JP7609702B2 - Defect Detection Method - Google Patents

Description

This disclosure relates to a defect detection method.

In recent years, additive manufacturing (AM) technology has been gaining attention in an effort to improve performance through complex structures, and devices that manufacture three-dimensional objects (3D models) through additive manufacturing using electron beams or laser beams have become widespread. For example, Patent Document 1 discloses a device that monitors the temperature of the growing part during additive manufacturing and adjusts the output of the irradiated beam based on that temperature.

JP 2019-73796 A

Conventionally, when constructing a complex structure, it is common to assemble multiple cast and forged products (cast and forged parts). In this case, inspections for defects in cast and forged products (cracks, shrinkage cavities, etc.) can be performed by applying relatively simple methods such as ultrasonic testing, eddy current testing, and radiography to each cast and forged part.

However, in the case of 3D modeling using AM technology, there are no intermediate products because the product is made from metal powder, and defect inspection must be performed on the final shape. In this case, it is difficult to evaluate defects at a position away from the outer surface of the final shape using the simple inspection method described above. Evaluation using X-ray CT is also possible, but there is a problem that it cannot be used for large 3D modeling products.
In addition, because defect inspection is performed on the final shape, if an internal defect is found, the modeling must be started again from the beginning, creating a risk of rework.
In order to solve these problems, it is important to be able to detect internal defects during modeling. Patent Document 1 does not disclose a method for solving such problems of internal defects.

The laser ultrasonic method is known as a method for detecting internal defects without contact. The laser ultrasonic method is a technology in which the surface of the object to be inspected is locally heated by irradiating the surface with pulsed laser light, generating ultrasonic waves through thermal expansion or ablation. The generated ultrasonic waves propagate through the object to be inspected, are reflected or scattered by internal defects, and then propagate back to the surface, where they are measured by a detection device such as a laser interferometer.

In defect detection using the laser ultrasonic method, it is necessary to observe the reflected waves from defects when irradiated with pulsed laser light. However, when inspecting defects located at a shallow position (near the surface), the reflected waves from the defect are buried in the surface vibration displacement caused by the incident wave. For this reason, it is difficult to apply this method to detect defects that occur at a shallow position from the surface during 3D modeling.

In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a defect detection method suitable for detecting internal defects in an object to be 3D printed.

(1) A defect detection method according to at least one embodiment of the present disclosure,
Irradiating a target with a pulsed laser beam to generate ultrasonic waves in the target;
detecting the presence or absence of an internal defect of the object based on a specific frequency component of the vibration of the object based on the ultrasonic wave;
Includes.

At least one embodiment of the present disclosure provides a defect detection method suitable for detecting internal defects in an object being 3D printed.

FIG. 1 is a diagram illustrating a schematic configuration of a molding apparatus according to an embodiment. FIG. 1 is a diagram illustrating a schematic configuration of a molding apparatus according to an embodiment. FIG. 1 is a diagram illustrating a schematic configuration of a molding apparatus according to an embodiment. FIG. 1 is a diagram illustrating a schematic configuration of a molding apparatus according to an embodiment. FIG. 1 is a diagram illustrating a schematic configuration of a molding apparatus according to an embodiment. 1 is a flowchart illustrating steps of a defect detection method according to some embodiments. FIG. 1 is a diagram illustrating an internal defect of an object. FIG. 13 is a diagram showing functional blocks of a detection device relating to processing in an internal defect detection step. 1 is an example of a graph showing the amplitude of vibration obtained from a detection device. 11 is an example of a graph showing vibrations after extracting information required for detecting the presence or absence of an internal defect. 11 is an example of a graph showing a processing result of FFT processing. FIG. 4 is a diagram showing an example of a map created by a map creating unit;

Hereinafter, some embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as the embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present disclosure.
For example, expressions expressing relative or absolute configuration, such as "in a certain direction,""along a certain direction,""parallel,""orthogonal,""center,""concentric," or "coaxial," not only strictly express such a configuration, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained.
For example, expressions indicating that things are in an equal state, such as "identical,""equal," and "homogeneous," not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained.
For example, expressions describing shapes such as a rectangular shape or a cylindrical shape do not only refer to rectangular shapes, cylindrical shapes, etc. in the strict geometric sense, but also refer to shapes that include uneven portions, chamfered portions, etc., to the extent that the same effect is obtained.
On the other hand, the expressions "comprise,""include,""have,""includes," or "have" of one element are not exclusive expressions excluding the presence of other elements.

(Overall configuration of a molding apparatus equipped with a defect detection device)
Hereinafter, a modeling apparatus 300 according to an embodiment will be described. Fig. 1 to Fig. 5 are diagrams that roughly show the configuration of the modeling apparatus 300 according to each embodiment. Note that optical systems such as collimator lenses and condenser lenses are omitted in Fig. 1 to Fig. 5. In the following description, the modeling apparatus 300 including the defect detection device 200 will be described, but the defect detection device 200 may be an apparatus independent of the modeling apparatus 300.

As shown in Figs. 1 to 5, the modeling apparatus 300 includes a beam irradiation device 100 for 3D modeling an object T, and a defect detection device 200 for detecting internal defects. The modeling apparatus 300 is, for example, an apparatus that performs additive modeling (AM) using a powder bed method. Note that the modeling apparatus 300 may also be an apparatus that performs modeling using an LMD (Laser Metal Deposition) method.

The beam irradiation device 100 is configured to irradiate the energy beam B1 along an arbitrary CAD-based shape onto raw material powder 303 (e.g., alloy powder) spread as a powder bed 302 on the base plate 301 of the modeling device 300 (see FIG. 5). In this way, the beam irradiation device 100 melts and solidifies the raw material powder to 3D model the object T. The beam irradiation device 100 is a device that irradiates laser light for processing as the energy beam B1. The modeling device 300 also includes a galvanometer mirror 101, which allows the direction of the energy beam B1 to be changed to scan the powder bed. The galvanometer mirror 101 is not necessarily required.

The beam irradiation device 100 is not limited to the above configuration. For example, the beam irradiation device 100 may be a device that irradiates an electron beam as the energy beam B1. In this case, an electronic optical system (not shown) may be provided in place of the galvanometer mirror. The modeling device 300 may be configured not to include the galvanometer mirror 101. For example, the modeling device 300 may be configured to move or rotate the beam irradiation device 100 itself to scan the energy beam B1.

1 to 5, the defect detection device 200 includes a pulsed laser irradiation device 201 configured to irradiate the object T with a pulsed laser beam B2, a detection device 202 configured to detect the presence or absence of an internal defect in the object T, and a control device 203 configured to control them. The detection device 202 includes the following functional blocks: a "time waveform storage memory" that stores the received ultrasonic waveform, a "window function extraction unit" that multiplies the ultrasonic waveform by a window function to extract an arbitrary waveform, an "FFT processing unit" that performs FFT processing on the extracted waveform, an "FFT result analysis unit" that analyzes the FFT processing result, and a "measurement result map creation unit" that plots the FFT processing result value in a map. The FFT result analysis unit extracts the sum of frequency components, the maximum amplitude value in a certain frequency range, the FFT amplitude value of a certain frequency, etc. The pulsed laser irradiation device 201 irradiates the object T with a pulsed laser beam B2 to continuously generate ultrasonic waves in the object T. It is preferable for the pulsed laser irradiation device 201 to irradiate the pulsed laser light B2 from directly above so that the intensity of the reflected wave is high.

In the embodiment shown in Figures 1 to 5, the detection device 202 is configured to detect vibrations of the surface of the object T based on ultrasonic waves. The detection device 202 is also configured to detect the presence or absence of internal defects in the object T based on specific frequency components in the vibrations of the object T. An internal defect is an internal molding defect, such as a void, that is not visible from the surface.

In the embodiment shown in Figures 1 to 3, the detection device 202 may include, for example, a laser interferometer 202A. In this case, the detection device 202 is configured to irradiate the object T with laser light B3 and receive the reflected light to measure the vibration, i.e., the displacement, of the surface of the object T.

In the embodiment shown in Figures 1 to 3, a Doppler vibrometer 202B may be provided instead of a configuration including a laser interferometer.

In the embodiment shown in Figures 4 and 5, the detection device 202 may be equipped with a contact transducer 202t, which is a probe that detects vibrations by being used in direct contact with the object T, instead of a non-contact detection device such as a laser interferometer 202A, and a data logger 202D.
As shown in FIG. 4, the contact transducer 202t may be installed on the upper surface of the target object T.
As shown in FIG. 5 , the contact transducer 202 t may be installed on a base plate 301 of a modeling apparatus 300 .

In the embodiment shown in Figs. 1 to 5, the defect detection device 200 may include, for example, a photodetector 206. The photodetector 206 is for detecting the timing at which the pulsed laser light B2 is irradiated onto the object T, and is configured to input a detection signal to a control device 203, which will be described later.

In the embodiment shown in Figures 1 to 5, the defect detection device 200 may further include a galvanometer mirror 204. In this case, the galvanometer mirror 204 can change the direction of the pulsed laser light B2 or the laser light B3 to scan the powder bed.

In the embodiment shown in FIG. 1, the defect detection device 200 may include a half mirror 205. In this case, as shown in FIG. 1, the pulsed laser light B2 and the laser light B3 can be made to enter the galvanometer mirror 204 via the half mirror 205, and the directions of the pulsed laser light B2 and the laser light B3 can be changed. This configuration is suitable for irradiating the laser light B3 at the same position as the irradiation position of the pulsed laser light B2.

The defect detection device 200 may not include the galvanometer mirror 204. For example, the defect detection device 200 may be configured to move or rotate the pulsed laser irradiation device 201 itself or the detection device 202 itself to scan the pulsed laser light B2 or the laser light B3.

Furthermore, the defect detection device 200 may not include the half mirror 205. For example, the defect detection device 200 may include a beam splitter instead of the half mirror 205. The defect detection device 200 may not include the half mirror 205 and the beam splitter, and may be configured to be capable of independently scanning the pulsed laser beam B2 and the laser beam B3, for example, as shown in FIG.
2, the defect detection device 200 includes a galvanometer mirror 207 that is different from the galvanometer mirror 204. In the embodiment shown in Fig. 2, the direction of the pulsed laser beam B2 can be changed by the galvanometer mirror 204 to scan the powder bed, and the direction of the laser beam B3 can be changed by the galvanometer mirror 207 that is different from the galvanometer mirror 204 to scan the powder bed.
According to the embodiment shown in FIG. 2, the laser beam B3 can also be irradiated to the same position as the irradiation position of the pulsed laser beam B2.

In the embodiment shown in FIG. 3, the defect detection device 200 includes a mirror 208 for reflecting the laser light B3. In the embodiment shown in FIG. 3, the irradiation position of the laser light B3 from the detection device 202 on the object T is a fixed position that is set in advance by adjusting the attitude of the mirror 208.

The control device 203 is composed of a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), etc. The control device 203 controls the operation of the entire device, for example, by executing a program stored in the ROM or RAM. The control device 203 also stores various data (e.g., design information for the target object T, a program related to the defect detection method described below, various setting values, etc.) in the ROM or RAM.

The control device 203 may be integrated with the pulsed laser irradiation device 201 or the detection device 202. The control device 203 may also be configured to control the galvanometer mirrors 204 and 207. The defect detection device 200 may not be configured to include the control device 203. For example, instead of automatic control by the control device 203, the user may manually operate the device.

(Defect Detection Method)
A defect detection method according to some embodiments will be described below. The defect detection method described below may be automatically executed by the control process of the control device 203, or some procedures may be executed by manual operation of the user instead of the control device 203. The defect detection method according to one embodiment is applied to, for example, powder bed additive manufacturing (AM). Note that the defect detection method can also be applied to an object when modeling by other methods such as the LMD method.

As a result of intensive research by the inventors, it was found that a method for detecting the presence or absence of internal defects in an area of the object T that is relatively close to the surface can be achieved by irradiating the object T with pulsed laser light B2 to generate ultrasonic waves, and detecting the presence or absence of internal defects in the object T based on specific frequency components in the vibration of the object T caused by these ultrasonic waves.

In addition, by irradiating the target object T with the pulsed laser light B2, longitudinal vibrations can be generated in the target object T, and the presence or absence of an internal defect in the target object T can be detected based on the presence or absence of resonance of the longitudinal vibrations occurring between the surface of the target object T and the internal defect.
That is, when an internal defect exists in a region relatively close to the surface of the object T, the resonance frequency of the longitudinal vibration changes depending on the depth from the surface of the object T to the internal defect to be detected. By repeatedly irradiating the pulsed laser with a repetition frequency set to correspond to this resonance frequency, resonance of the longitudinal vibration occurs, and if it is possible to detect an increase in the vibration of the surface of the object T, it can be inferred that an internal defect exists.

However, such resonance of longitudinal vibration has a smaller amplitude and a higher frequency than the flexural vibration generated in the object T when an internal defect exists in a region relatively close to the surface of the object T. Therefore, the above-mentioned resonance of longitudinal vibration tends to be buried in noise and difficult to detect.
Therefore, by utilizing the flexural vibration in the object T, it becomes easier to detect internal defects in the object T.

As a result of intensive research, the inventors have found that when an internal defect exists in a region relatively close to the surface of the object T, a flexural vibration occurs having a natural frequency according to the location of the internal defect, i.e., the distance from the surface of the object T, and the size of the internal defect. The inventors have also found that by extracting the amplitude at this natural frequency, the presence or absence of an internal defect in the object T can be detected based on the magnitude of the amplitude.
Therefore, in the defect detection method according to some embodiments, internal defects in the object T are detected as follows.
The process of detecting internal defects, which will be described later, is performed for each layer when 3D modeling is performed by additive modeling. However, it is not necessarily the case that the number of layers is one, but it may be the case that multiple layers are stacked. The thickness of one layer differs depending on the material, but is generally 50 um to 100 um. "Multiple layers" is set to any number, such as five layers.
In this way, in the defect detection methods according to some embodiments, it is preferable to detect the presence or absence of internal defects in the object T in the middle of being 3D printed by additive modeling. Since internal defects are detected in the middle of 3D printing, the risk of significant rework can be reduced.

6 is a flowchart showing a procedure of a defect detection method according to some embodiments. The defect detection method according to one embodiment includes an ultrasonic wave generating step S10, a vibration measuring step S20, an internal defect detecting step S30, and a repairing step S40.
7 is a schematic diagram showing an internal defect of the target object T. In this figure, the defect is shown as a void. However, the defect also includes cracks, incomplete fusion, and other internal molding defects that are not visible from the surface.

(Ultrasound generation step S10)
The ultrasonic wave generating step S10 is a step of irradiating the object T with the pulsed laser light B2 to generate ultrasonic waves in the object T.
In the ultrasonic wave generating step S10, the control device 203 irradiates the target object T with the pulsed laser light B2, and generates ultrasonic waves due to sudden thermal expansion and contraction of the area irradiated with the pulsed laser light B2.

The number of times of irradiation with the pulsed laser light B2 in the ultrasonic wave generating step S10 is one, but it may be multiple times. The irradiation position of the object T with the pulsed laser light B2 is stationary during the irradiation period of the pulsed laser light B2. Even if the number of times of irradiation with the pulsed laser light B2 is multiple, the irradiation position of the object T with the pulsed laser light B2 is the same position in each irradiation.
The beam diameter of the pulsed laser light B2 may be approximately the same as the size S of the internal defect to be detected, for example, several hundred μm. The size of the internal defect here refers to the size of the internal defect when viewed from the surface of the target object T. Note that in order to set the beam diameter of the pulsed laser light B2 to the above size, the defect detection device 200 may be provided with a beam diameter adjustment lens, but it is not essential to provide a beam diameter adjustment lens.
The pulse width of the pulsed laser light B2 is preferably 10 nsec or more and 1000 nsec or less.

In the ultrasonic wave generating step S10, ultrasonic waves can be generated in the object T by irradiating the object T with the pulsed laser light B2 under the irradiation conditions described above.
The ultrasonic waves generated in this manner are vibrations in a relatively wide band, so even if the natural frequency of the target T differs depending on the distance d from the surface of the target T and the size S of the internal defect, the flexural vibration of this natural frequency can be generated predominantly.

(Vibration measurement step S20)
The vibration measuring step S20 is a step of detecting vibrations on the surface of the object T based on ultrasonic waves.
In the vibration measurement step S20, the control device 203 causes the detection device 202 to detect the vibration of the surface of the object T.

In the embodiment shown in FIGS. 1, 2, and 3, vibrations on the surface of the target object T can be detected in a non-contact manner based on ultrasonic waves by a laser interferometer 202A or a Doppler vibrometer 202B.
In the embodiment shown in Fig. 1, the irradiation position of the pulsed laser beam B2 and the irradiation position of the laser beam B3 are the same. In the embodiment shown in Fig. 2, by controlling the attitude of the galvanometer mirrors 204 and 207, the laser beam B3 can be irradiated to the same position as the irradiation position of the pulsed laser beam B2.
Since it is possible to bring the ultrasonic excitation point and the receiving point closer to each other, vibrations on the surface of the object T can be detected even when the inspection surface of the object T is small or when the object T is complex.
1 and 2, if the irradiation position of the pulsed laser beam B2 and the irradiation position of the laser beam B3 are the same position, it is not necessary to consider the vibration transmission time from the irradiation position of the pulsed laser beam B2 to the irradiation position of the laser beam B3, which reduces the computation load in the internal defect detection step S30 described later.

In the embodiment shown in FIG. 1, the pulsed laser light B2 and the laser light B3 can be emitted coaxially. This makes it possible to detect vibrations on the surface of the object T without the laser light B3 being blocked by a part of the object T, even if the object T has a complex structure.

In the embodiment shown in FIG. 2, the position of the pulsed laser light B2 and the position of the laser light B3 can be irradiated so as to always maintain a constant distance between them by controlling the posture of the galvanometer mirrors 204 and 207. This allows the timing at which noise due to the irradiation of the pulsed laser light B2 is detected to be shifted from the timing at which the amplitude at the above-mentioned natural frequency is detected, making it easier to detect the amplitude at the natural frequency. In addition, in the embodiment shown in FIG. 2, by irradiating so that the irradiation position of the pulsed laser light B2 and the irradiation position of the laser light B3 are always maintained at a constant distance, the calculation load in the internal defect detection step S30 described later can be reduced compared to the case where the distance between the irradiation position of the pulsed laser light B2 and the irradiation position of the laser light B3 changes.

3, as described above, the irradiation position on the object T of the laser light B3 from the detection device 202 is a fixed position that is set in advance by adjusting the attitude of the mirror 208. Therefore, the state of the surface of the object T at the irradiation position of the laser light B3 remains unchanged, and therefore vibrations on the surface of the object T can be stably detected.
In addition, in the embodiment shown in FIG. 3, since it is not necessary to control the attitude of the galvanometer mirror 207, the calculation load on the control device 203 can be reduced.

In this manner, in the defect detection method according to some embodiments, vibrations on the surface of the target object T may be detected by the laser interferometer 202A or the Doppler vibrometer 202B.
This makes it possible to detect the presence or absence of internal defects in a non-contact manner.

4 and 5, the contact transducer 202t can directly detect ultrasonic vibrations on the surface of the object T. This allows the vibrations on the surface of the object T to be detected with better sensitivity than when the laser interferometer 202A or the Doppler vibrometer 202B detects the vibrations on the surface of the object T in a non-contact manner.
In the embodiment shown in Figure 4, the contact transducer 202t is installed on the upper surface of the object T, so that the distance between the irradiation position of the pulsed laser light B2 and the contact transducer 202t can be relatively close, thereby enabling vibrations on the surface of the object T to be detected with even better sensitivity.
In the embodiment shown in Figure 5, the contact transducer 202t is installed on the base plate 301 of the molding device 300, so that vibrations of the object T can be detected even when it is difficult to install the contact transducer 202t on the upper surface of the object T, such as when the inspection surface of the object T is small or when the object T is complex.

(Internal defect detection step S30)
The internal defect detection step S30 is a step of detecting the presence or absence of an internal defect in the object T based on the amplitude of a specific frequency component of the vibration of the object T based on ultrasonic waves.
8 is a diagram showing functional blocks of a detection device 202 relating to the process described later in the internal defect detection step S30. The detection device 202 virtually includes functional blocks of a time waveform accumulation memory 202a, an extraction unit using a window function 202b, an FFT processing unit 202c, an FFT result analysis unit 202d, and a map creation unit (measurement result map creation unit) 202e.
In the internal defect detection step S30, the detection device 202 detects the presence or absence of an internal defect in the object T as follows.
First, the detection device 202 acquires from the detection device 202, in a time waveform storage memory 202a, information on vibrations detected by the detection device 202 within a predetermined period following the irradiation timing of the pulsed laser light B2 detected by the photodetector 206, based on the irradiation timing.
FIG. 9A is an example of a graph showing the amplitude of vibration obtained from the detection device 202 as described above.

Next, the window function extracting section 202b of the detection device 202 extracts vibration information required for detecting the presence or absence of an internal defect from the vibration information acquired from the detection device 202 as described above.
FIG. 9B is an example of a graph showing vibrations after extracting information required to detect the presence or absence of an internal defect.

Specifically, the window function extraction unit 202b extracts vibration information on the first arriving wave from the vibration information acquired from the detection device 202 as described above. That is, the window function extraction unit 202b extracts vibration information corresponding to the period in which the first arriving wave was detected from the vibration information acquired from the detection device 202 as described above. In the example shown in Fig. 9B, the window function extraction unit 202b extracts vibration information from the vibration information acquired from the detection device 202 as described above, assuming that the irradiation timing of the pulsed laser light B2 detected by the photodetector 206 is 0 seconds, until 5.0 μsec has elapsed since the irradiation timing.
The above-mentioned method of extracting information on vibration regarding the first arriving wave is merely an example, and information on vibration regarding the first arriving wave may be extracted using other methods.
In addition, when the window function extraction unit 202b extracts information on vibrations for 5.0 μs after the irradiation timing, the window function extraction unit 202b excludes information on vibrations for a predetermined period after the irradiation timing from the acquisition target in order to remove noise caused by the irradiation of the pulsed laser beam B2. In the example shown in FIG. 9B, the control device 203 does not acquire information on vibrations for 0.5 μs after the irradiation timing.

The vibration information about the first arriving wave extracted as described above includes flexural vibration due to a natural frequency caused by the presence of an internal defect near the surface of the object T and a surface wave component. Therefore, the detection device 202 performs FFT (Fast Fourier Transform) processing on the vibration information about the first arriving wave extracted as described above in the FFT processing unit 202c to extract the flexural vibration due to the natural frequency.
FIG. 9C is an example of a graph showing the processing results of the FFT processing.
When an internal defect exists in a region relatively close to the surface of the object T, the amplitude of a frequency component that predominates in a relatively low frequency range occurs. This frequency range is determined by the shape of the internal defect, the position of the internal defect, the material of the object T, etc., but may be, for example, in the range of 0.5 MHz to 5.0 MHz.
Therefore, the FFT result analysis unit 202d detects an amplitude peak within the above-mentioned relatively low frequency range in the processing result of the above-mentioned FFT processing, acquires the peak value, and determines that an internal defect exists immediately below the irradiation position of the pulsed laser beam B2 if the peak value exceeds a preset threshold value.
In the example shown in FIG. 9C, a relatively large amplitude peak is observed at 1.20 MHz.
The FFT result analysis unit 202d may determine the presence or absence of an internal defect based on the sum of the results of the FFT processing in the FFT processing unit 202c, an FFT amplitude value at a specific frequency, or the like.

Thus, in the defect detection method according to the embodiment described above, in the step (S30) of detecting the presence or absence of an internal defect in the object T, it is preferable to detect the presence or absence of an internal defect in the object T based on frequency components determined by the shape of the internal defect, the position of the internal defect, the material of the object T, etc.
This makes it possible to detect the presence or absence of internal defects in a region of the object T that is relatively close to the surface.

The detection device 202 repeatedly performs the above-mentioned ultrasonic wave generation step S10 to internal defect detection step S30 while shifting the irradiation position of the pulsed laser light B2, thereby detecting the presence or absence of internal defects in areas relatively close to the surface over the entire surface of the object T.

The detection device 202 creates a map showing the relationship between the position on the surface of the target object T and the peak value acquired by the FFT result analysis unit 202d in the map creation unit 202e. That is, the map creation unit 202e creates the map by plotting the FFT processing result values in a map form.
Fig. 10 is a diagram showing an example of the map created by the map creating unit 202e. In the map shown in Fig. 10, the distribution of the peak values is represented by a density corresponding to the peak values.
In addition, when the FFT result analysis unit 202d acquires the sum of the results of the FFT processing in the FFT processing unit 202c, the map creation unit 202e creates a map showing the relationship between this sum and the position on the surface of the object T.
Furthermore, when the FFT result analysis unit 202d acquires an FFT amplitude value of a particular frequency, the map creation unit 202e creates a map showing the relationship between this FFT amplitude value and the position on the surface of the object T.

The defect detection method according to the above-described embodiment includes a step (S10) of irradiating the object T with pulsed laser light B2 to generate ultrasonic waves in the object T, and a step (S30) of detecting the presence or absence of an internal defect in the object T based on the amplitude of a dominant frequency component in the vibration of the object T based on the ultrasonic waves.
This makes it possible to detect internal defects even when the internal defects are located on the surface layer of the object T. Furthermore, because the pulsed laser light B2 is used, ultrasonic waves can be generated with a smaller spot diameter than in a method of generating ultrasonic waves in the object T via a probe. As a result, internal defects can be detected whether the measurement surface viewed from the irradiation direction is a point, line, or surface. Therefore, it is suitable for detecting internal defects in objects that are 3D printed.

In addition, in the defect detection method according to the embodiment described above, in the step (S30) of detecting the presence or absence of an internal defect in the object T, it is preferable to detect the presence or absence of an internal defect in the object T based on the amplitude of a frequency component in the region of flexural vibration of the object T.
This makes it possible to detect internal defects relatively easily.

In the defect detection method according to the embodiment described above, in the step (S30) of detecting the presence or absence of an internal defect in the object T, it is preferable to extract the amplitude at the natural frequency of the flexural vibration of the object T caused by the internal defect, and detect the presence or absence of an internal defect in the object T based on the magnitude of the amplitude.
This makes it possible to detect internal defects relatively easily.

In the defect detection method according to the embodiment described above, in the step (S30) of detecting the presence or absence of an internal defect in the object T, it is preferable to detect the presence or absence of an internal defect in the object T based on the amplitude of the frequency component in the first arriving wave of the flexural vibration of the object T.
This allows the detection accuracy of internal defects in the object T to be improved.

(Repair step S40)
The repair step S40 is a step in which, when an internal defect is detected in an object T being 3D-modeled by additive manufacturing, the next layer and the layer immediately below the next layer are melted so as to repair the internal defect when the next layer is formed directly above the internal defect.
In the defect detection method according to some embodiments, if the presence of an internal defect is detected in the internal defect detection step S30, a repair step S40 is performed.
That is, in some embodiments, when an internal defect is detected in an object T being 3D printed by additive manufacturing, the next layer and the layer immediately below the next layer may be melted so as to repair the internal defect when the next layer is formed directly above the internal defect. "Melting the next layer and the layer immediately below the next layer" means melting the layer including the internal defect together with the upper layer located above the internal defect.

It is difficult to repair internal defects located deep below the surface. In this regard, by carrying out the repair step S40, the internal defects are repaired when the next layer is formed, and therefore repairs can be carried out properly before the internal defects move away from the surface as the stacking progresses.

The present disclosure is not limited to the above-described embodiments, but also includes variations of the above-described embodiments and appropriate combinations of these embodiments.

The contents described in each of the above embodiments can be understood, for example, as follows.
(1) A defect detection method according to at least one embodiment of the present disclosure includes a step (S10) of irradiating an object T with pulsed laser light B2 to generate ultrasonic waves in the object T, and a step (S30) of detecting the presence or absence of an internal defect in the object T based on a prominent specific frequency component in the vibration of the object T caused by the ultrasonic waves.

According to the above method (1), internal defects can be detected even when the internal defects are located on the surface layer of the object T. In addition, because pulsed laser light B2 is used, ultrasonic waves can be generated with a smaller spot diameter than in a method in which ultrasonic waves are generated in the object T via a probe. As a result, internal defects can be detected whether the measurement surface viewed from the irradiation direction is a point, line, or surface. Therefore, it is suitable for detecting internal defects in objects that are 3D modeled.

(2) In some embodiments, in the method of (1) above, in the step (S30) of detecting the presence or absence of an internal defect in the object T, it is preferable to detect the presence or absence of an internal defect in the object T based on frequency components in the region of the flexural vibration of the object T.

By using method (2) above, internal defects can be detected relatively easily.

(3) In some embodiments, in the method of (2),
In the step (S30) of detecting the presence or absence of an internal defect in the object T, it is preferable to detect the presence or absence of an internal defect in the object T based on at least one of the sum of the above frequency components or the FFT amplitude value of a specific frequency component.

By using method (2) above, internal defects can be detected relatively easily.

(4) In some embodiments, in the method of (2) or (3) above, in the step (S30) of detecting the presence or absence of an internal defect in the object T, the amplitude at the natural frequency of the flexural vibration of the object T caused by the internal defect is extracted, and the presence or absence of the internal defect in the object T is detected based on the magnitude of the amplitude.

By using method (4) above, internal defects can be detected relatively easily.

(5) In some embodiments, in any of the methods (2) to (4) above, in the step (S30) of detecting the presence or absence of an internal defect in the object T, it is preferable to detect the presence or absence of an internal defect in the object T based on the amplitude of the frequency component in the first arriving wave of the flexural vibration of the object T.

The above method (5) can improve the detection accuracy of internal defects in the object T.

(6) In some embodiments, any of the methods (1) to (5) above may include a step (S20) of detecting vibrations on the surface of the object T based on the ultrasonic waves using a laser interferometer 202A or a Doppler vibrometer 202B.

According to the method (6) above, ultrasonic waves are generated using pulsed laser light B2, and vibrations based on the ultrasonic waves are detected using a laser interferometer 202A or a Doppler vibrometer 202B, making it possible to detect the presence or absence of internal defects in a non-contact manner.

(7) In some embodiments, in the method of (6) above, in the step (S20) of detecting vibration, it is preferable to irradiate the laser light B3 of the laser interferometer 202A or the Doppler vibrometer 202B to the same position on the target T as the irradiated position of the pulsed laser light B2.

According to the method (7) above, vibrations on the surface of the object T can be detected even if the inspection surface of the object T is small or the object T is complex.

(8) In some embodiments, in any of the methods (1) to (7) above, it is preferable to detect the presence or absence of internal defects in the object T while it is being 3D modeled by additive modeling.

According to the above method (8), internal defects can be detected during the 3D modeling process, reducing the risk of major rework.

(9) In some embodiments, in any of the methods (1) to (8) above, if an internal defect is detected in the object T being 3D printed by additive manufacturing, the method may include a step (S40) of melting the next layer and the layer immediately below the next layer so as to repair the internal defect when forming the next layer directly above the internal defect.

It is difficult to repair internal defects located deep below the surface. In this regard, according to the method (9) above, the internal defects are repaired when the next layer is formed, so that the repair is performed before the internal defects leave the surface as the stacking progresses, allowing for proper repair.

100 Beam irradiation device 200 Defect detection device 201 Pulse laser irradiation device 202 Detection device 202A Laser interferometer 202B Doppler vibrometer 202D Data logger 202t Contact transducer 203 Control device 206 Photodetector 300 Molding device

Claims (9)

Irradiating a target with a pulsed laser beam to generate ultrasonic waves in the target;
detecting the presence or absence of an internal defect of the object based on a specific frequency component of the vibration of the object based on the ultrasonic wave;
Including,
In the step of detecting the presence or absence of an internal defect of the object, the presence or absence of an internal defect of the object is detected based on the frequency component in a region of flexural vibration of the object.
Defect detection methods. a step of irradiating a target with a pulsed laser beam and generating ultrasonic waves in the target by thermal expansion and contraction of a portion irradiated with the pulsed laser beam;
detecting the presence or absence of an internal defect of the object based on a specific frequency component of the vibration of the object based on the ultrasonic wave;
Including,
In the step of detecting the presence or absence of an internal defect of the object, the presence or absence of an internal defect of the object is detected based on the frequency component in a region of flexural vibration of the object.
Defect detection methods. 3. A defect detection method according to claim 1 or 2, in which the step of detecting the presence or absence of an internal defect in the object detects the presence or absence of an internal defect in the object based on at least one of the amplitude of the frequency components, the sum of the frequency components, or an FFT amplitude value of a specific frequency component. 4. A defect detection method according to any one of claims 1 to 3, wherein in the step of detecting the presence or absence of an internal defect in the object, an amplitude at a natural frequency caused by the internal defect is extracted from the flexural vibration of the object, and the presence or absence of an internal defect in the object is detected based on the magnitude of the amplitude. A defect detection method according to any one of claims 1 to 4, wherein in the step of detecting the presence or absence of an internal defect in the object, the presence or absence of an internal defect in the object is detected based on the amplitude of the frequency component in a first arriving wave of the flexural vibration of the object . detecting vibrations of the surface of the object based on the ultrasonic waves by a laser interferometer or a Doppler vibrometer;
6. The defect detection method according to claim 1, further comprising: 7. The defect detection method according to claim 6, wherein in the step of detecting the vibration, the laser light from the laser interferometer or the Doppler vibrometer is irradiated to the same position on the object as the irradiated position of the pulsed laser light. The defect detection method according to claim 1 , further comprising the step of detecting the presence or absence of the internal defect in the object being 3D-modeled by additive manufacturing. When the internal defect is detected in the object being 3D-modeled by stacking additive manufacturing, melting the next layer and the layer immediately below the next layer so as to repair the internal defect when forming a next layer immediately above the internal defect;
9. The defect detection method according to claim 1, further comprising:

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