KR20220087078A - Method for monitoring of joining quality for self piercing rivet, process for joining of self piercing rivet, and apparatus system for the same - Google Patents

Abstract

Provided are a non-destructive-real-time monitoring method of fastening quality, such as a self-piercing rivet, a self-piercing rivet fastening process method including the same, and an equipment system for the same. The monitoring method is a self-piercing riveting process consisting of clamping, piercing and flaring in the order of, measuring an acoustic signal generated in the process, and based on the acoustic signal analyzed through Fourier Transform, self-piercing riveting Assess the quality of the process.

Description

Method for monitoring self-piercing riveting quality, self-piercing riveting process, and equipment system for the same

The present invention relates to mechanical fasteners comprising self-piercing rivets. In detail, the present invention relates to a non-destructive-real-time monitoring method of fastening quality such as a self-piercing rivet, a self-piercing rivet fastening process method including the same, and an equipment system for the same.

In general, bonding of heterogeneous materials or bonding of multiple materials means bonding or bonding a plurality of materials having different types, physical properties, and characteristics. Bonding of heterogeneous materials in a broad sense may be used to include bonding technology between materials, molding technology, surface treatment technology, and the like. Recently, as light weight and high strength of materials are required, various materials other than conventional metals are being used, and accordingly, various studies related to dissimilar material bonding technology are being conducted.

However, the existing melt-based welding technology for steel materials (eg, resistance spot welding, arc welding, laser welding, etc.) cannot be applied to joining dissimilar materials with different properties, so adhesive bonding Non-welding techniques such as adhesive bonding and mechanical joint have been proposed.

Mechanical fastening technology is a generic term for technology that maintains physical boundaries between joining materials and mechanically joins dissimilar materials using separate fastening members. In the traditional mechanical fastening methods such as bolt-nut coupling and blind riveting, hole processing of the joint member must be preceded, and the process is difficult because the alignment of holes and holes and holes and rivets are required. It has the disadvantages of being complicated and difficult to automate. Therefore, recently, mechanical fastening methods that do not require hole processing such as self-piercing riveting (SPR), flow drill screwing (FDS), and clinching are in the spotlight.

International Patent Publication No. WO/2014/013232 A1 (2014.01.23) (Patent Document 2) US Patent Publication 2018/0117666 A1 (2018.05.03) (Patent Document 3) Korean Patent Document 10-2016-0011060 A (2016.01) .29)

Self-piercing riveting (SPR) is one of the representative mold-based spot joining technologies as a mechanical fastening technology. In the case of self-piercing riveting, it is a widely used mechanical fastening method because the material does not undergo large deformation and can exhibit very strong bonding strength in a relatively simple way. Self-piercing riveting has been disclosed in Patent Literature 1 and Patent Literature 2, and the like.

Compared to bolt-nut fastening, self-piercing riveting has the advantages of high productivity, relatively low thermal deformation, and applicable to different materials and coating materials because the process is simple and automation is possible compared to bolt-nut fastening. In addition, it is evaluated as the most realistic alternative to spot bonding of dissimilar materials because it can be used for bonding different materials between non-ferrous metals and steel, and has excellent bonding strength and is environmentally friendly.

Self-piercing riveting is performed by inserting a rivet of a special shape from one side of two materials to be joined. In self-piercing riveting, the rivet penetrates the upper material, and the shape of the rivet is called flaring according to the shape of the forming table (or die) located below the lower material. The material and the lower material are strongly engaged and combined. Accordingly, in the case of self-piercing riveting, when the ductility of the lower material is low, the strength of the upper material is excessively large, or in the case of a miss-align, a fastening defect may occur.

Meanwhile, one of the most important factors of mechanical fastening technology is the evaluation of mechanical fastening quality. In particular, in the case of self-piercing riveting, etc., once the fastening is made, there is no adequate means for evaluating the coupling state, that is, the fastening quality without destroying it. In particular, from the viewpoint of automation of mechanical fastening, there is a great need for non-destructive inspection of the fastening part after fastening, and further real-time monitoring, and accordingly, various technologies are being developed. For example, Patent Document 3 discloses a rivet joint inspection method of a metal panel. Specifically, Patent Document 3 discloses a method for evaluating fastening quality using the load and displacement of a punch used for a rivet joint.

However, as in Patent Document 3, the inspection method of fastening quality based on load and displacement has a variety of variables, so it is inconvenient to dataize it and proceed with initial setting. There is a problem that is difficult to apply to the quality evaluation of mechanical fasteners.

Accordingly, the problem to be solved by the present invention is to provide a method capable of monitoring the quality of mechanical fasteners in the prior art and in a new method.

Another problem to be solved by the present invention is to provide a mechanical fastening process method that can be automated by using the same, including the monitoring method of the mechanical fastening quality as described above.

Another problem to be solved by the present invention is to provide an automated equipment system for a mechanical fastening process.

The problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

In the self-piercing riveting process consisting of clamping, piercing and flaring in the order of the quality monitoring method of the mechanical fastening according to an embodiment of the present invention for solving the above problems, the acoustic signal generated in the process is measured and Fourier The quality of the self-piercing riveting process is evaluated based on the acoustic signal analyzed through the Fourier Transform.

Measuring and analyzing the acoustic signal may include separating the sound generated during the clamping, the sound generated during the piercing, and the sound generated during the flaring, respectively.

In addition, as a result of the Fourier transform of the acoustic signal during the piercing, the ratio of the sum of the magnitude of the signal generated in the range of 100 Hz to 550 Hz to the sum of the magnitude of the signal generated in the range of 2,000 Hz to 2,550 Hz is 10 or more It is determined that it is normal, Otherwise, it may be judged as defective.

As a result of the Fourier transform of the acoustic signal during the piercing, if the magnitude of the signal having the maximum peak in the range of 100 Hz to 550 Hz is three times or more the magnitude of the signal having the maximum peak in the range of 2,000 Hz to 2,550 Hz, it is determined as normal, otherwise In this case, it can be judged as defective.

In addition, as a result of the Fourier transform of the acoustic signal during the piercing, if the ratio of the sum of the magnitude of the signal generated in the range of 400 Hz to 550 Hz to the sum of the magnitude of the signal generated in the range of 100 Hz to 150 Hz is less than 1, it is determined to be normal, otherwise If not, it can be judged as defective.

In addition, as a result of the Fourier transform of the acoustic signal during the piercing, if the magnitude of the signal having the maximum peak in the range of 100 Hz to 150 Hz is 2.5 times or more the magnitude of the signal having the maximum peak in the range of 400 Hz to 550 Hz, it is determined as normal, otherwise In this case, it can be judged as defective.

As a result of the Fourier transform of the acoustic signal during the piercing, if the ratio of the sum of the magnitudes of the signals generated in the range of 400 Hz to 550 Hz to the sum of the magnitudes of the signals generated in the range of 550 Hz to 2,000 Hz is 0.5 or less, it is determined as normal, otherwise can be judged as defective.

In addition, as a result of the Fourier transform of the acoustic signal during the piercing, if the sum of the signal magnitudes generated in the range of 550 Hz to 2,000 Hz is less than or equal to a predetermined standard, it may be determined as normal, otherwise, it may be determined as defective.

In addition, as a result of the Fourier transform of the acoustic signal during the flaring, if the ratio of the sum of the magnitudes of the signals generated in the range of 400 Hz to 550 Hz to the sum of the magnitudes of the signals generated in the range of 550 Hz to 2,000 Hz is 0.3 or less, it is determined as normal, otherwise If not, it can be judged as defective.

As a result of the Fourier transform of the acoustic signal during flaring, when the sum of the signal magnitudes generated in the range of 550 Hz to 2,000 Hz is less than a predetermined standard, it is determined that the signal is normal, otherwise, it can be determined that the signal is defective.

In the self-piercing riveting process consisting of clamping, piercing and flaring in the order of the quality monitoring method of the mechanical fastening according to another embodiment of the present invention for solving the above problems, the size of the sound signal generated during the piercing process is , If it is smaller than the size of the previously measured sound signal, it is judged as normal, otherwise it is judged as defective.

If the size of the sound signal generated during the entire process is 250 MPa or less, it is judged as normal, otherwise, it can be judged as defective.

The self-piercing rivet fastening process according to an embodiment of the present invention for solving the above other problem includes: a first stage step of self-piercing riveting a mechanical fastening object, measuring the sound, and analyzing the sound signal by Fourier transform; and a second stage of performing self-piercing riveting on the same object as the first stage with the same equipment, measuring the sound, and analyzing the sound signal by Fourier transform.

The first stage may be a stage of setting, correcting, and dataizing a reference value of an acoustic signal, and the second stage may be the main process of mechanical fastening.

Also, each of the first stage step and the second stage step may be performed including the method according to claim 1 .

The analysis result of the first stage can be machine-learned and reflected in the second stage, and real-time monitoring can be performed simultaneously with the self-piercing rivet fastening process.

Mechanical fastening equipment system according to an embodiment of the present invention for solving the another problem is a mechanical fastening unit including a rivet punch unit and a die; an acoustic measurement unit disposed adjacent to the mechanical fastening part and measuring an acoustic signal generated in the mechanical fastening process; and a sound processing unit configured to Fourier transform the measurement result of the sound measurement unit.

Details of other embodiments are included in the detailed description.

According to the embodiments of the present invention, it is possible to measure the sound generated in the mechanical fastening, in particular, the self-piercing riveting process, and to evaluate the presence or absence of defects and the quality of the mechanical fastening by capturing unique identification data from the measured sound data. .

In particular, real-time inspection as well as non-destructive inspection can be achieved by measuring and analyzing the sound generated during the fastening process in real time.

Effects according to the embodiments of the present invention are not limited by the contents exemplified above, and more various effects are included in the present specification.

1 is a block diagram of a mechanical fastening equipment system according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of the mechanical fastening equipment system of FIG. 1 .
3 is a schematic diagram showing the self-piercing riveting process in order.
4 is a flowchart illustrating a method for evaluating the quality of mechanical fastening according to an embodiment of the present invention.
5 is a flowchart illustrating a method for evaluating the quality of mechanical fastening according to another embodiment of the present invention.
6 is a flowchart illustrating a method for evaluating the quality of mechanical fastening according to another embodiment of the present invention.
7 to 13 are flow charts each illustrating a quality evaluation method of a mechanical fastening according to another embodiment of the present invention.
14 is a flowchart illustrating a mechanical fastening process method according to an embodiment of the present invention.
15 to 19 are images showing results according to Experimental Example 2.
20 to 24 are images showing results according to Experimental Example 3.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, and only the embodiments allow the disclosure of the present invention to be complete, and those of ordinary skill in the art to which the present invention pertains. It is provided to fully inform the person of the scope of the invention, and the present invention is only defined by the scope of the claims. That is, various changes may be made to the embodiments presented by the present invention. It should be understood that the embodiments described below are not intended to limit the embodiments, and include all modifications, equivalents, and substitutes thereto.

The size, thickness, width, length, etc. of the components shown in the drawings may be exaggerated or reduced for convenience and clarity of description, so that the present invention is not limited to the illustrated form.

Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used with the meaning commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, terms defined in a commonly used dictionary are not to be interpreted ideally or excessively unless clearly defined in particular.

Spatially relative terms 'above', 'upper', 'on', 'below', 'beneath', 'lower', etc. As illustrated, it may be used to easily describe a correlation between one element or components and another device or components. Spatially relative terms should be understood as terms including different orientations of the device when used in addition to the orientations shown in the drawings. For example, when an element shown in the drawing is turned over, an element described as 'below or beneath' of another element may be placed 'above' of the other element. Accordingly, the exemplary term 'down' may include both the direction of the bottom and the top.

In this specification, 'and/or' includes each and every combination of one or more of the recited items. The singular also includes the plural, unless the phrase specifically states otherwise. As used herein, 'comprises' and/or 'comprising' does not exclude the presence or addition of one or more other components in addition to the stated components. Numerical ranges indicated using 'to' indicate numerical ranges including the values stated before and after them as lower and upper limits, respectively. 'About' or 'approximately' means a value or numerical range within 20% of the value or numerical range recited thereafter.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of a mechanical fastening equipment system according to an embodiment of the present invention. FIG. 2 is a schematic diagram of the mechanical fastening equipment system of FIG. 1 . 3 is a schematic diagram showing the self-piercing riveting process in order.

1 to 3 , the mechanical fastening facility system 1 according to the present embodiment may include a mechanical fastening unit 10 , a sound measuring unit 21 , and a sound processing unit 23 .

The mechanical fastening part 10 may mean a component for performing mechanical fastening. For example, when the mechanical fastening is a self-piercing rivet, the mechanical fastening unit 10 may include a punch unit P and an anvil die D. In general, the self-piercing riveting process may be performed in the order of clamping, piercing, flaring, and releasing.

Clamping is a step of interposing the bonding object 100, for example, the upper piece 110 and the lower piece 120 between the anvil die D and the punch unit P, aligning them and then fixing them. can mean 3 illustrates a case in which the bonding object 100 includes only the upper piece 110 and the lower piece 120, but the present invention is not limited thereto, and the bonding object 100 is made of three or more pieces. may be

The upper piece 110 and the lower piece 120 may each include a metal material or a non-metal material. Examples of the metal material include iron (Fe), chromium (Cr), nickel (Ni), aluminum (Al), magnesium (Mg), or an alloy thereof. The non-metal material may be exemplified by carbon fiber reinforced plastic (CFRP).

Piercing may refer to a step of at least partially penetrating the rivet (R) to the bonding object (100) using the punch unit (P). Pressing of the rivet (R) may be performed through the punch unit (P).

Flaring may refer to a step in which the rivet R penetrates the bonding object 100 and the shape is deformed. For example, the shank of the rivet R may be opened as if exploding and the shape of the ductile piece, for example, the lower piece 120 may be deformed. The deformable shape may be deformed according to the shape of the upper surface of the anvil die D. 3 illustrates a shape in which the base surface of the anvil die D convexly protrudes, but the present invention is not limited thereto. The upper piece 110, the lower piece 120, and the rivet R, which are deformed in shape during the flaring process, may be engaged with each other, and the upper piece 110 and the lower piece 120 may be firmly fixed.

Finally, releasing (releasing) may refer to a step of releasing the fixed state by moving the punch unit (P) upward after the mechanical fastening is completed.

The acoustic measurement unit 21 may be positioned adjacent to the punch unit P and the anvil die D. That is, the sound measuring unit 21 is located adjacent to the process space between the punch unit P and the anvil die D, and can measure the sound generated in the process space. The acoustic measurement unit 21 may include an acoustic sensor such as a microphone.

The sound processing unit 23 may perform a function such as processing, converting, or analyzing the sound signal measured by the sound measuring unit 21 . In an exemplary embodiment, the sound processing unit 23 may Fourier transform the sound signal measured by the sound measurement unit 21 . A detailed example of the Fourier transform may include a Fast Fourier Transform (FFT).

The acoustic signal measured by the acoustic measurement unit 21 may be expressed as a magnitude of the acoustic signal over time. The magnitude of the sound signal may be expressed as pressure or decibels (dB). On the other hand, the sound signal converted by the sound processing unit 23 may be expressed as a size of the sound signal with respect to frequency (Hz). The magnitude of the sound signal may be expressed as pressure, decibels, or amplitude. That is, the sound processing unit 23 may convert the signal size according to the lapse of the process time into the signal size for each frequency band. The monitoring or evaluation method of the mechanical fastening quality according to the present embodiment may be performed based on the acoustic signal measured by the acoustic measurement unit 21 or the acoustic signal converted by the acoustic processing unit 23 . have. This will be described later.

The controller 30 may be a component that controls the mechanical fastening unit 10 and the sound measuring unit 21 and/or the sound processing unit 23 . The controller 30 may include a central processing unit (CPU), a micro processor unit (MPU), a micro controller unit (MCU), or any type of processor known in the art. Memory is random access memory (RAM), read only memory (ROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), flash memory, or any type of memory known in the art. It may be composed of

The controller 30 may perform a timing control role. For example, it is possible to control the start and end of the self-piercing riveting process performed in the mechanical fastening unit 10 , specifically, the timing of start and clamping, piercing, flaring and releasing. In addition, by combining the data regarding the timing and the data regarding the sound signal measured by the sound measurement unit 21 , the size of the sound signal according to the process time may be derived. In addition, the controller 30 may perform a determination in performing a method to be described later, or may be implemented through software for performing the determination.

Of course, in some embodiments, the controller 30 and the sound processing unit 23 may be implemented integrally.

Hereinafter, a method for evaluating or monitoring the quality of a mechanical fastening using the aforementioned mechanical fastening equipment system 1 will be described.

4 is a flowchart illustrating a method for evaluating the quality of mechanical fastening according to an embodiment of the present invention.

Referring further to FIG. 4 , the method for evaluating the quality of mechanical fasteners according to this embodiment separates the sound generated during clamping, the sound generated during piercing, the sound generated during flaring, and the sound generated during releasing (S110), respectively, during the piercing It may include performing the Fourier transform of the generated acoustic signal (S120) and comparing the sum of the magnitudes of the signals of the first frequency section with the sum of the magnitudes of the signals of the second frequency section (S130).

Separating the sound ( S110 ) may be performed by the sound processing unit 23 , but the present invention is not limited thereto. An acoustic signal of a predetermined magnitude may be detected during the aforementioned clamping, piercing, flaring and releasing.

The method of performing the step of separating the sound ( S110 ) is not particularly limited, but may be performed, for example, based on the time at which the sound measurement unit 21 starts measuring the sound and the time at which the sound measurement ends. As a more specific, non-limiting example, an acoustic signal of a predetermined size measured for about 0.2 milliseconds (ms) in a section from 1 second to 2 seconds after the start of the acoustic measurement may be generated during clamping. In addition, an acoustic signal of a predetermined size measured for about 0.5 ms in a section from 2 seconds to 2.5 seconds after the start of the acoustic measurement may be generated during piercing. An acoustic signal of a predetermined size measured for about 0.5 ms in a section from 2.5 seconds to 3 seconds after the start of the acoustic measurement may be generated during flaring. Also, an acoustic signal of a predetermined size measured for about 0.2 ms immediately after flaring, for example, in a section from 3 seconds to 3.5 seconds after the start of the acoustic measurement, may be generated during releasing. In this way, the sound may be separated based on the time period, or the sound may be sequentially separated from the sound signal detected to have a specific size or higher.

Performing the Fourier transform of the sound signal generated during piercing ( S120 ) may be performed by the sound processing unit 23 , but the present invention is not limited thereto. Through Fourier transform, the measured acoustic signal may be converted into the magnitude of the acoustic signal for each frequency band. For example, the measured acoustic signal may have a horizontal axis as time and a vertical axis as a magnitude of the acoustic signal, such as pressure (Pa) or decibel (dB). On the other hand, in the acoustic signal transformed through the Fourier transform, the horizontal axis may be the frequency (Hz) and the vertical axis may be the magnitude of the acoustic signal, for example, pressure, decibels, or dimensionless amplitude (amplitude).

In addition, the step ( S130 ) of comparing the sum of the magnitudes of the signals of a specific frequency section may be performed by the sound processing unit 23 , but the present invention is not limited thereto. The inventors of the present invention have found that there is a difference in signal characteristics for each frequency band in the case where the result of mechanical fastening, for example, self-piercing riveting, has excellent fastening strength and when it does not, and completed the present invention by paying attention to this.

In the present embodiment, the step of comparing the sum of the amplitudes of the acoustic signals ( S130 ) may be performed by comparing the sum of the amplitudes of the signals belonging to the first frequency period with the sum of the amplitudes of the signals belonging to the second frequency period.

In this embodiment, the first frequency section may be in the range of 100 Hz to 550 Hz, and the second frequency section may be in the range of 2,000 Hz to 2,550 Hz.

In an exemplary embodiment, the ratio (G1/G2) of the sum (G1) of the magnitudes of the signals generated in the first frequency section to the sum (G2) of the magnitudes of the signals generated in the second frequency section is greater than or equal to a predetermined standard In this case, it can be considered normal. And if not, it can be judged as defective.

Specifically, the ratio (G1/G2) of the sum (G1) of the magnitudes of the signals generated in the first frequency section to the sum (G2) of the signals generated in the second frequency section is about 5.0 or more, or about 5.5 or more, or about If it is 6.0 or more, or about 6.5 or more, or about 7.0 or more, or about 7.5 or more, or about 8.0 or more, or about 8.5 or more, or about 9.0 or more, or about 9.5 or more, or about 10.0 or more, normal riveting has been performed. can be judged. whereas, the ratio (G1/G2) is less than about 5.0, or less than about 4.5, or less than about 4.0, or less than about 3.5, or less than about 3.0, or less than about 2.5, or less than about 2.0, or less than about 1.5, or If it is less than about 1.0, it may be determined that poor riveting has occurred.

In the present specification, the sum of signals generated in a specific frequency section may be expressed as an integral value for the corresponding frequency section in a graph in which the horizontal axis is the frequency band and the vertical axis is the signal size.

The inventors of the present invention show a specific difference in behavior depending on whether the self-piercing rivet is normally fastened in a signal of a high frequency band during piercing, for example, a frequency band of 2,000 Hz or more and a signal of a low frequency band, for example, a frequency band of 550 Hz or less. came to the conclusion of the invention.

That is, although the present invention is not limited to any theory, when the rivet fastening is normally performed, the second frequency section, for example, 2,000 Hz to 2,550 Hz, or about 2,200 Hz to 2,500 Hz, or about 2,300 Hz to 2,450 Hz. On the other hand, when the rivet fastening is abnormally performed, an acoustic signal of a predetermined size may be generated in the second frequency section. This will be described later along with experimental examples.

Hereinafter, other embodiments of the present invention will be described. However, a description of the same or extremely similar configuration to the above-described embodiment will be omitted, which will be clearly understood by those skilled in the art.

5 is a flowchart illustrating a method for evaluating the quality of mechanical fastening according to another embodiment of the present invention.

Referring to FIG. 5 , the method for evaluating the quality of mechanical fastening according to this embodiment separates the sound generated during clamping, the sound generated during piercing, the sound generated during flaring, and the sound generated during releasing (S210), which occurred during the piercing. It may include performing the Fourier transform of the acoustic signal (S220) and comparing the magnitude of the signal having the maximum peak in the first frequency section with the magnitude of the signal having the maximum peak in the second frequency section (S230). .

Since the step of separating the sound ( S210 ) and the step of performing the Fourier transform ( S220 ) have been described above, a redundant description will be omitted.

In the present embodiment, the step of comparing the magnitude of the maximum acoustic signal ( S230 ) may be performed by comparing the magnitude of the signal having the maximum peak in the first frequency interval with the signal having the maximum peak in the second frequency interval.

In this embodiment, the first frequency section may be in the range of 100 Hz to 550 Hz, and the second frequency section may be in the range of 2,000 Hz to 2,550 Hz.

In an exemplary embodiment, the ratio (H1/H2) of the magnitude (H1) of the signal having the maximum peak in the first frequency interval to the magnitude (H2) of the signal having the maximum peak in the second frequency interval (H1/H2) is a predetermined value. If it exceeds the standard, it can be judged to be normal. And if not, it can be judged as defective.

Specifically, the ratio (H1/H2) of the magnitude (H1) of the signal having the maximum magnitude in the first frequency zone to the magnitude (H2) of the signal having the maximum magnitude in the second frequency zone is about 2.5 or more, or about 3.0 or more, or about 3.5 or more, or about 4.0 or more, or about 4.5 or more, or about 5.0 or more, it may be determined that normal riveting has been performed. On the other hand, when the ratio (H1/H2) is less than about 3.0, or less than about 2.5, or less than about 2.0, or less than about 1.5, or less than about 1.0, it may be determined that poor riveting has occurred.

In the present specification, the magnitude of the signal generated at a specific frequency value may be expressed as the magnitude of the signal at the corresponding frequency value, ie, the value on the vertical axis, in a graph in which the horizontal axis represents the frequency band and the vertical axis represents the signal magnitude.

The inventors of the present invention show a specific difference in behavior depending on whether the self-piercing rivet is normally fastened in a signal of a high frequency band during piercing, for example, a frequency band of 2,000 Hz or more and a signal of a low frequency band, for example, a frequency band of 550 Hz or less. came to the conclusion of the invention.

That is, although the present invention is not limited to any theory, when the rivet fastening is normally performed, the second frequency section, for example, 2,000 Hz to 2,550 Hz, or about 2,200 Hz to 2,500 Hz, or about 2,300 Hz to 2,450 Hz. On the other hand, when the rivet fastening is abnormally performed, an acoustic signal of a predetermined size may be generated in the second frequency section. This will be described later along with experimental examples.

6 is a flowchart illustrating a method for evaluating the quality of mechanical fastening according to another embodiment of the present invention.

Referring to FIG. 6 , the method for evaluating the quality of mechanical fasteners according to this embodiment separates the sound generated during clamping, the sound generated during piercing, the sound generated during flaring, and the sound generated during releasing (S310), which occurred during the piercing. It may include performing the Fourier transform of the acoustic signal (S320) and comparing the sum of the magnitudes of the signals in the 1-1 frequency section with the sum of the magnitudes of the signals in the 1-2 frequency section (S330). .

Since the step of separating the sound ( S310 ) and the step of performing the Fourier transform ( S320 ) have been described above, a redundant description will be omitted.

In the present embodiment, the step of comparing the sum of the amplitudes of the acoustic signals ( S330 ) is to be performed by comparing the sum of the amplitudes of the signals belonging to the 1-1 frequency interval with the sum of the amplitudes of the signals belonging to the 1-2 frequency interval. can

In this embodiment, the 1-1 frequency section may be in the range of 100 Hz to 150 Hz, and the 1-2 frequency section may be in the range of 400 Hz to 550 Hz.

In an exemplary embodiment, a ratio (G1) of the sum (G1-2) of the magnitudes of the signals generated in the 1-2th frequency section to the sum (G1-1) of the magnitudes of the signals generated in the 1-1 frequency section -2/G1-1) is less than or equal to a predetermined standard, it may be determined as normal. And if not, it can be judged as defective.

Specifically, the ratio (G1-2/G1-1) of the sum of the magnitudes of the signals generated in the 1-2 frequency section (G1-2) to the sum of the signals generated in the 1-1 frequency section (G1-1) Normal riveting is performed when this is about 1.0 or less, or about 1.0 or less, or about 0.9 or less, or about 0.8 or less, or about 0.7 or less, or about 0.6 or less, or about 0.5 or less, or about 0.4 or less, or about 0.3 or less. can be judged to have been On the other hand, poor rivets when the ratio (G1-2/G1-1) is about 1.0 or more, or about 1.0 or more, or about 1.2 or more, or about 1.4 or more, or about 1.6 or more, or about 1.8 or more, or about 2.0 or more. It can be judged that a contract has occurred.

The inventors of the present invention have developed the present invention based on the fact that it shows a specific behavioral difference depending on whether the self-piercing rivet is normally fastened in the low frequency band during piercing, for example, among the signals of the frequency band of 550 Hz or less, the ultra-low frequency signal and the middle and low frequency signal came to completion.

That is, although the present invention is not limited to any theory, when the rivets are normally fastened, the acoustic signal is mainly generated in the 1-1 frequency range, for example, 100Hz to 150Hz, and the 1-2 frequency range, for example 400Hz to While a weak acoustic signal is generated at 550 Hz, when the rivet is abnormally fastened, an acoustic signal of a predetermined size is generated in the 1-2 frequency section, or even compared to the signal sum in the 1-1 frequency section, the first- The signal sum of the two frequency sections may be larger. This will be described later along with experimental examples.

7 is a flowchart illustrating a method for evaluating the quality of mechanical fastening according to another embodiment of the present invention.

Referring to FIG. 7 , the method for evaluating the quality of mechanical fastening according to this embodiment separates the sound generated during clamping, the sound generated during piercing, the sound generated during flaring, and the sound generated during releasing (S410), respectively. Performing the Fourier transform of the acoustic signal (S420) and comparing the magnitude of the signal having the maximum peak in the 1-1 frequency section with the magnitude of the signal having the maximum peak in the 1-2 frequency section (S430) may include

Since the step of separating the sound ( S410 ) and the step of performing the Fourier transform ( G420 ) have been described above, a redundant description will be omitted.

In this embodiment, the step of comparing the magnitude of the maximum acoustic signal (S430) is to be performed by comparing the magnitude of the signal having the maximum peak in the 1-1 frequency section and the signal having the maximum peak in the 1-2 frequency section. can

In this embodiment, the 1-1 frequency section may be in the range of 100 Hz to 150 Hz, and the 1-2 frequency section may be in the range of 400 Hz to 550 Hz.

In an exemplary embodiment, the ratio of the magnitude (H1-1) of the signal having the maximum peak in the 1-1 frequency section to the magnitude (H1-2) of the signal having the maximum peak in the 1-2 frequency section When (H1-1/H1-2) is greater than or equal to a predetermined standard, it may be determined that the normal value is normal. And if not, it can be judged as defective.

Specifically, the ratio (H1-1/) of the magnitude (H1-1) of the signal having the maximum magnitude in the 1-1 frequency section to the magnitude (H1-2) of the signal having the maximum magnitude in the 1-2 frequency section (H1-1/ When H1-2) is about 2.0 or more, or about 2.5 or more, or about 3.0 or more, or about 3.5 or more, it may be determined that normal riveting has been performed. On the other hand, when the ratio (H1-1/H1-2) is less than about 2.0, or less than about 1.5, or less than about 1.0, it may be determined that poor riveting has occurred.

The inventors of the present invention have developed the present invention based on the fact that it shows a specific behavioral difference depending on whether the self-piercing rivet is normally fastened in the low frequency band during piercing, for example, among the signals of the frequency band of 550 Hz or less, the ultra-low frequency signal and the middle and low frequency signal came to completion.

That is, although the present invention is not limited to any theory, when the rivets are normally fastened, the acoustic signal is mainly generated in the 1-1 frequency range, for example, 100Hz to 150Hz, and the 1-2 frequency range, for example 400Hz to While a weak acoustic signal is generated at 550Hz, when the rivet is abnormally fastened, an acoustic signal of a predetermined size or more is generated in the 1st-2 frequency section, or even less than the maximum signal in the 1st-1 frequency section. A signal having a maximum magnitude in the 1-2 frequency interval may be larger. This will be described later along with experimental examples.

8 is a flowchart illustrating a method for evaluating the quality of mechanical fastening according to another embodiment of the present invention.

Referring to FIG. 8 , the method for evaluating the quality of mechanical fasteners according to the present embodiment separates the sound generated during clamping, the sound generated during piercing, the sound generated during flaring, and the sound generated during releasing (S510), which occurred during the piercing. It may include performing Fourier transform of the acoustic signal ( S520 ) and comparing the sum of the magnitudes of the signals in the 1-2 th frequency section with the sum of the magnitudes of the signals in the third frequency section ( S530 ).

Since the step of separating the sound ( S510 ) and the step of performing the Fourier transform ( S520 ) have been described above, a redundant description will be omitted.

In the present embodiment, the step of comparing the sum of the amplitudes of the acoustic signals ( S530 ) may be performed by comparing the sum of the amplitudes of the signals belonging to the 1-2 th frequency period and the sum of the amplitudes of the signals belonging to the third frequency period. .

In the present embodiment, the 1-2 frequency range may be in the range of 400 Hz to 550 Hz, and the third frequency range may be in the range of 550 Hz to 2,000 Hz.

In an exemplary embodiment, the ratio (G3/G1-2) of the sum (G3) of the magnitudes of the signals generated in the third frequency section to the sum (G1-2) of the magnitudes of the signals generated in the 1-2 first frequency section ) is less than or equal to a predetermined standard, it can be determined as normal. And if not, it can be judged as defective.

Specifically, the ratio (G3/G1-2) of the sum (G3) of the magnitudes of the signals generated in the third frequency section to the sum (G1-2) of the signals generated in the 1-2 frequency section is about 0.5 or less, or If it is about 0.4 or less, or about 0.3 or less, or about 0.2 or less, or about 0.1 or less, it may be determined that normal riveting has been performed. On the other hand, when the ratio (G3/G1-2) is greater than about 0.5, or greater than about 0.6, or greater than about 0.7, or greater than about 0.8, or greater than about 0.9, or greater than about 1.0, it may be determined that poor riveting has occurred. have.

The inventors of the present invention in the low frequency band during piercing, for example, a signal of a frequency band of 550 Hz or less and a signal of an intermediate frequency band, for example, a frequency band of 550 Hz to 2,000 Hz, a specific behavior difference depending on whether the self-piercing rivet is normally fastened. The present invention was completed by paying attention to what is shown.

That is, although the present invention is not limited to any theory, when the rivet fastening is normally made, the sound signal is substantially not generated in the third frequency section, for example, 550Hz to 2,000Hz, or even occurs, to a very weak degree, whereas the rivet When the fastening is abnormally performed, an acoustic signal having a predetermined size may be generated in the third frequency section. This will be described later along with experimental examples.

9 is a flowchart illustrating a method for evaluating the quality of mechanical fastening according to another embodiment of the present invention.

Referring to FIG. 9 , the method for evaluating the quality of mechanical fasteners according to this embodiment separates the sound generated during clamping, the sound generated during piercing, the sound generated during flaring, and the sound generated during releasing (S610), which occurred during the piercing. It may include performing the Fourier transform of the acoustic signal (S620) and comparing the sum of the magnitudes of the signals in the third frequency section with a predetermined reference (S630).

Since the step of separating the sound ( S610 ) and the step of performing the Fourier transform ( S620 ) have been described above, a redundant description will be omitted.

In the present embodiment, the step ( S630 ) of comparing the sum of the magnitudes of the acoustic signals with the predetermined reference may be performed by comparing the sum G3 of the magnitudes of the signals belonging to the third frequency section with the predetermined reference.

In this embodiment, the third frequency section may be in the range of 550 Hz to 2,000 Hz.

As described above, when the rivet fastening is normally performed, the sound signal is substantially not generated in the third frequency section, for example, 550 Hz to 2,000 Hz, or is very weak even if it occurs, whereas when the rivet fastening is abnormally performed, the third frequency signal is not generated. An acoustic signal having a predetermined size may be generated in the frequency section.

In particular, the above-described first frequency section and the second frequency section are frequency bands that are sensitively affected depending on the presence or absence of defects, but the third frequency section located between the first frequency section and the second frequency section is relatively dependent on the presence or absence of defects. It was confirmed through the experiment that it is a frequency band that is insensitively affected by .

Therefore, it can be seen that a serious defect has occurred when a signal having a predetermined magnitude or more or a signal exceeding a predetermined magnitude is generated in the third frequency section. The predetermined size may be set through data conversion or machine learning through repeated experiments.

10 is a flowchart illustrating a method for evaluating the quality of mechanical fastening according to another embodiment of the present invention.

Referring to FIG. 10 , the method for evaluating the quality of mechanical fasteners according to the present embodiment separates the sound generated during clamping, the sound generated during piercing, the sound generated during flaring, and the sound generated during release, respectively (S710), during flaring Performing a Fourier transform of the generated acoustic signal (S720) and comparing the sum of the magnitudes of the signals of the 1-1 frequency section with the sum of the magnitudes of the signals of the 1-2 frequency section (S730) have.

Since the step of separating the sound ( S710 ) has been described above, a redundant description will be omitted.

Unlike the above-described embodiments, the Fourier transform according to the present embodiment may use a sound generated during flaring. In the step S720 of performing the Fourier transform of the acoustic signal generated during flaring, similar to the Fourier transform of the acoustic signal generated during piercing, the horizontal axis may be the frequency and the vertical axis may be the size of the acoustic signal.

In the present embodiment, the step of comparing the sum of the amplitudes of the acoustic signals ( S730 ) may be performed by comparing the sum of the amplitudes of the signals belonging to the 1-2 th frequency interval with the sum of the amplitudes of the signals belonging to the third frequency period. .

In the present embodiment, the 1-2 frequency range may be in the range of 400 Hz to 550 Hz, and the third frequency range may be in the range of 550 Hz to 2,000 Hz.

In an exemplary embodiment, the ratio (F3/F1-2) of the sum of the magnitudes of the signals generated in the third frequency section (F3) to the sum (F1-2) of the magnitudes of the signals generated in the 1-2 first frequency section ) is less than or equal to a predetermined standard, it can be determined as normal. And if not, it can be judged as defective.

Specifically, the ratio (F3/F1-2) of the sum (F3) of the magnitudes of the signals generated in the third frequency section to the sum (F1-2) of the signals generated in the 1-2 frequency section is about 0.4 or less, or If it is about 0.3 or less, or about 0.2 or less, or about 0.1 or less, it may be determined that normal riveting has been performed. On the other hand, if the ratio (F3/F1-2) is greater than about 0.4, or greater than about 0.5, or greater than about 0.6, or greater than about 0.7, or greater than about 0.8, or greater than about 0.9, or greater than about 1.0, poor riveting is indicated. can be considered to have occurred.

The inventors of the present invention found that in the signal of the low frequency band during flaring, for example, the frequency band of 550 Hz or less, and the signal of the intermediate frequency band, for example, the frequency band in the range of 550 Hz to 2,000 Hz, a specific behavior difference depending on whether the self-piercing rivet fastening is normal The present invention was completed by focusing on showing.

That is, although the present invention is not limited to any theory, when the rivet fastening is normally made, the sound signal is substantially not generated in the third frequency section, for example, 550Hz to 2,000Hz, or is very weak even if it occurs, whereas the rivet When the fastening is abnormally performed, an acoustic signal having a predetermined size may be generated in the third frequency section. This will be described later along with experimental examples.

11 is a flowchart illustrating a method for evaluating the quality of mechanical fastening according to another embodiment of the present invention.

Referring to FIG. 11 , the method for evaluating the quality of mechanical fastening according to this embodiment separates the sound generated during clamping, the sound generated during piercing, the sound generated during flaring, and the sound generated during releasing (S810), respectively, during flaring It may include performing the Fourier transform of the generated sound signal (S820) and comparing the sum of the magnitudes of the signals in the third frequency section with a predetermined reference (S830).

Since the step of separating the sound ( S810 ) and the step of performing the Fourier transform ( S820 ) have been described above, a redundant description will be omitted.

In the present embodiment, the step of comparing the sum of the amplitudes of the acoustic signals with a predetermined criterion ( S830 ) may be performed by comparing the sum F3 of the amplitudes of the signals belonging to the third frequency section with the predetermined criterion.

In this embodiment, the third frequency section may be in the range of 550 Hz to 2,000 Hz.

As described above, when the rivet fastening is normally performed, the sound signal is not substantially generated in the third frequency section, for example, 550Hz to 2,000Hz, or is very weak even if it occurs, whereas when the rivet fastening is abnormally performed, the third frequency signal is not generated. An acoustic signal having a predetermined size may be generated in the frequency section.

In particular, the above-described first frequency section and the second frequency section are frequency bands that are sensitively affected depending on the presence or absence of defects, but the third frequency section located between the first frequency section and the second frequency section is relatively dependent on the presence or absence of defects. It was confirmed through the experiment that it is a frequency band that is insensitively affected by .

Therefore, it can be seen that a serious defect has occurred when a signal having a predetermined magnitude or more or a signal exceeding a predetermined magnitude is generated in the third frequency section. The predetermined size may be set through data conversion or machine learning through repeated experiments.

12 is a flowchart illustrating a method for evaluating the quality of mechanical fastening according to another embodiment of the present invention.

12 , the method for evaluating the quality of mechanical fastening according to the present embodiment separates the sound generated during clamping, the sound generated during piercing, the sound generated during flaring, and the sound generated during releasing (S910) and without Fourier transform , comparing the size of the sound generated during clamping with the level of the sound generated during piercing (S930).

Since the step of separating the sound (S910) has been described above, a redundant description will be omitted.

The quality evaluation method according to the present embodiment may be determined by directly using the sound signal measured by using the sound measuring unit, but without performing Fourier transform using the sound processing unit or the like. That is, the sound processing unit may only compare magnitudes of the measured sound signals and may not substantially perform Fourier transform.

In the present embodiment, the step of comparing the magnitude of the acoustic signal ( S930 ) may be performed by comparing the magnitude of the acoustic signal generated during clamping with the magnitude of the acoustic signal generated during piercing.

In an exemplary embodiment, when the magnitude of the acoustic signal generated during piercing is smaller than the magnitude of the previously measured acoustic signal, it may be determined as normal. And if not, it can be judged as defective. For example, the acoustic signal during piercing and the acoustic signal during clamping can be compared.

The magnitude of the acoustic signal may mean the magnitude of the acoustic signal having the maximum peak measured during the corresponding process, that is, during clamping or piercing, or may mean the sum of the magnitudes of the acoustic signals generated during the corresponding process.

As described above, clamping is a step of aligning and fixing the objects to be joined, and may be a step independent of the actual process result, that is, normal or defective. That is, the acoustic signals measured during clamping may have substantially the same results regardless of whether the process is defective. On the other hand, piercing is a stage at which the actual process is started or immediately after the start, and the measured acoustic signal may have a predetermined relationship with the actual process result. The inventors of the present invention have completed the present invention by paying attention to the fact that their acoustic signals show a specific difference in behavior depending on whether the self-piercing rivet fastening is normal. This will be described later along with experimental examples.

13 is a flowchart illustrating a method for evaluating the quality of mechanical fastening according to another embodiment of the present invention.

Referring to FIG. 13 , the method for evaluating the quality of mechanical fasteners according to the present embodiment may include comparing the magnitude of the maximum sound generated during clamping, piercing, flaring, and releasing with a predetermined criterion ( S1030 ). Although not represented in the drawings, the method according to this embodiment may further include a step of separating the sound generated during clamping, the sound generated during piercing, the sound generated during flaring, and the sound generated during releasing, respectively, before the step of comparing ( S1030 ). have.

The quality evaluation method according to the present embodiment may be determined by directly using the sound signal measured by using the sound measuring unit, but without performing Fourier transform using the sound processing unit or the like. That is, the sound processing unit may only compare magnitudes of the measured sound signals and may not substantially perform Fourier transform.

In an exemplary embodiment, the magnitude of the acoustic signal generated during clamping, piercing, flaring and releasing, in particular the magnitude of the acoustic signal generated during piercing and flaring, is about 250 MPa, or about 260 MPa, or about 270 MPa, or about 280 MPa; Or about 290 MPa, or about 300 MPa or less can be determined as normal. And if not, it can be judged as defective. The magnitude of the acoustic signal may mean the magnitude of the acoustic signal having a maximum peak during a corresponding process, that is, during a process from clamping to releasing, or during a process from piercing to flaring.

The inventors of the present invention have completed the present invention by paying attention to the fact that their acoustic signals show a specific difference in behavior depending on whether the self-piercing rivet fastening is normal. This will be described later along with experimental examples.

The quality evaluation method of mechanical fastening according to the present invention has been described above. In the above, only one element for measuring the quality of the rivet fastening has been expressed for each embodiment, but the method for evaluating the quality of the mechanical fastening according to the present invention may be performed by combining a plurality of the evaluation methods disclosed in FIGS. 4 to 13 . For example, the controller making the judgment may evaluate the quality by judging the methods according to FIGS. 4 to 13 sequentially or in a specific order.

Hereinafter, a mechanical fastening process method according to the present invention will be described.

14 is a flowchart illustrating a mechanical fastening process method according to an embodiment of the present invention.

Referring to FIG. 14 , the mechanical fastening process method according to the present embodiment may include a first stage step S10 and a second stage step S20 . The mechanical fastening may include a self-piercing riveting process. In addition, the first stage step ( S10 ) and the second stage step ( S20 ) may each be performed including the evaluation method of mechanical fastening quality according to any one or more of FIGS. 4 to 13 described above.

The first stage step S10 may be a pre-process performed prior to the second stage step S20 which is the present process. The first stage step S10 may be a step of setting, correcting, and/or dataizing a reference value of the above-described method for evaluating mechanical fastening quality.

The first stage step S10 may include a step S11 of evaluating the mechanical fastening quality and a step S12 of evaluating the actual quality at least once, respectively. That is, in the first stage step (S10), as described above, a self-piercing rivet process performed in the order of clamping, piercing, flaring, and releasing is performed to measure the sound, and selectively Fourier transform it, furthermore, the behavior of the sound signal Estimate the quality of mechanical fastening through analysis (S11), analyze the bonding strength or mechanical strength of the actual bonding body (S12), and set, optimize, or set parameters for behavior analysis of acoustic signals by reflecting the actual results in the estimation , it may be a step such as correction. The above correction and the like may be implemented through machine learning.

The step of analyzing the bonding strength of the actual bonded body ( S12 ) may be performed through fracture-cross-sectional inspection of the bonded body or measurement of mechanical strength.

Also, the second stage step S20 may correspond to the actual mechanical fastening process. The second stage step S20 may include evaluating the mechanical fastening quality one or more times. The second stage step S20 may be performed using the same mechanical fastening equipment system for a bonding target such as the same material as that of the first stage step S10 .

Based on the parameters or data set, optimized, or corrected in the first stage step ( S10 ), the mechanical fastening equipment system according to the present embodiment reflects the material characteristics of the bonding object, particularly the bonding object, to the second stage Step S20 may be performed.

The mechanical fastening process method according to the present embodiment may further increase the reliability of quality evaluation of mechanical fastening through acoustic measurement through the first stage step S10. In addition, the actual mechanical fastening is performed in the second stage step (S20), but based on the reflected set value, real-time-non-destructive monitoring can be performed, and furthermore, the automation of the self-piercing riveting process can be implemented.

Hereinafter, the present invention will be described in more detail with reference to experimental examples.

<Experimental Example 1>

As bonding objects, HFP steel (1.5 GPa) with a thickness of 1.6 mm, aluminum-5052 (Al-5052) with a thickness of 3 mm, and aluminum-5052 (Al-5052) with a thickness of 1.2 mm were prepared. And these were laminated as an upper piece, an intermediate piece and a lower piece, respectively.

And the mechanical fastening equipment system according to the present invention was implemented. As an acoustic measurement unit, a GRAS 46AE microphone from Bruel & Kjaer was prepared. As the sound processing unit, an NI-9234 module and Matlab were used. In addition, as a mechanical fastening part, an FM type 090-2-018 product was used for the anvil die, and a C-type (Φ5.3×6.5) rivet was used, and the pressure of the punch unit was set to 45kN.

The riveting process was repeated about 100 times using the prepared mechanical fastening equipment system. And through cross-sectional analysis, it was determined whether each session was normal or not.

<Experimental Example 2: Cross-section analysis and acoustic signal analysis in normal cases>

A cross-sectional microscope image of a typical normal case of the repeated riveting process is shown in FIG. 15 . And the acoustic signal measurement result of the acoustic measurement unit, that is, a graph of the magnitude of the acoustic signal over time is shown in FIG. 16 .

As a result of fast Fourier transform of A-2 of the acoustic signal of FIG. 16, specifically, the result of Fourier transform for the entire 4-second section is shown in FIG. 17 .

In addition, the results obtained by Fourier transforming the acoustic signal during piercing and the acoustic signal during flaring in A-2 among the acoustic signals of FIG. 16 are shown in FIGS. 18 and 19, respectively.

<Experimental Example 3: Cross-section analysis and acoustic signal analysis in case of failure>

A cross-sectional microscope image of a typical defect in the repeated riveting process is shown in FIG. 20 . In addition, a graph of the acoustic signal measurement result of the acoustic measurement unit, ie, the magnitude of the acoustic signal over time, is shown in FIG. 21 .

As a result of fast Fourier transform of B-2 of the acoustic signal of FIG. 21 , the result of performing Fourier transform on the entire 4-second section is shown in FIG. 22 .

In addition, the results obtained by Fourier transforming the acoustic signal during piercing and the acoustic signal during flaring in B-2 among the acoustic signals of FIG. 21 are shown in FIGS. 23 and 24, respectively.

First, comparing FIGS. 16 and 21 , it can be seen that an acoustic signal having a relatively very large peak is detected in the case of a defect compared to the case of the normal case. The largest peak detected around 2 seconds in FIG. 21 occurred during piercing. In some cases, a relatively large acoustic signal is detected in both normal and defective conditions during clamping, but it can be seen that the detection signal during piercing has a distinct difference between normal and defective cases. In addition, in the case of a defect, an acoustic signal of 250 Mpa or more was detected in all cases, whereas in the case of a normal case, this was not the case.

In addition, when normal, the size of the acoustic signal generated during piercing is smaller than the magnitude of the acoustic signal measured before, for example, the magnitude of the acoustic signal generated from the start of the measurement to just before the piercing, whereas when it is bad, the magnitude of the acoustic signal generated during piercing It can be seen that the larger

Then, comparing FIGS. 17 and 22 , it can be seen that the sum of the acoustic signals is relatively large over the entire frequency section in the case of a defect compared to the case of the normal case.

Next, comparing FIGS. 18 and 23 , the following results can be confirmed in the acoustic signal generated during piercing.

First, in the normal case, the sum of the signal magnitudes generated in the range of 2,000 Hz to 2,550 Hz is significantly smaller than in the case of the bad case. In addition, the sum of the magnitudes of the signals generated in the range of 100 Hz to 150 Hz in the normal case and the defective case were similar. In addition, in the case of a normal case, the sum of the signal magnitudes generated at 400 Hz to 550 Hz is significantly smaller than that in the case of a bad case.

That is, the sum of signal amplitudes of 100 Hz to 550 Hz, or 100 Hz to 150 Hz may be used as a reference, and a predetermined relationship may be established with the sum of signal amplitudes of other frequency bands based on this.

In the normal case, the ratio of the sum of the magnitudes of the signals generated in the range of 2,000 Hz to 2,550 Hz to the sum of the magnitudes of the signals generated in the range of 100 Hz to 550 Hz was about 20, but in the case of the failure, it was about 2.5.

In addition, the magnitude of the signal having the maximum peak in the range of 100 Hz to 550 Hz in the normal case was about 20 times the magnitude of the signal having the maximum peak in the range of 2,000 Hz to 2,550 Hz, but in the case of the failure, it was about 2 times.

In addition, the ratio of the sum of the magnitudes of the signals generated in the range of 100 Hz to 150 Hz to the sum of the magnitudes of the signals generated in the range of 400 Hz to 550 Hz in the normal case was about 1.7, but in the case of the bad case it was 0.9.

And in the case of normal, the magnitude of the signal having the maximum peak in the range of 100 Hz to 150 Hz was about 2.8 times the magnitude of the signal having the maximum peak in the range of 400 Hz to 550 Hz, but in the case of the failure, it was about 1.6 times.

In addition, the ratio of the sum of the magnitudes of the signals generated in the range of 400 Hz to 550 Hz to the sum of the magnitudes of the signals generated in the range of 400 Hz to 550 Hz in the normal case was about 0.5, but in the case of the failure, it was 0.9.

Next, comparing FIGS. 19 and 24 , the following results can be confirmed in the acoustic signal generated during flaring.

First, in the normal case, the sum of the signal amplitudes generated in the range of 2,000 Hz to 2,550 Hz is relatively small compared to the case of the bad case. In addition, the sum of the magnitudes of the signals generated in the range of 400 Hz to 550 Hz in the normal case and the bad case were similar.

That is, the sum of the signal amplitudes of 400 Hz to 550 Hz can be used as a reference, and a predetermined relationship can be established with the sum of the signal amplitudes of other frequency bands based on this.

In the case of normal, the ratio of the sum of the magnitudes of the signals generated in the range of 400 Hz to 550 Hz to the sum of the magnitudes of the signals generated in the range of 550 Hz to 2,000 Hz was about 0.3, but in the case of the failure, it was about 0.8.

In the above, the embodiment of the present invention has been mainly described, but this is only an example and does not limit the present invention. It will be appreciated that various modifications and applications not exemplified above are possible.

Therefore, it should be understood that the scope of the present invention includes changes, equivalents or substitutes of the technical idea exemplified above. For example, each component specifically shown in the embodiment of the present invention may be implemented by modification. And differences related to such modifications and applications should be construed as being included in the scope of the present invention defined in the appended claims.

In addition, each component in the configuration diagram or block diagram of the accompanying drawings may be implemented in software or hardware such as a field-programmable gate array (FPGA), an application specific integrated circuit (ASIC), or the like. However, each component on the block diagram or block diagram may be implemented in not only software and hardware but also an addressable storage medium, and may be configured to execute one or more processors.

Each component on the block diagram or block diagram may mean a module, segment, or part of code including one or more executable instructions for executing a specified logical function. Accordingly, a function provided by a component on a configuration diagram or a block diagram may be implemented by a plurality of more subdivided components, or a plurality of components on a configuration diagram or a block diagram may be implemented by a single integrated component. is of course

That is, within the scope of the object of the present invention, each component may operate by selectively combining one or more. In addition, all components may be implemented as one independent hardware, and some or all of the components are selectively combined to have a program module that performs some or all functions combined in one or a plurality of pieces of hardware. It may be implemented as a computer program. Codes and code segments constituting the computer program can be easily inferred to those skilled in the art of the present invention. Such a computer program may be stored in a computer-readable recording medium or storage medium, read and executed by the computer, thereby implementing the embodiment of the present invention. Examples of the recording medium include a magnetic recording medium and an optical recording medium.

1: Mechanical fastening system
10: mechanical fasteners
21: acoustic measurement unit
23: sound processing unit
30: controller
P: punch unit
D: Anvil Die
R: rivet

Claims (15)

In the self-piercing riveting process consisting of clamping, piercing, and flaring in the order, the quality of the self-piercing riveting process is measured based on the acoustic signal generated in the process and analyzed through Fourier Transform. A method of monitoring the quality of mechanical fasteners to evaluate. According to claim 1,
Wherein the measuring and analyzing the acoustic signal comprises separating the sound generated during the clamping, the sound generated during the piercing, and the sound generated during the flaring, respectively. 3. The method of claim 2,
Fourier transform result of the acoustic signal during the piercing,
When the ratio of the sum of the magnitudes of the signals generated in the range of 2,000 Hz to 2,550 Hz to the sum of the magnitudes of the signals generated in the range of 100 Hz to 550 Hz is 10 or more, it is judged as normal, otherwise it is judged as defective. monitoring method. 3. The method of claim 2,
Fourier transform result of the acoustic signal during the piercing,
When the magnitude of the signal having the maximum peak in the range of 100 Hz to 550 Hz is three times or more of the magnitude of the signal having the maximum peak in the range of 2,000 Hz to 2,550 Hz, it is judged as normal, otherwise it is judged as defective. monitoring method. 3. The method of claim 2,
Fourier transform result of the acoustic signal during the piercing,
If the ratio of the sum of the magnitudes of the signals generated in the range of 100Hz to 150Hz to the sum of the magnitudes of the signals generated in the range of 400Hz to 550Hz is less than 1, it is judged as normal, otherwise it is judged as defective. Way. 3. The method of claim 2,
Fourier transform result of the acoustic signal during the piercing,
When the magnitude of the signal having the maximum peak in the range of 100 Hz to 150 Hz is 2.5 times or more of the magnitude of the signal having the maximum peak in the range of 400 Hz to 550 Hz, it is determined as normal, otherwise it is judged as defective. Method for monitoring the quality of mechanical fasteners . 3. The method of claim 2,
Fourier transform result of the acoustic signal during the piercing,
When the ratio of the sum of the magnitudes of the signals generated in the range of 400Hz to 550Hz to the sum of the magnitudes of the signals generated in the range of 550Hz to 2,000Hz is 0.5 or less, it is judged as normal, otherwise it is judged as defective. Way. 3. The method of claim 2,
Fourier transform result of the acoustic signal during the piercing,
If the sum of the signal amplitudes generated in the range of 550 Hz to 2,000 Hz is less than a predetermined standard, it is determined as normal, otherwise, it is determined as defective, a quality monitoring method of mechanical fastening. 3. The method of claim 2,
A result of the Fourier transform of the acoustic signal during the flaring;
If the ratio of the sum of the magnitudes of the signals generated in the range of 400Hz to 550Hz to the sum of the magnitudes of the signals generated in the range of 550Hz to 2,000Hz is 0.3 or less, it is judged as normal, otherwise it is judged as defective. Way. 3. The method of claim 2,
A result of the Fourier transform of the acoustic signal during the flaring;
If the sum of the signal amplitudes generated in the range of 550 Hz to 2,000 Hz is less than a predetermined standard, it is determined as normal, otherwise, it is determined as defective, a quality monitoring method of mechanical fastening. In the self-piercing riveting process consisting of clamping, piercing, and flaring in the order, if the magnitude of the acoustic signal generated during the piercing process is smaller than the magnitude of the previously measured acoustic signal, it is determined as normal, otherwise it is defective Judging by the quality monitoring method of mechanical fasteners. 12. The method of claim 11,
A quality monitoring method for mechanical fasteners that judges normal when the size of the acoustic signal generated during the entire process is 250 MPa or less, otherwise it is judged as defective. A first stage step of self-piercing and riveting the mechanical fastening object, measuring the sound, and analyzing the sound signal by Fourier transform; and
A second stage step of self-piercing riveting for the same object as the first stage step with the same equipment, measuring the sound, and analyzing the sound signal by Fourier transform,
The first stage step is a step of setting, correcting, and dataizing a reference value of an acoustic signal, and the second stage step is a main process of mechanical fastening, a self-piercing rivet fastening process. 14. The method of claim 13,
The first stage step and the second stage step are each performed including the method according to claim 1,
A self-piercing rivet fastening process of machine learning the analysis result of the first stage step, reflecting the second stage step, and performing real-time monitoring simultaneously with the self-piercing rivet fastening process. a mechanical fastener comprising a rivet punch unit and a die;
an acoustic measuring unit disposed adjacent to the mechanical fastening part and measuring an acoustic signal generated in the mechanical fastening process; and
and a sound processing unit configured to Fourier transform the measurement result of the sound measurement unit.

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