Composite forming device and method based on pipe necking and bulging
By employing a composite forming method combining tube narrowing and bulging, the problem of forming nozzles with extremely small wall thicknesses has been solved, enabling efficient and low-cost nozzle manufacturing. This method is suitable for curved surface structural components with variable wall thickness, such as rocket engines.
Patent Information
- Application Number
- CN202510992450.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-18
- Publication Date
- 2025-10-28
AI Technical Summary
Existing technologies are difficult to efficiently form nozzles with extremely small wall thickness and extreme thickness-to-diameter ratio. Spinning processes are prone to cracking defects, and additive manufacturing suffers from problems such as low forming efficiency and high machining difficulty.
A composite forming device and method based on pipe necking and bulging is adopted. By setting up a die and an expansion component, the thickness deformation is achieved in the necking stage using hydrostatic stress field, and the overall deformation is carried out in the bulging stage to improve the uniformity of wall thickness distribution.
It effectively avoids nozzle rupture defects, improves forming quality, is suitable for curved surface structures with variable wall thickness, reduces production costs and weight, and improves processing efficiency.
Smart Images
Figure CN120838947A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of pipe forming technology, and in particular to a composite forming apparatus and method based on pipe necking and bulging. Background Technology
[0002] The nozzle is a key structural component in rocket and missile engines, responsible for expelling high-temperature, high-pressure combustion gases and generating thrust. Its primary function is to accelerate and eject the high-temperature, high-pressure gases from the combustion chamber, thereby providing propulsion. Due to structural design constraints, nozzles typically feature a thicker wall at the smaller end near the gas inlet and a relatively thinner wall at the larger end near the exhaust outlet. This results in a typical variable-thickness, thin-walled curved surface component, with its cross-sectional profile often being a high-order curve. In addition to the dramatic changes in wall thickness, nozzles must also operate stably for extended periods in harsh environments characterized by extreme temperatures, high pressures, and strong corrosion.
[0003] Traditional nozzles are often formed using spinning, a process based on localized thinning deformation, capable of producing high-precision parts with a thickness-to-diameter ratio of less than 2%. However, with space missions such as the Chang'e lunar exploration and Mars exploration placing higher demands on structural weight reduction, next-generation nozzles need further reductions in thickness-to-diameter ratio and small-end / large-end diameter ratio. However, with further reductions in thickness-to-diameter ratio, the spinning process is more prone to fracture defects. Furthermore, because spinning is a localized, incremental forming process, a large stress gradient exists between the deformed and undeformed zones, easily inducing instability problems such as wrinkling. In addition, although some research has attempted to form nozzle structures using additive manufacturing, for nozzles with extremely small wall thicknesses and extreme thickness-to-diameter ratios, additive manufacturing faces bottlenecks such as low forming efficiency and high difficulty in subsequent machining. Therefore, there is an urgent need to research advanced forming methods more suitable for manufacturing nozzles with small thickness-to-diameter ratios. Developing nozzle forming technology that meets extreme dimensional requirements while possessing both high precision and high reliability has significant engineering implications and application prospects. Summary of the Invention
[0004] In view of this, the present invention proposes a composite forming device and method based on pipe necking and bulging. By setting up a die and an expansion component, and setting a necking section and a bulging section within the die, a hydrostatic stress field can be introduced through the expansion component during the necking stage, transforming the traditional "thinning deformation" into "thickening deformation." This allows the small end of the pipe to achieve stable thickening while effectively avoiding cracking defects. During the bulging stage, the expansion component with built-in flexible fluid medium can transform the traditional "local deformation" into "overall deformation," improving the uniformity of wall thickness distribution and enhancing the forming quality. It is particularly suitable for typical variable wall thickness curved surface structures such as rocket engine nozzles, exhibiting good engineering adaptability and broad application prospects.
[0005] The technical solution of the present invention is achieved as follows: On one hand, the present invention provides a composite forming device based on tube narrowing and bulging, comprising a die, a pressure head, and an expansion component, wherein, The die has a forming cavity, which includes a narrowing section and an expanding section. The expanding section is located on the opening side of the die, and the opening side of the die is used to insert the tube to be formed. The inner diameter of the narrowing section is smaller than the outer diameter of the tube to be formed, and the inner diameter of the expanding section is larger than the outer diameter of the tube to be formed. The pressure head is located on the side of the die with an opening and can move toward the die to push the tube to be formed into the constricted section; An expansion member is placed on the pressure head and filled into the tube to be formed. The expansion member conforms to the inner wall of the tube to be formed by deformation and applies pressure to the inner wall of the tube to be formed.
[0006] Based on the above technical solutions, preferably, the pressure head is provided with a flow channel, and the expansion member is provided with an interface, which is connected to the flow channel so that pressurized fluid can be introduced into the expansion member.
[0007] More preferably, the expansion member is a thin film bag structure to contain the pressurized liquid, the opening side of the expansion member is the interface, and the material of the expansion member is at least one of polyurethane and rubber.
[0008] Based on the above technical solutions, preferably, the inner wall cross-sections of the constricted section and the bulging section are both continuous arcs, and the connection between the constricted section and the bulging section is smoothly transitioned.
[0009] Based on the above technical solutions, preferably, the die is provided with a sealing head, which is located at the end of the narrowing section and forms the bottom wall of the forming cavity.
[0010] More preferably, the end cap has a through hole.
[0011] On the other hand, the present invention provides a composite forming method based on pipe necking and bulging, which is implemented by the aforementioned composite forming device based on pipe necking and bulging. The composite forming method based on pipe necking and bulging includes the following steps: Place one end of the tube to be formed at the connection between the constriction section and the expansion section, and hold the other end against the pressure head, and place the expansion member inside the tube to be formed. The pressure head moves toward the die and pushes the tube to be formed. During the movement of the tube to be formed, the expansion component applies pressure to the inner wall of the tube to be formed and, together with the necking section, necks one end of the tube to be formed. After one end of the formed tube matches the shape of the inner wall of the constricted section, pressure is maintained to obtain the intermediate tube; The expansion component applies expansion pressure to the inner wall of the intermediate pipe to cause expansion deformation in the portion of the intermediate pipe located in the expansion section; After the outer wall of the intermediate pipe abuts against the inner wall of the bulging section, pressure is maintained to form the target pipe fitting.
[0012] Based on the above technical solutions, preferably, before the tube to be formed is narrowed, basic parameters are set. The basic parameters include at least one of a first pressure loading parameter, a second pressure loading parameter, and a downward speed parameter. The first pressure loading parameter is used to control the expansion member to apply supporting pressure to the inner wall of the tube to be formed. The second pressure parameter is used to control the expansion member to apply expansion pressure to the inner wall of the intermediate tube. The downward speed parameter is used to control the pressing speed of the pressure head on the tube to be formed.
[0013] Based on the above technical solutions, preferably, before the tube to be formed is narrowed, the forming preparation is also included, which includes cleaning the tube to be formed and the inner wall of the forming cavity, and applying a lubricant.
[0014] Based on the above technical solutions, preferably, the method also includes setting axial strain threshold and circumferential strain threshold, and monitoring the pressure on the inner wall of the die during the processing of the tube to be formed. During the narrowing process, the loading pressure of the expansion component on the inner wall of the tube to be formed and the feed speed of the pressure head are adjusted according to the pressure monitoring data. During the bulging process, the loading pressure of the expansion component on the inner wall of the intermediate tube is adjusted according to the pressure monitoring data.
[0015] The composite forming apparatus and method based on pipe necking and bulging of the present invention have the following advantages over the prior art: (1) By setting up a die and an expansion component, and setting a narrowing section and an expansion section in the die, a hydrostatic stress field can be introduced through the expansion component during the narrowing stage, which transforms the traditional "thinning deformation" into "thickening deformation", so that the small end of the pipe can achieve stable thickening while effectively avoiding cracking defects. During the expansion stage, the expansion component with built-in flexible fluid medium can transform the traditional "local deformation" into "overall deformation", improve the uniformity of wall thickness distribution, and improve the forming quality. It is especially suitable for typical variable wall thickness curved surface structural parts such as rocket engine nozzles, and has good engineering adaptability and broad application prospects. (2) By setting a flow channel on the pressure head and setting an interface on the expansion part, the interface is connected to the flow channel so that pressure fluid can be introduced into the expansion part. For the injection of pressure fluid, i.e. pressure medium, other equipment, such as hydraulic pump station, is required. With this setting, pressure fluid can be injected into the expansion part without affecting the processing effect, and the required pressure can be adjusted to form a stroke static pressure support when the neck is narrowed and pressure deformation is carried out when the expansion is formed. (3) Before the operation, the pipe to be formed is cleaned by grinding the impurities on the surface of the pipe to be formed. This can prevent irregular friction of particles with the inner wall of the die forming cavity during the shrinking process. After grinding, alcohol or other cleaning agents are used to clean the pipe to ensure that it is smooth and free of pollution. This can prevent stress concentration during the deformation process, effectively improve the yield, reduce production costs, and improve work efficiency. Attached Figure Description
[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0017] Figure 1 This is a schematic diagram of the composite forming device based on pipe necking and bulging according to the present invention; Figure 2 This is a cross-sectional view of the composite forming device based on pipe necking and bulging according to the present invention; Figure 3 This is a schematic diagram of the pressure during the pipe forming process of the composite forming device based on pipe necking and bulging according to the present invention; Figure 4 This is a schematic diagram showing the before and after comparison of the pipe processed by the composite forming method based on pipe necking and bulging according to the present invention; Figure 5 This is a schematic diagram comparing the internal pressure of two different embodiments of the composite forming method based on pipe narrowing and bulging according to the present invention. Detailed Implementation
[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0019] like Figure 1-4 As shown, the composite forming device based on tube narrowing and bulging of the present invention includes a die 1, a pressure head 2 and an expansion member 3.
[0020] The die 1 is provided with a forming cavity 11, which includes a constriction section 111 and an expansion section 112. The expansion section 112 is located on the opening side of the die 1. The opening side of the die 1 is used to insert the tube to be formed. The inner diameter of the constriction section 111 is smaller than the outer diameter of the tube to be formed, and the inner diameter of the expansion section 112 is larger than the outer diameter of the tube to be formed. Specifically, when setting the die 1, its opening side can face upward and its bottom can be set on a worktable. Then, from top to bottom, the expansion section 112 and the constriction section 111 are arranged in sequence. When the tube to be formed is put into the forming cavity 11, it first enters the expansion section 112 and then the bottom end contacts the connection between the expansion section 112 and the constriction section 111. When the tube to be formed moves toward the constriction section 111 again, it means that the forming operation has started.
[0021] In some embodiments, it is necessary to monitor the pressure on the die 1. This pressure monitoring can be achieved by setting up distributed fiber optic sensors. Specifically, a micro-milling cutter can be used to create a fine groove under the inner surface of the forming cavity 11 of the forming die 1, with a depth of 0.5~1mm. Then, axial distributed fiber optic sensors, oblique distributed fiber optic sensors, and circumferential distributed fiber optic sensors are arranged along the axial direction, 45° direction, and circumferential direction of the tube to be formed, respectively. Only one sensor is arranged in the axial and 45° directions, and one sensor is arranged in the upper, middle, and lower parts of the die in the circumferential direction. The sensors are then encapsulated with high-temperature epoxy or ceramic adhesive to prevent them from moving or being damaged under stress. A lead wire channel is reserved to the outside of the die 1, thus completing the pre-embedding of the distributed fiber optic sensors in the forming die 1. The three-dimensional strain of the tube can be effectively reflected by the distributed fiber optic sensors in the three directions. Furthermore, since significant heat is generated during the necking process, and the distributed fiber optic sensor is sensitive to temperature, a temperature-compensated distributed fiber optic sensor needs to be arranged on the outside of the die using the same method. It should be noted that the distributed fiber optic sensor does not directly acquire the stress and strain during the deformation of the pipe, but rather infers the stress and strain of the pipe through the deformation of the die. This technical solution is not within the scope of this invention and will not be described in detail here.
[0022] The pressure head 2 is located on the side of the die 1 with an opening and can move toward the die 1 to push the tube to be formed into the narrowing section 111. The bottom of the pressure head 2 is set as a support surface to support the tube to be formed and push the tube to be formed into the narrowing section 111. In some embodiments, a press is set up to apply pressure for the narrowing process of the tube. The pressure head 2 can be installed on the slider of the press. The press applies pressure to the pressure head 2 and pushes the pressure head 2 toward the die 1. The tube to be formed can then be narrowed by the die 1 under this pressure. After using the press, the die 1 needs to be fixed to the main platform of the press. The materials of both the pressure head 2 and the die 1 can be Cr12 steel.
[0023] The expansion member 3 is placed on the pressure head 2 and filled into the tube to be formed. The expansion member 3 conforms to the inner wall of the tube to be formed by deformation and applies pressure to the inner wall of the tube to be formed. The expansion member 3 can be made of a film material, which has good deformation ability and can be filled into the inside of the tube to be formed to support the inner wall of the tube to be formed. Specifically, it can be used to assist in shaping or expanding the tube to be formed according to the pressure of the filling medium. The expansion member 3 can be fixed on the pressure head 2 or connected to the pressure head 2 in other ways. In use, the expansion member 3 is first placed in the tube to be formed, and then the tube to be formed is placed between the pressure head 2 and the die 1.
[0024] During the processing of the tube to be formed, by setting up a concave mold 1 and an expansion component 3, and by setting a narrowing section 111 and a bulging section 112 within the concave mold 1, a hydrostatic stress field can be introduced through the expansion component 3 during the narrowing stage. This transforms the traditional "thinning deformation" into "thickening deformation," allowing the small end of the tube to achieve stable thickening while effectively avoiding cracking defects. During the bulging stage, the expansion component 3, using a flexible fluid medium, can transform the traditional "local deformation" into "overall deformation," improving the uniformity of wall thickness distribution and enhancing the forming quality. This is particularly suitable for typical variable wall thickness curved surface structures such as rocket engine nozzles, exhibiting good engineering adaptability and broad application prospects.
[0025] In some embodiments, in order to allow the medium to enter the expansion member 3 and form a pressurized environment, a flow channel is provided on the pressure head 2. At the same time, an interface is provided on the expansion member 3, which communicates with the flow channel so that pressurized fluid can be introduced into the expansion member 3. It should be noted that the injection of pressurized fluid, i.e., pressurized medium, requires other equipment, such as a hydraulic pump station, and pressure regulation is performed through this equipment. The flow channel provided on the pressure head 2 can be connected to the hydraulic pump station pipeline. During use, it is necessary to prevent problems such as excessive pressure or excessively rapid pressure changes.
[0026] With this setup, static pressure support can be achieved on the inner wall of the pipe by injecting a pressure medium during the pipe narrowing stage, while the pipe can be bulged by increasing the pressure during the bulging stage.
[0027] The expansion member 3 is a thin film bag structure for containing pressurized liquid. The opening side of the expansion member 3 is the interface. The material of the expansion member 3 is at least one of polyurethane and rubber.
[0028] In addition to the components mentioned above, this device can also be equipped with a hydraulic pump station and a control console. The hydraulic pump station controls the internal pressure of the expansion component 3 to achieve static pressure support and expansion shaping, while the distributed fiber optic sensors are used to transmit the monitored pressure data to the control console for display and judgment.
[0029] In some specific embodiments, the inner wall cross-sections of the constricted section 111 and the bulging section 112 are both continuous arcs, and the connection between the constricted section 111 and the bulging section 112 is smoothly transitioned. The overall inner wall cross-section of the constricted section 111 and the bulging section 112 can also be a single arc. The specific design and selection can be made according to the required workpiece.
[0030] This design is because the tube structure shaping achieved through bulging cannot effectively form corners. The continuous arc design can improve the workpiece qualification rate and processing accuracy. At the same time, it can also save time for operations such as pressure holding after forming.
[0031] In some embodiments, the die 1 is provided with a sealing head 12, which is disposed at the end of the narrowing section 111 and forms the bottom wall of the forming cavity 11. The sealing head 12 forms a narrowing barrier at the bottom of the die 1, and when the tube to be formed contacts the sealing head 12, a certain pressure is applied to the tube to be formed, so as to prevent the tube to be formed from leaving the forming cavity 11 during the narrowing process.
[0032] In one specific embodiment, the sealing head 12 is provided with a through hole. The through hole can be used to gradually discharge the air inside the forming cavity 11 during the narrowing action, so as to avoid the air compression affecting the overall processing.
[0033] The composite forming method based on pipe necking and bulging of the present invention is realized by the above-mentioned composite forming device based on pipe necking and bulging. Specifically, it should also include a press, a hydraulic pump station and a control console. The press is used to provide downward pressure to the pressure head 2, the hydraulic pump station is used to control the internal pressure formed on the inner wall of the pipe to be formed by the expansion component 3, and the control console is used to monitor the overall processing.
[0034] In some embodiments, it is necessary to preset parameters, that is, set basic parameters before the tube to be formed is narrowed. The basic parameters include at least one of a first pressure loading parameter, a second pressure loading parameter, and a downward speed parameter. The first pressure loading parameter is used to control the expansion member 3 to apply supporting pressure to the inner wall of the tube to be formed. The second pressure parameter is used to control the expansion member 3 to apply expansion pressure to the inner wall of the intermediate tube. The downward speed parameter is used to control the pressing speed of the pressure head 2 on the tube to be formed. All these parameters are stored in the control console to achieve fine control.
[0035] In addition to the preset parameters, the device also needs to be prepared. The die 1 is fixed on the press, the pressure head 2 is connected to the press slide, and the expansion member 3 is connected to the hydraulic pump station. In addition, if a distributed fiber optic sensor is installed, its lead wire, which is set on the die 1 and reserved, needs to be connected to the control console.
[0036] The expansion component 3 can be made of polyurethane. Correspondingly, a pipe of the same material as the expansion component 3 needs to be installed in the flow channel of the pressure head 2. The pipe passes through the pressure head 2 and can be connected to the pipeline of the hydraulic pump station through a connection structure such as threads. The joint needs to be effectively sealed with an O-ring.
[0037] After the preparation work is completed, the workpiece can be processed. That is, before the tube to be formed is narrowed, forming preparation is required. The forming preparation includes cleaning the tube to be formed and the inner wall of the forming cavity 11, and applying lubricant.
[0038] In some embodiments, the tube to be formed needs to be cleaned first. The cleaning includes polishing off impurities on the surface of the tube to be formed to avoid irregular friction of particles with the inner wall of the forming cavity 11 of the die 1 during the shrinking process. After polishing, alcohol or the like can be used as a cleaning agent for cleaning. During the cleaning process, it is essential to ensure that the tube is smooth and free of contamination to avoid stress concentration during deformation. MoS grease or graphite lubricant is then evenly applied to the cleaned tube and the inner wall of the forming cavity 11 of the die 1 with a brush.
[0039] One end of the tube to be formed is placed at the connection between the constriction section 111 and the expansion section 112, and the other end is held against the pressure head 2, and the expansion member 3 is placed inside the tube to be formed. During the insertion of the tube to be formed, the process needs to be as smooth as possible.
[0040] The pressure head 2 moves toward the die 1 and pushes the tube to be formed. In this process, the press pushes the pressure head 2 to move according to the downward speed parameter. At the same time, the expansion member 3 applies support pressure to the inner wall of the tube to be formed. The support pressure is controlled by the first pressure loading parameter. The expansion member 3 cooperates with the narrowing section 111 to narrow one end of the tube to be formed.
[0041] After one end of the tube to be formed is consistent with the inner wall shape of the constricted section 111, pressure is maintained to obtain the intermediate tube. The pressure maintenance time can be selected as 5-30 minutes. Under the combined action of the axial thrust provided by the pressure head 2 and the internal pressure of the expansion component 3, the tube is gradually pressed into the forming die 1 to undergo plastic deformation, thereby completing the constriction forming process and forming the intermediate tube.
[0042] The expansion member 3 applies expansion pressure to the inner wall of the intermediate pipe to push the portion of the intermediate pipe located in the expansion section 112 to undergo expansion deformation.
[0043] After the outer wall of the intermediate pipe abuts against the inner wall of the bulging section 112, pressure is maintained to form the target pipe fitting. The pressure maintenance time is set to 20-80 minutes.
[0044] In some embodiments, the method further includes setting an axial strain threshold and a circumferential strain threshold, and monitoring the pressure on the inner wall of the die 1 during the forming process of the tube to be formed. During the narrowing process, the loading pressure of the expansion member 3 on the inner wall of the tube to be formed and the feeding speed of the pressure head 2 are adjusted according to the pressure monitoring data. During the bulging process, the loading pressure of the expansion member (3) on the inner wall of the intermediate tube is adjusted according to the pressure monitoring data.
[0045] In one specific embodiment, the tube to be formed is made of 304 stainless steel with the following specifications: outer diameter 50mm, wall thickness 1mm, and length 150mm. The die 1 is made of Cr12 steel, the expansion component 3 is made of polyurethane, and the pressure medium is water-based emulsion.
[0046] First, fix the forming die 1 onto the main platform of the press. Both the pressure head 2 and the forming die 1 are made of Cr12 steel. The material of the pipe to be formed is 304 stainless steel. Clean the impurities on the surface of the 304 stainless steel pipe by grinding and cleaning it with 100% alcohol. During the cleaning process, be sure to ensure that the pipe is smooth and free of contamination to avoid stress concentration during deformation. Apply MoS2 grease or graphite lubricant evenly to the cleaned pipe and die with a brush, and then slowly and steadily place them in the forming die 1.
[0047] The assembled pressure head 2 is smoothly placed on the upper end of the tube to be formed. The preload of the slider on the press is set, and it pushes the pressure head 2 downward at an initial speed of 2 mm / s. At the same time, the hydraulic pump station injects water-based emulsion with an initial pressure of 8.4 MPa into the expansion member 3 at a rate of 1 MPa / min according to the pre-set pressure loading curve, i.e., the first pressure loading parameter. Under the combined action of the axial thrust provided by the pressure head 2 and the internal pressure of the expansion member 3, the tube is gradually pressed into the forming die 1 and undergoes plastic deformation, thereby completing the necking forming process. During this process, the fiber optic sensor demodulator inputs the acquired strain into the Siemens S7-1200 PLC control system.
[0048] When the detected axial strain reaches 90% of the set threshold (axial strain threshold) (i.e., 0.054), it indicates that continued strain growth may cause wrinkling defects in the pipe along the axial direction. At this point, the PLC sends control commands to the servo driver via the Modbus communication protocol, controlling the servo electric cylinder to reduce the downward speed of the pressure head to 10% of the initial speed, thereby reducing the axial feed and preventing wrinkling. Specifically, using ABAQUS software, the critical wrinkling axial strain threshold of 0.06 was determined based on the dimensions of the pipe to be formed (outer diameter 50mm, wall thickness 1mm, length 150mm) and material (304 stainless steel). It should be noted that the initial pressure of the water-based emulsion, 8.4MPa, refers to the maximum internal pressure required to be applied when the pressure head 2 reaches its downward endpoint. Such a high internal pressure is not required during the initial downward phase of the pressure head. In fact, the relationship between the supporting internal pressure and the stroke of the pressure head 2 is approximately parabolic.
[0049] When the tapered tube contacts the bottom of the forming die 1, the main cylinder of the press stops moving, and the upper slide stops moving accordingly. The method for determining whether the tube has bottomed out is as follows: before the tube contacts the bottom of the die, the load on the pressure head 2 changes relatively smoothly with the stroke; however, once the tube bottoms out, continued pressing will cause the load to rise rapidly, resulting in a sudden change in the slope of the load-displacement curve. According to ABAQUS simulation, the pressure threshold corresponding to this load change is 10 kN. Combining the load change characteristics with this threshold, it is possible to effectively determine whether the tube has bottomed out.
[0050] The pressure holding stage then begins, lasting 10 minutes. After the pressure holding period, the computer control console issues a command, and the hydraulic pump station performs bulging loading according to the pre-set pressure loading curve (second pressure loading parameter), with a pressure rise rate of 2 MPa / min until the maximum internal pressure of 24 MPa is reached, and this pressure is maintained for 45 minutes to complete the bulging process. During the bulging process, the fiber optic sensor demodulator inputs the demodulated strain into the Siemens S7-1500 PLC. When the circumferential strain reaches 90% of the threshold (i.e., 0.279), it indicates that further increase in circumferential strain will lead to rupture. At this point, the PLC sends a control signal to the servo driver via Modbus communication. The servo driver controls the servo pump to maintain the hydraulic pressure at this value as the maximum internal pressure for 60 minutes, preventing rupture during the forming process.
[0051] Using ABAQUS software, the critical circumferential strain threshold for rupture was determined to be 0.31 based on the dimensions (outer diameter 60mm, wall thickness 1.5mm, length 140mm) and material (6061 aluminum alloy) of the tube to be formed (8). If the circumferential strain increases very slowly and the pressure remains unchanged, the pressure should be increased. If the circumferential strain tends to stabilize and the pressure rises, it indicates film adhesion. At this point, the servo pump should be controlled to maintain a constant hydraulic pressure to avoid local stress concentration or rupture.
[0052] After hydraulic bulging is completed, the pressure holding is stopped, and the formed pipe fitting is removed. The thickness-to-diameter ratio of the formed pipe fitting is reduced to 0.5%, and the diameter ratio is reduced to 35%.
[0053] In another specific embodiment, the tube to be formed is made of 6061 aluminum alloy with the following specifications: outer diameter 60mm, wall thickness 1.5mm, and length 140mm. The die 1 is made of D2 steel, the expansion component 3 is made of rubber, and the pressure medium is hydraulic oil.
[0054] Fix the forming die 1 onto the main platform of the press. The preparation steps are the same as in the previous embodiment, until the tube is slowly and steadily placed in the forming die 1.
[0055] The assembled pressure head 2 is smoothly placed on the upper end of the tube to be formed. The preload of the slider on the press is set, and it pushes the pressure head 2 downward at an initial speed of 2 mm / s. At the same time, the hydraulic pump station injects synthetic hydraulic oil with an initial pressure of 6 MPa into the expansion member 3 at a rate of 2 MPa / min according to the pre-set pressure loading curve. Under the combined action of the axial thrust provided by the pressure head 2 and the internal pressure of the soft film, the tube 8 is gradually pressed into the forming die 9 and undergoes plastic deformation, thus completing the necking forming process.
[0056] The load is applied in the following ways: Figure 3 As shown. During this process, the fiber optic sensor demodulator inputs the acquired strain to the Siemens S7-1500 PLC control system. When the detected axial strain reaches 90% of the set threshold (i.e., 0.045), it indicates that continued strain growth may cause wrinkling defects in the pipe along the axial direction. At this time, the PLC sends control commands to the servo driver via the Modbus communication protocol, controlling the servo electric cylinder to reduce the downward speed of the pressure head to 10% of the initial speed, so as to reduce the axial feed in time and avoid wrinkling. Among them, the critical axial strain threshold for wrinkling is determined to be 0.05 based on the dimensions of the pipe to be formed (outer diameter 60mm, wall thickness 1mm, length 140mm) and material (6061 aluminum alloy) using ABAQUS software. It should be noted that the initial pressure of the synthetic hydraulic oil of 6MPa refers to the maximum expansion internal pressure required when the pressure head 6 reaches the end of its downward movement. In the initial downward stage of the pressure head, such a high expansion pressure is not required. In fact, the relationship between the support internal pressure and the pressure head stroke is an approximate parabolic one.
[0057] When the tapered tube contacts the bottom of the forming die 1, the main cylinder of the press stops moving, and the upper slide stops moving accordingly. The method for determining whether the tube has bottomed out is as follows: before the tube contacts the bottom of the die, the load on the pressure head 2 changes relatively smoothly with the stroke; however, once the tube bottoms out, continued pressing will cause the load to rise rapidly, resulting in a sudden change in the slope of the load-displacement curve. According to ABAQUS simulation, the pressure threshold corresponding to this load change is 10 kN. Combining the load change characteristics with this threshold, it is possible to effectively determine whether the tube has bottomed out.
[0058] Then the pressure holding stage begins, which lasts for 10 minutes.
[0059] After the pressure holding period, the computer control console issues a command, and the hydraulic pump station performs bulging loading according to the pre-set pressure loading curve, with a pressure rise rate of 2 MPa / min until the maximum internal pressure of 24 MPa is reached, and this pressure is maintained for 45 minutes to complete the bulging process. During the bulging process, the fiber optic sensor demodulator inputs the demodulated strain into the Siemens S7-1500 PLC. When the circumferential strain reaches 90% of the threshold (i.e., 0.279), it indicates that further increase in circumferential strain will lead to rupture. At this time, the PLC sends a control signal to the servo driver via Modbus communication. The servo driver controls the servo pump to maintain the hydraulic pressure at the maximum internal pressure for 60 minutes to prevent rupture during the forming process. The critical circumferential strain threshold for rupture was determined to be 0.31 using ABAQUS software based on the dimensions (outer diameter 60 mm, wall thickness 1.5 mm, length 140 mm) and material (6061 aluminum alloy) of the tube to be formed. If the circumferential strain increases very slowly and the pressure remains unchanged, the pressure should be increased. If the circumferential strain tends to stabilize and the pressure rises, it indicates that the film is attached. At this time, the servo pump should be controlled to keep the hydraulic pressure constant to avoid local stress concentration or rupture.
[0060] After hydraulic bulging is completed, pressure holding is stopped, and the formed pipe is removed. The thickness-to-diameter ratio of the formed pipe is reduced to 0.5%, and the diameter ratio is reduced to 35%.
[0061] In summary, the expansion component 3 introduces additional hydrostatic stress during the combined forming process of necking and bulging. While the small end of the pipe is thickened and deformed, the large end can be stably thinned. After forming, the pipe wall thickness is more uniform and ideal, which greatly reduces the weight of the nozzle. Compared with the traditional process, it can reduce the weight by nearly 40% and reduce fuel consumption.
[0062] like Figure 5 As shown, when different pipe materials and specifications are selected, the stroke pressure parameters during the processing will change.
[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.
Claims
1. A composite forming device based on pipe necking and bulging, characterized in that, It includes a die (1), a pressure head (2), and an expansion component (3), wherein, The die (1) is provided with a forming cavity (11), which includes a narrowing section (111) and an expanding section (112). The expanding section (112) is located on the opening side of the die (1). The opening side of the die (1) is used to insert the tube to be formed. The inner diameter of the narrowing section (111) is smaller than the outer diameter of the tube to be formed, and the inner diameter of the expanding section (112) is larger than the outer diameter of the tube to be formed. The pressure head (2) is located on the side of the die (1) with an opening and can move toward the die (1) to push the tube to be formed into the constricted section (111). An expansion member (3) is placed on the pressure head (2) and filled into the tube to be formed. The expansion member (3) conforms to the inner wall of the tube to be formed by deformation and applies pressure to the inner wall of the tube to be formed.
2. The composite forming device based on tube narrowing and bulging as described in claim 1, characterized in that, The pressure head (2) is provided with a flow channel, and the expansion member (3) is provided with an interface. The interface is connected to the flow channel so that pressure fluid can be introduced into the expansion member (3).
3. The composite forming device based on tube narrowing and bulging as described in claim 2, characterized in that, The expansion member (3) is a thin film bag structure for containing pressurized liquid. The opening side of the expansion member (3) is the interface. The material of the expansion member (3) is at least one of polyurethane and rubber.
4. The composite forming device based on tube narrowing and bulging as described in claim 1, characterized in that, The inner wall cross-sections of the constricted section (111) and the bulging section (112) are both continuous arcs, and the connection between the constricted section (111) and the bulging section (112) is smoothly transitioned.
5. The composite forming device based on tube narrowing and bulging as described in claim 1, characterized in that, The die (1) is provided with a sealing head (12), which is located at the end of the narrowing section (111) and forms the bottom wall of the forming cavity (11).
6. The composite forming device based on tube narrowing and bulging as described in claim 5, characterized in that, The sealing head (12) has a through hole.
7. A composite forming method based on tube necking and bulging, characterized in that, The composite forming apparatus based on tube narrowing and bulging, as described in any one of claims 1-6, is used to achieve this. The composite forming method based on tube narrowing and bulging includes the following steps: Place one end of the tube to be formed at the connection between the constriction section (111) and the expansion section (112), and hold the other end against the pressure head (2), and place the expansion member (3) inside the tube to be formed; The pressure head (2) moves toward the die (1) and pushes the tube to be formed. During the movement of the tube to be formed, the expansion member (3) applies pressure to the inner wall of the tube to be formed and, together with the necking section (111), necks one end of the tube to be formed. After one end of the formed tube matches the shape of the inner wall of the constricted section (111), pressure is maintained to obtain the intermediate tube; The expansion member (3) applies expansion pressure to the inner wall of the intermediate pipe to push the part of the intermediate pipe located in the expansion section (112) to produce expansion deformation; After the outer wall of the intermediate pipe abuts against the inner wall of the bulging section (112), pressure is maintained to form the target pipe fitting.
8. The composite forming method based on tube necking and bulging as described in claim 7, characterized in that, Before the tube to be formed is narrowed, basic parameters are set. The basic parameters include at least one of a first pressure loading parameter, a second pressure loading parameter and a downward speed parameter. The first pressure loading parameter is used to control the expansion member (3) to apply support pressure to the inner wall of the tube to be formed. The second pressure parameter is used to control the expansion member (3) to apply expansion pressure to the inner wall of the intermediate tube. The downward speed parameter is used to control the pressing speed of the pressure head (2) on the tube to be formed.
9. The composite forming method based on tube necking and bulging as described in claim 7, characterized in that, Before the tube to be formed is narrowed, the forming preparation is also included, which includes cleaning the tube to be formed and the inner wall of the forming cavity (11) and applying a lubricant.
10. The composite forming method based on tube necking and bulging as described in claim 7, characterized in that, It also includes setting axial strain threshold and circumferential strain threshold, and monitoring the pressure on the inner wall of the die (1) during the processing of the tube to be formed. During the narrowing process, the loading pressure of the expansion component (3) on the inner wall of the tube to be formed and the feeding speed of the pressure head (2) are adjusted according to the pressure monitoring data. During the expansion process, the loading pressure of the expansion component (3) on the inner wall of the intermediate tube is adjusted according to the pressure monitoring data.