A laser-cmt double-sided composite welding method for aluminum alloy sheet t-joint

Abstract

The present application relates to the technical field of aluminum alloy welding, in particular to a laser-CMT double-sided composite welding method for aluminum alloy sheet T-shaped joint, comprising the following steps: S1, surface treatment is performed on the web plate and the base plate, the web plate and the base plate are placed into an inverted T shape and fixed, and a welding wire is placed between the web plate and the base plate; S2, two groups of welding mechanisms are symmetrically arranged on both sides of the web plate, the welding mechanism comprises a second welding gun assembly, a first welding gun assembly, a laser beam assembly and a shielding gas nozzle which are sequentially arranged along the welding direction, a third welding assembly is arranged on the bottom surface of the base plate, and the third welding assembly is arranged opposite to the laser beam assembly; S3, welding is performed. The present application can improve the laser energy utilization rate and welding efficiency of the molten workpiece in the aluminum alloy welding process, improve the stability of the laser and CMT welding process, avoid the generation of welding defects such as incomplete penetration / incomplete fusion, pores and weld spatter, reduce the sheet welding deformation, and improve the weld structure performance.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy welding technology, and in particular to a laser-CMT double-sided composite welding method for T-joints of thin aluminum alloy plates. Background Technology

[0002] Aluminum alloys possess a range of advantages, including low density, high specific strength, strong corrosion resistance, good thermal and electrical conductivity, excellent plasticity and processing properties, and low cost. Laser welding offers numerous advantages, such as low heat input, high welding speed, and good flexibility, making it an ideal technology for welding thin-walled aluminum alloy components. Currently, laser welding technology for thin aluminum alloy sheets is widely used in the manufacturing fields of automobiles, aerospace, and rail transportation.

[0003] The following problems exist in the welding process of aluminum alloys: high thermal conductivity and high coefficient of thermal expansion, which easily leads to welding deformation; high chemical reactivity of aluminum alloys, with oxide films easily forming on the surface. Due to the high melting point of the oxide film, it is difficult to melt during the welding process, which seriously affects the wetting and spreading properties of the liquid metal on the base material. Moreover, the loose oxide film easily absorbs water vapor from the air, which easily leads to defects such as hydrogen pores and oxide film pores during the welding process; aluminum has a strong ability to reflect radiation, so the energy threshold is very high when welding with high-energy beams such as laser beams, which places relatively high demands on the equipment.

[0004] Chinese patent "A Spatter-Free, Low-Deformation, High-Efficiency Welding Method for T-Joints of Thin Aluminum Alloy Plates" (Authorization Announcement No.: CN101954543B), published on January 26, 2011, discloses a method that uses two relatively independent laser-precise waveform-controlled short-circuit transfer arc composite heat sources for double-sided welding from both sides of the stiffener. The precise waveform control arc mainly controls the current and voltage waveforms during the short-circuit transfer of the molten droplets, ensuring that the welding current is kept at a very low value when the molten droplet bridge breaks, thus preventing welding spatter when short-circuit transfer occurs. However, in this method, the laser is in front and the arc is behind along the welding direction. Due to the reflection of the laser beam by the solid aluminum alloy, the utilization rate of laser energy acting on the base material is reduced. Furthermore, the welding wire's melting and transfer process significantly affects the stability of laser welding. Relevant literature indicates that in laser-CMT hybrid welding, the CMT transition mode differs from that of ordinary MIG / MAG, being a short-circuit transition. When the filament spacing is too close, it can easily interfere with the laser effect, impacting the keyhole and causing defects such as porosity. When the filament spacing is large, a composite effect cannot be formed, affecting the stability of the arc and the stability of the droplet transfer. Summary of the Invention

[0005] The purpose of this invention is to provide a laser-CMT double-sided composite welding method for T-joints of aluminum alloy thin plates, which improves the laser energy utilization rate and welding efficiency of the molten workpiece, enhances the stability of the laser and CMT welding process, avoids welding defects such as incomplete penetration / fusion, porosity, and weld spatter, reduces welding deformation of thin plates, and improves the microstructure and properties of the weld, thereby solving the above-mentioned problems.

[0006] To achieve the above objectives, the present invention provides the following solution: A laser-CMT double-sided composite welding method for aluminum alloy thin plate T-joints includes the following steps: S1. Perform surface treatment on the stiffener and the substrate, arrange the stiffener and the substrate in an inverted T-shape and fix them, and place welding wire between the stiffener and the substrate. S2. Two sets of welding mechanisms are symmetrically arranged on both sides of the stiffener. The welding mechanism includes a second welding gun assembly, a first welding gun assembly, a laser beam assembly, and a protective gas nozzle arranged sequentially along the welding direction. A third welding gun assembly is arranged on the bottom surface of the substrate. The third welding gun assembly is arranged opposite to the laser beam assembly. S3, Welding.

[0007] Preferably, in step S2, the laser beam assembly includes a first laser beam and a second laser beam, the first laser beam being close to the protective gas nozzle, and the power of the first laser beam being greater than the power of the second laser beam.

[0008] Preferably, in step S2, the two first laser beams located on both sides of the stiffener are symmetrically arranged, and the two second laser beams located on both sides of the stiffener are symmetrically arranged, with the spot spacing between the two first laser beams being 0 mm and the spot spacing between the two second laser beams being 0 mm.

[0009] Preferably, in step S2, the first welding torch assembly includes a CMT welding torch, with two CMT welding torches symmetrically arranged on both sides of the stiffener, and the heat source distance between the two CMT welding torches is 0mm.

[0010] Preferably, in step S2, the second welding torch assembly includes a first TIG welding torch, and two first TIG welding torches located on both sides of the stiffener are symmetrically arranged, with the welding nozzles of the two first TIG welding torches located at the joint between the stiffener and the substrate.

[0011] Preferably, in step S2, the third welding torch assembly includes a second TIG welding torch, which is located below the substrate, with the nozzle of the second TIG welding torch located at the middle position in the width direction of the stiffener, and the nozzle of the second TIG welding torch located between the light spots of the two second laser beams.

[0012] Preferably, a gap is left between the stiffener and the base plate, and the width of the gap is 0.001~0.5mm.

[0013] Preferably, the distance between the first laser beam and the second laser beam is 0.6~2mm.

[0014] Preferably, the distance between the CMT welding torch and the second laser beam is 0~1mm.

[0015] Preferably, the distance between the CMT welding torch and the heat source of the first TIG welding torch is 0~8mm.

[0016] The present invention has the following technical effects: In this invention, the preheating and melting effects of the second welding gun assembly and the laser beam assembly enable the liquid droplets to rapidly enter the pre-reserved gap between the stiffener and the substrate under capillary attraction, improving the wettability and spreading of the liquid droplets, increasing welding efficiency and weld quality. Simultaneously, the second welding gun assembly accelerates the melting speed of the welding wire, improving its melting and filling efficiency. The laser beam assembly acts as a combination of attracting and compressing the arc, improving arc stability and droplet transition stability. Part of the heat from the second welding gun assembly is used to heat the joint between the stiffener and the substrate, and another part is used to melt the welding wire, improving welding efficiency and reducing welding deformation. Pre-filling the joint between the stiffener and the substrate with the welding wire significantly reduces the reflection and loss of laser energy from the solid base material, improving the energy utilization rate of the laser beam assembly. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram illustrating the working principle of the present invention; Figure 2 This is an image showing the effect of conventional laser-CMT double-sided composite welding. Figure 3 This is a diagram showing the effect after welding is completed using the method of the present invention; Among them, 1. Shielding gas nozzle; 2. First laser beam; 3. Second laser beam; 4. CMT welding torch; 5. CMT power supply; 6. First TIG welding torch; 7. Keyhole; 8. Molten pool; 9. Rib plate; 10. Substrate; 11. TIG power supply; 12. Second TIG welding torch; 13. Synchronous oscillation device. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Reference Figure 1-3 This invention provides a laser-CMT double-sided composite welding method for aluminum alloy thin plate T-joints, comprising the following steps: S1. Perform surface treatment on the stiffener 9 and the substrate 10, arrange the stiffener 9 and the substrate 10 into an inverted T-shape and fix them, and place welding wire between the stiffener 9 and the substrate 10. S2. Two sets of welding mechanisms are symmetrically arranged on both sides of the stiffener 9. The welding mechanism includes a second welding gun assembly, a first welding gun assembly, a laser beam assembly, and a protective gas nozzle 1 arranged sequentially along the welding direction. A third welding gun assembly is arranged on the bottom surface of the substrate 10. The third welding gun assembly and the laser beam assembly are arranged opposite each other. S3, Welding.

[0022] In this invention, the preheating and melting effect of the second welding gun assembly and the laser beam assembly enables the liquid droplets to rapidly enter the gap reserved between the stiffener 9 and the substrate 10 under the action of capillary attraction, improving the wettability and spreading of the liquid droplets, increasing welding efficiency and weld quality. Simultaneously, the second welding gun assembly accelerates the melting speed of the welding wire, improving the welding wire melting and filling efficiency. The laser beam assembly plays a combined role of attracting and compressing the electric arc, improving arc stability and droplet transition stability. Part of the heat from the second welding gun assembly is used to heat the joint between the stiffener 9 and the substrate 10, and part is used to melt the welding wire, improving welding efficiency and reducing welding deformation. The pre-filling of the welding wire into the joint between the stiffener 9 and the substrate 10 significantly reduces the reflection and loss of laser energy by the solid base material, improving the energy utilization rate of the laser beam assembly.

[0023] A third welding gun assembly is set on the bottom surface of the substrate. The welding point of the third welding gun assembly is directly opposite the irradiation point of the laser beam assembly. This creates a combined effect, improving welding efficiency and the stability of the welding process.

[0024] In a further optimized scheme, in step S2, the laser beam assembly includes a first laser beam 2 and a second laser beam 3. The first laser beam 2 is close to the protective gas nozzle 1, and the power of the first laser beam 2 is greater than the power of the second laser beam 3.

[0025] In a further optimized scheme, in step S2, two first laser beams 2 located on both sides of the stiffener 9 are symmetrically arranged, and two second laser beams 3 located on both sides of the stiffener 9 are symmetrically arranged. The spot spacing between the two first laser beams 2 is 0mm, and the spot spacing between the two second laser beams 3 is 0mm.

[0026] Along the welding direction, the second laser beam 3 is in front, and the first laser beam 2 is behind. The second laser beam 3 forms a heat-conducting weld pool, and the first laser beam 2 forms a keyhole-type weld pool. This arrangement reduces the amount of welding spatter in the weld pool of the first laser beam 2, improves the mechanical properties of the weld microstructure, reduces the impact on the keyhole, and improves the transition stability and frequency of the molten droplets. The two first laser beams 2 located on both sides of the stiffener 9 are symmetrically arranged, and the spot distance between the two first laser beams 2 is 0 mm, thereby forming a through keyhole 7 at the joint between the stiffener 9 and the substrate 10. This improves the stability of the keyhole 7, facilitates the escape of welding bubbles from the weld pool through the through keyhole 7, and reduces the porosity of the weld.

[0027] To further optimize the scheme, in step S2, the first welding gun assembly includes a CMT welding gun 4, with two CMT welding guns 4 symmetrically arranged on both sides of the stiffener 9, and the heat source distance between the two CMT welding guns 4 is 0mm.

[0028] Further optimization of the scheme: In step S2, the second welding gun assembly includes a first TIG welding gun 6. The two first TIG welding guns 6 located on both sides of the stiffener 9 are symmetrically arranged, and the welding nozzles of the two first TIG welding guns 6 are located at the joint between the stiffener 9 and the substrate 10.

[0029] In a further optimized scheme, in step S2, the third welding torch assembly includes a second TIG welding torch 12, which is located below the substrate 10. The nozzle of the second TIG welding torch 12 is located at the middle position in the width direction of the stiffener 9, and the nozzle of the second TIG welding torch 12 is located between the light spots of the two second laser beams 3.

[0030] The design was further optimized by leaving a gap between the stiffener 9 and the substrate 10, with a gap width of 0.001~0.5mm. When the gap width is 0.001mm-0.5mm, the molten droplets can achieve better wetting and spreading effects within the gap.

[0031] The scheme was further optimized so that the distance between the first laser beam 2 and the second laser beam 3 was 0.6~2mm.

[0032] When the distance between the first laser beam 2 and the second laser beam 3 is less than 0.6mm, the keyholes of the first laser beam 2 and the second laser beam 3 overlap to form a large keyhole. In this case, the welding wire of the CMT welding gun 4 is close to this large keyhole, which will impact the keyhole and reduce the stability of the welding process. When the distance between the first laser beam 2 and the second laser beam 3 is greater than 2mm, the molten droplets after the welding wire of the CMT welding gun 4 melts cannot enter the molten pool formed by the first laser beam 2 in time, affecting the stability of the droplet filling and resulting in poor weld formation.

[0033] The scheme was further optimized so that the distance between the CMT welding torch 4 and the second laser beam 3 is 0~1mm.

[0034] When the distance between the CMT welding torch 4 and the second laser beam 3 is less than 0mm, the welding wire of the CMT welding torch 4 is too close to the first laser beam 2 and will impact the keyhole formed by the first laser beam 2, reducing the stability of the welding process. When the distance between the CMT welding torch 4 and the second laser beam 3 is greater than 1mm, the distance between the welding wire of the CMT welding torch 4 and the second laser beam 3 is too far, which reduces the attraction and compression effect of the second laser beam 3 on the arc of the CMT welding torch 4, reduces the stability of the arc and droplet transfer, and thus reduces the stability of the welding process.

[0035] The design was further optimized so that the distance between the CMT welding torch 4 and the first TIG welding torch 6 heat source is 0~8mm.

[0036] When the distance between the CMT welding torch 4 and the first TIG welding torch 6 heat source is less than 0mm, the first TIG welding torch 6 will prevent the welding wire of the CMT welding torch 4 from melting and transitioning into the T-joint gap. When the distance between the CMT welding torch 4 and the first TIG welding torch 6 heat source is greater than 8mm, the preheating of the T-joint gap by the first TIG welding torch 6 is not conducive to the wetting and spreading properties of the molten droplets that melt the welding wire of the CMT welding torch 4.

[0037] In this invention, both the first laser beam 2 and the second laser beam 3 are generated by a laser, which is at least one of an Nd:YAG laser, a CO2 laser, and a fiber laser; the CMT welding torch 4 is electrically connected to the positive terminal of the CMT power supply 5, and the negative terminal of the CMT power supply 5 is electrically connected to the substrate 10 / rib plate 9; the two first TIG welding torches 6 are respectively electrically connected to the positive and negative terminals of the TIG power supply 11; the protective gas ejected from the protective gas nozzle 1 is argon or helium; the first TIG welding torch 6, the CMT welding torch 4, the second laser beam 3, and the first laser beam 4 are located on both sides. Laser beam 2 and shielding gas nozzle 1 are both fixedly mounted on a welding fixture (the welding fixture is existing technology and is not shown in the figure). The welding fixture is fixed on a synchronous oscillation device 13. The power of the first laser beam 2 is 500~10000W, the power of the second laser beam 3 is 80~5000W, the welding speed is 0.5m~15m / min, the thickness of the substrate 10 and the stiffener 9 is less than or equal to 5mm, the reserved gap width between the stiffener 9 and the substrate 10 is 0.001~0.5mm, and the wire feed speed of the CMT welding torch 4 is 0.1~10. The welding current of the CMT welding torch 4 is 10~270A, the welding current of the first TIG welding torch 6 is 8~200A, the welding current of the second TIG welding torch 12 is 4~100A, the distance between the first laser beam 2 and the second laser beam 3 is 0.6~2mm, the distance between the heat source of the CMT welding torch 4 and the filament of the second laser beam 3 is 0~1mm, the distance between the heat source of the first TIG welding torch 6 and the CMT welding torch 4 is 0~8mm, the flow rate of the protective gas (argon or helium) of the protective gas nozzle 1 is 1~30L / min, and the maximum swing speed of the synchronous swing device 13 is 1600mm / s.

[0038] Depend on Figure 2 It can be seen that the weld formation is asymmetrical and poor (with undercut and weld porosity defects); and Figure 3The weld formation is symmetrical and of good quality. This is mainly because existing laser-CMT hybrid welding methods, in order to achieve the desired effect, use close-pitch laser wires, which can easily cause impact on the keyhole after the welding wire melts. Moreover, due to the low heat input of CMT to the base material, the wettability and spread of the molten droplets in the T-joint gap are poor, which has a significant impact on the weld formation quality. In contrast, this invention relies on the capillary attraction of the small gap, the first TIG welding gun 6 located in front of the CMT welding gun 4 (due to the reserved butt gap in the T-joint, the arc between the first TIG welding guns 6 on both sides of the T-joint can pass through the gap and heat the inside of the gap), and the preheating and melting effect of the second laser beam 3 behind the CMT welding gun 4, to quickly achieve the entry of liquid droplets into the reserved gap between the stiffener 9 and the base plate 10. With a small gap in the T-joint, the molten droplets at the end of the welding wire can quickly fill the gap in the T-joint under the action of capillary attraction, improving its wettability and spreading, thus improving welding formation efficiency and weld quality. Moreover, the first TIG welding guns 6 on both sides of the T-joint can also melt the welding wire, improving the welding wire melting and filling efficiency. When the welding wire is fed forward or pulled back, the distance between the second laser beam 3 and the welding wire is relatively close, which can play a combined role of attracting and compressing the arc, improving the stability of the arc and the stability of the droplet transfer. When the welding wire is fed forward or pulled back, the welding wire is far away from the first laser beam 2, which will not impact the keyhole 7 formed by the first laser beam 2, improving the stability of the keyhole 7 and reducing the weld porosity, which is significantly different from conventional laser-CMT hybrid welding. The two poles of the TIG power supply 11 are respectively connected to the two first TIG welding torches 6, which has little impact on the heat input of the stiffener 9 and the substrate 10. Moreover, the arc stability of the first TIG welding torch 6 is good (the welding speed of the base material has little impact on the arc of the first TIG welding torch 6). In addition, the welding wire of the CMT welding torch 4 is close to the arc of the first TIG welding torch 6. Part of the heat of the arc of the first TIG welding torch 6 is used to preheat the base material (because the joint between the stiffener 9 and the substrate 10 has a reserved butt gap, the arc between the TIG welding torches on both sides of the joint between the stiffener 9 and the substrate 10 can pass through the gap and heat the inside of the gap), and part of it is used to melt the welding wire, which improves the welding efficiency, reduces welding deformation, and enables high-efficiency laser-CMT double-sided composite welding of thin plate T-joints, which is significantly different from conventional laser-CMT composite welding. Due to the preheating of the arc of the first TIG welding torch 6 and the pre-filling of the welding wire of the CMT welding torch 4 into the joint gap between the stiffener 9 and the substrate 10, the reflection and loss of laser energy by the solid base material is greatly reduced, and the utilization rate of laser energy is improved. Along the welding direction, the second laser beam 3 on both sides of the stiffener 9 is in front and the first laser beam 2 is behind, which can reduce the amount of welding spatter in the molten pool of the first laser beam 2 and improve the mechanical properties of the weld.The first laser beams 2 on both sides of the laser beam are symmetrically arranged, and the distance between the two laser beams is zero, which can form a through keyhole 7, improve the stability of the keyhole 7, and facilitate the escape of welding bubbles from the molten pool through the through keyhole 7, thereby reducing the porosity of the weld. Since the energy of the second laser beams 3 on both sides of the stiffener 9 is relatively small, it only forms a thermally conductive molten pool, resulting in poor welding stability. However, by arranging a second TIG welding torch 12 below the second laser beams 3 on both sides of the stiffener 9, and electrically connecting the second TIG welding torch 12 to the negative terminal of another TIG power supply 11, while the positive terminal of the other TIG power supply 11 is electrically connected to the substrate 10, the second TIG welding torch 12 can form a combined effect with the second laser beam 3, which not only improves the stability of the welding process of the second laser beam 3, but also improves the thermal efficiency of the laser energy acting on the base material. The CMT welding gun 4, the first laser beam 2, and the second laser beam 3 on both sides of the stiffening plate 9 are connected by a special welding fixture. The synchronous swing device 13 is connected to this special welding fixture to realize synchronous swing during the welding process. This can reduce the generation of welding defects such as weld porosity and lack of fusion, and improve the weld structure and mechanical properties.

[0039] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0040] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A laser-CMT double-sided composite welding method for aluminum alloy thin plate T-joints, characterized in that, Includes the following steps: S1. Perform surface treatment on the stiffener (9) and the substrate (10), arrange the stiffener (9) and the substrate (10) into an inverted T shape and fix them, and place welding wire between the stiffener (9) and the substrate (10). S2. Two sets of welding mechanisms are symmetrically arranged on both sides of the stiffener (9). The welding mechanism includes a second welding gun assembly, a first welding gun assembly, a laser beam assembly, and a protective gas nozzle (1) arranged sequentially along the welding direction. A third welding gun assembly is arranged on the bottom surface of the substrate (10). The third welding gun assembly is arranged opposite to the laser beam assembly. S3, Welding; In step S2, the laser beam assembly includes a first laser beam (2) and a second laser beam (3), the first laser beam (2) is close to the protective gas nozzle (1), and the power of the first laser beam (2) is greater than the power of the second laser beam (3); In step S2, the two first laser beams (2) located on both sides of the stiffener (9) are symmetrically arranged, and the two second laser beams (3) located on both sides of the stiffener (9) are symmetrically arranged. The spot spacing of the two first laser beams (2) is 0 mm, and the spot spacing of the two second laser beams (3) is 0 mm. In step S2, the first welding torch assembly includes a CMT welding torch (4), and the two CMT welding torches (4) located on both sides of the stiffener (9) are symmetrically arranged, and the heat source distance between the two CMT welding torches (4) is 0mm; In step S2, the third welding torch assembly includes a second TIG welding torch (12), which is located below the substrate (10). The nozzle of the second TIG welding torch (12) is located at the middle position in the width direction of the rib (9), and the nozzle of the second TIG welding torch (12) is located between the light spots of the two second laser beams (3).

2. The laser-CMT double-sided composite welding method for aluminum alloy thin plate T-joints according to claim 1, characterized in that: In step S2, the second welding torch assembly includes a first TIG welding torch (6), and two first TIG welding torches (6) are symmetrically arranged on both sides of the stiffener (9), with the welding nozzles of the two first TIG welding torches (6) located at the joint between the stiffener (9) and the substrate (10).

3. The laser-CMT double-sided composite welding method for aluminum alloy thin plate T-joints according to claim 1, characterized in that: A gap is left between the stiffener (9) and the base plate (10), and the width of the gap is 0.001~0.5mm.

4. The laser-CMT double-sided composite welding method for aluminum alloy thin plate T-joints according to claim 1, characterized in that: The distance between the first laser beam (2) and the second laser beam (3) is 0.6~2mm.

5. The laser-CMT double-sided composite welding method for aluminum alloy thin plate T-joints according to claim 1, characterized in that: The distance between the CMT welding gun (4) and the second laser beam (3) is 0~1mm.

6. The laser-CMT double-sided composite welding method for aluminum alloy thin plate T-joints according to claim 2, characterized in that: The distance between the CMT welding torch (4) and the heat source of the first TIG welding torch (6) is 0~8mm.

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