A sandwich structure stainless steel vacuum diffusion welding connection method

Abstract

This invention discloses a vacuum diffusion welding method for joining stainless steel sandwich structures, belonging to the field of metal joining technology. This method effectively solves the problems of severe edge deformation and wrinkling, and unstable welding quality during stainless steel joining by optimizing pretreatment, assembly methods, gasket design, and welding process parameters. The method includes steps such as material preparation, pretreatment, assembly, vacuum diffusion welding, cooling, and inspection. This invention can improve welding quality and stability, achieving wrinkle-free edges.

Description

Technical Field

[0001] This invention relates to a vacuum diffusion welding method for sandwich-structured stainless steel, and more particularly to a vacuum diffusion welding method for sandwich-structured stainless steel applied to the manufacture of ultra-thin stainless steel thermal insulation materials, relating to the field of metal joining technology. Background Technology

[0002] Stainless steel is widely used in aerospace, energy, and chemical industries due to its excellent corrosion resistance and mechanical properties. In some specialized applications, such as thermal insulation, it is necessary to combine extremely thin stainless steel foil sheets with other materials (such as felt) to form a sandwich structure. Vacuum diffusion welding is a solid-state bonding method capable of achieving high-quality metal connections; however, for extremely thin stainless steel foil sheets, traditional diffusion welding methods have the following problems:

[0003] Severe edge deformation and wrinkling: Due to the thinness of the stainless steel foil, it is prone to plastic deformation under high temperature and pressure, especially in the welded edge area, where wrinkles are easily generated, affecting the overall performance of the structure.

[0004] Unstable welding quality: An oxide film easily forms on the surface of stainless steel, affecting the bonding of the weld interface. In addition, uneven pressure distribution during the welding process can also easily lead to local incomplete welding.

[0005] It is difficult to achieve wrinkle-free edge connections: Traditional methods have difficulty controlling the deformation of edge areas, making it impossible to achieve high-quality connections without wrinkles.

[0006] Solder resist difficulties: In sandwich structures, specific areas need to be resisted by solder. Traditional methods make it difficult to accurately control the solder resist area, which affects the welding quality. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and solve the problems of severe edge deformation and wrinkling and unstable welding quality in the process of stainless steel connection.

[0008] The objective of this invention is achieved through the following technical solutions:

[0009] A method for vacuum diffusion welding of stainless steel sandwich structures includes:

[0010] (1) Material preparation: Select stainless steel foil, cotton felt, boron nitride gasket, graphite paper and graphite mold;

[0011] (2) Pretreatment: The stainless steel foil is polished, ultrasonically cleaned and pickled;

[0012] (3) Assembly: According to the pressing head Graphite paper Graphite mold Boron nitride gaskets Welded components (stainless steel foil + cotton felt) Boron nitride gaskets Graphite mold Graphite paper The upper pressure heads are assembled sequentially, with the cotton felt having flat edges and a convex center.

[0013] (4) Vacuum diffusion welding: Heating and pressurizing are performed in a vacuum environment according to a predetermined temperature and pressure process;

[0014] (5) Cooling and testing: After cooling, the joint is evaluated using non-destructive testing methods.

[0015] Preferably, the boron nitride gasket is a rectangular ring with chamfered or rounded inner edges.

[0016] Preferably, the pretreatment steps include: polishing the stainless steel foil with sandpaper (240-3000 grit) to remove the surface oxide film; immersing the polished stainless steel foil in anhydrous ethanol for ultrasonic cleaning; immersing the cleaned stainless steel foil in a 20% nitric acid solution for 2 minutes, then washing away the residual nitric acid with anhydrous ethanol, and drying it for later use.

[0017] Preferably, the temperature process for vacuum diffusion welding is: room temperature. Heat to 800℃ at a rate of 10℃ / min and hold for 20 min. Heat to 1000℃ at a heating rate of 10℃ / min and hold for 80 min. Cooled along with the furnace.

[0018] Preferably, the pressure process for vacuum diffusion welding is as follows: pre-pressurization of 1.5 MPa during vacuuming. The pressure was increased to 2.4 MPa at a rate of 0.03 MPa / min. Maintain for 30 minutes The pressure was increased to 3 MPa at a rate of 0.03 MPa / min. Maintain pressure until the heat preservation is completed. Release the pressure after the heat preservation is completed.

[0019] Preferably, the stainless steel foil is made of 1Cr18Ni9Ti stainless steel with a thickness of 0.05mm.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] A vacuum diffusion welding method for joining stainless steel sandwich structures effectively solves the problem of edge deformation and wrinkling during the stainless steel joining process by optimizing pretreatment, assembly methods, gasket design, and welding process parameters. This improves welding quality and stability, and achieves wrinkle-free edge joining. Attached Figure Description

[0022] Figure 1 This is an assembly diagram of an embodiment of the present invention.

[0023] Figure 2 This is a temperature process curve according to an embodiment of the present invention.

[0024] Figure 3 This is a pressure process curve according to an embodiment of the present invention.

[0025] Figure 4 This is a CT scan image of a sandwich-structured stainless steel welded component according to an embodiment of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0027] A vacuum diffusion welding method for sandwich-structured stainless steel includes the following steps:

[0028] (1) Material preparation:

[0029] Select 1Cr18Ni9Ti stainless steel foil as the base material, with a thickness of 0.05mm, and prepare cotton felt or other necessary interlayer materials. Prepare boron nitride gaskets in the shape of rectangular rings with chamfered or rounded inner edges to reduce edge stress concentration. Prepare graphite paper and graphite molds.

[0030] (2) Pretreatment:

[0031] Polish the stainless steel foil with sandpaper (240-3000 grit) to remove the surface oxide film. Then, ultrasonically clean the polished stainless steel foil in anhydrous ethanol to remove surface oil. Next, immerse the cleaned stainless steel foil in a 20% nitric acid solution for 2 minutes to remove surface residue. Finally, rinse off any remaining nitric acid with anhydrous ethanol and dry before use.

[0032] (3) Assembly:

[0033] Based on the requirements of the sandwich structure, the shape of the cotton felt was designed to have flat edges and a raised center to address the issue of large residual air volume in the center of the base material, which causes deformation of the center of the base material during vacuuming. Assembly should proceed in the following order: Lower pressure head... Graphite paper Graphite mold Boron nitride gaskets Welded components (including stainless steel foil + cotton felt) Boron nitride gaskets Graphite mold Graphite paper Upper pressure head. The welded part consists of two layers of stainless steel foil with cotton felt in between, forming a sandwich structure.

[0034] (4) Vacuum diffusion welding:

[0035] The assembled workpiece is placed in a vacuum diffusion welding furnace, and a vacuum is drawn to below 3 Pa. During vacuuming, a pre-pressure of 1.5 MPa is applied to prevent significant deformation and wrinkling of the base material in the felt area. Heating is then performed at the following temperature: room temperature. Heat to 800℃ at a rate of 10℃ / min and hold for 20 min. Heat to 1000℃ at a heating rate of 10℃ / min and hold for 80 min. Cooling with the furnace. Pressurize according to the following pressure process: pre-pressurize to 1.5 MPa during vacuuming. The pressure was increased to 2.4 MPa at a rate of 0.03 MPa / min. Maintain for 30 minutes The pressure was increased to 3 MPa at a rate of 0.03 MPa / min. Maintain pressure until the heat preservation is completed. Release the pressure after the heat preservation is completed.

[0036] (5) Cooling and testing:

[0037] After the workpiece has cooled to room temperature in the furnace, it is removed. The weld quality of the joint is evaluated using non-destructive testing methods such as ultrasonic testing or CT scanning.

[0038] A vacuum diffusion welding method for connecting stainless steel sandwich structures can effectively solve the problem of edge deformation and wrinkling during the stainless steel connection process by optimizing pretreatment, assembly method, gasket design, and welding process parameters, thereby improving welding quality and stability and achieving wrinkle-free edge connections.

[0039] This invention effectively reduces deformation and wrinkles in the edge area during welding by employing cotton felt of a specific shape, boron nitride gaskets, and optimized pressure processes, thereby improving the overall flatness of the structure. The inner edge chamfering and rounding process effectively mitigates stress concentration caused by pressure on the weld edges. The cotton felt with a convex center and flat sides prevents deformation at the sample center. The pretreatment method of ultrasonic cleaning + acid pickling effectively removes oxide film and oil stains from the surface of the stainless steel foil, improving the bonding quality of the weld interface and the stability of the weld. Applying a small pre-pressure during vacuuming prevents cotton felt fibers from flying into the welding area and affecting the weld. The pressure process of pre-pressure + stepped pressure ensures that the joint is evenly pressurized without damaging the gasket, while also improving surface quality. By optimizing the assembly method and welding process parameters, this invention achieves a high-quality connection with wrinkle-free edges, meeting the needs of special application scenarios. This invention provides feasible parameter ranges for temperature, pressure, and holding time in stainless steel diffusion welding, and gives optimal welding process parameters using disposable boron nitride gaskets, including at least a welding temperature of 1000℃, a welding pressure of 3MPa, and a holding time of 80 min.

[0040] Example:

[0041] A vacuum diffusion welding method for connecting stainless steel sandwich structures uses 1Cr18Ni9Ti stainless steel foil (0.05mm thick) and cotton felt as raw materials. The assembly diagram is shown below. Figure 1 As shown. The boron nitride gasket has its inner corners chamfered to reduce stress. Following the pretreatment steps described above, the cotton felt is designed with flat edges and a convex center. Assemble according to the assembly steps described above, and follow the temperature process curve described above. Figure 2 and pressure process curve Figure 3 Vacuum diffusion welding is performed.

[0042] After welding, the joint is inspected using a CT scan, such as... Figure 4 As shown, the results indicate that the welding is good, and the deformation and wrinkles at the edges and in the middle of the cotton felt area and the welding area are significantly reduced, with a welding rate of over 99.9%.

[0043] The contents not described in detail in this specification are common knowledge to those skilled in the art.

[0044] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for vacuum diffusion welding of stainless steel sandwich structures, characterized in that, include: (1) Select stainless steel foil, cotton felt, boron nitride gasket, graphite paper and graphite mold; Boron nitride gaskets are rectangular rings with chamfered or rounded inner edges; (2) Polishing, ultrasonic cleaning and pickling of stainless steel foil; (3) According to the pressing head Graphite paper Graphite mold Boron nitride gaskets Welded parts Boron nitride gaskets Graphite mold Graphite paper The upper pressure heads are assembled sequentially, with the cotton felt having flat edges and a convex center. (4) Perform vacuum diffusion welding; the pressure process for vacuum diffusion welding is as follows: pre-pressurize 1.5 MPa during vacuuming. The pressure was increased to 2.4 MPa at a rate of 0.03 MPa / min. Maintain for 30 minutes The pressure was increased to 3 MPa at a rate of 0.03 MPa / min. Maintain pressure until the heat preservation is completed. Release the pressure after the insulation is completed; (5) After cooling, the joint is evaluated using non-destructive testing methods.

2. The sandwich structure stainless steel vacuum diffusion welding method according to claim 1, characterized in that, Step (1) includes: using sandpaper to polish the stainless steel foil to remove the surface oxide film; immersing the polished stainless steel foil in anhydrous ethanol for ultrasonic cleaning; immersing the cleaned stainless steel foil in nitric acid solution for cleaning, then washing away the residual nitric acid on the surface with anhydrous ethanol, and drying it for later use.

3. The sandwich structure stainless steel vacuum diffusion welding connection method according to claim 1, characterized in that, The temperature process for vacuum diffusion welding is: room temperature. Heat to 800℃ at a rate of 10℃ / min and hold for 20 min. Heat to 1000℃ at a heating rate of 10℃ / min and hold for 80 min. Cooled along with the furnace.

4. The sandwich structure stainless steel vacuum diffusion welding connection method according to claim 1, characterized in that, The stainless steel foil is made of 1Cr18Ni9Ti stainless steel and has a thickness of 0.05mm.

5. The sandwich structure stainless steel vacuum diffusion welding method according to claim 1, characterized in that, The welding quality of the joint is evaluated using ultrasonic testing or CT scanning methods.

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