A laser remelt welding method

Abstract

The application provides a laser remelting welding method and belongs to the technical field of laser welding.The method comprises the following steps: providing at least two layers of vehicle door materials to be welded, and treating the surface of a welding area; stacking the at least two layers of vehicle door materials to be welded in an up-down mode, clamping the at least two layers of vehicle door materials to be welded by using a clamp, and tightly abutting the welding areas of the at least two layers of vehicle door materials; according to the thickness and the width requirement of the bonding surface of the at least two layers of vehicle door materials, configuring the process parameters of a first welding seam and the process parameters of a second welding seam; and a galvanometer welding head sequentially performs the welding of the first welding seam and the second welding seam according to the process parameters, and the length of the second welding seam is not less than that of the first welding seam and the direction of the second welding seam is opposite to that of the first welding seam. Through twice independent laser deep penetration welding and remelting welding, the apparent welding seam is guaranteed, the problem of the welding seam quality reduction caused by the lack of follow-up protection gas in the flight welding process or the galvanometer welding curve track is solved, and the design difficulty of the clamp is simplified.

Description

Technical Field

[0001] The present invention relates to the technical field of laser welding, and in particular to a laser reflow welding method. Background Art

[0002] Laser welding technology for aluminum car bodies has been implemented on the production lines of numerous domestic and international automotive brands. Leveraging the advantages of laser welding, it achieves lightweight, high-strength, and high-quality all-aluminum or hybrid car bodies. During laser welding of materials commonly used for automotive door and window frames and inner panels, a shielding atmosphere containing inert gases such as argon or nitrogen is often required. This shielding gas prevents oxidation in the molten pool and dissipates heat generated by the weld. With increasing production rates and increasingly complex weld paths, the shielding gas during galvanometer welding cannot effectively track and protect both sides of the weld in real time. Furthermore, shielding gas delivered to the fixtures supporting the door and window frames and inner panels cannot be ventilated in real time, and continuous shielding gas delivery leads to significant gas waste. Consequently, manufacturers are urgently seeking improvements to the shieldless welding process for automotive doors. The use of autogenous welding without a shielding atmosphere eliminates the need for shielding gas, simplifies fixture design, enhances weld quality, and is becoming increasingly common.

[0003] Traditional single-head autogenous welding produces a crater at the end of the weld, caused by the collapse and closure of the laser deep-penetration keyhole. Reducing the crater by extending the weld length and slowly reducing the power can result in insufficient weld penetration at the end of the weld, significantly reducing the effective weld length and making it impossible to effectively connect automotive door and window frames and inner panels. Therefore, it is crucial to develop a laser reflow welding method that ensures weld appearance and weld quality without the use of shielding gas. Summary of the Invention

[0004] In view of this, the present invention proposes a laser reflow welding method that does not use a protective atmosphere, reduces the difficulty of fixture design, welds two layers of door material by deep penetration welding, and covers the first weld with the second weld to optimize the weld appearance.

[0005] The present invention provides a laser reflow welding method, comprising the following steps:

[0006] Provide at least two layers of door material to be welded and prepare the surface of the welding area;

[0007] Stacking at least two layers of door material to be welded one above the other, and clamping the at least two layers of door material to be welded with a clamp so that the areas to be welded of the at least two layers of door material are closely attached to each other;

[0008] Configure the process parameters of the first weld and the second weld according to the thickness and joint width requirements of at least two layers of door material;

[0009] The galvanometer welding head welds the first weld and the second weld in sequence according to the process parameters. The length of the second weld is not less than that of the first weld and the direction is opposite.

[0010] Based on the above technical solution, preferably, the first weld is made by laser deep penetration welding, and at least one layer of vehicle door material is welded through along the set direction of the first weld, and the penetration depth of the bottom layer of vehicle door material exceeds 30% of the thickness of the bottom layer of vehicle door material; the second weld is made by laser remelting welding, and the penetration depth of the second weld is different from the penetration depth of the first weld; the swing mode of the first weld is not exactly the same as the swing mode of the second weld.

[0011] Preferably, the oscillation mode of the first weld is: a spiral trajectory with a point on the weld centerline as a path point, a sinusoidal wave trajectory with a point on the weld centerline as a path point, or a circular trajectory with a point on the weld centerline as the center of a circle; the oscillation mode of the second weld is: a spiral trajectory with a point on the weld centerline as a path point, a sinusoidal wave trajectory with a point on the weld centerline as a path point, a circular trajectory with a point on the weld centerline as the center of a circle, a broken line trajectory passing through discrete points equally spaced on the weld centerline, or an 8-shaped trajectory surrounding discrete points on the weld centerline.

[0012] Further preferably, the galvanometer welding head includes a laser fiber, a dynamic focusing mechanism, a collimator, a fixed reflector, an XY galvanometer and a field mirror arranged in sequence; the laser fiber is arranged in a vertical direction for outputting a laser beam; the dynamic focusing mechanism is arranged on the output optical path of the laser fiber, and the dynamic focusing mechanism moves along the axial direction of the laser fiber, and a collimator is fixedly arranged at the center of the dynamic focusing mechanism, and the collimator is coaxially arranged with the laser fiber; the fixed reflector is arranged in the light-emitting side direction of the collimator and is connected to the collimator optical path; the XY galvanometer is arranged in the light-emitting side direction of the fixed reflector, and a fulcrum is provided on the XY galvanometer, and the XY galvanometer is swung relative to the fulcrum to change the position of the laser beam spot; the field mirror is arranged in the light-emitting side direction of the XY galvanometer for outputting a laser beam; wherein the dynamic focusing mechanism drives the collimator to move to change the spot size of the laser beam acting on the car door material.

[0013] More preferably, the spot size of the laser beam acting on the door material is calculated according to the following formula:

[0014] If the focus of the laser beam is on the surface of the door material, the spot size of the laser beam acting on the door material is Among them D 焦点 is the spot size at the focus of the laser beam output by the galvanometer welding head; f聚焦焦距 f is the focal length of the field lens of the galvanometer welding head; 准直焦距 is the focal length of the collimator lens of the galvanometer welding head; d 芯径 is the fiber diameter;

[0015] If there is a defocus distance Z between the focus of the laser beam and the surface of the door material, the Rayleigh length Z r for Where λ is the wavelength of the laser beam; M 2 is the beam quality; at this time, the spot size of the laser beam acting on the door material is

[0016] Still further preferably, the total thickness of the at least two layers of vehicle door material is in the range of [1 mm, 5 mm].

[0017] More preferably, at least two layers of the vehicle door material are both non-ferrous metal materials or ferrous metal materials.

[0018] Further preferably, when at least two layers of door materials are non-ferrous metal materials, the range of the laser beam power of the given first weld is [1500W, 5000W]; the range of the welding speed of the first weld is [40mm / s, 150mm / s]; the spot size of the laser beam of the first weld acting on the door material is [0.2mm, 1mm]; the range of the spot swing amplitude A1 of the first weld is [0.2mm, 1.6mm]; the range of the spot swing frequency of the first weld is [60Hz, 25 0Hz]; the power of the given second weld is in the range of [500W, 4000W]; the welding speed of the second weld is in the range of [60mm / s, 300mm / s]; the spot size of the laser beam of the second weld acting on the door material is [1mm, 3mm]; the spot swing amplitude A2 of the second weld is in the range of A1+[0, 2mm]; the spot swing frequency of the second weld is in the range of [100Hz, 500Hz]; the lengths of the second weld at the beginning and end are respectively longer than those of the first weld by [0, 5mm].

[0019] Further preferably, when at least two layers of vehicle door materials are both ferrous metal materials, the power of the given first weld is in the range of [1500W, 5000W]; the welding speed of the first weld is in the range of [20mm / s, 200mm / s]; the spot size of the laser beam of the first weld acting on the vehicle door material is [0.2mm, 1mm]; the power of the given second weld is in the range of [1000W, 3000W]; the welding speed of the second weld is in the range of [50mm / s, 300mm / s]; the spot size of the laser beam of the second weld acting on the vehicle door material is [0.6mm, 3mm]; the length of the second weld at the beginning and end is respectively longer than the first weld by [0, 5mm].

[0020] More preferably, the power of the laser beam of the first weld is greater than the power of the laser beam of the second weld, and the penetration depth of the first weld is greater than the penetration depth of the second weld; the spot size of the second weld is greater than the spot size of the first weld.

[0021] The laser reflow welding method provided by the present invention has the following beneficial effects compared with the prior art:

[0022] The laser reflow welding method provided by the present invention uses laser welding process parameters adapted to the thickness of the two layers of vehicle door material for the first weld. The first weld is laser deep penetration welding to ensure weld penetration and joint width. The second weld is reflow welding. The reflow welding process parameters control the laser energy density to achieve laser thermal conduction welding, covering the first weld and ensuring weld appearance. This method can solve the problem of weld quality degradation caused by the on-the-fly welding process or the lack of a galvanometer welding curve trajectory with a protective gas. In addition, the galvanometer welding head can also adjust the focal position, thereby changing the size of the light spot projected on the vehicle door material to meet the welding requirements of both welds. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 A schematic diagram of the weld direction of a laser reflow welding method of the present invention;

[0025] Figure 2 This is a schematic diagram of the optical path of a laser beam of a galvanometer welding head in a laser reflow welding method of the present invention, with the focus located on the surface of a vehicle door material;

[0026] Figure 3 A schematic diagram of an optical path in which the focus of a laser beam of a galvanometer welding head deviates from the surface of a vehicle door material in a laser reflow welding method of the present invention;

[0027] Figure 4 This is a front view of the first weld of Example 1 of a laser reflow welding method of the present invention;

[0028] Figure 5 This is a three-dimensional diagram of the effect of laser reflow welding in Example 1 of a laser reflow welding method of the present invention;

[0029] Figure 6 A three-dimensional diagram of the first weld of Example 2 of a laser reflow welding method of the present invention;

[0030] Figure 7 This is a stereoscopic diagram of the effect of laser reflow welding in Example 2 of a laser reflow welding method of the present invention. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] In traditional single laser autogenous welding, a crater is formed at the end of the weld due to the collapse and closure of the laser deep penetration keyhole. The arc crater can be reduced by extending the weld length and slowly reducing the power. However, this will result in insufficient penetration at the end of the weld, greatly reducing the effective weld length and making it impossible to effectively connect the car door window frame and inner panel. Figure 1 As shown, the present invention provides a laser reflow welding method, comprising the following steps:

[0033] S1: Provide at least two layers of door material to be welded and prepare the surface of the welding area.

[0034] Surface treatment involves removing oil and dirt from the material surface. Further surface polishing may be performed if necessary. The total thickness of at least two layers of door material should be within the range of [1mm, 5mm]. Door material on at least two sides should consist of two layers, or if more than two layers are used, the total thickness should be minimal, as this can create a risk of weld penetration.

[0035] S2: stacking at least two layers of vehicle door materials to be welded up and down, and clamping the at least two layers of vehicle door materials to be welded with a clamp, so that the areas to be welded of the at least two layers of vehicle door materials are tightly attached together.

[0036] The clamp is used for maintaining the relative position of the two layers of door materials unchanged during the welding process, and a conventional pneumatic turnover clamp or a manual clamp is used on a fixed base which is also provided with a ball head guide column for limiting the position of the door materials, the ball head guide column abuts against the end surface of the door materials, and the clamp and the ball head guide column jointly prevent the position of the two layers of door materials from shifting.

[0037] S3: According to the thickness of the at least two layers of door materials and the width requirement of the bonding surface, the process parameters of the first welding seam and the process parameters of the second welding seam are configured.

[0038] As shown in Figure 1 , the first welding seam adopts laser deep penetration welding, penetrates at least one layer of door materials along the set direction of the first welding seam, and makes the penetration depth of the bottommost layer of door materials exceed 30% of the thickness of the bottommost layer of door materials; the second welding seam adopts laser remelting welding, and the penetration depth of the second welding seam is different from that of the first welding seam; the swing mode of the first welding seam is not completely the same as that of the second welding seam.

[0039] As a further improvement of the embodiment, the swing mode of the first welding seam is: a spiral trajectory with a point on the center line of the welding seam as a passing point, a sinusoidal trajectory with a point on the center line of the welding seam as a passing point, and a circular trajectory with a point on the center line of the welding seam as a center; the swing mode of the second welding seam is: a spiral trajectory with a point on the center line of the welding seam as a passing point, a sinusoidal trajectory with a point on the center line of the welding seam as a passing point, a circular trajectory with a point on the center line of the welding seam as a center, a polyline trajectory passing through discrete points arranged at equal intervals on the center line of the welding seam, or an 8-shaped trajectory surrounding the discrete points on the center line of the welding seam.

[0040] As shown in Figure 2 and Figure 3 , the galvanometer welding head of the application comprises a laser optical fiber, a dynamic focusing mechanism, a collimating mirror, a fixed mirror, an XY galvanometer and a field lens arranged in sequence; the laser optical fiber is arranged in a vertical direction and used for outputting a laser beam; the dynamic focusing mechanism is arranged on the output light path of the laser optical fiber, and the dynamic focusing mechanism moves along the axial direction of the laser optical fiber; the collimating mirror is fixedly arranged at the center of the dynamic focusing mechanism and coaxially arranged with the laser optical fiber; the fixed mirror is arranged in the light output side direction of the collimating mirror and connected with the light path of the collimating mirror; the XY galvanometer is arranged in the light output side direction of the fixed mirror, and the XY galvanometer is arranged to swing relative to the fulcrum to change the position of the laser beam spot; the field lens is arranged in the light output side direction of the XY galvanometer and used for outputting the laser beam; wherein the dynamic focusing mechanism drives the collimating mirror to move and changes the size of the laser beam spot acting on the door material.

[0041] As shown in Figure 2 and Figure 3 , the size of the laser beam spot acting on the door material is calculated according to the following formula:

[0042] If the focus of the laser beam is on the surface of the door material, the spot size of the laser beam acting on the door material is Among them D 焦点 is the spot size at the focus of the laser beam output by the galvanometer welding head; f 准直焦距 f is the focal length of the field lens of the galvanometer welding head; 准直焦距 is the focal length of the collimator lens of the galvanometer welding head; d 芯径 is the fiber diameter;

[0043] If there is a defocus distance Z between the focus of the laser beam and the surface of the door material, the Rayleigh length Z r for Where λ is the wavelength of the laser beam; M 2 is the beam quality; at this time, the spot size of the laser beam acting on the door material is

[0044] In the present invention, at least two layers of the vehicle door material are nonferrous metal materials or ferrous metal materials. The process parameters of the first weld and the process parameters of the second weld under different material conditions are now described.

[0045] 1) When at least two layers of door materials are non-ferrous metals, the range of the laser beam power for the first weld is [1500W, 5000W]; the range of the welding speed for the first weld is [40mm / s, 150mm / s]; the range of the spot size of the laser beam acting on the door material for the first weld is [0.2mm, 1mm]; the range of the spot swing amplitude A1 for the first weld is [0.2mm, 1.6mm]; the range of the spot swing frequency for the first weld is [60Hz, 250Hz] ; The power of the given second weld is in the range of [500W, 4000W]; the welding speed of the second weld is in the range of [60mm / s, 300mm / s]; the spot size of the laser beam of the second weld acting on the door material is [1mm, 3mm]; the spot swing amplitude A2 of the second weld is in the range of A1+[0, 2mm]; the spot swing frequency of the second weld is in the range of [100Hz, 500Hz]; the length of the second weld at the beginning and end is longer than that of the first weld by [0, 5mm].

[0046] 2) when the at least two layers of the door material are both black metal materials, the power of the given first weld is in the range of [1500W, 5000W]; the welding speed of the first weld is in the range of [20mm / s, 200mm / s]; the spot size of the laser beam acting on the door material of the first weld is [0.2mm, 1mm]; the power of the given second weld is in the range of [1000W, 3000W]; the welding speed of the second weld is in the range of [50mm / s, 300mm / s]; the spot size of the laser beam acting on the door material of the second weld is [0.6mm, 3mm]; the lengths of the first and second welds at the head and tail are respectively longer than the length of the first weld by [0, 5mm].

[0047] S4: the galvanometer welding head sequentially performs welding of the first and second welds according to the process parameters, and the length of the second weld is not less than the length of the first weld and the direction is opposite.

[0048] In the two welds with different directions, the first weld adopts laser deep penetration welding to ensure the welding penetration depth and the width of the bonding surface; the second weld adopts remelt welding, and the remelt welding process parameters control the laser energy density to realize laser heat conduction welding, cover the first weld, and ensure the weld appearance. Since no protective atmosphere is used, no protective gas is used, and the design difficulty of the clamp can be reduced, and it is not necessary to blow protective gas following the weld position.

[0049] In actual operation, it is necessary to ensure that the power of the laser beam of the first weld is greater than the power of the laser beam of the second weld, and the penetration depth of the first weld is greater than the penetration depth of the second weld; the spot size of the second weld is greater than the spot size of the first weld.

[0050] The specific content of the present application will be described below in combination with specific embodiments and drawings.

[0051] Embodiment 1: The door material with a two-layer structure is selected; the upper door material and the lower door material are both non-ferrous metal materials, wherein the upper door material is a 2mm-thick 5182 aluminum alloy plate, and the lower door material is a 1.5mm-thick 6061 aluminum alloy plate.

[0052] Use a clamp to press the two layers of door material tightly together. According to the material thickness and connection width requirements, set the laser welding process parameters for welding the first weld. The optical fiber core diameter is 200μm, the collimator focal length is 116mm, and the focusing lens focal length is 420mm. The specifications of the galvanometer welding head remain unchanged in subsequent embodiments. Only the XY galvanometer swing amplitude and the position of the dynamic focusing mechanism are changed to adjust the defocus amount, spot size and swing trajectory of the spot. The spot size of the laser beam on the surface of the upper door material is 0.72mm. The laser power of the first weld is 4000W, the welding speed is 80mm / s, the swing mode of the first weld is circular, the swing amplitude is 0.8mm, the frequency is 200Hz, and the welding direction is forward. Here we define Figure 1 The welding direction from left to right is the positive direction, and the welding direction from right to left is the negative direction. Ensure that the penetration depth of the lower door material is 1 / 2 of the lower door material thickness. The welding result of the first weld is shown in Figure 4 ; Then call the second weld, i.e., the melt-back welding parameters, adjust the position of the dynamic focus mechanism, so that the laser beam spot size on the surface of the upper door material is 1.5mm; the laser power of the second weld is 3800W, the welding speed is 200mm / s, the swing mode is circular, the swing amplitude is 1.2mm, the frequency is 200Hz, the welding direction is reversed, and the length of the second weld is 2mm longer than the first. According to this laser melt-back welding method, the aluminum alloy door weld can be well-formed and free of arc pits. The results after the second welding are shown in Figure 2. Figure 5 .

[0053] Example 2: A two-layer door material is selected; the upper door material and the lower door material are both non-ferrous metal materials, wherein the upper door material is a 1.5mm thick 5182 aluminum alloy plate, and the lower door material is a 2.5mm thick 6061 aluminum alloy plate.

[0054] The two layers of door material were tightly pressed together using a fixture. Laser welding parameters were set for the first weld based on the material thickness and joint width requirements. The galvanometer welding head used a 50μm fiber core diameter, a 125mm collimator focal length, a 400mm focusing lens focal length, and a 0.16mm spot size. Laser power was set to 3600W, a welding speed of 100mm / s, a circular oscillation pattern with an amplitude of 1mm, a frequency of 180Hz, and a forward welding direction, ensuring that the lower plate had a penetration depth of half that of the underlying material. For the second reflow welding pass, the laser power was adjusted to 3000W, a welding speed of 200mm / s, and the dynamic focus mechanism was adjusted to achieve a 2mm spot size on the workpiece. The oscillation pattern was linear with an amplitude of 1mm and a frequency of 220Hz. The second weld was the same length as the first, but in the opposite direction. This laser reflow welding method achieves a well-formed, crater-free weld seam on aluminum alloy doors.

[0055] Example 3: A two-layer door material is used; both the upper and lower door materials are ferrous metals, with the upper and lower layers being 1mm thick galvanized sheet metal. The parameters of the galvanometer welding head used are identical to those of Example 1.

[0056] Use a fixture to press the two layers of door material tightly together. According to the material thickness and connection width requirements, set the laser welding process parameters to weld the first weld. The spot size of the laser beam on the surface of the upper door material is 0.7mm. The laser power of the first weld is 3600W, the welding speed is 100mm / s, and the welding direction is forward. Ensure that the penetration depth of the lower door material is 1 / 2 of the lower door material plate thickness. The spot size of the laser beam acting on the workpiece is 0.7mm. The welding results of the first weld are shown in Figure 2. Figure 6 The second reflow welding parameters are: laser power 1800W, welding speed 200mm / s, laser beam spot size 1.2mm on the workpiece, and welding direction is reversed. According to this laser reflow welding method, the galvanized sheet door weld can be formed with good surface appearance, minimal arc pits, and good welding quality. The results after the second welding are shown in Figure 2. Figure 7 .

[0057] As can be seen from the above examples, the galvanometer welding head will vibrate when welding non-ferrous metals, but it does not need to vibrate when welding ferrous metals. The above examples illustrate two layers of car door material. In practice, the number of layers of car door material used in the above examples is not considered a limitation of the technical solution.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A laser reflow welding method, characterized in that: The steps include: Provide at least two layers of door material to be welded and prepare the surface of the welding area; Stacking at least two layers of door material to be welded one above the other, and clamping the at least two layers of door material to be welded with a clamp so that the areas to be welded of the at least two layers of door material are closely attached to each other; Configure the process parameters of the first weld and the second weld according to the thickness and joint width requirements of at least two layers of door material; The galvanometer welding head performs the first weld and the second weld in sequence according to the process parameters. The length of the second weld is not less than that of the first weld and the direction is opposite. The first weld is laser deep penetration welding, penetrating at least one layer of door material along the set direction of the first weld, and the penetration depth of the bottom layer of door material exceeds 30% of the thickness of the bottom layer of door material; the second weld is laser back welding, and the penetration depth of the second weld is different from the penetration depth of the first weld; the oscillation mode of the first weld is different from the oscillation mode of the second weld; The galvanometer welding head includes a laser fiber, a dynamic focusing mechanism, a collimator, a fixed reflector, an XY galvanometer and a field mirror arranged in sequence; the laser fiber is arranged in a vertical direction for outputting a laser beam; the dynamic focusing mechanism is arranged on the output optical path of the laser fiber, and the dynamic focusing mechanism moves along the axial direction of the laser fiber, a collimator is fixedly arranged at the center of the dynamic focusing mechanism, and the collimator is coaxially arranged with the laser fiber; the fixed reflector is arranged on the light-emitting side of the collimator and is connected to the collimator optical path; the XY galvanometer is arranged on the light-emitting side of the fixed reflector, a fulcrum is provided on the XY galvanometer, and the XY galvanometer is swung relative to the fulcrum to change the position of the laser beam spot; the field mirror is arranged on the light-emitting side of the XY galvanometer to output the laser beam; wherein the dynamic focusing mechanism drives the collimator to move to change the spot size of the laser beam acting on the door material; The spot size of the laser beam acting on the door material is calculated according to the following formula: If the focus of the laser beam is on the surface of the door material, the spot size of the laser beam acting on the door material is Among them D 焦点 is the spot size at the focus of the laser beam output by the galvanometer welding head; f 聚焦焦距 f is the focal length of the field lens of the galvanometer welding head; 准直焦距 is the focal length of the collimator lens of the galvanometer welding head; d 芯径 is the fiber diameter; If there is a defocus distance Z between the focus of the laser beam and the surface of the door material, the Rayleigh length Z r for Where λ is the wavelength of the laser beam; M 2 is the beam quality; at this time, the spot size of the laser beam acting on the door material is 2. The laser reflow welding method according to claim 1, characterized in that: The oscillation mode of the first weld is: a spiral trajectory with a point on the weld centerline as a path point, a sinusoidal wave trajectory with a point on the weld centerline as a path point, and a circular trajectory with a point on the weld centerline as the center of a circle; the oscillation mode of the second weld is: a spiral trajectory with a point on the weld centerline as a path point, a sinusoidal wave trajectory with a point on the weld centerline as a path point, a circular trajectory with a point on the weld centerline as the center of a circle, a broken line trajectory passing through discrete points set at equal intervals on the weld centerline, or an 8-shaped trajectory surrounding discrete points on the weld centerline.

3. The laser reflow welding method according to claim 1, characterized in that: The total thickness of the at least two layers of door material is in the range of [1mm, 5mm].

4. The laser reflow welding method according to claim 1, characterized in that: At least two layers of door materials are made of non-ferrous metal or ferrous metal.

5. The laser reflow welding method according to claim 4, characterized in that: When at least two layers of door materials are non-ferrous metal materials, the range of the laser beam power of the given first weld is [1500W, 5000W]; the range of the welding speed of the first weld is [40mm / s, 150mm / s]; the spot size of the laser beam acting on the door material of the first weld is [0.2mm, 1mm]; the range of the spot swing amplitude A1 of the first weld is [0.2mm, 1.6mm]; the range of the spot swing frequency of the first weld is [60Hz, 250Hz]; The power of the given second weld is in the range of [500W, 4000W]; the welding speed of the second weld is in the range of [60mm / s, 300mm / s]; the spot size of the laser beam of the second weld acting on the door material is [1mm, 3mm]; the spot swing amplitude A2 of the second weld is in the range of A1+[0, 2mm]; the spot swing frequency of the second weld is in the range of [100Hz, 500Hz]; the length of the second weld at the beginning and end is longer than that of the first weld by [0, 5mm].

6. The laser reflow welding method according to claim 4, characterized in that: When at least two layers of door materials are made of ferrous metal, the power of the given first weld is in the range of [1500W, 5000W]; the welding speed of the first weld is in the range of [20mm / s, 200mm / s]; the spot size of the laser beam of the first weld acting on the door material is [0.2mm, 1mm]; the power of the given second weld is in the range of [1000W, 3000W]; the welding speed of the second weld is in the range of [50mm / s, 300mm / s]; the spot size of the laser beam of the second weld acting on the door material is [0.6mm, 3mm]; the length of the second weld at the beginning and end is longer than that of the first weld by [0, 5mm] respectively.

7. The laser reflow welding method according to any one of claims 5 or 6, characterized in that: The power of the laser beam of the first weld is greater than that of the second weld, and the penetration depth of the first weld is greater than that of the second weld; the spot size of the second weld is greater than that of the first weld.

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