Thin plate laser lap welding method and laser welding equipment

Abstract

The invention belongs to the technical field of laser welding, and discloses a thin plate laser lap joint welding method and laser welding equipment. The power of the laser acting on the surface of the upper plate and the power of the laser acting on the lower plate are both smaller than the power of the laser acting on the center of the weld joint, that is, the laser power is in a low-high-low change trend in the direction from the upper plate to the center of the weld joint to the lower plate, and it is ensured that the laser in the center of the weld joint can penetrate through the upper plate; laser on the two sides of the center of the welding seam is controlled in the state that the laser cannot penetrate through the plate, so that energy input in different subareas of the welding seam is accurately controlled, it is guaranteed that the penetration depths of all the subareas are controllable and different, the problems that the penetration depths are unstable, the contour of a molten pool is discontinuous, and a lower plate is prone to penetrating are solved, the welding seam is good in consistency and free of inward concave or outward convex, and continuous smooth transition is achieved; the size measurement of the molten pool meets the standard requirements, the welding quality and the welding efficiency are effectively improved, welding wires are not needed, and the cost is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of laser welding, and in particular to a method for laser lap welding of thin plates and a laser welding device. Background Art

[0002] The most core part of an LNG ship is the LNG storage cargo hold, which needs to safely store liquefied natural gas at -163°C, ensuring no leakage while also keeping the evaporation rate low. Therefore, an LNG ship is also known as a super freezer at sea. Currently, the mainstream ship storage tank systems are mainly divided into self-supporting type and thin-film type. Among them, the thin-film liquid cargo system mainly includes the thin-film type MARK III liquid cargo hold and the No.96 liquid cargo hold. The No.96 liquid cargo hold mainly uses cryogenic Invar steel. Due to high material costs and difficult in-ship operation, its market share is relatively low. Therefore, the thin-film liquid cargo system mainly focuses on the MARK III liquid cargo hold.

[0003] The thin-film metal selected for the main screen wall of the MARK III liquid cargo hold is 1.2-mm corrugated 304L stainless steel, the material of the secondary screen wall is a 3-layer composite film, and the thermal insulation material is enhanced polyurethane foam. Among them, the welding result of the 304L stainless steel corrugated plate determines the integrity of the main screen wall and is the key to the successful construction of the LNG ship's containment system. However, due to the characteristics of 304L stainless steel, such as high resistance, large expansion coefficient, and low thermal conductivity, adverse results such as coarse grains and large thermal stress are likely to occur after welding. At the same time, due to the high content of alloying elements, the melt viscosity is large, and pores and weld bead undercut are likely to appear. TIG welding and metal inert gas welding (MIG welding) are often used welding methods. These two welding methods require filler wires and have low welding efficiency, often requiring manual secondary repair welding, resulting in relatively high overall costs. Therefore, the laser welding method is widely used.

[0004] In the existing laser lap welding method, single-laser non-oscillating welding is simple to operate, but this welding method mainly relies on the fluidity of the material itself for fusion and is suitable for welding scenarios with relatively narrow welds (such as about 0.1 mm). It is very difficult to increase the weld width. For materials with wider welds (such as more than 0.3 mm), the liquid in the molten pool may not be fully fused, and welding defects such as pores and sand holes are likely to occur. Single-laser oscillating welding controls the laser beam to oscillate in a single direction (such as the X-axis or Y-axis) through a galvanometer motor, thereby achieving precise movement of the laser beam. It can relatively easily widen the weld width, reduce the penetration depth, and effectively improve welding defects (such as pores and cracks), but Figure 6As shown in the figure, since a single laser cannot adjust the energy in real time according to the position, when the laser acts on the lower plate, the large energy is easy to penetrate, and when it acts on the upper plate, the penetration depth is insufficient, which cannot meet the dimensional requirements. Then, due to the large amplitude swing, the increase of the swing frequency is restricted. When the laser moves along the weld to be welded, the swing frequency in the direction perpendicular to the weld is low, which will cause the material not to be fully melted. Finally, on the section, it shows independent and discontinuous keyholes, and a whole molten pool is not formed. The penetration depth at the weld is unstable, and uneven concave and convex are likely to appear. At the upper plate, curling and incomplete fusion are likely to occur, and at the lower plate, unstable undercut is likely to occur, seriously affecting the weld quality. Summary of the Invention

[0005] The purpose of the present invention is to provide a thin-plate laser lap welding method and a laser welding device, which use multiple lasers to perform autogenous welding on the lap joint of the upper plate and the lower plate. While ensuring the weld width, the laser energy distribution can be optimized, the weld formation is good, there is no undercut on the bottom plate, and the welding efficiency is high and the cost is low.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] On the one hand, a thin-plate laser lap welding method is provided, including the following steps:

[0008] S1: Lap the upper plate and the lower plate to be welded and fix them on the welding fixture, and pre-weld at least one welding point between the upper plate and the lower plate;

[0009] S2: Select the number of laser paths according to the weld width and set the parameters of the laser array; wherein, the laser power at the center of the laser array is greater than that on both sides.

[0010] S3: Adjust the position of the laser welding head relative to the weld, so that the center of the laser array is placed inside the edge of the upper plate near the lap joint, and the long axis of the laser array is set at an angle to the welding direction;

[0011] S4: The laser array emits light, the laser welding head moves along the lap joint of the upper plate and the lower plate, and swings and welds along the long axis direction of the laser array to form a lap weld.

[0012] As an optional solution of the thin-plate laser lap welding method, in S2, the parameters of the laser array include the power of each single laser, the output spot diameter, and the collimation and focusing ratio. The power of each single laser in the laser array is independently adjustable. The center laser power of the laser array is controlled in a state where it can penetrate the upper plate but not penetrate the lower plate, and the laser power on both sides of the laser array is controlled in a state where it does not penetrate a single layer of sheet material.

[0013] As an alternative to the thin plate laser lap welding method, in S3, the center of the weld is at the edge of the upper plate near the lap joint, and the center of the laser array is placed 0.2 mm - 0.4 mm away from the center of the weld perpendicular to the center of the weld on the upper plate.

[0014] As an alternative to the thin plate laser lap welding method, in S3, the angle between the long axis of the laser array and the welding movement direction is 60° to 90°, preferably 90°.

[0015] As an alternative to the thin plate laser lap welding method, in S3, the laser welding head is inclined, and the angle between the axis of the laser welding head and the vertical direction is 10° - 15°.

[0016] As an alternative to the thin plate laser lap welding method, define the upper surface of the upper plate as the 0 focal position, and adjust the focal point of the laser array to -2 mm to 0 mm.

[0017] As an alternative to the thin plate laser lap welding method, in S4, the swing trajectory of the laser welding head is an "8" shape or a circle, and the adjacent light spots are externally tangent, preferably an "8" shape.

[0018] As an alternative to the thin plate laser lap welding method, the swing amplitude W of the laser welding head W = D - d f , where D is the center distance between two adjacent laser beams, and the focused light spot diameter d f = d * (F f / F c ), F f is the focal length of the focusing lens, F c is the focal length of the collimating lens, and d is the output light spot diameter;

[0019] And / or, preferably set the swing frequency of the laser array (3) to be not less than 30 times the welding speed, and swing frequency * swing amplitude < the limit speed of the swing motor of the laser welding head.

[0020] As an alternative to the thin plate laser lap welding method, the welding speed is set to 15 mm / s - 50 mm / s; the laser welding head can deliver shielding gas to the welding position, and the flow rate of the shielding gas is 15 L / min - 25 L / min.

[0021] On the other hand, a laser welding device is also provided, including a laser welding head, the laser welding head includes a laser array, the laser array includes multiple laser beams, the laser power at the center of the laser array is greater than the laser power on both sides, and the laser array can swing along the long axis direction. The laser welding device can be used to perform the above thin plate laser lap welding method.

[0022] Advantages of the present invention:

[0023] The present invention provides a thin - plate laser lap - welding method and a laser welding device. Self - fusion welding is performed on the lap joint of the upper plate and the lower plate using multiple lasers. Using multiple lasers can be applicable to a wider weld seam. The power of the laser acting on the surface of the upper plate and the power of the laser acting on the lower plate are both less than the power of the laser acting on the center of the weld seam. That is, along the direction from the upper plate to the center of the weld seam to the lower plate, the laser power shows a low - high - low change trend. By setting like this, it can be ensured that the laser in the center part of the weld seam can penetrate the upper plate, while the lasers on both sides of the weld seam center are controlled in a state where they cannot penetrate the plate, so as to achieve precise control of the energy input in different zones of the weld seam, ensure that the penetration depths of each zone are controllable and different, and there is no undercut and no penetration on the lower plate; during the welding process, the setting of multiple lasers can effectively increase the laser coverage of the weld seam width to form a wider molten pool, so that when the multiple lasers swing according to a preset movement trajectory, the laser swing amplitude can be reduced and the swing frequency can be increased. By setting like this, the laser energy distribution is uniform, the base metal in the center of the weld seam melts a large amount and naturally flows down under the action of gravity, the weld formation is good, there is no undercut on the lower plate, and at the same time, the energy is concentrated, effectively improving the welding efficiency. The cross - section of the formed weld seam is as Figure 1 and Figure 7 shown. The weld seam smoothly transitions from the upper plate to the lower plate, the surface is smooth, the consistency is good, there is no internal concavity or external convexity, it is a continuous and smooth transition, and the measurement of the molten - pool size meets the standard requirements, effectively improving the welding quality and welding efficiency. Without filling welding wire, the cost is effectively reduced. Brief Description of the Drawings

[0024] Figure 1 is a schematic diagram of the contour of a corrugated stainless - steel lap weld seam in actual ship operation provided by an embodiment of the specific implementation manner of the present invention;

[0025] Figure 2 is a schematic diagram of the relative position between a laser array and a weld seam provided by an embodiment of the specific implementation manner of the present invention;

[0026] Figure 3 is a schematic diagram of the "8" - shaped trajectory of the laser - array swing provided by an embodiment of the specific implementation manner of the present invention;

[0027] Figure 4 is a schematic diagram of the circular trajectory of the laser - array swing provided by an embodiment of the specific implementation manner of the present invention;

[0028] Figure 5 is a schematic diagram of the laser - array arrangement provided by an embodiment of the specific implementation manner of the present invention;

[0029] Figure 6 is a metallographic diagram of a single - laser swing - welded weld seam;

[0030] Figure 7 It is the actual weld metal phase diagram provided by the embodiments of the specific implementation manners of the present invention.

[0031] In the figure:

[0032] 1. Upper plate; 2. Lower plate; 3. Laser array; 4. Weld center. Specific implementation manners

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. Additionally, it should be noted that for the convenience of description, only the parts related to the present invention rather than all the structures are shown in the drawings.

[0034] In the description of the present invention, unless otherwise clearly defined and limited, the terms "connected", "connected to", and "fixed" shall be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] In the present invention, unless otherwise clearly defined and limited, the first feature being "above" or "below" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through other features between them. Moreover, the first feature being "above", "over", and "on" the second feature includes that the first feature is directly above and obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "below", "under", and "beneath" the second feature includes that the first feature is directly below and obliquely below the second feature, or merely indicates that the horizontal height of the first feature is lower than that of the second feature.

[0036] In the description of this embodiment, the orientation or positional relationships such as "upper", "lower", "right", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of description and simplifying the operation, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for distinction in description and have no special meanings.

[0037] Combined with the visual inspection, metallographic inspection, and sample geometric data analysis standards for corrugated stainless steel welding, the lap weld between the upper plate 1 and the lower plate 2 should meet the following standards:

[0038] 1. The surface of the weld should be as smooth as possible, transitioning smoothly from the upper plate 1 to the lower plate 2, and there should be no welding through defects on the back side;

[0039] 2. In the metallographic photograph, a clear and smooth weld curve can be seen on the base metal, and the weld must have a slight back arc surface. That is, there must be a slight smooth transition bulge on the surface of the weld, as Figure 7 shown. If the cross-section of the weld shows a concave shape, or the contour of the weld pool shows a circular shape or incomplete penetration, it does not meet the standards, as Figure 6 shown;

[0040] 3. Combining Figure 1 , the contour of the weld pool for lap welding must meet the parameter standards shown in Table 1.

[0041] Table 1

[0042]

[0043] For single-laser non-oscillating welding, the depth-to-width ratio is large, and it is easy to obtain a large penetration depth. However, it is very difficult to significantly increase the weld width while ensuring the welding quality and stability, and it is impossible to obtain a qualified weld that meets the standards in Table 1.

[0044] As Figure 6 shown, for single-laser oscillating welding, by introducing a scanning laser at the end of welding, it is relatively easy to control the weld width. However, as the oscillation amplitude increases, the energy at the position of the weld center 4 is likely to be insufficient, and the weld is prone to uneven concave and convex shapes. At the upper plate 1, curling and incomplete fusion are likely to occur, and at the lower plate 2, unstable undercutting is likely to occur. It is also difficult to form a continuous and uniform whole for the weld pool, especially manifested as insufficient penetration depth at the weld center 4. At the same time, the welding efficiency is severely limited by the oscillation speed. As the laser power increases, the stability of the entire welding process and the weld quality are both unstable, and it is difficult to obtain a qualified weld that meets the standards in Table 1.

[0045] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and through specific embodiments.

[0046] As Figures 2 to 5 shown, this embodiment provides a thin-plate laser lap welding method and a laser welding device, which are applied to thin plates that require precision welding and have high requirements for welding quality. Exemplarily, the thin plate to be welded in this embodiment is made of corrugated 304L stainless steel, that is, both the upper plate 1 and the lower plate 2 are made of corrugated 304L stainless steel. The method includes the following steps:

[0047] S1: The upper plate 1 and the lower plate 2 to be welded are overlapped and fixed on the welding jig, and at least one welding spot is pre-welded between the upper plate 1 and the lower plate 2.

[0048] In the specific implementation of the above steps, the upper plate 1 and the lower plate 2 are lapped and fixed on the welding jig to ensure that the upper plate 1 and the lower plate 2 are pressed and closely attached. Then, at least one solder joint is pre-welded along the lapping position to fix the plates and prevent excessive gaps caused by welding deformation. Exemplarily, the welding jig is a structure already disclosed in the prior art, and its specific structure refers to the prior art and will not be specifically described herein.

[0049] S2: Select the number of laser paths according to the weld width and set the parameters of the laser array 3; wherein, the laser array 3 includes multiple paths of lasers, and the laser power at the center of the laser array 3 is greater than that on both sides.

[0050] In the specific implementation of the above steps, the number of laser paths is selected according to the weld width to ensure that the laser array 3 can at least completely cover the weld; the parameters of the single-column laser array 3 are set according to the material of the plate to be welded, the weld width, and the laser swing amplitude. The laser power at the center of the laser array 3 is greater than that on both sides, that is: along the direction from the upper plate 1 to the weld center 4 to the lower plate 2, the laser power shows a low-high-low change trend, ensuring that the laser at the center of the laser array 3 can penetrate the upper plate 1, while the lasers on both sides are controlled in a state where they cannot penetrate the plate. Especially for the laser acting on the lower plate 2, precise power adjustment is required to avoid the problem of penetration of the lower plate 2.

[0051] Optionally, the parameters of the laser array 3 include the power of each single-path laser, and the power of each path of the laser array 3 is independently adjustable. Specifically, the maximum power of a single-path laser supports options of 500W / 1000W / 1500W / 2000W, with an adjustment range of 10%-100%, and precise control of the single-path output power is satisfied to achieve precise control of the energy input in different zones of the weld, so that the laser power at the center of the laser array 3 is controlled in a state where it can penetrate the upper plate 1 and does not penetrate the lower plate 2, while the laser power on both sides of the laser array 3 is controlled in a state where it does not penetrate the single-layer plate, that is, the lasers on both sides do not penetrate the upper plate 1 and do not penetrate the lower plate 2. Furthermore, it is ensured that the penetration depth of each zone is controllable, thereby solving the problems of unstable penetration depth, discontinuous weld pool profile, and easy penetration of the lower plate 2.

[0052] Specifically, the laser array 3 is generated by a laser welding device, with a width of 2mm - 4mm, and at most 9 paths of laser parameters can be adjusted in real time. Among them, the array laser acts on the lapping position of the upper plate 1 and the lower plate 2 at a specific angle after passing through the collimating mirror, the first swing mirror, the second swing mirror, and the focusing mirror.

[0053] Optionally, the parameters of the laser array 3 include the output spot diameter. The output spot diameter is related to the attributes of the laser welding device, and the output spot diameter is usually 0.02mm - 1.5mm, preferably 0.02mm or 0.05mm.

[0054] Optionally, the parameters of the laser array 3 include the collimation-focus ratio (collimation-focus ratio = focal length of the focusing mirror / focal length of the collimating mirror). Optionally, the collimation-focus ratio of the laser welding head 1 is 1:2, 1:2.5 or 1:3, preferably 1:2.

[0055] S3: Adjust the position of the laser welding head relative to the weld seam so that the center of the laser array 3 is placed inside the edge of the upper plate 1 near the lap joint, and the long axis of the laser array 3 is arranged at an angle to the welding direction.

[0056] In the above steps, specifically in this embodiment, the position of the laser welding head relative to the weld seam is adjusted so that the center of the laser array 3 is placed inside the edge of the upper plate 1 near the lap joint. Specifically, as Figure 2 shown, define the center of the weld seam 4 at the edge of the upper plate 1 near the lap joint, and the center of the laser array 3 is placed at a position 0.2 mm - 0.6 mm away from the upper plate 1 near the weld seam center 4, that is, the range of the distance x is 0.2 mm - 0.6 mm, so as to ensure a large amount of melting of the base material of the upper plate 1, which is conducive to the formation of the convex back arc surface of the weld seam.

[0057] The long axis of the laser array 3 is arranged at an angle to the welding movement direction. Specifically, continue to refer to Figure 2 . The angle α is 60° - 90°, preferably 90°, that is, preferably the long axis of the laser array 3 is perpendicular to the welding direction. By adjusting the angle α, the weld width can be finely adjusted. When the laser array 3 is inclined to the weld seam, as the angle α decreases, the length projected onto the direction perpendicular to the weld seam also decreases. However, due to the inclination of the laser array 3, in fact, the arrival time of each laser beam in the direction perpendicular to the weld seam will be different. Therefore, the angle α should not be too large.

[0058] If the method of increasing or decreasing the number of laser beams is used to adjust the weld width, the adjustment range of the weld width is relatively large. Assuming that the collimation-focus ratio is 100:200, then for each additional laser beam, the total width of the laser array 3 increases by 0.5 mm. Therefore, the method of adjusting the number of beams is only applicable to the coarse adjustment of the weld width. Fine-tuning the angle α can achieve the effect of fine-tuning the weld width. Without considering the heat conduction of the material and only considering the effective width of the laser array 3, the theoretical weld width when the laser array 3 is inclined = total width of the laser array 3 * sinα, which is the largest when α is 90° and 0.866 times when α is 60°. Assuming that the total width of the laser array 3 is 2.1 mm, by fine-tuning the angle α, the adjustment range of the weld width is between 1.8 mm and 2.1 mm.

[0059] Optionally, the laser welding head is inclined, and the angle between the axis of the laser welding head and the vertical direction is 10°-15°. The laser array 3 is inclined to be incident on the weld seam, which can reduce the problems of incomplete fusion between the upper plate 1 and the lower plate 2 and the curling of the upper plate 1. Specifically, when a single laser beam is placed near the edge of the upper plate 1 on the lower plate 2, since the focused beam is not vertically incident, part of the laser beam will be blocked by the upper plate 1, resulting in possible incomplete penetration of the lower plate 2 at the lap joint, thus causing the problem of incomplete fusion at the lap joint. At the same time, the molten droplets of the upper plate 1 tend to gather inward due to the surface tension, forming a curled edge. Moreover, the focal points of the upper plate 1 and the lower plate 2 are also prone to inconsistency, and tilting the laser welding head by a certain angle will improve the above problems. In addition, although stainless steel does not belong to high-reflectivity materials, it also has a certain reflectivity. At the same time, there will inevitably be some spatter during the stainless steel welding process. Tilting by a certain angle can better protect the laser welding head and extend the service life of the laser welding head.

[0060] Optionally, the upper surface of the upper plate 1 is defined as the 0 focal position, and the focal point of the laser array 3 is adjusted to -2 mm to 0 mm to ensure that the penetration depth of the weld seam meets the requirements.

[0061] S4: The laser array 3 emits light, and the laser welding head moves along the lap joint of the upper plate 1 and the lower plate 2 and swings along the long axis direction of the laser array 3 to form a lap weld;

[0062] In the above steps, specifically in this embodiment, the laser array 3 emits light, and the laser welding head moves along the lap joint of the upper plate 1 and the lower plate 2 and swings to form a lap weld. Specifically, the swinging trajectory of the laser welding head is in the shape of an "8" as shown in Figure 3 or a circle as shown in Figure 4 , and the adjacent light spots are externally tangent. Preferably, it is in the shape of an "8" to achieve more uniform heating of the weld seam and effectively reduce welding defects such as pores and cracks.

[0063] Further, the swinging amplitude of the laser welding head is the center distance of the laser minus the diameter of the focused light spot, that is, W W = D - d f . Among them, referring to Figure 5 , D is the center distance between adjacent two laser beams, generally the set value of the equipment, and the diameter of the focused light spot d f = d*(F f / F c ), F f is the focal length of the focusing lens, F c is the focal length of the collimating lens, and d is the diameter of the output light spot. Specifically, the diameter of the output light spot is usually 0.02 mm - 1.5 mm, preferably 0.02 mm or 0.05 mm. The collimation-to-focus ratio is 1:2, 1:2.5 or 1:3, preferably 1:2.

[0064] Compared with single laser oscillating welding, the oscillation amplitude of the laser array 3 for oscillating welding is the single laser oscillation amplitude divided by the number of laser array 3 channels. When welding to obtain a weld seam of the same width, the laser array 3 can achieve a smaller oscillation amplitude, thereby improving the weld quality. During single laser welding, a large oscillation amplitude causes the material inside the oscillation trajectory to have no laser action, and it can only rely on heat conduction to melt the internal material, easily resulting in a shallower penetration depth or even a situation where the plate is not melted, thus leading to poor weld quality. However, the reduction of the oscillation amplitude of the laser array 3 can optimize the energy distribution of the laser array 3, ensure sufficient energy at the position of the weld center 4, cause a large amount of the base material at the weld center 4 to melt and flow down naturally under the action of gravity, ensure sufficient penetration depth at the weld center 4, good weld formation, no undercut on the lower plate 2, and effectively avoid uneven concave and convex in the weld seam.

[0065] Optionally, the oscillation frequency of the laser array 3 is the single laser oscillation frequency multiplied by the number of laser array 3 channels. Compared with single laser beam welding, it can achieve a higher welding frequency. Preferably, the oscillation frequency of the laser array 3 is set to be not less than 30 times the welding speed to evenly deliver the energy of the laser to the weld seam. At the same time, the welding efficiency can be effectively improved. Moreover, the oscillation frequency of the laser array 3 * oscillation amplitude < the limit speed of the oscillation motor of the laser welding head. Specifically, the oscillation frequency of the laser welding head depends on its specific hardware parameters, and the oscillation of the laser welding head is achieved by driving the reflecting mirror to rotate by two oscillation motors. The limit speed of the oscillation motor will limit the oscillation frequency and amplitude of the laser welding head, that is, oscillation frequency * oscillation amplitude < the limit speed of the oscillation motor. In the prior art, the limit speed of the oscillation motor generally does not exceed 3000 mm / s. And in practical applications, usually the oscillation amplitude is determined first and then the oscillation frequency to achieve high-speed welding with a small amplitude and high frequency, thereby improving the weld quality.

[0066] Optionally, the welding speed is set to 15 mm / s to 50 mm / s. Moreover, when the laser welding head emits laser, it can also deliver shielding gas to the weld seam. The shielding gas is nitrogen or argon to protect the upper plate 1 and the lower plate 2 to be welded from being polluted by other gases and impurities, ensuring the welding quality. Exemplarily, the flow rate of the shielding gas is 15 L / min to 25 L / min. The specific value of the flow rate is related to the size of the gas outlet and the distance from the gas outlet to the welding position, and also needs to be adjusted in real time according to the actual effect.

[0067] After welding, a part of the weld seam is cut for metallographic mapping and then the morphology of the molten pool is observed. If the morphology of the molten pool is not a continuous and smooth transition and there is an internal concave or external convex, the power of the laser array 3 needs to be further adjusted.

[0068] In the specific implementation of the above steps, the weld seam after welding is cut, and metallographic mapping is performed to observe the morphology of the molten pool. If the morphology of the molten pool does not have a continuous and smooth transition and there is an inward concavity or outward convexity, the power of the laser array 3 is further adjusted according to the actual situation. That is to say, if the various parameters of the cross-section of the weld seam do not meet the standards in Table 1, the power of the laser array 3 needs to be further adjusted.

[0069] Exemplarily, the upper plate 1 and the lower plate 2 to be welded are both corrugated 304L stainless steels with a thickness of 1.2 mm, and the steps of lap welding are as follows:

[0070] Lap the upper plate 1 and the lower plate 2 with a lap width of 10 mm, and place them on the welding jig for fixing. Use a rigid special fixture for fixing to ensure that the upper plate 1 and the lower plate 2 are pressed tightly together, and the gap after pressing does not exceed 0.2 mm. At intervals of 20 mm along the lap joint, pre-weld at least one welding point to fix the upper plate 1 and the lower plate 2 and avoid excessive gaps caused by welding deformation. Specifically, pre-weld once every 20 mm along the welding direction to solve the problem of warping during the welding process due to the thin plate thickness and long welding length.

[0071] Set the laser array 3 of the laser welding equipment to have 5 light outputs. The maximum power of a single laser is 1500 W, the output spot diameter is 0.05 mm, the focal length of the collimating mirror of the laser welding head is 100 mm, the focal length of the focusing mirror is 200 mm, the focusing spot diameter is 0.1 mm, the distance between single lasers is 0.5 mm, and the total width of the laser array 3 is 2.1 mm; in other embodiments, a larger weld width can also be obtained by increasing the number of laser paths.

[0072] Then, according to the placement angles of the upper plate 1 and the lower plate 2, adjust the position of the laser array 3 so that the long axis of the laser array 3 is perpendicular to the weld seam; in other embodiments, the included angle α between the long axis of the laser array 3 and the weld seam can also be adjusted to finely adjust the weld width.

[0073] Deviate the axis of the laser welding head from the vertical direction by 10°, so that the laser array 3 is obliquely incident on the weld seam; move the center of the laser array 3 to 0.4 mm away from the inner side of the upper plate 1 at the center of the weld seam 4; adjust the focus of the laser array 3 to -2 mm.

[0074] Specifically, along the direction from the upper plate 1 to the lower plate 2, the first, second, and third laser beams act on the upper plate 1, the fourth laser beam acts on the lap joint between the lower plate 2 and the upper plate 1, and the fifth laser beam acts on the lower plate 2. The power of the first laser beam is set to 150 W, the power of the second laser beam is set to 250 W, the power of the third laser beam is set to 300 W, the power of the fourth laser beam is set to 150 W, and the power of the fifth laser beam is set to 100 W. The swing trajectory of the laser welding head is set to an "8" shape, and the long axis of the "8" shape is perpendicular to the weld seam. The swing amplitude is set to 0.4 mm, and the swing frequency is set to 500 Hz. After swinging, a part of the fourth laser beam acts on the upper plate 1, and the other part acts on the lower plate 2.

[0075] The welding speed is set to 15 mm / s. At the same time, the shielding gas synchronously fed to the weld seam is argon, and the flow rate is 15 L / min.

[0076] The laser array 3 emits light, and the laser welding head moves along the welding direction and the preset swing trajectory to form a lap weld seam, completing the lap welding.

[0077] After welding is completed, the weld seam is cut for metallographic sample preparation and then the morphology of the molten pool is observed. There are some concave or convex areas in the morphology of the molten pool, and the transition is not continuously smooth. Further adjust the power of each laser beam. The adjusted laser powers are as follows: the power of the first laser beam is 160 W, the power of the second laser beam is 240 W, the power of the third laser beam is 290 W, the power of the fourth laser beam is 170 W, and the power of the fifth laser beam is 120 W. Repeat the above steps to obtain a new weld seam, and take the weld seam sample for metallographic sample preparation again to obtain a qualified weld seam that meets the actual ship operation standard.

[0078] For the weld seam welded by the above method, the weld seam smoothly transitions from the upper plate 1 to the lower plate 2, the surface is smooth, the consistency is good, there is no concave or convex, the transition is continuously smooth, and the measurement of the molten pool size meets the standard requirements, effectively improving the welding quality and welding efficiency. At the same time, no filler wire is required, effectively reducing the cost.

[0079] On the other hand, this embodiment also provides a laser welding device. The laser welding device includes a laser welding head. The laser welding head includes a laser array 3. The laser array 3 includes multiple laser beams. The laser power at the center of the laser array 3 is greater than that on both sides. The laser array 3 can swing along the long axis direction.

[0080] In some embodiments, the maximum power of a single laser beam supports optional values of 500W / 1000W / 1500W / 2000W, with an adjustment range of 10%-100%, and it meets the precise control of the single-channel output power to achieve precise control of the energy input in different zones of the weld seam. During the welding process of the lap joint of thin plates, the parameters of the single-row laser array 3 are set according to the material of the plate to be welded, the weld width, and the laser swing amplitude. The number of laser beams is selected according to the weld width to ensure that the laser array 3 can at least completely cover the weld seam. The laser power at the center of the laser array 3 is greater than that on both sides, that is: along the direction from the upper plate 1 to the weld center 4 to the lower plate 2, the laser power shows a low-high-low change trend, ensuring that the laser at the center of the laser array 3 can penetrate the upper plate 1, while the lasers on both sides are controlled in a state where they cannot penetrate the plate. Especially for the laser acting on the lower plate 2, precise power adjustment is required to avoid the problem of penetration of the lower plate 2.

[0081] In some embodiments, as Figure 2 shown, the laser array 3 swings along the long axis direction of the laser array 3. Specifically, the long axis is set at an angle to the welding movement direction, and the angle α is 60°-90°, preferably 90°, that is, preferably the long axis of the laser array 3 is perpendicular to the welding direction. By adjusting the angle α, the weld width can be finely adjusted. The swing frequency of the laser array 3 is the single-laser swing frequency * the number of laser array 3 paths. Compared with single-laser beam welding, it can achieve a higher welding frequency. It is preferably set that the swing frequency of the laser array 3 is not less than 30 times the welding speed to evenly deliver the energy of the laser to the weld seam. At the same time, the welding efficiency can be effectively improved. And, the swing frequency of the laser array 3 * the swing amplitude < the limit speed of the swing motor of the laser welding head. Specifically, the swing frequency of the laser welding head depends on its specific hardware parameters, and the swing of the laser welding head is achieved by driving the reflecting mirror to rotate by two swing motors. The limit speed of the swing motor will limit the swing frequency and amplitude of the laser welding head, that is, the swing frequency * the swing amplitude < the limit speed of the swing motor. In the prior art, the limit speed of the swing motor generally does not exceed 3000mm / s. And, in practical applications, usually the swing amplitude is determined first and then the swing frequency is determined to achieve welding with a small amplitude, high frequency, and high speed, thereby improving the weld quality.

[0082] This laser device is used to perform the above-mentioned thin-plate laser lap welding method and has all the beneficial effects of the above-mentioned thin-plate laser lap welding method, which will not be elaborated here.

[0083] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, various obvious changes, re-adjustments and substitutions can be made without departing from the protection scope of the present invention. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A thin plate laser lap welding method, characterized in that: The steps include: S1: overlapping the upper plate (1) and the lower plate (2) to be welded, fixing them on a welding jig, and pre-welding at least one welding point between the upper plate (1) and the lower plate (2); S2: selecting the number of laser paths according to the width of the weld, and setting the parameters of the laser array (3); wherein the laser array (3) comprises multiple laser paths, and the laser power at the center of the laser array (3) is greater than the laser power at both sides; S3: adjusting the position of the laser welding head relative to the weld so that the center of the laser array (3) is placed on the inner side of the edge of the upper plate (1) close to the overlap, and the long axis of the laser array (3) is arranged at an angle to the welding direction; S4: the laser array (3) emits light, the laser welding head moves along the overlapping portion of the upper plate (1) and the lower plate (2), and swings along the long axis direction of the laser array (3) to form an overlapping weld.

2. The thin plate laser lap welding method according to claim 1, characterized in that: In S2, the parameters of the laser array (3) include the power of each single laser channel, the output spot diameter and the collimation and focusing ratio. The power of each single laser channel of the laser array (3) is independently adjustable. The central laser power of the laser array (3) is controlled to be able to melt through the upper plate (1) without penetrating the lower plate (2). The laser powers on both sides of the laser array (3) are controlled to be unable to penetrate a single layer of plate.

3. The thin plate laser lap welding method according to claim 1, characterized in that: In S3, the edge of the upper plate (1) close to the overlap is the weld center (4), and the center of the laser array (3) is placed on the upper plate (1) perpendicular to the weld center (4) and 0.2 mm to 0.6 mm away from the weld center (4).

4. The thin plate laser lap welding method according to claim 1, characterized in that: In S3, the angle between the long axis of the laser array (3) and the welding movement direction is 60° to 90°, preferably 90°.

5. The thin plate laser lap welding method according to claim 1, characterized in that: In S3, the laser welding head is tilted, and the angle between the axis of the laser welding head and the vertical direction is 10°-15°.

6. The thin plate laser lap welding method according to claim 1, characterized in that: The upper surface of the upper plate (1) is defined as the 0 focal position, and the focal point of the laser array (3) is adjusted to -2 mm to 0 mm.

7. The thin plate laser lap welding method according to claim 1, characterized in that: In S4, the swing trajectory of the laser welding head is an "8" shape or a circle, and adjacent light spots are circumscribed, preferably an "8" shape.

8. The thin plate laser lap welding method according to claim 7, characterized in that: The swing amplitude W of the laser welding head W =Dd f , where D is the center distance between two adjacent lasers, and the focus spot diameter d f =d*(F f / F c ), F f is the focal length of the focusing lens, F c is the focal length of the collimator, d is the output spot diameter; And / or, it is preferred to set the oscillation frequency of the laser array (3) to be not less than 30 times the welding speed, and the oscillation frequency*oscillation amplitude<the limiting speed of the oscillation motor of the laser welding head.

9. The thin plate laser lap welding method according to claim 8, characterized in that: The welding speed is set to 15mm / s-50mm / s; the laser welding head can deliver shielding gas to the welding position, and the flow rate of the shielding gas is 15L / min-25L / min.

10. A laser welding device, characterized in that: The laser welding head comprises a laser array (3), the laser array (3) comprises multiple lasers, the laser power at the center of the laser array (3) is greater than the laser power at both sides, and the laser array (3) can swing along the long axis direction.

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