Laser welding method

Abstract

A laser welding method, milling single edge groove on two workpieces to be welded respectively; assembling and aligning the two workpieces to be welded after cleaning; using laser swing filler wire welding method in heat conduction welding mode to carry out non-penetration welding, only using filler wire metal to fill the upper groove of the test plate, obtaining the first filler wire welding seam with obvious excess height; using laser self-melting welding method in keyhole welding mode to carry out full penetration welding, laser beam penetrating the first filler wire welding seam and the whole workpiece thickness at the same time, obtaining the second full penetration welding seam. In the process of the second full penetration welding, the upper first filling metal part is partially melted and moves to the lower part under the action of the melt pool convection, and under the action of surface tension, the upper surface of the final weld has only slightly reduced excess height, and the lower surface forms obvious excess height.

Description

Technical Field

[0001] This invention relates to the field of laser ablation technology, and in particular to a laser welding method. Background Technology

[0002] The requirements for surface forming control, surface deformation, and overall heat input of welds are becoming increasingly stringent. Among these, insufficient weld reinforcement and weld porosity defects have been persistent problems in the welding process. Insufficient weld reinforcement and weld porosity are major issues that plague the welding process, easily leading to porosity, stress concentration, and other problems. Therefore, reinforcement is a necessity in welding technology. Traditional arc welding methods, due to large residual deformation and processing efficiency, often cannot meet the precision and strength requirements of new structures, limiting the scope for innovative structural design. Laser welding has advantages such as high energy density, low heat input, small heating zone, small residual deformation, large weld depth-to-width ratio, and ease of automation, and has developed rapidly in recent years. However, the application of laser welding in the welding and manufacturing of aerospace vehicle structures is still relatively limited. Two-pass laser welding of large-size blunt edges in medium-thickness plates is a highly efficient welding method. Medium-thickness plate metal structures are widely used in aerospace, chemical, shipbuilding, transportation vehicles, and oil pipeline fields; therefore, the welding quality and efficiency of medium-thickness metal plates are common issues of great concern to the manufacturing industry.

[0003] For a long time, the most common method for welding medium-thickness metal plates has been multi-layer, multi-pass filler welding after beveling. The welding heat source used is typically a low-penetration electric arc, with a bevel root height of 1-2 mm to ensure complete penetration of the root area. This small bevel height results in a large filler space. Currently, arc welding of medium-thickness plates involves numerous layers and passes per layer, leading to a large filler metal volume, resulting in low welding efficiency, large welding deformation, severe performance degradation after repeated heating of the weld zone, and numerous interlayer defects. High-power laser welding offers significant advantages such as high energy density, strong penetration, and a large weld depth-to-hole ratio. For example, a 10kW multimode fiber laser can easily penetrate approximately 10mm thick low-alloy steel plates in a single pass, forming deep and narrow welds comparable to electron beam welding. Leveraging the advantages of laser welding, researchers both domestically and internationally have proposed a laser welding method for medium-thickness plates with large blunt edge heights. This method employs a bottom-up welding approach, first using full-penetration welding to achieve self-fusion welding of the large blunt edge butt joint area at the bottom. Then, filler wire welding is used to fill the bevel area near the upper surface, forming a weld reinforcement on the upper surface, thus obtaining a complete welded joint. Compared to single-pass laser full-penetration self-fusion welding, this method achieves good weld formation with weld reinforcement due to filler wire welding near the upper surface. Compared to arc welding, the increased blunt edge height significantly reduces the bevel space required for filling, the number of welding layers is greatly reduced, welding deformation is significantly decreased, and welding efficiency is greatly improved. However, this bottom-up laser welding method for medium-thickness plates has been found to have many problems in practical applications:

[0004] Firstly, during bottom-up welding, the quality of the first laser penetration weld is highly sensitive to the assembly gap. This places high demands on the pre-welding workpiece dimensions and assembly quality. For complex shapes and structures, this leads to an increase in the number of out-of-tolerance workpieces, reduced efficiency, and increased costs. Zero assembly gap during workpiece assembly is virtually impossible, and the assembly gap is typically not constant but rather randomly varying along the welding path. High-power multimode lasers typically have a spot diameter in the range of 0.2–0.4 mm. The presence and random variation of this gap will cause fluctuations in the reduction of laser energy absorption rate, ultimately resulting in unstable weld quality.

[0005] Secondly, during bottom-up welding, the total height of the molten pool is less than the thickness of the test plate during the first penetration weld. This causes the molten metal to tend to move upwards under surface tension, ultimately resulting in a depression on the lower surface of the weld. This depression weakens the load-bearing capacity of the weld joint, which is unacceptable, especially for welded structures operating under harsh conditions in aerospace, chemical, and other fields.

[0006] Secondly, during the "bottom-up" welding process, the interaction between "light-wire-molten pool-plasma" in the second non-penetrating laser filler wire welding is complex, resulting in complex droplet transition and molten pool flow behavior, poor molten pool stability, and thus a high porosity.

[0007] Finally, the composition of the welding wire used in the second non-penetrating laser filler wire welding process usually differs from that of the base metal. This could be due to differences in the types and amounts of beneficial elements that improve ductility and toughness, or stricter control over the content of harmful elements such as C, S, and P. When welding "from bottom to top," the molten metal from the welding wire can only fill the upper bevel and improve the ductility and toughness of the upper weld metal. The lower weld metal is formed by the resolidification of the base metal after melting, therefore, it is impossible to improve the ductility and toughness of the lower weld metal by using filler wire.

[0008] The information disclosed in the background section is only intended to enhance the understanding of the background of the present invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0009] To address the shortcomings or defects of the existing technology, a laser welding method is provided. It abandons the traditional "bottom-up" welding approach, which involves welding filler metal from the weld root and finally completing the upper surface weld filler. Instead, it adopts a "top-down" reverse construction approach, forming the upper weld first. During the first welding pass, filler wire is used, allowing for a larger assembly gap after workpiece assembly. After the first weld pass, the weld zone thickness is greater than the base metal thickness. Then, the weld penetrates the lower surface of the weld zone. Under surface tension, reinforcement can form on both the upper and lower surfaces of the weld, eliminating the phenomenon of lower surface depression. Full penetration welding has a lower tendency to produce porosity, and the molten first non-penetrating weld promotes the escape of pores from the first weld pass, effectively suppressing porosity defects in the final weld joint. After molten first non-penetrating weld pass, the beneficial alloying elements of the wire metal can be distributed throughout the entire thickness of the weld under the convection of the molten pool, which is beneficial for improving the ductility and toughness of the lower metal of the weld.

[0010] The objective of this invention is achieved through the following technical solutions.

[0011] A laser welding method includes,

[0012] Shielding gas is supplied to the upper and lower surfaces of the weld joints on the two workpieces to be welded, and a bevel is provided on the upper surface of the weld joints;

[0013] The bevel position of the upper surface of the weld joint is welded, and the bevel position of the upper surface of the weld joint is filled to obtain the first filler wire weld, which is higher than the upper surface of the weld joint.

[0014] Laser beam full-penetration welding simultaneously penetrates the first filler wire weld and the full thickness of the workpiece at the weld location to obtain a second full-penetration weld. The upper and lower surfaces of the second full-penetration weld both form reinforcement heights, where the full thickness is the thickness to be welded from the upper surface to the lower surface of the weld location.

[0015] In the method, a laser oscillating filler wire welding method is used to weld the bevel position on the upper surface of the weld area in the heat conduction welding mode to obtain the first filler wire weld.

[0016] In the method, laser autofusion welding is used to perform full-penetration welding in keyhole welding mode to obtain a second full-penetration weld.

[0017] In the method, the workpiece to be welded is a metal plate with a thickness of 5 to 25 mm, the blunt edge height of the bevel is 5 to 10 mm, and the amount of filler wire in the first laser filler wire oscillating welding is such that, in addition to filling the bevel space and the lower butt joint gap space, an additional height of 0.5 to 1.5 mm can be formed on the upper and lower surfaces of the workpiece to be welded.

[0018] In the method described above, when the laser full-penetration self-fusion welding method simultaneously penetrates the first filler weld on the upper surface and the lower blunt edge region, a keyhole that penetrates the entire thickness is formed in the molten pool. The keyhole provides a channel for the detachment and escape of bubbles in the molten pool. The laser beam oscillates laterally with an amplitude of 5% to 15% of the plate thickness to stir the molten pool. The molten pool metal flows around the keyhole, and material convection exchange occurs between the upper and lower parts of the molten pool.

[0019] In the method, a single-sided bevel is milled on each of the two workpieces to be welded, and the single-sided bevels on the two workpieces to be welded are assembled and aligned to form the bevel of the weld seam of the workpieces to be welded.

[0020] In the method, a single-sided bevel is milled on each of the two workpieces to be welded. After the two workpieces are ground and cleaned, they are assembled, aligned, clamped and fixed to form the bevel of the weld portion of the workpieces to be welded.

[0021] In the method described, the protective gas is argon.

[0022] In the method, before welding the bevel position on the upper surface of the weld seam, the robot sends the welding head to the welding position of the workpiece to be welded, and the robot and welding head are oriented and the welding path is planned. Without emitting laser light, the welding head moves along the welding path and the spot shape on the surface of the workpiece to be welded is observed. It is confirmed that the laser beam is perpendicularly incident on the surface of the workpiece to be welded and the defocusing amount is constant in the welding path planning.

[0023] In the method, the groove is first filled by laser oscillating filler wire welding, at which point the lower blunt edge region of the workpiece to be welded is not melted; then the laser full penetration self-fusion welding method is used to simultaneously penetrate the first filler wire weld on the upper surface and the lower blunt edge region at one time.

[0024] Beneficial effects

[0025] When the present invention adopts the "top-down" welding scheme of first forming the upper weld seam, in the first non-penetrating laser filler wire welding, after the "light-wire" interaction, the molten metal of the welding wire enters the groove and fills the gap at the root of the groove. The laser energy absorption behavior will no longer be affected by the gap, and the laser energy absorption rate and the flow behavior of the molten pool are greatly improved, resulting in stable welding quality.

[0026] Secondly, when the present invention adopts the "top-down" welding method of first forming the upper weld, the thickness of the welding area is greater than the thickness of the base material after the first welding. Then, the second full-penetration welding is performed to penetrate the upper weld and the entire thickness range of the base material. Under the action of surface tension, the upper and lower surfaces of the weld can form a reinforcement height, thereby eliminating the phenomenon of the lower surface of the weld being concave.

[0027] Secondly, when this invention employs a "top-down" welding approach, first forming the upper weld seam, the second full-penetration weld completely penetrates the upper weld seam and the entire thickness of the base material, forming a full-thickness "keyhole" in the molten pool. This "keyhole" provides a smooth "shortcut" for the detachment and escape of bubbles in the molten pool, thus significantly reducing porosity defects. In particular, for porosity defects formed in the upper weld seam during the first filler wire welding process, they may gain an additional opportunity to float and overflow during the second full-penetration weld due to the remelting of the metal surrounding the porosity, thereby eliminating the porosity defects already formed in the first filler wire welding seam.

[0028] Finally, when the present invention adopts the "top-down" welding method of first forming the upper weld, the second full-penetration welding completely penetrates the upper weld and the entire thickness of the base material, forming a "keyhole" and a molten pool that penetrates the entire thickness. The molten pool metal flows around the keyhole, and material convection exchange occurs between the upper and lower parts of the molten pool, thereby convectioning the beneficial elements in the welding wire that improve plasticity and toughness to the middle and lower parts of the molten pool, which plays a role in improving the plasticity and toughness of the metal in the middle and lower parts of the weld.

[0029] The description provided is merely an overview of the technical solution of this invention. In order to make the technical means of this invention clearer and more understandable, so that those skilled in the art can implement it according to the contents of the specification, and to make the described and other objects, features and advantages of this invention more obvious and understandable, specific embodiments of this invention are described below. Attached Figure Description

[0030] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0031] In the attached diagram:

[0032] Figure 1 This is a schematic diagram of the laser oscillation welding process of D406A ultra-high strength steel described in this invention;

[0033] Figure 2 This is a schematic diagram of the narrow gap bevel dimensions of the D406A ultra-high strength steel described in this invention;

[0034] Figure 3 The cross-section of the weld of the D406A ultra-high strength steel butt test plate described in this invention under the "top-down" laser welding process method of this invention;

[0035] Figure 4 The images show X-ray flaw detection images of the weld seam of the D406A ultra-high strength steel butt test plate described in this invention under the "top-down" laser welding process method of this invention.

[0036] Figure 5 This is a scanning image of the alloy element distribution surface of the weld cross section of the D406A ultra-high strength steel butt test plate described in this invention under the "top-down" laser welding process method of this invention;

[0037] Figure 6 The cross-section of the D406A ultra-high strength steel butt weld test plate described in this invention under the traditional "bottom-up" laser welding process;

[0038] Figure 7 The images show X-ray flaw detection images of the weld seam of the D406A ultra-high strength steel butt test plate described in this invention under the traditional "bottom-up" laser welding process.

[0039] Figure 8 This is a scanning image of the alloy element distribution in the weld cross-section of the D406A ultra-high strength steel butt weld test plate described in this invention, under the traditional "bottom-up" laser welding process.

[0040] Figure 9 This is a schematic diagram comparing the present invention with traditional laser welding processes.

[0041] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0042] The following will refer to the appendix. Figures 1 to 9 Specific embodiments of the invention will be described in more detail below. While specific embodiments of the invention are shown in the accompanying drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0043] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0044] To facilitate understanding of the embodiments of the present invention, the following will provide further explanation and description with reference to the accompanying drawings and several specific embodiments, and the accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0045] like Figures 1 to 8 As shown, laser welding methods include,

[0046] a) Mill a single-sided bevel on the two workpieces 1 and 2 to be welded respectively;

[0047] b) After grinding and cleaning the two workpieces 1 and 2 to be welded, assemble and align them, and then clamp and fix them in place.

[0048] c) Argon protective gas is introduced to the front and back of the weld area of ​​the workpiece;

[0049] d) The robot's motion delivers the welding head to the welding area on the workpiece surface;

[0050] e) Robot and welding head posture planning, welding path planning;

[0051] f) Without laser beam, move the welding head along the welding path and observe the shape of the laser spot on the workpiece surface;

[0052] g) Confirm that the laser beam is perpendicularly incident on the workpiece surface throughout the entire path, and that the defocusing amount is constant;

[0053] h) Welding is performed in thermal conductive welding mode using laser oscillating filler wire welding method to fill the bevel near the upper surface and obtain the first filler wire weld 3.

[0054] i) Using laser autofusion welding in keyhole welding mode, full penetration welding is performed. The laser beam simultaneously penetrates the weld obtained by the first filler wire welding and the full thickness of the workpiece to obtain the second full penetration weld 4.

[0055] In a preferred embodiment, it is suitable for welding medium-thickness metal plates with a thickness of about 5 to 25 mm; the weld groove depth near the upper surface of the medium-thickness plate is much smaller than the groove depth of conventional arc welding; the blunt edge height of the groove near the lower surface of the medium-thickness plate, 5 to 10 mm, is much larger than the blunt edge height of conventional arc welding groove (1 to 2 mm).

[0056] In a preferred embodiment, a reverse welding sequence is adopted. The first pass uses laser oscillating filler wire welding to fill the weld bevel near the upper surface of the medium-thickness plate, at which point the lower blunt edge region remains unmelted. Then, the second pass uses laser full-penetration autofusion welding to simultaneously penetrate both the weld metal near the upper surface and the lower blunt edge region, forming a complete weld joint. A schematic diagram of the welding process is shown below. Figure 1 As shown.

[0057] In a preferred embodiment, the first pass uses a laser oscillating filler wire welding method to weld the weld bevel near the upper surface of the medium-thickness plate. During the welding process, the "light-wire" interaction melts the welding wire and enters the bevel. These liquid metals fill the assembly gap at the root of the bevel, so the laser energy absorption behavior will no longer be affected by the gap, the stability of the molten pool is improved, and the stability of the welding quality is improved.

[0058] In a preferred embodiment, after the first laser filler wire oscillating welding, not only is the groove filled but a significant excess height is formed on the upper surface of the workpiece, so that the thickness of the weld zone is greater than the thickness of the base material; when performing the second laser full penetration welding, the upper weld and the entire thickness range of the base material are completely penetrated, and under the action of surface tension, excess height can be formed on both the upper and lower surfaces of the weld, thereby eliminating the phenomenon of depression on the lower surface of the weld.

[0059] In a preferred embodiment, the second full-penetration weld penetrates the entire thickness of the upper weld and the base metal, forming a full-thickness "keyhole" in the molten pool. This "keyhole" provides a smooth "shortcut" for the detachment and escape of bubbles in the molten pool, thereby significantly reducing porosity defects. In particular, porosity defects formed in the upper weld during the first filler weld may have an additional opportunity to float and overflow during the second full-penetration weld due to the remelting of the metal surrounding the pores, thus eliminating the porosity defects already formed in the first filler weld 3.

[0060] In a preferred embodiment, during the second full-penetration welding, the upper weld and the base material are completely penetrated throughout their thickness, forming a "keyhole" and a molten pool that penetrate the entire thickness. The laser beam oscillates laterally at an amplitude of 5% to 15% of the plate thickness to stir the molten pool. The molten pool metal flows around the keyhole, and material convection exchange occurs between the upper and lower parts of the molten pool. This convection of beneficial elements in the welding wire that improve plasticity and toughness to the middle and lower parts of the molten pool improves the plasticity and toughness of the metal in the middle and lower parts of the weld.

[0061] In a preferred embodiment, the amount of filler wire in the first laser filler wire oscillation welding should be sufficient to fill the groove space and the lower butt joint gap space with a significant margin, so as to form a weld reinforcement of 0.5 to 1.5 mm on both the upper and lower surfaces of the workpiece.

[0062] In a preferred embodiment, during the second full-penetration welding process, the upper first filler metal portion melts and moves downwards under the convection of the molten pool. Under the action of surface tension, the final weld seam upper surface reinforcement only slightly decreases, while the lower surface forms a significant reinforcement.

[0063] In one embodiment, the test material was 6.6 mm thick annealed D406A ultra-high strength steel, with chemical element composition as shown in Table 1, annealing temperature of 650℃, microstructure of granular pearlite, and H10 welding wire (H10SiMnCrNiMoV) was selected.

[0064] Table 1 Chemical composition of annealed D406A ultra-high strength steel (wt%)

[0065]

[0066] Table 2 Chemical composition of H10 welding wire (H10SiMnCrNiMoVA) / wt%

[0067]

[0068] The main equipment of the D406A ultra-high strength steel laser oscillating wire feeding welding system includes a Pretzker YW52 laser oscillating welding head, a MOTOMAN 6-axis robotic arm, a YASKAWA MOTOMAN-HP20D robot, a precision 3D platform, an IPG YLS-8000 fiber laser, and an MXN-10 wire feeder. To protect the laser lens and other protective devices, the laser head is tilted 5° to the right. A side-axis front-mounted wire feeding method is used, and the angle between the wire feed gun head and the horizontal direction is 45°. Unless otherwise specified, the above parameters are constants.

[0069] Currently mainly adopted Figure 2The bevel configuration shown is used for narrow-gap laser oscillating filler wire welding of D406A ultra-high strength steel, with a plate thickness of 6.6mm, a bevel bottom width of 2mm, a blunt edge height of 5mm, and an outward tilt angle of 5 degrees on both sides of the bevel.

[0070] The following welding method was adopted:

[0071] Mill a single-sided bevel on each of the two workpieces to be welded, 1 and 2.

[0072] After grinding and cleaning the two workpieces 1 and 2 to be welded, assemble and align them, then clamp and fix them in place.

[0073] Argon protective gas is introduced to both the front and back of the weld area of ​​the workpiece;

[0074] The robot moves to deliver the welding head to the welding area on the workpiece surface;

[0075] Robot and welding head posture planning, welding path planning;

[0076] Without laser, the welding head moves along the welding path, and the shape of the laser spot on the workpiece surface is observed to confirm that the laser beam is perpendicularly incident on the workpiece surface throughout the entire path and that the defocusing amount is constant.

[0077] Welding was performed in thermal conductive welding mode using the laser oscillating filler wire welding method to fill the groove and obtain the first filler wire weld 3. The specific welding parameters are shown in Table 3.

[0078] Laser autofusion welding is used to perform full penetration welding in keyhole welding mode. The laser beam simultaneously penetrates the first filler wire weld 3 and the entire thickness of the workpiece to obtain the second full penetration weld 4. The specific welding parameters are shown in Table 3.

[0079] The specific welding parameters used are shown in the table below:

[0080] Table 3 Welding parameters of the "top-down" laser welding embodiment of the present invention

[0081]

[0082] The cross-section of the weld seam in the "top-down" laser welding process of this invention is as follows: Figure 3 As shown, the corresponding X-ray flaw detection image is as follows: Figure 4 As shown, the number of weld pores is significantly reduced, and defects such as pores, lack of fusion, and cracks meet industry requirements. This indicates that the welding process effectively suppresses weld pore defects and has the advantages of high efficiency, large weld depth-to-width ratio, and low defect rate. It is a low-defect laser welding method.

[0083] By adjusting the welding wire composition, replacing H10 welding wire with stainless steel welding wire, alloy element distribution surface scanning was performed on the weld cross-section and longitudinal section under both the traditional "bottom-up" laser welding process and the "top-down" laser welding process of this invention. The surface scanning results are as follows: Figure 5 and Figure 8 As shown in the figure, the elemental composition of the welding wire can adjust the composition and properties of the weld. The molten metal flows around the keyhole, and convection exchange of materials occurs between the upper and lower parts of the molten pool. This convection of beneficial elements in the welding wire that improve ductility and toughness to the middle and lower parts of the molten pool improves the ductility and toughness of the metal in the middle and lower parts of the weld. Therefore, the "top-down" laser welding process of this invention is a low-defect laser welding method.

[0084] Comparative Example

[0085] To illustrate the technical advantages of the "top-down" reverse multi-layer welding scheme employed in this invention through comparison, the implementation results of the traditional "bottom-up" multi-layer welding scheme are presented below:

[0086] The experimental material was 6.6 mm thick annealed D406A ultra-high strength steel. The chemical element composition is shown in Table 1. The annealing temperature was 650℃. The microstructure was granular pearlite. H10 welding wire (H10SiMnCrNiMoV) was used.

[0087] Table 1 Chemical composition of annealed D406A ultra-high strength steel (wt%)

[0088]

[0089] Table 2 Chemical composition of H10 welding wire (H10SiMnCrNiMoVA) / wt%

[0090]

[0091] The main equipment for laser oscillating wire welding of D406A ultra-high strength steel includes a Pretzker YW52 laser oscillating welding head, a MOTOMAN 6-axis robotic arm, a YASKAWA MOTOMAN-HP20D robot, a precision 3D platform, an IPG YLS-8000 fiber laser, and an MXN-10 wire feeder. To protect the laser lens and other protective devices, the laser head is tilted 5° to the right. A side-axis front-mounted wire feed method is used, and the angle between the wire feed gun head and the horizontal direction is 45°. Unless otherwise specified, the above parameters are constants.

[0092] Currently mainly adopted Figure 2 The bevel configuration shown is used for narrow-gap laser oscillating filler wire welding of D406A ultra-high strength steel, with a plate thickness of 6.6mm, a bevel bottom width of 2mm, a blunt edge height of 5mm, and an outward tilt angle of 5 degrees on both sides of the bevel.

[0093] The following welding method was adopted:

[0094] Mill a single-sided bevel on each of the two workpieces to be welded, 1 and 2.

[0095] 2) After grinding and cleaning the two workpieces 1 and 2 to be welded, assemble and align them, and clamp and fix them in place;

[0096] Argon protective gas is introduced to both the front and back of the weld area of ​​the workpiece;

[0097] The robot moves to deliver the welding head to the welding area on the workpiece surface;

[0098] Robot and welding head posture planning, welding path planning;

[0099] Without laser, the welding head moves along the welding path, and the shape of the laser spot on the workpiece surface is observed to confirm that the laser beam is perpendicularly incident on the workpiece surface throughout the entire path and that the defocusing amount is constant.

[0100] Laser autofusion welding was used to perform full penetration welding in keyhole welding mode to connect the lower blunt edge region and form the lower weld. Specific welding parameters are shown in Table 4.

[0101] Welding was performed using the laser oscillating filler wire welding method in the heat conduction welding mode to fill the upper bevel and complete the first filler wire weld at the top, thus obtaining a complete welded joint. Specific welding parameters are shown in Table 4 below.

[0102] The specific welding parameters used are shown in the table below:

[0103] Table 4 Welding parameters for a traditional "bottom-up" laser welding example

[0104]

[0105] The cross-section of this traditional "bottom-up" laser welding weld is as follows: Figure 6 As shown, the X-ray flaw detection image of the weld is as follows: Figure 7 As shown. See also Figure 9 By comparing the traditional bottom-up laser welding process with the top-down laser welding process of this invention, it can be found that the top-down laser welding process of this invention can form reinforcement on both the upper and lower surfaces of the weld, thereby eliminating the phenomenon of bottom surface depression; the number of weld pores is significantly reduced, and non-fusion defects are eliminated, with pores, non-fusion, and crack defects meeting industry requirements. This indicates that the top-down laser welding process of this invention effectively suppresses weld pore defects, eliminates bottom surface depression, and is highly efficient, representing a low-defect laser welding method.

[0106] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described herein. The specific embodiments described are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other modifications based on the guidance of this specification and without departing from the scope of the claims of the present invention, and all such modifications are within the scope of protection of the present invention.

Claims

1. A laser welding method, characterized in that, It includes, Shielding gas is supplied to the upper and lower surfaces of the weld joints on the two workpieces to be welded, and a bevel is provided on the upper surface of the weld joints; The bevel position of the upper surface of the weld joint is welded, and the bevel position of the upper surface of the weld joint is filled to obtain the first filler wire weld, which is higher than the upper surface of the weld joint. Laser beam full-penetration welding simultaneously penetrates the first filler wire weld and the full thickness of the workpiece at the weld joint to obtain a second full-penetration weld. Both the upper and lower surfaces of the second full-penetration weld form reinforcement. The full thickness is the thickness to be welded from the upper to the lower surface of the weld joint. Laser autofusion welding is performed in keyhole welding mode to obtain the second full-penetration weld. When the laser full-penetration autofusion welding method simultaneously penetrates the first filler wire weld on the upper surface and the lower blunt edge region, a keyhole penetrating the full thickness is formed in the molten pool. The keyhole provides a channel for the detachment and escape of bubbles in the molten pool. The laser beam oscillates laterally with an amplitude of 5% to 15% of the plate thickness to stir the molten pool. The molten pool metal flows around the keyhole, and material convection exchange occurs between the upper and lower parts of the molten pool.

2. The method according to claim 1, characterized in that, The first filler wire weld is obtained by welding the bevel position on the upper surface of the weld area in the heat conduction welding mode using a laser oscillating filler wire welding method.

3. The method according to claim 2, characterized in that, The workpiece to be welded is a metal plate with a thickness of 5 to 25 mm. The blunt edge height of the bevel is 5 to 10 mm. The amount of filler wire in the first laser filler wire oscillating welding is such that, in addition to filling the bevel space and the lower butt joint gap space, an additional height of 0.5 to 1.5 mm can be formed on the upper and lower surfaces of the workpiece to be welded.

4. The method according to claim 1, characterized in that, Single-sided bevels are milled on two workpieces to be welded, and the single-sided bevels on the two workpieces to be welded are assembled and aligned to form the bevel of the weld seam of the workpieces to be welded.

5. The method according to claim 4, characterized in that, Single-sided bevels are milled on the two workpieces to be welded. After the two workpieces are ground and cleaned, they are assembled, aligned and clamped to form the bevel of the weld seam of the workpieces to be welded.

6. The method according to claim 1, characterized in that, The protective gas is argon.

7. The method according to claim 1, characterized in that, Before welding the bevel position on the upper surface of the weld seam, the robot sends the welding head to the welding position of the workpiece to be welded to perform robot and welding head posture planning and welding path planning; without emitting laser, the welding head moves along the welding path and observes the spot shape on the surface of the workpiece to be welded; confirm that the laser beam is perpendicularly incident on the workpiece surface along the entire path and the defocusing amount is constant.

8. The method according to claim 1, characterized in that, First, the groove is filled by laser oscillating filler wire welding, at which point the lower blunt edge area of ​​the workpiece to be welded is not melted; then, the first filler wire weld on the upper surface and the lower blunt edge area are simultaneously penetrated by laser full penetration self-fusion welding.

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