Method and system for large-area ultrafast laser welding

Abstract

The invention provides a method and system for large-area ultrafast laser welding, and the method comprises the following steps: a workpiece attaching step: enabling flat welding surfaces of two workpieces to be attached to each other; an image acquisition step: acquiring images of the mutually attached welding surfaces, identifying areas which are not welded but have formed optical contact on the welding surfaces according to the acquired images of the welding surfaces, and taking the identified areas as areas to be welded in the next step; an area welding step: welding the to-be-welded area by using ultrafast laser, so that the two workpieces are welded in the to-be-welded area; repeating the image acquisition step and the area welding step until a preset condition is met; wherein the preset condition comprises one or more of the following items: repeating for a preset number of times, not identifying a new non-welded area which is in optical contact on the welding surface any more, and enabling the proportion of the welded area on the welding surface to exceed a preset threshold value. The problem of ultrafast laser welding of a large-area welding surface can be solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser processing, in particular to a method and system for large-area ultrafast laser welding. BACKGROUND

[0002] The ultrafast laser welding method has the characteristics of small heat-affected zone, no need for solder, and can be used for ultra-precision welding, and is widely used in the fields of semiconductors, automobile manufacturing, scientific research, and medical health. In principle, the ultrafast laser welding utilizes the nonlinear absorption effect of the interaction between the ultrashort pulse laser and the material, and the ultrafast laser welding acts on the local area to make the material melt. However, since the volume of the molten material that can be produced by the ultrafast laser welding is very small, the tolerance of the welding interface gap is very small, and it is generally required that the welding interface can achieve optical contact (the gap between the contact surfaces is less than 1 / 4 of the wavelength). Since the larger the welding area, the more difficult it is to control the overall fluctuation and the more difficult it is to maintain optical contact, how to use ultrafast laser welding to perform high-quality large-area welding becomes a problem to be solved.

[0003] Prior art 1 (patent number CN114160975A) proposes a large-area high-strength laser welding method for dissimilar materials, which realizes the composite output of long pulse laser and ultrafast laser by beam combination, and separates the focal points of the long pulse laser and the ultrafast laser to the predetermined position by optical regulation, so as to realize the optical lamination of the thermal expansion of the metal material and the transparent hard brittle material. However, since this scheme needs to use two beams of laser to combine, and needs to precisely regulate the focal point positions of the two beams of laser, the requirement for the optical system is high, the system structure is complex, and at the same time, this method depends on the thermal expansion of the metal, and for the metal material with low thermal expansion coefficient, this scheme may fail.

[0004] Prior art 2 (patent number CN119260171A) proposes a large-area high-strength laser welding method for dissimilar materials, which uses a multiple scanning method to utilize the absorption of the lower layer material to generate plasma, and the plasma expands and overflows to make the material near the welding surface melt and fill the gap, so as to achieve the quasi-optical contact condition. However, this scheme needs to perform multiple repeated ultrafast laser scanning, which reduces the processing efficiency.

[0005] Therefore, how to realize large-area, stable and high-quality ultrafast laser welding is a technical problem to be solved. SUMMARY

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

[0007] In one aspect of the present application, a method for large-area ultrafast laser welding is provided, comprising the following steps: a workpiece fitting step, in which flat welding surfaces of two workpieces are fitted to each other; at least one of the two workpieces is transparent to the operating wavelength of the ultrafast laser; an image acquisition step, in which images of the fitted welding surfaces are acquired, and un-welded but optically contacted areas on the welding surfaces are identified according to the acquired images of the welding surfaces, and the identified areas are used as the next areas to be welded; a regional welding step, in which the ultrafast laser is used to weld the areas to be welded, so that the two workpieces are welded in the areas to be welded; the image acquisition step and the regional welding step are repeated until a preset condition is reached; the preset condition includes one or more of the following: the repetition reaches a preset number of times, no new un-welded but optically contacted areas can be identified on the welding surface, and the proportion of the welded areas on the welding surface exceeds a preset threshold.

[0008] In some embodiments of the present application, before the workpiece fitting step, the method further comprises a workpiece pretreatment step, in which the two workpieces are treated using a chemical cleaning method.

[0009] In some embodiments of the present application, the images of the welding surfaces are optical interference images acquired by an optical image acquisition system; the image acquisition step includes moving the two workpieces fitted to each other under an optical image acquisition system using a horizontal displacement platform, and acquiring optical interference images of the two workpieces on the welding surface using the optical image acquisition system.

[0010] In some embodiments of the present application, identifying the un-welded but optically contacted areas on the welding surface includes: pre-processing the acquired optical interference images to improve the contrast of the interference fringes contained therein; extracting the fringe coordinates of each interference fringe contained in the pre-processed optical interference images, and determining the order of each interference fringe; determining the un-welded but optically contacted areas on the welding surface according to the interference fringes that meet the preset order.

[0011] In some embodiments of the present application, identifying the un-welded but optically contacted areas on the welding surface includes: inputting the optical interference images into a pre-trained deep learning model to obtain the output area boundary coordinates of the un-welded but optically contacted areas on the welding surface; the training set of the deep learning model includes optical interference images formed before workpiece welding and annotations of the equal-thickness interference fringes in the optical interference images according to the welding effect.

[0012] In some embodiments of the present application, the region to be welded is welded by using ultrafast laser, including: determining an ultrafast laser welding track capable of filling the region to be welded by using a Z-shaped scanning filling algorithm, a bias filling algorithm, a sub-region scanning filling algorithm, a spiral scanning filling algorithm, a concentric arc filling algorithm or a fractal scanning filling algorithm; and moving the ultrafast laser generated by a laser through an optical system along the ultrafast laser welding track, thereby achieving welding of the workpiece in the region to be welded.

[0013] In some embodiments of the present application, when the preset condition includes that the proportion of the welded region in 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 pixel points occupied by the welding surface in the image, and counting the pixel points occupied by the welded region in the image before the region welding step; and calculating the quotient of the pixel points occupied by the welded region in the image and the pixel points occupied by the welding surface in the image as the proportion of the welded region in the welding surface.

[0014] In some embodiments of the present application, the image acquisition step and the region welding step are repeated until the preset condition is reached, and the method further includes: again using the ultrafast laser to scan the welding surface to enhance the welding strength of the workpiece.

[0015] Corresponding to the above method, the present application also provides a system for large-area ultrafast laser welding, which is used to implement the steps of the method according to any one of the above embodiments, and the system includes: a horizontal displacement platform for placing two workpieces with flat welding surfaces adhered to each other; wherein at least one of the two workpieces is transparent to the working wavelength of the ultrafast laser; an optical image acquisition system for acquiring images of the adhered welding surfaces; a computing system for identifying, according to the acquired images of the welding surfaces, regions on the welding surfaces that have not been welded but have formed optical contact as regions to be welded; and an ultrafast laser welding system for welding the regions to be welded by using ultrafast laser, so that the two workpieces are welded in the regions to be welded; the computing system is further used to judge whether a preset condition for control termination is reached when the image acquisition step and the region welding step are repeated; wherein the preset condition includes one or more of the following: repeated for a preset number of times, no new region that has not been welded but has formed optical contact can be identified on the welding surface, and the proportion of the welded region in the welding surface exceeds a preset threshold.

[0016] In some embodiments of the present application, the ultrafast laser welding system includes a laser for generating ultrafast laser and an optical system for controlling the ultrafast laser welding track.

[0017] In some embodiments of the present application, the optical system is 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 the change of two-dimensional light path; or the optical system is composed of a focusing lens, during ultrafast laser welding, the ultrafast laser is focused on the welding surface or near the welding surface, and welding is realized along the ultrafast laser welding trajectory through the movement of the horizontal displacement platform.

[0018] By using the method and system for large-area ultrafast laser welding provided in the present application, the area welded by the ultrafast laser is reduced in the gap of the surrounding unwelded area, thereby the characteristics of outward expansion of the optical contact area can be used to weld the newly added optical contact area, so as to realize the overall ultrafast laser welding of two workpieces. This method not only solves the problem of ultrafast laser welding of a large-area welding surface, but also does not need to repeatedly scan the entire welding surface by the ultrafast laser, which is beneficial to saving processing efficiency. Moreover, the outward expansion of the optical contact area can be observed in various materials, so the method has stronger universality for welding materials.

[0019] Additional advantages, objects, and features of the application will be set forth in part by the description that follows, and will become apparent to those skilled in the art upon examination of the following detailed description and drawings in which

[0020] Those skilled in the art will appreciate that the objects and advantages of the application can be accomplished by the devices and processes described in detail herein, and that the application can be used in any number of ways not specifically described in the specification. The novel devices and processes described herein can be implemented in a convenient, efficient, and effective manner by using, as appropriate, any of the devices and processes described in the specification. BRIEF DESCRIPTION OF DRAWINGS

[0021] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description, serve to explain the principles of the application. The components in the drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the application. Portions of some embodiments of the application can be exaggerated in order to emphasize its features, which can make those portions appear larger than in a real-world implementation of the exemplary device. In the drawings: Figure 1 Flow chart of the method for large-area ultrafast laser welding in an embodiment of the present application.

[0022] Figure 2 Structure schematic diagram of the system for large-area ultrafast laser welding in an embodiment of the present application.

[0023] Figure 3 Flow chart of the method for large-area ultrafast laser welding in another embodiment of the present application.

[0024] Figure 4 The figure is a schematic diagram of the identification principle of the optical contact area in an embodiment of the present application.

[0025] Figure 5 The figure is a schematic diagram of the principle of ultrafast laser welding in an embodiment of the present application.

[0026] Figure 6 The figure is a schematic diagram of the structure of the optical system in an embodiment of the present application. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments and the accompanying drawings. Herein, the illustrative embodiments of the present application and the descriptions thereof are used to explain the present application, but are not intended to limit the present application.

[0028] It should be noted that, in order to avoid the present application being obscured by unnecessary details, only the structures and / or processing steps closely related to the solutions according to the present application are shown in the accompanying drawings, and other details not closely related to the present application are omitted.

[0029] It should be emphasized that the term “comprises / comprising” as used herein means the presence of the stated features, elements, steps or components, but does not preclude the presence or addition of one or more other features, elements, steps or components.

[0030] It should be noted that, if not specifically stated, the term “connected” as used herein can not only mean direct connection, but also indirect connection with an intermediate object.

[0031] In the following, embodiments of the present application will be described with reference to the accompanying drawings. In the accompanying drawings, the same reference signs represent the same or similar parts or the same or similar steps.

[0032] In order to achieve large-format, stable, and high-quality ultrafast laser welding, and to avoid the dependence on the thermal expansion of the metal and the reduction of the processing efficiency caused by repeated ultrafast laser scanning, the present application proposes a method and system for large-area ultrafast laser welding. The principle is that the area welded by the ultrafast laser will reduce the gap of the surrounding unwelded area, thereby expanding the optical contact area, and by continuously welding the newly added optical contact area, the welding of the entire sample is ultimately achieved.

[0033] It needs to be declared that the optical contact in the present application is used to refer to the area with better contact on the welding surface, which means that the width of the air gap formed on the welding surface is less than the preset proportion of the wavelength of the monochromatic light (or laser) used for observing and measuring the interference fringes. The preset proportion can be 1 / 4 or 1 / 2, and can also be 2 times, 4 times or 10 times. The present application is not limited to this, and the preset proportion is only an example.

[0034] Figure 1 The flow chart of the method for large-area ultrafast laser welding in an embodiment of the present application. The method comprises the following steps: Step S110: workpiece fitting step, fitting the flat welding surfaces of two workpieces to each other. Among them, at least one of the two workpieces is transparent to the working wavelength of the ultrafast laser.

[0035] Step S120: image acquisition step, acquiring the image of the mutually fitted welding surface, identifying the area on the welding surface which is not welded but has formed optical contact according to the acquired image of the welding surface, and taking the identified area as the next area to be welded.

[0036] Among them, the image of the welding surface can be the image of the welding surface obtained by cutting along the welding surface profile on the basis of the originally acquired image.

[0037] Step S130: area welding step, welding the area to be welded by using the ultrafast laser, so that the two workpieces are welded in the area to be welded.

[0038] In the field of optics, the definition of optical contact is that the gap between two pieces of glass is less than one quarter of the wavelength of the illuminating light source, but in actual application, it does not need to be strictly limited within one quarter, and can be relaxed as appropriate, for example, it can be relaxed to one half of the wavelength, two times the wavelength or ten times the wavelength.

[0039] Step S140: repeating the image acquisition step and the area welding step until a preset condition is reached; wherein the preset condition includes one or more of the following: repeating a preset number of times, no new area on the welding surface which is not welded but has formed optical contact can be identified, and the proportion of the welded area on the welding surface exceeds a preset threshold.

[0040] Among them, the large area of the present application refers to the area of the laser welding surface greater than 10mm*10mm, and the current laser welding area is generally within 10mm*10mm.

[0041] The method for large-area ultrafast laser welding provided by the application can reduce the gap of the surrounding non-welded area of the area welded by the ultrafast laser, thereby forming the characteristics of the outward expansion of the optical contact area, welding the newly added optical contact area, and realizing the overall ultrafast laser welding of the two workpieces. The method solves the problem of large-area welding surface ultrafast laser welding and does not need to repeatedly scan the entire welding surface by the ultrafast laser, which is beneficial to saving processing efficiency. Moreover, the outward expansion of the optical contact area can be observed in various materials, and the method has stronger universality for welding materials. The material above the workpiece can be a silicon wafer.

[0042] In some embodiments of the application, before the workpiece bonding step, the method further comprises a workpiece pretreatment step of treating the two workpieces by a chemical cleaning method. The chemical cleaning method includes but is not limited to using a degreasing cleaning agent to remove oil stains on the surface of the workpiece and using a rust removal cleaning agent to remove the oxide layer on the surface of the workpiece.

[0043] By using the embodiments of the application, the oil stains and / or oxide layer that may exist on the surface of the workpiece can be removed by the chemical cleaning method, which can make the welding surface of the workpiece more flat and avoid the interference of the oil stains and / or oxide layer on the ultrafast laser welding.

[0044] In some embodiments of the application, the image of the welding surface is an optical interference image collected by an optical image collection system.

[0045] Correspondingly, the collection of the image of the mutually bonded welding surface comprises moving the two workpieces that are mutually bonded to below an optical image collection system by using a horizontal displacement platform, and collecting the optical interference image of the two workpieces on the welding surface by using the optical image collection system.

[0046] The principle of identifying the area of the welding surface that is not welded but has formed optical contact by using the optical interference image is that when two pieces of glass are tightly bonded, the interference fringes formed by the optical contact area are an equal-thickness interference, which can be described by the following formula: wherein e is the gap between the two pieces of glass, is the wavelength of the illumination light source, and k is the order of the interference fringes (also known as bright and dark fringes). The definition of optical contact is , and the calculation by using the above formula can obtain that it corresponds to the first-order bright fringe (in actual application, the optical contact does not need to be strictly limited within , and it can be relaxed as appropriate). Therefore, the problem of finding the boundary of the optical contact area is transformed into the problem of finding the corresponding fringes (i.e. the equal-thickness interference fringes) in the optical interference image, which can be solved by using traditional computer vision methods or deep learning methods. Refers to the wavelength of monochromatic light or laser used for observing and measuring interference fringes.

[0047] With the embodiment of the application, image acquisition can be realized by using a horizontal displacement platform and an optical image acquisition system, and the area on the welding surface that has not been welded but has formed optical contact can be accurately acquired, which is beneficial to subsequent accurate local area ultrafast laser welding and avoids repeated scanning (welding) of the entire welding surface by the ultrafast laser. The method converts the problem of finding the boundary of optical contact into the problem of finding the equal-thickness interference fringes in the optical interference image, and the problem can be solved by using a traditional computer vision method or a deep learning method.

[0048] In some embodiments of the application, the area on the welding surface that has not been welded but has formed optical contact is identified by: pre-processing 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 pre-processed optical interference image and determining the order of each interference fringe; and determining the area on the welding surface that has not been welded but has formed optical contact according to the interference fringes that meet the preset order. The interference fringes formed based on the method proposed in the application are all equal-thickness interference, and the concept of equal-thickness interference refers to that the same interference fringe is formed at the position of the same thickness gap.

[0049] The step of determining the region of the welding surface which has not been welded but has formed optical contact according to the interference fringes of the preset order can be implemented in the following manner: according to the order of each interference fringe which has been determined, selecting the interference fringes according to a preset rule, and taking the region enclosed by the selected interference fringes as the optical contact region which needs to be welded. The preset rule can be selecting the interference fringes of the nth order according to the priority from low to high. In an embodiment of the present application, the region of the welding surface which has not been welded but has formed optical contact is identified by using a traditional computer vision method, including the following steps: (1) an image preprocessing step, according to the quality of the collected optical interference image, performing operations such as graying, filtering, binarization, normalization and / or equalization on the collected optical interference image, so as to improve the contrast of the interference fringes contained in the optical interference image. (2) extracting the fringe coordinates of each interference fringe contained in the optical interference image after preprocessing, and determining the order of each interference fringe. The fringe coordinates are extracted in order to associate the fringes with the positions on the welding surface, and the order is established in order to indirectly determine which positions on the welding surface have a gap width which has been reduced to the standard of forming optical contact based on the order of the interference fringes. (3) determining the region of the welding surface which has formed optical contact according to the interference fringes of the preset order. The regions which have formed optical contact are integrated, so as to determine the region of the welding surface which has not been welded but has formed optical contact. In addition, the interference fringes of the appropriate order can also be selected or adjusted as the boundary of the optical contact region according to welding experience. Optionally, in a preferred embodiment, the image after the image preprocessing step can also be subjected to morphological operations, edge detection and contour searching operations.

[0050] By using the embodiment of the present application, the system used in the method for large-area ultrafast laser welding has a simple structure, and only needs to add an optical image acquisition system on the basis of an existing ultrafast laser welding system. The traditional computer vision method used in the embodiment of the present application can quickly identify the region of the welding surface which has not been welded but has formed optical contact by using the characteristics of the interference fringes, and greatly simplifies the process of determining the region which has formed optical contact.

[0051] In some embodiments of the present application, the region of the welding surface which has not been welded but has formed optical contact is identified by inputting the optical interference image into a pre-trained deep learning model to obtain the output region boundary coordinates of the region of the welding surface which has not been welded but has formed optical contact. The training set of the deep learning model includes optical interference images formed before workpiece welding and annotations of the equal-thickness interference fringes in the optical interference images, so as to select the equal-thickness interference fringes and determine the region boundary coordinates of the region of the welding surface which has not been welded but has formed optical contact according to the region enclosed by the selected equal-thickness interference fringes.

[0052] In a specific embodiment of the present application, a pre-trained deep learning model is used to identify the area on the welding surface that has not been welded but has formed optical contact, including the following steps: (1) constructing a training set step. An optical interference image formed before welding of a workpiece sample is photographed, and the fringes contained in the optical interference image are labeled according to the welding effect (only the equal-thickness interference fringes can be labeled, or different types of fringes can be labeled separately), forming a training set, and the total number of pictures in the training set is generally not less than 10. (2) training model step. Using the constructed training set, select a suitable semantic segmentation model as the initial model for training, these algorithm models include but are not limited to: U-Net, DeepLabV3+, HRNet, MobieNet and PSPNet model.

[0053] By adopting the embodiment of the present application, the system used in the method for large-area ultrafast laser welding has a simple structure, and only needs to add an optical image acquisition system on the basis of the existing ultrafast laser welding system. The deep learning method used in the embodiment of the present application can quickly identify the area on the welding surface that has not been welded but has formed optical contact by using the characteristics of interference fringes, greatly simplifying the process of judging the area where optical contact is formed.

[0054] In some embodiments of the present application, the area to be welded is welded by ultrafast laser, including: determining the ultrafast laser welding track capable of filling the area to be welded by using Z-shaped scanning filling algorithm, offset filling algorithm, regional scanning filling algorithm, spiral scanning filling algorithm, concentric arc filling method or fractal scanning filling algorithm; the optical system is used to control the ultrafast laser generated by the laser to move along the ultrafast laser welding track, thereby realizing the welding of the workpiece in the area to be welded.

[0055] By adopting the embodiment of the present application, the ultrafast laser welding track can be determined by using various filling algorithms, and the ultrafast laser is controlled to move along the ultrafast laser welding track determined in the foregoing step, thereby realizing the ultrafast laser welding of the workpiece to form the optical contact area.

[0056] In some embodiments of the present application, when the preset condition includes that the proportion of the welded area on the welding surface exceeds a preset threshold, from the second time of executing the image acquisition step, the image acquisition step further includes: counting the pixel points occupied by the welding surface in the image, and counting the pixel points occupied by the welded area in the image before the area welding step; calculating the quotient of the pixel points occupied by the welded area in the image and the pixel points occupied by the welding surface in the image as the proportion of the welded area on the welding surface.

[0057] In some embodiments of the present application, the image acquisition step and the region welding step are repeated until a preset condition is reached, and the method further comprises: using the ultrafast laser to scan the welding surface again to enhance the welding strength of the workpiece.

[0058] According to the embodiments of the present application, the proportion of the welded region in the welding surface can be determined by the pixel point proportion, so as to determine the progress of the ultrafast laser welding, which is beneficial to accurately grasp the progress and welding strength of the ultrafast laser welding.

[0059] Figure 3 For the method flowchart for large-area ultrafast laser welding in another embodiment of the present application, the method comprises the following steps: firstly, the workpieces to be welded are closely attached, and then the workpieces are placed under the optical image acquisition system to obtain the initial optical picture of the welding surface. Then, the optical contact region analysis and welding step are performed, the region which is not welded but has formed optical contact is analyzed, the ultrafast laser welding track for filling the region with optical contact is determined based on the filling algorithm, welding is performed according to the planned ultrafast laser welding track, the image is acquired by moving under the optical image acquisition system, and it is judged whether the welding has been completed. If yes, the process is ended, and if no, the optical contact region analysis and welding step are repeated.

[0060] Corresponding to the above method, the present application also provides a system for large-area ultrafast laser welding, which is used to implement the steps of the method in any of the above embodiments. The system comprises: a horizontal displacement platform for placing two workpieces with flat welding surfaces attached to each other; wherein at least one of the two workpieces is transparent to the working wavelength of the ultrafast laser; an optical image acquisition system for acquiring images of the attached welding surfaces; a computing system for identifying, according to the acquired images of the welding surfaces, the region on the welding surface which is not welded but has formed optical contact as a region to be welded; an ultrafast laser welding system for welding the region to be welded using an ultrafast laser, so that the two workpieces are welded in the region to be welded; and the computing system is further configured to judge whether a preset condition for control termination is reached when the image acquisition step and the region welding step are repeated; wherein the preset condition comprises one or more of the following: repeated for a preset number of times, no new region which is not welded but has formed optical contact can be identified on the welding surface, and the proportion of the welded region in the welding surface exceeds a preset threshold.

[0061] According to the embodiments of the present application, the method for large-area ultrafast laser welding in the above embodiments can be implemented.

[0062] In some embodiments of the welding system of the present application, 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 optical system and / or a horizontal displacement platform.

[0063] In some embodiments of the welding system of the present application, in one aspect, the optical system can be composed of a scanning galvanometer and a field lens, which 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. In another aspect, the optical system can be composed of a focusing lens, which focuses the ultrafast laser on or near the welding surface, and the welding is achieved along the ultrafast laser welding trajectory by the movement of the horizontal displacement platform.

[0064] Using the above embodiments of the present application, the ultrafast laser welding trajectory can be controlled by either the "scanning galvanometer + field lens" or the "focusing lens + horizontal displacement platform", i.e., the workpiece itself can be moved while the laser remains stationary, or the laser can be moved while the workpiece remains stationary.

[0065] Figure 2A schematic diagram of a system structure for large-area ultrafast laser welding in an embodiment of the present application. The workpiece 202 is placed on the horizontal displacement platform 201, and by moving the horizontal displacement platform 201, the workpiece can be moved under the optical image acquisition system 203, and the optical interference image of the workpiece 202 is acquired by the optical image acquisition system 203. Since at least the part above the welding surface of the workpiece 202 is transparent in the preset waveband (which can be the infrared waveband or a certain range near the working wavelength of the ultrafast laser), the optical interference image of the welding surface can be observed by means of the optical image acquisition system (for example, the silicon wafer can be viewed through an infrared microscope), and the optical interference image is transmitted to the operation system 206. The operation system 206 uses a traditional image recognition algorithm or a pre-trained deep learning model to identify the equal-thickness interference fringes in the optical interference image, and based on the area covered or occupied by the equal-thickness interference fringes, the area where the two workpieces have met the optical contact condition is circled, and then the ultrafast laser welding system composed of the laser 204 and the optical system 205 is used to weld the area that meets the optical contact condition. The operation 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 the set image acquisition rule, determine the positional relationship between the optical interference sub-images based on the set image acquisition rule, and then splice the optical interference image covering the entire workpiece based on all the acquired optical interference sub-images. The set image acquisition rule can be that the adjacent image acquisition systems are spaced at a fixed distance, and based on the fixed distance, 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 based on the positional relationship between the multiple preset points, the positional relationship between the optical interference sub-images can be determined.

[0066] Figure 4 A schematic diagram of the identification principle of the optical contact area in an embodiment of the present application, that is, the analysis process of the operation system 206 after receiving the optical interference image. The 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 trained traditional computer vision algorithm, and outputting the boundary of the optical contact area. In the training process of the deep learning neural network, a dataset made by multiple welding feedbacks is used for training.

[0067] Figure 5 A schematic diagram of the ultrafast laser welding principle in an embodiment of the present application. It shows the gradual expansion process of the welding area in multiple welding processes, and gives a graphical representation of the newly added optical contact area in multiple welding. Figure 5 The implementation principle of the present scheme can be more clearly shown, and this principle has been experimentally demonstrated on many materials.

[0068] Figure 6 Figure 1 is a schematic diagram of an optical system according to an embodiment of the present application. Figure 6 (a) is composed of a beam expander 601, a scanning galvanometer 602 and a field lens 603, Figure 6 (b) is composed of a beam expander 601 and a focusing lens 604, which are two optional modes of the optical system. Figure 6 The embodiment of (a) can keep the horizontal displacement platform stationary and adjust the trajectory of the ultrafast laser by adjusting the scanning galvanometer 602. Figure 6 The embodiment of (a) can move the position of the workpiece by moving the horizontal displacement platform. Alternatively, the beam expander 601 can be omitted.

[0069] The method and system for large-area ultrafast laser welding according to the present application can reduce the gap of the surrounding non-welded area by using the area welded by the ultrafast laser, thereby expanding the area of optical contact outward, welding the newly added optical contact area, and achieving the overall ultrafast laser welding of two workpieces. This method not only solves the problem of large-area welding surface ultrafast laser welding, but also does not require the ultrafast laser to repeatedly scan the entire welding surface, which is beneficial to saving processing efficiency. Moreover, the outward expansion of the optical contact area can be observed in various materials, and the method has stronger universality for welding materials.

[0070] Furthermore, the system for large-area ultrafast laser welding is simple in structure, and only needs to add an optical image acquisition system to the existing ultrafast laser welding system to achieve the welding.

[0071] Furthermore, the present scheme only needs to scan the non-welded area once by the ultrafast laser to complete the welding, without the need to use the ultrafast laser to repeatedly scan the entire welding surface multiple times, which is beneficial to improving the welding efficiency.

[0072] Those skilled in the art should 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 the implementation is in hardware or software depends on the specific application and design constraints imposed on the overall system. Skilled persons can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application. When implemented in hardware, it can be, for example, an electronic circuit, an application specific integrated circuit (ASIC), appropriate firmware, a plug-in, a functional card, etc. When implemented in software, the elements of the present application are program or code segments used to perform the required tasks. The program or code segments can be stored in a machine-readable medium or transmitted through a data signal carried in a carrier wave in a transmission medium or communication link.

[0073] It is to be understood that the application is not limited to particular configurations and processes described herein and shown in the drawings, which can vary. For the sake of brevity and clarity, detailed descriptions of well-known methods and processes are omitted. In the above embodiments, several specific steps are described and / or illustrated as examples. However, the method processes of the present application are not limited to the specific steps described and / or illustrated, and the order of the steps can be changed, and / or two or more steps can be combined into a single step, and / or a single step can be divided into two or more steps.

[0074] In the present application, features described and / or illustrated for one embodiment can be used in the same or a similar way for one or more other embodiments and / or combined with or substituted for features of other embodiments.

[0075] The above description is merely illustrative of the application, and is not intended to limit the scope of the application. Various modifications and changes can be made by persons of ordinary skill in the art, which should be included in the scope of the application as defined by the following claims.

Claims

1. A method for large-area ultrafast laser welding, characterized in that, include: The workpiece bonding step involves bonding the flat welding surfaces of two workpieces together; wherein at least one of the two workpieces is transparent relative to the working wavelength of the ultrafast laser. The image acquisition step involves acquiring images of the welded surfaces that are in contact with each other. Based on the acquired images of the welded surfaces, areas on the welded surfaces that are not welded but have formed optical contact are identified, and these identified areas are used as the areas to be welded in the next step. The area welding step utilizes an ultrafast laser to weld the area to be welded, thereby enabling the two workpieces to be welded in the area to be welded. 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.

2. The method according to claim 1, characterized in that, 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.

3. The method according to claim 1, characterized in that, The image of the welding surface is an optical interference image acquired using an optical image acquisition system; The acquisition of 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.

4. The method according to claim 3, characterized in that, Identify areas on the weld surface that are not welded but have already formed optical contacts, including: The acquired optical interference image is preprocessed to improve the contrast of the interference fringes contained therein; Extract the fringe coordinates of each interference fringe contained in the preprocessed optical interference image and determine the order of each interference fringe; The area on the welding surface that is not welded but has formed optical contact is determined based on interference fringes that meet a preset order.

5. The method according to claim 3, characterized in that, Identifying areas 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 areas 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 annotations of equal-thickness interference fringes in the optical interference image based on the welding effect.

6. The method according to claim 1, characterized in that, The area to be welded is welded using an ultrafast laser, including: Using Z-scan filling algorithm, offset filling algorithm, regional scanning filling algorithm, spiral scanning filling algorithm, concentric circular arc filling algorithm or fractal scanning filling algorithm, an ultrafast laser welding trajectory that can fill the area to be welded is determined; An ultrafast laser generated by a laser is controlled by an optical system and moved along the ultrafast laser welding trajectory to achieve welding of the workpiece in the area to be welded.

7. The method according to claim 1, characterized in that, When the preset conditions include the proportion of the welded area on the welded surface exceeding a preset threshold, starting from the second execution of the image acquisition step, the image acquisition step further includes: The number of pixels occupied by the welded surface in the image is counted, and the number of pixels occupied by the welded area in the previous welding steps is counted. The ratio of the number of pixels occupied by the welded area in the image to the number of pixels occupied by the welded surface in the image is calculated as the proportion of the welded area to the welded surface.

8. The method according to claim 1, characterized in that, The method further includes repeating the image acquisition step and the area welding step until the preset conditions are met, and then using an ultrafast laser to scan the welding surface again 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 as described in claims 1-8 above, and the system includes: A horizontal displacement platform is used to place 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 is used to acquire images of the welded surfaces that are in contact with each other; The computing system is used to identify areas on the welding surface that are not welded but have formed optical contact, based on the acquired images of the welding surface, as areas to be welded; An ultrafast laser welding system is used to weld the area to be welded using an ultrafast laser, so that the two workpieces are welded in the area to be welded. The computing system is also used to determine whether a preset condition for control termination has been met when repeating the image acquisition step and the area welding step; 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 welded areas on the welding surface exceeds a preset threshold.

10. The system according to claim 9, characterized in that, The ultrafast laser welding system includes a laser and an optical system. The laser is used to generate ultrafast laser light, and the optical system and / or a horizontal displacement platform are used to control the ultrafast laser welding trajectory.

11. The system according to claim 10, characterized in that, The optical system consists of a scanning galvanometer and a field mirror. During ultrafast laser welding, the field mirror remains stationary, while the scanning galvanometer controls the ultrafast laser welding trajectory by controlling changes in the two-dimensional optical path; or The optical system consists of a focusing lens, which focuses the ultrafast laser onto the welding surface or near the welding surface during ultrafast laser welding. Welding is achieved by moving the horizontal displacement platform along the ultrafast laser welding trajectory.

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