JP7153874B2 - LASER WELDING APPARATUS AND LASER WELDING METHOD - Google Patents

Description

The present invention relates to a laser welding apparatus and a laser welding method for welding using laser light.

As a first conventional laser welding device, there is a device that evaluates the quality of a welded portion using light emitted by molten metal of the welded portion (see, for example, Patent Document 1).

FIG. 9 shows an example of a first conventional laser welding device. A laser beam is continuously output from a laser oscillator 11 at a constant intensity. The laser light is transmitted to the condensing optical system 13 via the optical system 12 for laser light transmission, and condensed by the condensing optical system 13 onto the welded portion 2 of the material 1 to be welded. During welding, the molten metal in the weld 2 emits light. Light emitted from the molten metal is condensed by the condensing optical system 13 and transmitted to the interference filter 15 via the monitor light transmission optical system 14 . The interference filter 15 selects the wavelength component of the light emitted by the molten metal from the light transmitted to the interference filter 15 . The light of the wavelength component selected by the interference filter 15 is received by the photodiode 16 . The photodiode 16 outputs a signal corresponding to the emission intensity of the received light. A signal output from the photodiode 16 is input to the computer 19 via the amplifier 17 and the A/D converter 18 . The computer 19 stores in advance the correlation between the luminous intensity of the molten metal and the penetration depth, and the computer 19 applies the input signal to this correlation to derive the penetration depth of the welded portion 2. The computer 19 also evaluates the quality of the welded portion 2 based on the derived penetration depth of the welded portion 2 .

In addition, as a second conventional laser welding device, a technique called OCT (Optical Coherence Tomography), which visualizes the structure inside the sample using an optical interferometer, is used to measure the depth of the keyhole generated during welding. A device has been proposed (see Patent Document 2).

Specifically, in the conventional second laser welding apparatus, the optical system is configured so that the laser beam for welding and the laser beam emitted by the optical interferometer are coaxial. In the welded part, the bottom surface of the keyhole formed by the pressure when the molten metal evaporates is irradiated with the laser beam of the optical interferometer. The depth of the keyhole is calculated based on the optical path difference between the light reflected by the keyhole (measurement light) and the reference light. Since the keyhole is filled with surrounding molten metal immediately after it is formed, the depth of the keyhole is the same as the penetration depth of the weld. Thereby, the penetration depth of the weld is measured.

JP-A-3-207587 Japanese Patent Publication No. 2016-538134

In the conventional first laser welding device, instead of directly measuring the penetration depth, by using the correlation between the luminous intensity of the molten metal and the penetration depth, the luminous intensity of the molten metal in the welded portion 2 , the penetration depth of the welded portion 2 is measured. However, this correlation may fluctuate due to factors such as variations in the material of the material to be welded 1, ambient temperature, and changes in the state of formation of keyholes. For this reason, it is difficult to measure the penetration depth with sufficient accuracy if the state of formation of the keyhole during welding is not constant.

Further, the second conventional laser welding apparatus directly measures the depth of the keyhole generated during welding. For this reason, it is difficult to measure the penetration depth with sufficient accuracy if the state of formation of the keyhole during welding is not constant.

As described above, in the conventional first and second laser welding apparatuses, the measurement accuracy of the penetration depth is not sufficient, so it is difficult to evaluate the quality of the welded portion with high accuracy.

SUMMARY OF THE INVENTION The present invention provides a laser welding apparatus and a laser welding method capable of accurately measuring the penetration depth of a welded portion even when the state of formation of a keyhole during welding is not constant.

In order to achieve the above object, the laser welding apparatus of the present invention includes a laser oscillator that irradiates a laser beam toward a welded portion of a material to be welded, and interference light between a measurement beam reflected by the welded portion and a reference beam. and an optical interferometer that generates an interference signal that indicates the intensity of the two-dimensional relationship between the distance in the welding direction in the weld, the depth of the weld, and the intensity of the interference signal based on the interference signal. Generate tomographic image data, extract specific depth tomographic image data in which the welding depth is a specific depth range including a non-defective product depth range from the two-dimensional tomographic image data, and extract the specific depth tomographic image data in the specific depth tomographic image data a deriving unit that derives the depth for each distance based on the intensity of the interference signal for each distance.

The laser welding method of the present invention includes irradiating a laser beam onto a welded portion of a material to be welded, generating an interference signal indicating the intensity of interference light between a measurement beam and a reference beam reflected by the welded portion, and Based on the interference signal, two-dimensional tomographic image data is generated that indicates the relationship between the distance in the welded portion in the welding direction, the depth of the welded portion, and the intensity of the interference signal, and from the two-dimensional tomographic image data Extracting specific depth tomographic image data in which the welding depth is a specific depth range including a non-defective product depth range, and extracting the distance based on the intensity of the interference signal for each distance in the specific depth tomographic image data Derive the depth of each

ADVANTAGE OF THE INVENTION According to this invention, even when the formation state of the keyhole during welding is not constant, the penetration depth of a weld can be measured accurately.

A diagram showing an outline of a laser welding apparatus according to the present invention. A diagram showing an example of change over time in the central wavelength of object light emitted by a wavelength scanning light source. Flowchart for explaining an operation example of the laser welding device Diagram showing an example of A-scan data A diagram showing an example of B-scan data FIG. 4 is a diagram showing an example of a specific depth range; Diagram to explain how to determine depth Diagram showing an example of 2D point cloud data Diagram showing an example of 2D point cloud data A diagram showing an example of two-dimensional point cloud data when the specific depth tomographic image data is not cut out. A diagram showing an example of two-dimensional point cloud data when the specific depth tomographic image data is extracted. A diagram showing an example of a specific depth range according to the second embodiment. A diagram showing an example of a tomographic image when the specific depth range is constant regardless of the distance in the welding direction. Diagram showing an example of a tomographic image when the specific depth range varies depending on the distance in the welding direction A diagram showing an example of a conventional first laser welding device

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a diagram showing an overview of a laser welding device 100 according to the present invention. As shown in FIG. 1, a laser welding apparatus 100 welds a welded portion 102 of a material to be welded 101 extending in the horizontal direction (x direction in FIG. 1). Welding laser light is emitted from a laser oscillator 107 to the upper surface of the material to be welded 101 in the vertical direction (z direction). In this specification, the laser beam for laser welding emitted by the laser oscillator 107 may be simply referred to as a laser beam. A portion of the material to be welded 101 irradiated with the laser beam is melted to form a molten pool 103 . Further, the molten metal evaporates from the molten pool 103, and the keyhole 104 is formed by the vapor pressure generated during evaporation. Below, the molten pool 103 and the keyhole 104 are collectively referred to as the welded portion 102 .

The optical interferometer 105 irradiates the welded portion 102 with laser light having a wavelength different from that of the laser oscillator 107, and measures the depth (penetration depth) of the welded portion 102 by light interference. The penetration depth means the distance between the highest vertex of the melted portion of the material to be welded 101 (base material) and the surface of the surface to be welded.

The laser beam for depth measurement emitted from the optical interferometer 105 is coaxially superimposed on the laser beam from the laser oscillator 107 by the beam splitter 106 , and the inside of the keyhole 104 is irradiated with the laser beam. In the following description, the light emitted by the optical interferometer 105 is referred to as object light in order to distinguish it from the welding laser light emitted by the laser oscillator 107 .

The object light applied to the welded portion 102 is reflected by the bottom portion 104 a of the keyhole 104 and enters the optical interferometer 105 via the beam splitter 106 . The optical interferometer 105 measures the optical path length of the object light, and specifies the depth of the keyhole 104 as the penetration depth from the measured optical path length. Based on the identified penetration depth, laser welding apparatus 100 determines the quality of welded portion 102 .

The outline of the laser welding apparatus 100 has been described above. Next, each configuration of the laser welding device 100 will be described.

<Components responsible for laser welding function>
First, a configuration for realizing a laser welding function in laser welding apparatus 100 will be described. The laser welding function is a function of welding the material 101 to be welded.

A laser oscillator 107 oscillates laser light for welding. A laser beam oscillated from a laser oscillator 107 is condensed by a first condensing optical system 109 via a laser beam transmitting optical system 108 . The laser light condensed by the first condensing optical system 109 is transmitted through the beam splitter 106 and condensed on the welded portion 102 . As a result, welding of the material to be welded 101 is performed. A direct diode laser, for example, is used for the laser oscillator 107 .

The moving stage 110 is a base for moving the material 101 to be welded. A material to be welded 101 is fixed to a moving stage 110 . The moving stage 110 moves according to commands from the control section 112 a of the computer 112 via the stage controller 111 . The moving direction of the moving stage 110 is the horizontal direction in FIG. 1, that is, the direction along the x-axis shown in FIG. While the laser oscillator 107 is oscillating the laser beam, the moving stage 110 is moved by the control unit 112a, thereby changing the irradiation position of the laser beam on the material to be welded 101 and performing laser welding in a desired range. will be

The controller 112 a controls each part of the laser welding device 100 . Specifically, the control unit 112a controls the start or stop of the output of the laser light by the laser oscillator 107, the adjustment control of the output intensity of the laser light, the control of the optical interferometer 105 described later, and the like.

<Components responsible for the penetration depth measurement function>
Next, a configuration for realizing a penetration depth measurement function in the laser welding device 100 will be described. The penetration depth measurement function is a function of measuring the penetration depth of the welded portion 102 (keyhole 104) being welded in the material 101 to be welded. The laser welding apparatus 100 measures the penetration depth of the welded portion 102 by SS-OCT (Swept Source Optical Coherence Tomography) technology using an optical interferometer 105 .

The wavelength scanning light source 113 continuously emits object light having a shorter wavelength width than the welding laser light under the control of the control unit 112a. The control unit 112a periodically changes the central wavelength of the object light emitted by the wavelength scanning light source 113 as shown in FIG. FIG. 2 is a diagram showing an example of change over time in the central wavelength of the object light emitted by the wavelength scanning light source 113. In FIG. In FIG. 2, the vertical axis corresponds to the wavelength of the object light, and the horizontal axis corresponds to time. Such scanning performed by periodically changing the central wavelength of the object light is called wavelength scanning.

The object light emitted from the wavelength scanning light source 113 passes through the optical fiber system 114 and enters the first fiber coupler 115 as shown in FIG. The first fiber coupler 115 splits the incident object light into two. The two split object beams are hereinafter referred to as measuring beam and reference beam. The measurement light is the light of the object light that irradiates the welded portion 102 to be measured. The reference light is the light that is irradiated onto the reference mirror 116, which is a separately provided reference plane, out of the object light. The first fiber coupler 115 causes the branched measurement light to enter the first optical fiber system 114a and the reference light to enter the second optical fiber system 114b, respectively.

The measurement light emitted from the first optical fiber system 114 a of the optical interferometer 105 enters the beam splitter 106 via the interference filter 121 and the second condensing optical system 120 . The interference filter 121 is a filter that transmits only the wavelength of the measurement light. The interference filter 121 is provided to prevent the laser light reflected by the welded portion 102 and the light emitted by the welding of the welded portion 102 from entering the first optical fiber system 114a. Second condensing optical system 120 converges measurement light emitted from first optical fiber system 114 a of optical interferometer 105 onto welded portion 102 via beam splitter 106 . Also, the second condensing optical system 120 causes the measurement light reflected from the welded portion 102 to enter the first optical fiber system 114 a again via the beam splitter 106 .

The beam splitter 106 transmits the laser light from the laser oscillator 107 and reflects the measurement light from the optical interferometer 105 to combine the laser light and the measurement light into a coaxial light beam. By irradiating the welded portion 102 with the laser light and the measurement light that are combined into a coaxial light flux by the beam splitter 106, the penetration depth of the welded portion 102 is measured at the same time as the laser welding. Beam splitter 106 is, for example, a dichroic mirror. A wavelength to be transmitted and a wavelength to be reflected are preset in the beam splitter 106 so as to transmit the laser light from the laser oscillator 107 and reflect the measurement light from the optical interferometer 105 .

The wavelength difference between the laser light and the measurement light is desirably 100 nm or more so that the laser light can be properly transmitted and the measurement light can be reflected by the beam splitter 106 . In Embodiment 1, the wavelength of the laser light oscillated by the laser oscillator 107 is 975 nm, and the wavelength of the physical light (measurement light) emitted by the wavelength scanning light source 113 is 1270 to 1370 nm.

As described above, the measurement light from the optical interferometer 105 is applied to the welded portion 102 . Part of the measurement light irradiated to welded portion 102 is reflected by welded portion 102 . The measurement light reflected by the welded portion 102 enters the optical interferometer 105 via the beam splitter 106 , the second condensing optical system 120 and the interference filter 121 . The measurement light incident on the optical interferometer 105 passes through the first optical fiber system 114 a and enters the second fiber coupler 117 . At this time, the length of the optical path through which the measurement light passes from the first fiber coupler 115 to the second fiber coupler 117 is taken as the optical path length of the measurement light.

On the other hand, the reference light branched by the first fiber coupler 115 is transmitted through the second optical fiber system 114b and applied to the reference mirror 116. FIG. The reference light applied to the reference mirror 116 is reflected by the reference mirror 116 and then enters the second optical fiber system 114b. The reference light incident on the second optical fiber system 114 b passes through the second optical fiber system 114 b and enters the second fiber coupler 117 . At this time, the length of the optical path through which the reference light passes from the first fiber coupler 115 to the second fiber coupler 117 is taken as the optical path length of the reference light. It is desirable to measure the optical path length of the reference light in advance as a reference value.

The second fiber coupler 117 passes the measurement light incident from the first optical fiber system 114a and the reference light incident from the second optical fiber system 114b to the first input 118a and the second input 118b of the differential detector 118, respectively. It is branched and injected. Specifically, the second fiber coupler 117 causes 50% of the measurement light incident from the first optical fiber system 114a to enter the first input 118a, and the remaining 50% of the measurement light to the second input 118b. make it incident.

Similarly, the second fiber coupler 117 causes 50% of the reference light coming from the second optical fiber system 114b to enter the second input 118b and the remaining 50% of the reference light to enter the first input 118a. At this time, the second fiber coupler 117 couples the branched reference light and measurement light into one light beam to obtain interference light. The two interfering lights combined by the second fiber coupler 117 enter the first input 118a and the second input 118b, respectively.

The differential detector 118 removes the influence of noise contained in the interference light by taking the difference between the interference lights respectively input from the first input 118a and the second input 118b, and then produces an electrical signal based on the intensity of the interference light. generate some interfering signal. Differential detector 118 outputs an interference signal to A/D converter 119 .

The A/D converter 119 receives from the wavelength scanning light source 113 a trigger signal synchronized with the wavelength scanning repetition frequency of the wavelength scanning light source 113 . Based on the input trigger output, the A/D converter 119 samples the interference signal output from the differential detector 118 in synchronization with the wavelength scanning period and converts it into a digital signal. The A/D converter 119 outputs the digital interference signal to the computer 112 .

The computer 112 includes the control section 112a described above and a derivation section 112b that derives the penetration depth of the welded portion 102 based on the input interference signal. Interference according to the optical path length difference between the measurement light and the reference light occurs in the interference light, and the lead-out part 112b derives the penetration depth of the welded part 102 based on the interference of this interference light. Details of the derivation of the penetration depth in the derivation portion 112b will be described later. The penetration depth derived by the lead-out part 112 b is displayed on the display part 122 or the like as the penetration depth measured by the laser welding device 100 .

The computer 112 also includes an evaluation unit 112c that evaluates the quality of the welded portion 102 from the measured penetration depth. In the laser welding apparatus 100 of Embodiment 1, information about a desired penetration depth range is stored in advance in a storage unit or the like (not shown). A desired range of penetration depth means a range of penetration depth in the welded material 101 judged to be a non-defective product after welding. This desired penetration depth range is hereinafter referred to as a non-defective product depth range. The evaluation unit 112c evaluates the quality of the welded part 102 by determining whether the penetration depth is within the range of the depth of the non-defective product. The evaluation result is displayed on the display unit 122, for example. Although both the penetration depth and the evaluation result are displayed on the display unit 122, only one of them may be displayed.

As described above, the laser welding apparatus 100 has a configuration for a laser welding function and a penetration depth measuring function. Thereby, the laser welding apparatus 100 can sequentially perform laser welding and measurement of the penetration depth of the welded welded portion 102 .

<Example of operation of laser welding equipment>
Next, an operation example of the laser welding apparatus 100 according to Embodiment 1 will be described in detail. FIG. 3 is a flowchart for explaining an operation example of the laser welding device 100. As shown in FIG.

In step S101, operation of laser welding apparatus 100 is started. Specifically, the control unit 112a causes the stage controller 111 to start moving the moving stage 110, and causes the laser oscillator 107 to start outputting laser light. Further, the control unit 112a causes the wavelength scanning light source 113 of the optical interferometer 105 to start outputting object light.

In step S102, the A/D converter 119 of the optical interferometer 105 starts sampling the interference signal. In step S<b>103 , the derivation unit 112 b acquires the interference signal of the digital signal as the sampling result from the A/D conversion unit 109 .

In step S104, the deriving unit 112b executes a fast Fourier transform (FFT) on the acquired interference signal and stores the result in a storage unit (eg, storage area of the computer 112) not shown.

In step S105, the deriving unit 112b determines whether or not sampling by the A/D converter 119 should be terminated. If the sampling has not ended (No in step S105), the process proceeds to step S104, and if the sampling has ended (Yes in step S105), the process proceeds to step S106. When the sampling ends, the control unit 112a causes the laser oscillator 107 to stop outputting laser light, and causes the stage controller 111 to stop moving the moving stage 110. FIG. This completes the laser welding of the material to be welded 101 . It should be noted that whether or not the sampling has ended may be determined based on, for example, a user's operation on an operation unit (not shown).

In step S106, the deriving unit 112b reads out the result of performing FFT on the interference signal, and based on this, generates two-dimensional tomographic image data.

FIG. 4A is a diagram showing the relationship between the distance in the welding depth direction (hereinafter simply referred to as depth) and the intensity I of the interference signal at one point (measurement point) in the welding direction of the material to be welded 101. FIG. be. The welding direction is the direction in which laser welding proceeds, and corresponds to the x-axis direction in FIG. The depth direction corresponds to the z-axis direction shown in FIG. Corresponds to the deep side. Obtaining information on the depth of the weld at the measurement point in this way is generally called an A-scan, and the data obtained by the A-scan is called A-scan data.

Two-dimensional tomographic image data relating to the welding direction, the depth direction, and the intensity of the interference signal can be obtained by scanning the A-scan along the direction in which laser welding progresses. This two-dimensional tomographic image data is generally called B-scan data. FIG. 4B is a diagram showing an example of B-scan data. In FIG. 4B, the vertical axis z is the depth direction (corresponding to the z-axis direction shown in FIG. 1), the horizontal axis x is the welding direction (corresponding to the x-axis direction shown in FIG. 1), and the shading on the image is the intensity of the interference signal. It shows I.

In step S107, the deriving unit 112b cuts out the two-dimensional tomographic image data in a preset specific depth range from the two-dimensional tomographic image data created in step S106. The specific depth range is defined by a preset upper limit (upper limit depth) of the clipping position and a preset lower limit (lower limit depth) of the clipping position. FIG. 4C is a diagram showing an example of a specific depth range. FIG. 4C shows an example of the upper limit depth Zut and the lower limit depth Zlt of the specific depth range. The two-dimensional tomographic image data cut out in the specific depth range is hereinafter referred to as specific depth tomographic image data 401 . In the example shown in FIG. 4C, the specific depth tomographic image data 401 is two-dimensional tomographic image data in a range from the lower limit depth Zlt to the upper limit depth Zut. The upper limit depth Zut and the lower limit depth Zlt of the specific depth range may be set based on the non-defective product depth range described above.

The method for setting the good product depth range may be, for example, as follows. In other words, laser welding is performed on a plurality of materials to be welded in advance, and information on the penetration depth of the welded portion determined to be non-defective among them is collected. In the first embodiment, the information about the penetration depth of the plurality of welds determined to be non-defective is the average value Ave and the standard deviation σ. The upper limit and lower limit of the non-defective product depth range are set by an arbitrary method using the average value Ave and standard deviation σ. For example, the upper limit is set to Ave+3σ and the lower limit is set to Ave−3σ.

The specific depth range described above is desirably set wider than the non-defective product depth range so as to provide a margin based on the non-defective product depth range. Specifically, when the non-defective product depth range has the above upper limit and lower limit, the upper limit depth Zut of the specific depth range is set to Ave+4σ, for example, and the lower limit depth Zlt is set to Ave−4σ, for example. be done. The derivation unit 112b cuts out the two-dimensional tomographic image data within the specific depth range set in this manner.

In step S108, the deriving unit 112b identifies the welding depth at the measurement point based on the specific depth tomographic image data 401 extracted in step S107, and based on this, creates two-dimensional point cloud data. The two-dimensional point cloud data generated by the derivation unit 112b is point set data indicating the relationship between a certain measurement point and the welding depth at that measurement point. The depth of the weld at the measurement point in the welding direction is specified, for example, as the distance at which the intensity of the interference signal at the measurement point, that is, the intensity of the reflection of the measurement light from the weld 102, is maximized.

FIG. 4D is a diagram for explaining a depth identification method. FIG. 4D shows A-scan data at a certain measurement point X1 in FIG. 4C, that is, the relationship between the depth and the intensity of the interference signal. In FIG. 4D, P1 is the point where the intensity of the interference signal is the strongest between the upper limit depth Zut and the lower limit depth Zlt. Therefore, in the example shown in FIG. 4D, the depth Z1 corresponding to the point P1 is the welding depth at the measurement point X1 shown in FIG. 4C.

The two-dimensional point cloud data is generated by plotting points indicating the relationship between the position of the measurement point in the welding direction and the welding depth specified for each measurement point as described above on a two-dimensional plane. 5A and 5B are diagrams showing examples of two-dimensional point cloud data generated as described above. 5A and 5B, the vertical axis z indicates the welding depth, and the horizontal axis x indicates the welding direction.

FIG. 5A shows an example of two-dimensional point cloud data created using welds whose depth is within the non-defective product depth range (determined to be a non-defective product). On the other hand, FIG. 5B shows an example of two-dimensional point cloud data created using welds whose depth is not within the depth range of non-defective products (determined as defective products). Specifically, the two-dimensional point cloud data shown in FIG. 5B is created using welds welded with a penetration depth shallower than the non-defective product depth range. A starting point Xs in FIGS. 5A and 5B indicates a starting position in the welding direction where welding depth measurement is performed in the laser welding apparatus 100 . Also, the end point Xe indicates the end position in the welding direction where the welding depth measurement is performed in the laser welding apparatus 100 .

The two-dimensional point cloud data generated in the first embodiment is generated using the specific depth tomographic image data cut out in the specific depth range in step S107 described above. Therefore, as shown in FIGS. 5A and 5B, each point of the two-dimensional point cloud data is included in a range equal to or greater than the lower limit depth Zlt and equal to or less than the upper limit depth Zut. The two-dimensional point cloud data of FIG. 5A, which is the data of the non-defective product, is scattered and distributed in the range of the lower limit depth Zlt or more and the upper limit depth Zut or less. Each point of the dimensional point cloud data is concentrated near the shallow upper limit depth Zut.

FIGS. 6A and 6B are diagrams for explaining the difference between the case where the specific depth tomographic image data 401 is not extracted from the two-dimensional point cloud data (conventional) and the case where it is not extracted (the present invention). be. FIG. 6A shows an example of two-dimensional point cloud data when the specific depth tomographic image data 401 is not cut out, and FIG. 6B shows a two-dimensional point cloud data when the specific depth tomographic image data 401 is cut out. An example of point cloud data is shown. 6A and 6B use the same two-dimensional tomographic image data as the basis of the two-dimensional point cloud data.

FIG. 6A shows an example of two-dimensional point cloud data generated using the two-dimensional tomographic image data generated in step S106 of the flowchart of FIG. 3 without cutting out the specific depth tomographic image data in step S107. there is Therefore, in FIG. 6A, two-dimensional point cloud data is generated over the entire depth direction. Generally, in the two-dimensional point cloud data, the distribution of points existing at the deepest position corresponds to interference signals originating from the bottom surface of the keyhole 104 . Therefore, the penetration depth of welding has a high correlation with the distribution of points positioned near the lower limit in the depth direction of the two-dimensional point cloud data. As shown in FIG. 6A, in the two-dimensional point cloud data generated without cutting out the specific depth tomographic image data, the distribution of points located near the lower limit value in the depth direction may have omissions 601. (Area from X3 to X4 in the welding direction, shown in FIG. 6A). Such a phenomenon is considered to occur as a result of variation in the interference signal generated by the optical interferometer 105 when the state of formation of the keyhole 104 during welding is not constant.

As shown in FIG. 6A, when the distribution of the two-dimensional point cloud data has a gap 601, it is difficult to accurately calculate the penetration depth of the welded portion 102, and it is difficult to accurately determine the penetration depth. It becomes difficult to do well.

On the other hand, as shown in FIG. 6B, in the two-dimensional point cloud data generated based on the specific depth tomographic image data cut out in the specific depth range, there is no missing even in the region from X3 to X4 in the welding direction. . As described above, in Embodiment 1, the two-dimensional point cloud data is generated using the specific depth tomographic image data. Dimensional point cloud data can be generated.

Returning to the description of FIG. 3, in step S109, the derivation unit 112b derives the penetration depth based on the two-dimensional point cloud data generated in step S108. Then, in step S110, the evaluation unit 112c evaluates the welded portion 102 based on the derived penetration depth.

As described above, according to the first embodiment of the present invention, even if the interference signal generated by the optical interferometer fluctuates when the state of formation of the keyhole 104 during welding is not constant, Accurate measurement of penetration depth during laser welding. Therefore, the quality of the welded portion can be evaluated based on the accurate penetration depth, and the quality of the welded portion can be evaluated with high accuracy.

(Embodiment 2)
As described above, in Embodiment 1, the derivation unit 112b cuts out tomographic image data in a specific depth range from two-dimensional tomographic image data, and based on this, generates two-dimensional point cloud data. At this time, in Embodiment 1, the upper limit depth and the lower limit depth of the specific depth range are constant values with respect to the welding direction.

However, depending on the welding, the desired penetration depth may not be constant in the welding direction, and the desired penetration depth may differ depending on the position in the welding direction. Specifically, when changing the welding speed during welding, when changing the laser output of the laser oscillator during welding, when welding the material to be welded along a curve, or when the heat diffusion state of the material to be welded is For example, a case where different parts are continuously welded. In the second embodiment, in order to cope with such a case, a case will be described in which the upper limit depth and the lower limit depth of the specific depth range are changed according to the distance in the welding direction. In addition, in the following description, the same reference numerals are given to the same configurations as in the first embodiment, and description thereof is omitted.

FIG. 7 is a diagram showing an example of a specific depth range cut out in the second embodiment. In FIG. 7, the vertical axis z indicates the welding depth direction (corresponding to the z direction in FIG. 1), and the horizontal axis x indicates the welding direction (corresponding to the x direction in FIG. 1). Also, the gradation on the image indicates the intensity of the interference signal.

As shown in FIG. 7, the specific depth range 701 is an area surrounded by the upper limit depth of variation and the lower limit depth of variation. Since the value of the upper limit depth of variation and the value of the lower limit depth of variation vary depending on the welding direction (x direction), they are expressed as a function of x on the xz plane shown in FIG. In the following description, Zu(x) is the upper limit depth of variation, and Zl(x) is the lower limit depth of variation.

The specific depth range is set based on the upper and lower limits of the non-defective product depth range, as in the first embodiment. However, in the second embodiment, since the non-defective product depth range also varies depending on the position in the welding direction, the specific depth range is specifically set as follows.

In other words, laser welding is performed on a plurality of materials to be welded in advance, and information on the penetration depth of the welded portion determined to be non-defective among them is collected. In the second embodiment, the information on the penetration depth of the plurality of welds determined to be non-defective is the average value Ave(x) and the standard deviation σ(x). In the second embodiment, the penetration depth average value Ave(x) and standard deviation σ(x) are expressed as a function of the distance x in the welding direction.

The upper and lower limits of the non-defective product depth range are set by an arbitrary method using this average value Ave(x) and standard deviation σ(x). For example, the non-defective product depth range is set to be equal to or greater than the lower limit value Tl(x) and equal to or less than the upper limit value Tu(x) shown in Equations (1) and (2) below.

Tu(x)=Ave(x)+3σ(x) (1)
Tl(x)=Ave(x)−3σ(x) (2)

Also in the second embodiment, as in the first embodiment, the specific depth range is set to be wider than the non-defective product depth range. Specifically, the upper limit value (variation upper limit depth value) Zu(x) and the lower limit value (variation lower limit depth value) Zl(x) of the specific depth range are an arbitrary offset amount Zoff in the depth direction. , they are represented by the following equations (3) and (4).

Zu(x)=Tu(x)+Zoff (3)
Zl(x)=Tl(x)-Zoff (4)

Each curve Tu(x), Tl(x), Zu(x), and Zd(x) in the xz plane shifts the average value Ave(x) of the penetration depth in the case of a non-defective product in the depth direction. The curves are all the same shape.

As described above, in the second embodiment, the deriving unit 112b changes the specific depth range to be extracted depending on the position in the welding direction when extracting the image data of the specific depth range from the two-dimensional tomographic image data. With such a configuration, the following effects are obtained.

8A and 8B are diagrams for explaining the effects of the second embodiment. FIG. 8A shows a constant specific depth range regardless of the distance x in the weld direction when the desired depth Zd varies with the distance x in the weld direction. In FIG. 8A, the upper limit depth Zut and the lower limit depth range Zlt of the specific depth range are set so as to include all the depths Zd that vary depending on the distance x in the welding direction.

On the other hand, FIG. 8B shows the specific depth range in the second embodiment. In FIG. 8B, a depth Zd that varies depending on the distance x in the welding direction and an upper limit depth Zu(x) and a lower limit depth Zl(x) that have the same shape on the xz plane are set.

Comparing FIGS. 8A and 8B, the width in the depth direction of the specific depth range at a certain distance X2 is smaller in FIG. 8B (width Wd2) than in FIG. 8A (width Wd1). In the second embodiment shown in FIG. 8B, the width of the specific depth range in the depth direction is constant regardless of the distance x in the welding direction, whereas in the example shown in FIG. This is because the specific depth range is set so as to include the desired depth Zd at the distance x.

That is, in the second embodiment, only the minimum required range in the vicinity of the desired penetration depth Zd can be set as the specific depth range. Accordingly, in the second embodiment, when the derivation unit 112b cuts out the specific depth tomographic image data from the two-dimensional tomographic image data, it is possible to cut out only the minimum necessary range corresponding to the desired penetration depth. As a result, the penetration depth can be measured with high accuracy even if the state of formation of the keyhole during welding is not uniform, for example.

As described above, according to the laser welding apparatus 100 according to the second embodiment, when the desired penetration depth differs depending on the position in the welding direction, even if the formation state of the keyhole during welding is not constant, the welding It is possible to accurately measure the penetration depth of the part. Therefore, according to the laser welding apparatus 100 according to the second embodiment, it is possible to evaluate the quality of the welded portion based on the accurate penetration depth, and the quality of the welded portion can be evaluated with high accuracy. can be done.

<Modification>
Although various embodiments have been described above with reference to the drawings, the present invention is not limited to such examples. It is obvious that a person skilled in the art can conceive of various modifications or modifications within the scope of the claims, and these also belong to the technical scope of the present invention. Understood. Also, the components in the above embodiments may be combined arbitrarily within the scope of the invention.

In the embodiment described above, the moving stage 110 that moves the material to be welded 101, which is the irradiated side, is employed as means for moving the irradiation position of the laser beam for welding. The present invention is not limited to this, and the first condensing optical system 109 or the like, which is the side irradiated with the laser beam for welding, may be moved. Means for moving the first condensing optical system 109 and the like include, for example, a galvanometer scanner, a robot arm, and the like.

Further, in the above-described embodiment, the penetration depth is measured using the principle of SS-OCT, in which scanning is performed by changing the frequency in accordance with laser oscillation. OCT includes TD-OCT (Time Domain OCT), which measures the distance to an object by moving a reference mirror. It is necessary to move the reference mirror by , which is difficult to implement. Therefore, as the penetration depth measuring mechanism of the present invention, it is desirable to adopt SS-OCT instead of TD-OCT.

In the embodiment described above, it is assumed that the welding conditions (intensity of the welding laser beam, moving speed of the material to be welded 101, etc.) are not changed after welding is started. However, for example, the control unit 112a changes the welding conditions before the penetration depth measured at the lead-out portion 112b becomes out of the desired depth range, thereby preventing the occurrence of defective products. . In this case, the penetration depth range (welding condition holding range) for changing the welding conditions is newly set, and the lead-out portion 112b is set before the measured penetration depth deviates from the non-defective product depth range. When it is detected that the holding range is exceeded, the controller 112a is caused to change the welding conditions. The control unit 112a may change the welding conditions by adjusting the output intensity of the laser beam and the moving speed of the workpiece 101 to be welded.

In the embodiment described above, it is assumed that the spot diameter of the measurement light of the optical interferometer 105 on the surface of the material to be welded 101 is smaller than the spot diameter of the laser beam of the laser oscillator 107 on the surface of the material to be welded 101. board. However, the spot diameter of the measurement light from the optical interferometer 105 on the surface of the material to be welded 101 may be set larger than the spot diameter of the laser beam from the laser oscillator 107 on the surface of the material to be welded 101 . In such a case, it is known that in the two-dimensional tomographic image data, a distribution of high reflection intensity always appears in the unmelted portion. Although details are omitted, even in such a case, the penetration depth measuring method described in the above embodiment can be applied.

In the above-described embodiment, in step S105 shown in FIG. 3, it is determined whether or not sampling by the A/D converter 119 is to be terminated. The invention is not limited to this. That is, while continuing the sampling by the A/D converter 119, the procedures for deriving the penetration depth from step S106 onward may be performed successively. In this case, for example, when tomographic image data corresponding to a predetermined region in the welding direction is accumulated, the penetration depth in that region can be sequentially derived.

In the above-described embodiment, the non-defective product depth range is determined based on the variation in penetration depth among a plurality of non-defective products, but the present invention is not limited to this. For example, the acceptable depth range may be determined based on product design limitations.

INDUSTRIAL APPLICABILITY The present invention can be applied to a laser welding apparatus for laser welding automobiles, electronic parts, and the like.

REFERENCE SIGNS LIST 100 laser welding device 101 material to be welded 102 welded portion 103 molten pool 104 keyhole 104a bottom portion 105 optical interferometer 106 beam splitter 107 laser oscillator 108 optical system for laser beam transmission 109 first condensing optical system 110 moving stage 111 stage controller 112 Computer 112a Control unit 112b Derivation unit 112c Evaluation unit 113 Wavelength scanning light source 114 Optical fiber system 114a First optical fiber system 114b Second optical fiber system 115 First fiber coupler 116 Reference mirror 117 Second fiber coupler 118 Differential detector 118a First Input 118b Second Input 119 A/D Converter 120 Second Condensing Optical System 121 Interference Filter 122 Display Unit

Claims (5)

a laser oscillator that irradiates a laser beam toward a welded portion of a material to be welded;
an optical interferometer that generates an interference signal indicative of the intensity of interference light between the measurement light and the reference light reflected at the weld;
Based on the interference signal, two-dimensional tomographic image data is generated that indicates the relationship between the distance in the welding direction of the weld, the depth of the welding, and the intensity of the interference signal, and from the two-dimensional tomographic image data Extracting specific depth tomographic image data in which the welding depth is a specific depth range including a non-defective product depth range, and extracting the distance based on the intensity of the interference signal for each distance in the specific depth tomographic image data a derivation unit for deriving the depth of each
A laser welding device comprising: The non-defective product depth range is a range of penetration depths in the material to be welded at which the welded portion is determined to be a non-defective product after welding.
The laser welding device according to claim 1. Further comprising an evaluation unit that evaluates the quality of welding at the weld based on the derived depth for each distance,
The laser welding device according to claim 1. The upper limit value and the lower limit value of the specific depth range are set so as to vary in accordance with the variation of the non- defective product depth range when the non-defective product depth range varies depending on the distance in the welding progress direction of the welded portion. to be
The laser welding device according to any one of claims 1 to 3 . Irradiate the laser beam toward the welded part of the material to be welded,
generating an interference signal indicating the intensity of interference light between the measurement light and the reference light reflected at the weld;
based on the interference signal, generating two-dimensional tomographic image data showing the relationship between the distance in the welding direction of the weld, the depth of the weld, and the intensity of the interference signal;
Extracting specific depth tomographic image data in which the welding depth is a specific depth range including a non-defective product depth range from the two-dimensional tomographic image data,
deriving the depth for each distance based on the intensity of the interference signal for each distance in the specific depth tomographic image data;
laser welding method.

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