Manufacturing method for titanium alloy special-shaped curved-surface thin-wall skin of ramjet engine

Abstract

The invention discloses a method for manufacturing a titanium alloy special-shaped curved-surface thin-wall skin of a ramjet, which adopts a non-contact selective laser melting forming constraint mode to carry out deformation control in a 3D printing process of a thin-wall skin structure, and completes full release of internal stress of a product through a reasonable heat treatment system. The consistency of the actual product molded surface and the theoretical molded surface of the curved surface skin of the thin-wall structure is guaranteed, the polishing and removing workload of the process support in the 3D printing process is reduced, and the machining efficiency and the surface quality of the product are improved. By applying the method, small-batch rapid development of the curved surface skin of the titanium alloy special-shaped storage tank of the ramjet can be realized, the molded surface of the skin is ensured to be within a theoretical tolerance range, and the number of molds and the development period of a traditional thermal forming process of the titanium alloy thin-wall part are effectively reduced; the method can be used as a rapid, efficient, high-quality and low-cost development method for various titanium alloy special-shaped thin-wall structural parts.

Description

Technical Field

[0001] The invention relates to a method for manufacturing a titanium alloy thin-walled skin with a special-shaped curved surface for a ramjet engine, and belongs to the key technical field of manufacturing thin-walled parts with special-shaped structures such as tanks and cabins of ramjet engines. Background Art

[0002] As the preferred propulsion device for hypersonic vehicles, ramjet engines have good cruise performance in the Mach number range of Ma3 to Ma7, and its related technology is one of the hot research areas that countries around the world are competing to develop. Because supersonic vehicles usually have compact structures, high integration, and special aerodynamic shapes, increasingly higher requirements are currently being placed on the lightweight and integrated nature of various functional parts.

[0003] In addition to its conventional functional use as the fuel storage unit for the entire engine, the tank adopts a product structure in which a frame and skin are assembled and welded, and the material is TC4 titanium alloy, in order to make full use of the limited space, increase the fuel capacity, and bear part of the structural load of the aircraft. The skin, as part of the aerodynamic shape of the aircraft, has significant special-shaped curved surface features. With the increasingly high requirements for lightweight aircraft, the skin thickness is also constrained to less than 1.5mm. The skin size is approximately 300mm×300mm, reflecting typical thin-walled features.

[0004] Due to the serious springback of titanium alloy cold processing, the traditional titanium alloy thin-walled parts forming process, such as forging blank machining or hot stamping, shows the disadvantages of high mold manufacturing and scheme repetition cost and long processing cycle in the single-piece small batch development and production. Chinese patent CN114309293A discloses a method for forming titanium alloy thin-walled sheet metal parts with special-shaped structure, which adopts a combination mold including a concave mold, a curved surface pressure ring and a punch to solve the problem that the double curvature bidirectional tensile stress structure titanium alloy sheet metal parts produce wrinkles or are easy to tear after forming. This method controls the process parameters such as heating temperature, main cylinder pressure, pressing speed, pressing position, and holding time, and combines the mold surface to form the titanium alloy thin-walled sheet metal parts with special-shaped structure. Although it solves the problems of cracking and wrinkling in the process of titanium alloy sheet metal forming, the disadvantage is that there are many types of molds used, the range of hot stamping process parameters is narrow, the mold trial and mold calibration cycle is long, the economic cost is high, and it is not suitable for single-piece small batch development and production.

[0005] In addition, direct laser selective melting of thin-walled parts has problems such as large thermal stress deformation and poor cutting quality during the printing process. Summary of the invention

[0006] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art, propose a method for manufacturing titanium alloy special-shaped curved thin-walled skins for ramjet engines, solve the problems of low efficiency and high cost in the development of small batches of titanium alloy special-shaped curved thin-walled parts by traditional processes and thermal deformation of thin-walled parts printed by conventional methods, and realize efficient, high-quality and flexible production of thin-walled skins with different curved surfaces.

[0007] The technical solution of the present invention is:

[0008] A method for manufacturing a ramjet engine titanium alloy thin-walled skin with a special-shaped curved surface, comprising:

[0009] S1: According to the printing growth direction, the thin-walled skin 3D model is placed vertically on the printing substrate model;

[0010] S2: non-contact control frame structures are arranged on both sides of the thin-walled skin 3D model to form a skin frame combination structure for printing; the non-contact control frame structure is a self-supporting molding structure used to control the nonlinear deformation of the thin-walled skin during the printing process;

[0011] S3: The skin model is divided along the growth direction of the skin printing, the thickness of the printed single layer is set, the printed substrate is installed on the printing device, and the skin frame combined structure is formed by laser selective melting in an argon atmosphere to obtain a special-shaped curved thin-walled skin component with a printed substrate and a frame structure;

[0012] S4: Remove the powder from the inner cavity of the thin-walled skin components with special-shaped curved surfaces;

[0013] S5: Perform vacuum annealing heat treatment to eliminate the residual thermal stress of the thin-walled skin components with special-shaped curved surfaces;

[0014] S6: Use wire cutting to separate the skin-frame assembly structure from the printed substrate, and then separate the frame structure from the thin-walled skin.

[0015] Furthermore, in step S5, the vacuum annealing heat treatment parameters are: temperature 750°C to 850°C, heat preservation for 3h to 4h, and cooling with the furnace after filling with argon.

[0016] Furthermore, the cross-section of the non-contact control frame structure is a diamond-shaped fishing net, and the columns are arranged at intervals in the direction of the long diagonal of the diamond; the non-contact control frame structure does not contact the skin of the special-shaped thin-walled part, and the gap range is 0.5mm to 1.0mm.

[0017] Furthermore, multiple thin-walled skins with special-shaped curved surfaces are printed simultaneously, that is, multiple three-dimensional models of thin-walled skins with special-shaped curved surfaces are arranged vertically on the same printing substrate model, and the distance between adjacent skins does not exceed 10 mm.

[0018] Furthermore, a solid connection structure with a density of 80% to 90% is used to connect the edges of the thin-walled skins with various profiled curved surfaces to form a closed structure, thereby improving the stability of the printing process and facilitating later removal.

[0019] Furthermore, at the transition position between the physical connection structure and the printed substrate, a R6mm to R8mm rounded corner structure is used for transition to reduce stress concentration at this location and reduce the risk of cracking.

[0020] Furthermore, before the skin frame combined structure is formed by laser selective melting, the following operations are performed:

[0021] Screen and dry the powder for no less than 2 hours;

[0022] Use a grinder to grind the printed substrate surface to a flatness within 0.01mm;

[0023] Level the printed substrate and adjust the flatness to within 0.02mm.

[0024] Furthermore, the powder in the inner cavity of the special-shaped curved thin-walled skin component is removed, and the removal process includes rotary vibration and compressed air blowing. The compressed air is not less than 0.6Mpa, and the blowing time exceeds 5 minutes.

[0025] Furthermore, it extends downward by 5 to 10 mm in the starting direction of the skin printing as a process margin for connection with the printing substrate.

[0026] Furthermore, for thin-walled skins with irregular curved surfaces, the direction with the smallest curvature change is selected as the growth direction for printing and forming to maximize the stability of the printing process.

[0027] The advantages of the present invention compared with the prior art are:

[0028] (1) The present invention adopts laser selective melting molding to develop special-shaped curved surface skins. Special-shaped thin-walled skins of different specifications can be printed and formed at the same time without the use of complex molding molds, which can effectively reduce the cost of single-piece small-batch development and production and improve development efficiency.

[0029] (2) The present invention adopts a 3D printing control method. Through the design and application of a frame structure, a rounded corner structure, and a connecting structure, the thermal deformation of thin-walled parts during printing can be effectively controlled, thereby improving product quality.

[0030] (3) The separate control process structure used in the present invention has no physical connection with the thin-walled product, which can greatly reduce the large amount of finishing and polishing work after the skin printing is completed, reduce the probability of damage during the polishing process, effectively ensure the surface quality of the skin, and reduce the labor intensity of fitters.

[0031] (4) The present invention is a general process method, which has application value and reference significance in the rapid, efficient and high-quality development of various types of ramjet engine titanium alloy special-shaped thin-walled structural parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0033] Figure 1 This is a schematic diagram of a titanium alloy thin-wall skin product;

[0034] Figure 2 Schematic diagram of the structure of a titanium alloy thin-walled skin prepared by laser selective melting forming in an embodiment of the present invention, (a) is an isometric view, (b) is a top view, and (c) is a side view;

[0035] Figure 3 The present invention is a flow chart of a method for manufacturing a titanium alloy thin-walled skin with a special-shaped curved surface for a ramjet engine according to an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0037] The present invention proposes a method for manufacturing a titanium alloy thin-walled skin with a special-shaped curved surface for a ramjet engine. Figure 3 As shown, the following steps are included:

[0038] (1) Establish a three-dimensional model of the thin-walled skin 1 with a special-shaped curved surface, such as Figure 1 As shown, the thickness of the thin-walled skin 1 ranges from 0.5 mm to 1.5 mm, and the direction with the smallest curvature change is selected as the growth direction of the printing to maximize the stability of the printing process. A single skin printing starting direction extends downward by 5 to 10 mm as a process margin for connecting with the printed substrate 2.

[0039] (2) In the model processing software, the established three-dimensional model is placed vertically close to the printing substrate 2 according to the determined printing growth direction to facilitate product self-forming.

[0040] In this step, multiple skins can be arranged vertically on the same printing substrate 2 to increase the number of products produced in a single printing; the distance between the skins on the same substrate shall not exceed 10 mm, such as Figure 2 As shown in (a) to (c). The skin edge is connected to each skin by using a solid connection structure 3 with a density of 80% to 90% to form a closed structure, which improves the stability of the printing process and facilitates later removal. A R6mm to R8mm rounded structure 4 is used for transition between the connection structure and the substrate to reduce stress concentration here and reduce the risk of cracking. The model is placed in the middle area of ​​the printing substrate 2, with a distance of not less than 80mm from the edge of the substrate, so as to facilitate the simultaneous use of multiple beams to improve printing efficiency. The splicing area needs to be processed accordingly to ensure the splicing quality; adjust the product placement direction to reduce the probability of scraper powder jamming during laser selective melting printing.

[0041] (3) In the model processing software, for the skin and substrate determined in step (2), a non-contact control frame structure 5 is arranged to constrain both sides of each skin, such as Figure 2 As shown. The design principle of the frame structure is to have good rigidity, light weight and meet the requirements of self-supporting molding during the printing process. The designed frame cross-section presents a diamond-shaped fishing net structure. The side length of a single diamond is 13 mm, the acute angle of the diamond is 60°, the thickness of the outermost frame is 10-13 mm, the thickness of the frame between the skins is consistent with the spacing of the skins arranged in step (2), the frame structure does not contact the thin-walled skin product itself, the gap 6 ranges from 0.5 to 1.0 mm, and Φ2 diameter columns 7 are arranged at intervals in the diagonal direction of the long diamond to improve the structural rigidity and control the nonlinear deformation of the thin-walled skin during the printing process.

[0042] (4) The skin model is divided along the growth direction of the skin in the pre-printing software, and the thickness of the printed single layer is set to 0.04-0.05 mm. The printing process parameters such as the scraper powder spreading direction and powder spreading speed are reasonably set, and the printing program is compiled to reduce the influence of the scraper and parameters on the forming stability of the printed product.

[0043] (5) Before printing, the powder is screened and dried, and the drying time is not less than 2 hours; the surface of the printed substrate 1 is ground to within 0.01 mm using a grinder, and the printed substrate 1 is mounted on the corresponding printing equipment and leveled to within 0.02 mm. In an argon atmosphere, laser selective melting is performed according to the printing program obtained in step (4) to obtain a special-shaped curved thin-walled skin component with a substrate and a frame shape control structure.

[0044] (6) The powder inside the cavity of the special-shaped curved thin-walled skin component with a base plate and a frame control structure is subjected to rotational vibration and compressed air blowing treatment. The compressed air is not less than 0.6Mpa and the blowing time exceeds 5 minutes.

[0045] (7) Vacuum annealing heat treatment technology is used to eliminate residual thermal stress after printing parts and frames. The heat treatment parameters are temperature 750℃~850℃, insulation for 3h~4h, and cooling with the furnace after filling with argon. This heat treatment system can ensure that the surface of the product remains in its original state after heat treatment and no oxide is produced; at the same time, the vacuum heat treatment system is different from the insulation temperature, insulation time and cooling method of conventional titanium alloy heat treatment. The insulation temperature and time can ensure that the titanium alloy matrix after laser forming is completely recrystallized and the mechanical properties of the matrix are guaranteed; vacuum heat treatment uses furnace cooling to reduce internal stress and prevent deformation of curved thin-walled parts.

[0046] (8) Using the wire cutting method, the thin-walled skin with a special-shaped curved surface and a surrounding control structure is separated from the base plate at a distance of 2 mm to 5 mm from the base plate. Since the surrounding frame and the thin-walled skin are not in contact, the skin can be easily separated after only the connection between the skin parts is interrupted. There is no need for tedious grinding and support work on the surfaces of both sides of the skin.

[0047] Wire cutting is then used to cut and separate the connections between the outer skins, and finally the individual excess is removed to obtain the final skin product.

[0048] The present invention is particularly suitable for the parallel development of multiple schemes in the early stage of development, rapid verification of small batches, improving product production efficiency and adapting to the requirements of flexible skin profiles. The present invention is further described below through specific embodiments:

[0049] (1) According to the skin size of 300mm×300mm×1.5mm, a 430mm×430mm printing substrate is selected for skin layout;

[0050] (2) Carry out process design of the frame structure to ensure that the gap between the frame and the skin product is 1.0 mm;

[0051] (3) connecting the outer periphery of the arranged skin to form a closed shape;

[0052] (4) Use a grinder to grind the surface of the substrate to a flatness within 0.01 mm, and install the substrate on the corresponding printing equipment for leveling to adjust the flatness to within 0.02 mm;

[0053] (5) Laser selective melting is used to print titanium alloy special-shaped curved thin-walled skins, with a spot diameter of 80 μm, a laser power of 100 W, a scanning speed of 800 mm / s, a line spacing of 0.09 mm, and a phase angle of 67°.

[0054] (6) After printing, all skin products are subjected to vacuum stress relief heat treatment along with the substrate: 800°C, heat preservation for 3 hours, and furnace cooling.

[0055] (7) Use wire cutting to separate the product from the substrate, and then cut off the connecting structure around each skin. Use high-speed reciprocating wire EDM wire cutting with a pulse width of 15 μs, a pulse interval of 120 μs, and a rectangular pulse to separate the skin and the frame structure.

[0056] The above-described embodiments are only preferred specific implementations of the present invention. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for manufacturing a ramjet engine titanium alloy thin-walled skin with a special-shaped curved surface, characterized in that: include: S1: According to the printing growth direction, the thin-walled skin 3D model is placed vertically on the printing substrate model; S2: non-contact control frame structures are arranged on both sides of the thin-walled skin 3D model to form a skin frame combination structure for printing; the non-contact control frame structure is a self-supporting molding structure used to control the nonlinear deformation of the thin-walled skin during the printing process; S3: The skin model is divided along the growth direction of the skin printing, the thickness of the printed single layer is set, the printed substrate is installed on the printing device, and the skin frame combined structure is formed by laser selective melting in an argon atmosphere to obtain a special-shaped curved thin-walled skin component with a printed substrate and a frame structure; S4: Remove the powder from the inner cavity of the thin-walled skin components with special-shaped curved surfaces; S5: Perform vacuum annealing heat treatment to eliminate the residual thermal stress of the thin-walled skin components with special-shaped curved surfaces; S6: Use wire cutting to separate the skin-frame assembly structure from the printed substrate, and then separate the frame structure from the thin-walled skin.

2. The method for manufacturing a ramjet engine titanium alloy thin-walled skin with a special-shaped curved surface according to claim 1, characterized in that: In step S5, the vacuum annealing heat treatment parameters are: temperature 750° C. to 850° C., heat preservation for 3 h to 4 h, and cooling with the furnace after filling with argon.

3. The method for manufacturing a ramjet engine titanium alloy thin-walled skin with a special-shaped curved surface according to claim 1, characterized in that: The cross-section of the non-contact control frame structure is in the shape of a diamond fishing net, and columns are arranged at intervals in the direction of the long diagonal of the diamond; the non-contact control frame structure does not contact the skin of the special-shaped thin-walled part, and the gap range is 0.5mm to 1.0mm.

4. The method for manufacturing a ramjet engine titanium alloy thin-walled skin with a special-shaped curved surface according to claim 1, characterized in that: Multiple thin-walled skins with special-shaped curved surfaces are printed simultaneously, that is, multiple three-dimensional models of thin-walled skins with special-shaped curved surfaces are arranged vertically on the same printing substrate model, and the distance between adjacent skins does not exceed 10 mm.

5. The method for manufacturing a ramjet engine titanium alloy thin-walled skin with a special-shaped curved surface according to claim 4, characterized in that: A solid connection structure is used to connect the edges of various thin-walled skins with special-shaped surfaces to form a closed structure, which improves the stability of the printing process and facilitates later removal.

6. The method for manufacturing a ramjet engine titanium alloy thin-walled skin with a special-shaped curved surface according to claim 5, characterized in that: At the transition point between the physical connection structure and the printed substrate, a R6mm to R8mm rounded corner structure is used to reduce stress concentration and cracking risk.

7. The method for manufacturing a ramjet engine titanium alloy thin-walled skin with a special-shaped curved surface according to claim 1, characterized in that: In step S3, before the skin frame combined structure is formed by laser selective melting, the following operations are performed: Screen and dry the powder for no less than 2 hours; Use a grinder to grind the printed substrate surface to a flatness within 0.01mm; Level the printed substrate and adjust the flatness to within 0.02mm.

8. The method for manufacturing a ramjet engine titanium alloy thin-walled skin with a special-shaped curved surface according to claim 1, characterized in that: In step S4, the powder in the inner cavity of the special-shaped curved thin-walled skin component is removed. The removal process includes rotary vibration and compressed air blowing. The compressed air is not less than 0.6Mpa and the blowing time exceeds 5 minutes.

9. The method for manufacturing a ramjet engine titanium alloy thin-walled skin with a special-shaped curved surface according to claim 1, characterized in that: In step S1, the skin is extended downward by 5 to 10 mm in the starting direction of skin printing as a process margin for connection with the printed substrate.

10. The method for manufacturing a ramjet engine titanium alloy thin-walled skin with a special-shaped curved surface according to claim 1, characterized in that: In step S1, for the thin-walled skin with irregular curved surface, the direction with the smallest curvature change is selected as the growth direction of printing and forming, so as to improve the stability of the printing process as much as possible.

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