Variable size three-dimensional space bending forming apparatus and method for titanium alloy double-walled tube

Abstract

The application discloses a variable-size three-dimensional space bending forming device and method for a titanium alloy double-wall pipe, and belongs to the technical field of pipe bending forming. The device integrates electric pulse heating, insulation protection and internal support functions, and the core comprises a bending die provided with a mica insulation ring, a multi-stage insulation guide mechanism and a ceramic particle filling structure between the inner pipe and the outer pipe. Meanwhile, a space curved surface bending forming process method suitable for the titanium alloy double-wall pipe is provided. During the forming process, the double-wall pipe is continuously fed in the axial direction, the bending die moves according to a preset space curved surface track, and pulse current is applied to the pipe, so that the whole pipe is softened by Joule heat. By adjusting the length of the forming area and the internal support state, the deformation process can be accurately controlled, the springback, cross-section distortion and wall slip are effectively inhibited, the problems of insulation and forming precision in the multi-degree-of-freedom electric heating bending of the double-wall pipe are solved, and the device is suitable for high-quality manufacturing of complex space curved surface components.

Description

Technical Field

[0001] This invention belongs to the field of metal tube bending and forming processing, and specifically relates to a variable-size three-dimensional spatial bending and forming device and method for titanium alloy double-walled tubes. Background Technology

[0002] Three-dimensional free bending forming technology is widely used in the manufacturing of high-precision structural components such as aerospace engine pipelines, lightweight automotive body frames, ship piping systems, and nuclear power plant main pipelines. During the bending forming process, defects such as cross-sectional deformation, wrinkling, distortion, and even cracking often occur. A well-designed mandrel filling device can effectively improve the bending forming effect.

[0003] Electrically pulsed assisted forming achieves dynamic softening of materials through the Joule heating effect, effectively reducing the deformation resistance of titanium alloys and suppressing springback. Existing electrically assisted bending technologies for double-walled tubes are mostly used for bending around surfaces, which is insufficient for complex spatial forming requirements. For electrically pulsed assisted three-dimensional free-space curved surface bending of titanium alloy double-walled tubes, both the inner and outer tubes must simultaneously meet conductivity and insulation requirements under energized conditions. The electrothermal path is complex, and the curvature changes continuously during the spatial curved surface bending process. Patent CN107008787B is only applicable to free-space curved surface bending of single-walled tubes and does not involve double-walled tubes or electrically pulsed assisted forming. Although CN116475281A proposes an electrically heated device for double-walled tubes, it is only applicable to bending around surfaces and does not address the insulation design and spatial curved surface forming issues under free bending conditions for double-walled tubes. Current technologies generally lack a conductivity-insulation synergistic free bending forming structure suitable for double-walled tubes, and there is no dedicated process method for free-space curved surface bending of double-walled tubes. Directly using single-layer tube forming schemes easily leads to problems such as current failure, short circuits, or forming instability. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a variable-size three-dimensional spatial bending forming device and method for titanium alloy double-walled tubes, so as to solve the problems of cross-sectional distortion, springback and equipment insulation that are prone to occur when titanium alloy double-walled spatial curved tubes are bent in three-dimensional space.

[0005] The technical solution of this invention is: a variable-size three-dimensional spatial bending forming device for titanium alloy double-walled tubes. This forming device includes: a double-walled tube electrically heated unit, a bending die unit, a bending die unit, a fixing die unit, and a fixing die base unit, wherein: The double-walled tube electric heating unit connects the titanium alloy double-walled tube to a pulse power supply. During the bending and forming process of the titanium alloy double-walled tube, a high-frequency electric pulse is applied to heat the double-walled tube, softening the material of the double-walled tube. The bending die unit acts on the outer wall of the titanium alloy double-walled tube to achieve plastic bending and forming of the titanium alloy double-walled tube. The bending die holder unit is used to support and guide the bending die unit, forming a spherical fit with the bending die unit to constitute a rotatable spherical pair; it can move in multi-dimensional space, providing the bending die unit with three-dimensional motion freedom; Fixed mold base unit, used to rigidly fix the fixed mold unit; The fixed mold unit, located at the front end of the bending mold base unit, serves to guide and position the double-walled tube to be formed. The relative motion between the bending die unit and the fixed die unit enables continuous bending of the titanium alloy double-walled tube at any angle and curvature. Both the bending die unit and the fixing die unit integrate multi-layer insulation structures to isolate the double-walled tube heating unit from other metal parts in the forming device, thereby achieving local dynamic heating and thermo-mechanical coupling forming of the double-walled tube.

[0006] Preferably, the double-walled tube electric heating unit includes a front limiting unit, a rear limiting unit, and a steel wire rope. The front limiting unit and the rear limiting unit are connected by a steel wire rope passing through the inner tube of the double-walled tube. The front limiting unit and the rear limiting unit are electrically connected to both ends of the double-walled tube, so that the positive and negative poles of the pulse power supply can be connected to both ends of the double-walled tube respectively, and the double-walled tube can be electrically heated as a whole.

[0007] Preferably, the front limiting unit includes a front limiting sleeve, a locking sleeve, and a set screw, and the rear limiting unit includes a rear limiting sleeve and a round nut; The front and rear limit sleeves are identical in shape, forming a cylindrical structure. Each cylinder has a central through hole, and an annular blind hole is located on the outer side of the through hole for inserting into the wall of the double-walled tube to limit the gap between the inner and outer tubes. The inner and outer tubes of the double-walled tube are coaxial. The steel wire rope passes through the central through hole at one end of the front limit sleeve and is locked by a locking device and a set screw. The other end passes through the central through hole of the rear limit sleeve and is fixed by a round nut. Both the front and rear limit sleeves have power connectors and fixing screws on their sides for connecting the electrodes of the power supply.

[0008] Preferably, the variable-size three-dimensional spatial bending forming device further includes a filling unit, which is placed between the inner and outer tubes of the double-walled tube to keep the gap between the inner and outer tubes consistent during the bending process of the double-walled tube, prevent cross-sectional distortion, wrinkling or collapse of the double-walled tube during bending, and ensure forming quality.

[0009] Preferably, the filling unit is ceramic particles with a particle size of 0.5~2 mm.

[0010] Preferably, the bending die holder unit includes a front spherical bearing, a rear spherical bearing, and a bending die holder, wherein the front spherical bearing and the rear spherical bearing are fixed to the bending die holder; The rear spherical bearing adopts a split design, consisting of two upper and lower half bearings, which facilitates the assembly and disassembly of the bending die. The front and rear spherical bearings are aligned and assembled to ensure coaxiality. The spherical grooves inside the bearings are adapted to the outer contour of the bending die unit, providing the bending die unit with three-dimensional motion freedom and achieving radial positioning.

[0011] Preferably, the bending die unit includes a bending die, a stepped insulating mica ring, and an inner ring of the bending die; Inside the bending die, from the outside to the inside, a stepped insulating mica ring is coaxially installed with the inner ring of the bending die. The bending die, the stepped insulating mica ring, and the inner ring of the bending die are fixed by ceramic screws. The stepped mica ring bears the axial shear stress while achieving insulation between the bending die and the inner ring of the bending die, and at the same time, it avoids the ceramic screws from being affected by overload stress and thus prevents them from being disassembled.

[0012] Preferably, the fixed mold unit includes a front guide insulating mica ring, a fixed mold, a rear guide insulating mica ring, an inner guide insulating mica pad, a guide insulating mica ring, a guide sleeve, and an end cap; One end of the fixed mold has a spherical structure on the outside, which is used to cooperate with the spherical surface of the bending mold to realize multi-angle rotational movement; the other end is rigidly locked to the fixed mold base unit through a threaded-flange composite connection. The guide sleeve passes through the inside of the fixed mold and is coaxially fitted with the fixed mold. The guide sleeve is fitted over the double-walled tube and is used to guide the unformed double-walled tube. A front guide insulating mica ring, a rear guide insulating mica ring, and an inner guide insulating mica pad are provided between the guide sleeve and the fixed mold to achieve reliable insulation between the guide sleeve and the fixed mold. The end cap has an internal thread that mates with the external thread at the tail end of the guide sleeve, allowing for adjustment of the axial position of the guide sleeve through the threaded connection. A guide insulating mica ring is embedded between the end cap and the fixed mold to form an electrical isolation layer.

[0013] Preferably, the fixed mold base unit is an annular structure with a through hole, the central through hole of which mates with the fixed mold unit and is installed together with the fixed mold by fixing bolts; during assembly, the fixed mold is first inserted into the through hole of the fixed mold base unit for positioning, and then locked with the fixing bolts through the threaded hole to form a stable connection.

[0014] Another technical solution of the present invention is: a method for spatial curved surface bending forming of a titanium alloy double-walled tube, the method comprising the following steps: Titanium alloy double-walled tubes are installed in a three-dimensional free bending tube device, and a supporting medium is filled between the inner and outer tubes; While the titanium alloy double-walled tube is continuously fed axially along the Z direction, the bending die is controlled to move in the XOY plane perpendicular to the feeding direction, so that the bending die performs spatial bending of the double-walled tube according to the preset spatial curved surface trajectory. During the bending process of the titanium alloy double-walled tube, a pulsed current is applied to the double-walled tube, and the forming area is locally heated and softened by the electrothermal effect, thus completing the spatial curved surface bending forming of the double-walled tube.

[0015] Preferably, the motion trajectory of the bending die is as follows: Starting from the initial position O with an eccentricity of 0, the movement proceeds upwards along the Y-axis to a position with an eccentricity of 0 in the Y-axis. Position, then deflected N times, from Position movement to X-axis eccentricity Position, the first deflection and pause forms a complete single-turn space curve length L, each subsequent deflection and pause forms half a space curve length L / 2, the bending die moves to the X-axis eccentricity. After reaching the position, it returns to the initial position O without stopping, moving in a straight line.

[0016] Preferably, the length L of the single-loop spatial curved surface is:

[0017] Where D is the diameter of the target spatial curved tube, and S is the pitch.

[0018] Preferably, the eccentricity in the Y direction for:

[0019] in, Let A be the bending radius of the target spatial curved surface tube, and let A be the distance between the center of the bending mold and the front end of the fixed mold unit.

[0020] Preferably, the movement starts from the initial position O where the eccentricity is 0, and moves upward along the Y-axis to the point where the eccentricity in the Y-axis is 0. Location Time And the offset in the Y direction The formula for calculating the dwell time t2 is:

[0021]

[0022] in, The Z-axis feed speed of the pipe. The angular velocity of the bending mold about the initial point O; Preferably, for a spatial curved surface tube with a total number of spatial curved surface loops of n, the number of deflections N and the deflection angle for each deflection are... for:

[0023]

[0024] Preferably, the time required for the bending die to rotate around point O for the first time and their corresponding stay time The time required for each subsequent rotation around point O and their corresponding stay time The following relationship must be satisfied to ensure that the feed length matches the length of the forming space curve:

[0025]

[0026] in, .

[0027] Preferably, the distance between the center of the bending die and the front end of the fixed die unit is determined by the following steps: S1. Set the initial distance between the center of the bending die and the front end of the fixed die unit; S2. A three-dimensional bending model is established using the finite element method, and iterative simulation calculations of finite element simulation forming are performed to obtain the diameter D' and pitch S' of the spatial curved tube cylinder. S3. Introduce a correction coefficient k to correct the distance between the center of the bending die and the front end of the fixed die unit. Continuously adjust the value of the correction coefficient k and repeat step S2 until the error between the diameter D' and pitch S' of the spatial curved tube cylinder formed by the finite element simulation and the target values ​​D and S is less than 1%. in: A'=kA; A' is the distance between the corrected bending die center and the front end of the fixed die unit, and A is the distance between the corrected bending die center and the front end of the fixed die unit. At this point, the corresponding correction coefficient k is the optimal correction coefficient. Based on the optimal correction coefficient, the distance A' between the center of the bending die and the front end of the fixed die unit is obtained.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention achieves dynamic adjustment of the forming zone length and process optimization: Through the threaded connection design, the position of the guide sleeve can be easily adjusted, thereby precisely controlling the range of the plastic deformation zone of the pipe. This allows for active optimization of the bending angle, radius of curvature, and forming accuracy, and can adapt to the forming requirements of different pipes. Combined with the local softening effect of the electric pulse, this design effectively improves the stress distribution during bending, suppresses springback and cross-sectional distortion, and solves the problems of poor flexibility and low precision of traditional fixed molds.

[0029] (2) This invention constructs a safe and reliable high-voltage electrical isolation system: by integrating multi-layer insulation structures (such as mica rings and mica pads), an effective insulation barrier is established between the pipe fittings and the metal structure of the pipe bending machine. This ensures that the electrical pulse current can be safely and centrally used to heat the pipe fittings, completely avoiding the risk of short circuit caused by current leakage to the equipment body, thus successfully integrating the electrical pulse assisted heating technology safely into the free pipe bending process. Attached Figure Description

[0030] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the free bending of the electric pulse double-walled spatial curved tube in a specific embodiment of the present invention; Figure 2 This is a schematic diagram of the bending die structure of the free bending forming device in a specific embodiment of the present invention; Figure 3 This is a cross-sectional view of the basic structure of the electric pulse free bending forming device in a specific embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the bending principle of the electric pulse free bending forming device in a specific embodiment of the present invention; Figure 5 This is a schematic diagram of the structure of the rear spherical bearing in a specific embodiment of the present invention; Figure 6 This is a schematic diagram of the bending die in a specific embodiment of the present invention; Figure 7 This is a schematic diagram of the stepped insulating mica ring in a specific embodiment of the present invention; Figure 8 This is a schematic diagram of the inner ring of the bending mold in a specific embodiment of the present invention; In the diagram: 1. Bending die base unit; 11. Front spherical bearing; 12. Rear spherical bearing; 2. Bending die base; 3. Bending die unit; 31. Bending die; 32. Stepped insulating mica ring; 33. Inner ring of bending die; 34. Ceramic screw; 4. Fixed die unit; 41. Front guide insulating mica ring; 42. Fixed die; 43. Rear guide insulating mica ring; 44. Inner guide insulating mica pad; 45. Fixing bolt; 5. Fixed die base unit; 6. Guide insulating mica ring; 7. End cap; 8. Inner guide sleeve; 9. Double-walled tube; 10. Double-walled tube energized heating unit; 101. Front limit sleeve; 102. Locking device; 103. Steel wire rope; 104. Locking screw; 105. Front power connector; 106. Rear limit sleeve; 107. Rear power connector; 108. Round nut. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] To make the technical problems, solutions, and advantages of this invention clearer, a detailed and complete description will be provided below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0033] like Figures 1-4 As shown, in an illustrative embodiment of the variable-size three-dimensional space titanium alloy double-walled tube electric pulse assisted bending forming device and method of the present invention, the variable-size three-dimensional space titanium alloy double-walled tube electric pulse assisted bending forming device includes: double-walled tube electric heating unit 10, filling unit, bending mold base unit 1, bending mold unit 3, fixing mold unit 4, fixing mold base unit 5 and end cap 7. The double-walled tube electric heating unit connects the titanium alloy double-walled tube to a pulse power supply. During the bending and forming process of the titanium alloy double-walled tube, a high-frequency electric pulse is applied to heat the double-walled tube, which softens the material of the double-walled tube, reduces the deformation resistance, improves the forming performance, and ensures that heating and bending are synchronized.

[0034] The bending die unit acts on the outer wall of the titanium alloy double-walled tube to achieve plastic bending and forming of the titanium alloy double-walled tube; the surface is designed according to the target bending radius, has good insulation, prevents current short circuit, and ensures efficient transmission of electrical pulses.

[0035] The bending die holder unit 1 is used to support and guide the bending die unit, forming a spherical fit with the bending die unit to constitute a rotatable spherical pair, enabling the bending die to rotate adaptively around the contact point, reducing friction and improving forming accuracy and surface quality; the bending die holder unit can move in multi-dimensional space, providing the bending die unit with three-dimensional motion freedom; The fixed mold base unit serves as the overall structural support base, used to rigidly fix the mold unit and ensure the stability and safety of the system under high loads and dynamic currents.

[0036] The fixed mold unit, located at the front end of the bending mold base unit 1, is used to guide and position the double-walled tube to be formed; The relative motion between the bending die unit and the fixed die unit enables continuous bending of the titanium alloy double-walled tube at any angle and curvature. Both the bending die unit and the fixing die unit integrate multi-layer insulation structures to isolate the double-walled tube heating unit from other metal parts in the forming device, thereby achieving local dynamic heating and thermo-mechanical coupling forming of the double-walled tube.

[0037] like Figure 3 As shown, the double-walled tube electric heating unit 10 includes a front limiting unit, a rear limiting unit, and a steel wire rope 103. The front limiting unit and the rear limiting unit are connected by the steel wire rope 103 passing through the inner tube of the double-walled tube. The front limiting unit and the rear limiting unit are electrically connected to both ends of the double-walled tube 9, so that the positive and negative poles of the pulse power supply can be connected to both ends of the double-walled tube 9 respectively, and the double-walled tube 9 can be electrically heated as a whole.

[0038] The front limiting unit includes a front limiting sleeve 101, a locking device 102, a locking screw 104, a front power connector 105, and a fixing screw. The rear limiting unit includes a rear limiting sleeve 106, a round nut 108, a rear power connector 107, and a fixing screw.

[0039] The front and rear limit sleeves are identical in shape, forming a cylindrical structure. Each cylinder has a central through hole, and an annular blind hole is located on the outer side of the through hole for inserting into the wall of the double-walled tube to limit the gap between the inner and outer tubes. The inner and outer tubes of the double-walled tube are coaxial. The steel wire rope passes through the central through hole at one end of the front limit sleeve and is locked by the locking device 102 and the set screw 104. The other end passes through the central through hole of the rear limit sleeve and is fixed by a round nut. Both the front and rear limit sleeves have power connectors and fixing screws on their sides for connecting the electrodes of the power supply.

[0040] The power connector and fixing screws connect to the power source; the round nut 108 is used to fix and adjust the position of the handle at the end of the wire rope 103. The entire unit is used to connect the power source to heat the double-walled tubes. The filling unit is placed between the inner and outer tubes of the double-walled tube to keep the gap between the inner and outer tubes consistent during the bending process of the double-walled tube, preventing cross-sectional distortion, wrinkling or collapse during bending of the double-walled tube, and ensuring forming quality.

[0041] The filling unit preferably uses ceramic particles with a particle size of 0.5 to 2 mm or an equivalent heat-resistant filling medium.

[0042] like Figure 4 As shown, the bending die unit 1 is installed at the key rotating part of the bending system, supporting and guiding the bending die unit. Its angle can be freely adjusted in multi-dimensional space to adapt to complex three-dimensional bending requirements. The bending die unit 1 includes a front spherical bearing, a rear spherical bearing, and a bending die. The front spherical bearing 11 and the rear spherical bearing 12 are fixed to the bending die unit 2 by hexagonal bolts and washers. like Figure 5As shown, the rear spherical bearing 12 adopts a split design, consisting of two upper and lower half bearings assembled together, which facilitates the assembly and disassembly of the bending die 31. The front spherical bearing 11 and the rear spherical bearing 12 are aligned and assembled to ensure coaxiality. The spherical groove inside them matches the outer contour of the bending die 31, providing the bending die 31 with three-dimensional freedom of movement and achieving radial positioning.

[0043] like Figures 6-8 As shown, the bending die unit 3 includes a bending die 31, a stepped insulating mica ring 32, an inner ring of the bending die 33, and a ceramic screw 34.

[0044] The bending die 31 is mounted within the spherical bearing unit 1 via a spherical pair, enabling multi-angle rotation. Inside, from the outside in, an insulating mica ring 32 and a bending die inner ring 33 are coaxially mounted. The bending die, the stepped insulating mica ring, and the bending die inner ring are fixed by ceramic screws 34. The stepped mica ring 32, while bearing the main axial shear stress, provides reliable insulation between the bending die 31 and the bending die inner ring 33, preventing the ceramic screws 34 from being affected by overload stress and hindering disassembly. The fixed mold unit 4 includes a front guide insulating mica ring 41, a fixed mold 42, a rear guide insulating mica ring 43, an inner guide insulating mica pad 44, a guide insulating mica ring 6, a guide sleeve 8, an end cap 7, and a fixing bolt 45. One end of the fixed mold 43 has a spherical structure on the outside, which is used to cooperate with the spherical surface of the bending mold to realize multi-angle rotational motion; the other end is rigidly locked to the fixed mold base unit 5 through a threaded-flange composite connection. The guide sleeve passes through the inside of the fixed mold and is coaxially fitted with the fixed mold. The guide sleeve 8 is fitted on the outside of the double-walled tube and is used to guide the unformed double-walled tube. A front guide insulating mica ring 41, a rear guide insulating mica ring 43, and an inner guide insulating mica pad 44 are provided between the guide sleeve and the fixed mold to achieve reliable insulation between the guide sleeve and the fixed mold. The end cap 7 has an internal thread in its inner hole, which mates with the external thread at the tail end of the guide sleeve 8. The axial position of the guide sleeve 8 can be flexibly adjusted through the threaded connection. Specifically, rotating the end cap can precisely adjust the extension and retraction of the inner guide sleeve, so that the length of the forming area can be flexibly adjusted to adapt to different specifications and process requirements.

[0045] The guide insulating mica ring 6 is embedded between the end cap and the fixed mold, forming an electrical isolation layer to ensure insulation between the two. This structure balances the adjustability of the guide sleeve 8 position with the insulation safety of the rotating parts under electrical pulse conditions.

[0046] The fixed mold base unit is a ring structure with a through hole. Its central through hole mates with the fixed mold unit and is installed together with the fixed mold by fixing bolts. During assembly, the fixed mold is first inserted into the through hole of the fixed mold base unit for positioning, and then locked with the fixing bolts through the threaded hole to form a stable connection. This double constraint structure ensures working stability and facilitates quick assembly and disassembly. In some embodiments, the stepped insulating mica ring 32, the guiding insulating mica ring, and the inner guiding insulating mica pad 44 are all made of mica material, which has both excellent insulation performance and sufficient compressive strength, and is easy to install and disassemble.

[0047] In some embodiments, after the double-walled tube fitting 9 to be processed and filled is installed, the positive and negative terminals of the pulse power supply are electrically connected to both ends of the double-walled tube 9 through the front and rear limiting units, respectively. This allows the pulse current to pass through the tube along the axial direction of the double-walled tube 9 to form a closed loop, thus providing overall energization and heating to the double-walled tube 9. This results in a uniformly distributed temperature field along the tube length during the bending process. During the bending process, the electric pulse system applies a high-frequency pulse current to the fitting to achieve overall thermal softening of the material and simultaneously performs three-dimensional free bending. At the same time, an infrared thermometer monitors the surface temperature of the tube in real time to monitor and regulate the energization and heating process, thereby improving the material's plasticity and reducing forming defects such as cracking, wrinkling, and springback during the bending process.

[0048] In particular, before experimental or production applications, it is essential to ensure that the mica insulation components are installed in the correct position. If necessary, a multimeter can be used to monitor whether the main body of the equipment is insulated from the power supply device.

[0049] In summary, the forming device provided by this invention achieves continuous bending of pipe fittings at arbitrary angles and curvatures through the relative movement of an adjustable bending die and a fixed die unit. Its integrated multi-layer insulation structure effectively isolates the electric pulse heating system from the metal parts of the pipe bending machine, ensuring electrical safety and enabling localized dynamic heating and thermo-mechanical coupling forming of the pipe fittings. Simultaneously, by filling the double-walled pipe with ceramic particles or equivalent heat-resistant filling media with a particle size of 0.5~2 mm to provide internal support, combined with the adjustable die structure, high-precision forming of complex variable curvature paths for thin-walled, high-strength pipe fittings is achieved.

[0050] The present invention will now be described in further detail regarding the spatial curved surface bending forming method for titanium alloy double-walled tubes, including the following steps: 1) Install the titanium alloy double-walled tube in the three-dimensional free bending tube equipment and fill the space between the inner and outer tubes with a supporting medium; 2) While continuously feeding the titanium alloy double-walled tube axially along the Z direction, control the bending die to move in the XOY plane perpendicular to the feeding direction, so that the bending die performs spatial bending of the double-walled tube according to the preset spatial curved surface trajectory. 3) During the bending process of the titanium alloy double-wall tube, a pulsed current is applied to the double-wall tube to locally heat and soften the forming area using the electrothermal effect, thereby completing the spatial curved surface bending forming of the double-wall tube.

[0051] By adjusting the eccentricity of the bending die, the motion trajectory, and the length of the forming zone, spatial curved surface bending forming with different pitches and diameters can be achieved; The pipe is fed at a constant speed along the Z-axis, and the bending die moves in the XY plane perpendicular to the feeding direction. The trajectory of the bending die is as follows: Starting from the initial position O with an eccentricity of 0, the movement proceeds upwards along the Y-axis to a position with an eccentricity of 0 in the Y-axis. Position, then deflected N times, from Position movement to X-axis eccentricity Position, the first deflection and pause forms a complete single-turn space curve length L, each subsequent deflection and pause forms half a space curve length L / 2, the bending die moves to the X-axis eccentricity. After reaching the position, it returns to the initial position O without stopping, moving in a straight line.

[0052] Its specific motion trajectory and process parameters are analyzed and calculated according to the following steps: Step 1: Determine basic bending parameters: Based on the cylindrical diameter D and pitch S of the target spatial curved surface tube, calculate the bending radius R and the length L of a single turn of the spatial curved surface line.

[0053]

[0054] Calculate the eccentricity in the Y direction based on the bending radius R and the distance A between the center of the bending die and the front end of the fixed die unit. The bending die moves from its initial position to... The time t1 at the position and the dwell time t2 at that position (used to form the initial semicircular arc):

[0055]

[0056]

[0057] in, The Z-axis feed speed of the pipe. Let ω be the angular velocity of the bending mold around the initial point O.

[0058] The second step is to determine the deflection strategy of the bending modulus: For a spatial surface tube with a total number of spatial surface turns of n, the bending modulus deflects from... Position movement to X-axis eccentricity During the positioning process, the number of deflections (N) and the deflection angle for each rotation are required. for:

[0059]

[0060] After each deflection, the bending die needs to remain in place for a period of time to allow the tube to form the corresponding spatial curve segment. The first deflection and pause forms a complete spatial curve length L, and each subsequent deflection and pause forms half a spatial curve length L / 2.

[0061] The third step is to calculate the deflection and dwell time: set the bending die to rotate around point O each time. The time required to angle is (First time) or (Subsequent times), the corresponding stay time is or They must satisfy the following relationship to ensure that the feed length matches the length of the forming space curve:

[0062]

[0063] in, .

[0064] Step 4, Bending die return: The bending die moves to the X-axis eccentricity. Location( After that, without stopping, it immediately returns to the initial position O along a straight line within time t3. The return time t3 is determined according to the speed of the equipment.

[0065] Step 5: Modification and iteration of process parameters: Due to nonlinear factors such as springback in actual forming, the theoretical parameters need to be corrected.

[0066] S1. Set the initial distance between the center of the bending die and the front end of the fixed die unit; S2. A three-dimensional bending model is established using the finite element method, and iterative simulation calculations of finite element simulation forming are performed to obtain the diameter D' and pitch S' of the spatial curved tube cylinder. S3. Introduce a correction coefficient k to correct the distance between the center of the bending die and the front end of the fixed die unit. Continuously adjust the value of the correction coefficient k and repeat step S2 until the error between the diameter D' and pitch S' of the spatial curved tube cylinder formed by the finite element simulation and the target values ​​D and S is less than 1% (i.e., |D'-D| / D<1% and |S'-S| / S<1%). in: A'=kA; A' is the distance between the corrected bending die center and the front end of the fixed die unit, and A is the distance between the corrected bending die center and the front end of the fixed die unit. At this point, the corresponding correction coefficient k is the optimal correction coefficient. Based on the optimal correction coefficient, the distance A' between the center of the bending die and the front end of the fixed die unit is obtained.

[0067] Step 6, Actual Forming: All process parameters calculated using the final correction factor k', including U... y ,t1,t2,N, , ,t f ,t n ,t ff ,t nn By inputting the data into a three-dimensional free bending device, the actual bending and forming of a spatial curved tube can be performed. Among them, U... y t represents the Y-direction displacement of the bending mold center. f t n t ff t nn These are the motion time parameters for the corresponding stages.

[0068] The above description represents the preferred embodiments of the present invention. Finally, it should be noted that those skilled in the art should understand that improvements and modifications can be made to the technical solutions of the present invention without departing from the technical solutions described herein, and such improvements and modifications should also be considered within the scope of protection of the present invention.

[0069] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A variable-size three-dimensional spatial bending forming device for titanium alloy double-walled tubes, characterized in that... include: The unit comprises a double-walled tube electric heating unit, a bending die unit (1), a bending die unit (3), a fixed die unit (4), and a fixed die unit (5), wherein: The double-walled tube electric heating unit connects the titanium alloy double-walled tube to a pulse power supply. During the bending and forming process of the titanium alloy double-walled tube, a high-frequency electric pulse is applied to heat the double-walled tube, softening the material of the double-walled tube. The bending die unit acts on the outer wall of the titanium alloy double-walled tube to achieve plastic bending and forming of the titanium alloy double-walled tube. The bending die base unit (1) is used to support and guide the bending die unit, and forms a spherical fit with the bending die unit to constitute a rotatable spherical pair; it can move in multi-dimensional space, providing three-dimensional motion freedom for the bending die unit. Fixed mold base unit, used to rigidly fix the fixed mold unit; The fixed mold unit, located at the front end of the bending mold base unit (1), is used to guide and position the double-walled tube to be formed; The relative motion between the bending die unit and the fixed die unit enables continuous bending of the titanium alloy double-walled tube at any angle and curvature. Both the bending die unit and the fixing die unit integrate multi-layer insulation structures to isolate the double-walled tube heating unit from other metal parts in the forming device, thereby achieving local dynamic heating and thermo-mechanical coupling forming of the double-walled tube.

2. The variable-size three-dimensional spatial bending forming device for titanium alloy double-walled tubes according to claim 1, characterized in that: The double-walled tube electric heating unit includes a front limiting unit, a rear limiting unit and a steel wire rope. The front limiting unit and the rear limiting unit are connected by a steel wire rope passing through the inner tube of the double-walled tube. The front limiting unit and the rear limiting unit are electrically connected to both ends of the double-walled tube (9) respectively, so that the positive and negative poles of the pulse power supply can be connected to both ends of the double-walled tube (9) respectively, and the double-walled tube (9) can be electrically heated as a whole.

3. The variable-size three-dimensional spatial bending forming device for titanium alloy double-walled tubes according to claim 1, characterized in that: The bending die unit includes a front spherical bearing, a rear spherical bearing, and a bending die, with the front and rear spherical bearings fixed to the bending die. The rear spherical bearing adopts a split design, consisting of two half bearings assembled together, which facilitates the assembly and disassembly of the bending die. The front and rear spherical bearings are aligned and assembled to ensure coaxiality. The spherical grooves inside them are adapted to the outer contour of the bending die unit, providing the bending die unit with three-dimensional motion freedom and achieving radial positioning.

4. The variable-size three-dimensional spatial bending forming device for titanium alloy double-walled tubes according to claim 1, characterized in that: The bending die unit includes a bending die, a stepped insulating mica ring, and an inner ring of the bending die; Inside the bending die, from the outside to the inside, a stepped insulating mica ring is coaxially installed with the inner ring of the bending die. The bending die, the stepped insulating mica ring, and the inner ring of the bending die are fixed by ceramic screws. The stepped mica ring bears the axial shear stress while achieving insulation between the bending die and the inner ring of the bending die, and at the same time, it avoids the ceramic screws from being affected by overload stress and thus prevents them from being disassembled.

5. The variable-size three-dimensional spatial bending forming device for titanium alloy double-walled tubes according to claim 1, characterized in that: The fixed mold unit (4) includes a front guide insulating mica ring (41), a fixed mold (42), a rear guide insulating mica ring (43), an inner guide insulating mica pad (44), a guide insulating mica ring (6), a guide sleeve (8), and an end cap (7). One end of the fixed mold (42) is provided with a spherical structure to cooperate with the spherical surface of the bending mold to realize multi-angle rotational motion; the other end is rigidly locked to the fixed mold base unit (5) through a threaded-flange composite connection. The guide sleeve passes through the inside of the fixed mold and is coaxially fitted with the fixed mold. The guide sleeve (8) is fitted on the outside of the double-walled tube and is used to guide the unformed double-walled tube. A front guide insulating mica ring (41), a rear guide insulating mica ring (43), and an inner guide insulating mica pad (44) are provided between the guide sleeve and the fixed mold to achieve reliable insulation between the guide sleeve and the fixed mold. The end cap (7) has an internal thread in its inner hole, which engages with the external thread at the tail end of the guide sleeve (8), and the axial position of the guide sleeve (8) is adjusted through the threaded connection. The guide insulating mica ring (6) is embedded between the end cap and the fixed mold to form an electrical isolation layer.

6. A method for variable-size three-dimensional spatial bending forming of titanium alloy double-walled tubes, characterized in that, Includes the following steps: Titanium alloy double-walled tubes are installed in a three-dimensional free bending tube device, and a supporting medium is filled between the inner and outer tubes; While the titanium alloy double-walled tube is continuously fed axially along the Z direction, the bending die is controlled to move in the XOY plane perpendicular to the feeding direction, so that the bending die performs spatial bending of the double-walled tube according to the preset spatial curved surface trajectory. During the bending process of the titanium alloy double-walled tube, a pulsed current is applied to the double-walled tube, and the forming area is locally heated and softened by the electrothermal effect, thus completing the spatial curved surface bending forming of the double-walled tube.

7. The variable-size three-dimensional spatial bending forming method for the titanium alloy double-walled tube according to claim 6, characterized in that: The motion trajectory of the bending die is as follows: Starting from the initial position O with an eccentricity of 0, the movement proceeds upwards along the Y-axis to a position with an eccentricity of 0 in the Y-axis. Position, then deflected N times, from Position movement to X-axis eccentricity Position, the first deflection and pause forms a complete single-turn space curve length L, each subsequent deflection and pause forms half a space curve length L / 2, the bending die moves to the X-axis eccentricity. After reaching the position, without stopping, return to the initial position O along a straight line; Y-axis eccentricity for: in, Let A be the bending radius of the target spatial curved tube, and let A be the distance between the center of the bending mold and the front end of the fixed mold unit; Starting from the initial position O with an eccentricity of 0, the movement proceeds upwards along the Y-axis to a position with an eccentricity of 0 in the Y-axis. Location Time And the offset in the Y direction The formula for calculating the dwell time t2 is: in, The Z-axis feed speed of the pipe. Let ω be the angular velocity of the bending mold around the initial point O.

8. The variable-size three-dimensional spatial bending forming method for titanium alloy double-walled tubes according to claim 7, characterized in that: For a spatial surface tube with a total number of spatial surface loops of n, the number of deflections N and the deflection angle per cycle are... for: 。 9. The variable-size three-dimensional spatial bending forming method for titanium alloy double-walled tubes according to claim 7, characterized in that: Time required for the bending die to rotate around point O for the first time and their corresponding stay time The time required for each subsequent rotation around point O and their corresponding stay time The following relationship must be satisfied to ensure that the feed length matches the length of the forming space curve: in, .

10. The variable-size three-dimensional spatial bending forming method for titanium alloy double-walled tubes according to claim 7, characterized in that: The distance between the center of the bending die and the front end of the fixed die unit is determined by the following steps: S1. Set the initial distance between the center of the bending die and the front end of the fixed die unit; S2. A three-dimensional bending model is established using the finite element method, and iterative simulation calculations of finite element simulation forming are performed to obtain the diameter D' and pitch S' of the spatial curved tube cylinder. S3. Introduce a correction coefficient k to correct the distance between the center of the bending die and the front end of the fixed die unit. Continuously adjust the value of the correction coefficient k and repeat step S2 until the error between the diameter D' and pitch S' of the spatial curved tube cylinder formed by the finite element simulation and the target values ​​D and S is less than 1%. in: A'=kA; A' is the distance between the corrected bending die center and the front end of the fixed die unit, and A is the distance between the corrected bending die center and the front end of the fixed die unit. At this point, the corresponding correction coefficient k is the optimal correction coefficient. Based on the optimal correction coefficient, the distance A' between the center of the bending die and the front end of the fixed die unit is obtained.

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