JP2022086741A - Method and device for detecting hardness abnormality of work material - Google Patents

Abstract

To provide a method for detecting the hardness abnormality of a work material capable of inspecting the hardness abnormality of the total number of work materials to be ground without an inspection process.SOLUTION: Disclosed is a method for detecting the hardness abnormality of a work material 12 in which the hardness abnormality of the hardened work material 12 is detected, which includes: a grinding step of performing the grinding of the work material 12 hardened by using a grind stone 20; and a hardness abnormality determination step for determining the hardness abnormality of the hardened work material 12 based on an AE signal SAE generated from a grinding point of the grind stone 20 during a grinding process. As a result, regarding the hardness abnormality for the work materials 12, the total number of the work materials 12 can be inspected without an inspection process, and the reliability of the work materials 12 after grinding can be enhanced.SELECTED DRAWING: Figure 1

Description

The present invention relates to a hardness abnormality detection device for a work material that detects that the hardness of the work material is abnormal from an AE signal obtained during grinding, and a hardness abnormality detection method using the same.

For example, a work material made of hardened steel such as an outer ring, an inner ring, a sprocket, and a camshaft of a bearing may be ground by using a grinding wheel for finishing or the like. Since such quenching of the work material has a relatively large variation, it is desirable to inspect that the quenching of the work material is as specified prior to the grinding process in order to increase the product yield. Is done.

As such an inspection, for example, a hardness measuring method (JIS Z 2244: 2009, JIS Z) in which the hardness is measured by measuring the size of the dent formed when the indenter is pressed against the surface of the work material. 2245: 2016) is known. However, in the hardness measuring method in which the hardness is measured by measuring the size of the dent formed when the indenter is pressed against the surface of the work material in this way, inspection marks are left on the surface of the work material. Therefore, there is a possibility that progressive scratches starting from the inspection marks may occur, or undulations due to the inspection marks may occur and the component performance may be impaired. In addition, since such a hardness measurement method is a kind of destructive inspection, it may have to be a sampling inspection. Could reduce the reliability of.

On the other hand, in Patent Document 1, such a work material has a longitudinal groove shape having a length or depth indicating a reference of the quenching discoloration range on the surface or the quenching discoloration range in the depth direction. It has been proposed that the mark is provided so as to protrude from the hardened portion of the work material in the pressure forming process of the work material. According to this, when the quenching inspection on the surface of the work material is performed, whether or not the quenching range is within the allowable range is determined by comparing the quenching discoloration range on the surface with the length of the longitudinal groove-shaped mark. Judgment is made and the work material is inspected for quenching. In addition, when inspecting the quenching depth of the work material, the work material is cut so that the inner wall surface of the groove of the longitudinal groove-shaped mark appears, and the discoloration range in the depth direction from the surface and the longitudinal groove-shaped mark are formed. By comparing with the groove depth of, it is determined whether the quenching depth is within the allowable range, and the quenching of the work material is inspected. The above-mentioned mark (longitudinal groove) is formed shallower than the allowance in the grinding process which is the post-processing, and does not remain in the work material after the grinding process.

Japanese Unexamined Patent Publication No. 2012-246522

However, in such a quenching inspection method described in Patent Document 1, for example, in the inspection of the quenching depth, it is necessary to independently provide an inspection process, and in the inspection of the quenching depth range, the work material is used. There is a problem that it is necessary to destroy the material, and even if the quenching depth is a sampling inspection, if the quenching depth is large, the depth of the mark (longitudinal groove) is also large. As a result, the allowance for removing the mark (longitudinal groove) is also large, so there are inconveniences that the grinding load is large in the grinding process, the grinding time is long, and the life of the grinding wheel is shortened. rice field.

The present invention has been made in the background of the above circumstances, and an object of the present invention is to inspect all the hardness abnormalities of the work material to be ground without providing an inspection process. It is an object of the present invention to provide a hardness abnormality detecting method and a hardness abnormality detecting apparatus for a work material.

As a result of repeated studies based on the above circumstances, the present inventors conducted frequency analysis of the AE signal obtained in the process of grinding the hardened work material, and repeated studies, while performing a high-speed sampling period. When the frequency analysis of the AE signal digitized by using the A / D converter of the above, a specific frequency band that reacts sensitively to the hardness of the work material is found in the frequency band of 45 to 65 kHz in the frequency analysis of the frequency spectrum. The points included and the threshold value based on the vibration intensity value of the specific frequency band obtained from the work material with normal quenching are determined in advance, and the vibration intensity value of the specific frequency band obtained from the actual work material is determined in advance. By comparing with the threshold value, it was found that an abnormality in hardness of the work material, that is, an abnormality in quenching can be detected during the grinding process. The present invention has been made based on such findings.

The gist of the first invention is (a) a method for detecting a hardness abnormality of a hardened work material, and (b) a method for detecting a hardness abnormality of the hardened work material, which is (b) hardened using a grinding grindstone. Based on the grinding process of grinding the work material and (c) the AE signal generated from the grinding point of the grinding wheel during the grinding process, the hardness abnormality of the hardened work material is detected. It includes a hardness abnormality determination step for determining.

The gist of the second invention is that, in the first invention, when the method for detecting a hardness abnormality of the work material is determined not to be a hardness abnormality by the hardness abnormality determination step, the ground work material is ground. Is flowed to the next step of the grinding process, but when it is determined by the hardness abnormality determination step that the hardness is abnormal, the ground work material is sent to the next step of the grinding process. It is not done.

The gist of the third invention is that in the first invention or the second invention, the hardness abnormality determination step is (a) generated from the grinding point of the grinding wheel during the grinding process of the hardened work material. An AE sensor that detects the AE signal, a frequency analysis unit that frequency-analyzes the AE signal digitized using an A / D converter having a sampling period of 10 μsec or less, and (c) the frequency analysis. By integrating and calculating the vibration intensity value in the specific frequency band whose intensity changes according to the hardness of the hardened work material, which is included in the frequency band of 45 to 65 kHz in the frequency spectrum analyzed by the unit. The vibration intensity integrated value calculation unit that calculates the vibration intensity integrated value, and (d) the vibration intensity integrated value actually measured during grinding of the hardened work material and the preset hardness abnormality determination threshold value. The present invention is to determine the hardness abnormality of the hardened work material by using a hardness abnormality detection device including a hardness abnormality determination unit for determining the hardness abnormality of the hardened work material based on the above. ..

The gist of the fourth invention is that, in the third invention, the hardness abnormality detecting device is subjected to the cumulative grinding cross-sectional area of the grinding process of the work material which has been normally quenched and the normal quenching. It has an approximate relational expression generation unit that obtains an approximate relational expression between the measured vibration intensity integral value of the work material, and the value of a predetermined ratio of the expected vibration intensity integrated value obtained from the approximate relational expression is the hardness. A threshold determination unit for determining an abnormality determination threshold is provided.

The gist of the fifth invention is that in the fourth invention, the hardness abnormality determination unit actually measures the expected value of the integral value of the vibration strength and the hardened work material during the grinding process. The purpose is to determine the hardness abnormality of the hardened work material based on the fact that the difference value from the integrated value is lower than the hardness abnormality determination threshold.

The gist of the sixth invention is (a) a hardness abnormality detecting device for a work material that detects a hardness abnormality of the hardened work material, and (b) the hardened work material. Frequency to frequency-analyze the digitized early AE signal using an AE sensor that detects the AE signal generated from the grinding point of the grinding wheel during grinding and (c) an A / D converter with a sampling period of 10 μsec or less. Within the analysis unit and (d) a specific frequency band whose intensity changes according to the hardness of the hardened work material, which is included in the frequency band of 45 to 65 kHz in the frequency spectrum analyzed by the frequency analysis unit. The vibration intensity integrated value calculation unit that calculates the vibration intensity integrated value by integrating the vibration intensity value of (e) and the vibration intensity integrated value actually measured during grinding of the hardened work material. The hardness abnormality determination unit for determining the hardness abnormality of the hardened work material based on the hardness abnormality determination threshold set in advance is included.

The gist of the seventh invention is that, in the sixth invention, the hardness abnormality detecting device of the work material is the cumulative grinding cross-sectional area of the grinding process of the work material that has been normally quenched and the normal quenching. It has an approximate relational expression generation unit that obtains an approximate relational expression between the measured vibration intensity integrated value and the work material subjected to the above, and is a value of a predetermined ratio of the expected vibration intensity integrated value obtained from the approximate relational expression. Is provided with a threshold determination unit for determining the hardness abnormality determination threshold.

The gist of the eighth invention is that in the seventh invention, the hardness abnormality determination unit actually measures the expected value of the integral value of the vibration intensity and the hardened work material during the grinding process. The purpose is to determine the hardness abnormality of the hardened work material based on the fact that the difference value from the integrated value is lower than the hardness abnormality determination threshold.

According to the method for detecting hardness abnormality of a work material of the first invention, in the hardness abnormality determination step, the hardened work material is obtained based on the AE signal generated from the grinding point of the grinding wheel during the grinding process. Since the hardness abnormality is determined, 100% of the hardness abnormality of the work material can be inspected without providing an inspection step, and the reliability of the work material after grinding can be improved.

According to the method for detecting a hardness abnormality of a work material of the second invention, when it is determined by the hardness abnormality determination step that the hardness is not abnormal, the ground work material is transferred to the next step of the grinding process. However, if it is determined by the hardness abnormality determination step that the hardness is abnormal, the ground work material is not flown to the next step of the grinding process, so that the work material is a defective product. Is prevented from flowing to the post-process, so that the waste of labor in the post-process can be eliminated.

According to the hardness abnormality detecting method of the third invention and the hardness abnormality detecting apparatus of the sixth invention, (a) the AE signal generated from the grinding point of the grinding wheel during the grinding process of the hardened work material. The AE sensor for detecting the above, (b) a frequency analysis unit that frequency-analyzes the AE signal obtained by digitizing the AE signal using an A / D converter having a sampling period of 10 μsec or less, and (c) the frequency analysis unit. Vibration intensity is calculated by integrating the vibration intensity value in the specific frequency band, which is included in the frequency band of 45 to 65 kHz in the frequency analysis and whose intensity changes according to the hardness of the hardened work material. Based on the vibration intensity integrated value calculation unit that calculates the integrated value, and (d) the vibration intensity integrated value actually measured during grinding of the hardened work material and the preset hardness abnormality determination threshold value. It includes a hardness abnormality determining unit for determining the hardness abnormality of the hardened work material. As a result, it is possible to detect an abnormality in the hardness of the work material in the grinding process of the hardened work material, so that all the abnormal hardness of the work material can be inspected without providing an inspection process, and the grinding process can be performed. The reliability of the later work material can be improved.

According to the method for detecting an abnormality in hardness of a work material of the fourth invention and the device for detecting an abnormality in hardness of a work material of the seventh invention, the cumulative grinding cross-sectional area of the grinding process of a normally hardened work material It has an approximate relational expression generation unit that obtains an approximate relational expression between the measured vibration intensity integrated value and the normally hardened work material, and has an expected vibration intensity integrated value obtained from the approximate relational expression. A threshold determination unit for determining a value of a predetermined ratio as the hardness abnormality determination threshold is provided. From this, since the hardness abnormality determination threshold value is determined as a value of a predetermined ratio of the expected value of the vibration intensity integrated value obtained from the approximate relational expression, the hardness abnormality determination of the work material becomes accurate.

According to the method for detecting an abnormality in hardness of a work material of the fifth invention and the device for detecting an abnormality in hardness of a work material of the eighth invention, the hardness abnormality determination unit is hardened with the expected value of the vibration intensity integrated value. The hardness abnormality of the hardened work material is determined based on the difference value from the vibration intensity integrated value actually measured during the grinding process of the work material is below the hardness abnormality determination threshold. From this, since the hardness abnormality of the work material is performed based on the difference value between the expected value of the integral value of vibration intensity and the actually measured integrated value of vibration intensity being lower than the hardness abnormality determination threshold, it is cumulative. Even if the expected value of the integral value of the vibration strength varies depending on the ground cross-sectional area, the hardness abnormality determination of the work material is accurate.

It is a figure explaining the structure of the grinding processing apparatus and an electronic control apparatus of a work material provided with the hardness abnormality detecting apparatus which detects the hardness abnormality of a work material during the grinding process of one Embodiment of this invention. It is a figure explaining the generation mechanism of the AE signal generated from the grinding point of the grinding wheel during the grinding process by the grinding machine of FIG. 1. It is a flowchart explaining the main part of the control operation of the electronic control device of FIG. It is a bar graph which shows the Vickers hardness HV of the work material (normal product) with normal hardness and the work material (abnormal product) with abnormal hardness used in the grinding test in a comparable manner. FIG. 1 is a diagram showing an example of a frequency spectrum obtained by frequency analysis of an AE signal detected by an AE sensor by a frequency analysis unit. Two-dimensional coordinates consisting of a horizontal axis representing the cumulative grinding cross-sectional area SG and a vertical axis representing the vibration intensity integrated value IV, and the vibration intensity integrated value IVS of the normal product and the vibration strength of the abnormal product that change with the cumulative grinding cross-sectional area SG. It is a figure which shows the value of the integral value IVS for four small areas F1, F2, F3, F4 respectively. It is a figure which shows the value of the vibration intensity integrated value IVS of a normal product, and the value of the vibration intensity integrated value IVS of an abnormal product in the 3rd small region F3 of FIG. The difference value ΔIVSn between the expected value of the integral vibration intensity obtained from the approximate relational expression (1) that approximates the value of the normal product in FIG. 7 and the measured value of the integral vibration intensity obtained from the normal product during grinding. , The difference value ΔIVSa between the expected value of the integral value of vibration intensity and the measured value of the integrated value of vibration intensity obtained from the abnormal product during grinding, and 2.5% of the expected value of the integrated value of vibration intensity. It is a figure which shows.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following examples, the drawings are appropriately simplified or modified, and the dimensional ratios and shapes of each part are not always drawn accurately.

FIG. 1 is a diagram illustrating a configuration of a grinding apparatus 14 provided with a hardness abnormality detecting apparatus 10 for a work material 12 according to an embodiment of the present invention. The grinding apparatus 14 uses the grinding wheel 20 to grind a work material 12 made of, for example, hardened steel. The work material 12 is a metal part made of hardened steel, for example, an inner ring and an outer ring of a bearing, a sprocket, and a camshaft. The hardened steel is, for example, carburized and hardened chrome steel SCr420, hardened chrome molybdenum steel SCM440, or the like. Further, in the grinding wheel 20, general abrasive grains such as molten alumina-based abrasive grains, silicon carbide-based abrasive grains, and ceramic abrasive grains, and super-abrasive grains such as CBN abrasive grains and diamond abrasive grains are inorganic, organic, or metal. It is a well-known grinding wheel such as a vitrified grindstone, a resinoid grindstone, a metal bond grindstone, and an electrodeposition grindstone bonded by a binder such as.

In FIG. 1, the grinding apparatus 14 includes a grinding wheel 20, a spindle drive motor 62 that rotationally drives a rotating spindle that rotatably supports the grinding wheel 20 around the rotation center line C1 of the grinding wheel 20, and a grinding wheel 20. A rotation center parallel to the rotation center line C1 of a work material moving motor 66 that moves the work material 12 in the radial direction in order to press the work material 12 against the outer peripheral surface of the columnar work material 12 and a rotary dresser 46 used as a truing tool. It includes a turling tool rotation drive motor 68 that rotationally drives around the line C2, a turwing tool feed motor 70 that feeds the rotary dresser 46 in the direction of the rotation center line C2, and a grinding control device 72.

The grinding wheel 20 has a cylindrical or drum-shaped metal core, that is, a main body 20a, and a grindstone portion 20b composed of a plurality of segment grindstones fixed to the outer peripheral surface of the main body 20a. It is mounted on a rotating spindle that is rotationally driven around the rotation center line C1 of the grinding wheel 20.

The hardness abnormality detecting device 10 serves as a transmission circuit 26 provided in the main body 20a, which transmits the AE signal SAE amplified by the AE sensor 22, the preamplifier 24, and the preamplifier 24 using a predetermined carrier, and a power source thereof. A receiving circuit 30, a bandpass filter 32, a demodulator circuit 33, and an A / D converter having a functioning storage battery 44 and an antenna 28 for receiving the AE signal SAE transmitted from the transmitting circuit 26, which is provided at a fixed position. 34, and an electronic control device 36.

The AE sensor 22 causes an extremely high frequency crushing vibration (acoustic vibration) of the grindstone portion 20b, which is generated at the time of crushing of the abrasive grains contained in the grindstone portion 20b and propagates in the grindstone portion 20b, for example, in an ultrasonic region of 20 kHz or higher. It detects from the inner peripheral surface and outputs the AE signal SAE, which is an analog signal representing the crushing vibration. The preamplifier 24 amplifies the AE signal SAE output from the AE sensor 22. The bandpass filter 32 includes a predetermined passing frequency band through which the carrier wave received by the receiving circuit 30 is passed. The A / D converter 34 converts the AE signal SAE demodulated from the carrier wave by the demodulation circuit 33 into a digital signal. The electronic control device 36 processes the AE signal SAE converted into a digital signal, and the hardened work piece is based on the AE signal SAE generated from the grinding point of the grindstone portion 20b of the grinding wheel 20 during the grinding process. The hardness abnormality of the material 12 is determined.

The A / D converter 34 has a high-speed sampling cycle and high resolution, for example, a sampling cycle of 10 μsec (microsecond) or less, preferably a sampling cycle of 5 μsec or less, and more preferably 1 μsec or less. The AE signal SAE is converted into a digital signal in a cycle. The shorter the sampling period of the A / D converter 34 (the higher the speed), the clearer the waveform of the frequency spectrum obtained by the frequency analysis of the AE signal SAE. In this embodiment, 1 μsec is used as the sampling period of the A / D converter 34.

As shown in FIG. 2, for example, the grindstone portion 20b of the grinding wheel 20 is a well-known grindstone composed of abrasive grains 38, an inorganic binder (vitrified bond) 40 for binding the abrasive grains 38, and pores 42. It is composed of organizations. Due to the sliding contact between the grindstone portion 20b of the grinding wheel 20 and the work material (work) 12, vibrations presumed to be caused by crack Ca of the abrasive grains 38 itself, that is, crushing, and the abrasive grains 38 and the work material 12 Vibrations generated by contact with, that is, rubbing Cb, or vibrations presumed to be derived from elastic vibrations are generated, and grinding vibrations including those vibrations, that is, AE waves are detected by the AE sensor 22.

In the frequency band of the frequency spectrum obtained by frequency analysis of the AE wave detected by the AE sensor 22, crack Ca of the abrasive grains 38 itself, that is, a peak of signal strength considered to be derived from the occurrence of crushing is shown in 25 to 25. The first frequency band B1 of 40 kHz and the second frequency band of 45 to 65 kHz showing the peak of the signal strength considered to be derived from the frictional vibration or elastic vibration generated by the contact between the abrasive grains 38 and the work material 12, that is, the rubbing Cb. B2 is observed. Then, it was found that a specific frequency band SHFR, which is a small region in which the strength changes relatively sensitively to the quenching hardness of the work material 12, exists in the second frequency band B2. The above specific frequency band SHFR is set experimentally in advance. Based on the vibration intensity integral value IVS in this specific frequency band SHFR, it is possible to determine whether the hardness of the work material 12 being ground, that is, the quenching state is normal or abnormal, so that the work material 12 can be determined. It is not necessary to independently provide a hardness abnormality detection step.

The electronic control device 36 of FIG. 1 is a so-called microcomputer including a CPU, ROM, RAM, interface, etc., and the CPU processes an input signal according to a program stored in advance in the ROM while using the temporary storage function of the RAM. As a result, the hardness abnormality determination threshold HATH for determining the hardness of the work material 12 during grinding is obtained in advance, and the hardness abnormality determination threshold HATH and the vibration intensity in the specific frequency band SHFR actually measured during grinding are obtained. Based on the integrated value IVS, the hardness abnormality of the work material 12 is determined, the determination result is displayed on the display device 48, and is transmitted to the grinding control device 72.

The electronic control device 36 functionally includes a frequency analysis unit 50, a vibration intensity integral value calculation unit 52, a hardness abnormality determination unit 54, and a threshold value determination unit 58 having an approximate relational expression generation unit 56.

During the grinding process of the work material 12 by the grinding wheel 20, the frequency analysis unit 50 continuously performs frequency analysis (FFT analysis) of the AE signal SAE input from the A / D converter 34 at predetermined analysis cycles. In the two-dimensional coordinates of the vertical axis indicating the vibration intensity value (power) Ir and the horizontal axis indicating the frequency, the vibration intensity value indicating the magnitude of the frequency component is calculated as a peak waveform for each frequency on the frequency axis (horizontal axis). Generate the frequency spectrum shown above. FIG. 5, which will be described later, shows an example of the frequency spectrum.

The vibration intensity integral value calculation unit 52 is relatively sensitive to the hardness of the work material 12 contained in the second frequency band B2 (45 to 65 kHz) in the frequency spectrum analyzed by the frequency analysis unit 50. The vibration intensity integrated value IVS is sequentially calculated by integrating the vibration intensity value Ir in the specific frequency band SHFR, which is a small region where the intensity changes, at each predetermined analysis cycle. In the vibration intensity integrated value IVS, the vibration intensity value Ir, which is an effective value of the amplitude at each frequency in the specific frequency band SHFR of the frequency spectrum, is integrated with respect to the frequency axis in the frequency section of the specific frequency band SHFR. The value.

The hardness abnormality determination unit 54 determines the hardness of the work material 12 being ground based on the vibration intensity integral value IVS actually measured for the work material 12 being ground and the preset hardness abnormality determination threshold HATH. Judge an abnormality.

The threshold determination unit 58 includes the cumulative ground cross-sectional area SG of the grinding process for the normally hardened work material 12 and the vibration intensity integrated value IVS measured for the normally hardened work material 12. It has an approximate relational expression generation unit 56 for obtaining the approximate relational expression (1) between them, and has an average value of the expected value IVS1 of the integral value of the vibration intensity obtained from the approximate relational expression (1) (vibration corresponding to normal quenching hardness). A predetermined ratio (for example, a value of 2.5 to 5%) of (the average value for one cut of the intensity integral value) is determined as the hardness abnormality determination threshold HATH. In the approximate relational expression (1), for example, the vibration intensity integrated value IVS in the specific frequency band SHFR of 59.0 to 61.0 kHz is obtained from the work material 12 having a normal quenching hardness as shown in FIG. 7 described later. It is an equation obtained by logarithmically approximating the values of the black circles shown for each cumulative grinding cross-sectional area obtained.

y = -452.2ln (x) +6288.3 ... (1)
Here, y represents the vibration intensity integrated value IVS, which is a variable on the vertical axis, and x represents the cumulative grinding cross-sectional area SG (mm ² ), which is a variable on the horizontal axis.

The hardness abnormality determination unit 54 has an average value of the expected value IVS1 of the preset vibration intensity integrated value (an average value for one cut of the work material 12) and the vibration intensity integrated value IVS actually measured during the grinding process. If the difference value ΔIVS from the average value of (the average value of one cut of the work material 12) is equal to or higher than the hardness abnormality determination threshold HATH, it is determined that the hardness of the work material 12 being ground is normal. When the hardness falls below the hardness abnormality determination threshold HATH, it is determined that the hardness of the work material 12 during the grinding process is abnormal.

The grinding control device 72 is composed of a microcomputer similar to the electronic control device 36, and functionally includes an automatic grinding control unit 74 and a growing control unit 76. Upon receiving the grinding start command signal, the automatic grinding control unit 74 grinds the work material 12 by relatively moving the grinding wheel 20 and the work material 12 while rotationally driving them in a preset operation to grind the work material 12. When the grinding of the material 12 is completed, the rotation of the grinding wheel 20 and the work material 12 is stopped and returned to the original position. Further, when the grinding control device 72 receives a signal from the electronic control device 36 indicating the determination of the hardness abnormality of the work material 12, the automatic grinding control unit 74 immediately stops the grinding process and returns it to the original position.

The grinding control device 72 determines, for example, whether or not the cumulative grinding time has reached the preset true-toothing start condition (truing cycle), and if it is determined that the cumulative grinding time has reached the true-toothing start condition, the grinding control unit 72 determines. Outputs a command to 76 to start growing. In the case of true troughing by traverse, the trueuing control unit 76 cuts the rotary dresser 46 used as a trueuing tool into the outer peripheral surface of the cylindrical grindstone portion 20b of the grinding wheel 20 with a preset depth of cut, and the grinding wheel. It is scanned in parallel with the rotation center line C1 of 20 and this operation is repeatedly executed until the grinding completion determination output is received from the grinding control device 72.

FIG. 3 is a flowchart illustrating a main part of the control operation of the electronic control device 36. In step S1 of FIG. 3 (hereinafter, the step is omitted), it is determined whether or not the hardness abnormality determination threshold value HATH has been set.

If the judgment of S1 is affirmed, S4 or less is executed, but if it is denied, the work that has been normally hardened as described above in S2 corresponding to the approximate relational expression generation unit 56. Approximation relationship which is a logarithmic approximation formula obtained by logarithmically approximating the value of the vibration intensity integral value IVS with respect to the cumulative grinding cross-sectional area in the specific frequency band SHFR of 59.0 to 61.0 kHz from the frequency spectrum obtained from the material 12. Equation (1) is created.

Next, in S3 corresponding to the threshold determination unit 58, the cumulative grinding cross-sectional area SG of the grinding process for the work material 12 by the grinding wheel 20 and the vibration intensity integration measured for the work material 12 that has been normally quenched. An approximate relational expression (1) with the value IVS is obtained, and the vibration intensity integrated value obtained from the approximate relational expression (1), that is, the expected value of the vibration intensity integrated value, the average value of IVS1 (corresponding to the normal quenching hardness). A predetermined ratio (the average value of one cut of the target value of the vibration intensity integrated value), for example, 2.5 to 5% such as 2.5, 3, 4, 5, etc., is determined as the hardness abnormality determination threshold HATH.

In S4 corresponding to the subsequent grinding process, the grinding process of the work material 12 by the grinding wheel 20, that is, the grinding process is started.

Next, in S5, the AE signal SAE at the time of grinding, which is output from the AE sensor 22 during the grinding process and A / D converted by the A / D converter 34, is read.

In S6 corresponding to the frequency analysis unit 50, the frequency analysis (FFT analysis) of the AE signal SAE input from the A / D converter 34 is continuously performed at predetermined analysis cycles to show the vibration intensity (power). In the two-dimensional coordinates of the vertical axis and the horizontal axis indicating the frequency, the vibration intensity indicating the magnitude of the frequency component is expressed as a peak waveform for each frequency on the frequency axis (horizontal axis), and the frequency spectrum as shown in FIG. 5 described later. Is generated.

In S7 corresponding to the vibration intensity integrated value calculation unit 52, comparison is made according to the hardness of the work material 12 contained in the second frequency band B2 (45 to 65 kHz) in the frequency spectrum generated by the frequency analysis in S6. The effective value of the amplitude indicating the vibration intensity value Ir at each frequency in the specific frequency band SHFR (preferably 59 to 61 kHz), which is a predetermined small region where the intensity changes sensitively, is determined for each predetermined analysis cycle. By performing the integral calculation, the vibration intensity integrated value IVS is sequentially calculated.

In the hardness abnormality determination unit 54 or S8 corresponding to the hardness abnormality determination step, the average value of one cut of the vibration intensity integrated value IVS actually measured for the work material 12 being ground is calculated at the end of the grinding process. Will be done.

Next, in the hardness abnormality determination unit 54 or S9 corresponding to the hardness abnormality determination step, the average value for one cut of the actually measured vibration intensity integrated value IVS and the preset hardness abnormality determination threshold HATH are used. It is determined that the hardness of the work material 12 during the grinding process is abnormal. That is, the average value of the expected value IVS1 of the preset vibration intensity integrated value (the average value of one cut of the work material 12) and the average value of the vibration intensity integrated value IVS actually measured during the grinding process (subject). It is determined whether or not the difference value ΔIVS from the average value for one cut of the cutting material 12 is equal to or higher than the hardness abnormality determination threshold HATH. If the difference value ΔIVS is equal to or higher than the hardness abnormality determination threshold HATH, it is determined that the hardness of the ground work material 12 is normal (pass), but if the difference value ΔIVS is lower than the hardness abnormality determination threshold HATH. , The hardness of the ground work material 12 is determined to be abnormal.

If the judgment of S9 is denied because the difference value ΔIVS falls below the hardness abnormality determination threshold HATH, an alert indicating that the work material 12 has an abnormality in hardness, that is, an abnormality in quenching is output in S10, and an alert is output. The ground work material 12 is marked to indicate that it is an abnormal hardness product, or is sorted into a box for accommodating the abnormal hardness product, and S1 or less is executed for the next work material 12. To. If the determination of S9 is affirmed because the difference value ΔIVS is equal to or higher than the hardness abnormality determination threshold value HATH, the ground work material 12 is sorted into a box for accommodating a product having normal hardness, and the process proceeds to the subsequent steps. At the same time as being washed away, S1 or less is executed for the next work material 12.

The present inventors prepare a work material having a normal hardness (hardened steel) and a work material having an abnormal hardness (hardened steel), and when grinding is performed under the following grinding test conditions. The AE signal SAE was measured and the AE signal SAE was analyzed.

(Grinding test conditions)
Grinding wheel specs: CB 80 NV
(Outer diameter 409 mm x Thickness 30 mm x Inner diameter 127 mm)
Grinding method: Wet plunge grinding wheel Circumferential speed: 2700 m / min (2122 rpm)
Work material peripheral speed: 0.45 m / sec
Work material: SCM435
Cutting speed: R0.8mm / min
Replacement allowance: 80 ^mm in cross-sectional area of grinding allowance Spark out: 10 rev
Number of cuts: 60 cuts Grinding oil: SEC700 (× 50)
Grinding oil flow rate: 20 L / min
Dresser spec: SD 40 Q 75 MW7
(Diameter 100 mm x grindstone layer thickness 1 mm)
Dress peripheral speed: 45m / sec
Dress lead: 0.10 mm / r. o. w.
Dress cut amount: R0.002mm / pass x 10 pass

The present inventors measured the Vickers hardness HV (JIS Z 2244: 2009) of the work material 12 having a normal hardness and the work material 12 having an abnormal hardness used in the above-mentioned grinding test. FIG. 4 is a bar graph showing the measured Vickers hardness HV in a contrastable manner. The Vickers hardness HV of the work material 12 having a normal hardness was about 537, and the Vickers hardness HV of the work material 12 having an abnormal hardness was about 533. In this measurement of Vickers hardness HV, a pushing load of 10 kgf was used. The above-mentioned normally hardened work material 12 means a work material 12 having a normal (quenched) hardness, and the normal hardness is a preset normal hardness range, for example. It means the hardness in the range of HV534 or more, and the abnormal hardness means the hardness in the range below the normal hardness.

FIG. 5 shows a frequency spectrum obtained by frequency analysis of an AE signal SAE obtained when a work material 12 having a normal hardness is ground using the above grinding test conditions.

Next, the present inventors consider that when the work material 12 having a normal hardness and the work material 12 having an abnormal hardness are alternately ground, they are easily affected by the hardness of the work material 12. In order to find a specific frequency band SHFR that fluctuates with high sensitivity to the hardness of the work material in the second frequency band B2 of FIG. 5, 53.5 Hz to 56. Including a plurality of main peaks in the second frequency band B2. 0 Hz "first small region F1", 57.0 Hz to 58.5 Hz "second small region F2", 59.0 Hz to 61.0 Hz "third small region F3", 62.0 Hz to 63.0 Hz The "fourth small area F4" was set.

Then, from the measured value of the vibration strength value Ir at the time of grinding the work material 12 having a normal hardness and the work material 12 having an abnormal hardness, the vibration strength integrated value IVS of the work material 12 having a normal hardness. And the vibration intensity integrated value IVS of the work material 12 having an abnormal hardness was repeatedly calculated for each of the above four small regions as the cumulative grinding cross-sectional area SG (mm ² ) increased, and is shown in FIG. It is shown in two-dimensional coordinates consisting of a horizontal axis representing the cumulative grinding cross-sectional area SG and a vertical axis representing the vibration intensity integrated value IVS. In FIG. 6, the difference between the vibration intensity integrated value IVS of the work material 12 having normal hardness and the vibration intensity integrated value IVS of the work material 12 having abnormal hardness is the largest among the four small regions. It was the third small region F3 of 59.0 Hz to 61.0 Hz.

In FIG. 7, the integrated vibration intensity IVS of the work material 12 having normal hardness in the third small region F3 of 59.0 Hz to 61.0 Hz is indicated by a black circle, and the work material 12 having abnormal hardness is shown. The vibration intensity integrated value IVS of is indicated by a white circle. Since the change of the vibration intensity integral value IVS with respect to the cumulative grinding cross-sectional area SG is close to the logarithmic curve, the cumulative grinding cross-sectional area SG is defined as x, and the work material 12 having the normal hardness indicated by the black circle is used. Assuming that the vibration intensity integrated value IVS is y, the relationship between the cumulative grinding cross-sectional area SG and the vibration intensity integrated value IVS is shown by the approximate relational expression shown in the above equation (1).

FIG. 8 shows the expected value of the integral value of the vibration intensity (integration of the vibration intensity of the work material 12 having normal hardness) in the third small region F3 of 59.0 Hz to 61.0 Hz obtained from the approximate relational expression (1). Value IVS target value) Difference value (expected value-measured value) ΔIVSn between IVS1 and the measured value of the integral value IVS of the vibration intensity obtained from the work material 12 having normal hardness is indicated by a black circle and the vibration strength. The difference value (expected value-measured value) ΔIVSa between the expected integrated value IVS1 and the measured value of the vibration intensity integrated value IVS obtained from the work material 12 having an abnormal hardness is indicated by a white circle. Further, the broken line in FIG. 8 is a tentative threshold value for distinguishing the work material 12 having an abnormal hardness, and is an expected value of the integrated vibration strength value (the integrated vibration strength IVS of the work material 12 having a normal hardness). Target value) A predetermined ratio of IVS1, for example, a value of 2.5% is shown on the negative side.

As is clear from FIG. 8, among the white circles indicating the difference value ΔIVSa between the expected value IVS of the integrated vibration intensity value and the measured value of the integrated vibration intensity IVS obtained from the work material 12 having an abnormal hardness. 90% is below the threshold indicated by the broken line, and is surrounded by a circle with a broken line indicating an abnormality determination. From this, the expected value of the integral value of vibration intensity (the target value of the integral value of vibration intensity of the work material 12 having normal hardness) IVS1, the expected value of the integral value of vibration intensity IVS1, and the work material 12 having abnormal hardness. By using the average value for one cut (one grinding process) for the difference value (expected value-measured value) ΔIVSa from the measured value of the vibration intensity integrated value IVS obtained from the above, the work material 12 is surely used. Hardness abnormality can be detected.

As described above, according to the hardness abnormality detecting device 10 and the hardness abnormality detecting method of the present embodiment, the AE generated from the grinding point of the grinding wheel 20 during the grinding process in the hardness abnormality determination unit 54 or the hardness abnormality determination step. Since the hardness abnormality of the hardened work material 12 is determined based on the signal SAE, all the work materials 12 can be inspected for the hardness abnormality of the work material 12 without providing an inspection step, and the grinding process can be performed. The reliability of the later work material 12 can be improved.

Further, according to the hardness abnormality detection device 10 and the hardness abnormality detection method of the present embodiment, when it is determined by the hardness abnormality determination unit 54 or the hardness abnormality determination step that the hardness is not abnormal, the ground work material 12 Is sent to the next step of the grinding process, but if it is determined by the hardness abnormality determination unit 54 or the hardness abnormality determination step that the hardness is abnormal, the ground work material 12 is next to the grinding process. Since the defective work material 12 is prevented from flowing to the subsequent process, it is possible to eliminate the waste of manpower in the subsequent process.

Further, according to the hardness abnormality detecting device 10 and the hardness abnormality detecting method of the present embodiment, the AE signal SAE generated from the grinding point of the grinding wheel (grinding grindstone) 20 during the grinding process of the hardened work material 12 is generated. In the frequency analysis unit 50 for frequency analysis of the AE signal SAE digitized by using the AE sensor 22 to be detected and the A / D converter 34 with a sampling period of 10 μsec or less, and the frequency spectrum analyzed by the frequency analysis unit 50. The vibration intensity integrated value IVS is calculated by integrating the vibration intensity value Ir in the specific frequency band SHFR whose strength changes according to the hardness of the work material 12, which is included in the second frequency band B2 of 45 kHz or more and 65 kHz or less. Vibration intensity integrated value calculation unit 52, vibration intensity integrated value IVS actually measured during grinding of the work material 12, and hardness abnormality determination threshold HATH set in advance, the hardness abnormality of the work material 12 The hardness abnormality determination unit 54 for determining the above is included. As a result, it is possible to detect an abnormality in the hardness of the work material 12 in the grinding process of the hardened work material 12, so that the entire number of objects to be subjected to the hardness abnormality of the work material 12 can be covered without providing an inspection process. The work material 12 can be inspected, and the reliability of the work material 12 after grinding can be improved.

Further, according to the hardness abnormality detecting device 10 and the hardness abnormality detecting method of this embodiment, the cumulative grinding cross-sectional area SG (mm ² ) and the normal quenching of the work material 12 which has been normally quenched can be obtained. It has an approximate relational expression generation unit 56 for obtaining an approximate relational expression (1) with the vibration intensity integrated value IVS measured for the applied work material 12, and an approximate vibration intensity integrated value obtained from the approximate relational expression (1). A threshold determination unit 58 for determining a predetermined ratio of the expected value IVS1 as a hardness abnormality determination threshold HATH is provided. From this, since the hardness abnormality determination threshold value HATH is determined as a value of a predetermined ratio of the expected value IVS1 of the vibration intensity integral value obtained from the approximate relational expression (1), the hardness abnormality determination of the work material 12 becomes accurate. ..

Further, according to the hardness abnormality detection device 10 and the hardness abnormality detection method of the present embodiment, the hardness abnormality determination unit 54 grinds the hardened work material 12 and the preset vibration intensity integrated value expected value IVS1. Based on the fact that the difference value ΔIVS from the vibration intensity integrated value IVS actually measured therein is lower than the hardness abnormality determination threshold HATH, the hardness abnormality of the hardened work material 12 is determined. As described above, the hardness abnormality of the work material 12 is performed based on the difference value ΔIVS between the expected vibration intensity integrated value IVS1 and the actually measured vibration intensity integrated value IVS being lower than the hardness abnormality determination threshold HATH. Therefore, even if the expected value IVS1 of the vibration intensity integral value varies for each cumulative grinding cross-sectional area, the hardness abnormality determination of the work material 12 is accurate.

Although the embodiments of the present invention have been described in detail with reference to the drawings, the present invention is also applicable to other aspects.

For example, the hardness abnormality detecting device 10 of the above-described embodiment includes the threshold value determination unit 58 for determining the hardness abnormality determination threshold value HATH, but the hardness abnormality detection device 10 is predetermined by another control device having the function of the threshold value determination unit 58. The hardness abnormality determination threshold value HATH may be input prior to the hardness abnormality detection operation, and the hardness abnormality determination threshold value HATH may be used to determine the hardness abnormality. In this case, the hardness abnormality detection device 10 does not have to include the threshold value determination unit 58.

Further, in the above-described embodiment, the AE sensor 22 is provided in the main body 20a of the grinding wheel 20, but in the flange where the grinding wheel is sandwiched and fixed to the rotating spindle and in the table where the work material 12 is fixed. It may be provided in.

Further, in the above-mentioned hardness abnormality determination unit 54, the expected value of the integral value of the vibration intensity set in advance, the average value of the IVS1 (the average value of one cut of the work material 12) and the vibration actually measured during the grinding process. It was determined whether or not the difference value ΔIVS from the average value of the intensity integrated value IVS (the average value for one cut of the work material 12) was equal to or higher than the hardness abnormality determination threshold HATH. However, the difference value ΔIVS is the average value of the difference between the expected value IVS1 of the vibration intensity integrated value and the vibration intensity integrated value IVS actually measured during the grinding process (the average value for one cut of the work material 12). There may be.

Further, in the hardness abnormality determination unit 54 described above, among the cumulative grinding cross-sectional areas SG shown in FIG. 7, for example, the vibration strength on the approximate relational expression (1) corresponding to a predetermined cumulative grinding cross-sectional area SG1 set in advance. A hardness abnormality determination threshold HATH lower than the expected integrated value IVS1 is set, and the vibration intensity integrated value IVS actually measured during grinding in the predetermined cumulative grinding cross-sectional area SG1 sets the hardness abnormality determination threshold HATH. The hardness abnormality of the work material 12 may be determined based on the fact that the hardness is lower. In short, the hardness abnormality determination unit 54 may determine the hardness abnormality of the work material 12 based on the actually measured vibration intensity integrated value IVS and the preset hardness abnormality determination threshold value HATH.

It should be noted that the above is only one embodiment, and the present invention can be carried out in a mode in which various changes and improvements are made based on the knowledge of those skilled in the art.

10: Hardness abnormality detection device 12: Work material 20: Grinding wheel (grinding grindstone)
22: AE sensor 34: A / D converter 50: Frequency analysis unit 52: Vibration intensity integral value calculation unit 54: Hardness abnormality determination unit 56: Approximate relational expression generation unit 58: Threshold determination unit B2: Second frequency band (45) ~ 65kHz frequency band)
HATH: Hardness abnormality judgment threshold Ir: Vibration intensity value IVS: Vibration intensity integrated value IVS1: Vibration intensity integrated value expected value S4: Grinding process S8, S9: Hardness abnormality judgment process SAE: AE signal SG, SG1: Cumulative grinding cross-sectional area SHFR: Specific frequency band F3: Third small region (specific frequency band)
ΔIVS, ΔIVSa, ΔIVSn: Difference value

Claims (8)

It is a method for detecting hardness abnormality of hardened work material, which is a method for detecting hardness abnormality of hardened work material.
A grinding process for grinding the hardened work material using a grinding wheel, and
A hardness abnormality determination step of determining a hardness abnormality of the hardened work material based on an AE signal generated from a grinding point of the grinding wheel during the grinding process is included.
A method for detecting abnormal hardness of a work material. When it is determined by the hardness abnormality determination step that the hardness is not abnormal, the ground work material is flowed to the next step of the grinding process, but it is determined by the hardness abnormality determination step that the hardness is abnormal. The method for detecting an abnormality in the hardness of a work material according to claim 1, wherein the ground work material is not flown to the next step of the grinding process. The hardness abnormality determination step is
An AE sensor that detects the AE signal generated from the grinding point of the grinding wheel during grinding of the hardened work material, and
A frequency analysis unit that frequency-analyzes the AE signal digitized using an A / D converter with a sampling period of 10 μsec or less.
Integral calculation of vibration intensity values in a specific frequency band whose strength changes according to the hardness of the hardened work material, which is included in the frequency band of 45 to 65 kHz in the frequency spectrum analyzed by the frequency analysis unit. The vibration intensity integrated value calculation unit that calculates the vibration intensity integrated value by doing
Hardness for determining hardness abnormality of the hardened work material based on the vibration intensity integrated value actually measured during grinding of the hardened work material and a preset hardness abnormality determination threshold value. The method for detecting a hardness abnormality of a work material according to claim 1 or 2, wherein the hardness abnormality detection device including the abnormality determination unit is used to determine the hardness abnormality of the hardened work material. The hardness abnormality detection device is
Approximate relational expression for obtaining the approximate relational expression between the cumulative grinding cross-sectional area of the grinding process for the work material that has been normally hardened and the vibration intensity integral value measured for the work material that has been normally hardened. 2. A method for detecting abnormal hardness of a material. In the hardness abnormality determination unit, the difference value between the expected vibration intensity integrated value and the vibration intensity integrated value actually measured during grinding of the hardened work material is lower than the hardness abnormality determination threshold value. The method for detecting an abnormality in hardness of a work material according to claim 4, wherein the abnormality in hardness of the hardened work material is determined based on the above. It is a hardness abnormality detection device for the work material that detects the hardness abnormality of the hardened work material.
An AE sensor that detects an AE signal generated from the grinding point of a grinding wheel during grinding of the hardened work material, and
A frequency analysis unit that frequency-analyzes the AE signal digitized using an A / D converter with a sampling period of 10 μsec or less.
Integral calculation of vibration intensity values in a specific frequency band whose strength changes according to the hardness of the hardened work material, which is included in the frequency band of 45 to 65 kHz in the frequency spectrum analyzed by the frequency analysis unit. The vibration intensity integrated value calculation unit that calculates the vibration intensity integrated value by doing
Hardness for determining hardness abnormality of the hardened work material based on the vibration intensity integral value actually measured during grinding of the hardened work material and a preset hardness abnormality determination threshold value. A hardness abnormality detection device for a work material, which comprises an abnormality determination unit. The hardness abnormality detection device is
Approximate relational expression for obtaining the approximate relational expression between the cumulative grinding cross-sectional area of the grinding process for the work material that has been normally hardened and the vibration intensity integral value measured for the work material that has been normally hardened. The subject of claim 6 is provided with a generation unit, and a threshold determination unit for determining a predetermined ratio of an expected value of an integral value of vibration intensity obtained from the approximate relational expression as the hardness abnormality determination threshold. Hardness abnormality detection device for cutting materials. In the hardness abnormality determination unit, the difference value between the expected vibration intensity integrated value and the vibration intensity integrated value actually measured during grinding of the hardened work material is lower than the hardness abnormality determination threshold value. The device for detecting a hardness abnormality of a work material according to claim 7, wherein the hardness abnormality of the hardened work material is determined based on the above.

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