A method and system for large area ultrafast laser welding

Abstract

The application provides a method and system for large-area ultrafast laser welding, which comprises: a workpiece fitting step, in which flat welding surfaces of two workpieces are fitted to each other; an image acquisition step, in which images of the fitted welding surfaces are acquired, and an area on the welding surface, which is not welded but has formed optical contact, is identified according to the acquired images of the welding surfaces, and the identified area is taken as a next area to be welded; an area welding step, in which the area to be welded is welded by using ultrafast laser welding, so that the two workpieces are welded in the area to be welded; and the image acquisition step and the area welding step are repeated until a preset condition is reached; wherein the preset condition comprises one or more of the following: repeated reaching of a preset number of times, no new area on the welding surface that is not welded but has formed optical contact can be identified, and a proportion of the welded area on the welding surface exceeds a preset threshold. The application can solve the problem of ultrafast laser welding of a large-area welding surface.

Description

Technical Field

[0001] This invention relates to the field of laser processing technology, and in particular to a method and system for large-area ultrafast laser welding. Background Technology

[0002] Ultrafast laser welding boasts advantages such as low heat-affected zone, no solder required, and suitability for ultra-precision welding, making it widely applicable in semiconductors, automotive manufacturing, scientific research, and healthcare. In principle, ultrafast laser welding utilizes the nonlinear absorption effect of the interaction between an ultrashort pulse laser and the material, melting the material in a localized area. However, due to the very small molten volume produced by ultrafast laser welding, its tolerance for gaps at the weld interface is very low, generally requiring optical contact at the weld interface (contact gap < wavelength / 4). As the weld area expands, overall undulations become increasingly difficult to control, and maintaining optical contact becomes more challenging. Therefore, achieving high-quality, large-format welding using ultrafast laser welding remains a pressing issue.

[0003] Existing technology 1 (patent number CN114160975A) proposes a large-format high-intensity laser welding method for dissimilar materials. This method achieves composite output of long-pulse lasers and ultrafast lasers through beam combining, and uses optical control to separate the focal points of the long-pulse lasers and ultrafast lasers to predetermined positions, thereby achieving optical bonding between the thermally expanded metal material and the transparent, hard, and brittle material. However, because this method requires the use of two laser beams combined and precise control of their focal points, it places high demands on the optical system, resulting in a complex system configuration. Furthermore, this method relies on the thermal expansion of the metal, and may fail for metal materials with low coefficients of thermal expansion.

[0004] Existing technology 2 (patent number CN119260171A) proposes a large-format high-intensity laser welding method for dissimilar materials. This method employs multiple scanning, utilizing the absorption of ultrafast laser light by the underlying material to generate plasma. The plasma expands and overflows, melting and filling the gaps in the material near the welding surface, thus achieving quasi-optical contact conditions. However, this method requires multiple repeated ultrafast laser scans, reducing processing efficiency.

[0005] Therefore, how to achieve large-scale, stable, and high-quality ultrafast laser welding is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] In view of this, embodiments of the present invention provide a method and system for large-area ultrafast laser welding to eliminate or improve one or more defects existing in the prior art.

[0007] One aspect of the present invention provides a method for large-area ultrafast laser welding, the method comprising the following steps: a workpiece bonding step, wherein flat welding surfaces of two workpieces are bonded together; wherein at least one of the two workpieces is transparent relative to the operating wavelength of the ultrafast laser; an image acquisition step, wherein an image of the bonded welding surfaces is acquired, and an unwelded but optically contacted area on the welding surface is identified based on the acquired image, and the identified area is used as the area to be welded in the next step; a region welding step, wherein the region to be welded is welded using an ultrafast laser, thereby achieving welding of the two workpieces in the region to be welded; and the image acquisition step and the region welding step are repeated until a preset condition is met; wherein the preset condition includes one or more of the following: the repetition reaches a preset number of times, no new unwelded but optically contacted areas can be identified on the welding surface, and the proportion of the welded area on the welding surface exceeds a preset threshold.

[0008] In some embodiments of the present invention, prior to the workpiece bonding step, the method further includes a workpiece pretreatment step, in which the two workpieces are treated with a chemical cleaning method.

[0009] In some embodiments of the present invention, the image of the welding surface is an optical interference image acquired using an optical image acquisition system; the acquisition of the image of the mutually bonded welding surface includes: using a horizontal displacement platform to move the two mutually bonded workpieces below the optical image acquisition system, so as to acquire the optical interference image of the two workpieces on the welding surface using the optical image acquisition system.

[0010] In some embodiments of the present invention, identifying areas on the welding surface that are not welded but have formed optical contact includes: preprocessing the acquired optical interference image to improve the contrast of the interference fringes contained therein; extracting the fringe coordinates of each interference fringe contained in the preprocessed optical interference image and determining the order of each interference fringe; and determining the areas on the welding surface that are not welded but have formed optical contact according to the interference fringes that meet the preset order.

[0011] In some embodiments of the present invention, identifying regions on the welding surface that are not welded but have formed optical contact includes: inputting the optical interference image into a pre-trained deep learning model to obtain the output boundary coordinates of the regions on the welding surface that are not welded but have formed optical contact; wherein, the training set of the deep learning model includes an optical interference image formed before the workpiece is welded and annotations of equal-thickness interference fringes in the optical interference image based on the welding effect.

[0012] In some embodiments of the present invention, welding the area to be welded using ultrafast laser includes: determining an ultrafast laser welding trajectory capable of filling the area to be welded using a Z-shaped scanning filling algorithm, an offset filling algorithm, a sub-regional scanning filling algorithm, a spiral scanning filling algorithm, a concentric circular arc filling algorithm, or a fractal scanning filling algorithm; and using an optical system to control the ultrafast laser generated by the laser to move along the ultrafast laser welding trajectory, thereby realizing the welding of the workpiece in the area to be welded.

[0013] In some embodiments of the present invention, when the preset condition includes the proportion of the welded area on the welding surface exceeding a preset threshold, starting from the second execution of the image acquisition step, the image acquisition step further includes: counting the number of pixels occupied by the welding surface in the image, counting the number of pixels occupied by the welded area in the image in the previous region welding step; calculating the quotient of the number of pixels occupied by the welded area in the image and the number of pixels occupied by the welding surface in the image as the proportion of the welded area on the welding surface.

[0014] In some embodiments of the present invention, the method further includes repeating the image acquisition step and the area welding step until a preset condition is met, and then using an ultrafast laser to scan the welding surface again to enhance the welding strength of the workpiece.

[0015] Corresponding to the above method, the present invention also provides a system for large-area ultrafast laser welding. This system implements the steps of any of the methods described in the above embodiments. The system includes: a horizontal displacement platform for placing two workpieces with flat welding surfaces in contact with each other; wherein at least one of the two workpieces is transparent relative to the working wavelength of the ultrafast laser; an optical image acquisition system for acquiring images of the welded surfaces in contact with each other; a computing system for identifying, based on the acquired images of the welded surfaces, unwelded areas that have formed optical contact on the welded surfaces as areas to be welded; an ultrafast laser welding system for welding the areas to be welded using an ultrafast laser, thereby achieving welding of the two workpieces in the areas to be welded; the computing system is further configured to determine, during the repetition of the image acquisition step and the area welding step, whether a preset condition for control termination has been met; wherein the preset condition includes one or more of the following: the repetition reaches a preset number of times, no new unwelded areas that have formed optical contact can be identified on the welded surfaces, and the proportion of welded areas on the welded surfaces exceeds a preset threshold.

[0016] In some embodiments of the present invention, the ultrafast laser welding system includes a laser and an optical system, the laser being used to generate an ultrafast laser, and the optical system and / or a horizontal displacement platform being used to control the ultrafast laser welding trajectory.

[0017] In some embodiments of the present invention, the optical system consists of a scanning galvanometer and a field mirror. During ultrafast laser welding, the field mirror remains stationary, and the scanning galvanometer controls the ultrafast laser welding trajectory by controlling the change of the two-dimensional optical path. Alternatively, the optical system consists of a focusing mirror, which focuses the ultrafast laser onto the welding surface or near the welding surface during ultrafast laser welding, and welding is achieved along the ultrafast laser welding trajectory by moving the horizontal displacement platform.

[0018] The method and system for large-area ultrafast laser welding proposed in this invention utilize the characteristic that the area welded by the ultrafast laser reduces the gap between the surrounding unwelded areas, thereby expanding to form an optical contact area. This allows welding of the newly added optical contact area, achieving ultrafast laser welding of two workpieces as a whole. This method solves the problem of ultrafast laser welding of large-area welding surfaces and eliminates the need for repeated ultrafast laser scanning of the entire welding surface, thus saving processing efficiency. Furthermore, since the phenomenon of outward expansion of the optical contact area can be observed in various materials, this method has greater applicability to welding materials.

[0019] Additional advantages, objects, and features of the invention will be set forth in part in the description which follows, and will also become apparent in part to those skilled in the art upon studying the description, or may be learned by practice of the invention. The objects and other advantages of the invention can be realized and obtained by means of the structures specifically pointed out in the description and drawings.

[0020] Those skilled in the art will understand that the objectives and advantages achievable with the present invention are not limited to those specifically described above, and that the above and other objectives achievable with the present invention will become clearer from the following detailed description. Attached Figure Description

[0021] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, are not intended to limit the scope of the invention. The components in the drawings are not drawn to scale but are merely illustrative of the principles of the invention. For ease of illustration and description of certain parts of the invention, corresponding portions in the drawings may be enlarged, i.e., may appear larger relative to other components in an exemplary device actually manufactured according to the invention. In the drawings:

[0022] Figure 1 This is a flowchart of a method for large-area ultrafast laser welding according to an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of a system structure for large-area ultrafast laser welding according to an embodiment of the present invention.

[0024] Figure 3 This is a flowchart of a method for large-area ultrafast laser welding according to another embodiment of the present invention.

[0025] Figure 4 This is a schematic diagram illustrating the identification principle of the optical contact area in one embodiment of the present invention.

[0026] Figure 5 This is a schematic diagram of the ultrafast laser welding principle in one embodiment of the present invention.

[0027] Figure 6 This is a schematic diagram of the structure of an optical system in one embodiment of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments and accompanying drawings. Here, the illustrative embodiments and descriptions of this invention are used to explain the invention, but are not intended to limit the invention.

[0029] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the structures and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0030] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, element, step, or component, but does not exclude the presence or addition of one or more other features, elements, steps, or components.

[0031] It should also be noted that, unless otherwise specified, the term "connection" in this article can refer not only to a direct connection, but also to an indirect connection involving an intermediary.

[0032] In the following description, embodiments of the invention will be illustrated with reference to the accompanying drawings. In the drawings, the same reference numerals represent the same or similar parts, or the same or similar steps.

[0033] To achieve large-area, stable, and high-quality ultrafast laser welding, and to avoid dependence on the thermal expansion of metals and the reduction in processing efficiency caused by repeated ultrafast laser scanning, this application proposes a method and system for large-area ultrafast laser welding. The principle behind this method is that the area welded by the ultrafast laser reduces the gap between the surrounding unwelded areas, thereby expanding the optical contact area. By continuously welding the newly added optical contact area, the entire sample is eventually welded.

[0034] It should be noted that, in this invention, optical contact refers to the area of ​​good contact on the welding surface, meaning that the width of the air gap formed on the welding surface is less than a predetermined proportion of the wavelength of the monochromatic light (or laser) used to observe and measure the interference fringes. The predetermined proportion can be 1 / 4 or 1 / 2, or it can be 2 times, 4 times, or 10 times. This invention is not limited to these proportions; they are merely examples.

[0035] Figure 1 This is a flowchart of a method for large-area ultrafast laser welding according to an embodiment of the present invention. The method includes the following steps:

[0036] Step S110: Workpiece bonding step, in which the flat welding surfaces of two workpieces are bonded together. At least one of the two workpieces is transparent relative to the operating wavelength of the ultrafast laser.

[0037] Step S120: Image acquisition step, acquire images of the welded surfaces that are in contact with each other, identify the areas on the welded surfaces that are not welded but have formed optical contact based on the acquired images of the welded surfaces, and use the identified areas as the areas to be welded in the next step.

[0038] The image of the welding surface can be obtained by cropping the welding surface along its contour based on the original acquired image.

[0039] Step S130: Area welding step, using ultrafast laser to weld the area to be welded, so that the two workpieces are welded in the area to be welded.

[0040] In the field of optics, optical contact is defined as a gap between two pieces of glass that is less than one-quarter of the wavelength of the light source. However, in practical applications, it is not strictly limited to one-quarter and can be relaxed as appropriate. For example, it can be relaxed to half the wavelength, twice the wavelength, or ten times the wavelength.

[0041] Step S140: Repeat the image acquisition step and the area welding step until a preset condition is met; wherein, the preset condition includes one or more of the following: repeating to a preset number of times, no new unwelded but optically contacted areas can be identified on the welding surface, and the proportion of welded areas on the welding surface exceeds a preset threshold.

[0042] In this invention, "large area" refers to the area of ​​a laser welding surface greater than 10mm*10mm, while the current laser welding area is generally within 10mm*10mm.

[0043] The method for large-area ultrafast laser welding proposed in this invention utilizes the characteristic that the area welded by the ultrafast laser reduces the gap between the surrounding unwelded areas, thereby expanding to form an optical contact area. This allows for welding of the newly added optical contact area, achieving ultrafast laser welding of two workpieces as a whole. This method solves the problem of ultrafast laser welding of large-area welding surfaces and eliminates the need for repeated ultrafast laser scanning of the entire welding surface, thus saving processing efficiency. Furthermore, since the outward expansion of the optical contact area can be observed in various materials, this method has greater applicability to welding materials; the material on top of the workpiece can be a silicon wafer.

[0044] In some embodiments of the present invention, prior to the workpiece bonding step, the method further includes a workpiece pretreatment step, which involves treating the two workpieces using a chemical cleaning method. The chemical cleaning method includes, but is not limited to, using a degreasing cleaner to remove oil stains from the workpiece surface and using a rust-removing cleaner to remove the oxide layer from the workpiece surface.

[0045] By employing this embodiment of the invention, oil and / or oxide layers that may exist on the surface of the workpiece can be removed by chemical cleaning. On the one hand, this can make the welding surface of the workpiece smoother, and on the other hand, it can prevent oil and / or oxide layers from interfering with ultrafast laser welding.

[0046] In some embodiments of the present invention, the image of the welding surface is an optical interference image acquired using an optical image acquisition system.

[0047] Accordingly, acquiring images of the welded surfaces that are in contact with each other includes: using a horizontal displacement platform to move the two workpieces that are in contact with each other below the optical image acquisition system, so as to acquire optical interference images of the two workpieces on the welded surfaces using the optical image acquisition system.

[0048] The method of using optical interference imaging to identify areas on the welded surface that are not welded but have formed optical contact is based on the principle that when two pieces of glass are tightly bonded, the interference fringes formed in the optical contact area are of equal thickness, which can be described by the following formula:

[0049] Where e represents the gap between the two pieces of glass. Let λ be the wavelength of the illumination source, and k be the order of the interference fringes (also known as bright and dark fringes). The definition of optical contact is... Substituting into the formula above, we can calculate that it corresponds to a first-order bright fringe (in practical applications, optical contact does not need to be strictly limited to...). Within this range (which can be relaxed depending on the situation). Therefore, the problem of finding the boundary of the optical contact region is transformed into the problem of finding the corresponding fringes (i.e., equal-thickness interference fringes) in the optical interference image, which can be solved by traditional computer vision methods or deep learning methods. This refers to the wavelength of monochromatic light or laser light used to observe and measure interference fringes.

[0050] This invention enables image acquisition using a horizontal displacement platform and an optical image acquisition system. It accurately captures areas on the welding surface that are not welded but have formed optical contacts, facilitating subsequent precise localized ultrafast laser welding and avoiding repeated scanning (welding) of the entire welding surface by the ultrafast laser. This method transforms the problem of finding the boundary of optical contacts into finding equal-thickness interference fringes in an optical interference image, which can then be solved using traditional computer vision methods or deep learning methods.

[0051] In some embodiments of the present invention, identifying areas on the welding surface that are not welded but have formed optical contact includes: preprocessing the acquired optical interference image to improve the contrast of the interference fringes contained therein; extracting the fringe coordinates of each interference fringe contained in the preprocessed optical interference image and determining the order of each interference fringe; and determining the areas on the welding surface that are not welded but have formed optical contact based on the interference fringes that meet a preset order. Wherein, the interference fringes formed by the method proposed in this invention are all of equal thickness interference. The concept of equal thickness interference means that the same interference fringe will be formed at the location of gaps of the same thickness.

[0052] The above-mentioned step of determining the area on the welding surface that has not been welded but has formed optical contact based on the interference fringes that meet the preset order can be carried out in the following way: according to the order of each determined interference fringe, select the interference fringes according to the preset rules, and take the area enclosed by the selected interference fringes as the optical contact area to be welded. Wherein, the preset rules can be to select the nth order interference fringe according to the priority from low to high order. In a specific embodiment of the present invention, the identification of the area on the welding surface that has not been welded but has formed optical contact using the traditional computer vision method includes the following steps: (1) Image preprocessing step, according to the quality of the acquired optical interference image, perform grayscale conversion, filtering, binarization, normalization and / or equalization on the acquired optical interference image to improve the contrast of the interference fringes contained in the optical interference image. (2) Extract the fringe coordinates of each interference fringe contained in the preprocessed optical interference image and determine the order of each interference fringe. Wherein, extracting the fringe coordinates is to establish a correlation between the fringe and the position on the welding surface, and establishing the order relationship is to indirectly determine which positions on the welding surface have a gap width small enough to meet the standard of forming optical contact based on the order of the interference fringes. (3) Determine the area where optical contact is formed on the welding surface based on interference fringes of a preset order. Combine all areas where optical contact is formed to determine the area on the welding surface where optical contact has been formed but not welded. Alternatively, interference fringes of a suitable order can be selected or adjusted as the boundary of the optical contact area based on welding experience. Optionally, in a preferred embodiment, morphological operations, edge detection, and contour finding can also be performed on the image after image preprocessing.

[0053] Using this embodiment of the invention, the system structure for large-area ultrafast laser welding is simple. It only requires adding an optical image acquisition system to the existing ultrafast laser welding system. The traditional computer vision method used in this embodiment of the invention can quickly identify areas on the welding surface that have not been welded but have formed optical contact by utilizing the characteristics of interference fringes, which greatly simplifies the process of determining the areas that have formed optical contact.

[0054] In some embodiments of the present invention, identifying regions on the welding surface that are not welded but have formed optical contact includes: inputting the optical interference image into a pre-trained deep learning model to obtain the output boundary coordinates of the regions on the welding surface that are not welded but have formed optical contact. The training set of the deep learning model includes an optical interference image formed before welding of the workpiece and equal-thickness interference fringe markings in the optical interference image, thereby selecting equal-thickness interference fringes, and determining the boundary coordinates of the regions on the welding surface that are not welded but have formed optical contact based on the areas circled by the selected equal-thickness interference fringes.

[0055] In a specific embodiment of the present invention, a pre-trained deep learning model is used to identify areas on the welding surface that have not been welded but have formed optical contact, including the following steps: (1) Constructing a training set. An optical interference image of the workpiece sample before welding is captured, and the fringes contained in the optical interference image are labeled according to the welding effect (only equal-thickness interference fringes can be labeled, or different types of fringes can be labeled separately) to form a training set. The total number of images in the training set is generally not less than 10. (2) Training the model. Using the constructed training set, a suitable semantic segmentation model is selected as the initial model for training. These algorithm models include, but are not limited to: U-Net, DeepLabV3+, HRNet, MobieNet, and PSPNet models.

[0056] Using this embodiment of the invention, the system structure for large-area ultrafast laser welding is simple. It only requires adding an optical image acquisition system to the existing ultrafast laser welding system. The deep learning method used in this embodiment of the invention can utilize the characteristics of interference fringes to quickly identify areas on the welding surface that have not been welded but have formed optical contact, which greatly simplifies the process of determining the areas that have formed optical contact.

[0057] In some embodiments of the present invention, welding the area to be welded using ultrafast laser includes: determining an ultrafast laser welding trajectory capable of filling the area to be welded using a Z-shaped scanning filling algorithm, an offset filling algorithm, a sub-regional scanning filling algorithm, a spiral scanning filling algorithm, a concentric circular arc filling method, or a fractal scanning filling algorithm; and using an optical system to control the ultrafast laser generated by the laser to move along the ultrafast laser welding trajectory, thereby realizing the welding of the workpiece in the area to be welded.

[0058] Using this embodiment of the invention, the ultrafast laser welding trajectory can be determined using a variety of filling algorithms. By controlling the ultrafast laser to move along the ultrafast laser welding trajectory determined in the aforementioned steps, ultrafast laser welding that forms an optical contact area on the workpiece can be achieved.

[0059] In some embodiments of the present invention, when the preset condition includes the proportion of the welded area on the welding surface exceeding a preset threshold, starting from the second execution of the image acquisition step, the image acquisition step further includes: counting the number of pixels occupied by the welding surface in the image, counting the number of pixels occupied by the welded area in the image in the previous region welding steps; calculating the quotient of the number of pixels occupied by the welded area in the image and the number of pixels occupied by the welding surface in the image as the proportion of the welded area on the welding surface.

[0060] In some embodiments of the present invention, the method further includes repeating the image acquisition step and the area welding step until a preset condition is met, and then using an ultrafast laser to scan the welding surface again to enhance the welding strength of the workpiece.

[0061] By employing this embodiment of the invention, the proportion of the welded area on the welding surface can be determined by utilizing the pixel ratio, thereby determining the "progress" of ultrafast laser welding, which is beneficial for accurately grasping the progress and welding reliability of ultrafast laser welding.

[0062] Figure 3 The following is a flowchart of a method for large-area ultrafast laser welding according to another embodiment of the present invention. The method includes the following steps: First, the workpieces to be welded are tightly fitted together. Then, the workpieces are placed below an optical image acquisition system to obtain an initial optical image of the welding surface. Next, optical contact area analysis and welding steps are performed. The analysis identifies areas that have not been welded but have formed optical contact. Based on a filling algorithm, an ultrafast laser welding trajectory is determined to fill the optical contact area. Welding is performed according to the planned ultrafast laser welding trajectory. The system moves below the optical image acquisition system to acquire an image and determines whether welding has been completed. If so, the process ends; otherwise, the optical contact area analysis and welding steps are repeated.

[0063] Corresponding to the above method, the present invention also provides a system for large-area ultrafast laser welding. This system implements the steps of any of the methods described in the above embodiments. The system includes: a horizontal displacement platform for placing two workpieces with flat welding surfaces in contact with each other; wherein at least one of the two workpieces is transparent relative to the working wavelength of the ultrafast laser; an optical image acquisition system for acquiring images of the welded surfaces in contact with each other; a computing system for identifying, based on the acquired images of the welded surfaces, unwelded areas that have formed optical contact on the welded surfaces as areas to be welded; an ultrafast laser welding system for welding the areas to be welded using an ultrafast laser, thereby achieving welding of the two workpieces in the areas to be welded; the computing system is further used to determine, during the repetition of the image acquisition step and the area welding step, whether a preset condition for control termination has been met; wherein the preset condition includes one or more of the following: the repetition reaches a preset number of times, no new unwelded areas that have formed optical contact can be identified on the welded surfaces, and the proportion of welded areas on the welded surfaces exceeds a preset threshold.

[0064] Using this embodiment of the invention is beneficial for realizing the method for large-area ultrafast laser welding described in the foregoing embodiments of the invention.

[0065] In some embodiments of the welding system of the present invention, the ultrafast laser welding system includes a laser and an optical system, the laser being used to generate an ultrafast laser, and the ultrafast laser welding trajectory being controlled by the optical system and / or a horizontal displacement platform.

[0066] In some embodiments of the welding system of the present invention, on the one hand, the optical system can be composed of a scanning galvanometer and a field lens. During ultrafast laser welding, the field lens remains stationary, and the scanning galvanometer controls the ultrafast laser welding trajectory by controlling changes in the two-dimensional optical path. On the other hand, the optical system can be composed of a focusing lens. During ultrafast laser welding, the ultrafast laser is focused on or near the welding surface, and welding is achieved along the ultrafast laser welding trajectory by moving the horizontal displacement platform.

[0067] Using the above-described embodiments of the invention, ultrafast laser welding trajectory control can be achieved either through a "scanning galvanometer + field mirror" or through a "focusing mirror + horizontal displacement stage". That is, the workpiece can be controlled to move while the laser does not move, or the laser can be controlled to move while the workpiece does not move.

[0068] Figure 2This is a schematic diagram of a system structure for large-area ultrafast laser welding according to an embodiment of the present invention. A workpiece 202 is placed on a horizontal displacement platform 201. By moving the horizontal displacement platform 201, the workpiece can be moved below an optical image acquisition system 203. The optical image acquisition system 203 acquires an optical interference image of the workpiece 202. Since at least the portion above the welding surface of the workpiece 202 is transparent in a preset wavelength band (this preset wavelength band can be the infrared band or a certain range near the working wavelength of the ultrafast laser), the optical interference image of the welding surface can be observed using the optical image acquisition system (for example, by using an infrared microscope to examine the silicon wafer). The optical interference image is transmitted to a computing system 206. The computing system 206 uses a traditional image recognition algorithm or a pre-trained deep learning model to identify equal-thickness interference fringes in the optical interference image. Based on the area covered or occupied by the equal-thickness interference fringes, it delineates the area where the two workpieces have met the optical contact condition. The ultrafast laser welding system, composed of a laser 204 and an optical system 205, then welds the identified area that meets the optical contact condition. The computing system 206 can be a computer. The horizontal displacement platform 201 can be a horizontal precision displacement stage, and the optical image acquisition system 203 can acquire multiple optical interference sub-images according to a set image acquisition rule. Based on the set image acquisition rule, the positional relationship between the optical interference sub-images is determined, and thus an optical interference image covering the entire workpiece is obtained by stitching together all the acquired optical interference sub-images. The set image acquisition rule can be a fixed distance between adjacent acquisitions by the image acquisition system, based on which the positional relationship between the optical interference sub-images can be determined; or the image acquisition area can be divided into multiple preset points, and the positional relationship between the optical interference sub-images can be determined based on the positional relationship between the multiple preset points.

[0069] Figure 4 This is a schematic diagram illustrating the principle of optical contact area recognition in one embodiment of the present invention, specifically the analysis process of the computing system 206 after receiving the optical interference image. This analysis process includes: inputting the optical interference image of the workpiece contact surface before welding into a pre-trained deep learning neural network or a tuned traditional computer vision algorithm, and outputting the boundary of the optical contact area. During the training of the deep learning neural network, a dataset created from multiple welding feedbacks is used for training.

[0070] Figure 5 This is a schematic diagram of the ultrafast laser welding principle in one embodiment of the present invention. It illustrates the gradual expansion of the weldable area during multiple welding rounds and provides a graphical representation of the newly added optical contact area after multiple welding processes. Figure 5 This allows for a clearer demonstration of the implementation principle of this solution, the feasibility of which has been experimentally verified in numerous materials.

[0071] Figure 6 This is a schematic diagram of the structure of an optical system in one embodiment of the present invention. Figure 6 (a) is composed of a beam expander 601, a scanning galvanometer 602, and a field lens 603. Figure 6 (b) consists of a beam expander 601 and a focusing lens 604, representing two optional optical system configurations. Figure 6 In embodiment (a), the horizontal displacement platform can be kept stationary while the trajectory of the ultrafast laser is moved by adjusting the scanning galvanometer 602. Figure 6 In embodiment (a), the position of the workpiece can be moved by moving the horizontal displacement platform. Optionally, the beam expander 601 may be omitted.

[0072] The method and system for large-area ultrafast laser welding proposed in this invention utilize the characteristic that the area welded by the ultrafast laser reduces the gap between the surrounding unwelded areas, thereby expanding to form an optical contact area. This allows welding of the newly added optical contact area, achieving ultrafast laser welding of two workpieces as a whole. This method solves the problem of ultrafast laser welding of large-area welding surfaces and eliminates the need for repeated ultrafast laser scanning of the entire welding surface, thus saving processing efficiency. Furthermore, since the phenomenon of outward expansion of the optical contact area can be observed in various materials, this method has greater applicability to welding materials.

[0073] Furthermore, the system for large-area ultrafast laser welding is simple in structure, requiring only the addition of an optical image acquisition system to an existing ultrafast laser welding system.

[0074] Furthermore, this solution only requires one scan of the unwelded area by an ultrafast laser to complete the welding process, eliminating the need for repeated scans of the entire welding surface by an ultrafast laser, which is beneficial for improving welding efficiency.

[0075] Those skilled in the art will understand that the exemplary components, systems, and methods described in conjunction with the embodiments disclosed herein can be implemented in hardware, software, or a combination of both. Whether implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this invention. When implemented in hardware, it can be, for example, electronic circuits, application-specific integrated circuits (ASICs), appropriate firmware, plug-ins, function cards, etc. When implemented in software, the elements of this invention are programs or code segments used to perform the desired tasks. The programs or code segments can be stored in a machine-readable medium or transmitted over a transmission medium or communication link via data signals carried in a carrier wave.

[0076] It should be clarified that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of the present invention.

[0077] In this invention, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with or in place of features of other embodiments.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications and variations of the embodiments of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for large area ultrafast laser welding, characterized in that, The method comprises: a workpiece fitting step of fitting flat welding surfaces of two workpieces to each other, wherein at least one of the two workpieces is transparent to a working wavelength of the ultrafast laser; an image acquisition step of acquiring an image of the welding surfaces fitted to each other, identifying an area on the welding surface that is not welded but has formed optical contact according to the acquired image of the welding surface, and taking the identified area as a next area to be welded; a region welding step of welding the area to be welded by using the ultrafast laser, so that the two workpieces are welded in the area to be welded, and the area welded by the ultrafast laser reduces the gap of the surrounding non-welded area, thereby expanding the area of optical contact outward, and thus welding the newly added optical contact area to achieve the overall ultrafast laser welding of the two workpieces; repeating the image acquisition step and the region welding step until a preset condition is reached, wherein the preset condition comprises one or more of the following: repeating a preset number of times, no longer being able to identify a new area on the welding surface that is not welded but has formed optical contact, and the proportion of the welded area on the welding surface exceeding a preset threshold.

2. The method of claim 1, wherein, Before the workpiece fitting step, the method further comprises a workpiece pretreatment step of treating the two workpieces by using a chemical cleaning method.

3. The method of claim 1, wherein, The image of the welding surface is an optical interference image acquired by using an optical image acquisition system; The image acquisition of the welding surfaces fitted to each other comprises moving the two workpieces fitted to each other below an optical image acquisition system by using a horizontal displacement platform, so as to acquire an optical interference image of the two workpieces on the welding surface by using the optical image acquisition system.

4. The method of claim 3, wherein, The identification of the area on the welding surface that is not welded but has formed optical contact comprises: preprocessing the acquired optical interference image to improve the contrast of the interference fringes contained therein; extracting the fringe coordinates of each interference fringe contained in the preprocessed optical interference image, and determining the order of each interference fringe; determining the area on the welding surface that is not welded but has formed optical contact according to the interference fringes that meet the preset order.

5. The method of claim 3, wherein, The identification of the area on the welding surface that is not welded but has formed optical contact comprises inputting the optical interference image into a pre-trained deep learning model to obtain the output area boundary coordinates of the area on the welding surface that is not welded but has formed optical contact. The training set of the deep learning model comprises optical interference images formed before workpiece welding and annotations of equal-thickness interference fringes in the optical interference images according to welding effects.

6. The method of claim 1, wherein, The welding of the area to be welded by using the ultrafast laser comprises: determining an ultrafast laser welding track capable of filling the area to be welded by using a Z-scan filling algorithm, a bias filling algorithm, a regional scanning filling algorithm, a spiral scanning filling algorithm, a concentric arc filling algorithm, or a fractal scanning filling algorithm; moving the ultrafast laser generated by the optical system along the ultrafast laser welding track, thereby achieving the welding of the workpiece in the area to be welded.

7. The method of claim 1, wherein, When the preset condition includes that the proportion of the welded area on the welding surface exceeds a preset threshold, from the second time the image acquisition step is performed, the image acquisition step further includes: counting the pixels occupied by the welding surface in the image, and counting the pixels occupied by the welded area in the image before the area welding step; calculating the quotient of the pixels occupied by the welded area in the image and the pixels occupied by the welding surface in the image as the proportion of the welded area on the welding surface.

8. The method of claim 1, wherein, After repeating the image acquisition step and the area welding step until the preset condition is reached, the method further includes: again using the ultrafast laser to scan the welding surface to enhance the welding strength of the workpiece.

9. A system for large area ultrafast laser welding, characterized in that, The system is used to implement the steps of the method according to any one of claims 1-8, and the system includes: a horizontal displacement platform for placing two workpieces with flat welding surfaces abutting each other; wherein at least one of the two workpieces is transparent to the operating wavelength of the ultrafast laser; an optical image acquisition system for acquiring images of the abutting welding surfaces; a computing system for identifying, based on the acquired images of the welding surfaces, areas on the welding surfaces that have not been welded but have formed optical contact as areas to be welded; an ultrafast laser welding system for welding the areas to be welded using an ultrafast laser, so that the two workpieces are welded at the areas to be welded; the computing system is further configured to determine whether a preset condition for terminating control is reached when repeating the image acquisition step and the area welding step; wherein the preset condition includes one or more of the following: repeating a preset number of times, no new area on the welding surface that has not been welded but has formed optical contact can be identified, and the proportion of the welded area on the welding surface exceeds a preset threshold.

10. The system of claim 9, wherein, The ultrafast laser welding system includes a laser for generating an ultrafast laser, and an optical system for controlling the ultrafast laser welding trajectory using the horizontal displacement platform and / or the optical system.

11. The system of claim 10, wherein, The optical system is composed of a scanning galvanometer and a field lens, and the field lens remains stationary during ultrafast laser welding, and the scanning galvanometer controls the ultrafast laser welding trajectory by controlling the change of the two-dimensional light path; or The optical system is composed of a focusing lens, which focuses the ultrafast laser on or near the welding surface during ultrafast laser welding, and the welding is achieved along the ultrafast laser welding trajectory by moving the horizontal displacement platform.

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