High-strength pipe with high diameter-thickness ratio and method for forming the same by multi-stage continuous bending

Abstract

The application provides a large-diameter-thickness-ratio high-strength pipe multi-section continuous bending combined forming device and method. A straight pipe to be processed is arranged between an upper bulging die and a lower bulging die. A baffle plate is in contact or abuts against one end of the straight pipe to be processed. A push plate is in contact or abuts against the other end of the straight pipe to be processed. Two groups of liquid-filled core molds cooperate with the inner wall of the straight pipe to be processed to form a working area. The tail ends of the two groups of liquid-filled core molds respectively pass through the baffle plate and the push plate and are in sliding cooperation with the baffle plate and the push plate. One liquid-filled core mold has a channel allowing the bulging medium to be sent into the working area from the outside. Through the steps of installing the pipe, pre-filling, bending forming, unloading, moving the core mold for next processing and cutting, the composite forming technology combining "extrusion forming to control the wall thickness" and "bulging to control the size" is used to effectively prevent material thinning, ensure the size precision, make the wall thickness thinning less than or equal to 10%, the size precision be ±0.2mm and realize the collaborative regulation of the "wall thickness and size precision".

Description

Technical Field

[0001] This invention belongs to the field of thin-walled tube forming technology, specifically, it relates to a device and method for continuous bending and forming of a high-strength tube with a large diameter-to-thickness ratio in multiple segments. Background Technology

[0002] In spacecraft such as launch vehicles, deep space probes, and missiles, conduits mainly include gas and liquid pipelines, which function similarly to blood vessels in the human body to transport fuel. The quality of their forming directly determines the success or failure of the spacecraft's flight test. Their product quality requirements are higher than those of ordinary conduits. Not only is the product thinning rate required to be no more than 20%, but the surface of the parts must also be free of defects such as wrinkles and scratches. Furthermore, as the size and load of spacecraft increase, the diameter of conduits is getting larger and larger, expanding from the traditional φ50~φ100mm range to φ50~φ300mm. At the same time, with increasingly higher requirements for lightweighting, the wall thickness of conduits is getting thinner and thinner, with most conduit wall thicknesses required to be δ≤1mm.

[0003] Traditionally, aerospace duct products are manufactured using a half-pipe welding process, which results in long processing cycles and low product consistency. Currently, adaptive processing methods are adopted for different bulging and extrusion composite forming processes. For pipes with a relative bulging and extrusion composite radius of 1.5D or more, a CNC bending bulging and extrusion composite forming process is used, while for pipes with a relative bulging and extrusion composite radius of less than 1.5D, a push bending bulging and extrusion composite forming process is used. These two forming processes are mainly for bent pipe products with a diameter of less than 160mm. However, for bent pipes with a diameter of more than 160mm, due to the small relative wall thickness and large diameter-to-thickness ratio of the bend, the pipe rigidity is poor, and the cross-section is prone to distortion during bulging and extrusion. The neutral layer will shift inward, and the actual thinning rate is greater than the theoretical value. Therefore, it is very difficult to use CNC bending and push bending processes for bends with very small relative wall thickness (the ratio of material thickness to pipe diameter is less than 0.01), and it is very easy to produce defects such as wrinkling and distortion.

[0004] The existing Chinese patent application document with publication number CN110814121A discloses a small-diameter tube small-expansion composite radius push-bending method and a small-diameter tube. The method is mainly for small-diameter tubes using low-melting-point metal as the filling medium for push-bending. During the push-bending forming process, a partition layer needs to be set to isolate the low-melting-point metal from the tube blank. Subsequently, the metal also needs to be heated and separated.

[0005] The existing Chinese patent application document with publication number CN1799722A discloses a thin-walled tube variable curvature push-bending process and mold. The method uses a hydraulic press as the loading method. There is no filling medium inside the tube during the push-bending process, which is suitable for tubes with low precision requirements.

[0006] The technical solution of this application proposes a composite forming process of "extrusion-expansion-shaping" for large-diameter (φ≥160mm) thin-walled (δ≤1mm) stainless steel bends, which solves the wrinkling and distortion defects and achieves integral forming. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a device and method for continuous bending and forming of high-strength tubes with a large diameter-to-thickness ratio.

[0008] The present invention provides a method for continuous bending and forming of a large-diameter-to-thickness high-strength tube in multiple segments, comprising the following steps: Pipe installation: Install the upper bulging mold inside the upper mold and the lower bulging mold inside the lower mold. Then place the straight pipe to be processed between the upper and lower bulging molds and close the molds. Push the two sets of liquid-filled core molds into the designated positions inside the straight pipe from one end. The two sets of liquid-filled core molds cooperate with the inner wall of the straight pipe to form a working area. One of the liquid-filled core molds has a channel that allows the bulging medium to be sent into the working area from the outside. Place a baffle at one end of the straight pipe to be processed and press a push plate at the other end of the straight pipe to be processed. The tail ends of the two sets of liquid-filled core molds pass through the baffle and the push plate respectively. Pre-filling: The expansion medium is injected into the working area through the channel on the liquid filling core mold. The pressure is P for pre-filling, which completes the filling of the gap in the working area of ​​the straight pipe to be processed; the push plate moves inward by a first distance, causing the straight pipe to be processed to be squeezed and deformed. After deformation, the material enters the cavity of the expansion mold, causing the pipe to undergo expansion and extrusion composite, which lasts for a first preset time. Pipe bending forming: The bulging pressure P is set to pressurize and bulge the working area inside the straight pipe to be processed. At the same time, the pusher plate further applies a lateral thrust F to the straight pipe to be processed. Under the support of hydraulic bulging P, as the pusher plate moves laterally, the pipe is further bulged and extruded to form a composite shape, which continues for a second preset time. After the bulging and extrusion composite shape is completed, the pressure inside the pipe is maintained by pressure P, and the pressure is gradually increased to P shaping to pressurize and shape the inside of the pipe. Unloading: Unload pressure P to separate the upper and lower molds; Next processing step of moving core mold: After placing the other processing position of the straight tube to be processed between the upper bulging mold and the lower bulging mold, close the mold and push the two sets of liquid-filled core molds into the interior of the other processing position. Repeat the pre-filling, tube bending and unloading operations to complete the bulging and extrusion composite forming operation of the other processing position. Cutting: Remove all tooling and cut the formed pipe to achieve the processing of multiple bends.

[0009] In one feasible implementation, the pusher plate displacement and pressure are controlled in a coordinated manner. During pre-filling, the pressure is 0 and the pusher plate displacement is 2mm. As the expansion pressure increases to 15MPa, the pusher plate displacement increases to 7mm, so that the tube blank material flows evenly into the cavity. By replenishing the material, the wall thickness of the tube is ensured to be ≤10%.

[0010] In one feasible implementation, the push plate no longer needs to be replenished during the pressure holding and shaping process. The tube is pressed and bulged to fit the mold, ensuring the dimensional accuracy of the parts is ±0.2mm.

[0011] In one feasible implementation, a polyethylene film is wrapped around the outside of the straight tube to be processed before the tube is installed in the bulging mold.

[0012] In one feasible implementation, the working area of ​​the straight tube to be processed corresponds to the arc-shaped cavity in the bulging mold.

[0013] In one feasible implementation, the bulging medium comprises pure water and / or steel balls.

[0014] In one feasible implementation, the bulging die is provided with a springback compensation of 0.3 mm to 0.7 mm.

[0015] In one feasible implementation, the diameter of the thin-walled tube is φ≥160mm; the thickness is δ≤1mm.

[0016] According to the present invention, a multi-segment continuous bending and forming device for high-strength pipe with large diameter-to-thickness ratio is provided. The device includes: an upper bulging mold, a lower bulging mold, an upper mold, a lower mold, a straight pipe to be processed, a baffle, a push plate, and two sets of liquid-filled core molds. The upper bulging mold is set inside the upper mold, and the lower bulging mold is set inside the lower mold. The straight tube to be processed is set between the upper bulging mold and the lower bulging mold. The baffle contacts or abuts one end of the straight tube to be processed, and the push plate contacts or abuts the other end of the straight tube to be processed. The two sets of liquid-filled core molds cooperate with the inner wall of the straight tube to be processed to form a working area. The tail ends of the two sets of liquid-filled core molds pass through the baffle and the push plate respectively and slide with them. One of the liquid-filled core molds has a channel that allows the expansion medium to be delivered from the outside into the working area.

[0017] In one feasible implementation, dynamic sealing rings are provided on the outer walls of the two sets of liquid-filled mandrels that are in contact with the inner wall of the straight pipe to be processed; Heating components are provided inside the upper and lower bulging molds.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. By using internal liquid filling, this invention reduces internal scratches on pipes caused by traditional molds and increases the internal support pressure of large-diameter (φ≥160mm) thin-walled (δ≤1mm) pipes, thereby effectively reducing the risk of wrinkling and improving product forming quality.

[0019] 2. This invention utilizes a composite forming technology that combines "extrusion forming to control wall thickness" and "bulging forming to control dimensions." It features lateral auxiliary material pushing, resulting in a low material thinning rate while maintaining dimensional accuracy. The wall thickness reduction is ≤10%, and the dimensional accuracy is ±0.2mm, achieving coordinated control of "wall thickness and dimensional accuracy."

[0020] 3. This invention addresses the problem of instability during the forming process of large-diameter thin-walled bent pipes. By progressively loading pressure, it avoids the formation of suspended areas. The surface of the pipe after expansion and extrusion is molded and shaped, improving the molding accuracy of the formed parts and reducing springback. In addition, the pipe includes an elbow area, a transition area, and a straight edge area, enabling the overall forming of bent pipes with straight edge sections.

[0021] 4. The overall mold of this invention adopts an interchangeable structure. For bends of different sizes, only the bulging mold and the liquid filling core mold need to be replaced, thereby reducing costs and improving interchangeability.

[0022] 5. The formed parts of this invention include an elbow area, a transition area, and a straight edge area, which can realize the overall forming of a bend with a straight edge section. At the same time, the liquid-filled core mold is a movable structure, realizing "one mold for multiple parts" of a long pipe, and realizing the one-time processing of multiple bends through subsequent cutting, which greatly improves processing efficiency and saves energy and has low power consumption. Attached Figure Description

[0023] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram illustrating the overall device of the present invention; Figure 2 This is a schematic diagram of the overall device that mainly embodies the pre-filling stage of the present invention; Figure 3 This is a schematic diagram of the overall device for the pipe bending and forming stage of the present invention. Figure 4 This is a schematic diagram of the assembly structure of another location on the straight pipe to be processed, which is the main embodiment of the present invention; Figure 5 The main feature of this invention is the multiple segmented connecting bends after molding; Figure 6 This invention primarily focuses on the cut parts product; Figure 7 This is a schematic diagram illustrating the principle of liquid-filled expansion and extrusion composite molding in this invention. Figure 8 This is a schematic diagram illustrating the bulging pressure and axial displacement loading of the present invention. Figure 9 This invention primarily demonstrates the simulation of product part dimensions and provides physical images.

[0024] Figure label: Detailed Implementation

[0025] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0026] Example 1 like Figures 1 to 9 As shown, a method for continuous bending and forming of a large-diameter-to-thickness high-strength tube according to the present invention includes the following steps: Pipe Installation: Install the upper bulging mold 1 inside the upper mold 3, and the lower bulging mold 2 inside the lower mold 4. Then, place the straight pipe 5 to be processed between the upper bulging mold 1 and the lower bulging mold 2, and close the molds. Specifically, before installing the straight pipe 5 to be processed inside the bulging mold, wrap a polyethylene film around the outside of the straight pipe 5. Push two sets of liquid-filled core molds 8 into designated positions inside the straight pipe 5 from one end of the pipe to be processed. The two sets of liquid-filled core molds 8 cooperate with the inner wall of the straight pipe 5 to form a working area. Dynamic sealing rings are provided on the outer walls of the two sets of liquid-filled core molds 8 that contact the inner wall of the straight pipe 5 to be processed, and lubricant is evenly applied to the dynamic sealing rings. One of the liquid-filled core molds 8 has a channel that allows the bulging medium to be sent into the working area from the outside. A baffle 6 is placed at one end of the straight pipe 5 to be processed, and a push plate 7 is pressed onto the other end of the straight pipe 5 to be processed. The tail ends of the two sets of liquid-filled core molds 8 protrude from the baffle 6 and the push plate 7, respectively. Specifically, the designated position of the straight tube 5 to be processed, i.e., the position of the working area, corresponds to the arc-shaped cavity in the bulging mold. The movement of the liquid-filled core mold 8 within the straight tube 5 to be processed can be achieved by sliding the liquid-filled core mold 8 directly through the action of a hydraulic forming cylinder, a pneumatic cylinder, or an electric cylinder on the tail end of the liquid-filled core mold 8.

[0027] Pre-filling: An expansion medium is injected into the working area through the channel on the liquid-filling core mold 8 at a pressure of P, completing the filling of the gaps in the working area of ​​the straight pipe 5 to be processed. The push plate 7 moves inward a first distance, causing the straight pipe 5 to be processed to undergo extrusion deformation. After deformation, the material enters the cavity of the expansion mold, causing the pipe to undergo expansion and extrusion composite, lasting for a first preset time. It should be noted that the push plate 7 can be driven linearly by a cylinder, hydraulic cylinder, or other driving component. In one feasible embodiment, the first distance is 2mm; the first preset time is 20 seconds. Since the part is a thin-walled pipe with a large diameter-to-thickness ratio, pre-filling ensures internal support during pipe bending and prevents cracking due to low pressure. For straight pipes that are difficult to deform, an expansion medium consisting of steel balls and liquid is used. During the pre-filling process, the straight pipe 5 to be processed undergoes slight deformation in the working area, facilitating subsequent pipe bending.

[0028] Pipe bending forming: A bulging pressure P is set to apply pressure to the working area inside the straight pipe 5 to be processed, and at the same time, the pusher plate 7 further applies a lateral thrust F to the straight pipe 5 to be processed. Under the support of the bulging pressure P, as the pusher plate 7 moves laterally, the pipe is further bulged and extruded to form a composite shape, which continues for a second preset time. After the bulging and extrusion composite shape is completed, the inside of the pipe is held under pressure P, and the pressure is gradually increased to P-shaping to form the inside of the pipe. During the pressure holding and shaping process, the pusher plate 7 no longer moves to replenish material. The pipe is pressed and bulged to fit the mold, ensuring the dimensional accuracy of the part is ±0.2mm. In one feasible embodiment, the second preset time is 5 seconds, P 保压 =15MPa, holding time 5 seconds, P 整形 =40MPa, forming time is 5 seconds. Subsequent bulging ensures the part can be formed, prevents wrinkling when thin-walled parts are bent, and holding pressure and forming achieve precision control of the part and prevent springback.

[0029] Unloading: Unload pressure P to separate the upper mold 3 and lower mold 4. Designed for thin-walled parts with a large diameter-to-thickness ratio, low-pressure feeding and bulging prevent cracking, while high-pressure shaping improves accuracy to prevent defects such as cracking, wrinkling, and springback.

[0030] Next processing step of moving core mold: After placing the other processing position of the straight tube 5 to be processed between the upper bulging mold 1 and the lower bulging mold 2, close the mold and push the two sets of liquid-filled core molds 8 into the interior of the other processing position. Repeat the pre-filling, tube bending and unloading operations to complete the bulging and extrusion composite forming operation of the other processing position.

[0031] Cutting: Remove all tooling and cut the formed pipe to achieve the processing of multiple bends.

[0032] It should be noted that the diameter of the thin-walled tube in this application is φ≥160mm; the thickness is δ≤1mm. The working area at the designated position of the straight tube 5 to be processed includes the elbow area, transition area, and straight edge area, which can realize the integral forming of the bend with a straight edge section. It should be further noted that the bulging die includes an upper bulging die 1 and a lower bulging die 2. In one feasible implementation, the displacement of the pusher plate 7 is controlled in conjunction with the pressure. During pre-filling, the pressure is 0 and the displacement of the pusher plate 7 is 2mm. As the expansion pressure increases to 15MPa, the displacement of the pusher plate 7 increases to 7mm, so that the tube blank material flows evenly into the cavity. By replenishing the material, the wall thickness of the tube is ensured to be ≤10%.

[0033] In a preferred embodiment, the bulging die is provided with a springback compensation of 0.3 mm to 0.7 mm, preferably 0.5 mm, which effectively reduces the springback deformation of the part after the combined bulging and extrusion unloading, and achieves effective precision control.

[0034] In one feasible implementation, the forming medium includes purified water and / or steel balls. It should be noted that the forming medium in this application can be purified water, or a mixture of steel balls and purified water. When processing straight pipes that are not easily deformable, such as high-temperature alloy pipes, titanium alloy pipes, and other straight pipes with high inherent strength, conventional hydraulic forming and pneumatic forming techniques are difficult to use. The preferred technical solution of this application uses a mixture of steel balls and purified water as the forming medium. First, the steel balls are fed into the working area. During pre-filling, two liquid-filled mandrels 8 can be driven to move towards each other, squeezing the steel balls to form a pre-pressure P pre-filling, causing the straight pipe 5 to undergo initial minor deformation. After deformation, the material enters the cavity of the forming mold, causing the pipe to undergo expansion and extrusion composite, lasting for a first preset time. It should be noted that during the squeezing of the steel balls, an appropriate amount of purified water can be added to prevent the straight pipe from being wrinkled. In the subsequent pressurization process, the two liquid-filled mandrels 8 can be driven to move towards each other to squeeze the mixture of steel balls and water, or pressurization can be achieved by injecting purified water. It should be further explained that when steel balls are used as the expansion medium, the steel balls can be placed at the same time as the liquid-filled core mold 8 is placed in the designated position of the straight tube 5 to be processed. During the movement of the liquid-filled core mold 8, the steel balls are pushed into the working area of ​​the designated position of the straight tube 5 to be processed.

[0035] In this application's technical solution, the bulging mold is a detachable structure, employing a modular mold design that allows for stacking. The structure is tailored to different pipe size requirements, thereby reducing costs and improving interchangeability. The liquid-filled core mold 8 is a movable structure, its dimensions adjusted according to different pipe size requirements. By moving the liquid-filled core mold 8 within the mold cavity, "one mold, multiple parts" for long pipes can be achieved, and subsequent cutting enables the one-time processing of multiple pipe bends.

[0036] According to the present invention, a multi-segment continuous bending and forming device for large diameter-to-thickness pipes is provided. The device includes: an upper bulging mold 1, a lower bulging mold 2, an upper mold 3, a lower mold 4, a straight pipe to be processed 5, a baffle 6, a push plate 7, and two sets of liquid-filled core molds 8. The upper mold 3 and the lower mold 4 can be opened and closed by mechanical equipment.

[0037] An upper bulging mold 1 is set inside an upper mold 3, and a lower bulging mold 2 is set inside a lower mold 4. The straight tube 5 to be processed is placed between the upper bulging mold 1 and the lower bulging mold 2. A baffle 6 contacts or abuts one end of the straight tube 5 to be processed, and a pusher plate 7 contacts or abuts the other end of the straight tube 5 to be processed. Two sets of liquid-filled core molds 8 cooperate with the inner wall of the straight tube 5 to be processed to form a working area. The tail ends of the two sets of liquid-filled core molds 8 pass through the baffle 6 and the pusher plate 7 respectively and slide with them. The technical solution of this application can use sliding bearings to achieve the sliding cooperation between the tail ends of the liquid-filled core molds 8 and the baffle 6 and the pusher plate 7. Both sets of liquid-filled core molds 8 and the pusher plate 7 can be driven by hydraulic cylinders, pneumatic cylinders or electric cylinders to move along the central axis of the straight tube 5 to be processed.

[0038] One of the liquid-filled core molds 8 has a channel that allows the forming medium to be fed into the working area from the outside. Dynamic sealing rings are provided on the outer walls of both sets of liquid-filled core molds 8 that contact the inner wall of the straight pipe 5 to be processed. Heating components 9 are provided inside the upper forming mold 1 and the lower forming mold 2, allowing the straight pipe 5 to be processed to be heated during the bulging and extrusion compound forming operation. The heating components 9 include electric heating rods.

[0039] In processing high-strength pipes that are difficult to form, such as high-temperature alloy pipes and titanium alloy pipes, the technical solution of this application can heat the straight pipe 5 to be processed by the heating component 9 and drive two liquid-filled mandrels 8 to move towards each other, squeezing steel balls to form a pre-pressure P for pre-filling. This causes the straight pipe 5 to undergo preliminary micro-deformation. After deformation, the material enters the cavity of the bulging mold and is then hydraulically bulged, achieving the goal of first forming the most difficult part to form, and then hydraulically shaping to achieve local trimming. Furthermore, in the pre-filling stage, pre-forming is achieved through heating and steel ball extrusion, with a deformation of 80%. Then, liquid filling (for thin-walled steel pipes) or heating and gas filling (for even more difficult-to-form high-temperature alloys and titanium alloys) is used to achieve fine shaping. In the technical solution of this application, different process methods can be selected according to different materials. Liquid-filled cold forming is used for easily formable stainless steel, while heating and gas filling forming is used for high-temperature alloys and titanium alloys.

[0040] Compared to traditional welding processes, the significance of this invention lies in: The integral forming process reduces weld seams and improves product precision and reliability. It breaks through the manufacturing bottleneck of traditional processes constrained by "thin walls and large diameter-to-thickness ratio", realizing the overall flexible processing of the conduit. It effectively solves defects such as wrinkling and distortion, and improves dimensional accuracy from 2mm to 0.5mm, significantly improving product reliability.

[0041] The technology improves processing efficiency by over 50%, shortening the supply chain and development cycle. Based on this technology, the overall bent tube structure changes the traditional model of aerospace product structural design and manufacturing, significantly simplifying the production process. It reduces the traditional conduit manufacturing process from 14 steps to 7, shortening the supply chain and development cycle, accelerating component production and system integration, and improving processing efficiency by over 40%. This provides technical support for promoting the efficient development of aerospace products.

[0042] This invention integrates and applies a variety of advanced technologies, utilizing a composite forming technology that combines "extrusion forming to control wall thickness" and "pressure bulging to control dimensions" to achieve coordinated control of "wall thickness and dimensional accuracy" in the thin-walled tube bending process of aircraft. This is a powerful measure to achieve high overall reliability manufacturing.

[0043] Example 2 Based on Example 1, such as Figures 1 to 4 As shown, according to the present invention, a method for continuous bending and forming of a large diameter-to-thickness pipe in multiple segments is provided, such as... Figure 1 As shown, the inner cavity depth of the upper bulging mold 1 is greater than that of the lower bulging mold 2. The inner cavity of the bulging mold is a complete arc surface with uniform curvature. The inner cavity of the lower bulging mold 2 gradually deepens from the side closer to the push plate 7 to the side farther away from the plate, then gradually becomes shallower until it is flush with the straight line segment, then gradually deepens again, and then gradually becomes shallower again.

[0044] Example 3 Based on Embodiment 1, according to the present invention, a multi-segment continuous bending and forming method for large diameter-to-thickness pipes is provided. A heating component 9 is added to the mold to achieve local heating of the bent pipe, which is used to meet the bending forming of difficult-to-form parts such as high-temperature alloys. The liquid medium is changed to hydraulic oil to prevent water from vaporizing after heating.

[0045] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0046] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for continuous bending and forming of multi-segment high-strength tubes with large diameter-to-thickness ratio, characterized in that, Includes the following steps: Pipe installation: Install the upper bulging mold (1) inside the upper mold (3), and the lower bulging mold (2) inside the lower mold (4). Then place the straight pipe (5) to be processed between the upper bulging mold (1) and the lower bulging mold (2) and close the mold. Push the two sets of liquid-filled core molds (8) into the designated position inside the straight pipe (5) from one end of the straight pipe (5) to be processed. The two sets of liquid-filled core molds (8) cooperate with the inner wall of the straight pipe (5) to be processed to form a working area. One of the liquid-filled core molds (8) has a channel that allows the bulging medium to be sent into the working area from the outside. Place a baffle (6) at one end of the straight pipe (5) to be processed and press a push plate (7) at the other end of the straight pipe (5) to be processed. The tail ends of the two sets of liquid-filled core molds (8) pass through the baffle (6) and the push plate (7) respectively. Pre-filling: Inject the expansion medium into the working area through the channel on the liquid filling core mold (8) at a pressure of P to pre-fill and complete the filling of the gap in the working area of ​​the straight pipe (5) to be processed; the push plate (7) moves inward by a first distance to cause the straight pipe (5) to be processed to be squeezed and deformed. After deformation, the material enters the cavity of the expansion mold, causing the pipe to undergo expansion and extrusion composite for a first preset time. Pipe bending forming: Set the bulging pressure P to pressurize and bulge the working area inside the straight pipe (5) to be processed. At the same time, the push plate (7) further applies a lateral thrust F to the straight pipe (5) to be processed. Under the support of the bulging P, as the push plate (7) moves laterally, the pipe is further bulged and extruded to form a composite shape for a second preset time. After the bulging and extrusion composite shape is completed, the inside of the pipe is pressure-held P and the pressure is gradually increased to P-shaped to pressurize and shape the inside of the pipe. Unloading: Unload pressure P and separate the upper mold (3) and lower mold (4); Next processing step of moving core mold: After placing the other processing position of the straight tube (5) to be processed between the upper bulging mold (1) and the lower bulging mold (2), close the mold and push the two sets of liquid-filled core molds (8) into the interior of the other processing position. Repeat the pre-filling, tube bending and unloading operations to complete the bulging and extrusion composite forming operation of the other processing position. Cutting: Remove all tooling and cut the formed pipe to achieve the processing of multiple bends; The displacement of the pusher plate (7) is controlled in conjunction with the pressure. When the pressure is 0 during pre-filling, the displacement of the pusher plate (7) is 2mm. As the expansion pressure increases to 15MPa, the displacement of the pusher plate (7) increases to 7mm, so that the tube blank material flows evenly into the cavity. The wall thickness of the tube is ≤10% by replenishing the material.

2. The method for continuous bending and forming of a large-diameter-to-thickness high-strength tube in multiple segments according to claim 1, characterized in that, During the pressure holding and shaping process, the push plate (7) no longer adds material. The tube is attached to the mold by applying pressure and expanding, ensuring the dimensional accuracy of the parts is ±0.2mm.

3. The method for continuous bending and forming of a large-diameter-to-thickness high-strength pipe in multiple segments according to claim 1, characterized in that, Before installing the straight tube (5) to be processed into the bulging mold, wrap a polyethylene film around the outside of the straight tube (5) to be processed.

4. The method for continuous bending and forming of a large-diameter-to-thickness high-strength pipe in multiple segments according to claim 1, characterized in that, The working area of ​​the straight tube (5) to be processed corresponds to the arc cavity in the bulging mold.

5. The method for continuous bending and forming of large-diameter-to-thickness high-strength pipes in multiple segments according to claim 1, characterized in that, The bulging medium includes pure water and / or steel balls.

6. The method for continuous bending and forming of a large-diameter-to-thickness high-strength pipe in multiple segments according to claim 1, characterized in that, The springback compensation of the bulging die is set to 0.3mm to 0.7mm.

7. The method for continuous bending and forming of a large-diameter-to-thickness high-strength pipe in multiple segments according to claim 1, characterized in that, The diameter of the thin-walled tube is φ≥160mm; the thickness is δ≤1mm.

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