A heat pipe bending and forming jig and a design method thereof

Abstract

The application discloses a kind of heat pipe bending forming clamps and its design method, the clamp adopts modular assembly, including center mould, track type adjustable base and rolling mould, implementation method includes the following steps: first, design bending process experiment, determine heat pipe outer diameter, bending radius and other process parameters;Then complete the assembly of each module of clamp, including rolling mould, center mould and track type adjustable base;Then the wedge-shaped stretching clamp of single-direction stretching machine is used to fix one end of heat pipe;Immediately adjust base according to the position of heat pipe, so that heat pipe is attached to straight section groove wall surface;According to the process parameters such as bending radius determined, complete the selection of rolling mould movement track and bending angle;Finally, load is applied to the annular structure of rolling mould, so that it drives heat pipe to complete bending process experiment. The overall adjustable parameter range of the clamp is larger, and the bending process experiment of heat pipe with different outer diameters and different bending radii can be completed.

Description

Technical Field

[0001] This invention belongs to the field of precision tube plastic forming technology, and relates to a heat pipe bending forming fixture and its design method. Background Technology

[0002] As consumer electronics and aerospace equipment evolve towards higher integration and thinner designs, serious heat dissipation problems inevitably arise. Heat pipes, with their ultra-high heat flux density and adaptability to microgravity environments, have become a core component for solving the microscale heat dissipation dilemma. However, heat pipe bending and forming faces two major technical barriers. First, there are limitations imposed by material properties; commonly used thin-walled copper pipes inevitably experience springback and cross-sectional distortion after bending, leading to the collapse of the internal capillary structure. Second, heat pipes themselves are highly sensitive to defects; changes in wall thickness during bending and surface microcracks significantly reduce the fatigue life of the heat pipe.

[0003] To further study the heat pipe bending forming mechanism, it is necessary to simulate the heat pipe bending forming process based on finite element simulation platforms such as ABAQUS, establish a multi-body coupled finite element model of heat pipe bending, and analyze the stress and strain state of the heat pipe. To ensure the prediction accuracy of the material model, bending process experiments are an essential verification step. An existing device for bending forming pipes with large bending radius and large bending angle (CN222767039U) mainly includes: a bending die, an upper die cover, a clamp, a limiting die, a clamp baffle, a gimbal, a base, and a roller conveyor. The basic working principle is as follows: one end of the pipe is fixed to the cavity where the inner edge end cover of the bending die mates with the upper die cover; the limiting die moves to the inner edge end cover of the die via a chain and fits tightly against the pipe, then is clamped by the gimbal clamp; the operating table starts the motor to drive the bending die to rotate and the limiting die to move synchronously, ultimately bending the pipe into the target part. While this device is suitable for processing pipes with large bending radii, its lack of real-time stress-strain monitoring and high manufacturing cost significantly limit its application in the bending forming research of small-radius heat pipes. An existing bending die (CN111318598A) for rectangular pipes mainly includes a bending die, inserts, clamping dies, pressing dies, and anti-wrinkle blocks. Its basic principle is to solve the cross-sectional instability and distortion caused by excessive clamping force during bending of rectangular pipes by internally filling the die. Analysis shows that this die system cannot monitor parameter changes in the heat pipe bending forming process in real time, nor can it be adapted to the forming of circular cross-section heat pipes. Therefore, in summary, the development of dedicated equipment for heat pipe bending forming experiments is still lacking, and traditional bending equipment has limitations in the heat pipe forming process. First, its die structure adopts a fixed single-arc surface design, making it difficult to flexibly adapt to different bending radii and pipe diameter requirements, thus limiting forming accuracy. Second, the experimental system lacks real-time stress-strain monitoring capabilities, failing to provide complete data support for process optimization. In addition, although high-precision CNC pipe bending equipment has certain processing capabilities, its application in heat pipe bending experiments is limited by cost and small radius processing capabilities. Summary of the Invention

[0004] This invention addresses the specific needs of heat pipe bending process experiments by designing and developing a multifunctional adjustable special fixture. This fixture, integrated with a unidirectional stretching machine, constructs a complete experimental platform for pipe plastic forming. Its advantages are twofold: First, the modular mold design allows for rapid replacement of different mold components and motion trajectory parameters, accurately simulating various pipe bending conditions. Second, because the fixture is based on the unidirectional stretching machine platform and integrates a high-precision sensor array, it can detect and record bending torque, load, and other data in real time, significantly improving the integrity and traceability of experimental data. This provides efficient experimental research equipment for studying heat pipe forming mechanisms and optimizing processes.

[0005] The present invention is achieved by at least one of the following technical solutions.

[0006] A heat pipe bending forming fixture includes a rolling die, a center die, and an adjustable track base;

[0007] The central mold includes a clamping slider, a central mold base, a straight section groove, and a circular section groove. The central mold base and the circular section groove are fixedly connected by a connector. The straight section groove is fixed on the base by the clamping slider. The heat pipe is located in the semicircular groove of the clamping slider and the semicircular groove of the straight section groove.

[0008] The rolling die includes a double-ended stud, a first track, a rolling die, a second track, and a locking component. The first and second tracks are provided with multiple tracks. The double-ended stud passes through the internal through hole of the locking component and its two ends are inserted into the arc-shaped through holes of the first and second tracks. The rolling die is installed on the locking component and is located between the first and second tracks. The surface of the rolling die is in contact with the surface of the heat pipe.

[0009] The adjustable track base includes a shaft connector, a guide rail, and a slider base. The shaft connector is located on the surface of the guide rail and is fixed to the unidirectional stretching machine through the shaft connector. The slider base is located on the guide rail, and the center mold base, the first track, and the second track are fixed on the slider base.

[0010] Furthermore, the surface of the central mold base is provided with a groove, and the protrusion of the straight section groove is located in the groove.

[0011] Furthermore, the central mold base has a U-shaped structure, and the two sides of the central mold base, as well as the first and second tracks, are fixed to the slider base.

[0012] Furthermore, one end of the rolling mold is provided with multiple equidistant through holes, through which the locking component passes.

[0013] Furthermore, an annular structure is provided at the top of the end of the rolling die away from the through hole to connect to the external load.

[0014] Furthermore, a semi-circular groove is provided on the side of the rolling mold, the depth of which is the radius of the heat pipe, and the semi-circular groove is in contact with the heat pipe.

[0015] Furthermore, a central thickness block is provided inside the groove of the central mold base, and a side thickness block is provided on the protrusion of the groove of the central mold base.

[0016] The design method for a heat pipe bending forming fixture includes the following steps:

[0017] S1. Determine the values ​​of the process parameters for the bending process experiment;

[0018] S2. Complete the assembly of parts for each module of the fixture, including the rolling mold, the center mold, and the adjustable track base;

[0019] S3. Fix the non-bending end of the heat pipe, i.e. the undeformed area at the end, in the wedge-shaped stretching fixture of the unidirectional stretching machine;

[0020] S4. Adjust the position of the slider base according to the position of the heat pipe, and at the same time ensure that the heat pipe is in contact with the inner side of the circular groove, and constrain the position of the heat pipe by fixing and clamping the slider.

[0021] S5. Based on the determined bending radius and other process parameters, select the rolling mold motion trajectory and bending angle;

[0022] S6. Apply a load to the annular structure on the rolling mold to drive the heat pipe to complete the bending process experiment.

[0023] Furthermore, in step S5, the bending parameters are adjusted by replacing the circular groove, the straight groove, and the rolling die.

[0024] Furthermore, the rolling mold moves along the track along a predetermined path under the action of external load, while simultaneously driving the heat pipe to perform an involute unfolding motion, with a bending angle range of 0 to 180°.

[0025] Compared with existing technologies, the beneficial effects of the present invention are as follows:

[0026] 1. The special heat pipe fixture of the present invention consists of three modules: a central mold, a rolling mold, and an adjustable track base. It can realize the dynamic adjustment of the outer diameter adaptation range, the bending radius, and the efficiency of process switching. It avoids the cumulative positioning error and the surge in hidden production costs caused by the physical replacement of molds in traditional fixtures.

[0027] 2. The fixture of the present invention is based on the triaxial force-displacement synchronous acquisition system of the uniaxial stretching machine, which can record the changes in load, displacement and other parameters during the bending and forming of the heat pipe in real time. In addition, combined with strain circle, DIC and other technologies, the stress and strain changes in the process can be further studied to establish a more accurate material constitutive model.

[0028] 3. In terms of cost-effectiveness, the special fixture of the present invention has low design cost, low manufacturing difficulty, and convenient disassembly and replacement of parts. Compared with traditional fixtures, the operation, maintenance and storage costs are significantly reduced.

[0029] 4. The high precision and control capabilities of the fixture of this invention ensure consistent experimental conditions for each experiment, improving data reliability. In contrast, traditional fixtures may introduce errors due to position adjustments, leading to inconsistent experimental conditions and affecting the credibility of the results. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments 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.

[0031] Figure 1 This is a flowchart illustrating the design method of a heat pipe bending forming fixture according to an embodiment of the present invention.

[0032] Figure 2 This is an overall assembly drawing of a heat pipe bending forming fixture according to this embodiment.

[0033] Figure 3 This is an assembly diagram of the central mold and heat pipe in this embodiment.

[0034] Figure 4 This is a schematic diagram of the central mold in this embodiment.

[0035] Figure 5 This is a schematic diagram of the structure of the rolling mold in this embodiment.

[0036] Figure 6 This is a schematic diagram of the structure of a heat pipe bending forming fixture after the heat pipe bending is completed in this embodiment.

[0037] Explanation of reference numerals: 1-M5X70-S double-ended stud; 2-shaft connector; 3-clamping slider; 4-base; 5-first track; 6-rolling mold; 7-second track; 8-connector; 9-guide rail; 10-slider base; 11-straight groove; 12-heat pipe; 13-positioning piece; 14-side thickness block; 15-circular groove; 16-intermediate thickness block. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and specific examples. Preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the textual part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0039] To better understand the selection of this invention, a brief introduction to its technological basis—the heat pipe bending forming process—is necessary. This process belongs to cold-state mandrel-less bending forming technology, and its core mechanism lies in achieving plastic deformation of the pipe through pure rolling contact. Specifically, multi-directional constraints are applied to the positioning end of the heat pipe to establish fixed boundary conditions, while the central mold achieves full-degree-of-freedom constraint through the base. The key forming unit—the rolling mold—uses the outer diameter of the heat pipe as its envelope surface and performs fixed-axis rotational motion around the central mold axis based on the pure rolling contact mechanism, achieving progressive and precise forming of the heat pipe's curvature radius. This effectively reduces defects such as wrinkling of the pipe wall in traditional bending processes, and significantly improves the control accuracy of cross-sectional distortion rate through strain path optimization.

[0040] Based on current finite element simulation results, it is known that differences in the combination of process parameters significantly affect the forming quality of the tube. When key process parameters such as bending radius, heat pipe diameter, heat pipe wall thickness, and bending angle are improperly combined, forming defects such as a surge in cross-sectional distortion rate and dispersion of springback angle will directly occur in the heat pipe. Therefore, it is of great significance to study the material properties by reproducing the bending forming process, thereby clarifying the bending forming mechanism and analyzing defects.

[0041] This invention proposes a design method for a heat pipe bending forming fixture and details a method for reproducing the forming process, aiming to solve technical problems such as difficulty in obtaining material performance parameters and poor process repeatability in existing bending experiments. Based on a uniaxial tensile testing platform, this fixture utilizes techniques such as DIC and strain circle to monitor the stress-strain evolution during the pipe bending process in real time, providing reliable experimental data support for establishing a high-precision finite element simulation constitutive model.

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the embodiments of this invention will be described in further detail below with reference to examples of heat pipe bending and forming and accompanying drawings.

[0043] like Figure 1 The diagram shows the installation and usage steps of a heat pipe bending forming fixture in this example, which consists of six steps. These steps are: designing the heat pipe bending experiment and determining the combination of process parameters; assembling each module mold; fixing the position of the heat pipe and determining its stability; appropriately adjusting the base position; determining the experimental process parameters such as bending angle and bending radius; and applying a load to the annular structure of the rolling mold to complete the bending experiment.

[0044] like Figures 2-5As shown, this example illustrates a heat pipe bending forming fixture, comprising a rolling die, a central die, and an adjustable track base. The non-bending end of the heat pipe 12, i.e., the straight section of the heat pipe, is fixed in a wedge-shaped stretching fixture of a unidirectional stretching machine. The clamping position is located in the undeformed area at the end of the heat pipe 12. The clamping length of the heat pipe 12 needs to be optimized according to the pipe size, typically controlled within the range of 10–20 mm to ensure reliable constraint. The other end of the heat pipe 12 is driven by the rolling die 6 to complete the bending forming experiment. The entire motion process is controllable, following an involute motion trajectory. By adjusting the relative positions of the rolling die 6 on the first track 5 and the second track 7 (arc-shaped through-hole tracks), bending forming with different radii can be achieved.

[0045] like Figure 3 , Figure 4 As shown, the central mold includes a clamping slider 3, a central mold base 4, a connector 8, a straight section groove 11, and a circular section groove 15. The heat pipe 12 is fixed to the straight section groove 11 and the circular section groove 15 by the clamping slider 3; the base 4 and the circular section groove 15 are fixedly connected by the connector 8; a groove is provided in the central area of ​​the surface of the central mold base 4, in which a middle thickness block 16 can be fixed, and the protrusions on both sides of the groove can fix the side thickness blocks 14. A groove is formed between the side thickness blocks 14 and the middle thickness block 16. The middle protrusion of the straight section groove 11 is located in the groove or directly in the groove of the central mold base 4. The straight section groove 11 is fixed to the central mold base 4 by the clamping slider 3.

[0046] In one embodiment, the clamping slider 3 is provided with a semi-circular groove that mates with the heat pipe 12 for fixing the heat pipe 12. The semi-circular groove of the clamping slider 3 has a through hole, which, through the engagement of a screw with the semi-circular groove of the straight section groove 11, ensures the precise positioning of the heat pipe 12 in the central mold module. In addition, the clamping slider 3 has through holes at both ends, which, through screws, fix it to the central mold base 4 to achieve a tight fit between the clamping slider 3 and the central mold base 4.

[0047] The structure of the circular groove 15 is based on the R-angle process requirements of heat pipe bending. The semi-circular groove inside the circular groove 15 fits against the heat pipe 12 during the bending process, providing support and fixation. A rectangular groove is provided on each side of the circular groove 15, and the rectangular grooves are connected to the central mold base 4 via connectors 8. The connectors 8 are L-shaped, designed to connect the circular groove 15 and the central mold base 4 through a mating connection. A countersunk hole is provided at the transition point of the rectangular groove, allowing for further reinforcement of the circular groove 15's position on the central mold base 4 using screws.

[0048] The straight section groove 11 adopts a structure design with a double rectangular base and a central connecting groove. Two countersunk holes are provided in each of the base areas on both sides. When there is no side thickness block 14 between the straight section groove 11 and the central mold base 4, the straight section groove 11 can be directly fixed to the position of the central mold base 4 with screws. When there is a side thickness block 14, the straight section groove 11 is fixed to the side thickness block 14 with screws, and then the two countersunk holes on the side thickness block 14 are connected and fixed to the central mold base 4 with screws. The straight section groove 11 has a groove with a semi-circular cross-section and a depth consistent with the radius of the heat pipe 12. This groove is mainly used to support the straight section of the heat pipe 12, ensuring accurate starting position of the bend and preventing axial movement.

[0049] The intermediate thickness block 16 and the side thickness block 14 have similar structures, differing only in size. Both have two countersunk holes and two through holes along their length. The countersunk holes are designed to fix each thickness block to the central mold base 4, while the through holes are used to connect the side thickness block 14 to the straight groove 11 via screws. The through holes in the intermediate thickness block 16 have no practical function; they only maintain structural consistency.

[0050] The overall geometry of the central mold base 4 is relatively complex. The central mold base 4 has a U-shaped structure. The rectangular groove on the surface of the central mold base 4 has three through holes. When there is no intermediate thickness block 16, it is fixed to the straight section groove 11 by screws. When the intermediate thickness block 16 is present, the three through holes and the intermediate thickness block 16 are positionally constrained by screws. The raised areas on both sides of the groove of the central mold base 4 each have four through holes. When there is no side thickness block 14, it is directly fixed to the straight section groove 11 by screws. When the side thickness block 14 is present, it is first fixed to the side thickness block 14 and then connected to the central mold base 4. The two parallel sides of the central mold base 4 have rectangular grooves for fixing the circular section groove 15 via the connector 8; each of the two end faces has a shaped groove for connecting the first track 5 and the second track 7.

[0051] The installation process of the entire central mold module is as follows: the central mold base 4 and the circular groove 15 are fixedly connected by the connector 8; the side thickness block 14 is fixed to the groove boss of the central mold base 4 by screws; the middle thickness block 16 is fixed in the groove of the central mold base 4 by the corresponding through hole mounting screws; the heat pipe 12 is constrained and fixed by the semi-circular groove of the clamping slider 3 and the semi-circular groove of the straight groove 11; the clamping slider 3 fastens the straight groove 11 to the central mold base 4 by screws, thereby completing the overall assembly.

[0052] like Figure 5 As shown, the rolling die module includes an M5X70-S double-ended stud 1, a first track 5, a rolling die 6, a second track 7, and a locking component 13.

[0053] The first track 5 and the second track 7 have identical geometric dimensions. Considering manufacturing costs and subsequent experimental observation of heat pipe deformation, their shapes are both fan-shaped, with four arc-shaped through-hole tracks on the fan. The two ends of the M5X70-S double-ended stud 1 are respectively located in the arc-shaped through-hole tracks of the first track 5 and the second track 7. The arc-shaped through-hole tracks serve as the tracks for the rolling mold 6, representing the motion trajectories of the rolling mold 6 under different bending radii during the bending experiment, and their trends are all involute curves. The tops of the first track 5 and the second track 7 are provided with circular protrusions, and the centers of the circular protrusions are provided with through holes. The two sides of the concentric mold base 4, the first track 5, and the second track 7 are respectively mounted on the slider base 10. The protrusions cooperate with the concentric mold base 4 and the slider base 10 to achieve fixed constraints at corresponding positions.

[0054] As one embodiment, the fan-shaped section is provided with four arc-shaped through-hole tracks, and the bending angle of the rolling mold 6 is in the range of 0 to 180°.

[0055] The locking component 13 adopts a frustum design. The internal through hole of the locking component 13 is engaged with the threaded hole of the M5X70-S double-ended stud 1 and tightened. The locking component 13 passes through the through hole of the rolling mold 6 and fits tightly with the rolling mold 6, effectively preventing the rolling mold 6 from shifting during the bending process.

[0056] The design of the rolling die 6 is derived from the rolling die in the actual heat pipe bending forming process, and its geometric structure adopts a cuboid base. One end of the rolling die 6 is provided with multiple equidistant through holes (for example, four equidistant through holes). The rolling die 6 is connected to the M5X70-S double-ended stud 1 through the through holes to achieve a mating connection with the M5X70-S double-ended stud 1.

[0057] The top of the end of the rolling die 6 furthest from the through hole has an annular structure to provide a mechanical interface (such as an anchor point for a chain or elastic traction rope) to connect to external loads, such as the traction force driven by a motor, which is effectively transmitted to the die to achieve its controllable rotation. Its core is to convert linear or circumferential traction loads into torque through structural optimization, driving the rolling die 6 to complete bending motion, while ensuring uniform load distribution and transmission efficiency. The side of the rolling die 6 has a semi-circular groove with a depth equal to the radius of the heat pipe 12, and the semi-circular groove contacts the heat pipe 12.

[0058] The installation steps of the rolling mold module are as follows: the locking piece 13 is screwed into the threaded hole of the M5X70-S double-ended stud 1, the locking piece 13 passes through the through hole of the rolling mold 6, the arc-shaped through hole track corresponding to the determined bending radius is selected on the first track 5 and the second track 7, the M5X70-S double-ended stud 1 is inserted into the selected arc-shaped through hole track of the first track 5 and the second track 7, and the locking piece 13 is installed to form a precise positioning structure, and the annular structure of the rolling mold 6 is connected to the external load.

[0059] The bending forming of heat pipe 12 is achieved as follows: Heat pipe 12 is reliably fixed at its positioning end by a fixed clamping slider 3 and a wedge-shaped clamp at the upper end of a unidirectional stretching machine. Throughout the experiment, the central mold module remains fixed, and the rolling mold 6 remains tangent to the outer surface of heat pipe 12 and the circular groove 15. The rolling mold 6 performs pure rolling motion around the circular groove 15 at a certain angular velocity: the rotational motion is converted into the progressive bending deformation of heat pipe 12 through non-slip rolling friction. This pure rolling mechanism ensures that heat pipe 12 is uniformly subjected to radial pressure during the forming process, avoiding surface damage caused by traditional sliding friction and ensuring precise control of the bending radius. As the rolling mold 6 continues to operate, the material of heat pipe 12 undergoes plastic flow along the semi-circular groove surface of the circular groove 15, ultimately forming a bending angle and bending radius that meet the design requirements, such as... Figure 6 As shown.

[0060] The adjustable base module includes a shaft connector 2, a guide rail 9, and a slider base 10. The shaft connector 2 serves as the lower clamp of the unidirectional stretching machine, playing a crucial connecting role in the heat pipe bending experiment. It ensures precise alignment and rigid fixation between the guide rail 9 and the stretching machine. The guide rail 9 has a through hole on its lower surface for connection with the shaft connector 2, ensuring the stability of the bending experiment. The upper surface of the guide rail 9 has symmetrically arranged linear grooves on both sides. The slider base 10 is located within these linear grooves and can be quickly fixed to any target position using four screws. When experimental parameters need adjustment, simply loosen the screws and move the slider base 10 along the guide rail 9 to the new position, then re-tighten it to achieve flexible position adjustment. The slider base 10 includes a square base and two triangular support side plates. The square base has four symmetrically distributed mounting holes, primarily used to constrain the position of the slider base 10 with screws after determining the specific position. The symmetrical layout of the mounting holes facilitates quick positioning and repeated assembly. Furthermore, the triangular support side plates provide additional structural support, enhancing overall rigidity. The two sides of the concentric mold base 4, the first track 5 and the second track 7 are respectively installed on the two triangular bracket side plates.

[0061] The fixture of this invention adopts a modular quick-change design. When a local unit is worn or fails abnormally, it can be disassembled and replaced at a single point without the need for overall scrapping. Since the parts are designed with quick changeover capability in mind, maintenance time is significantly reduced compared to traditional welding or overall machining.

[0062] This example describes a design method for a heat pipe bending forming fixture. The installation of the fixture and the realization of bending forming include the following steps:

[0063] Step 10: Determine the values ​​of the process parameters for the bending experiment. Different parameters have varying effects on various defects such as wall thickness variation and cross-sectional distortion during heat pipe bending. Specific process parameters include: heat pipe diameter and wall thickness, bending angle, and bending radius.

[0064] Step 20: Complete the assembly of the heat pipe bending forming fixture, including a rolling mold, a center mold, and a track-type adjustable base.

[0065] The fixture adopts a modular quick-change interface design, which allows for single-point disassembly and replacement when a local unit wears or fails abnormally, without the need for overall scrapping. Because the parts are designed with quick changeover capability in mind, maintenance time is significantly reduced compared to traditional welding or overall machining.

[0066] Step 30: The non-bending end of the heat pipe, i.e. the straight section end of the heat pipe, is fixed by the wedge-shaped stretching clamp of the unidirectional stretching machine. The clamping position is located in the undeformed area of ​​the heat pipe end. The clamping length of the heat pipe needs to be optimized according to the pipe size, usually controlled within the range of 10 to 20 mm to ensure reliable constraint. The wedge-shaped clamp has a built-in centering mechanism to ensure that the heat pipe is vertically positioned during initial clamping.

[0067] Step 40: Adjust the base position appropriately according to the heat pipe fixing position to ensure that the heat pipe is tightly attached to the inside of the circular groove;

[0068] The slider base 10 adopts a guide rail-guided displacement structure. After the target workstation is determined, the position is fixed using four hexagon socket screws. This design avoids the rigid constraints of traditional fixed bases and achieves a stroke range adjustment within 50mm.

[0069] The guide rail 9 and the unidirectional tensioning machine can be directly connected through the shaft joint 2, which ensures that the tooling adaptation time is reduced while meeting the fatigue life requirements of a high number of cyclic assembly and disassembly.

[0070] Step 50: Based on the determined bending radius and other process parameters, complete the selection of the rolling mold motion trajectory and bending angle.

[0071] The experiment has a wide range of adjustable parameters. By replacing components such as the circular groove 15, the straight groove 11, and the rolling mold 6, it can flexibly adapt to the bending and forming requirements of heat pipes of different specifications, realize experimental research on various bending radii and pipe diameters, and avoid the limitations of traditional fixtures that can only adapt to a single working condition.

[0072] When implementing the bending process, the forming quality of the heat pipe under different combinations of process parameters can be studied by changing process parameters such as bending speed, surface roughness, and the gap between the mold and the heat pipe based on the fixture platform.

[0073] Step 60: Apply a load to the annular structure on the rolling mold to complete the heat pipe bending experiment.

[0074] The movement trajectory of the rolling die 6 is restricted by the track, and the rolling die 6 will not slip relative to each other during the forming process, making the whole process relatively stable.

[0075] The trajectory of point A in the rolling die is an involute motion, that is, it completes pure rolling along the central die. The trajectory equation is calculated as follows.

[0076]

[0077] θ=ωt

[0078] In the formula, x and y represent the horizontal and vertical coordinates of point A, respectively, ω is the rolling speed of the rolling mold, r is the rolling radius of point A on the rolling mold, t is the motion time, and θ is the rolling angle of the rolling mold, i.e., the bending angle of the heat pipe.

[0079] Real-time acquisition of load-displacement curves is achieved through a uniaxial stretching machine: After fixture assembly and heat pipe fixing, a load is applied to drive the rolling die for bending forming. The stretching machine's built-in sensors automatically record data and directly output the load-displacement curves through software such as TestXpert. Simultaneously, circumferential strain field measurements are performed using triaxial strain gauges (arranged at 0°, 45°, and 90°). The strain gauges are precisely bonded and connected to a Wheatstone bridge (with temperature compensation). The acquisition system obtains multi-directional strain signals during the loading process, and finally, the principal strain, principal direction, and principal stress data are obtained analytically through the principal strain calculation formula, achieving a comprehensive mechanical characterization of the forming process.

[0080] The bending forming process of a heat pipe involves driving a rolling die along a track, which pulls the heat pipe, fixed at one end, to complete the plastic deformation along an involute trajectory. In this process, the rolling die moves along the track along a predetermined path under external load, simultaneously driving the heat pipe to perform an involute unfolding motion, thereby achieving precise bending forming. The bending angle can be arbitrarily adjusted, ranging from 0 to 180°.

[0081] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A heat pipe bending forming fixture, characterized in that, Includes rolling molds, center molds, and an adjustable track base; The central mold includes a clamping slider (3), a central mold base (4), a straight section groove (11), and a circular section groove (15). The circular section groove (15) is fixed on the central mold base (4) by a connector (8); the straight section groove (11) is fixed on the base (4) by the clamping slider (3); the heat pipe (12) is located in the semicircular groove of the clamping slider (3) and the semicircular groove of the straight section groove (11). The rolling mold includes a double-headed stud (1), a first track (5), a rolling mold (6), a second track (7), and a locking component (13). The first track (5) and the second track (7) are provided with multiple tracks. The double-headed stud (1) passes through the internal through hole of the locking component (13) and its two ends are inserted into the arc-shaped through hole tracks of the first track (5) and the second track (7). The rolling mold (6) is installed on the locking component (13) and is located between the first track (5) and the second track (7). The surface of the rolling mold (6) is in contact with the surface of the heat pipe (12). The adjustable track base includes a shaft connector (2), a guide rail (9) and a slider base (10). The shaft connector (2) is located on the surface of the guide rail (9) and is fixed to the unidirectional stretching machine through the shaft connector (2). The slider base (10) is located on the guide rail (9). The central mold base (4), the first track (5) and the second track (7) are fixed on the slider base (10).

2. The heat pipe bending forming fixture according to claim 1, characterized in that, The surface of the central mold base (4) is provided with a groove, and the protrusion of the straight section groove (11) is located in the groove.

3. The heat pipe bending forming fixture according to claim 1, characterized in that, The central mold base (4) has a U-shaped structure, and the two sides of the central mold base (4) as well as the first track (5) and the second track (7) are fixed on the slider base (10).

4. A heat pipe bending forming fixture according to claim 1, characterized in that, The rolling mold (6) has multiple equidistant through holes at one end, and the locking piece (13) passes through the through holes of the rolling mold (6).

5. A heat pipe bending forming fixture according to claim 4, characterized in that, The rolling die (6) has an annular structure at the top of the end away from the through hole to connect to the external load.

6. A heat pipe bending forming fixture according to claim 4, characterized in that, The rolling mold (6) has a semi-circular groove on its side. The depth of the semi-circular groove is the radius of the heat pipe (12). The semi-circular groove is in contact with the heat pipe (12).

7. A heat pipe bending forming fixture according to any one of claims 2 to 6, characterized in that, The central mold base (4) has a central thickness block (16) inside the groove, and a side thickness block (14) is provided on the groove boss of the central mold base (4).

8. A design method for a heat pipe bending forming fixture as described in claim 7, characterized in that, Includes the following steps: S1. Determine the values ​​of the process parameters for the bending process experiment; S2. Complete the assembly of parts for each module of the fixture, including the rolling mold, the center mold, and the adjustable track base; S3. Fix the non-bending end of the heat pipe, i.e. the undeformed area at the end, in the wedge-shaped stretching fixture of the unidirectional stretching machine; S4. Adjust the position of the slider base (10) according to the position of the heat pipe, and at the same time ensure that the heat pipe fits the inner side of the circular groove (15), and constrain the position of the heat pipe by fixing the clamping slider (3); S5. Based on the determined bending radius and other process parameters, select the motion trajectory and bending angle of the rolling mold (6); S6. Apply a load to the annular structure on the rolling mold (6) to drive the heat pipe to complete the bending process experiment.

9. The design method according to claim 8, characterized in that, In step S5, the bending parameters are adjusted by replacing the circular groove (15), the straight groove (11), and the rolling mold (6).

10. The design method according to claim 8, characterized in that, The rolling mold (6) moves along the track along a predetermined path under the action of external load, while driving the heat pipe to perform involute unfolding motion, with a bending angle range of 0~180°.

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