Laser welding method for T-shaped structure

Abstract

The invention provides a T-shaped structure laser welding method. The T-shaped structure laser welding method comprises the following steps that alloy powder is prepared; establishing the relevance between the cold spraying process parameters and the thickness and density of the alloy powder deposition layer; designing a surface deposition layer on the contact surface of the skin and the stringer, and designing a weld leg deposition layer in a to-be-welded area of the skin and the stringer; cleaning the surfaces of the skin and the stringer; performing cold spraying on alloy powder by adopting a first cold spraying process parameter to form a surface deposition layer; placing a stringer on the surface deposition layer along the center line of the surface deposition layer; performing cold spraying on the alloy powder by adopting a second cold spraying process parameter to obtain a weld leg deposition layer with a second design size; and the to-be-welded area is subjected to laser welding according to preset laser welding process parameters, and the T-shaped structure is formed. According to the method, the occupied precision of stringer assembly and the laser energy utilization rate of materials can be improved, overlarge assembly gaps are filled, flexible regulation and control of filling welding material components are achieved, and the stability of the welding process and the welding quality are improved.

Description

Technical Field

[0001] The invention relates to the technical field of welding, and more specifically to a T-shaped structure laser welding method. Background Art

[0002] In order to meet the demand for lightweight aircraft, large and complex curved panels have become one of the most important components of the fuselage. The T-shaped structure of the fuselage panel is mainly composed of skin-long stringers. The traditional manufacturing method of this type of structure often uses mechanical connection. However, this type of connection method not only has low production efficiency but also cannot achieve weight reduction. Laser welding has the advantages of fast welding speed, low heat input, and small welding deformation. Therefore, using laser welding instead of mechanical connection to achieve the connection of T-shaped structures can achieve weight reduction and reduce aircraft energy consumption on the one hand; on the other hand, the welding process is simple, the production efficiency is high, and the small-to-large combination can increase material utilization and reduce manufacturing costs. In the 1990s, Airbus developed a dual-beam laser welding technology, which fills the burning and evaporation of alloy elements during welding by filling welding wire on both sides, inhibits welding defects such as undercuts, holes, and cracks, ensures the quality of weld formation, improves the mechanical properties of welds, and is successfully applied to the connection of T-shaped structures of fuselage panels of various models, greatly reducing the weight of the fuselage, improving the fuel economy of the aircraft, and significantly reducing the manufacturing cost of the fuselage. The T-type structure has a large structural constraint during the laser welding process, the stress concentration problem is more prominent, and the cracking tendency is more obvious. The chemical composition of the weld can be adjusted by filling the welding wire to avoid the occurrence of crystallization cracks and improve the joint strength. However, the existing commercial welding wire is difficult to meet the requirements of weld alloy regulation and crack suppression. If a welding wire with a new composition ratio is prepared according to actual needs, the research and development and production costs will be greatly increased. Moreover, in the process of using the filling welding wire to realize the laser welding of the T-type structure, the feeding conditions of the welding wire (direction, angle, speed and position) have an important influence on the stability of the welding process, which puts forward strict requirements on the stability of the wire feeding mechanism, and the welding wire is easily affected by laser parameters (power, incident angle, focal position), welding speed, plasma, spatter and other factors when being fed into the molten pool. The fluctuations of the above factors will cause the welding wire to be unable to be continuously and stably fed into the molten pool, affecting the stability of the T-type structure double-beam laser welding process and the forming quality of the weld.

[0003] In addition, the T-shaped structure needs to accurately position the long stringer before welding, and the positioning tolerance does not exceed 1mm. The existing technology generally uses other tooling fixtures or measuring tools to achieve its positioning. The high assembly precision requirement of the workpiece before welding reduces the reliability and production efficiency of the T-shaped structure dual-beam laser welding.

[0004] Furthermore, due to the unique molten pool flow field of the T-type structure, the components of the base material and the welding wire in the molten pool are not evenly mixed, resulting in weak uniformity of the welding structure at the contact interface between the skin and the long stringer. And due to the influence of the processing accuracy of the raw materials, there is a local excessive gap during the assembly of the skin and the long stringer, which affects the welding quality of the T-type structure. And because the alloy has a high reflectivity to the laser, the energy utilization rate is low during the laser welding process, which limits the expansion and application of laser welding technology. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] The technical problem to be solved by the present invention is that the existing T-shaped structure has the problems of unstable welding process, low assembly accuracy and poor weld forming quality; and the existing aluminum alloy T-shaped structure has the problems of low long truss assembly positioning accuracy, low welding laser energy utilization, unstable welding process and poor weld forming quality.

[0007] (II) Technical solution

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A T-shaped structure laser welding method is provided, which is used to weld a skin and a long stringer to form a T-shaped structure, comprising the following steps:

[0010] S1. preparing alloy powder, wherein the alloy powder is a base material powder, or a base material powder containing a strengthening element, or a mixed powder consisting of a base material powder and a single strengthening element powder, or a mixed powder consisting of a base material powder and a powder containing a strengthening element, wherein the composition of the base material powder is consistent with the material composition of the T-shaped structure;

[0011] S2. Conducting a cold spraying process test of the alloy powder to form an alloy powder deposition layer, and establishing a correlation between cold spraying process parameters and the thickness and density of the alloy powder deposition layer;

[0012] S3, designing a surface deposition layer on the contact surface between the skin and the long stringer, designing a weld foot deposition layer in the area to be welded between the skin and the long stringer, determining a first design size of the surface deposition layer according to the size of the long stringer, and determining a second design size of the weld foot deposition layer according to laser welding parameters;

[0013] S4. Surface cleaning of skin and long stringers;

[0014] S5, determining the design thickness of the surface deposition layer, determining the first cold spraying process parameters of the alloy powder according to the design thickness, placing a surface deposition layer mold corresponding to the first design size on the skin, and cold spraying the alloy powder in the surface deposition layer mold using the first cold spraying process parameters to form the surface deposition layer having the first design size and design thickness;

[0015] S6, placing the long stringer on the surface sediment layer along the center line of the surface sediment layer;

[0016] S7, determining the second cold spraying process parameters of the alloy powder according to the second design size, placing a weld foot deposition layer mold corresponding to the second design size in the welding area on both sides of the long stringer, and cold spraying the alloy powder in the weld foot deposition layer mold using the second cold spraying process parameters to obtain a weld foot deposition layer with the second design size;

[0017] S8. Laser welding is performed on the area to be welded using preset laser welding process parameters to form a T-shaped structure, wherein the size of the weld pool during the welding process is not less than the second design size.

[0018] Preferably, the method further comprises the following steps:

[0019] S9. Perform non-destructive testing on T-type structure welding joints. Non-destructive testing methods include X-ray testing and penetration testing.

[0020] Preferably, in step S1, the alloy powder is a base material powder containing strengthening elements, and when the base material powder is an aluminum alloy powder, the base material powder containing strengthening elements includes a Sc element in a mass fraction range of 0.15%-0.30%, and / or a Zr element in a mass fraction range of 0.10%-0.20%, and the particle size of the alloy powder is 15μm to 53μm.

[0021] Preferably, in step S1, when the alloy powder is a base material powder or a base material powder containing strengthening elements, the preparation method of the alloy powder includes at least one of an inert gas atomization method, a plasma rotating electrode method, and a radio frequency plasma method;

[0022] When the alloy powder is a mixed powder composed of a base material powder and a single strengthening element powder, or a mixed powder composed of a base material powder and a powder containing a strengthening element, the preparation method of the alloy powder is a mechanical mixing method.

[0023] Preferably, in step S3, the first design dimension includes the length of the surface deposition layer and the width of the surface deposition layer, wherein the length of the surface deposition layer is L, the width of the surface deposition layer is 1δ~1.2δ, L is the length of the long stringer, and δ is the width of the long stringer.

[0024] Preferably, in step S3, the calculation formula of the second design size is as follows:

[0025]

[0026] Among them, x2 is the second design weld leg size, x1 is the first design weld leg size, x1 is the length of the right angle side of the largest isosceles right triangle drawn in the cross section of the fillet weld, r is the radius of the welding wire used in conventional double-beam laser wire welding, which is generally 0.4mm~0.6mm, and v w is the wire feeding speed, v is the welding speed, and ρ is the coating density under specific cold spraying process parameters. The value of coating density ρ can be determined based on the database of cold spraying process parameters and coating density, which is generally 75% to 95%.

[0027] Preferably, in step S4, mechanical cleaning, chemical cleaning or laser cleaning is used to clean the surface of the skin and the long stringer; when the laser cleaning method is used to clean the surface of the skin and the long stringer, the process parameters of the laser cleaning method include pulse laser power P, scanning speed v and pulse frequency f, the pulse laser power P is 160W-250W, the scanning speed is 1500mm / s-3000mm / s, and the pulse frequency is 2kHz-4kHz.

[0028] Preferably, in step S5, the first cold spraying process parameters include gas pressure p, working gas temperature T, spraying angle α and spraying distance d, wherein the gas pressure p is 2MPa~5MPa, the working gas temperature T is 300℃~600℃, the spraying angle α is 40°-60°, and the spraying distance d is 10mm~50mm.

[0029] Preferably, in step S7, the second cold spraying process parameters include gas pressure p, working gas temperature T, spraying angle α and spraying distance d, wherein the gas pressure p is 2MPa~5MPa, the working gas temperature T is 300℃~600℃, the spraying angle α is 40°-60°, and the spraying distance d is 10mm~50mm.

[0030] Preferably, in step S8, the preset laser welding process parameters include the welding plane angle θ, the laser processing head deflection angle η, the laser offset y, the laser power P and the welding speed v, wherein the welding plane angle θ is 20°-70°, the laser processing head deflection angle η is 0°~15°, the laser offset y is -1mm~3mm, the laser power P is 2000W~4000W, and the welding speed is 2m / min~4m / min.

[0031] (III) Beneficial effects

[0032] The above technical solution of the present invention has at least the following advantages:

[0033] 1. In the present invention, a surface deposition layer having a first design size and a design thickness is cold sprayed on a specific area of ​​the skin. The surface deposition layer can assist in accurately positioning the long stringer on the skin. Compared with the method of manually measuring and positioning in the prior art, the present invention improves the positioning accuracy of the long stringer assembly.

[0034] 2. In the present invention, in particular, when the base material is an aluminum alloy, a weld foot deposition layer is designed in the area to be welded between the skin and the long stringer. The weld foot deposition layer is formed by cold spraying an alloy powder with a specific composition, thereby reducing the surface roughness of the area to be welded between the skin and the long stringer, reducing its reflection of the laser, and improving the absorption rate of the material in the area to be welded to the laser and the utilization rate of the laser energy.

[0035] 3. In the present invention, during the welding process, the weld foot deposit layer absorbs the welding heat to form a molten pool, and the molten pool will flow to the assembly gap between the skin and the long stringer under the action of gravity, thereby effectively filling the locally excessive assembly gap between the skin and the long stringer, thereby improving the forming quality of the T-shaped welded joint.

[0036] 4. In the present invention, a surface deposition layer is formed by alloy powder with specific composition. The surface deposition layer participates in the formation of the weld during the welding process, and can regulate the welding structure of the contact interface between the skin and the long stringer, optimize the welding structure, and further improve the mechanical properties of the T-type structure welded joint; by adjusting the types of strengthening elements in the alloy powder, flexible regulation of the alloy elements of the weld can be achieved.

[0037] 5. In the present invention, alloy powder with specific composition is sprayed onto specific parts of the T-shaped structure by cold spraying technology, so that a surface deposition layer with a first design size and a weld foot deposition layer with a second design size are formed at the specific parts, so as to replace conventional laser wire welding. This not only solves the problem of difficult control of the stability of the filler wire, but also facilitates the flexible regulation of the composition of the filler welding material, reduces the probability of welding defects, and can also improve the stability of the T-shaped structure welding process and the welding quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. 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 creative work.

[0039] Figure 1 It is a three-dimensional structural schematic diagram of a T-shaped structure provided by an embodiment of the present invention.

[0040] Figure 2 yes Figure 1 A partial enlarged view of point A in the middle.

[0041] Figure 3 It is a schematic diagram of the position of the surface deposition layer mold provided in an embodiment of the present invention.

[0042] Figure 4 It is a schematic diagram of the cross-sectional morphology of the T-shaped structure before and after laser welding provided by an embodiment of the present invention.

[0043] Figure 5 It is a schematic diagram of a T-shaped structure laser welding method provided in an embodiment of the present invention.

[0044] The reference numerals in the figures are:

[0045] 1. Surface deposition layer; 2. Weld foot deposition layer; 3. Skin; 4. Long stringer; 5. Surface deposition layer mold; 6. Welding seam; 7. Laser beam. DETAILED DESCRIPTION

[0046] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0047] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly located on the other element or indirectly located on the other element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or indirectly connected to the other element.

[0048] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention, and do not indicate that a device or element must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0049] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating relative importance or indicating the number of technical features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. The specific implementation of the present invention is described in more detail below in conjunction with specific embodiments:

[0050] like Figure 1As shown, an embodiment of the present invention provides a T-shaped structure laser welding method for welding a skin 3 and a long stringer 4 to form a T-shaped structure, comprising the following steps:

[0051] S1. Prepare alloy powder, which is a base material powder, or a base material powder containing strengthening elements, or a mixed powder composed of a base material powder and a single strengthening element powder, or a mixed powder composed of a base material powder and a powder containing strengthening elements; wherein the composition of the base material powder is consistent with the material composition of the T-shaped structure; specifically, the base material powder refers to a powder of a metal alloy element, for example, when the base material is an aluminum alloy, the base material powder is an aluminum alloy powder of a corresponding composition; when the base material is a titanium alloy, the base material powder is a titanium alloy powder of a corresponding composition; a single strengthening element powder refers to a powder of a pure metal element, for example, when the base material is an aluminum alloy, the single strengthening element powder may be zirconium powder or scandium powder; a strengthening element-containing powder refers to an alloy powder containing strengthening elements, and the strengthening element-containing powder contains other metal elements in addition to the strengthening elements, for example, the strengthening element-containing powder may be a powder made of an alloyed ingot formed by Zr and Al, or a powder made of an alloyed ingot formed by Sc and Al. More specifically, when the base material powder containing strengthening elements is an aluminum alloy powder, the base material powder containing strengthening elements includes Sc (scandium) element preferably in the mass fraction range of 0.15%-0.30%, and Zr (zirconium) element preferably in the mass fraction range of 0.10%-0.20%, and the particle size of the alloy powder is preferably 15μm to 53μm. Single strengthening element powders include but are not limited to Sc and Zr, and the strengthening elements in the strengthening element powder include but are not limited to Sc and Zr. Sc and Zr elements are effective nucleating agents in aluminum alloys, which can effectively refine the weld structure, inhibit the generation of welding cracks, and improve the mechanical properties of the weld. The shape of the alloy powder can be irregular or regular spherical. In some embodiments, the composition, composition, shape and particle size of the alloy powder can be designed based on the microstructure and metallurgical characteristics of the joint of the T-type structure. The joint microstructure of the T-type structure has five different characteristic areas from the center of the weld to the parent material area, which are equiaxed crystal area, columnar crystal area, partial melting area, overheating area and parent material area. The T-type structure has the following metallurgical characteristics: in the process of laser welding, it is easy to have metallurgical defects such as pores and cracks due to the influence of the materials of the skin 3 and the long stringer 4, its own structural characteristics and process parameters. Further, when the alloy powder is a parent material powder, or a parent material powder containing strengthening elements, the preparation method of the alloy powder includes at least one of an inert gas atomization method, a plasma rotating electrode method and a radio frequency plasma method; when the alloy powder is a mixed powder composed of a parent material powder and a single strengthening element powder, or a mixed powder composed of a mixture of a parent material powder and a powder containing strengthening elements, the preparation method of the alloy powder is a mechanical mixing method.

[0052] S2. Conduct a cold spraying process test on alloy powder to form an alloy powder deposition layer, and establish the correlation between the cold spraying process parameters and the thickness and density of the alloy powder deposition layer; specifically, the specific operation process of the cold spraying process test is as follows: select multiple groups of cold spraying process parameters with a single variable, and in the same environment, cold spray the alloy powder onto the surface of the same material through multiple groups of different cold spraying process parameters, to form multiple groups of alloy powder deposition layers on the surface, measure the thickness and density of the multiple groups of alloy powder deposition layers, and find out the correlation (positive correlation or negative correlation) between the cold spraying process parameters and the thickness and density of the alloy powder deposition layer through multiple groups of data.

[0053] S3, such as Figure 1 and Figure 2 As shown, a surface deposition layer 1 is designed on the contact surface between the skin 3 and the long stringer 4, a weld foot deposition layer is designed in the area to be welded between the skin 3 and the long stringer 4, a first design dimension of the surface deposition layer 1 is determined according to the dimension of the long stringer 4, and a second design dimension of the weld foot deposition layer 2 is determined according to the laser welding parameters; specifically, the first design dimension includes the length of the surface deposition layer 1 and the width of the surface deposition layer 1, wherein the length of the surface deposition layer 1 is L, the width of the surface deposition layer 1 is 1δ~1.2δ, L is the length of the long stringer 4, and δ is the width of the long stringer 4. The calculation formula of the second design dimension is as follows:

[0054]

[0055] Among them, x2 is the second design weld leg size, x1 is the first design weld leg size, x1 is the length of the right angle side of the largest isosceles right triangle drawn in the cross section of the fillet weld, r is the radius of the welding wire used in conventional double-beam laser wire welding, which is generally 0.4mm~0.6mm, and v w is the wire feeding speed, v is the welding speed, and ρ is the coating density under specific cold spraying process parameters. The value of coating density ρ can be determined based on the database of cold spraying process parameters and coating density, which is generally 75% to 95%.

[0056] S4. Surface cleaning of the skin 3 and the long stringer 4 is performed to remove impurities such as oxide film and oil stains on the surface of the skin 3 and the long stringer 4; the cleaning area is 5mm-10mm larger than the welding area. Specifically, mechanical cleaning, chemical cleaning or laser cleaning is used to clean the surface of the skin 3 and the long stringer 4; when the laser cleaning method is used to clean the surface of the skin 3 and the long stringer 4, the process parameters of the laser cleaning method include pulse laser power P, scanning speed v and pulse frequency f, and the pulse laser power P is 160W-250W, the scanning speed is 1500mm / s-3000mm / s, and the pulse frequency is 2kHz-4kHz.

[0057] S5, such as Figure 3As shown, the design thickness of the surface deposition layer 1 is determined, and the first cold spraying process parameters of the alloy powder are determined according to the design thickness. A surface deposition layer mold 5 corresponding to the first design size is placed on the skin 3, and the alloy powder is cold sprayed in the surface deposition layer mold 5 using the first cold spraying process parameters to form a surface deposition layer 1 with the first design size and design thickness; specifically, the design thickness of the surface deposition layer 1 is controlled within the range of 0.1 mm to 0.5 mm.

[0058] S6, placing the long stringer 4 on the surface sediment layer 1 along the center line of the surface sediment layer 1;

[0059] S7. According to the second design size, determine the second cold spraying process parameters of the alloy powder, place the weld foot deposition layer mold corresponding to the second design size in the welding area on both sides of the long stringer 4, and cold spray the alloy powder in the weld foot deposition layer mold using the second cold spraying process parameters to obtain the weld foot deposition layer 2 with the second design size; the first cold spraying process parameters include gas pressure p, working gas temperature T, spraying angle α and spraying distance d, wherein the gas pressure p is 2MPa~5MPa, the working gas temperature T is 300℃~600℃, the spraying angle α is 40°-60°, and the spraying distance d is 10mm~50mm. The second cold spraying process parameters include gas pressure p, working gas temperature T, spraying angle α and spraying distance d, wherein the gas pressure p is 2MPa~5MPa, the working gas temperature T is 300℃~600℃, the spraying angle α is 40°-60°, and the spraying distance d is 10mm~50mm.

[0060] S8. Laser welding is performed on the area to be welded with preset laser welding process parameters to form a weld 6 in the area to be welded, so that the skin 3 and the long stringer 4 are welded and connected to form a T-shaped structure, wherein the size of the weld pool during the welding process is not less than the second design size. Specifically, laser welding can use two laser beams to achieve bilateral synchronous welding or bilateral asynchronous welding, or a single laser beam can be used to achieve single-sided double-sided welding. During the welding process, a protective gas can be introduced to form a protective gas atmosphere. The protective gas includes argon and helium, and the protective gas flow rate is generally selected to be 5L / min-25L / min. The protective gas can be applied in a coaxial gas supply with the laser beam or in a side-axis gas supply. More specifically, the preset laser welding process parameters include the welding plane angle θ, the laser processing head deflection angle η, the laser offset y, the laser power P and the welding speed v, wherein the welding plane angle θ is 20°-70°, the laser processing head deflection angle η is 0°~15°, the laser offset y is -1mm~3mm, the laser power P is 2000W~4000W, and the welding speed is 2m / min~4m / min.

[0061] S9. Perform non-destructive testing on T-type structure welding joints. Non-destructive testing methods include X-ray testing and penetration testing.

[0062] The following is a specific embodiment provided by this application:

[0063] Embodiment 1

[0064] The technical solution of this embodiment is adopted to realize laser welding of a 7075 high-strength aluminum alloy T-shaped structure. The T-shaped structure is composed of a horizontally placed skin 3 and a vertically placed long stringer 4. The materials of the skin 3 and the long stringer 4 are both 7075 high-strength aluminum alloy. The length of the skin 3 is 1000 mm, the width is 600 mm, and the thickness is 2 mm. The length L of the long stringer 4 is 400 mm, the height w is 30 mm, and the thickness δ is 2 mm. The specific welding method is realized by the following steps:

[0065] Step 1: In order to refine the microstructure of the 7075 high-strength aluminum alloy T-shaped structural joint, inhibit the generation of welding cracks, and improve the forming quality and mechanical properties of the weld, a powder particle size of 15 to 53 μm is designed, and the 7075 high-strength aluminum alloy powder containing strengthening elements Sc and Zr is used, wherein the content of Sc element is 0.20% and the content of Zr element is 0.15%.

[0066] Step 2: Use inert gas atomization technology to prepare alloy powder containing strengthening elements Sc and Zr, and establish the correlation between cold spraying process parameters of 7075-ScZr aluminum alloy powder and deposition layer thickness t and density ρ through cold spraying process test. Quantify through formula, gas pressure p, working gas temperature T, spraying angle α, spraying distance d.

[0067] Step 3: Determine the first design size based on the size of the long stringer 4, and design the length, width and thickness of the surface deposition layer 1 to be 400 mm, 2 mm and 0.1 mm respectively. The wire radius used in conventional high-strength aluminum alloy double-beam laser welding is 0.6 mm, and the wire feeding speed v w The welding speed v is 3m / min and the welding speed v is 6m / min, so the first design weld leg size x1 of the T-shaped structure is determined to be 1.06mm. According to the first design weld leg size, the process parameters of cold spraying are selected: gas pressure p is 3MPa, working gas temperature T is 300℃, spray angle α is 45°, and spray distance d is 10mm. The coating density ρ under the cold spray process parameters is 90%, so the second design weld leg size x2 of the weld leg deposition layer 4 is determined to be 1.12mm.

[0068] Step 4: Use laser cleaning method to clean the surface of the skin 3 and the long stringer 4 within 10mm of the welding area to remove the oxide film and oil and other impurities on the surface of the skin 3 and the long stringer 4. Parameters of the laser cleaning method: pulse laser power P is 200W, scanning speed is 1500mm / s, and pulse frequency is 2kHz.

[0069] Step 5: According to the designed thickness of the surface deposition layer 1, select the process parameters of cold spraying: gas pressure p is 3MPa, working gas temperature T is 300℃, spray angle α is 45°, and spray distance d is 10mm. Place the surface deposition layer mold 5 on the surface of the skin 3, and use the cold spray system to obtain the surface deposition layer 1 in the connection area between the surface of the skin 3 and the long stringer 4, to assist the precise positioning of the long stringer 4 on the skin 3.

[0070] Step 6: Place the long stringer 4 on the surface deposition layer 1 along the center line of the surface deposition layer 1. With the help of the deposition layer, the positioning accuracy of the long stringer assembly is improved from ±1mm to ±0.5mm, realizing the precise assembly of the 7075 high-strength aluminum alloy T-shaped structure.

[0071] Step 7. According to the second design size of the weld foot deposition layer 4, select the process parameters of cold spraying: gas pressure p is 3MPa, working gas temperature T is 300℃, spray angle α is 45°, and spray distance d is 10mm. Place the weld foot deposition layer mold in the area to be welded on both sides of the long stringer 4, and use the cold spray system to obtain the weld foot deposition layer 2 in the area to be welded on both sides of the long stringer 4. In the process of cold spraying the weld foot deposition layer, the powder particles will fill the excessive assembly gap between the skin and the long stringer, thereby improving the welding quality of the T-shaped structural joint.

[0072] Step 8: Figure 4 and Figure 5 As shown, in the dual-beam laser welding process of the T-shaped structure, two laser beams 7 are symmetrically placed on both sides of the long stringer 4, and the dual-beam laser welding process is protected in real time by coaxial argon gas delivery, and the protective gas flow rate is 15L / min. The skin 3 and the long stringer 4 are laser welded by a dual-beam double-sided synchronous welding system to ensure that the size of the weld pool is greater than or equal to the size of the weld foot deposition layer, and a bilaterally symmetrical weld 6 is obtained. The process parameters of dual-beam laser welding are: welding plane angle θ is 45°, laser processing head deflection angle η is 10°, laser offset y is 1mm, and welding speed is 6m / min. Since the weld foot deposition layer reduces the surface roughness of the T-shaped structure to be welded, the absorption rate of the aluminum alloy to the laser and the utilization rate of the laser energy are improved, and the laser power P can be reduced from 2500W to 2000W.

[0073] Step 9: Quality inspection: Perform X-ray nondestructive testing on the T-shaped structure welding joints.

[0074] The surface of the 7075 high-strength aluminum alloy T-shaped structural joint obtained by double-beam laser welding is well formed, without obvious surface depression and undercut, the convexity of the fillet weld is moderate, and welding defects such as cracks and pores are effectively controlled. The tensile strength of the T-shaped joint can reach 60% to 70% of the tensile strength of the parent material. In summary, this technical solution is reasonable and feasible, and is especially suitable for the laser welding process of the T-shaped structure of 7xxx and 2xxx series high-strength aluminum alloys such as 7075, 7050, and 2024.

[0075] Embodiment 2

[0076] The technical solution of this embodiment is adopted to realize laser welding of a TC4 titanium alloy T-shaped structure. The T-shaped structure is composed of a horizontally placed skin 3 and a vertically placed long stringer 4. The materials of the skin 3 and the long stringer 4 are both TC4 titanium alloy. The length of the skin 3 is 1200 mm, the width is 800 mm, and the thickness is 2 mm. The length L of the long stringer 4 is 600 mm, the height w is 30 mm, and the thickness δ is 1.5 mm. The specific welding method is realized by the following steps:

[0077] Step 1: To improve the mechanical properties of the weld of the TC4 titanium alloy T-shaped structural joint, a powder particle size of 15 to 53 μm is designed, and the TC4 titanium alloy powder containing the strengthening element Ce is spherical in shape, wherein the content of the Ce element is 0.30%.

[0078] Step 2: Use inert gas atomization technology to prepare alloy powder containing strengthening element Ce, and establish the correlation between cold spraying process parameters of TC4-Ce titanium alloy powder and deposition layer thickness t and density ρ through cold spraying process test. Quantify through formula, gas pressure p, working gas temperature T, spraying angle α, spraying distance d.

[0079] Step 3: Determine the first design size based on the size of the long stringer 4, and design the length, width and thickness of the surface deposition layer 1 to be 600 mm, 1.5 mm and 0.1 mm respectively. The wire radius used for conventional TC4 titanium alloy double-beam laser welding is 0.5 mm, and the wire feeding speed v w The welding speed v is 6m / min and the welding speed v is 8m / min, so the first design weld leg size x1 of the T-shaped structure is determined to be 1.09mm. According to the first design weld leg size, the process parameters of cold spraying are selected: gas pressure p is 4MPa, working gas temperature T is 600℃, spray angle α is 45°, and spray distance d is 10mm. The coating density ρ under the cold spray process parameters is 80%, so the second design weld leg size x2 of the weld leg deposition layer 4 is determined to be 1.22mm.

[0080] Step 4: Use laser cleaning method to clean the surface of the skin 3 and the long stringer 4 within 10mm of the welding area to remove the oxide film and impurities such as oil on the surface of the skin 3 and the long stringer 4. Parameters of the laser cleaning method: pulse laser power P is 250W, scanning speed is 1500mm / s, and pulse frequency is 2kHz.

[0081] Step 5: According to the designed thickness of the surface deposition layer 1, the process parameters of cold spraying are selected: the gas pressure p is 4 MPa, the working gas temperature T is 600°C, the spraying angle α is 45°, and the spraying distance d is 10 mm. A surface deposition layer mold 5 is placed on the surface of the skin 3, and a cold spraying system is used to obtain the surface deposition layer 1 in the connection area between the surface of the skin 3 and the long stringer 4, to assist in the precise positioning of the long stringer 4 on the skin 3.

[0082] Step 6: Place the long stringer 4 on the surface deposition layer 1 along the center line of the surface deposition layer 1. With the help of the deposition layer, the positioning accuracy of the long stringer assembly is improved from ±1mm to ±0.5mm, so as to achieve the precise assembly of the TC4 titanium alloy T-shaped structure.

[0083] Step 7. According to the second design size of the weld foot deposition layer 4, select the process parameters of cold spraying: gas pressure p is 4MPa, working gas temperature T is 600℃, spray angle α is 45°, and spray distance d is 10mm. Place the weld foot deposition layer mold in the area to be welded on both sides of the long stringer 4, and use the cold spray system to obtain the weld foot deposition layer 2 in the area to be welded on both sides of the long stringer 4. In the process of cold spraying the weld foot deposition layer, the powder particles will fill the excessive assembly gap between the skin and the long stringer, thereby improving the welding quality of the T-shaped structural joint.

[0084] Step 8: Figure 4 and Figure 5 As shown, in the dual-beam laser welding process of the T-shaped structure, two laser beams 7 are symmetrically placed on both sides of the long stringer 4, and the dual-beam laser welding process is protected in real time by coaxial argon gas delivery, and the protective gas flow rate is 25L / min. The skin 3 and the long stringer 4 are laser welded by a dual-beam double-sided synchronous welding system to ensure that the size of the weld pool is greater than or equal to the size of the weld foot deposition layer, and a bilaterally symmetrical weld 6 is obtained. The process parameters of dual-beam laser welding are: welding plane angle θ is 30°, laser processing head deflection angle η is 0°, laser offset y is 1mm, laser power P is 3000W, and welding speed is 8m / min.

[0085] Step 9: Quality inspection: Perform X-ray nondestructive testing on the T-shaped structure welding joints.

[0086] The surface of the TC4 titanium alloy T-shaped structural joint obtained by double-beam laser welding is well formed, without obvious surface depression and undercut, the convexity of the fillet weld is moderate, and welding defects such as cracks and pores are effectively controlled. The tensile strength of the T-joint is basically equivalent to that of the parent material.

[0087] In summary, the technical solution of the present invention is reasonable and feasible, and can be applied to the laser welding process of T-shaped structures such as aluminum alloy, titanium alloy, and stainless steel.

[0088] 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 and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A T-shaped structure laser welding method, used to weld a skin and a long stringer to form a T-shaped structure, characterized in that: The following steps are involved: S1. preparing alloy powder, wherein the alloy powder is a base material powder, or a base material powder containing a strengthening element, or a mixed powder consisting of a base material powder and a single strengthening element powder, or a mixed powder consisting of a base material powder and a powder containing a strengthening element, wherein the composition of the base material powder is consistent with the material composition of the T-shaped structure; S2. Conducting a cold spraying process test of the alloy powder to form an alloy powder deposition layer, and establishing a correlation between cold spraying process parameters and the thickness and density of the alloy powder deposition layer; S3, designing a surface deposition layer on the contact surface between the skin and the long stringer, designing a weld foot deposition layer in the area to be welded between the skin and the long stringer, determining a first design size of the surface deposition layer according to the size of the long stringer, and determining a second design size of the weld foot deposition layer according to laser welding parameters; S4. Surface cleaning of skin and long stringers; S5, determining the design thickness of the surface deposition layer, determining the first cold spraying process parameters of the alloy powder according to the design thickness, placing a surface deposition layer mold corresponding to the first design size on the skin, and cold spraying the alloy powder in the surface deposition layer mold using the first cold spraying process parameters to form the surface deposition layer having the first design size and design thickness; S6, placing the long stringer on the surface sediment layer along the center line of the surface sediment layer; S7, determining the second cold spraying process parameters of the alloy powder according to the second design size, placing a weld foot deposition layer mold corresponding to the second design size in the welding area on both sides of the long stringer, and cold spraying the alloy powder in the weld foot deposition layer mold using the second cold spraying process parameters to obtain a weld foot deposition layer with the second design size; S8. Laser welding is performed on the area to be welded using preset laser welding process parameters to form a T-shaped structure, wherein the size of the weld pool during the welding process is not less than the second design size.

2. The T-shaped structure laser welding method according to claim 1, characterized in that: The following steps are also included: S9. Perform non-destructive testing on T-type structure welding joints. Non-destructive testing methods include X-ray testing and penetration testing.

3. The T-shaped structure laser welding method according to claim 1, characterized in that: In step S1, the alloy powder is a base material powder containing strengthening elements, and when the base material powder is an aluminum alloy powder, the base material powder containing strengthening elements includes a Sc element in a mass fraction range of 0.15%-0.30%, and / or a Zr element in a mass fraction range of 0.10%-0.20%, and the particle size of the alloy powder is 15μm to 53μm.

4. The T-shaped structure laser welding method according to claim 1, characterized in that: In step S1, when the alloy powder is a base material powder or a base material powder containing strengthening elements, the preparation method of the alloy powder includes at least one of an inert gas atomization method, a plasma rotating electrode method, and a radio frequency plasma method; When the alloy powder is a mixed powder composed of a base material powder and a single strengthening element powder, or a mixed powder composed of a base material powder and a powder containing a strengthening element, the preparation method of the alloy powder is a mechanical mixing method.

5. The T-shaped structure laser welding method according to claim 1, characterized in that: In step S3, the first design dimension includes the length and width of the surface deposition layer, wherein the length of the surface deposition layer is L, the width of the surface deposition layer is 1δ-1.2δ, L is the length of the long stringer, and δ is the width of the long stringer.

6. The T-shaped structure laser welding method according to claim 1, characterized in that: In step S3, the calculation formula of the second design size is as follows: Among them, x2 is the second design weld leg size, x1 is the first design weld leg size, x1 is the length of the right angle side of the largest isosceles right triangle drawn in the cross section of the fillet weld, r is the radius of the welding wire used in conventional double-beam laser wire welding, which is generally 0.4mm~0.6mm, and v w is the wire feeding speed, v is the welding speed, and ρ is the coating density under specific cold spraying process parameters. The value of coating density ρ can be determined based on the database of cold spraying process parameters and coating density, which is generally 75% to 95%.

7. The T-shaped structure laser welding method according to claim 1, characterized in that: In step S4, the skin and the long stringer are surface cleaned by mechanical cleaning, chemical cleaning or laser cleaning. When the skin and the long stringer are surface cleaned by laser cleaning, the process parameters of the laser cleaning method include pulse laser power P, scanning speed v and pulse frequency f, the pulse laser power P is 160W-250W, the scanning speed is 1500mm / s-3000mm / s, and the pulse frequency is 2kHz-4kHz.

8. The T-shaped structure laser welding method according to claim 1, characterized in that: In step S5, the first cold spraying process parameters include gas pressure p, working gas temperature T, spraying angle α and spraying distance d, wherein the gas pressure p is 2MPa~5MPa, the working gas temperature T is 300℃~600℃, the spraying angle α is 40°-60°, and the spraying distance d is 10mm~50mm.

9. The T-shaped structure laser welding method according to claim 1, characterized in that: In step S7, the second cold spraying process parameters include gas pressure p, working gas temperature T, spraying angle α and spraying distance d, wherein the gas pressure p is 2MPa~5MPa, the working gas temperature T is 300℃~600℃, the spraying angle α is 40°-60°, and the spraying distance d is 10mm~50mm.

10. The T-shaped structure laser welding method according to claim 1, characterized in that: In step S8, the preset laser welding process parameters include the welding plane angle θ, the laser processing head deflection angle η, the laser offset y, the laser power P and the welding speed v, wherein the welding plane angle θ is 20°-70°, the laser processing head deflection angle η is 0°~15°, the laser offset y is -1mm~3mm, the laser power P is 2000W~4000W, and the welding speed is 2m / min~4m / min.

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