Method for preparing thin-wall part with snake-shaped hollow channel by adopting superplastic forming / diffusion bonding

Abstract

The invention discloses a method for preparing a thin-wall part with a snakelike hollow channel by adopting superplastic forming / diffusion bonding. The method comprises the following specific steps: step 1, plate preparation and surface cleaning treatment; and step 2, solder resist coating: using a mask plate to deposit on a specific area of the plate and coating the solder resist according to an S-shaped shape, and removing the protective adhesive tape after spraying is completed. And 3, assembling and sealing, wherein the plates are stacked according to the design sequence, the edges are sealed and welded, and an air inlet / outlet is reserved to be connected with an air pipe. And 4, heating is conducted, specifically, the assembly is put into a mold, then the mold is uniformly put into a superplastic forming machine tool, and heating is conducted till the plate superplastic forming temperature is reached. And fifthly, diffusion bonding is conducted, specifically, uniform pressure is applied to the mold through a pressing head in the superplastic machine tool, so that diffusion bonding combination is conducted on the contact face, not coated with the solder resist, of the plate at high temperature and high pressure, and a connecting rib is formed. And 6, superplastic forming / diffusion bonding is conducted, specifically, the temperature is kept, and high-pressure inert gas is introduced into the assembly through a reserved air inlet according to an air pressure loading curve. And the plate coated with the solder resist is subjected to superplastic deformation and is attached to a mold cavity, diffusion connection between the plates is completed in the area not coated with the solder resist, and finally the needed thin-wall part with the serpentine channel cavity is formed. And 7, cooling and demolding are conducted, specifically, the thin-wall part with the snake-shaped hollow channel is taken out after cooling to the room temperature, and the residual solder resist is cleaned.

Description

Technical Field

[0001] This invention relates to the field of multilayer hollow thin-walled design and its precision thermoforming technology, and particularly to a method for preparing thin-walled parts with serpentine hollow channels using superplastic forming / diffusion bonding. Background Technology

[0002] Superplastic forming / diffusion bonding technology utilizes the excellent elongation and good diffusion properties of specific metallic materials in the high-temperature range. During thermal cycling, appropriate pressure is applied to bring the materials together for diffusion at the contact surface, and the separated parts are then superplastically formed. This technology can form complex structures in a single, integral process, reducing riveting and welding processes, and minimizing subsequent machining steps.

[0003] With the increasing demand for multifunctional structures, such as the thermal protection systems of hypersonic aircraft, metal sandwich structures have been adopted in some areas and have attracted more and more attention. Advanced metal sandwich structures are not only lighter but also require better load-bearing and heat dissipation performance. Sandwich structures provide functions such as heat insulation, sound insulation, and shock load mitigation. The internal structures of the sandwiches include various types, such as square / triangular honeycomb structures, corrugated and rhomboid truss structures, pyramidal and tetrahedral truss structures, and X-shaped truss structures.

[0004] Among them, the serpentine channel structure is a typical multifunctional structure, possessing not only excellent convective heat transfer performance but also superior surface compression performance and significant weight reduction, making it highly valuable for applications. Existing technologies include an invention of a turbine stator blade with a serpentine channel, demonstrating that a stator blade with an internal airflow path roughness can enhance heat transfer and improve operational stability; a lightweight titanium alloy turbine airfoil can reduce the temperature gradient of the hollow heat exchanger's outer wall through an internal serpentine air passage, but this serpentine air passage is not a serpentine spatial structure and has little impact on improving mechanical properties; a gas turbine blade with a serpentine channel also has similar beneficial effects. Most of the above methods focus on the structural design of the serpentine channel but do not mention the specific fabrication process.

[0005] A serpentine channel structure can be fabricated using a combination of sheet metal bending and vacuum brazing technology. Its superior mechanical and heat dissipation properties have been verified through testing and optimization of compressive strength and fluid mobility. Existing methods for fabricating hollow serpentine channel components mainly include casting, sheet metal welding, brazing, and additive manufacturing. However, these methods suffer from low material utilization, poor dimensional accuracy, internal structural defects, and insufficient overall structural strength, making it unsuitable for manufacturing large-scale, complex curved serpentine channel structures. Additive manufacturing, due to the high cost of raw materials such as metal powders or wires, suffers from high production costs, low efficiency, and poor forming accuracy when fabricating large-sized workpieces, thus it is not yet suitable for mass production of serpentine channel structures.

[0006] Currently, superplastic forming / diffusion bonding technology has been widely used in the fabrication of various complex hollow structures, and serpentine channels have been proven to have beneficial effects on related functions. However, no inventions have been proposed that use superplastic forming / diffusion bonding technology to fabricate two-layer, three-layer, four-layer plates, or multi-layer thin-walled parts with serpentine hollow channels. Summary of the Invention

[0007] To address the above problems, this invention proposes an integral forming method for fabricating thin-walled parts with serpentine hollow channels using superplastic forming / diffusion bonding. While ensuring the strength of large-sized structural components, the optimized serpentine structure minimizes structural weight and improves heat dissipation, achieving a lightweight design for the serpentine hollow channel thin-walled part. The manufacturing of the serpentine hollow channel thin-walled part is achieved through superplastic forming / diffusion bonding technology.

[0008] This invention is achieved through the following technical solution: Step 1: Sheet preparation and surface treatment: Select and cut superplastic sheets, and perform grinding, cleaning, and pickling to remove contaminants and oxide film; Step 2, Solder resist coating: Using a mask deposition method, high-temperature resistant solder resist is precisely coated on specific areas of the board in a serpentine channel shape to prevent adhesion to the mold. After spraying, the protective tape is removed. Step 3, Stacking and Sealing: Stack the plates in the design order, ensuring accurate alignment of the solder resist pattern. Seal the perimeter to form an airtight assembly and reserve air inlet / outlet ports for connecting air pipes; Step 4, Heating: Place the component into the mold, and place the sheet and mold into the superplastic forming machine tool, and heat to the superplastic forming temperature of the material; Step 5, Diffusion Bonding Stage: Using the pressure head in the superplastic machine tool, uniform pressure is applied to the mold, causing the contact surfaces of the uncoated solder resist plates to undergo diffusion bonding under high temperature and high pressure, forming the connecting ribs of the corresponding structure; Step Six, Superplastic Forming / Diffusion Bonding Stage: Under constant temperature conditions, high-pressure inert gas is injected into the component through a pre-reserved air inlet. Under the continuous action of gas pressure, the area of ​​the board coated with solder resist undergoes superplastic deformation, gradually achieving conformal fitting with the mold cavity, and finally precisely forming a preset serpentine channel cavity structure; Step 7: Cooling and Demolding: After superplastic forming / diffusion bonding is completed, cool to room temperature, remove the serpentine hollow channel thin-walled part, and clean off any residual solder resist.

[0009] Furthermore, for titanium alloys, the diffusion bonding temperature is 900~940℃, the diffusion bonding time is 1~2.5h, and the diffusion pressure is 1~3MPa. The diffusion bonding and superplastic forming process parameters will differ for different serpentine channel structures.

[0010] Furthermore, the following key differences exist in the processes for superplastic forming / diffusion bonding of two-, three-, four-, or multi-layer thin-walled parts with serpentine hollow channels: Difference 1: Solder resist position: two layers (single-sided bottom layer), three layers (middle layer, double-sided), four layers / multi-layer (middle layer, double-sided, multi-layer stacking); Difference 2: Channel morphology: Two-layer (single-sided hollow channel), three-layer (double-sided symmetrical hollow channel), four-layer / multi-layer (multi-layer independent or interconnected hollow channel network); Difference 3: Structural complexity and alignment requirements: The more layers there are, the higher the requirements for the precision of solder resist coating and the alignment of stacked plates, and the more complex the process control.

[0011] The serpentine hollow channel thin-walled part of the present invention includes a serpentine channel and serpentine ribs obtained by superplastic forming / diffusion bonding. The specific forming process includes the following steps:

[0012] Step 1: Sheet metal cutting: Based on the load and dimensional requirements of the parts, topology optimization is used to obtain the internal mesh design of the serpentine channel of the core board and the thickness of the ribs, and 2D drawings of the panel and core board are designed. Laser cutting equipment is used to cut the materials according to the design, producing the upper panel, lower panel, upper core board, and lower core board that meet the dimensions, and the edge burrs are ground off; Step 2: Pre-treatment of panel bulging: The upper and lower panels are further sanded with 400#, 800#, 1000#, 1500#, and 2000# sandpaper respectively. The panel surface is cleaned with a small amount of anhydrous ethanol to remove surface spatter, solder joints, and oil stains. Then, it is pickled with an acid pickling solution with a ratio of HF:HNO3:H2O = 1:3:16. According to the design drawings, the air intake channels are ground and engraved on the panel and core board. Afterwards, boron nitride solder resist is sprayed onto the outer sides of the upper and lower panels. Step 3, Pre-treatment of core board for diffusion: Apply acid-resistant tape to the designed ribs on the upper and lower core boards and perform acid pickling, the pickling steps are the same as in Step 2. Obtain the stepped morphology and air inlet of the core board surface. Remove the acid-resistant tape and perform acid pickling again. After cleaning, spray boron nitride solder resist on the non-diffusion connection area of ​​the core board. Step 4, Assembly: Assemble the pre-treated panels in the order of upper panel, upper core panel, lower core panel, and lower panel. Spray solder resist on the outside of the upper and lower panels, align them, and perform edge sealing argon arc welding. Weld the gas pipe at the reserved air inlet. Step 5: Panel Air Expansion Forming and Core Board Superplastic Forming / Diffusion Connection: Place the assembled panel and core board into the superplastic forming / diffusion connection mold, and then place the entire assembly into the superplastic forming machine. A stepped heating program is used to heat the panel, core board, and mold. A press is used to apply a blank holder force to the superplastic forming / diffusion connection mold to ensure the sealing of the upper and lower panels. The superplastic forming temperature for the panel and core board is 900~940℃. After reaching the temperature, argon gas is introduced between the upper panel and upper core board, and between the lower panel and lower core board, according to the gas pressure loading curve. While completing the expansion of the upper and lower panels, the back pressure during panel expansion is used to complete the diffusion connection of the upper and lower core boards. The diffusion temperature of the core board is 900~940℃, the diffusion time is 1~2.5h, and the diffusion pressure is 1~3MPa.

[0013] Step Six: After the panel is formed, argon gas is introduced between the upper and lower core boards according to the specified gas pressure curve to induce superplastic forming. During the forming process, different undiffused connection areas within the core board can be connected through vent holes, allowing the gas pressure to be uniformly and synchronously applied to the serpentine channel. After the core board is fully formed, diffusion connection begins to occur with the panel. At this point, the welded areas between the upper and lower core boards form upright serpentine ribs, completing the superplastic forming between the core boards and the diffusion connection between the core board and the panel.

[0014] Step 7: Turn off the heating and wait for the part to cool to room temperature before removing it to obtain a four-layer plate serpentine hollow channel thin-walled part with superplastic forming / diffusion bonding.

[0015] Step 1: Sheet metal cutting: Based on the load and dimensional requirements of the parts, topological optimization design is used to obtain the internal mesh design of the serpentine channel of the core board and the thickness of the ribs, and 2D drawings of the panel and core board are designed. Laser cutting equipment is used to cut the materials according to the design, producing the top panel, bottom panel, and core board that meet the dimensions, and the edge burrs are polished. Step 2: Pre-treatment of panel and core board for bulging: The upper and lower panels and core board are further sanded with 400#, 800#, 1000#, 1500#, and 2000# sandpaper respectively. The surfaces of the panels and core board are cleaned with a small amount of anhydrous ethanol to remove surface spatter, solder joints, and oil stains. Then, they are pickled with an acid pickling solution with a ratio of HF:HNO3:H2O = 1:3:16. The air intake channel is ground onto the panel according to the design drawings. Then, solder resist is sprayed onto the outer sides of the upper and lower panels. Acid-resistant tape is applied to the designed ribs on the core board, and then pickled to obtain the uneven surface and air intake channel. After removing the acid-resistant tape, pickling is performed again. After cleaning, solder resist is sprayed onto the non-diffusion bonding area of ​​the core board, and air pipes are welded at the retained air intake channels. Step 3: Diffusion Bonding of Panels and Core Boards: After placing the pre-treated upper and lower panels and core board as a whole into the mold, place it into the superplastic forming machine. Vacuum the machine interior and heat the panels, core board, and mold using a stepped heating program. The diffusion bonding temperature of the material is 900~940℃. After reaching the temperature, apply pressure to the mold using a press to initiate the diffusion bonding of the upper panel, core board, and lower panel. The diffusion bonding time is 1~2.5 hours, and the diffusion pressure is 1~3 MPa.

[0016] Step 4: Superplastic Forming of Panels and Core Boards: After the upper panel, core board, and lower panel have completed diffusion bonding, argon gas is introduced between the upper and lower panels according to a preset pressure loading curve to induce superplastic forming of the panels. The panels undergo superplastic deformation under pressure until they conform to the mold. The core board, after diffusion bonding with the panels, undergoes plastic deformation under the tensile force of the panel deformation. During the forming process, different non-diffusion-bonded areas within the core board can be connected through vents in the diffusion bonding area, allowing for uniform and synchronous loading of the three serpentine channels. This completes the superplastic forming / diffusion bonding of the panels and core board.

[0017] Step 5: Turn off the heating and wait for the part to cool to room temperature before removing it to obtain a three-layer serpentine hollow channel thin-walled part with superplastic forming / diffusion bonding.

[0018] Step 1, Panel Cutting: For two-layer panel structures, use laser cutting equipment to cut the upper and lower panels to the required dimensions according to the design, and grind off the burrs on the edges. Step 2: Pre-treatment of sheet metal for bulging: Further polish the upper and lower sheets with sandpaper of different grits. Clean the surfaces of the upper and lower sheets with a small amount of anhydrous ethanol to remove surface spatter, weld spatter, and oil stains. Then, perform pickling with an acid pickling solution of HF:HNO3:H2O = 1:3:16. Grind and engrave the air intake channels on the inner sides of the upper and lower sheets according to the design drawings. Then, spray solder resist onto the outer sides of the upper and lower sheets. Apply acid-resistant tape to the designed ribs on the sheets and perform pickling to obtain the uneven surface and air intake channels of the inner surfaces of the upper and lower sheets. Remove the acid-resistant tape and perform pickling again. After cleaning, spray solder resist onto the non-diffusion bonding area on the inner sides of the upper and lower sheets and weld the air pipe at the retained air intake channels. Step 3: Diffusion Bonding of Upper and Lower Sheets: After placing the pre-treated upper and lower sheets into the mold, place them into the superplastic forming machine. Vacuum the machine and heat the upper and lower sheets and the mold using a stepped heating program. The diffusion bonding temperature of the material is 900~940℃. After reaching the temperature, apply pressure to the mold using a press to initiate diffusion bonding in the designated diffusion bonding area between the upper and lower sheets. The diffusion bonding time is 1~2.5 hours, and the diffusion pressure is 1~3 MPa.

[0019] Step 4: Superplastic forming of upper and lower sheets: After the diffusion bonding of the upper and lower sheets is completed, argon gas is introduced between the upper and lower sheets according to the specified gas pressure curve to induce superplastic forming of the panel. Areas in the upper and lower sheets that have not undergone diffusion bonding are subjected to superplastic deformation under gas pressure until they adhere to the mold. After the core board is formed, it is attached to the panel, and serpentine ribs are formed in the areas where the core board and panel are not welded together. This completes the superplastic forming / diffusion bonding of the upper and lower sheets.

[0020] Step 5: Turn off the heating and wait for the part to cool to room temperature before removing it to obtain a two-layer serpentine hollow channel thin-walled part with superplastic forming / diffusion bonding.

[0021] Furthermore, the internal structure of the thin-walled part with the four-layer plate and serpentine hollow channel is decomposed as follows: inside the already formed upper and lower panels, there is a serpentine channel area formed by the upper core plate and the lower core plate through superplastic forming / diffusion connection, and the serpentine channel is separated by forming ribs.

[0022] The internal structure of the thin-walled part with the three-layer plate and serpentine hollow channel is decomposed as follows: inside the already formed upper and lower panels, there is a serpentine channel area formed by the core plate through superplastic forming / diffusion connection, and the serpentine channel is separated by forming ribs.

[0023] The structure of the thin-walled component with two-layer plate and serpentine hollow channel is decomposed into: a serpentine channel region formed by superplastic forming / diffusion connection between the formed upper plate and the lower plate.

[0024] The internal structure of the thin-walled multilayer board with serpentine hollow channels can be decomposed into: inside the already formed upper and lower panels, there is a serpentine channel area formed by the core board through superplastic forming / diffusion connection, and the serpentine channels are separated by forming ribs.

[0025] Furthermore, when using superplastic forming / diffusion bonding technology to fabricate multilayer serpentine (N>4) channel hollow thin-walled parts, the fabrication steps are similar to those for three-layer and four-layer serpentine structures, but generally include the following steps: First, cut N layers of board material and perform surface treatment. In the non-diffusion bonding areas, scribing lines and spraying solder resist are done. Then, stack and assemble the panel and core board, sealing the perimeter with solder. This completes the first stage of diffusion bonding: through heating and pressurization, diffusion bonding is achieved between the panel and core board, and between core boards themselves. Next, the second stage of superplastic forming / diffusion bonding is completed: inert gas is introduced, causing the unbonded areas to expand and form serpentine channels, superplastic forming of the core board, and diffusion bonding between the core board and panel.

[0026] The beneficial effects of this invention are as follows: The method of this invention yields thin-walled parts with serpentine hollow channels, which not only meet the requirements for lightweighting but also provide functions such as heat dissipation and insulation, sound absorption and noise reduction, and impact damping. Manufacturing through superplastic forming / diffusion bonding results in lower costs, better mechanical properties, and the ability to form large-sized thin-walled parts with serpentine hollow channels. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the forming process of the titanium alloy four-layer serpentine hollow channel aircraft panel in Example 1; Figure 2 This is a schematic diagram of the final forming of the serpentine hollow channel arc skin of the titanium alloy three-layer high-speed aircraft in Example 2; Figure 3 This is a schematic diagram of the final forming of the titanium alloy two-layer aero-engine serpentine hollow channel cone component in Example 3. Detailed Implementation

[0028] To clearly illustrate the technical features of this patent, the superplastic forming / diffusion bonding process of the serpentine hollow channel thin-walled part in this patent will be described in detail below through specific embodiments and in conjunction with its accompanying drawings. Example

[0029] This embodiment focuses on a four-layer TA15 titanium alloy serpentine hollow channel aircraft panel component, and specific examples are given below for illustration: Process according to the following steps: (1) Based on the design of the four-layer plate serpentine hollow channel aircraft wall panel, complete the design and manufacturing of the corresponding superplastic forming / diffusion connection mold; (2) Based on the load and size requirements of the parts, the internal mesh design of the serpentine channel of the core board is designed and the rib thickness is obtained by using the topology optimization method. Two-dimensional drawings of the panel and core board are designed, and the original upper and lower panel materials and the original upper and lower core board materials are obtained by laser cutting. (3) The surfaces of the panel and the core board are successively sanded with 400#, 800#, 1000#, 1500# and 2000# sandpaper. The surface of the core board is cleaned with a small amount of anhydrous ethanol to remove surface spatter, solder joints and oil stains, etc., and then pickled with pickling solution to complete the preliminary surface pretreatment of the core board. The pickling solution is prepared in the ratio of HF:HNO3:H2O=1:3:16.

[0030] (4) According to the internal grid design of the core plate of the four-layer plate serpentine hollow channel aircraft wall panel, the anti-acid tape is pasted on the inner side of the upper and lower core plates and the lines are engraved according to the set internal structure of the core plate. The tape on the core plate that does not need to diffuse the connection area is removed, and the tape on the area that needs to diffuse the connection is retained. The upper and lower core plates are put into the acid solution for pickling, the oxide layer on the surface of the core plate is corroded and the non-diffusion area is corroded. After the pickling is completed, the core plate is cleaned and the remaining anti-acid tape is removed. (5) After aligning the upper panel, upper core plate, lower core plate and lower panel, perform edge sealing argon arc welding and weld the gas pipe at the reserved air inlet. (6) Place the assembled upper panel, upper core plate, lower core plate and lower panel into the superplastic forming / diffusion connection mold, and put the plate and mold into the superplastic forming machine tool to draw a vacuum. Use a press to apply a pressing load to the pressing area of ​​the upper and lower panels to ensure the airtightness between the upper and lower panels.

[0031] (7) Heat the mold and sheet metal to 920℃ using a superplastic forming machine and keep it at that temperature for 20 minutes. Apply a pressure load of 2.5MPa to the diffusion area around the panel and core plate through the pressure control system to complete the diffusion connection between the panel and core plate while ensuring the sealing between the panel and core plate. According to the gas pressure loading curve, argon gas is introduced between the upper panel and the upper core plate and between the lower panel and the lower core plate to make the panel inside the mold superplastic form and complete the bonding with the mold. While completing the expansion of the upper and lower panels, the back pressure during the expansion of the panels is used to apply a diffusion connection pressure of 2.5MPa to the upper and lower core plates. Keep it at 920℃ for 2 hours to complete the diffusion connection of the upper and lower core plates. After the panel expansion is completed, maintain a low back pressure to prevent the panel from collapsing due to insufficient internal pressure of the upper and lower panels. (8) Maintain the forming temperature and blank holder force in the machine tool, and introduce argon gas between the upper and lower core plates according to the gas pressure loading curve to make the core plates undergo superplastic forming. At this time, the unwelded area between the upper and lower core plates is subjected to gas pressure and undergoes superplastic forming; the core plate diffusion connection area between the upper and lower core plates does not deform. During the forming process, different undiffused connection areas of the core plates can be connected through the vent holes in the core plate diffusion connection area, so that the gas pressure can be uniformly applied to the three serpentine channels simultaneously. After the core plate is formed and the panel is attached, continue to introduce argon gas according to the gas pressure loading curve. At this time, diffusion connection occurs between the core plate and the panel. At the same time, the welded area between the upper and lower core plates deforms to form vertical ribs. After completion, reduce the gas pressure to 0.2MPa~0.3MPa for pressure holding and cooling treatment; (9) After the part has cooled to room temperature, demolding and sampling are performed to obtain the formed four-layer serpentine hollow channel aircraft wall panel, such as Figure 1 As shown. Example

[0032] This embodiment focuses on the serpentine hollow channel arc surface skin of a three-layer Ti60 titanium alloy high-speed aircraft. Specific examples are provided below for illustration: Process according to the following steps: (1) Based on the design of the serpentine hollow channel arc skin of the three-layer plate high-speed aircraft, complete the design and manufacturing of the corresponding superplastic forming / diffusion connection mold; (2) Based on the load and size requirements of the parts, the internal mesh design of the serpentine channel of the core board and the thickness of the ribs are designed by using the topology optimization method. Two-dimensional drawings of the upper and lower panels and the core board are designed. The original upper and lower panel materials and the original core board materials are obtained by laser cutting. (3) The surface of the board is polished in sequence with 400#, 800#, 1000#, 1500# and 2000# sandpaper. The core board surface is cleaned with a small amount of anhydrous ethanol to remove surface spatter, weld spatter and oil stains, etc., and then pickled with pickling solution to complete the preliminary surface pretreatment of the core board. The pickling solution ratio is HF:HNO3:H2O=1:3:16.

[0033] (4) According to the internal grid design of the core plate of the serpentine hollow channel arc skin of the three-layer plate high-speed aircraft, the anti-acid tape is pasted on the upper and lower sides of the core plate and the lines are engraved according to the set internal structure of the core plate. The tape on the core plate that does not need to diffuse the connection area is removed, and the tape on the area that needs to diffuse the connection is retained. The core plate is put into the acid solution for pickling, the oxide layer on the surface of the core plate is corroded and the non-diffusion area is corroded. After the pickling is completed, the core plate is cleaned and the remaining anti-acid tape is removed. (5) Apply protective tape to the core board again and scribing according to the set internal structure of the core board. Remove the tape from the non-diffusion connection area of ​​the core board and spray boron nitride solder resist. After completion, remove the remaining protective tape. (6) Do not stick protective tape to the connection of the air pipes between the upper and lower panels. Spray boron nitride solder resist on other areas inside the panel that are not diffused and on the outside of the entire panel to prevent it from sticking to the mold. Remove the protective adhesive after spraying. (7) Align the upper panel, core board and lower panel along the outer edge in sequence, seal the edge with argon arc welding, and weld the gas pipe at the reserved air inlet.

[0034] (8) Place the assembled panel and core board into the superplastic forming / diffusion bonding mold, and use a vacuum superplastic forming machine to heat the mold, panel and core board to 920°C in a vacuum environment and hold for 10 minutes. During the heating process, apply a diffusion bonding pressure of 3MPa to the board through a press and hold at 920°C for 1 hour. The diffusion bonding area between the core board and the upper panel and lower panel will undergo diffusion bonding. (9) Argon gas is introduced into the panel according to the gas pressure loading curve to make the core board superplastically formed. At this time, the core board and the upper and lower panels are subjected to gas pressure and undergo superplastic forming; the area where the core board is welded to the upper and lower panels does not deform. During the forming process, different non-diffused connection areas in the core board can be connected through the air vents in the diffusion connection area of ​​the core board, so that the gas pressure can be uniformly applied to the three serpentine channels simultaneously. After the forming is completed, the gas pressure is reduced to 0.2~0.3MPa and then pressure is maintained and the temperature is lowered to prevent the collapse caused by insufficient pressure in the forming area of ​​the board during the cooling process. (10) After the part has cooled to room temperature, demolding and sampling are performed to obtain the formed high-speed aircraft three-layer plate serpentine hollow channel arc surface skin, such as Figure 2 As shown. Example

[0035] This embodiment focuses on a two-layer Ti55 titanium alloy serpentine hollow channel cone component for aero-engines, and specific examples are provided below for illustration: Process according to the following steps: (1) Based on the design of the serpentine hollow channel cone component of the two-layer plate aero-engine, complete the design and manufacturing of the corresponding superplastic forming / diffusion connection mold; (2) Based on the load and size requirements of the parts, the internal mesh design of the serpentine channel of the core board and the thickness of the ribs are designed by using the topology optimization method. Two-dimensional drawings of the board are designed, and the original upper and lower original boards are obtained by laser cutting. (3) The surface of the board is polished sequentially with 400#, 800#, 1000#, 1500#, and 2000# sandpaper. The core board surface is cleaned with a small amount of anhydrous ethanol to remove surface spatter, weld spatter, and oil stains. Then, it is pickled with pickling solution to complete the preliminary surface pretreatment of the core board. The pickling solution ratio is HF:HNO3:H2O=1:3:16. (4) According to the design of the internal serpentine channel of the thin-walled part with two-layer plate and serpentine hollow channel, the anti-acid tape is pasted on the inner side of the upper and lower plates and the lines are engraved according to the set core plate internal structure. The tape on the plate that does not need to diffuse the connection area is removed, and the tape on the area that needs to diffuse the connection is retained. The upper and lower plates are put into the acid solution for pickling, the oxide layer on the surface of the plate is corroded and the non-diffusion area is corroded. After the pickling is completed, the plate is cleaned and the remaining anti-acid tape is removed. (5) Apply protective tape to the board again and scribing according to the set internal structure of the core board. Remove the tape from the non-diffusion bonding area on the board and spray boron nitride solder resist. After completion, remove the remaining protective tape. (6) After merging and aligning the outer edges of the upper and lower plates, perform edge sealing argon arc welding and weld the gas pipe at the reserved air inlet. (7) Place the assembled upper and lower plates into the superplastic forming / diffusion bonding mold. Place the plate and mold as a whole into the superplastic forming machine and evacuate. Heat the mold and plate to 940℃ in a vacuum environment and hold for 20 minutes. Apply a diffusion bonding pressure of 2.2MPa to the plate using a press and hold at 940℃ for 2 hours to complete the diffusion bonding of the plate; (8) After the diffusion connection of the plates is completed, argon gas is introduced into the plates according to the gas pressure loading curve to cause the non-diffusion connection area between the plates to expand and form until it fits the mold, thus completing the superplastic forming of the plates. After the forming is completed, the gas pressure is reduced to 0.2~0.3MPa and then pressure is maintained and the temperature is lowered to prevent the plate from collapsing due to insufficient pressure in the forming area during the cooling process. (9) After the part has cooled to room temperature, demolding and sampling are performed to obtain the formed two-layer plate aero-engine serpentine hollow channel cone part, such as Figure 3 As shown.

[0036] There are many specific ways to implement this invention. The above description is only a preferred embodiment of this invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of this invention, and these improvements should also be considered within the scope of protection of this invention.

Claims

1. A method for preparing thin-walled parts with serpentine hollow channels using superplastic forming / diffusion bonding, characterized in that, The method is as follows: Step 1: Sheet preparation and surface treatment: Select and cut superplastic sheets, and perform grinding, cleaning, and pickling to remove contaminants and oxide film; Step 2, Solder resist coating: Using a mask deposition method, high-temperature resistant solder resist is precisely coated on specific areas of the board in a serpentine channel shape to prevent adhesion to the mold. After spraying, the protective tape is removed. Step 3, Stacking and Sealing: Stack the plates in the design order to ensure accurate alignment of the solder resist pattern; seal the perimeter to form an airtight assembly and reserve air inlet / outlet ports for connecting air pipes; Step 4, Heating: Place the component into the mold, and place the sheet and mold into the superplastic forming machine tool, and heat to the superplastic forming temperature of the material; Step 5, Diffusion Bonding Stage: Using the pressure head in the superplastic machine tool, uniform pressure is applied to the mold, causing the contact surfaces of the uncoated solder resist plates to undergo diffusion bonding under high temperature and high pressure, forming the connecting ribs of the corresponding structure; Step 6, Superplastic forming / diffusion bonding stage: Under constant temperature conditions, high-pressure inert gas is injected into the component through the reserved air inlet; under the continuous action of gas pressure, the area of ​​the board coated with solder resist undergoes superplastic deformation, gradually achieving conformal fitting with the mold cavity, and finally precisely forming a preset serpentine channel cavity structure. Step 7: Cooling and Demolding: After superplastic forming / diffusion bonding is completed, cool to room temperature, remove the serpentine hollow channel thin-walled part, and clean off any residual solder resist; The method described is capable of superplastic forming / diffusion bonding of thin-walled parts with serpentine hollow channels in two-layer, three-layer, four-layer or multi-layer boards (N layers, N>4).

2. The method for preparing a thin-walled part with a serpentine hollow channel using superplastic forming / diffusion bonding according to claim 1, characterized in that, The internal structure of the thin-walled part with the four-layer plate and serpentine hollow channel is decomposed as follows: inside the already formed upper and lower panels, there is a serpentine channel area formed by the upper core plate and the lower core plate through superplastic forming / diffusion connection, and the serpentine channel is separated by forming ribs. The internal structure of the thin-walled part with the three-layer plate and the serpentine hollow channel is decomposed into: inside the already formed upper and lower panels, there is a serpentine channel area formed by the core plate through superplastic forming / diffusion connection, and the serpentine channel is separated by forming ribs; The structure of the thin-walled component with two-layer plate and serpentine hollow channel is decomposed into: a serpentine channel region formed by superplastic forming / diffusion connection between the formed upper plate and the lower plate. The internal structure of the thin-walled multilayer board with serpentine hollow channels can be decomposed into: inside the already formed upper and lower panels, there is a serpentine channel area formed by the core board through superplastic forming / diffusion connection, and the serpentine channels are separated by forming ribs.

3. The method for preparing a thin-walled part with a serpentine hollow channel using superplastic forming / diffusion bonding according to claim 2, characterized in that: The superplastic forming / diffusion bonding method for two-layer thin-walled parts with serpentine hollow channels is as follows: Step 1, Panel Cutting: For two-layer panel structures, use laser cutting equipment to cut the material according to the design, cut the upper and lower panels to the correct dimensions, and grind off the burrs on the edges; Step 2, Pre-treatment of sheet metal for bulging: Further polish the upper and lower sheets with sandpaper of different grits, and clean the surfaces of the upper and lower sheets; according to the design drawings, grind the air intake channels on the inner side of the upper and lower sheets, and then spray solder resist on the outer side of the upper and lower sheets; apply acid-resistant tape to the ribs designed on the sheets and perform acid pickling treatment to obtain the uneven surface of the inner surface of the upper and lower sheets and the air intake channels. After removing the acid-resistant tape, perform acid pickling again. After cleaning, spray solder resist on the non-diffusion bonding area on the inner side of the upper and lower sheets, and weld the air pipe at the retained air intake channel; Step 3: Diffusion bonding of upper and lower plates: After placing the pre-treated upper and lower plates into the mold, place them into the superplastic forming machine. Vacuum the inside of the machine and heat the upper and lower plates and the mold using a stepped heating program. The diffusion bonding temperature of the material is 900~940℃. After reaching the temperature, apply pressure to the mold through a press to cause diffusion bonding to begin in the designated diffusion bonding area between the upper and lower plates. The diffusion bonding time is 1~2.5h, and the diffusion pressure is 1~3MPa. Step 4: Superplastic forming of upper and lower plates: After the diffusion connection of the upper and lower plates is completed, argon gas is introduced between the upper and lower plates according to the specified gas pressure curve to perform superplastic forming of the panel. The areas of the upper and lower plates that have not undergone diffusion connection will undergo superplastic deformation under the action of gas pressure until they fit into the mold; after the core board is formed, it is molded with the panel, and the areas between the core board and the panel that are not welded form serpentine ribs; the superplastic forming / diffusion connection of the upper and lower plates is completed. Step 5: Turn off the heating and wait for the part to cool to room temperature before removing it to obtain a two-layer serpentine hollow channel thin-walled part with superplastic forming / diffusion bonding.

4. The method for preparing a thin-walled part with a serpentine hollow channel using superplastic forming / diffusion bonding according to claim 2, characterized in that, The superplastic forming / diffusion bonding method for three-layer thin-walled parts with serpentine hollow channels is as follows: Step 1: Sheet metal cutting: Based on the load and size requirements of the parts, the internal mesh design of the serpentine channel of the core board and the thickness of the ribs are obtained by using topology optimization design. Two-dimensional drawings of the panel and core board are designed. Laser cutting equipment is used to cut the materials according to the design, and the upper panel, lower panel and core board that meet the dimensions are cut out. The edge burrs are polished. Step 2: Pre-treatment of panel and core board bulging: The upper and lower panels and core board are further polished with sandpaper of 400#, 800#, 1000#, 1500# and 2000# in sequence, and the surfaces of the panels and core board are cleaned; the air intake channel is ground on the panel according to the design drawings, and then the outer side of the upper and lower panels is sprayed with solder resist; the ribs designed on the core board are covered with acid-resistant tape and acid-washed to obtain the uneven surface of the core board and the air intake channel. After removing the acid-resistant tape, acid-washing is performed again. After cleaning, solder resist is sprayed on the non-diffusion connection area of ​​the core board, and the air pipe is welded at the retained air intake channel. Step 3, Diffusion Connection of Panel and Core Board: After placing the pre-treated upper and lower panels and core board into the mold, place them into the superplastic forming machine. Vacuum the inside of the machine and heat the panel, core board and mold using a stepped heating program. The diffusion connection temperature of the material is 900~940℃. After reaching the temperature, apply pressure to the mold through a press to start the diffusion connection of the upper panel, core board and lower panel. The diffusion connection time is 1~2.5h and the diffusion pressure is 1~3MPa. Step 4: Superplastic forming of panel and core board: After the upper panel, core board and lower panel have completed diffusion connection, argon gas is introduced between the upper and lower panels according to the preset gas pressure loading curve and the specified gas pressure curve to make the panel superplastic form. The panel undergoes superplastic deformation under the action of gas pressure until it fits the mold. The core board, after the diffusion connection with the panel has been completed, undergoes plastic deformation under the action of the panel deformation tension. During the forming process, different non-diffused connection areas within the core board can be connected through the vent holes in the diffusion connection area of ​​the core board, allowing the air pressure to be uniformly applied to the three serpentine channels simultaneously; thus completing the superplastic forming / diffusion connection of the panel and the core board; Step 5: Turn off the heating and wait for the part to cool to room temperature before removing it to obtain a three-layer serpentine hollow channel thin-walled part with superplastic forming / diffusion bonding.

5. A method for preparing a thin-walled part with a serpentine hollow channel using superplastic forming / diffusion bonding according to claim 2, characterized in that, The superplastic forming / diffusion bonding method for four-layer thin-walled parts with serpentine hollow channels is as follows: Step 1: Sheet metal cutting: Based on the load and size requirements of the parts, the internal mesh design of the serpentine channel of the core board and the thickness of the ribs are obtained by using topology optimization. Two-dimensional drawings of the panel and core board are designed. Laser cutting equipment is used to cut the material according to the design, and the upper panel, lower panel, upper core board and lower core board that meet the dimensions are cut out. The edge burrs are polished. Step 2, Panel bulging pretreatment: The upper and lower panels are further polished with sandpaper of 400#, 800#, 1000#, 1500# and 2000# in sequence, and the panel surface is cleaned; the air intake channel is ground and engraved on the panel and core board according to the design drawings, and then boron nitride solder resist is sprayed on the outer side of the upper and lower panels. Step 3, Pre-treatment of core board diffusion: Apply acid-resistant tape to the ribs designed on the upper and lower core boards and perform acid pickling. The acid pickling steps are the same as in Step 2. Obtain the stepped morphology and air inlet of the core board surface. Remove the acid-resistant tape and perform acid pickling again. After cleaning, spray boron nitride solder resist on the non-diffusion connection area of ​​the core board. Step 4, Assembly: Assemble the pre-treated panels in the order of upper panel, upper core panel, lower core panel, and lower panel. Spray solder resist on the outside of the upper and lower panels, align them, and perform edge sealing argon arc welding. Weld the gas pipe at the reserved air inlet. Step 5: Panel Air Expansion Forming and Core Board Superplastic Forming / Diffusion Connection: Place the assembled panel and core board into the superplastic forming / diffusion connection mold, and then place the whole assembly into the superplastic forming machine. A stepped heating program is used to heat the panel, core board, and mold. A press is used to apply a blank holder force to the superplastic forming / diffusion connection mold to ensure the sealing of the upper and lower panels. The superplastic forming temperature of the panel and core board is 900~940℃. After reaching the temperature, argon gas is introduced between the upper panel and upper core board, and between the lower panel and lower core board, according to the gas pressure loading curve. While completing the expansion of the upper and lower panels, the back pressure during panel expansion is used to complete the diffusion connection of the upper and lower core boards. The diffusion temperature of the core board is 900~940℃, the diffusion time is 1~2.5h, and the diffusion pressure is 1~3MPa. Step 6: After the panel is formed, argon gas is introduced between the upper and lower core boards according to the specified gas pressure curve to perform superplastic forming. During the forming process, different non-diffused connection areas within the core board can be connected through ventilation holes, allowing air pressure to be uniformly and synchronously applied to the serpentine channel. After the core board is fully formed, it begins to diffusely connect with the panel. At this time, the area where the upper and lower core boards are welded together forms an upright serpentine rib, completing the superplastic forming between the core boards and the diffusion connection between the core board and the panel. Step 7: Turn off the heating and wait for the part to cool to room temperature before removing it to obtain a four-layer plate serpentine hollow channel thin-walled part with superplastic forming / diffusion bonding.

6. A method for preparing a thin-walled part with a serpentine hollow channel using superplastic forming / diffusion bonding according to claim 2, characterized in that, The method for superplastic forming / diffusion bonding of thin-walled parts with multilayer serpentine hollow channels is as follows: First, cut the multi-layer (N-layer) board material and perform surface treatment. Then, scribing lines in the non-diffusion bonding area and spraying solder resist, stacking and assembling the panel and core board, and sealing the perimeter with solder. Complete the first stage of diffusion bonding: through heating and pressurization, diffusion bonding is achieved between the panel and the core board, and between the core boards themselves; Then, the second stage of superplastic forming / diffusion bonding is completed: inert gas is introduced to cause the unbonded areas to expand and form serpentine channels, the core board is superplastic formed, and diffusion bonding is performed between the core board and the panel.

7. A method for preparing a thin-walled part with a serpentine hollow channel using superplastic forming / diffusion bonding according to claim 2, characterized in that, For superplastic forming / diffusion bonding methods of thin-walled parts with serpentine hollow channels in two-layer, three-layer, four-layer, or multi-layer boards (N layers, N>4): The specific locations for solder resist application are as follows: for two-layer boards, the solder resist is applied to the bottom layer on one side; for three-layer boards, the solder resist is applied to both sides of the middle layer; for four-layer / multi-layer boards, the solder resist is applied to both sides of the middle layer, with multiple layers stacked. The specific channel configurations are as follows: for two-layer boards, the channel configuration is a single-sided hollow channel; for three-layer boards, the channel configuration is a double-sided symmetrical hollow channel; and for four-layer / multi-layer boards, the channel configuration is a multi-layer independent or interconnected hollow channel network.

8. A method for preparing a thin-walled part with a serpentine hollow channel using superplastic forming / diffusion bonding according to claim 1, characterized in that: For titanium alloys, the diffusion bonding temperature is 900~940℃, the diffusion bonding time is 1~2.5h, and the diffusion pressure is 1~3MPa.

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