JPS6069550A - Method and device for detecting grinding crack - Google Patents

Abstract

PURPOSE:To detect a grinding crack through a simple device and realize automatic, labor-saving grinding work by converting acoustic emission generated in grinding work into an electric signal, detecting its amplified signal after passing it through a band-pass filter, and generating a warning of the grinding crack when the detected value is larger than a set threshold value. CONSTITUTION:A grinding crack detector consists of a sensor 5 which is fitted to a chuck 3 and converts the acoustic emission into the electric signal, an amplifier 6 for the signal, a band-pass filter 7 connected to the amplifier 6, a detector 8, and an amplitude discriminator 9 which compares the amplitude of the output of the band-pass filter 7 with the set threshold value. Then, the AE generated in the grinding work is converted by the sensor 5 into the electric signal, which is amplified by the amplifier 6, passed through the band-pass filter 7 to remove the AE, mechanical noise, and electric noise generated in the normal grinding work, and detected by the detector 8. Then, a buzzer 10 sounds to warn a grinding crack when a value larger than the preset threshold value, e.g. 10mV is detected by the amplitude discriminator 9.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention detects grinding cracks that occur during grinding and immediately after the end of grinding, and dresses the grindstone based on this, thereby preventing the production of defective products. The present invention relates to an effective grinding crack detection method and an apparatus for implementing the detection method.

In recent years, with advances in production technology, there has been an increasing demand for labor-saving and unmanned grinding processes, but grinding processes require higher precision and quality than cutting processes, so automation is much more difficult. One of these is the occurrence of defective products due to grinding cracks.

This has been a problem for some time, but there was no suitable means of detection other than visual observation after grinding.

The present inventors have conducted various experiments and research on methods that utilize acoustic emissions (hereinafter abbreviated as AE) that occur during and immediately after the grinding process as a means for in-process detection of grinding cracks. As a result, it was discovered that the power of the AE becomes noticeable in a specific frequency band as grinding cracks occur during grinding, and based on this knowledge, the present invention was completed.

During the grinding process, if the working surface of the grinding wheel deteriorates due to clogging of abrasive grains, etc., the temperature of the grinding surface is extremely high, and grinding cracks (thermal cracks) occur in the workpiece. When the workpiece is made of steel, the power of
As a result of experiments, it has been confirmed that the frequency is noticeable in the band of 5 skins or 1 stone. It was also confirmed that immediately after the grinding process was completed, minute grinding cracks (thermal cracks) were generated in the workpiece due to the drop in grinding heat, resulting in AE.

The present invention is based on this knowledge, and is based on the acoustic emission (AE) generated during grinding.
Converts the signal into an electrical signal, and converts the signal amplified by an amplifier into a specific frequency of 0, 5 & 1 stone, at which the power of the acoustic takeoff and emission (AE) caused by grinding cracks (thermal cracks) of the workpiece becomes apparent. Grinding characterized in that the wave is passed through a band pass filter corresponding to the band and then detected, and when this value is larger than a preset threshold value, this is detected by an amplitude discriminator and a warning of grinding cracks is issued. This relates to a crack detection method.

A second invention relates to a device used to carry out the above detection method, and includes: an L transducer that converts through acoustic emissions generated during grinding into an electrical signal; an amplifier that amplifies the electrical signal; and an amplifier that amplifies the electrical signal. It is characterized by comprising a bandpass filter connected to its output, and an amplitude discriminator that compares the amplitude of the output of the bandpass filter with a preset threshold.

According to the present invention, in-process detection of grinding cracks is possible, and if grinding cracks occur during grinding and there is a risk of producing a defective product, this can be detected and the grinding cracks can be detected to be unacceptable. The occurrence of defective products can be prevented by dressing the grindstone before the grinding process occurs or by relaxing the grinding conditions. In addition, the present invention saves labor in grinding,
This can contribute to automation.

Further, according to the second aspect of the present invention, the above detection method can be implemented using a relatively simple device.

Embodiments of the present invention will be specifically described below based on the drawings.

FIG. 1 is a system diagram of a grinding crack detection apparatus that implements the method of the present invention. In the figure, 1 is a grinding wheel, 2 is a table of a surface grinder, 3 is a magnetic chuck installed on the table 2, and 4. A workpiece 4 is held by a magnetic chuck 3, and the upper surface of the workpiece 4 is ground by a grinding wheel 1.

The grinding crack detection device includes a sensor 5 attached to the chuck 3 that converts acoustic emission (AE) into an electrical signal, an amplifier G that amplifies the signal, a bandpass filter 7 connected to the booster 6, '+'t'J is formed by a detector 8 and an amplitude discriminator 9 that compares the amplitude of the output of the bandpass filter 7 with a preset threshold. The frequency band of the band-pass filter corresponds to a specific frequency band of 5 to 1, since the AE multiplied signal power becomes noticeable as grinding cracks occur during grinding, and it is designed to not include electrical noise. In order to achieve this, in this embodiment, it is set to 0.6& to 0-8Lfi&.

Next, the effect will be explained. AE generated during grinding is converted into an electrical signal by a sensor 5, amplified by an amplifier 6, and passed through a bandpass filter 7.
After removing noise and electrical noise, the wave is detected by a wave detector 8. Thereafter, when the amplitude discriminator 9 detects a value larger than a preset threshold value, for example 10 mV, a buzzer 10 in response issues a warning of grinding cracks.

Figure 2 shows an example in which grinding cracks were detected by the above-mentioned detection device during surface grinding under the following processing conditions.
The figure shows the case where no grinding cracks occur during the same grinding, and
A comparison of the power spectra of AE measured when it occurs is shown.

Workpiece: SK3 steel, Depth of cut: 3Q7zm grinding wheel;
WA60 LmV, grinding wheel peripheral speed: 1800'77'm
x table speed: 10y>t/, , in dry grinding Figure 2, threshold value 10mV set 0.17 seconds after the start of grinding
The AE exceeding

Furthermore, according to Fig. 3, when no grinding cracks occur, the components above sail 6 t + ffh are very small, whereas when grinding cracks occur, the components from sail 6 &ih to 0
, 81. Ifh component is increasing. From this, the AE that occurs when grinding cracks occur is 0.6 stone or 81. It can be seen that this is noticeable in a specific frequency band of the abdomen.

The detection device shown in Fig. 1 can detect grinding cracks that occur during grinding, but during grinding, AE occurs due to plastic deformation and destruction of the workpiece, and this includes a certain amount of 0.6+,
Components in the frequency band from lIk to 0 and 8 hub are also included. Therefore, in order to reliably detect only grinding cracks, the threshold value must be set larger than this. Conversely, relatively small grinding cracks may be overlooked. Such minute grinding cracks occur even immediately after the end of the grinding process with little noise, and cause a unique AE, so the detection device described above can also be used to detect minute grinding cracks.

FIG. 4 shows an example of a device for detecting grinding cracks after grinding. This device includes the grinding crack detection device shown in FIG.
A timer discriminator 13 that detects the end time of the grinding process based on a signal from the machine and sends a signal to monitor for a set period of time thereafter;
It is constructed by adding an AND gate 14 that ANDs two signals.

In this case, the frequency band of the bandpass filter 7 is not necessarily limited to AE due to the occurrence of grinding cracks as in the device shown in FIG.
0, 61.1 & or 0 where signal power becomes noticeable
．． It is not necessary to limit it to around 8LTh, and a wider frequency band, for example 0.1 to 1-, may be used.

The timer discriminator 13 includes microswitches 11 and 12.
The end time of the grinding process is detected based on the signal from This prevents alarms from being issued due to AEs caused by this. The AND gate 14 detects an output from the amplitude discriminator 9 during the time when the signal is output from the timer discriminator 13, that is, within the monitoring time, and notifies the buzzer 1o of the occurrence of grinding cracks. G
issue a report.

FIG. 5 shows an example in which the detection device detects minute grinding cracks that occur immediately after the grinding process is completed. 54th
According to the figure, monitoring was started after 0.1" had passed after the end of grinding, and when it was 0.221nstx after the start of monitoring,
A signal exceeding the set threshold of 0.07V is detected,
We were able to detect the occurrence of microcracks.

[Brief explanation of drawings]

Figure 1 is a system diagram of a detection device that implements the method of the present invention;
The figure is a diagram showing the output signal measured by the same detector, Figure 3 is a comparison diagram of the power spectrum of AE measured by the same detector, and Figure 4 is a system diagram showing another example. , 5th
The figure shows the output signal measured by the same detection device. It is a diagram. 1...Grinding wheel 4...Workpiece 5...Sensor 6...Amplifier 7...・Band pass filter 8...
...Detector 9...Amplitude discriminator 10...
...buzzer - 11. 12...Micro switch 13...
- Timer discriminator 14... ANDGATE patent applicant Jiang 1) Hirodo Kami Yoshiaki Kakino Agent Patent attorney Yoshihide Ko

Claims (1)

[Claims] 1. Acoustic emissions generated during grinding are converted into electrical signals, and the signals amplified by an amplifier are used to significantly increase the power of the acoustic emissions generated by grinding cracks (thermal cracks) on the workpiece. It is detected after passing through a band pass filter corresponding to a specific frequency band of 0, 5+, h or 1 m, and when this value is larger than a preset threshold, this is detected by an amplitude discriminator, A grinding crack detection method characterized by issuing a notification of grinding cracks. 2. The grinding crack detection method according to claim 1, wherein the passband of the bandpass filter is 0.61 to 0.811'ib. 3. A transducer that converts acoustic emissions generated during grinding into an electrical signal, an amplifier that amplifies the electrical signal, a bandpass filter connected to the output of the amplifier, and the amplitude of the output of the bandpass filter. A grinding crack detection device comprising an amplitude discriminator that compares the amplitude with a preset threshold.