A moldless gas-liquid mixing forming method and device for large-size spherical members

Abstract

The present application belongs to the technical field of manufacturing thin-walled special-shaped metal components, and discloses a mold-free gas-liquid mixed forming method and device for large-size spherical components. The device comprises a pressure medium unit, a liquid filling unit, an air filling unit, an expansion unit, a sealing unit and a pressure measuring unit. The present application does not need traditional molds and large-scale tooling equipment support, and through the synergistic effect of the compressibility of gas and the incompressibility of liquid, only a simple sealing device is needed to realize the forming of the sphere, greatly reducing the mold design and manufacturing cost, and being suitable for low-cost batch manufacturing of spherical components and flexible production of small-batch and multi-variety spherical components. Through the dynamic pressure regulation of the gas-liquid mixed medium, the present application realizes continuous forming after single liquid filling. The gas-liquid mixed medium system of the present application has both gas pressure adjustability and liquid flow supportability. The forming process of the present application has a pressure testing function, and the gas-liquid mixed medium can be directly converted into a pressure maintaining medium after completing plastic deformation.

Description

Technical Field

[0001] This invention belongs to the field of thin-walled irregular metal component manufacturing technology, and relates to a moldless gas-liquid mixing forming method and apparatus for large-size spherical components. Background Technology

[0002] To meet the demands of energy, chemical, and aerospace industries for lightweight, high-pressure-resistance, and long-service-life large pressure-bearing structures, large-size thin-walled spherical components made from thin-walled sheets can optimize both material consumption and weight while ensuring structural strength and sealing performance. Therefore, they are widely used in strategic fields such as gas and liquid storage and deep space exploration. However, the integral forming of large-size thin-walled spherical components is a core challenge in extreme manufacturing fields. The technological bottleneck lies in the contradictory relationship between geometric precision control, ensuring wall thickness uniformity, and manufacturing cost constraints.

[0003] Currently, the industrial production of large-sized thin-walled spherical components mainly involves stamping and welding processes and moldless hydraulic spherical expansion processes. The stamping and welding process requires multiple stamping, cutting, and welding passes, resulting in a long production cycle per piece. Furthermore, stamping and welding require corresponding tooling equipment, leading to high costs. Additionally, the challenge of coordinating residual stress and deformation in the weld seam can easily cause localized cracking or geometric distortion, resulting in high subsequent straightening costs. While the moldless hydraulic spherical expansion process can achieve sufficient material deformation and strengthening and eliminate mold costs, it faces the fundamental drawback of structural instability caused by the weight of the liquid: under non-uniform pressure fields, the blank is prone to localized excessive thinning, wrinkling, or shape loss. When the diameter exceeds 3 meters, the hydrostatic pressure gradient causes the bottom pressure to be 15%-20% higher than the top, resulting in uneven wall thickness distribution (30% thicker at the bottom and 40% thinner at the top). More seriously, for every 10-fold increase in diameter, the weight of the liquid increases by 1000 tons. This means that a 10-meter-class sphere will bear 535 tons of liquid weight, causing the shell to buckle and deform (finite element analysis shows that the Von Mises stress exceeds 550 MPa).

[0004] Therefore, in order to overcome the technical bottlenecks in the production of large-size thin-walled spherical components and achieve mass production of large-size spherical components while ensuring forming accuracy, wall thickness uniformity, and lightweighting, thus meeting the urgent needs of energy, chemical, aerospace, and other fields for efficient and low-cost manufacturing, it is imperative to develop a new moldless gas-liquid hybrid forming method and apparatus for large-size spherical components. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a moldless gas-liquid mixing forming method and apparatus for large-size spherical components, enabling moldless and precise forming of large-size spherical components, significantly improving product forming quality and structural stability, while effectively shortening the production cycle and reducing the investment cost of tooling equipment.

[0006] The technical solution of this invention:

[0007] A method for moldless gas-liquid mixing molding of large-sized spherical components includes the following steps:

[0008] Step 1: Sheet Material Preparation: Based on the dimensions, wall thickness, and forming accuracy requirements of the target spherical component, determine the shape, size, and structural form of the blank to form the initial shell. Determine the welding scheme for the blank based on the forming accuracy and performance requirements of the target spherical component. By adjusting the blank shape and seam distribution, improve the local load-bearing capacity of the target spherical component, control the wall thickness variation trend, and optimize the geometric accuracy of the formed spherical component. The initial shell structure can be a conical initial shell, a melon-shaped initial shell, a soccer ball-shaped initial shell, a volleyball-shaped initial shell, a tennis ball-shaped initial shell, or a regular polygonal initial shell. Select a suitable initial shell structure according to the application. For example, a melon-shaped seam structure can enhance the pressure-bearing stability in the equatorial region and is suitable for extremely high internal pressure applications; a soccer ball-shaped polygonal splicing structure helps to disperse overall deformation stress, reduce local thinning rate, and improve material utilization efficiency and service life.

[0009] Step 2, Shell Welding: The blanks from Step 1 are rolled up, and then welded according to the welding scheme determined in Step 1 to obtain the initial shell. During welding, spot welding is first used to weld the various blanks together to avoid the situation where the cumulative error leads to excessive positional error of the subsequent plates, making them unable to be welded. After fixing the position of the blanks with spot welding, the blanks are then completely welded together to obtain the initial shell. At the same time, a pressure sensor is added inside the initial shell to obtain the bulging unit.

[0010] Step 3, Pre-filling stage: Connect the initial shell (expansion unit) after welding to the low-pressure medium unit, sealing unit, and pressure measuring unit. First, perform a sealing test on the initial shell. Assuming good sealing, determine the gas volume based on the gas-liquid mixture compression characteristics, i.e., the relationship between the pressure provided by the gas-liquid mixture during compression and the volumes of the gas, liquid, and target spherical component; specifically, as shown in the following formula: V g0 P is the gas volume. m Let P0 be the pressure required for the initial bulging, P0 be standard atmospheric pressure, and V-V0 be the volume difference of the spherical component before and after bulging. Since the solubility of gas in liquid at room temperature is low and can be neglected, the liquid volume is the initial volume of the shell cavity minus the gas volume, as shown in the following formula: V l0 =V0-V g0 The volumes of liquid and gas were determined based on the compressibility characteristics of the gas-liquid mixture. Then, a suitable volume of liquid was injected into the initial shell through the filling unit to form an inner wall support.

[0011] Step 4, Inflation and Shaping Stage: Determine the corresponding inflation pressure curve based on the material flow characteristics and gas-liquid mixing ratio of the target spherical component; the specific determination method is shown in the following formula: Where k0 is the ratio of gas to liquid volume within the spherical component, P0 is standard atmospheric pressure, P is the pressure required for bulging, and c is a coefficient representing the material flow characteristics. Based on the inflation pressure curve, an appropriate amount of gas is injected into the initial shell using an inflation unit. A multi-stage dynamic control mechanism for the gas-liquid ratio is established during the inflation bulging stage to improve the control capability of the local shell thickness. For scenarios requiring high production efficiency and low requirements for wall thickness and shape accuracy, inflation can be performed to the target bulging pressure in one step. For complex spherical structures requiring strict control of material flow during the forming process to meet the requirements of uniform wall thickness distribution and forming accuracy, a staged, pressure-level inflation method is adopted based on the pressure curve, gradually adjusting the gas injection volume and pressure level. After each stage, the shell expansion state and local wall thickness changes are fed back through a pressure measuring unit, adjusting the gas-liquid ratio for the next stage to achieve precise control of the bulging process.

[0012] Compared to pure liquid bulging, this gas-liquid mixture reduces the weight of the liquid significantly, effectively improving structural instability caused by the liquid's own weight. At the same time, the gas-liquid mixture bulging is a low-pressure forming process, which greatly improves safety and stability and effectively avoids stress concentration and local wrinkles.

[0013] Step 5, Pressure Holding Stage: After expansion is complete, continue pressurizing using the inflation unit while simultaneously using the pressure measuring unit to reach 1.5 times the maximum operating pressure (according to ISO 5171 standard, the pressure holding test pressure should be 1.5 times the maximum operating pressure), and maintain this pressure for 30 minutes to 2 hours. If no sudden pressure drop, gas or liquid leakage occurs during this process, it indicates that the expanded shell structure is stable, has good sealing performance, and meets the requirements.

[0014] Step Six: Depressurization and Part Removal: After completing the bulging and pressure holding tests, first control the inflation unit to discharge the gas inside the shell to reduce the pressure. After the pressure drops to the normal atmospheric pressure, remove the liquid filling unit, inflation unit, sealing unit and pressure testing device connected to the shell. Then clean out the residual liquid inside the shell, thus completing the moldless forming of the spherical component.

[0015] A moldless gas-liquid mixing forming device for large-size spherical components includes a low-pressure medium unit, a liquid filling unit, a gas filling unit, an expansion forming unit, a sealing unit, and a pressure measuring unit.

[0016] The low-pressure medium unit includes a gas source and a liquid source. The gas source is automatically inflated through an inflation unit, and the liquid source is automatically filled through a liquid filling unit. The low-pressure medium unit is connected to the expansion unit and can automatically switch between gas and liquid sources according to the forming requirements.

[0017] The expansion unit mainly consists of an initial housing and a pressure sensor inside the initial housing. The expansion unit is connected to the low-pressure medium unit, the sealing unit, and the pressure measuring unit. The expansion of the initial housing is controlled by the pressure feedback from the pressure sensor.

[0018] The sealing unit mainly functions at the connection between the low-pressure medium unit and the expansion unit to ensure sealing and prevent gas and liquid leakage.

[0019] The pressure measuring unit is connected to the bulging unit. The pressure sensor in the pressure measuring unit observes the pressure inside the initial shell in real time during bulging, which is used to control the bulging of the initial shell.

[0020] The beneficial effects of this invention are:

[0021] I. This invention does not require traditional molds and large tooling equipment. Through the synergistic effect of gas compressibility and liquid incompressibility, spherical forming can be achieved with only a simple sealing device, which greatly reduces the mold design and manufacturing cost. It is suitable for both low-cost mass production of spherical components and flexible production of small batches and multiple varieties of spherical components.

[0022] II. This invention achieves continuous forming after a single filling by dynamically controlling the pressure of a gas-liquid mixture. Compared with multi-stage molding processes, the production cycle is reduced by more than 40%, significantly reducing production costs. Furthermore, during the forming process, materials such as stainless steel undergo work hardening due to plastic deformation, increasing the yield strength by more than 15%, thus significantly enhancing load-bearing capacity while ensuring lightweight structure.

[0023] Third, the gas-liquid mixed medium system of the present invention has both the adjustable gas pressure and the support of liquid flow: the gas provides a uniformly distributed surface pressure, and the liquid weight is balanced by the gas pressure, which effectively avoids the problem of uneven wall thickness caused by the weight of the fluid in pure hydraulic forming; by adjusting the gas-liquid ratio in real time, the local thinning rate can be controlled within 8%, ensuring the geometric accuracy of the sphere.

[0024] Fourth, the forming process of this invention also has a pressure testing function. After the gas-liquid mixture completes plastic deformation, it can be directly converted into a pressure-holding medium. The pressure-bearing performance is verified simultaneously at this stage, eliminating the need for a separate pressure test in traditional processes, thus improving the product qualification rate.

[0025] V. This invention provides various initial spherical shell structures (such as conical, melon-shaped, soccer ball-shaped, tennis ball-shaped, etc.), which can be flexibly selected according to the pressure requirements, geometric accuracy requirements, and service scenarios of the target component, enhancing the adaptability and customization capabilities of the forming process. The joint arrangement and plate shape of different structures help to control the local stress distribution and wall thickness evolution law, thereby further improving the forming accuracy and service performance of the sphere while ensuring lightweight, and is particularly suitable for the manufacture of large, asymmetrical, and special functional spherical components. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a conical initial shell and its component blanks according to the present invention; wherein, (a) is a design drawing of the conical initial shell, (b) is a three-dimensional model of the conical initial shell, and (c) is a schematic diagram of the component blanks of the conical initial shell;

[0027] Figure 2 This is a schematic diagram of a soccer ball-shaped initial shell and its component blanks according to the present invention; wherein, (a) is a design drawing of the soccer ball-shaped initial shell, (b) is a three-dimensional model of the soccer ball-shaped initial shell, and (c) is a schematic diagram of the component blanks of the soccer ball-shaped initial shell;

[0028] Figure 3 This is a schematic diagram of a melon-shaped initial shell and its component blanks according to the present invention; wherein, (a) is a design drawing of the melon-shaped initial shell, (b) is a three-dimensional model of the melon-shaped initial shell, and (c) is a schematic diagram of the component blanks of the melon-shaped initial shell.

[0029] Figure 4 The initial shell types of the present invention include volleyball-shaped, tennis ball-shaped, and regular polyhedron-shaped shells; wherein, (a) is a volleyball-shaped initial shell, (b) is a tennis ball-shaped initial shell, (c) is a regular pentagonal polyhedron initial shell, and (d) is an equilateral triangular polyhedron initial shell;

[0030] Figure 5 This is a schematic diagram of the moldless gas-liquid mixing forming device for large-size spherical components according to the present invention;

[0031] Figure 6 This is a schematic diagram of the pre-filling liquid stage of the present invention;

[0032] Figure 7 This is a schematic diagram of the inflation and shaping stage of the present invention. Detailed Implementation

[0033] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0034] A method for moldless gas-liquid mixing molding of large-sized spherical components includes the following steps:

[0035] Step 1: Sheet Material Preparation: Based on the dimensions, shape, wall thickness, and forming accuracy requirements of the target spherical component, determine the shape, size, and structural form of the blank to form the initial shell, specifically as follows: Figure 1 (c) Figure 2 (c) Figure 3 The blank shown in (c) is used as an example; the welding scheme for the blank is determined based on the forming accuracy and performance requirements of the target spherical component. Figure 1 (a) Figure 2 (a) Figure 3 (a) and Figure 4Different welding schemes are used; by adjusting the shape of the blank and the distribution of the seams, the local load-bearing capacity of the target spherical component is improved, the wall thickness variation trend is controlled, and the geometric accuracy of the formed spherical component is optimized. The initial shell structure can be... Figure 1 Conical initial shell, Figure 2 melon-shaped initial shell, Figure 3 soccer ball-shaped initial shell, Figure 4 (a) Volleyball-shaped initial shell, Figure 4 (b) Tennis-shaped initial shell and Figure 4 (c) and (d) Original shell structures of regular polygons. Select a suitable initial shell structure based on the application, such as... Figure 3 The melon-shaped splicing structure can enhance the pressure-bearing stability in the equatorial region and is suitable for extremely high internal pressure applications. Figure 2 The soccer ball-shaped polygonal splicing structure helps to disperse overall deformation stress, reduce local thinning rate, and improve material utilization efficiency and service life.

[0036] Step Two: Shell Welding: The blanks from Step One are rolled up, and then welded according to the welding scheme determined in Step One to obtain the initial shell. During welding, spot welding is first used to weld the various blanks together to avoid the situation where the cumulative error leads to excessive positional errors in the subsequent plates, preventing proper welding. After fixing the position of the blanks with spot welding, the blanks are then completely welded together to obtain the initial shell. A pressure sensor is also added inside the initial shell to obtain... Figure 5 Medium-expansion unit.

[0037] Step 3, Pre-filling stage: Connect the initial shell (medium expansion unit) after welding to the low-pressure medium unit, sealing unit, and pressure measuring unit as follows: Figure 5 As shown. First, using Figure 5 The intermediate sealing unit seals the initial housing and utilizes Figure 5 The pressure measurement unit undergoes a sealing test. Assuming good sealing, the gas volume is determined based on the compressibility characteristics of the gas-liquid mixture, specifically the relationship between the pressure provided during compression and the volumes of the gas, liquid, and the target spherical component. The specific formula is as follows: Gas volume is determined: V g0 P is the gas volume. m Let P0 be the pressure required for the initial bulging, P0 be standard atmospheric pressure, and V-V0 be the volume difference of the spherical component before and after bulging. Since the solubility of gas in liquid at room temperature is low and can be neglected, the liquid volume is the initial volume of the shell cavity minus the gas volume, as shown in the following formula: V l0 =V0-V g0 The volumes of liquid and gas were determined based on the compressibility characteristics of the gas-liquid mixture, and then... Figure 5 In the medium and low pressure medium unit, the liquid filling unit injects a suitable volume of liquid into the initial shell to form an inner wall support.

[0038] Step 4, Inflation and Shaping Stage: Determine the corresponding inflation pressure curve based on the material flow characteristics and gas-liquid mixing ratio of the target spherical component; the specific determination method is shown in the following formula: Where k0 is the ratio of gas to liquid volume within the spherical component, P0 is standard atmospheric pressure, P is the pressure required for bulging, and c is a coefficient representing the material flow characteristics. Based on the inflation pressure curve... Figure 5 In the low- and medium-pressure medium unit, the inflation unit injects an appropriate amount of gas into the initial shell. A multi-stage dynamic control mechanism for the gas-liquid ratio is established during the inflation and bulging stage to improve the control capability of the local shell thickness. For scenarios requiring high production efficiency and with low requirements for wall thickness and shape accuracy, inflation can be performed in one step to the target bulging pressure. For complex spherical structures requiring strict control of material flow during the forming process to meet the requirements of uniform wall thickness distribution and forming accuracy, a staged, pressure-level inflation method is adopted based on the pressure curve, gradually adjusting the gas injection volume and pressure level. After each stage, through... Figure 5 The pressure measurement unit provides feedback on the shell expansion state and local wall thickness changes, and adjusts the gas-liquid ratio in the next stage to achieve precise control over the expansion process.

[0039] Compared to pure liquid bulging, this gas-liquid mixture reduces the weight of the liquid significantly, effectively improving structural instability caused by the liquid's own weight. At the same time, the gas-liquid mixture bulging is a low-pressure forming process, which greatly improves safety and stability and effectively avoids stress concentration and local wrinkles.

[0040] Step 5, Pressure Holding Stage: After bulging is completed, use... Figure 5 The gas filling unit in the medium and low pressure medium unit continues to pressurize while combining Figure 5 In the medium- and low-pressure medium unit, the pressure measuring unit is set to 1.5 times the maximum operating pressure and maintained at that pressure for 1 hour. If no sudden pressure drop, gas or liquid leakage occurs during this process, it indicates that the expanded shell structure is stable, has good sealing performance, and meets the requirements.

[0041] Step Six: Depressurization and Part Removal: After completing the bulging and pressure holding tests, first control... Figure 5 In the medium and low pressure medium unit, the gas filling unit expels the gas inside the shell to reduce the pressure. After the pressure drops to the normal atmospheric pressure, the liquid filling unit, gas filling unit, sealing unit and pressure testing device connected to the shell are removed. Then the residual liquid inside the shell is cleaned out, thus completing the moldless forming of the spherical component.

[0042] A moldless gas-liquid mixing forming device for large-size spherical components includes a low-pressure medium unit, a liquid filling unit, a gas filling unit, an expansion forming unit, a sealing unit, and a pressure measuring unit.

[0043] The low-pressure medium unit includes a gas source and a liquid source. The gas source is automatically inflated through an inflation unit, and the liquid source is automatically filled through a liquid filling unit. The low-pressure medium unit is connected to the expansion unit and can automatically switch between gas and liquid sources according to the forming requirements.

[0044] The expansion unit mainly consists of an initial housing and a pressure sensor inside the initial housing. The expansion unit is connected to the low-pressure medium unit, the sealing unit, and the pressure measuring unit. The expansion of the initial housing is controlled by the pressure feedback from the pressure sensor.

[0045] The sealing unit mainly functions at the connection between the low-pressure medium unit and the expansion unit to ensure sealing and prevent gas and liquid leakage.

[0046] The pressure measuring unit is connected to the bulging unit. The pressure sensor in the pressure measuring unit observes the pressure inside the initial shell in real time during bulging, which is used to control the bulging of the initial shell.

Claims

1. A method for moldless gas-liquid mixing and forming of large-sized spherical components, characterized in that, Includes the following steps: Step 1: Sheet material preparation: Based on the size, shape, wall thickness, and forming accuracy requirements of the target spherical component, determine the shape, size, and structural form of the blank to form the initial shell; The welding scheme of the blank is determined based on the forming accuracy and performance requirements of the target spherical component; by adjusting the shape of the blank and the distribution of the joints, the local load-bearing capacity of the target spherical component is improved, the trend of wall thickness variation is controlled, and the geometric accuracy of the formed spherical component is optimized. Select the appropriate initial housing structure based on the application scenario; Step 2, Shell Welding: The blank from Step 1 is rolled up, and then welded according to the welding scheme determined in Step 1 to obtain the initial shell; during the welding process, spot welding is first used to weld each part of the blank to fix its position, and then complete welding is performed to obtain the initial shell; a pressure sensor is added inside the initial shell to obtain the bulging unit; Step 3, Pre-filling stage: Connect the expansion unit to the low-pressure medium unit, sealing unit, and pressure measuring unit; first, perform a sealing test on the initial shell. Assuming good sealing, determine the gas volume based on the compression characteristics of the gas-liquid mixture, i.e., the relationship between the pressure provided by the gas-liquid mixture during compression and the volumes of the gas, liquid, and target spherical component, as shown in the following formula: , For gas volume, The pressure required for initial bulging. Standard atmospheric pressure The volume difference before and after the spherical component is expanded is given. Since the solubility of gas in liquid at room temperature is low, it is negligible; therefore, the liquid volume is the initial volume within the shell cavity. Subtract gas volume The formula is as follows: The volumes of liquid and gas are determined based on the compressibility characteristics of the gas-liquid mixture. Then, a suitable volume of liquid is injected into the initial shell through the filling unit to form an inner wall support. Step 4, Inflation and Shaping Stage: Determine the corresponding inflation pressure curve based on the material flow characteristics and gas-liquid mixing ratio of the target spherical component; the specific determination method is shown in the following formula: ,in It is the ratio of gas to liquid volume within the spherical component. Standard atmospheric pressure The pressure required for bulging. This is a coefficient representing the material's flow characteristics; Based on the inflation pressure curve, gas is injected into the initial shell using an inflation unit; a multi-stage dynamic control mechanism for the gas-liquid ratio is established during the inflation and expansion stage; after each stage, the initial shell expansion state and local wall thickness changes are fed back through a pressure measuring unit to adjust the gas-liquid ratio for the next stage, so as to achieve precise control of the expansion process. The multi-stage gas-liquid ratio dynamic control mechanism in step four is as follows: For scenarios where production efficiency is required and the wall thickness and shape accuracy of the formed spherical components are not critical, the gas is inflated to the target expansion pressure in one go; for spherical components with complex shapes, where the flow of material during the forming process needs to be strictly controlled to meet the requirements of uniform wall thickness distribution and forming accuracy, a staged, pressure-level inflation method is adopted according to the inflation pressure curve to gradually adjust the gas injection volume and pressure level. Step 5, Pressure Holding Stage: After the expansion is completed, continue to pressurize using the inflation unit while using the pressure measuring unit to make the pressure reach 1.5 times the maximum operating pressure and hold the pressure for 30 minutes to 2 hours; Step 6, Depressurization and Part Removal: After completing the bulging and pressure holding tests, first control the inflation unit to discharge the gas inside the initial shell to reduce the pressure. After the pressure drops to normal atmospheric pressure, remove the liquid filling unit, inflation unit, sealing unit and pressure measuring unit connected to the initial shell. Then clean out the residual liquid inside the initial shell, thus completing the moldless forming of the spherical component.

2. The method for moldless gas-liquid mixing and forming of large-size spherical components according to claim 1, characterized in that, The initial shell is a conical initial shell, a melon-shaped initial shell, a soccer ball-shaped initial shell, a volleyball-shaped initial shell, a tennis ball-shaped initial shell, or a regular polygonal initial shell.

3. A moldless gas-liquid mixing forming apparatus for large-size spherical components, employing the moldless gas-liquid mixing forming method for large-size spherical components as described in claim 1 or 2, characterized in that... The moldless gas-liquid mixing forming device for large-size spherical components includes a low-pressure medium unit, a liquid filling unit, a gas filling unit, an expansion unit, a sealing unit, and a pressure measuring unit. The low-pressure medium unit includes a gas source and a liquid source. The gas source is automatically inflated through an inflation unit, and the liquid source is automatically filled through a liquid filling unit. The low-pressure medium unit is connected to the expansion unit and can automatically switch between gas and liquid sources according to the forming requirements. The expansion unit mainly consists of an initial housing and a pressure sensor inside the initial housing. The expansion unit is connected to the low-pressure medium unit, the sealing unit, and the pressure measuring unit. The expansion of the initial housing is controlled by the pressure feedback from the pressure sensor. The sealing unit mainly functions at the connection between the low-pressure medium unit and the expansion unit to ensure sealing and prevent gas and liquid leakage. The pressure measuring unit is connected to the bulging unit. The pressure sensor in the pressure measuring unit observes the pressure inside the initial shell in real time during bulging, which is used to control the bulging of the initial shell.

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