A method for suppressing surface groove defects of a multi-layer hollow structure

Abstract

The present invention discloses a method for suppressing surface groove defects of a multi-layer hollow structure, belonging to the field of precision sheet metal processing. Local enhancement is carried out at the sunken part of the panel to control surface defects of different sandwich structures such as four-layer plate structure, lattice structure, egg box structure, etc., achieving the purpose of effectively suppressing the generation of surface defects. The base element material to be processed is titanium alloy and magnesium alloy, and the structure of the base element to be processed is a four-layer plate structure, lattice structure or egg box structure, including two panels and a core plate located between the two panels. The panels and the core plate are diffusion-bonded and the base element is processed by superplastic forming; a gasket is further provided between the panel and the core plate, and the gasket is arranged at the diffusion-bonding position between the panel and the core plate. The parts formed by this method have significant advantages in terms of processing efficiency, manufacturing cost and mechanical properties.

Description

Technical Field

[0001] The present invention relates to a method for locally strengthening the sunken part of the panel during superplastic forming / diffusion bonding of titanium alloy / magnesium alloy plates with different structures, so as to control the generation of groove defects during forming, and belongs to the field of precision sheet metal processing. Background Art

[0002] The superplastic forming / diffusion bonding process is an advanced process for manufacturing advanced aerospace titanium alloy complex thin-walled integral hollow structural parts, which has the advantages of reducing the structural weight of aircraft and saving production costs, and has important practical significance for the further development of China's aerospace industry.

[0003] Through the superplastic forming / diffusion bonding technology, various complex structural parts can be obtained, such as: four-layer structure, lattice structure and egg box structure. These structural parts are extremely prone to surface groove defects during the forming process, and the groove defects can be reduced by changing the thickness ratio of the panel and the core plate. However, in actual industrial applications, in order to ensure the mechanical properties and service performance of the formed parts, the thickness of the core plate should not be chosen too thin. In order to meet the lightweight of the overall structure, only the panel thickness can be appropriately reduced, which aggravates the problem of groove defects. Therefore, there is an urgent need to propose a method for controlling surface groove defects of various structures.

[0004] In the publicly available prior art, Patent CN109396676A discloses a method for controlling surface groove defects of a three-layer hollow sandwich structure. By adding upper and lower jackets between the upper and lower panels and the mold, the forming integrity of the part can be ensured, and the surface groove problem of the three-layer structure can be effectively controlled. However, for large three-layer structures, this method has a high manufacturing cost, and due to the addition of the layer jacket, it is difficult for the forming fillet area and other positions of the three-layer structure to be completely molded, and the forming accuracy cannot be guaranteed.

[0005] Patent CN108746312A discloses a method for eliminating surface grooves of a superplastic forming / diffusion bonding four-layer structure. By applying back pressure by ventilating between the panel and the core plate to eliminate the influence of surface grooves. Although the steps of this method are simple and can effectively eliminate the groove defects generated on the surface of the four-layer structure, since two paths of gas need to be introduced during its forming, it is time-consuming and laborious during the gas path connection. At the same time, if the back pressure time introduced between the panel and the core plate is too long, the triangular area cannot be closed during the forming process of the core plate, and a large gap will be generated, and it cannot be formed well. Summary of the Invention

[0006] In view of the above problems, the present invention proposes a method for locally strengthening with special-shaped gaskets to suppress surface groove defects of multi-layer hollow structures, locally strengthening the sunken part of the panel to control surface defects of different sandwich structures such as four-layer plate structures, lattice structures, and egg box structures of titanium alloy / magnesium alloy materials, and achieving the purpose of effectively suppressing the generation of surface defects.

[0007] The technical solution of the present invention is as follows: The base element of the sheet material is finally processed. That is, the base element to be processed is a four-layer board structure, a lattice structure or an egg box structure, including two panel boards and a core board located between the two panel boards. The panel board and the core board are diffusion-connected and the base element is processed by superplastic forming;

[0008] A gasket is also provided between the panel board and the core board, and the gasket is arranged at the diffusion connection position between the panel board and the core board; The processing is carried out according to the following steps:

[0009] Step 1: Manufacture corresponding superplastic forming or diffusion connection molds according to the shape of the base element to be processed. According to the load conditions of different parts, optimize and design the size of the core board with different structures and the number of ribs, and design the width b1 of the ribs of the four-layer board structure or the radius r1 of the solder joints of the lattice structure and the egg box structure;

[0010] Step 2: Select the core board thickness d1 and the panel board thickness d2 for different structural parts according to the requirements;

[0011] Among them, in order to ensure the performance of the formed part, the thickness d1 of the core board is selected to be between 1.2 mm and 2 mm. In order to meet the overall lightweight requirement, the thickness d2 of the panel board is selected to be between 0.8 mm and 1.5 mm;

[0012] Step 3: Select the maximum thickness d3 and the maximum radius r2 of the gasket for different panel board and core board thicknesses: d3 = 1 / 4(d1 + d2) ~ 1 / 2(d1 + d2);

[0013] Furthermore, a gasket with a uniform wall thickness or a gasket with a non-uniform wall thickness can be selected. The gasket is in a cylindrical shape, a frustum shape or a special shape with the center of the top surface arched upward.

[0014] When the base element to be processed in Step 3 is a four-layer board structure, the maximum radius r2 is selected according to r2 / b1 = 1~2; When the base element to be processed is a lattice structure and an egg box structure, the maximum radius r2 is selected according to r2 / r1 = 2~3;

[0015] Step 4: Laser-weld the gasket and the diffusion welding area of the panel board in advance;

[0016] Step 5: Core board treatment, apply a welding stop agent to the non-diffusion areas on both sides of the core board according to the design;

[0017] Step 6: Combine the panel board and the core board;

[0018] Specifically, the lattice structure and the egg box structure are combined in the order of the panel board, the core board, and the panel board from top to bottom. Or, the rib parts of the two core boards of the four-layer board structure are combined correspondingly;

[0019] Step 7: Perform diffusion bonding on the assembly to achieve diffusion welding between the gasket and the core plate;

[0020] Step 8: Perform pre-treatment before gas inflation on the assembly after diffusion bonding, leave an air inlet channel, and arrange a trachea in the air inlet channel;

[0021] Specifically, place the assembly after diffusion bonding of the lattice structure and the egg carton structure into a mold, seal-weld the peripheral edge pressing area, and leave air inlet channels between the core plate and the upper panel and between the core plate and the lower panel respectively;

[0022] Or, combine the four-layer plate structure from top to bottom as: panel, core plate, core plate, panel, seal-weld the peripheral edge pressing area, and leave air inlet channels between the upper panel and the upper core plate, between the lower panel and the lower core plate, and between the two core plates respectively;

[0023] Step 9: Introduce argon gas for superplastic forming;

[0024] Specifically, introduce argon gas into each reserved air channel of the lattice structure and the egg carton structure, and achieve superplastic forming / diffusion bonding under high-temperature conditions;

[0025] The forming of the four-layer plate structure is divided into two stages. First, introduce argon gas between the upper panel and the upper core plate, and between the lower panel and the lower core plate. After the panel is completely formed, introduce argon gas between the two core plates, and achieve superplastic forming / diffusion bonding under high-temperature conditions; As Figures 3 to 4 shown, compared with the forming result without a gasket, locally adding a gasket at the concave part of the surface of the sandwich structure panel can significantly control the generation of defects;

[0026] Step 10: After the formed part cools to room temperature, take out the formed base element from the superplastic forming mold, remove the trachea and excess material by methods such as wire electrical discharge machining or laser cutting, and finally machine the base element of the four-layer plate structure, lattice structure or egg carton structure.

[0027] The beneficial effects of the present invention are as follows: By using the method of the present invention to form sandwich structures such as superplastic forming / diffusion bonding four-layer plate structures, lattice structures and egg carton structures, it is possible to successfully avoid the defects generated on the panel surface and effectively ensure its surface quality. Aiming at the defect problems that occur during the forming of different sandwich structures, the gasket enhancement method is adopted in the local area of the panel, and the quantitative design of the parameters of the uniform wall thickness gasket reinforcement is realized, which can be applied to the forming of sandwich structures under different parameters. In addition, for the defect problems that occur during the forming of the four-layer plate structure and the lattice structure, a special-shaped gasket with non-uniform wall thickness is designed, which more specifically improves the groove defects. At the same time, the parts formed by this method have significant advantages in terms of processing efficiency, manufacturing cost and mechanical properties. Description of the Drawings

[0028] Figure 1 Schematic diagram of the gasket Figure 1 ;

[0029] Figure 2 Schematic diagram of the gasket Figure 2 ;

[0030] Figure 3 Cross-sectional view of the processed base component of this case;

[0031] Figure 4 Schematic diagram of the defects after forming in the prior art;

[0032] Figure 5 Schematic diagram of the core board of the base component with a four-layer board structure;

[0033] Figure 6 Schematic diagram of the core board of the base component with a lattice structure;

[0034] Figure 7 Schematic diagram of the forming when adding cylindrical gaskets to the four-layer board structure;

[0035] Figure 8 Schematic diagram of the forming when adding non-standard shaped gaskets to the four-layer board structure;

[0036] Figure 9 Schematic diagram of the forming when adding frustum-shaped gaskets to the lattice structure. Specific implementation manners

[0037] To clearly illustrate the technical features of this patent, the following will elaborate on this patent through specific implementation manners and in combination with its accompanying drawings.

[0038] Example 1: This implementation plan aims to locally strengthen the groove defects at the solder joints of the four-layer board structure. The selected reinforcement is a gasket with a uniform wall thickness. The face plate is made of AZ31 magnesium alloy with a thickness of 1 mm, the core board is made of AZ31 magnesium alloy with a thickness of 1.4 mm, and the gasket is made of AZ31 magnesium alloy with a thickness of 0.8 mm and a radius of 4 mm;

[0039] The specific forming method process is as follows:

[0040] Step 1: Establish a model of the required four-layer board forming base component. According to the stress conditions of the formed part, determine the rib width and cell size of the core board of the four-layer board structure, as Figure 5 shown;

[0041] Step 2: Select the thicknesses of the core board and the face plate to be 1.4 mm and 1 mm respectively;

[0042] Step 3: Select the gasket thickness to be 0.8 mm and the radius to be 4 mm; Such gaskets are cylindrical;

[0043] Step 4: Laser-weld all the gaskets to the central defect area of the panel in advance;

[0044] Step 5: Core plate treatment. Before diffusion welding, apply a stop-off flux to the non-rib area of the core plate according to the design;

[0045] Step 6: Combine the rib parts of the two core plates in the four-layer plate structure correspondingly;

[0046] Step 7: Heat and press the assembly for diffusion bonding to achieve diffusion welding between the two core plates;

[0047] Step 8: Pretreat the assembly after diffusion bonding for gas inflation, leaving an air inlet channel, and arrange a gas pipe in the air inlet channel: Combine the four-layer plate structure from top to bottom: panel, core plate, core plate, panel, seal-weld the peripheral edge-pressing area, and reserve air inlet channels between the upper panel and the upper core plate, the lower panel and the lower core plate, and the two core plates respectively;

[0048] Step 9: The forming of the four-layer plate structure is divided into two stages. First, introduce argon between the upper panel and the upper core plate, and between the lower panel and the lower core plate. After the panel is completely formed, introduce argon between the two core plates to achieve superplastic forming / diffusion bonding at 400 °C. The forming schematic diagram is as Figure 7 shown; where the vacuum degree is 5.0×10 -2 Pa~1.0×10 -3 Pa, the final pressure is 2 MPa, and the pressure holding time is 1 h;

[0049] Step 10: After the formed part cools to room temperature, take out the formed base element from the superplastic forming die, remove the gas pipe and excess material by methods such as wire electrical discharge machining or laser cutting, and finally machine the four-layer plate hollow structure base element.

[0050] Example 2: This implementation plan aims to locally strengthen the groove defects at the solder joints of the four-layer plate structure. The selected reinforcement is a gasket with non-uniform wall thickness. The panel is made of TA15 titanium alloy with a thickness of 1 mm, the core plate is made of TA15 titanium alloy with a thickness of 1.4 mm, and the gasket with non-uniform wall thickness is made of TA15 titanium alloy with a bottom radius of 4 mm;

[0051] The specific forming method process is as follows:

[0052] Step 1: Establish a model of the required four-layer plate forming base element. According to the stress situation of the formed part, determine the rib width and cell size of the core plate in the four-layer plate structure, as Figure 5 shown;

[0053] Step 2: Select the core plate and the panel with thicknesses of 1.4 mm and 1 mm respectively;

[0054] Step 3: Select gaskets with a thickness of 0.8 mm and a maximum bottom radius of 4 mm; such gaskets are of an irregular shape with the center of the top surface arched upward.

[0055] Step 4: Laser-weld the circular bottoms of all gaskets to the central defect area of the panel in advance.

[0056] Step 5: Core plate treatment. Before diffusion welding, apply a welding stop agent to the non-rib area of the core plate according to the design.

[0057] Step 6: Combine the rib parts of the two core plates in the four-layer plate structure correspondingly.

[0058] Step 7: Heat and pressurize the assembly for diffusion connection to achieve diffusion welding between the two core plates.

[0059] Step 8: Perform pre-treatment before pneumatic bulging on the assembly after diffusion connection, leaving an air inlet channel, and arrange air pipes in the air inlet channel: Combine the four-layer plate structure from top to bottom: panel, core plate, core plate, panel, seal-weld the surrounding edge pressing area, and reserve air inlet channels between the upper panel and the upper core plate, the lower panel and the lower core plate, and the two core plates respectively.

[0060] Step 9: The forming of the four-layer plate structure is divided into two stages. First, introduce argon between the upper panel and the upper core plate, and between the lower panel and the lower core plate. After the panel is completely formed, introduce argon between the two core plates, and achieve superplastic forming / diffusion connection at 930 °C. The forming schematic diagram is as Figure 8 shown; where the vacuum degree is 5.0×10 -2 Pa ~ 1.0×10 -3 Pa, the final pressure is 2 MPa, and the pressure holding time is 1 h.

[0061] Step 10: After the formed part cools to room temperature, take out the formed base element from the superplastic forming die, remove the air pipes and excess materials by methods such as wire electrical discharge machining or laser cutting, and finally machine the four-layer plate hollow structure base element.

[0062] Example 3: This implementation plan aims to locally strengthen the groove defects at the solder joints of the lattice structure base element. The selected reinforcing body is a gasket with non-uniform wall thickness. The panel is made of TA15 titanium alloy with a thickness of 1 mm, the core plate is made of TA15 titanium alloy with a thickness of 1.4 mm, the gasket is made of TA15 titanium alloy with a thickness of 0.8 mm and a maximum bottom radius of 4 mm. The number of panel layers is two, the solder joint radius of the core plate is 2 mm, and the number of gaskets is 25; the specific forming method process is as follows:

[0063] Step 1: Establish the model of the required formed base element. According to the stress condition of the formed part, determine the rib size, rib number, and diffusion solder joint area of the lattice structure core plate, as Figure 6 shown.

[0064] Step 2: Select the core board and the panel with thicknesses of 1.4 mm and 1 mm respectively.

[0065] Step 3: Select a frustum-shaped spacer with a thickness of 0.8 mm and bottom and top radii of 4 mm and 2 mm respectively.

[0066] Step 4: Pre-weld all the spacers to the central defect area of the panel, i.e., the diffusion welding area on the panel, by laser welding.

[0067] Step 5: Core board treatment: Before diffusion welding, apply a stop-off flux to the non-diffusion areas on both sides of the core board according to the design.

[0068] Step 6: Assemble the lattice structure from top to bottom: panel, core board, panel.

[0069] Step 7: Perform diffusion bonding on the assembled parts to achieve diffusion welding between the spacers and the core board.

[0070] Step 8: Perform pre-treatment before pneumatic bulging on the assembled parts after diffusion bonding, leaving an air inlet channel, and arrange a trachea in the air inlet channel: Place the assembled parts after diffusion bonding of the lattice structure into a mold, seal-weld the peripheral edge pressing area, and reserve air inlet channels between the core board and the upper panel and between the core board and the lower panel respectively.

[0071] Step 9: Introduce argon into each reserved air inlet channel of the lattice structure and achieve superplastic forming / diffusion bonding at 930 °C. The forming schematic diagram is as shown in Figure 9 shown; where the vacuum degree is 5.0×10 -2 Pa~1.0×10 -3 Pa, the final pressure is 2 MPa, and the pressure holding time is 1 h.

[0072] Step 10: After the formed part cools to room temperature, take out the formed base component from the superplastic forming mold, remove the trachea and excess material by methods such as wire electrical discharge machining or laser cutting, and finally machine the lattice structure base component.

[0073] There are many specific implementation ways for the present invention. The above description is only the preferred implementation manner of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements can still be made, and these improvements should also be regarded as the protection scope of the present invention.

Claims

1. A method for suppressing surface groove defects of a multi-layer hollow structure. The base component to be processed is a four-layer plate structure, lattice structure or egg box structure made of titanium alloy or magnesium alloy material, including two panels and a core plate between the two panels. The panels and the core plate are diffusion-bonded and the base component is processed by superplastic forming; characterized in that, A gasket is also provided between the panel and the core plate, and a special-shaped gasket is used for local strengthening to suppress surface groove defects of the multi-layer hollow structure. The gasket is arranged at the diffusion bonding position between the panel and the core plate; The processing is carried out according to the following steps: Step 1: Manufacture a corresponding superplastic forming die according to the shape of the base component to be processed. According to the load conditions of different parts, optimize the design of the size of the core plate with different structures and the number of ribs, and design the width b1 of the ribs of the four-layer plate structure or the radius r1 of the solder joints of the lattice structure and the egg box structure; Step 2: Select the core plate thickness d1 and the panel thickness d2 according to the requirements for different structure parts; Step 3: For different panel and core plate thicknesses, select the maximum thickness d3 and the maximum radius r2 of the gasket: d3 = 1 / 4(d1 + d2) ~ 1 / 2(d1 + d2); Step 4: Laser-weld the gasket and the diffusion welding area of the panel in advance; Step 5: Core plate treatment, apply a stop-off flux to the non-diffusion areas on both sides of the core plate according to the design; Step 6: Combine the panel and the core plate; Step 7: Carry out diffusion bonding on the combined component to realize diffusion welding between the gasket and the core plate; Step 8: Carry out pre-treatment before gas bulging on the combined component after diffusion bonding, leave an air inlet channel, and arrange a trachea in the air inlet channel; Step 9: Introduce argon for superplastic forming; introduce argon into each reserved air duct of the lattice structure and the egg box structure, and realize superplastic forming / diffusion bonding under high temperature conditions; Among them, the forming of the four-layer plate structure is divided into two stages. First, introduce argon between the upper panel and the upper core plate, and between the lower panel and the lower core plate. After the panel is completely formed, introduce argon between the two core plates, and realize superplastic forming / diffusion bonding under high temperature conditions; Step 10: After the formed part is cooled to room temperature, take out the formed base component from the superplastic forming die, remove the trachea and excess material by wire electrical discharge machining or laser cutting, and finally process the base component of the four-layer plate structure, lattice structure or egg box structure.

2. A method for suppressing surface groove defects of a multi-layer hollow structure according to claim 1, characterized in that, In Step 2, the thickness d1 of the core plate is taken between 1.2 mm and 2 mm, and the thickness d2 of the panel is taken between 0.8 mm and 1.5 mm.

3. A method for suppressing surface groove defects of a multi-layer hollow structure according to claim 1, characterized in that In Step 3, select a gasket with a uniform wall thickness or a gasket with a non-uniform wall thickness. The gasket is in a cylindrical shape, a frustum shape or a special shape with the center of the top surface arched upward.

4. A method for suppressing surface groove defects of a multi-layer hollow structure according to claim 1, characterized in that, In Step 3, when the base component to be processed is a four-layer plate structure, select the maximum radius r2 according to r2 / b1 = 1~2; when the base component to be processed is a lattice structure and an egg box structure, select the maximum radius r2 according to r2 / r1 = 2~3.

5. A method for suppressing surface groove defects of a multi-layer hollow structure according to claim 1, characterized in that, Step 8 is specifically: Put the combined component after diffusion bonding of the lattice structure and the egg box structure into the die, seal-weld the surrounding edge pressing area, and reserve air inlet channels between the core plate and the upper panel and between the core plate and the lower panel respectively; Alternatively, a four-layer board structure is combined from top to bottom as follows: a panel, a core board, a core board, and a panel. The edge regions around the board are sealed by welding, and air inlets are respectively reserved between the upper panel and the upper core board, between the lower panel and the lower core board, and between the two core boards.

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