriminator 3 was set to 50 KHz to 1 MHz (narrowly), and only outputs having frequency components in this range were extracted and summed by an integrator. The data obtained from this experiment are shown in Table 2.

[Table] The work material, tool, and cutting conditions in this experiment were exactly the same as in the first experiment. If the relationship between output and tool damage rate is displayed graphically from the data in Table 2, it will be as shown in Figure 3.Although the value of the above output is smaller, there is a correlation between it and the tool damage rate. It will be done. In other words, the correlation between Figures 2 and 3 is
This means that the low frequency component of 50KHz or less in the AE signal has almost no relation to tool damage. If the lower limit frequency is 50KHz, preferably 100KHz or higher, thermal crack damage can be detected with sufficient accuracy. In addition, the upper limit frequency is 500KHz or higher, and the output of the AE signal is extremely small, so it is necessary to remove noise from high frequency components.
It is limited to components of 1 MHz, preferably 500 KHz or higher. This invention embodies the above idea, and FIG. 4 shows one embodiment of the device in block form. In the figure, 1 is an AE signal detector, 2 is an amplifier, 3 is a frequency discriminator, 4 is an integrator, 5 is a comparator, 6 is an alarm, and 7 is the AE of the above 1 only when not cutting.
This is the gate through which the signal from the signal detector passes. The above-mentioned detector 1 is attached to a cutting tool or a machine tool, and is configured to detect an AE signal using an AE signal measuring element. Among the detected AE signals, the AE signal only during non-cutting is inputted to the next amplifier 2 by the gate 7 and amplified. Augmented AE
Frequency components of 50 KHz or less and 1 MHz or more of the signal are removed by the next frequency discriminator 3, and the output of only the remaining frequency components is input to the next integrator 4. The AE signal input to the integrator 4 is integrated over time, and the value is compared with a preset reference value in the next comparator 5.
When the total output p of the frequency components of the signal exceeds the reference value _p1 , the alarm device 6 is activated and an alarm is issued.
Stop the work by stopping the machine tool or returning the cutting tool to its original setting position. FIG. 5 shows time t on the horizontal axis and output p of the frequency component of the 50KHz to 1MHz AE signal generated during non-cutting on the vertical axis in the above embodiment. As cracks occur and grow, they grow larger, and when they exceed the standard value _p1 , a warning is issued. This invention has discovered that there is a high degree of correlation between the AE signal of the frequency component of 50KHz to 1MHz that occurs during non-cutting in the cutting process and the thermal crack damage rate of the tool, and based on this, This system automatically detects thermal crack damage to tools. Therefore, according to the device of the present invention, it is possible to detect thermal crack damage of a cutting tool with high precision and with a simple device. In particular, as cutting speeds such as milling and gear cutting, which involve interrupted cutting, progress to higher cutting speeds, tool life variations due to thermal crack damage will become greater, and the effects of the present invention will be significant. . In addition, to operate the gate 7 in Fig. 4, a commercially available electric contact signal, cutting force signal, accelerometer or AE
Signals etc. can be used.

[Brief explanation of the drawing]

Figure 1 occurs during cutting and non-cutting processing.
AE signal output diagram, Figure 2 is 0 to 0 during non-cutting process.
Correlation diagram between the total output of AE signals in the frequency range of 2MHz and the thermal crack damage rate of the tool. Figure 3 shows the total output of the AE signals in the frequency range of 50KHz to 1MHz during non-cutting process and the thermal crack damage of the tool. Correlation diagram with rate. Fig. 4 is a block diagram showing an embodiment of the present invention, Fig. 5 is a graph of the relationship between the total output of AE signals in the frequency range of 50KHz to 1MHz during non-cutting process and time, and Fig. 6 is an intermittent FIG. 2 is a diagram showing an outline of a device for investigating the relationship between the total output of AE signals in machining and tool damage rate. 1 is a detector, 2 is an intensifier, 3 is a frequency discriminator,
4 is an integrator, 5 is a comparator, 6 is an alarm, and 7 is a gate through which the signal from the AE signal detector in 1 passes only when not cutting.

Claims (1)

[Claims] 1. A detector that detects an acoustic emission signal that occurs during non-cutting in the intermittent cutting process, a discriminator that discriminates frequency components in the range of 50 KHz to 1 MHz from the signal, and the discriminated frequency components described above. A damage detection device for a cutting tool, comprising a comparator that compares the sum of the outputs with a preset reference value.