Welding pool internal contour detection device, welding device and method

Abstract

The present invention relates to a device for detecting the internal contour of a welding molten pool, a welding device and a method thereof. The detection method comprises the following steps: using a pulsed laser to irradiate the surface of the molten pool to form a column of light spots, and generating ultrasonic signals in the light spots of the molten pool; scanning the light spots in sequence, and synchronously collecting the ultrasonic signals of the light spots; obtaining the first peak arrival time and amplitude of the ultrasonic signal corresponding to each light spot through the base material and the thermal insulation wedge, wherein any area with too low amplitude is marked as a molten pool bubble; calculating the relevant propagation time to obtain the column of internal cross-sectional contour curves of the molten pool; repeating the above detection steps until the entire molten pool is covered, and obtaining multiple columns of internal cross-sectional contour curves of the molten pool in sequence; smoothing and connecting the multiple columns of internal cross-sectional contour curves of the molten pool to obtain a complete internal three-dimensional contour surface of the molten pool, connecting the y-direction dimensions of the projections of the multiple columns of molten pool bubbles on the xoy plane, and obtaining the projections of the molten pool bubbles on the xoy plane, thereby adjusting the welding process parameters accordingly and improving the welding quality.

Description

Technical Field

[0001] The present invention relates to the field of welding technology, and in particular to a device for detecting the internal contour of a welding pool, a welding device and a method thereof. Background Art

[0002] The internal contour of the welding pool is a factor closely related to the welding process and welding quality. It not only determines the shape of the weld, but also has a close relationship with the crystallization process of the weld. It has an important influence on the microstructure and mechanical properties of the weld and the welding quality. For example, the most important element of the internal contour of the weld is the depth of penetration, which directly affects the bearing capacity of the joint. The depth-to-width ratio of the weld directly affects the welding quality of the joint.

[0003] Reliably detecting and extracting the internal contour of the weld pool is crucial for understanding fundamental welding theories, such as the coupling between the weld heat source and the weld pool and the weld penetration state. However, in actual welding, the internal contour of the weld pool cannot be directly observed, making accurate acquisition of this characteristic information extremely difficult. Traditional weld pool topography measurement methods (arc voltage, arc light, and structured light) suffer from low signal-to-noise ratios, poor robustness, and an inability to characterize the internal shape of the weld pool.

[0004] In summary, how to solve the problem of detecting the internal contour of the high-temperature liquid molten pool during the welding process has become a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0005] In response to the problems existing in the prior art, one of the objectives of the present invention is to provide a method for detecting the internal contour of a welding molten pool, which can realize online measurement of the internal contour of a high-temperature liquid molten pool and the projection of bubbles inside the molten pool on the xoy plane during welding, thereby facilitating the adjustment of welding process parameters and improving welding quality.

[0006] A second object of the present invention is to provide a device for detecting the internal contour of a welding pool.

[0007] The third object of the present invention is to provide a welding device that can realize online measurement of the internal contour of the high-temperature liquid molten pool and the projection of bubbles inside the molten pool on the xoy plane during welding, and adjust the welding process parameters based on the obtained measurement results to improve the welding quality.

[0008] A fourth object of the present invention is to provide a welding method.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A method for detecting the internal contour of a welding pool comprises the following steps:

[0011] The base material is placed on an insulating wedge, and a pulsed laser is used to irradiate one side of the molten pool surface to form a row of light spots. Based on the photoacoustic effect, an ultrasonic signal is generated in each light spot on the molten pool.

[0012] Scan each light spot in the column in sequence, and the data acquisition card synchronously collects the ultrasonic signal of each light spot;

[0013] Obtain the first peak arrival time and amplitude of the ultrasonic signal corresponding to each spot through the base material and the insulation wedge. If there is an amplitude that is too low, it is marked as a bubble in the molten pool;

[0014] Calculate the relevant propagation time based on the thickness of the base material and the thermal insulation wedge, as well as the ultrasonic velocity and first peak arrival time of the ultrasonic signal in the relevant medium in the propagation path;

[0015] The propagation distance of ultrasound inside the molten pool is calculated based on the ultrasonic velocity and the related propagation time in the relevant medium, and the contour points of the molten pool boundary are obtained;

[0016] Get the y-dimension of the melt pool bubble projected on the xoy plane, then remove the contour points of the melt pool bubble, and smooth the curve obtained by connecting the remaining contour points of the melt pool boundary, which is the internal cross-section contour curve of the melt pool;

[0017] Repeat the above detection steps, scanning in sequence along the welding direction until the entire molten pool is covered, and obtain multiple columns of molten pool internal cross-sectional profile curves and the y-direction dimensions of the molten pool bubbles projected on the xoy plane;

[0018] The multiple columns of internal cross-sectional contour curves of the molten pool are connected by smoothing to obtain the complete internal three-dimensional contour surface of the molten pool, and the y-direction dimensions of the projections of the multiple columns of molten pool bubbles on the xoy surface are connected to obtain the projections of the molten pool bubbles on the xoy surface.

[0019] Furthermore, when collecting the ultrasonic signal of the light spot, the pulse laser and the data acquisition card are controlled at a certain frequency by the synchronous controller to ensure synchronization of the excitation and detection of the ultrasonic signal.

[0020] Furthermore, the method for calculating the relevant propagation time is to obtain the ultrasonic velocity in the molten pool, the ultrasonic velocity in the base material, the ultrasonic velocity in the insulating wedge, the base material thickness, the insulating wedge thickness and the first peak arrival time, and establish an equation system consisting of the following multiple equations and solve them to obtain:

[0021] Ultrasonic velocity in the molten pool x propagation time in the molten pool + ultrasonic velocity in the base material x propagation time in the base material = base material thickness; ultrasonic velocity in the insulating wedge x propagation time in the insulating wedge = insulating wedge thickness; propagation time in the molten pool + propagation time in the base material + propagation time in the insulating wedge = first peak arrival time.

[0022] Furthermore, the contour points of the molten pool boundary are calculated as follows:

[0023] The propagation distance of ultrasound in the molten pool = ultrasonic velocity in the molten pool x propagation time in the molten pool.

[0024] Furthermore, the ultrasonic velocity in the relevant medium is obtained by combining the molten pool temperature measurement results and the welding parameter library established by the temperature simulation system of the base material, molten pool and insulating wedge in the expert system, and establishing the stepped sound velocity in the molten pool, base material and insulating wedge according to the material temperature ladder. According to the propagation path, the formula The average sound velocity in the medium corresponding to the propagation path is calculated, which is the ultrasonic velocity in the medium related to the propagation path.

[0025] Furthermore, when scanning the spot, all spot columns are evenly distributed, all rows are evenly distributed, and the column distance and row distance are both larger than the laser spot diameter. By adjusting the column distance, row distance and spot size, the lateral resolution of detecting the internal contour of the molten pool is adjusted, and the spot scanning surface covers the surface of the high-temperature liquid molten pool and avoids the keyhole entrance area.

[0026] A device for detecting the internal contour of a welding pool, comprising a heat-insulating wedge for placing a base material, a pulsed laser, a data acquisition card, and a control unit;

[0027] The pulsed laser is used to irradiate the surface of the molten pool of the parent material to form multiple rows of light spots in sequence, and an ultrasonic signal is generated in each light spot on the molten pool based on the photoacoustic effect;

[0028] The data acquisition card is used to collect the ultrasonic signal of each light spot and send it to the control unit;

[0029] The control unit obtains the first peak arrival time and amplitude of the ultrasonic signal corresponding to each light spot through the base material and the insulating wedge based on the received ultrasonic signal. According to the thickness of the base material and the insulating wedge and the ultrasonic velocity and first peak arrival time of the ultrasonic signal in the relevant medium in the propagation path, the complete internal three-dimensional contour surface of the molten pool is calculated. According to the amplitude of the ultrasonic signal corresponding to each light spot, the projection of the molten pool bubble on the xoy plane is calculated.

[0030] Furthermore, it also includes an optical path system, a two-dimensional galvanometer, a high-temperature resistant ultrasonic coupling agent, a piezoelectric sensor, a data acquisition card, a high-speed camera and an infrared temperature measurement system. The pulse laser is used to transmit laser shaping to the two-dimensional galvanometer through the optical path system. The two-dimensional galvanometer is used to perform two-dimensional laser scanning of the molten pool. The piezoelectric sensor is tightly connected to the lower surface of the insulating wedge through the high-temperature resistant ultrasonic coupling agent. The detection laser irradiates the surface of the molten pool to generate an ultrasonic signal based on the photoacoustic effect. The ultrasonic signal in the molten pool is transmitted to the insulating wedge through the high-temperature resistant ultrasonic coupling agent, and then transmitted to the piezoelectric sensor through the ultrasonic coupling agent on the lower surface of the insulating wedge. The data acquisition card synchronously collects the ultrasonic signal detected by the piezoelectric sensor and transmits it to the control unit for data analysis. The high-speed camera is used to identify the distribution area of ​​the molten pool surface and the keyhole entrance. The infrared temperature measurement system is used to measure the surface temperature of the molten pool and send it to the control unit to establish a stepped sound velocity in the molten pool, the base material and the insulating wedge.

[0031] A welding device includes a welding unit and a welding pool internal contour detection device. The control unit includes a host computer, a motion control module and a synchronization controller. The host computer is used to program and modulate parameters of the welding unit and the molten pool internal contour detection device, and analyze and process detection signals. The motion control module is used to control a three-dimensional motion platform to move in three dimensions according to a set program, and at the same time control a two-dimensional galvanometer to perform pulsed laser two-dimensional scanning according to a set program. The synchronization controller is used to provide a unique timing for triggering and ending the welding unit and the molten pool internal contour detection device, thereby ensuring synchronization of excitation and detection of ultrasonic signals.

[0032] A welding method, using a welding device, comprises the following steps:

[0033] The internal contour detection device of the welding molten pool is used to obtain the complete internal three-dimensional contour surface of the molten pool and the projection of the molten pool bubbles on the xoy surface.

[0034] By projecting the three-dimensional contour surface inside the molten pool and the molten pool bubbles on the xoy surface, the molten pool penetration depth and width information are obtained. Combined with the expert system, the welding process parameters are adjusted to improve the welding quality.

[0035] In general, the present invention has the following advantages:

[0036] The present invention generates an ultrasonic signal within a light spot on the molten pool based on the photoacoustic effect, performs relevant calculations based on the ultrasonic signal, obtains a cross-sectional profile curve inside the molten pool, and marks bubbles inside the molten pool according to the amplitude of the ultrasonic signal. This enables online measurement of the internal profile of the high-temperature liquid molten pool and the projection of bubbles inside the molten pool on the xoy plane during welding, thereby adjusting welding process parameters and improving welding quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a structural schematic diagram of the welding device of the present invention;

[0038] Figure 2 Schematic diagram of the xoy surface of the molten pool internal contour detection solution of the present invention;

[0039] Figure 3 Schematic diagram of the yoz surface of the molten pool internal contour detection solution of the present invention;

[0040] Figure 4 This is a flow chart of the molten pool internal contour detection solution of the present invention;

[0041] Figure 5 This is the distribution diagram of the molten pool and keyhole during arc welding of the present invention.

[0042] In the picture:

[0043] 11- host computer, 12- synchronization controller;

[0044] 21- welding system, 22- three-dimensional motion platform;

[0045] 31-Pulsed laser, 32-Optical path system, 33-Two-dimensional galvanometer, 34-Piezoelectric sensor, 35-Data acquisition card, 36-High-speed camera, 37-Infrared temperature measurement system;

[0046] 41-insulation wedge;

[0047] 51-base material, 52-weld, 53-light spot, 54-bubble;

[0048] 61-molten pool, 62-keyhole. DETAILED DESCRIPTION

[0049] The present invention will be described in further detail below.

[0050] like Figure 1 As shown, a welding device includes a control unit, a welding unit and an internal contour detection device of a molten pool 61.

[0051] The control unit is connected to the welding unit and the internal contour detection device of the molten pool 61 via signal connection lines. The control unit includes a host computer 11, a motion control module, and a synchronization controller 12. The host computer 11 programs and modulates the parameters of the internal contour detection devices of the welding unit and the molten pool 61, and analyzes and processes the detection signals. The motion control module controls the three-dimensional motion platform 22 to move three-dimensionally according to the set program, and simultaneously controls the two-dimensional galvanometer 33 to perform pulsed laser two-dimensional scanning according to the set program. The synchronization controller 12 provides a unique timing for triggering and terminating the internal contour detection devices of the welding unit and the molten pool 61, ensuring synchronization of the excitation and detection of the ultrasonic signal.

[0052] Specifically, the welding unit includes a welding system 21 and a three-dimensional motion platform 22. The welding system 21 outputs the required welding heat source according to the welding parameter control program of the host computer 11. The three-dimensional motion platform 22 is fixedly connected to the insulating wedge 41. The upper surface of the insulating wedge 41 is tightly connected to the base material 51 through a high-temperature resistant ultrasonic coupling agent. The upper and lower surfaces of the insulating wedge 41 are smooth and neat. The three-dimensional motion platform 22 drives the base material 51 for mobile welding according to the control program of the host computer 11.

[0053] Specifically, the internal contour detection device of the molten pool 61 includes a pulse laser 31, an optical path system 32, a two-dimensional galvanometer 33, a piezoelectric sensor 34, a data acquisition card 35, a high-speed camera 36 and an infrared temperature measurement system 37. The pulse laser 31 generates a detection laser of a specific frequency and power according to the control program of the host computer 11, and transmits the laser shaping to the two-dimensional galvanometer 33 through the optical path system 32. The two-dimensional galvanometer 33 performs two-dimensional scanning of the laser according to the control program of the host computer 11. The piezoelectric sensor 34 is tightly connected to the lower surface of the insulating wedge 41 through a high-temperature resistant ultrasonic coupling agent. The detection laser irradiates the surface of the molten pool 61 to generate an ultrasonic signal based on the photoacoustic effect. The ultrasonic signal in the molten pool 61 is transmitted to the insulating wedge 41 through the high-temperature resistant ultrasonic coupling agent, and finally transmitted to the piezoelectric sensor 34 through the ultrasonic coupling agent on the lower surface of the insulating wedge 41. The data acquisition card 35 collects the ultrasonic signal detected by the piezoelectric sensor 34 according to the trigger signal of the synchronization controller 12, and transmits it to the host computer 11 for data analysis. The high-speed camera 36 identifies the distribution area of ​​the surface of the molten pool 61 and the entrance of the keyhole 62. The infrared temperature measurement system 37 can measure the surface temperature of the molten pool 61 non-contact.

[0054] Specifically, the detection laser irradiates the molten pool 61 in a direction perpendicular to the upper surface of the base material 51 through the two-dimensional galvanometer 33, and the piezoelectric sensor 34 is located directly below the molten pool 61. The effective distribution area of ​​the piezoelectric sensor 34 is greater than the width of the molten pool 61 and the length of the weld 52.

[0055] like Figure 4 As shown, a welding method comprises the following steps:

[0056] S1: Device initialization (the host computer 11 controls and adjusts the motion platform to ensure that the laser focus is located on the upper surface of the base material 51, the scanning area of ​​the two-dimensional galvanometer 33 is located directly above the molten pool 61, and can scan the entire surface of the molten pool 61), and program initialization (the host computer 11 sets relevant welding parameters);

[0057] S2: Start welding;

[0058] S3: detection of the internal contour of the molten pool 61 based on the photoacoustic effect;

[0059] S3.1: The host computer 11 controls the pulse laser 31 and the data acquisition card 35 at a certain frequency through the synchronization controller 12. The pulse laser 31 generates a detection laser of a specific frequency, and the data acquisition card 35 collects the corresponding signal from the piezoelectric sensor 34.

[0060] S3.2: If Figure 2 As shown, the two-dimensional galvanometer 33 scans the base material 51 and the weld 52 along the welding direction, and sequentially scans the first column of light spots 53 (1, 1), (2, 1), ..., (n, 1), and records the first peak arrival time t of the ultrasonic signals U (1, 1), U (2, 1), ..., U (n, 1) corresponding to the first column of light spots 53 (1, 1), (2, 1), ..., (n, 1). 11 , t 21 ,…,t n1 Amplitude a 11 、a 21 ,…,a n1 ;

[0061] S3.3: If Figure 3 As shown, the relevant propagation time is calculated according to the ultrasonic velocity v and propagation distance L of the ultrasonic signal U(i, j) in the relevant medium in each propagation path;

[0062] S3.3.1: The propagation path is A1-B1-C1, passing through the base material 51 and the insulating wedge 41 in sequence. Combining equations (1)-(3) yields the times t1 and t2;

[0063] S3.3.2: The propagation path A2-B2-C2 passes through the molten pool 61, the base material 51 and the insulating wedge 41 in sequence. Combining equations (4) and (6), we can obtain the times t3, t4, and t5;

[0064] S3.3.3: The propagation path A3-B3-C3 passes through the molten pool 61 and the insulating wedge 41 in sequence, and the formula is Combining equations (7) and (9) yields the times t6 and t7;

[0065] S3.3.4: The propagation path A4-B4-C4 passes through the molten pool 61, the base material 51 and the insulating wedge 41 in sequence. There is a bubble 54 on the propagation path. The bubble 54 corresponds to the signal amplitude a ij Much smaller than the amplitude at the position without bubbles 54, there is a formula Combining equations (10) and (12) yields the times t8, t9, and t10;

[0066] S3.4: By calculating the propagation distance of ultrasound inside the molten pool 61, The contour points D11, D21, ..., Dn1 of the first row of the molten pool 61 boundary can be obtained;

[0067] S3.5: Connect all amplitudes a ij The too small spot 53 (i, j) is the y-direction size of the bubble 54 in the molten pool 61 projected on the xoy plane, and then the amplitude a is removed. ij The curve obtained by smoothing the remaining contour points D11, D21, ..., Dn1 connecting the boundary of the molten pool 61 for the contour point Dij that is too small is the first column internal cross-sectional contour curve of the molten pool 61;

[0068] S3.6: Scan the 2nd, 3rd, ..., nth columns and repeat steps S3.2-S3.5 to obtain the internal cross-sectional contour curves of the 2nd, 3rd, ..., nth columns of the melt pool 61 and the y-dimensions of the bubbles 54 in the melt pool 61 projected on the xoy plane. Smoothly connect the internal cross-sectional contour curves of the 1st, 2nd, ..., nth columns of the melt pool 61 to obtain the complete internal three-dimensional contour surface of the melt pool 61. Connect the y-dimensions of the bubbles 54 in the melt pool 61 projected on the xoy plane in the 1st, 2nd, ..., nth columns to obtain the projection of the bubbles 54 in the melt pool 61 on the xoy plane.

[0069] S4: Obtain information such as the penetration depth and width of the molten pool 61 by projecting the internal three-dimensional contour of the molten pool 61 and the bubbles 54 of the molten pool 61 on the xoy plane, and adjust the welding process parameters according to the expert system to improve the welding quality;

[0070] S5: End detection and welding.

[0071] Specifically, such as Figure 2 As shown, in step S3.2, the two-position galvanometer scans all columns evenly distributed, all rows evenly distributed, the column distance a and the row distance b are both larger than the diameter of the laser spot 53, and the column distance a, the row distance b and the size of the spot 53 are adjusted to adjust the lateral resolution of the internal contour of the molten pool 61. The scanning surface of the spot 53 covers the surface of the high-temperature liquid molten pool 61 and avoids the entrance area of ​​the keyhole 62.

[0072] Specifically, the ultrasonic velocity v in the relevant medium of step S3.3 is combined with the actual measurement results of the infrared temperature measurement system 37 and the welding parameter library established by the temperature simulation system of the base material 51, the molten pool 61 and the insulating wedge 41 in the expert system, and the stepped sound velocity v in the molten pool 61, the base material 51 and the insulating wedge 41 is established according to the material temperature ladder. According to the propagation path, the formula The average sound velocity in the medium corresponding to the propagation path is calculated to be the ultrasonic velocity v in the medium related to the propagation path.

[0073] Specifically, in step S3, 1≤i≤n, 1≤j≤n.

[0074] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for detecting the internal contour of a welding pool, characterized in that: The following steps are included: The base material is placed on an insulating wedge, and a pulsed laser is used to irradiate one side of the molten pool surface to form a row of light spots. Ultrasonic signals are generated in each light spot on the molten pool based on the photoacoustic effect. Scan each spot in the array of spots in sequence, and the data acquisition card synchronously collects the ultrasonic signal of each spot; Obtain the first peak arrival time and amplitude of the ultrasonic signal corresponding to each spot through the base material and the insulation wedge. If there is an amplitude that is too low, it is marked as a bubble in the molten pool; Calculate the relevant propagation time based on the thickness of the base material and the thermal insulation wedge, as well as the ultrasonic velocity and first peak arrival time of the ultrasonic signal in the relevant medium in the propagation path; The propagation distance of ultrasound inside the molten pool is calculated based on the ultrasonic velocity and related propagation time in the relevant medium, and the contour points of the molten pool boundary corresponding to the column of spots are obtained; Get the y-dimension of the molten pool bubble projected on the xoy plane, then remove the contour points of the molten pool bubble, and smooth the remaining contour points connecting the molten pool boundary to obtain the internal cross-sectional contour curve of the molten pool corresponding to this column of spots; Repeat the above steps and scan in sequence along the welding direction until the entire molten pool is covered, and obtain multiple columns of molten pool internal cross-sectional profile curves and the y-direction dimensions of the molten pool bubbles projected on the xoy plane. Smoothing multiple columns of internal cross-sectional contour curves of the connected molten pool to obtain the complete internal three-dimensional contour surface of the molten pool, and connecting the y-direction dimensions of multiple columns of molten pool bubbles projected on the xoy surface to obtain the projection of the molten pool bubbles on the xoy surface; The method for calculating the relevant propagation time is to obtain the ultrasonic velocity in the molten pool, the ultrasonic velocity in the base material, the ultrasonic velocity in the insulating wedge, the base material thickness, the insulating wedge thickness and the first peak arrival time, and establish an equation system consisting of the following multiple equations and solve them to obtain: Ultrasonic velocity in the molten pool x propagation time in the molten pool + ultrasonic velocity in the base material x propagation time in the base material = base material thickness; ultrasonic velocity in the insulating wedge x propagation time in the insulating wedge = insulating wedge thickness; propagation time in the molten pool + propagation time in the base material + propagation time in the insulating wedge = first peak arrival time; The contour points of the melt pool boundary are calculated as follows: The propagation distance of ultrasound in the molten pool = ultrasonic velocity in the molten pool x propagation time in the molten pool.

2. A method for detecting the internal contour of a welding pool according to claim 1, characterized in that: When collecting the ultrasonic signal of the light spot, the pulse laser and the data acquisition card are controlled at a certain frequency by the synchronous controller to ensure the synchronization of the excitation and detection of the ultrasonic signal.

3. The method for detecting the internal contour of a welding pool according to claim 1, wherein: The method of obtaining the ultrasonic velocity in the relevant medium is to combine the molten pool temperature measurement results and the welding parameter library established by the temperature simulation system of the base material, molten pool and insulating wedge in the expert system, and establish the stepped sound velocity in the molten pool, base material and insulating wedge according to the material temperature gradient. , according to the propagation path, through the formula , calculate the average sound speed in the corresponding medium of the propagation path, which is the ultrasonic speed in the relevant medium of the propagation path.

4. The method for detecting the internal contour of a welding pool according to claim 1, wherein: When scanning the spot, all spot columns are evenly distributed, all rows are evenly distributed, and the column distance and row distance are both larger than the laser spot diameter. By adjusting the column distance, row distance and spot size, the lateral resolution of detecting the internal contour of the molten pool is adjusted. The spot scanning surface covers the surface of the high-temperature liquid molten pool and avoids the keyhole entrance area.

5. A device for detecting the internal contour of a welding pool using the method for detecting the internal contour of a welding pool according to any one of claims 1 to 4, characterized in that: It includes a thermal insulation wedge for placing the parent material, a pulsed laser, a data acquisition card and a control unit; The pulsed laser is used to irradiate the surface of the molten pool of the parent material to form multiple rows of light spots in sequence, and an ultrasonic signal is generated in each light spot on the molten pool based on the photoacoustic effect; The data acquisition card is used to collect the ultrasonic signal of each light spot and send it to the control unit; The control unit obtains the first peak arrival time and amplitude of the ultrasonic signal corresponding to each light spot through the base material and the insulating wedge based on the received ultrasonic signal. According to the thickness of the base material and the insulating wedge and the ultrasonic velocity and first peak arrival time of the ultrasonic signal in the relevant medium in the propagation path, the complete internal three-dimensional contour surface of the molten pool is calculated. According to the amplitude of the ultrasonic signal corresponding to each light spot, the projection of the molten pool bubble on the xoy plane is calculated.

6. The device for detecting the internal contour of a welding pool according to claim 5, characterized in that: It also includes an optical path system, a two-dimensional galvanometer, a high-temperature resistant ultrasonic coupling agent, a piezoelectric sensor, a data acquisition card, a high-speed camera and an infrared temperature measurement system. The pulse laser is used to transmit laser shaping to the two-dimensional galvanometer through the optical path system. The two-dimensional galvanometer is used to perform two-dimensional laser scanning of the molten pool. The piezoelectric sensor is tightly connected to the lower surface of the insulating wedge through the high-temperature resistant ultrasonic coupling agent. The detection laser irradiates the surface of the molten pool and generates an ultrasonic signal based on the photoacoustic effect. The ultrasonic signal in the molten pool is transmitted to the insulating wedge through the high-temperature resistant ultrasonic coupling agent, and then transmitted to the piezoelectric sensor through the ultrasonic coupling agent on the lower surface of the insulating wedge. The data acquisition card synchronously collects the ultrasonic signal detected by the piezoelectric sensor and transmits it to the control unit for data analysis. The high-speed camera is used to identify the distribution area of ​​the molten pool surface and the keyhole entrance. The infrared temperature measurement system is used to measure the surface temperature of the molten pool and send it to the control unit to establish a stepped sound velocity in the molten pool, the base material and the insulating wedge.

7. A welding device, characterized in that: It includes a welding unit and the internal contour detection device of the welding pool as described in claim 5 or 6. The control unit includes a host computer, a motion control module and a synchronization controller. The host computer is used to program and modulate the parameters of the welding unit and the internal contour detection device of the molten pool, and analyze and process the detection signals. The motion control module is used to control the three-dimensional motion platform to move three-dimensionally according to the set program, and at the same time control the two-dimensional galvanometer to perform pulsed laser two-dimensional scanning according to the set program. The synchronization controller is used to provide a unique timing for triggering and ending the welding unit and the internal contour detection device of the molten pool to ensure the synchronization of excitation and detection of ultrasonic signals.

8. A welding method, characterized in that: The welding device according to claim 7 comprises the following steps: The internal contour detection device of the welding molten pool is used to obtain the complete internal three-dimensional contour surface of the molten pool and the projection of the molten pool bubbles on the xoy surface. By projecting the three-dimensional contour surface inside the molten pool and the molten pool bubbles on the xoy surface, the molten pool penetration depth and width information are obtained. Combined with the expert system, the welding process parameters are adjusted to improve the welding quality.

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