Lightweight titanium alloy hollow sandwich three-layer pipe with special cross section and electric auxiliary integrated manufacturing method thereof

Abstract

This invention relates to a lightweight, irregularly shaped cross-section titanium alloy hollowed-out three-layer pipe fitting and its electro-assisted integrated manufacturing method. The lightweight, irregularly shaped cross-section titanium alloy hollowed-out three-layer pipe fitting consists of an inner tube with an irregular cross-section, an outer tube with an irregular cross-section, and an irregularly shaped hollowed-out sandwich structure. This invention also provides an electro-assisted integrated molding process for the lightweight, irregularly shaped cross-section titanium alloy hollowed-out three-layer pipe fitting, the key technical points of which include the following steps: first, material preparation; second, diffusion welding; third, overall high-temperature and high-pressure internal bulging; fourth, cooling; and fifth, electro-assisted layered gas expansion of the outer tube. The lightweight, irregularly shaped cross-section titanium alloy hollowed-out three-layer pipe fitting proposed in this invention improves the structural strength, stability, and impact resistance of the pipe fitting. Simultaneously, the proposed integrated molding process enhances the degree of production automation, resulting in high forming efficiency and good precision.

Description

Technical Field

[0001] This invention relates to the field of structural design and manufacturing technology, and in particular to the design and manufacture of a lightweight, irregularly shaped cross-section titanium alloy hollow sandwich three-layer pipe fitting. Background Technology

[0002] With the rapid development of aerospace technology, hypersonic vehicles have an urgent need for lightweight and multifunctional structures. Lightweight alloy three-dimensional sandwich structures are a novel type of lightweight structure with higher structural design flexibility. The shape, size, density, and distribution of the support lattice can be designed and optimized according to actual application requirements, and the overall lightweight effect of three-dimensional sandwich structures is more significant. Furthermore, three-dimensional sandwich structures not only possess high load-bearing capacity, but their open internal space also facilitates the integration of structural-functional properties such as load-bearing capacity, stealth, vibration reduction, noise reduction, energy absorption, and thermal control, making them considered one of the most promising structures in the aerospace industry.

[0003] Current research on sandwich structures mainly focuses on flat and curved surfaces, while research and fabrication of sandwich structures for pipe fittings, especially irregularly shaped cross-section pipe fittings, are relatively limited.

[0004] A search revealed a Chinese invention patent: a method for preparing a superplastic forming / diffusion-bonded three-layer hollow component, publication number: CN 108326395 B, application number: 201611016005.9. This invention discloses a method for preparing a superplastic forming / diffusion-bonded three-layer hollow component: "Including: 1) Selecting a core board and a panel, and cleaning and degreasing their surfaces to ensure a smooth surface; 2) Applying a weld resist to the surface of the core board and placing it between two panels, then placing two sheaths on the outside of the panels respectively to form a five-layer board; 3) Sealing and welding the five-layer board, leaving air channels, and welding the air channels to the vent pipe; 4) After testing the sealing performance of the sealing board blank, heating the sealing board to the diffusion bonding temperature, and applying pressure to the outer surface of the sealing board to achieve diffusion bonding between the panel and the core board." 5) Inert gas is introduced between the core board and the two side panels to deform the panels, and the temperature is controlled to slowly deform the panels and the core board; 6) After forming, the sheath is removed, and the final external dimensions of the designed three-layer hollow structural component are obtained. Structurally, the three-layer hollow component of this patent is a flat sandwich structure. The blank of the three-layer hollow component includes a core board and panels placed on both sides of the core board. During processing, two sheath plates are placed on the outside of the two panels respectively, forming five layers of plates; after welding the panels and the core board, superplastic forming is performed. The core board deforms under the tensile stress of the panels to form reinforcing ribs. After forming, the sheath is removed, and the three-layer hollow structural component is finally formed. This differs structurally from the irregular cross-section tube three-layer sandwich structure proposed in this patent. The irregular cross-section sandwich three-layer tube proposed in this patent consists of three parts: an irregular cross-section inner tube, an irregular cross-section outer tube, and an irregular hollow sandwich structure. Its cross-sectional profile is a continuous curvature shape. Furthermore, regarding the preparation method of the irregular cross-section titanium alloy hollow sandwich three-layer pipe fitting of this patent, the traditional method uses superplastic / diffusion bonding technology, which requires at least three sets of thermoforming molds for integral bulging and layered bulging. The mold design is complex and the manufacturing cost is high, the forming time is long, the micro-grain growth of the material is obvious, and the demolding and part removal are difficult after forming. In contrast, the forming method proposed in this patent only requires two sets of molds: diffusion welding and integral bulging. Moreover, the electric assisted heating speed is extremely fast, the forming time is short, the quality is good, and there is no internal support mold, which makes part removal simple.

[0005] A search revealed a Chinese invention patent: Hyperbolic Lattice Sandwich Structure and its Preparation Method, publication number: CN114670508. B, application number: 202210301901.9, discloses a hyperbolic lattice sandwich structure and its preparation method: "It includes: cutting arc-shaped core frames and wavy arc-shaped rods on a flat plate according to the shape and size of the curved surface to be assembled; preparing an assembly mold for stably placing the arc-shaped core frames; placing all the arc-shaped core frames on the assembly mold; connecting the wavy arc-shaped rods to the arc-shaped core frames; bonding the assembled core structure with the first curved panel and the second curved panel; filling the connection position with brazing coating; and placing it in a vacuum brazing furnace for integrated welding to complete the preparation of the hyperbolic lattice sandwich structure." Structurally, this patent is a design and manufacturing of a curved sandwich structure. The hyperbolic lattice sandwich structure includes: a first curved panel, a second curved panel, multiple arc-shaped core frames, and multiple wavy arc-shaped rods. Its structure is composed of multiple arc-shaped core frames and wavy arc-shaped rods spliced ​​together, which differs structurally from the three-layer sandwich structure of the irregular cross-section tube proposed in this patent. This patent proposes a three-layer tubular fitting with an irregular cross-section, consisting of an inner tube with an irregular cross-section, an outer tube with an irregular cross-section, and an irregularly shaped hollowed-out sandwich structure. Its cross-sectional profile is a continuous curvature shape. From a manufacturing perspective, core layer splicing has a low degree of automation and low precision, resulting in low brazing strength. This patent uses integral diffusion welding, which provides high welding strength. This patent employs an integrated forming method combining high-temperature, high-pressure internal bulging and electrically assisted layered air expansion of the outer tube, resulting in short forming time and high quality.

[0006] A search revealed a Chinese invention patent: an aircraft engine air intake duct and its integrated molding process, publication number: CN 115111060 A, Application No.: 202210596529.9, this invention discloses an S-shaped air intake duct integrally molded from metal-composite material and injection molding process: "Including: S1. Bending a cylindrical hollow metal tube into an S-shape using a pre-forming mold; S2. Laying composite material reinforcement (such as wire, mesh) or prepreg on the outer surface of the S-shaped metal tube using an automatic wire laying or tape laying device; S3. Placing the S-shaped metal tube with the composite material reinforcement or prepreg on a heating station and heating the metal tube to the temperature range with optimal molding performance; S4. Heating the mold to the metal tube molding temperature range, then moving the heated S-shaped metal tube into the molding mold and quickly closing the mold, sealing both ends of the S-shaped metal tube and filling it with high-pressure gas to expand the S-shaped metal tube into the mold cavity shape to obtain the S-shaped metal tube; S5. Adjusting the temperature of the molding mold and the S-shaped metal tube to reach the suitable temperature range for resin curing; S6. If the composite material is used for injection molding, the process is as follows: If the composite reinforcement is wire or mesh, RTM or HP-RTM technology is used to inject the matrix resin into the composite reinforcement. Utilizing the injection port, plastic reinforcing rib injection channel, and flow cavity of the molding die, the injection molding machine injects reinforcing ribs into the air intake duct simultaneously with the injection of the composite matrix resin through the injection port and the plastic reinforcing rib injection channel. If the composite is a prepreg, the injection molding machine injects reinforcing ribs into the air intake duct through the plastic reinforcing rib injection channel and flow cavity. S7. Using the heating rod and cooling water channel in the molding die, thermosetting, thermoplastic, or resin co-curing is achieved, thereby obtaining an aircraft engine air intake duct integrating metal, composite, and injection-molded mixture structures. The patented S-shaped air intake duct, from the inside out, consists of a thermally expanded S-shaped metal tube, a cured composite material layer, and an external composite reinforcing rib structure, which is significantly different in structure and materials from the three-layer tube with an irregular cross-section composed of an inner tube with an irregular cross-section, an irregular hollow sandwich structure, and an outer tube with an irregular cross-section in this patent. In terms of forming method, the patent (CN 115111060 A) only uses a high-temperature gas expansion composite material layer for the S-bend irregular metal inner tube and an RTM or HP-RTM composite curing forming method for the external composite material reinforcing rib, which is significantly different from the overall high-temperature internal high-pressure expansion forming and electrically assisted outer tube layered gas expansion method of this patent. Summary of the Invention

[0007] To address the aforementioned problems in the existing technology, this invention provides a lightweight, irregularly shaped cross-section titanium alloy three-layer hollowed-out tubular fitting and its electrically assisted integrated manufacturing method. The lightweight, irregularly shaped cross-section titanium alloy three-layer tubular fitting consists of an inner tube with an irregular cross-section, an outer tube with an irregular cross-section, and an irregularly shaped hollowed-out sandwich structure. The irregularly shaped hollowed-out sandwich structure is a cellular structure resembling a pyramid lattice, integrally formed from a thin-walled, mesh-like hollowed-out metal tube. This structure improves impact resistance, enhances fatigue resistance, strengthens the survivability and competitiveness of aircraft, and meets the requirements of high speed, long service life, and safety for aircraft.

[0008] The present invention provides a lightweight titanium alloy three-layer pipe with irregular cross-section, which consists of an inner pipe with irregular cross-section (1), an outer pipe with irregular cross-section (3) and an irregular hollow sandwich structure (2).

[0009] Furthermore, the irregular hollow sandwich structure is a cellular structure of a pyramid-shaped lattice structure formed by integrally expanding a metal thin-walled mesh hollow structure tube.

[0010] Furthermore, the metal thin-walled mesh-like hollow structure tube is an ultra-thin-walled tube with an inner tube of irregular cross-section and an outer tube of irregular cross-section, each having a thickness of one-third.

[0011] Furthermore, the height of the irregularly shaped hollow interlayer structure between the irregularly shaped inner tube and the irregularly shaped outer tube needs to be calculated based on the heat transfer model so that the irregularly shaped inner and outer tubes can play a heat insulation role under aviation working conditions, with the irregularly shaped outer tube in a high-temperature state and the irregularly shaped inner tube in a low-temperature state.

[0012] Furthermore, the adjacent lattice points of the irregularly shaped hollowed-out sandwich structure are welded to the inner wall surface of the irregularly shaped cross-section outer tube and the outer wall surface of the irregularly shaped cross-section inner tube, respectively.

[0013] Optionally, the materials of the irregular cross-section inner tube, the irregular cross-section outer tube, and the intermediate irregular hollow sandwich structure are titanium alloy or high-temperature alloys, which are difficult to deform, lightweight, and high-strength alloys.

[0014] The present invention provides an electrically assisted integrated molding process for a lightweight, irregularly shaped cross-section titanium alloy hollow sandwich three-layer pipe fitting, comprising the following steps: first, material preparation; second, diffusion welding; third, overall high-temperature and high-pressure internal expansion; fourth, cooling; and fifth, electrically assisted layered air expansion of the outer tube.

[0015] Furthermore, in the material preparation step, according to the design size requirements of the lattice structure, the pipe fitting is processed into a mesh-like hollow intermediate pipe (4) by a subtractive machining method.

[0016] Furthermore, in the diffusion welding step, firstly, insulating and heat-resistant welding agent needs to be applied to the inner and outer surfaces of all areas of the middle hollow tube except for the dot area. Welding agent is applied to one side of the dot dot position and the coating state of the adjacent dot side is reversed (e.g., positions (5, 6)). Then, the inner tube, the middle hollow tube, and the outer tube are combined and installed in the support mold (9) and placed in a high-temperature hot press furnace. The temperature is heated to 800℃~1000℃ and kept for 0.5h~1h. Then, inert gas is introduced into the inner tube to apply a pressure of 0.1MPa~4MPa and kept for 1h~3h to obtain a three-layer integral pipe fitting (7).

[0017] Furthermore, in the high-temperature and high-pressure expansion step, the three-layer integral pipe obtained in the previous step is placed in the cavity of the irregular cross-section pipe mold (10), and the inner tube is vented with pressure inert gas at a thermoforming temperature of 800℃~1000℃ to perform high-temperature gas expansion until the three-layer integral pipe is attached to the mold, thus obtaining the three-layer integral irregular cross-section pipe (8), which is then cooled to room temperature.

[0018] Furthermore, in the electric-assisted internal high-pressure bulging step, the primary bulging tube is placed in the cavity of the electric-assisted internal high-pressure forming mold, electrodes are connected to both ends of the tube and energized, and internal high-pressure bulging is performed between the inner tube and the outer tube until the outer tube adheres to the mold, resulting in a closed-section three-dimensional lattice sandwich support structure irregular cross-section tube.

[0019] Further, in the electric-assisted outer tube layered air expansion step, the three-layer integral irregular cross-section tube is placed in the final forming mold (11). The two ends of the irregular cross-section outer tube are heated to the forming temperature. Under the action of the insulating and heat-insulating welding agent, the irregular cross-section inner tube is in a low temperature state that is difficult to deform. Then, inert gas of equal pressure is introduced into the irregular cross-section inner tube and between the irregular cross-section inner and outer tubes. The irregular cross-section inner tube is in a low temperature state that is difficult to deform and its inner and outer surface pressure is balanced, and no plastic deformation or elastic deformation occurs. The irregular cross-section outer tube, which is in a high temperature state that is easy to form, expands to the mold under the action of air pressure to obtain a three-layer tube with a hollow sandwich structure of irregular cross-section titanium alloy. Attached Figure Description

[0020] The accompanying drawings are provided to further illustrate the invention.

[0021] Figure 1 This is a schematic diagram of an irregularly shaped pipe fitting with a closed-section three-dimensional lattice sandwich support structure.

[0022] Figure 2 This is a schematic diagram of a hollowed-out tube in the middle.

[0023] Figure 3 This is a schematic diagram of a three-dimensional dot matrix structure.

[0024] Figure 4 A diagram illustrating the forming steps of an irregularly shaped cross-section pipe fitting for a closed-section three-dimensional lattice sandwich support structure.

[0025] Figure 5 This diagram illustrates the forming steps of a closed-section three-dimensional lattice sandwich support structure pipe fitting.

[0026] Figure 6 This is a mold drawing.

[0027] In the diagram: 1. Outer tube of a closed-section three-dimensional lattice sandwich support structure with irregular cross-section; 2. Three-dimensional lattice sandwich support structure; 3. Inner tube of a closed-section three-dimensional lattice sandwich support structure with irregular cross-section; 4. Hollowed-out tube in the middle; 5. Welding area between the hollowed-out tube in the middle and the inner tube; 6. Welding area between the hollowed-out tube in the middle and the outer tube; 7. Three-layer integral tube; 8. Three-layer integral irregular cross-section tube; 9. Diffusion welding mold; 10. Integral bulging mold; 11. Electrically assisted layered bulging mold. Detailed Implementation

[0028] To make the present invention easier to understand, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0029] like Figure 1 As shown, a lightweight, irregularly shaped cross-section titanium alloy three-layer pipe fitting of the present invention is composed of an irregularly shaped cross-section inner pipe (1), an irregularly shaped cross-section outer pipe (3), and an irregularly shaped hollow sandwich structure (2). The pipe material of the metal thin-walled mesh hollow structure is an ultra-thin-walled pipe material with a thickness of one-third of the thickness of the irregularly shaped cross-section inner pipe and the irregularly shaped cross-section outer pipe. The lightweight, irregularly shaped cross-section titanium alloy three-layer pipe fitting is formed by integral three-layer metal pipe through diffusion welding and integral high-temperature gas expansion, and then the outer pipe is separately formed by electric pulse assisted gas expansion. The adjacent grid points of the irregularly shaped hollow sandwich structure are respectively welded to the inner wall surface of the irregularly shaped cross-section outer pipe and the outer wall surface of the irregularly shaped cross-section inner pipe.

[0030] like Figure 3 As shown, the irregular hollow sandwich structure is a cellular structure of a pyramid-shaped lattice structure formed by integrally expanding a metal thin-walled mesh hollow structure tube.

[0031] The three-dimensional lattice sandwich support structure is a pyramid lattice structure formed by the overall expansion of a thin-walled metal tube after processing it into a rib structure through a material reduction process. Its top and two sides are respectively welded to the inner (outer) wall surface of the outer (inner) tube and the outer (inner) wall surface of the inner (outer) tube by diffusion welding.

[0032] The height of the irregularly shaped hollow interlayer structure between the irregularly shaped inner tube and the irregularly shaped outer tube needs to be calculated based on the heat transfer model so that the irregularly shaped inner and outer tubes can play a heat insulation role under aviation working conditions, with the irregularly shaped outer tube in a high-temperature state and the irregularly shaped inner tube in a low-temperature state.

[0033] The irregularly shaped inner tube, the irregularly shaped outer tube, and the intermediate irregularly shaped hollow sandwich structure are made of titanium alloy or high-temperature alloy, which are difficult to deform, lightweight, and high-strength alloys.

[0034] like Figure 4 The diagram shows the forming steps of a closed-section three-dimensional lattice sandwich support structure for irregularly shaped pipe fittings. The electrically assisted integrated forming process of a lightweight irregularly shaped titanium alloy hollow sandwich three-layer pipe fitting includes the following steps: Step 1, material preparation; Step 2, diffusion welding; Step 3, overall high-temperature and high-pressure internal expansion; Step 4, cooling; Step 5, electrically assisted layered air expansion of the outer pipe.

[0035] According to the design size requirements of the lattice structure, the pipe fittings are processed into a mesh-like hollow intermediate pipe by subtractive machining method (4).

[0036] In the diffusion welding step, firstly, insulating and heat-resistant welding agent needs to be applied to the inner and outer surfaces of all areas except the dot area of ​​the middle hollow tube. The welding agent is applied to one side of the dot dot position and the coating state of the adjacent dot is opposite (such as positions (5, 6)). Then, the inner tube, the middle hollow tube and the outer tube are combined and installed in the support mold (9) and placed in the high temperature hot press furnace. The temperature is heated to 800℃~1000℃ and kept for 0.5h~1h. Then, inert gas is introduced into the inner tube to apply a pressure of 0.1MPa~4MPa and kept for 1h~3h to obtain a three-layer integral pipe fitting (7).

[0037] In the high-temperature and high-pressure expansion step, the three-layer integral pipe obtained in the previous step is placed in the cavity of the irregular cross-section pipe mold (10). At a thermoforming temperature of 800℃~1000℃, pressure inert gas is introduced into the inner tube to carry out high-temperature gas expansion until the three-layer integral pipe is attached to the mold, and the three-layer integral irregular cross-section pipe (8) is obtained. Then it is cooled to room temperature.

[0038] In the electrically assisted outer tube layered air expansion step, the three-layer integral irregular cross-section tube is placed in the final forming mold (11). The two ends of the irregular cross-section outer tube are heated to the forming temperature. Under the action of the insulating and heat-insulating welding agent, the irregular cross-section inner tube is in a low temperature state that is difficult to deform. Then, inert gas of equal pressure is introduced into the irregular cross-section inner tube and between the irregular cross-section inner and outer tubes. The irregular cross-section inner tube is in a low temperature state that is difficult to deform and its inner and outer surface pressure is balanced, and no plastic deformation or elastic deformation occurs. The irregular cross-section outer tube, which is in a high temperature state that is easy to form, expands to the mold under the action of air pressure to obtain a three-layer tube with a hollow sandwich structure of titanium alloy with an irregular cross-section.

Claims

1. A method for electrically assisted integrated manufacturing of a lightweight, profiled cross-section, titanium alloy, hollowed sandwich, three-layer pipe, characterized by, The lightweight, irregularly shaped cross-section titanium alloy hollow sandwich three-layer pipe fitting is as follows: The part is made of titanium alloy and consists of an inner tube with an irregular cross-section, an irregular hollow sandwich structure, and an outer tube with an irregular cross-section. The billet is composed of an inner tube, a hollowed-out middle tube (4), and an outer tube, all coaxially arranged. The irregular hollow sandwich structure is a cell structure of a pyramid-shaped lattice structure formed by the overall expansion of the hollow tube (4) in the middle; The height of the irregularly shaped hollow interlayer structure between the irregularly shaped inner tube and the irregularly shaped outer tube is calculated based on the heat transfer model, so that the irregularly shaped inner and outer tubes can play a heat insulation role under aviation working conditions, with the irregularly shaped outer tube in a high temperature state and the irregularly shaped inner tube in a low temperature state. The adjacent lattice points of the irregularly shaped hollow sandwich structure are welded to the inner wall surface of the irregularly shaped cross-section outer tube and the outer wall surface of the irregularly shaped cross-section inner tube, respectively. The manufacturing method includes the following steps: (a) Diffusion welding forming Insulating and heat-insulating welding agent is fully coated on the outer and inner surfaces of the non-array area of ​​the middle hollow tube (4) to ensure that the coating state of the same side surface of the adjacent array points is opposite. The inner tube, the middle hollow tube, and the outer tube are assembled and installed in the support mold (9) and placed in the high temperature hot press furnace. After heating to 800℃~1000℃ and holding for 0.5h~1h, pressure inert gas is introduced into the inner tube to apply a pressure of 0.1MPa~4MPa and maintain it for 1h~3h, so that diffusion connection is achieved at the array points, and a three-layer integral pipe fitting (7) is obtained. (b) High-temperature and high-pressure expansion The welded three-layer pipe fitting is placed into the cavity of the irregular cross-section pipe mold (10), and the inner pipe is bulged by passing pressure inert gas at 800℃~1000℃ until the three-layer integral pipe fitting is attached to the mold, and the pre-formed three-layer integral irregular cross-section pipe fitting (8) is obtained, and then cooled to room temperature. (c) Electrically assisted layered bulging Place the pre-formed three-layer integral irregular cross-section tube into the final forming mold (11) and perform the following operations: The outer tube (3) is heated to the forming temperature by applying electricity to both ends, and the inner tube is kept in a low temperature state that is difficult to deform by using an insulating and heat-resistant welding agent; Then, an inert gas of equal pressure is simultaneously introduced into the inner cavity of the inner tube (1) and the gap between the inner and outer tubes, so that the outer tube at high temperature expands and forms a mold separately. The final product is a three-dimensional hollowed-out sandwich tube with an irregular cross-section made of titanium alloy.

2. The electrically assisted integrated manufacturing method of a lightweight, profiled cross-section, titanium alloy, hollowed sandwich, three-layer pipe fitting according to claim 1, characterized in that: The hollowed-out tube (4) in the middle is an ultra-thin walled tube with an inner tube of irregular cross-section and an outer tube of irregular cross-section, with a thickness of one-third.

3. The electrically assisted integrated manufacturing method for a lightweight, irregularly shaped cross-section titanium alloy hollow sandwich three-layer pipe fitting as described in claim 1, characterized in that: According to the design size requirements of the lattice structure, the pipe fittings are processed into a grid-shaped hollow tube with a central hollow core by subtractive machining method (4).

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