Hydroforming Method of Ellipsoidal Container under Combined Loading of Hydrostatic Load and Rotational Load

Abstract

A hydroforming method for an ellipsoidal container under combined hydrostatic load and rotational load, the method comprising: Step 1, determination of an initial lantern-shaped single-curvature thin shell member: Select an appropriate segmenting scheme; determine the size of the pole plate and fabricate the initial single-curvature thin shell; Step 2, fix the initial single-curvature thin shell using a fixture, and fix near the weld with relatively small displacement between the fixture and the thin shell during the bulging process and achieve soft contact by relying on a jacket, so as to drive the ellipsoidal shell to rotate and reduce the limitation on deformation during the rotational bulging of the ellipsoid; Step 3, rotate the fixture and gradually increase the rotational speed, and increase the hydrostatic pressure during the process of increasing the rotational speed, ensure that the hydrostatic pressure and the rotational pressure increase linearly synchronously, and after the loading reaches the total load, keep it stable for a certain time to make it fully deformed and then unload to obtain the bulged ellipsoidal container. The present invention realizes the forming of an ellipsoidal shell structure with a high axial length ratio by changing the stress state of the spherical shell using a non-uniformly distributed hydraulic load.

Description

Technical Field

[0001] The present invention relates to a hydroforming method for an ellipsoidal container, and more particularly to a hydroforming method for an ellipsoidal container with combined hydrostatic load and rotational load, belonging to the field of container manufacturing. Background Art

[0002] Ellipsoidal pressure vessels have advantages such as low center of gravity and small windward area, and are suitable for use as large water towers and pressure vessels for storing volatile liquids. In addition, due to the beautiful appearance, unique shape and good stability of the ellipsoidal container, it is often used as a decoration on microwave communication transmission towers.

[0003] The traditional forming method for an ellipsoidal container is the die pressing method, which has disadvantages such as inaccurate blanking, long manufacturing cycle, high difficulty in assembly and welding, difficult to guarantee accuracy, large size of the forming die and press, and poor adaptability, greatly limiting the wide application of ellipsoidal containers. To break through the limitations brought by the above technologies, a prior art has proposed a die-less hydroforming method for an ellipsoidal container. The process is to roll and bend the sheet metal and then weld it into a lantern-shaped single-curvature shell. Fill the lantern-shaped single-curvature shell with liquid and increase the liquid pressure, so that the lantern-shaped shell gradually expands into an ellipsoidal shell under the action of hydraulic pressure. However, due to the different curvatures at each part of the ellipsoid, for an ellipsoid with an axial ratio λ greater than during the die-less hydroforming process, circumferential compressive stress is generated at the equator under the action of internal pressure, and wrinkling is likely to occur at the equator, as shown in Figure 1 shown.

[0004] To solve the problem of equatorial wrinkling during the ellipsoidal expansion process, the applicant has proposed a double-generatrix ellipsoidal shell expansion method, etc., to improve the equatorial wrinkling problem encountered during the ellipsoidal expansion process by adjusting the initial geometric shape of the expansion, and effectively avoid the problem of equatorial wrinkling in the actual forming process. Although this process solves the problem of wrinkling during the ellipsoidal expansion process, due to the tendency of the hydrostatic pressure load to make the closed shell tend to be spherical, the load required at the poles during the ellipsoidal expansion process is less than the load required at the equator. When the poles expand to the ideal height, the average radius difference at the equator cannot be controlled within the ideal range. When further increasing the hydraulic load to meet the expansion conditions at the equator, due to the spherical tendency of the hydrostatic pressure load, the height at the poles further increases, and the axial ratio of the ellipsoid decreases. Finally, the shape obtained by the expansion is still difficult to break through 1.3 and is difficult to achieve the expected forming effect.

[0005] To solve the problem of pole height increase in the expansion of high-axial-ratio ellipsoids, a prior art has proposed a die-less hydroforming method for an ellipsoidal container with pole plate limiting and central tube limiting. Among them, the substrate limiting method uses a press to compress the upper and lower pole plates for axial restraint, and this method has high requirements for the size and opening height of the press; the central tube limiting forming method refers to the ellipsoidal expansion with central limiting, and this method has disadvantages such as complex process and the need for secondary expansion.

[0006] Patent document CN110743956A relates to a method and system for controlling the axial length dimension of an ellipsoidal shell based on liquid volume loading. The forming of the ellipsoidal shell is achieved by controlling the volume of the injected liquid, and a mathematical relationship model needs to be established, but the actual forming effect is not ideal.

[0007] Patent document CN109909395A relates to an ellipsoidal pneumatic forming method based on current self-resistance heating. The ellipsoidal hot-state pneumatic forming is carried out by using current self-resistance heating to enclose a multi-faceted shell, and it still uses high-pressure gas inside to cause pneumatic bulging to achieve deformation, which solves the problem of cracking during normal-temperature forming of an ellipsoid. Summary of the Invention

[0008] In order to overcome the deficiencies of the prior art, the present invention provides a hydroforming method for an ellipsoidal container with a combined loading of hydrostatic load and rotational load. This method utilizes a non-uniformly distributed hydrostatic load to change the stress state of the spherical shell and finally realizes the forming of an ellipsoidal shell structure with a high axial length ratio.

[0009] The hydroforming method for an ellipsoidal container with a combined loading of hydrostatic load and rotational load includes:

[0010] Step 1: Determination of the initial lantern-shaped single-curvature thin-shell component

[0011] (1) Select an appropriate lobing scheme. The side plates for ellipsoidal hydroforming are processed from the initial blank with 8 - 24 lobes.

[0012] (2) Determination of the pole plate size. Select the size of the cross-section of the pole plate at a distance of 5% - 20% of the short axis length from the pole. According to the number of lobes and the pole plate size of the designed thin-shell component, calculate and analyze the shape of the plate before bending of the side plate by the unfolding method or the finite element method on this basis, and cut the plate according to this size.

[0013] (3) Process the obtained plate into a side plate structure, check and correct the side plate structure size, use the determined pole plate and side plate to weld and fabricate a single-curvature ellipsoidal shell, verify the welding tightness, and obtain the initial single-curvature thin shell.

[0014] Step 2: Fix the initial single-curvature thin shell with a fixture. The fixture is fixed near the weld with a small displacement during the bulging process between the fixture and the thin shell and realizes soft contact by relying on the jacket, so as to drive the ellipsoidal shell to rotate and reduce the restriction on deformation during the ellipsoidal rotary bulging process.

[0015] Step 3: Rotate the fixture and gradually increase the rotation speed. During the process of increasing the rotation speed, increase the hydrostatic pressure to ensure that the hydrostatic pressure and the rotational pressure increase linearly synchronously. The maximum hydrostatic load p' and the maximum rotational speed n' satisfy the following formula:

[0016]

[0017]

[0018] Among them, n' is the rotational speed, p' is the hydrostatic pressure, t is the thickness of the ellipsoidal thin shell, σ s is the material yield strength, λ is the ratio of the major axis radius to the minor axis radius of the ellipsoid, a is the major axis radius, and ρ is the liquid density; after the loading reaches the total load, it is stabilized for 5 - 10 s to allow sufficient deformation and then unloaded to obtain the expanded ellipsoidal container.

[0019] The beneficial effects of the present invention compared with the prior art are as follows:

[0020] The present invention realizes the forming of ellipsoidal thin shell components with an axis length ratio within the range of , solves the problem of pole rise and minor axis elongation faced during the hydroforming of the mentioned ellipsoid, and finally realizes the forming of a high axis length ratio ellipsoidal shell structure by changing the stress state of the spherical shell using a non-uniformly distributed hydraulic load. In addition, through finite element simulation, it is found that the forming of ellipsoidal thin shell components within the range of 2 < λ < 2.4 can be realized. Although there is a wrinkling tendency at the equator when λ > 2, when the total load is further increased, the generatrix of the component does not approach a perfect ellipse, but an ellipse-like shape with a larger meridional curvature radius at the equator, which makes the equatorial circumferential compressive stress generated in the initial stage of bulging transform into tensile stress, thereby eliminating the wrinkling tendency that appears in the initial stage of bulging.

[0021] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments: Description of the Drawings

[0022] Figure 1 is a schematic diagram showing wrinkling at the weld in the major axis region of an ellipsoidal container with an axis length ratio greater than in traditional integral die-less hydroforming;

[0023] Figure 2 is a schematic diagram of the hydroforming process of an ellipsoidal container using the combined loading of hydrostatic load and rotational load in the present invention;

[0024] Figure 3 is a schematic diagram of the stress distribution of the combined action of hydrostatic load and rotational hydraulic load on the ellipsoidal shell during the forming process of the present invention;

[0025] Figure 4 is a schematic diagram of the finite element simulation result of forming an ellipsoidal shell with an axis length ratio λ of 2.4 by the hydroforming method of an ellipsoidal container using the combined loading of hydrostatic load and rotational load. Specific Embodiments

[0026] See Figures 2 - 4As shown in the figure, the hydroforming method of an ellipsoidal container with combined hydrostatic load and rotational load in this embodiment includes:

[0027] Step 1: Determination of the initial lantern-shaped single-curvature thin-shell component

[0028] (1) Select an appropriate splitting scheme. Generally, the more splits, the higher the accuracy, and at the same time, the width of the sheet metal decreases. It is usually used for forming high-precision or large-sized components. The fewer splits, the lower the total weld length and the lower the processing cost. It is generally used for cases with lower dimensional accuracy and low cost. Considering both accuracy and cost, the side plates of the ellipsoidal hydroforming are processed with 8 - 24 splits for the initial blank.

[0029] (2) Determination of the pole plate size. A larger pole plate size is less restricted by the weld and is more prone to deformation. Similarly, the thinning of the pole plate is more obvious. Generally, it is designed according to the usage. The pole plate is usually a regular polygon or a circle with the number of splits. Select the size of the cross-section of the pole plate at 5% - 20% of the short-axis length from the pole point. According to the number of splits and the pole plate size of the designed thin-shell component, calculate and analyze the shape of the sheet metal before bending of the side plate by the unfolding method or the finite element method in sheet metal design, and cut the sheet metal according to this size.

[0030] (3) Process the obtained sheet metal into the side plate structure, check and correct the side plate structure size, use the above-determined pole plate and side plate to weld and manufacture the single-curvature ellipsoidal shell, and verify the welding tightness to obtain the initial single-curvature thin shell.

[0031] Specifically, it can be implemented as follows: Feed the obtained sheet metal into a rolling machine to process the side plate structure. It can be used only after checking and correcting the side plate structure size. Finally, manufacture the single-curvature ellipsoidal shell. Use the prepared pole plate and side plate to weld the single-curvature ellipsoidal shell. After welding, an opening needs to be made on one of the pole plates to ensure subsequent pressurization. After completing the above work, inject water and increase a certain pressure to verify the welding tightness.

[0032] Step 2: Fix the initial single-curvature thin shell with a fixture. The fixture and the thin shell are fixed near the weld with a small displacement during the bulging process and rely on a jacket to achieve soft contact, so as to drive the ellipsoidal shell to rotate and reduce the restriction on deformation during the ellipsoidal rotational bulging process; rely on a jacket made of materials such as rubber that are easy to deform to achieve soft contact.

[0033] Step 3: Rotate the fixture and gradually increase the rotational speed. During the process of increasing the rotational speed, increase the hydrostatic pressure to ensure that the hydrostatic pressure and the rotational pressure increase linearly synchronously. The maximum hydrostatic load p′ and the maximum rotational speed n′ satisfy the following formula:

[0034]

[0035]

[0036] Wherein, n' is the rotational speed, ρ' is the hydrostatic pressure, t is the thickness of the ellipsoidal thin shell, σ s is the material yield strength, λ is the ratio of the major axis radius to the minor axis radius of the ellipsoid, a is the major axis radius, and ρ is the liquid density; after the loading reaches the total load, it is stabilized for 5 - 10 s to allow sufficient deformation and then unloaded to obtain the expanded ellipsoidal container.

[0037] In this embodiment, the fixture is rotatably fixed on the corresponding power output mechanism.

[0038] To solve the difficulties in manufacturing an ellipsoidal shell container with a high axis - length ratio, the inventive concept of this embodiment is a hydroforming method for an ellipsoidal container with combined hydrostatic load and rotational load. Its basic principle is to use the non - uniform load generated by the rotating liquid to reduce the total load in the vertical direction of the shell, so as to suppress the pole - heightening phenomenon that appears in the above - mentioned hydrostatic hydroforming process, and control the axis - length ratio of the final formed component within an ideal range. Its basic technological process is as follows: using the initial structure manufacturing method in the die - less hydroforming method of the ellipsoidal container, a lantern - shaped single - curvature closed structure is processed by means of rolling and welding plates. A fixture is used to impose certain constraints on this initial shape, and a liquid pressure medium such as water or oil is injected. The rotating fixture drives the liquid - filled spherical shell to start rotating around the minor axis. The rotational speed and the hydrostatic pressure are increased synchronously, so that the rotational load and the hydrostatic load acting at the equator increase in proportion. Under the combined action of the hydrostatic load and the rotational load, the lantern - shaped single - curvature initial structure expands into an ellipsoidal shell structure, as Figure 2 shown.

[0039] Furthermore, in the initial stage of the loading in step three, the total load is gradually increased by 10% each time. After the load in step three increases to 80% of the total load, the load is increased by 2% each time. In this way of forming, the requirements for mass production can be met. After the load in step three increases to 95% of the total load, the load is increased by 1% each time. In step three, after the loading reaches the total load, it is stabilized for 10 s to allow sufficient deformation and then unloaded.

[0040] When selecting the liquid - filling medium in this embodiment, the greater the liquid density, the more obvious the advantages. Usually, water is selected as the liquid - filling medium.

[0041] As a possible embodiment, the number of segments in step one is 16 segments or 12 segments. With such a setting, the requirements for deformation during high - precision forming are met.

[0042] As another possible embodiment, the jacket in step two is a rigid sponge. With such a setting, the requirements for an ellipsoid with high surface quality are met.

[0043] Based on the above - mentioned embodiment, the following combines Figures 2 - 4The description and embodiments further elaborate on the present invention:

[0044] Embodiment 1

[0045] In this embodiment, the bulging of a low-carbon steel ellipsoidal shell with a thickness of 1 mm, a major axis of 300 mm, and an axis length ratio λ = 1.6 is taken as an example for analysis. The splitting scheme adopts 12 splits, the cross-sectional size of the pole plate is 15 mm (the distance from the extremely low center to the pole), and the liquid medium is water. At the same time, on this basis, a geometric software is used to draw the lantern-shaped initial closed structure, and the curvatures of the two pole plates and the twelve single-curvature curved side petals are determined. The geometry of the single-curvature curved side petals is unfolded using a finite element analysis software to obtain the size of the blank before bending; the above-mentioned pole plate size and the side petal blank size are processed and welded together to form a lantern-shaped initial closed structure, and a water injection port is processed at the pole plate; the fixture equipped with rubber sheath material is fixed on the initial structure, and the connection between the upper and lower fixtures is ensured through buckles; the fixture is installed at the high-speed motor and sufficient connection strength is ensured; water is injected into the initial closed spherical shell, and after the water is full, the motor is started. Taking the maximum hydrostatic load p′ and the maximum rotational speed n′ as 1.3 MPa and 44 r / s respectively, the motor speed and the hydrostatic pressure are gradually increased, and it is ensured that the hydrostatic pressure is linearly related to the square of the motor speed. In the initial stage of loading, the load is gradually increased by 10% per step; when the load increases to 80% of the maximum load, the load is increased by 2% per step; when the load increases to 95% of the maximum load, the load is increased by 1% per step; when the loading reaches the maximum load, it is stabilized for about 10 s to allow it to deform fully and then unloaded, and the bulging of the ellipsoidal shell is completed. The applicant finally realized the forming of an ellipsoid with an axis length ratio of λ = 1.6 by using finite element software, and the equatorial radius difference is controlled within 0.295%.

[0046] Embodiment 2

[0047] In this embodiment, the bulging of a low-carbon steel ellipsoidal shell with a thickness of 1 mm, a major axis of 300 mm, and an axis length ratio λ = 2.0 is taken as an example for analysis. The splitting scheme adopts 12 splits, the cross-sectional size of the pole plate is 15 mm (the distance from the extremely low center to the pole), and the liquid medium is water. At the same time, on this basis, a geometric software is used to draw the lantern-shaped initial closed structure, and the curvatures of the two pole plates and the twelve single-curvature curved side petals are determined. The geometry of the single-curvature curved side petals is unfolded and the size of the blank before bending is obtained by using a finite element analysis software; the above-mentioned pole plate size and the side petal blank size are processed and welded together to form a lantern-shaped initial closed structure, and a water injection port is processed at the pole plate; the fixture with a rubber sleeve is fixed on the initial structure, and the reliable connection between the upper and lower fixtures is ensured through a buckle; the fixture is installed at the high-speed motor and sufficient connection strength is ensured; water is injected into the initial closed spherical shell, and after the water is full, the motor is started. Taking the maximum hydrostatic load p′ and the maximum rotational speed n′ as 0.6 MPa and 54 r / s respectively, the motor speed and the hydrostatic pressure are gradually increased, and it is ensured that the hydrostatic pressure is linearly related to the square of the motor speed. In the initial stage of loading, the load is gradually increased by 10% per step; when the load increases to 80% of the maximum total load, the load is increased by 2% per step; when the load increases to 95% of the maximum total load, the load is increased by 1% per step; when the loading reaches the maximum load, it is stabilized for about 10 s to allow it to deform fully and then unloaded, and the bulging of the ellipsoidal shell is completed. Finally, the forming of an ellipsoid with an axis length ratio of λ = 2.0 is realized by using finite element software, and the equatorial radius difference is controlled within 0.567%.

[0048] Example 3

[0049] In this example, a low-carbon steel ellipsoidal shell with a thickness of 1 mm, a major axis of 300 mm, and an axis length ratio λ = 2.4 is used as an example for analysis. The splitting scheme is 12 splits, the cross-sectional size of the pole plate is 15 mm (the distance from the extremely low center to the pole), and water is used as the liquid medium. At the same time, on this basis, a geometric software is used to draw the lantern-shaped initial closed structure, and the curvatures of the two pole plates and the twelve single-curvature curved side lobes are determined. The geometry of the single-curvature curved side lobes is used in the finite element analysis software to expand and obtain the size of the blank before bending; the above-mentioned pole plate size and side lobe blank size are processed and welded together to form a lantern-shaped initial closed structure, and a water injection port is processed at the pole plate; the fixture equipped with rubber sleeve material is fixed on the initial structure, and the connection between the upper and lower fixtures is ensured through a buckle; the fixture is installed at the high-speed motor and sufficient connection strength is ensured; water is injected into the initial closed spherical shell, and after the water is full, the motor is started. Taking the maximum hydrostatic load p′ and the maximum rotation speed n′ as 0 MPa and 62 r / s respectively, the motor speed and hydrostatic pressure are gradually increased, and it is ensured that the hydrostatic pressure is linearly related to the square of the motor speed. In the initial stage of loading, the load is gradually increased by 10% per step; when the load increases to 80% of the maximum total load, the load is increased by 2% per step; when the load increases to 95% of the maximum total load, the load is increased by 1% per step; when the loading reaches the maximum total load, it is stabilized for about 10 s to allow sufficient deformation and then unloaded, and the bulging of the ellipsoidal shell is completed. The applicant finally realized the forming of an ellipsoid with an axis length ratio of λ = 2.4 by using finite element software, and the equatorial radius difference is controlled within 0.666%.

[0050] The working principle based on the above scheme is as follows:

[0051] The thin-walled shell filled with liquid is affected by hydrostatic pressure and the internal pressure of the rotating liquid during rotation. The load acting on the inner wall consists of hydrostatic load and rotating load. According to the principle of communicating vessels and Bernoulli's equation, the hydrostatic load is a constant p0; the rotating load is a function that is quadratic with the distance r from the load application point to the central axis. Then the load P(r) (the total load during loading) acting on the inner wall is expressed as:

[0052]

[0053] where r is the distance from the stress point to the central axis, ρ represents the pressure density, ω represents the angular velocity of rotation. Reaching 80% of the maximum load means that p0 reaches 80% of the maximum value, that is, p′ reaches 80% of the maximum value. ω 2 Reaching 80% of the maximum value, ω reaches 80% of the maximum value That is, n′ reaches 80% of the maximum value

[0054] Since the existing thin film theory of ellipsoidal shells is only for stress distribution under hydrostatic pressure, and the load is a function related to r when analyzing and calculating the force of rotating loads, the existing thin film theory of ellipsoidal shells cannot be directly used. The applicant analyzed the force of the ellipsoidal shell and obtained the meridional stress σ of the rotating ellipsoidal shell. l and the latitudinal stress σ θ There are the following differential relations:

[0055]

[0056]

[0057] Where t is the thickness of the ellipsoid shell, z is the height position in the ellipsoid equation, z′(r) is the first-order derivative of the function z with respect to r, and R is the function of the radial curvature radius, which is expressed as follows:

[0058]

[0059] Where z″(r) is the second-order derivative of function z with respect to r.

[0060] Combining and solving the above differential relations, we can obtain the longitudinal stress σ l and the latitudinal stress σ θ They are:

[0061]

[0062]

[0063] Where λ is the axial length ratio of the ellipsoidal shell.

[0064] Analyze the latitudinal stress σ at the equator (r = a) θ :

[0065]

[0066] For the wrinkling condition under the combined load of static water load and rotation load, that is, σ θ (r=a)=0 for analysis, where:

[0067]

[0068] So σ θ The wrinkling condition of (r=a)=0 is equivalent to:

[0069]

[0070] Solving the above equation λ yields:

[0071]

[0072] because:

[0073]

[0074] Therefore, λ ≤ 2, and λ = 2 when p0 = 0.

[0075] In summary, the hydroforming method of an ellipsoidal container with combined hydrostatic load and rotational load can extend the range of the axial length ratio λ of the equatorial circumferential tensile stress under the existing hydrostatic pressure from to the range of the axial length ratio λ of the equatorial circumferential tensile stress under the combined load condition, which is 1 < λ < 2. The wrinkling problem during the bulging process of the ellipsoidal thin-shell component within the range is solved.

[0076] In the hydroforming of an ellipsoid under only hydrostatic pressure, it is difficult to simultaneously reach the ideal state at the equator and the poles. During the hydroforming process of an ellipsoid with a high axial length ratio, the hydrostatic pressure often reaches the load required for bulging at the poles first. At this time, the equator has not been bulged to the ideal state. To make the bulging at the equator reach the ideal state, it is necessary to further increase the hydrostatic load, which causes the poles to rise and the axial length ratio to decrease. This is because there is only pressure as a controllable variable during the loading process, and it is impossible to adjust the loads at various bulging positions. The hydroforming method of an ellipsoidal container with combined hydrostatic load and rotational load adopted in the present invention solves the problem that it is impossible to adjust the loads at the poles and the equator during hydrostatic pressure bulging through two controllable variables, namely hydrostatic pressure and rotational load, as Figure 3 shown ( Figure 3 in which x is the coordinate of the long axis of the ellipse, and the y-axis is the coordinate of the short axis of the ellipse, both representing length coordinates).

[0077] Analyzing the stress at the poles gives:

[0078]

[0079] The hydrostatic pressure p0 is:

[0080]

[0081] Analyzing the forces at the equator:

[0082]

[0083] Through the analysis of the simulation of the forming process, it is obtained that the meridional stress and the circumferential stress at the equator in the later stage of forming are close in magnitude, that is:

[0084] σ l (r = a) ≈ σ θ (r = a) ≈ σ s

[0085] The rotational angular velocity ω is obtained as

[0086]

[0087] Furthermore, the rotational speed n obtained is

[0088]

[0089] Due to the extremely high nonlinearity of plastic deformation, it is difficult for general formulas to accurately predict. Therefore, the above formula is corrected in the following way:

[0090] p′ = 2p0 - 2.1

[0091] n′ = 1.84n - 16.74

[0092] Where p′ and n′ respectively represent the final bulging pressure and the final bulging rotational speed.

[0093] To verify the effectiveness of the above forming method, the applicant uses the finite element method to simulate the ellipsoidal bulging under the condition of combined loading, and obtains that the axis length ratio of the ellipsoidal thin shell formed by this combined method can reach up to 2.4, as Figure 4 shown. Above, the hydrostatic pressure load and the rotational load are used to conform to the loading of the ellipsoidal container hydroforming method, and the axis length ratio of the ellipsoidal shell bulging is expanded from 1 < λ < 1.3 to 1 < λ < 2.4.

[0094] The present invention has been disclosed above with preferred embodiments. However, it is not intended to limit the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, can make some changes or modifications to the above-disclosed structure and technical content as equivalent embodiments of equivalent changes, and all still fall within the scope of the technical solution of the present invention.

Claims

1. Hydroforming method for an ellipsoidal container under combined hydrostatic load and rotational load, the method comprising: Step 1: Determination of the initial lantern-shaped single-curvature thin-shell member (1) Select an appropriate splitting scheme, and the side plates of the ellipsoidal hydroforming are processed from the initial blank with 8 - 24 splits. (2) Determination of the pole plate size. Select the size of the cross-section of the pole plate at a distance of 5% - 20% of the short-axis length from the pole. According to the number of splits of the thin-shell member and the pole plate size obtained from the design, calculate and analyze the shape of the sheet before bending of the side plates by the unfolding method or the finite element method on the basis of this size, and cut the sheet according to this size. (3) Process the obtained sheet into the side plate structure, check and correct the side plate structure size, and use the determined pole plate and side plates to fabricate the single-curvature ellipsoidal shell by welding, verify the welding tightness, and obtain the initial single-curvature thin shell. Step 2: Fix the initial single-curvature thin shell with a fixture. The fixture and the thin shell are fixed near the weld with relatively small displacement during the bulging process and rely on the jacket to achieve soft contact, so as to drive the ellipsoidal shell to rotate and reduce the restriction on deformation during the ellipsoidal rotational bulging process. Step 3: Rotate the fixture and gradually increase the rotational speed. During the process of increasing the rotational speed, increase the hydrostatic pressure to ensure that the hydrostatic pressure and the rotational pressure increase linearly synchronously. The maximum hydrostatic load p' and the maximum rotational speed n' satisfy the following formula: Among them, n' is the rotational speed, p' is the hydrostatic pressure, t is the thickness of the ellipsoidal thin shell, σ s is the material yield strength, λ is the ratio of the major axis radius to the minor axis radius of the ellipsoid, a is the major axis radius, and ρ is the liquid density; after the loading reaches the total load, it is stabilized for 5 - 10 s to allow it to fully deform and then unloaded to obtain the expanded ellipsoidal container.

2. The hydroforming method of an ellipsoidal container with combined hydrostatic load and rotational load according to claim 1, characterized in that: In the initial stage of loading in Step 3, gradually increase the total load by 10% each time.

3. The hydroforming method of an ellipsoidal container with combined hydrostatic load and rotational load according to claim 1, characterized in that: In Step 3, when the load increases to 80% of the total load, increase the load by 2% each time.

4. The hydroforming method of an ellipsoidal container with combined hydrostatic and rotational loads according to claim 1, characterized in that: In Step 3, when the load increases to 95% of the total load, increase the load by 1% each time.

5. The hydroforming method of an ellipsoidal container with combined hydrostatic load and rotational load according to claim 1, characterized in that: In Step 3, when the loading reaches the total load, keep it stable for 10 s to allow sufficient deformation and then unload.

6. The hydroforming method of an ellipsoidal container with combined hydrostatic and rotational loading according to claim 1, characterized in that: The jacket in Step 2 is made of rigid sponge.

7. The hydroforming method of an ellipsoidal container with combined hydrostatic load and rotational load according to claim 1, characterized in that: The number of splits in Step 1 is 16 splits or 12 splits.

8. The hydroforming method of an ellipsoidal container with combined hydrostatic load and rotational load according to claim 1, characterized in that: For a low-carbon steel ellipsoidal container with a forming thickness of 1 mm, a major axis of 300 mm, and an axis length ratio λ of 1.6, the maximum hydrostatic load p' and the maximum rotational speed n' are 1.3 MPa and 44 r / s respectively.

9. The hydroforming method of an ellipsoidal container with combined hydrostatic and rotational loads according to claim 1, characterized in that: For a low-carbon steel ellipsoidal container with a forming thickness of 1 mm, a major axis of 300 mm, and an axis length ratio λ of 2.0, the maximum hydrostatic load p' and the maximum rotational speed n' are 0.6 MPa and 54 r / s respectively.

10. The hydroforming method of an ellipsoidal container with combined hydrostatic and rotational loads according to claim 1, characterized in that: For a low-carbon steel ellipsoidal container with a forming thickness of 1 mm, a major axis of 300 mm, and an axis length ratio λ of 2.4, the maximum hydrostatic load p' and the maximum rotational speed n' are 0 MPa and 62 r / s respectively.

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