Micro-miniature heat pipe bending forming quality control method

Abstract

The invention discloses a bending forming quality control method for a microminiature heat pipe. The bending forming quality control method comprises the following steps that the microminiature heat pipe needing to be bent is installed at the corresponding position of a bending forming die; the heating device is used for heating the pipe, so that the temperature of the microminiature heat pipe is increased, a heat transfer working medium in the pipe is vaporized to form internal pressure, and the pipe wall is internally supported; the bending machine is started, bending operation is conducted on the pipe fitting, in the bending process, the rolling die does involute motion along the bending path, the surface of the micro heat pipe is prevented from being scratched, gas pressure in the pipe fitting always provides pressure support for the inner wall of the pipe fitting, and the pipe fitting is prevented from wrinkling and collapsing during bending; and after bending is completed, the heating clamping device is removed, and the target bent pipe fitting is obtained. The bending forming defects of the ultra-thin-wall pipe such as outer side wall tension crack, inner side wall wrinkling, cross section oval distortion and uneven wall thickness are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material processing, and particularly to a method for controlling the bending forming quality of a micro heat pipe. Background Art

[0002] At present, micro heat pipes, as the core heat transfer components of heat dissipation systems, are widely used in products such as computers and high-power LEDs. In order to meet the heat dissipation requirements of various products, micro heat pipes usually need to be bent into different shapes. However, since the pipe is a hollow structure, various forming defects are likely to occur during the bending process, including: wall thickness thinning, bending cracking, wrinkling, cross-sectional distortion, collapse, etc. In order to improve the bending quality of the pipe, ordinary pipe bending usually places a mandrel, a soft leather bag or other filling materials inside the pipe as internal support to prevent the above-mentioned defect problems from occurring during the bending process.

[0003] In a new type of pipe bending forming process (CN114210789A), the process realizes internal support by placing a plug in the inner cavity of the pipe and injecting pressure liquid, effectively preventing wrinkling and collapse during the pipe bending process, while simplifying the operation process, improving production efficiency, and obtaining higher quality bent pipe products. A method for assisted push-bending forming of large-diameter and small-bending-radius thin-walled pipes with particle fillers (CN110576089A) describes a method for using particle fillers to assist in the push-bending forming of large-diameter and small-bending-radius thin-walled pipes. By controlling the internal pressure and axial force of the particle fillers, the stress state during pipe bending is adjusted, thereby overcoming defects such as uneven wall thickness, wrinkling, and cracking, and realizing high-quality pipe bending forming.

[0004] However, as a kind of micro pipe, the outer diameter of the micro heat pipe is usually 2-6 mm, the wall thickness is usually 0.3 mm or less, and both ends of the pipe are closed. During the actual bending process, it is impossible to prevent the mandrel and the soft leather bag from wrinkling due to instability during the bending process as fillers. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for controlling the bending forming quality of a micro heat pipe. By heating one end of the micro heat pipe, the heat transfer working medium inside the heat pipe is vaporized to realize internal pressure support. By controlling the temperature of the pipe, the internal pressure during bending of the pipe is controlled, and it is possible to process a micro heat pipe with a large diameter-thickness ratio and a small bending radius. At the same time, it can also well overcome the bending forming defects of special thin-walled pipes such as cracking of the outer side wall, wrinkling of the inner side wall, elliptical distortion of the cross-section, and uneven wall thickness. The present invention is easy to operate, the pipe bending operation process is simple, so it has higher production efficiency and higher pipe forming quality.

[0006] The present invention is realized by at least one of the following technical solutions.

[0007] A quality control method for bending of micro heat pipes, comprising the following steps:

[0008] Step 1: Install the micro heat pipe to be bent at the corresponding position on the bending forming die;

[0009] Step 2: The heating device heats the pipe, increasing the temperature of the micro heat pipe, vaporizing the heat transfer working medium inside the pipe to form internal pressure, which provides internal support for the pipe wall;

[0010] Step 3: Start the bending machine to perform bending operation on the pipe fitting. During the bending process, the rolling die moves along the involute path to avoid scratching the surface of the micro heat pipe. The gas pressure inside the pipe fitting always provides pressure support for the inner wall of the pipe fitting to prevent the pipe fitting from wrinkling and collapsing during bending;

[0011] Step 4: After bending is completed, remove the heating device to obtain the target bent pipe fitting.

[0012] Furthermore, the micro heat pipe has both ends completely closed, and it is not easy to insert a mandrel or fill other substances to prevent the pipe wall from buckling during bending forming.

[0013] Furthermore, the bending forming die includes a rolling die, a bending center die, a pressing block, and a heating device.

[0014] Furthermore, the micro heat pipe is clamped on the bending center die, and the pressing block presses the micro heat pipe. According to whether the pipe section of the micro heat pipe changes relative to the initial position during the bending forming process, it is divided into a fixed end and a mobile end. The pipe section of the micro heat pipe that does not change is the fixed end, and the pipe section of the micro heat pipe that changes is the mobile end. The fixed end and the mobile end are bounded by the pressing block, and the heating device is located at the fixed end of the micro heat pipe during bending forming.

[0015] Furthermore, the rolling die is located on the other side of the pressing block, i.e., the mobile end side. The rolling die rolls along the bending center die, and the mobile end of the micro heat pipe is bent into the target shape under the driving action of the rolling die.

[0016] Furthermore, the surfaces of the rolling die, the bending center die, and the pressing block that are in contact with the micro heat pipe are covered with an adiabatic coating to reduce heat dissipation of the pipe.

[0017] Furthermore, the heating device is an electromagnetic induction heater, and the micro heat pipe is heated by passing through the heating coil of the electromagnetic induction heater.

[0018] Furthermore, the maximum internal pressure that the micro heat pipe can withstand is calculated by the following calculation method:

[0019]

[0020] Wherein, P is the maximum internal pressure that the micro heat pipe can withstand, t is the wall thickness of the pipe, D is the outer diameter of the pipe, and σ s is the initial yield stress of the pipe, and k is a correction factor to correct the decrease in the yield stress of the heat pipe due to temperature rise and other defects of the pipe.

[0021] Furthermore, the temperature value when the micro heat pipe reaches the maximum internal pressure is preliminarily calculated according to the Antoine equation:

[0022]

[0023] Where A, B, and C are constants, which can be obtained from "Chemical Engineering Thermodynamics" or other handbooks on the physical properties of substances according to different working fluids and temperature conditions. P is the maximum internal pressure that the micro heat pipe can withstand, and T is the temperature that the heat pipe needs to be heated.

[0024] Furthermore, the temperature T that the heat pipe needs to be heated and the maximum internal pressure P that the micro heat pipe can withstand are verified and corrected according to the following steps:

[0025] Step 1): Calculate the internal cavity volume V of the micro heat pipe according to the geometric dimensions of the micro heat pipe;

[0026] Step 2): According to the mass m of the heat transfer working fluid contained in the micro heat pipe and the molar mass M of the heat transfer working fluid, convert the molar mass M of the heat transfer working fluid into the number of moles n:

[0027]

[0028] Step 3): Substitute the maximum internal pressure P that the micro heat pipe can withstand, the temperature T that the heat pipe needs to be heated, the internal cavity V of the micro heat pipe, and the ideal gas constant R into the ideal gas equation to calculate the number of moles of the heat transfer working fluid required at this temperature and pressure:

[0029]

[0030] Step 4): Compare the number of moles n of the heat transfer working fluid in the micro heat pipe in Step 2) and the number of moles n' of the heat transfer working fluid required at this temperature and pressure. When n > n', it means that the calculated temperature T that the heat pipe needs to be heated meets the requirements, and the maximum heating temperature of the micro heat pipe can be set to T, and the loop is exited; when n < n', it means that the maximum internal pressure P and temperature that the micro heat pipe can withstand at this time are too high, and it turns to Step 5);

[0031] Step 5): When the internal pressure P is too high, there will be risks such as the explosion of the heat pipe. It is necessary to reduce the internal pressure of the pipe material to within the bearing range of the pipe material, and make the new internal pressure of the pipe material be P'. The new internal pressure of the pipe material is calculated according to the following method: Let P' = f * P, where the value range of f is (0, 1). Then substitute P' into the Antoine equation to calculate T', and then enter Step 3) for judgment and comparison.

[0032] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0033] 1. In the prior art, when bending a pipe material, a mandrel or other fillers are mostly added inside the pipe material to prevent wrinkles, cross-sectional ovality and other conditions during the bending process of the pipe material. Since both ends of the micro heat pipe are in a closed state, these methods cannot be applied to prevent wrinkling during the bending process of the micro heat pipe. The present invention utilizes the self-characteristics of the heat pipe to heat the micro heat pipe, and the heat transfer medium inside it vaporizes to form air pressure, which directly acts on the inner cavity of the pipe fitting, and can prevent the pipe fitting from wrinkling and collapsing during the bending process, and the bending forming effect is good.

[0034] 2. A method for controlling the bending forming quality of a micro heat pipe according to the present invention can be applied to the bending forming of heat pipes with a small bending radius and a large diameter-thickness ratio. Brief Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 is a control flow chart of a method for controlling the bending forming quality of a micro heat pipe according to the present invention.

[0037] Figure 2 is a schematic diagram of a bending center die and a micro heat pipe to be bent provided by an optional embodiment of the present invention.

[0038] Figure 3 is a schematic cross-sectional structure diagram of a micro heat pipe according to the present invention.

[0039] Figure 4 is a schematic diagram of the groove of a bending forming die provided by an optional embodiment of the present invention

[0040] Explanation of the reference numerals in the drawings: 1 - heating clamping device; 2 - micro heat pipe; 3 - pressing block; 4 - rolling die; 5 - bending center die; 6 - heat transfer working medium; 7 - bending center die groove. Detailed Embodiment

[0041] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "left" and "right" is based on the orientation and positional relationship shown in the drawings, and is only for the convenience of describing the structure and operation mode, rather than indicating or implying that the parts referred to must have a specific orientation and be operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention.

[0042] To better understand the selection of the present invention, the micro heat pipe and its working principle will be briefly introduced first. The micro heat pipe is an efficient heat transfer device that uses the phase change principle to transfer heat. Its working principle is to use the phase change of the internal working fluid (such as water) to transfer heat. When the heat source heats one end of the heat pipe, the working fluid inside the pipe absorbs heat and evaporates into water vapor. Due to the lower density of the water vapor, it naturally flows to the cooler condensation section, where it releases heat and condenses into liquid water. The condensed liquid water returns to the heating section by gravity or capillary action and is heated and evaporated again, thus forming a continuous cycle. The inside of the heat pipe is usually vacuum to reduce the convective heat resistance of the gas and improve the heat conduction efficiency. And the internal capillary structure helps the liquid to flow back, ensuring stable operation even in complex positions. In this way, the heat pipe can transfer a large amount of heat at a small temperature difference and maintain good isothermal properties.

[0043] Therefore, when the temperature of the heating end is too high, it is very likely that all the internal heat transfer medium is converted into gas state, the liquid at the heating end "dries up", and the heat transfer cycle inside the heat pipe cannot proceed normally, resulting in an abnormal increase in the temperature of the local heating end and then the damage of the heat pipe. Therefore, when using the heating method to increase the internal pressure of the heat pipe and form internal support, not only the limitation of the structural strength of the material on the internal pressure needs to be considered, but also the limitation of the content of the heat transfer medium in the micro heat pipe on the maximum internal pressure that can be formed needs to be considered.

[0044] The purpose of the present invention is to provide a method for controlling the wrinkling of the micro heat pipe during bending forming, so as to solve the problems existing in the prior art and make the obtained formed micro heat pipe have the characteristics of small bending radius, high forming accuracy, excellent shaping performance, etc.

[0045] To make the purpose, technical solution and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below in combination with the bending examples of the micro heat pipe and the drawings.

[0046] As Figure 1 shown, a method for controlling the wrinkling of the micro heat pipe during bending forming in this embodiment. This method heats one end of the micro heat pipe 2 to vaporize the heat transfer working fluid inside the heat pipe to achieve internal pressure support, uses the heating device at one end to heat the pipe material and controls the temperature of the pipe material of the micro heat pipe 2, thereby controlling the internal pressure of the pipe material, and further controlling the bending forming deformation behavior of the micro heat pipe 2.

[0047] As Figure 3 shown in the schematic structural diagram of the micro heat pipe, the interior of the micro heat pipe 2 is a hollow structure, and both ends are sealed. At normal temperature, a small amount of liquid heat transfer medium is filled inside. When the temperature rises, due to the vacuum environment inside, the heat transfer medium is easily vaporized into a gas state, forming air pressure. And because the micro heat pipe 2 is in a fully enclosed state, the internal heat transfer medium cannot escape to the outside world. That is, within a certain range, the higher the temperature, the higher the internal air pressure will be.

[0048] A method for controlling the bending forming quality of a micro heat pipe in this embodiment includes the following steps:

[0049] Step 10: Install the micro heat pipe 2 to be bent at the correct position on the bending forming die;

[0050] The micro heat pipe has both ends completely sealed, and it is not easy to insert a mandrel or fill other substances to prevent the tube wall from buckling during the bending forming process.

[0051] The bending forming die includes a heating device 1, a pressing block 3, a rolling die 4, and a bending center die 5. One end of the micro heat pipe 2 is heated by the heating device 1, and the other end is placed at the groove of the bending center die. The pressing block 3 presses the micro heat pipe 2, and the rolling die 4 rolls along the bending center die.

[0052] The correct position is as shown in Figure 2 the micro heat pipe 2 is placed on the groove of the bending center die 5, and the schematic diagram of the groove shape is as shown in Figure 4 After the micro heat pipe 2 is placed at the correct position on the bending center die 5, the pressing block 3 presses on the micro heat pipe 2 to restrict its displacement movement. Among them, as shown in Figure 2 the orientation shown, the left side of the micro heat pipe 2 relative to the pressing block is the section where the relative position does not change during the bending forming process, regarded as the fixed end, and its length is at least 40 mm, which is convenient for the heating device 1 to heat the pipe. The other side is the mobile end side. The rolling die rolls along the bending center die, and the mobile end of the micro heat pipe is bent into the target shape under the driving action of the rolling die.

[0053] The rolling die 4, the bending center die, and the pressing block 3 are covered with an adiabatic coating on the surface in contact with the micro heat pipe 2 to minimize the heat loss of the micro heat pipe 2 during the bending process.

[0054] Step 20: The heating clamping device 1 clamps the other side of the micro heat pipe 2 during the bending forming process, and the heating device at the end of the clamping end of the micro heat pipe 2 is turned on to heat the micro heat pipe 2, so that the temperature of the pipe rises, and the internal heat transfer medium in the pipe is vaporized to form pressure, which plays an internal support role for the pipe wall;

[0055] The heating device is an electromagnetic induction heater, which uses high-frequency induction heating to quickly heat the micro heat pipe 2 to the specified temperature.

[0056] The heating temperature of the micro heat pipe 2 tube material is temperature-limited, and its temperature range is determined by the maximum internal pressure that the material can withstand and the amount of the heat transfer working fluid 6 inside the micro heat pipe 2 that can be converted into gas. The internal pressure formed by the vaporization of the heat transfer medium inside the tube wall is determined according to the geometric dimensions and material parameters of the micro heat pipe 2 to be bent.

[0057] The maximum internal pressure that the described micro heat pipe can withstand is calculated by the following calculation method:

[0058]

[0059] Among them, P is the maximum internal pressure that the micro heat pipe can withstand, t is the wall thickness of the tube material, D is the outer diameter size of the tube material, and σ s is the initial yield stress of the tube material, and k is a correction coefficient to correct the decrease in the yield stress of the heat pipe due to temperature rise and other defect values of the tube material.

[0060] According to the Antoine equation, the temperature value when the micro heat pipe reaches the maximum internal pressure is preliminarily calculated:

[0061]

[0062] Among them, A, B, and C are constants, which can be obtained from data according to different working fluids and temperature conditions. P is the maximum internal pressure that the micro heat pipe can withstand, and T is the temperature to which the heat pipe needs to be heated.

[0063] Step 30: Start the bending machine and perform a bending operation on the pipe fitting. During the bending process, the gas pressure inside the pipe fitting always provides pressure support for the inner wall of the pipe fitting to prevent the pipe fitting from wrinkling and collapsing during bending;

[0064] Step 40: After bending is completed, remove the heating device to obtain the target bent pipe fitting.

[0065] The temperature T to which the heat pipe needs to be heated and the maximum internal pressure P that the micro heat pipe can withstand are verified and corrected according to the following steps:

[0066] Step 1: Calculate the internal cavity volume V of the tube material according to the geometric dimensions of the micro heat pipe;

[0067] Step 2): According to the mass m of the heat transfer working fluid contained in the micro heat pipe and the molar mass M of the heat transfer working fluid, convert it into the number of moles n:

[0068]

[0069] Step 3): Substitute the maximum internal pressure P that the micro heat pipe can withstand, the temperature T that the heat pipe needs to be heated, the internal cavity V of the micro heat pipe, and the ideal gas constant R into the ideal gas equation, and the number of moles of the heat transfer working fluid required at this temperature and air pressure can be calculated as follows:

[0070]

[0071] Step 4): Compare the number of moles n of the heat transfer working fluid in the micro heat pipe in Step 2) with the number of moles n' of the heat transfer working fluid required at this temperature and air pressure. When n > n', it indicates that the calculated temperature T for heating the heat pipe meets the requirements. The maximum heating temperature of the pipe material can be set to T, and the loop is exited. When n < n', it means that the maximum internal pressure P and temperature that the micro heat pipe can withstand are too high, and it transfers to Step 5).

[0072] Step 5): Let P' = f * P, where the value range of f is (0, 1). Then substitute P' into the Antoine equation to calculate T', and then enter Step 3) for judgment and comparison.

[0073] In an embodiment of the present invention, the material of the micro heat pipe is TU2 oxygen-free copper, and its initial yield strength σ s = 240 Mpa, the outer diameter D of the pipe is 6 mm, the wall thickness t is 0.2 mm, the thickness s of the copper powder sintered on the heat pipe in the sintering process is 0.2 mm, the length L of the heat pipe is 300 mm, and the internal heat transfer working fluid is H2O with a mass of 0.2 g. Then, according to the formula, the internal cavity V of the micro heat pipe can be calculated as follows:

[0074]

[0075] The molar mass of the water as the internal heat transfer working fluid in the pipe is M = 18 g / mol, so its molar content is: L is the length of the heat pipe.

[0076] According to the initial yield strength of the micro heat pipe material, and after substituting the correction coefficient k = 0.4, the maximum internal pressure that the pipe can withstand can be calculated as follows:

[0077]

[0078] Among them, P is the maximum internal pressure that the micro heat pipe can withstand, t is the wall thickness of the pipe, D is the outer diameter size of the pipe, σ s is the initial yield stress of the pipe, k is the correction coefficient, which corrects the value of the yield stress decrease of the heat pipe due to temperature rise and other defect values of the pipe.

[0079] Based on the maximum internal pressure calculated from the initial yield strength of the micro heat pipe material, the temperature value when reaching this internal pressure can be calculated according to the Antoine equation, and its formula is:

[0080]

[0081] Among them, A, B, and C are constants, which can be obtained according to "Chemical Engineering Thermodynamics" or other handbooks on physical properties according to different working fluids and temperature conditions. After consulting the data, they are selected as: A = 8.14019, B = 1810.94, C = 244.485. The applicable range is 99 °C to 374 °C. P is the maximum internal pressure that the micro heat pipe can withstand, and T is the temperature that the heat pipe needs to be heated. It should be noted that the unit of P in the above formula is mmHg, and after conversion: P = 6.86 Mpa = 51454 mmHg.

[0082] Substituting A, B, C, and the previously obtained C into the formula, the temperature at this time can be obtained as: T = 283 °C.

[0083] At this time, verify whether the water content in the micro heat pipe is sufficient according to the ideal gas equation:

[0084] The calculated required water content H is: R is the ideal gas constant.

[0085] That is, the micro heat pipe is in the gas-liquid two-phase equilibrium state at 283 °C. At this time, the heat cycle of the micro heat pipe can proceed continuously, and the micro heat pipe can be bent and formed at this temperature.

[0086] In another feasible embodiment of the present invention, the material of the micro heat pipe is TU2 oxygen-free copper, and its initial yield strength σ s = 240 Mpa, the outer diameter D of the pipe is 6 mm, the wall thickness t is 0.2 mm, copper powder with a thickness of s = 0.2 mm is sintered on the heat pipe in the sintering process, the length of the heat pipe is 250 mm, and the internal heat transfer working fluid is H2O with a mass of 0.1 g. Therefore, according to the formula, the internal cavity V of the micro heat pipe can be approximately calculated as:

[0087]

[0088] The molar mass of the internal heat transfer working fluid water in the pipe is M = 18 g / mol, so its molar content number is:

[0089] According to the initial yield strength of the micro heat pipe material, and after substituting the correction coefficient k = 0.4, the maximum internal pressure that the pipe can withstand can be calculated as:

[0090]

[0091] According to the maximum internal pressure calculated from the initial yield strength of the micro heat pipe material, the temperature value when reaching this internal pressure can be calculated according to the Antoine equation, and its formula is:

[0092] log 10 P = A - B / (T + C);

[0093] Among them, the constants A, B, and C are selected after referring to data as: A = 8.14019, B = 1810.94, C = 244.485. Then, substituting A, B, C and the previously obtained C into the formula, the temperature at this time can be obtained as: T = 283 °C.

[0094] At this time, verify whether the water content in the micro heat pipe is sufficient according to the ideal gas equation:

[0095] The calculated required water content is:

[0096] That is, in this method of controlling the bending and forming of wrinkles of the micro heat pipe, when the set temperature is 283 °C, the water inside the pipe has already been completely converted into water vapor, and the phenomenon of "dry burning" appears at the heating end of the pipe, and it is necessary to recalculate the heating temperature during the bending and forming process of the micro heat pipe.

[0097] When recalculating the heating temperature during the bending and forming process of the micro heat pipe, let the new internal pressure be:

[0098] P' = 0.6 * P = 4.166 Mpa;

[0099] At the new internal pressure, according to the Antoine equation, the calculated temperature at this time is: T = 252 °C.

[0100] At this time, verify whether the water content in the micro heat pipe is sufficient according to the ideal gas equation.

[0101] The calculated required water content is: H = 0.00481 mol < 0.0056 mol.

[0102] That is, the temperature value of 252 °C calculated after reducing the internal pressure of the pipe enables the micro heat pipe to be in a gas-liquid two-phase equilibrium state. At this time, the heat cycle of the micro heat pipe can be continuously carried out, and the micro heat pipe can be bent and formed at this temperature.

[0103] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor limit the invention to the specific embodiments described. Obviously, according to the content of this specification, many modifications and changes can be made. This specification selects and specifically describes these embodiments to better explain the principle and practical application of the present invention, so that those skilled in the art can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A method for controlling the quality of a micro heat pipe bending process, characterized in that: The following steps are involved: Step 1: Install the micro heat pipe that needs to be bent to the corresponding position on the bending forming mold; Step 2: The heating device heats the pipe to increase the temperature of the micro heat pipe, vaporize the heat transfer medium inside the pipe, form internal pressure, and play an internal supporting role on the pipe wall; Step 3: Start the bending machine to bend the pipe. During the bending process, the rolling die moves involute along the bending path to avoid scratching the surface of the micro heat pipe. The gas pressure in the pipe always provides pressure support to the inner wall of the pipe to avoid wrinkling and collapse of the pipe when bending. Step 4: After the bending is completed, the heating device is removed to obtain the target bent pipe.

2. A method for controlling the quality of a micro heat pipe bending process according to claim 1, characterized in that: The micro heat pipe is completely closed at both ends, and it is not easy to insert a core rod or fill other materials to prevent the pipe wall from becoming unstable during bending.

3. A method for controlling the quality of a micro heat pipe bending process according to claim 1, characterized in that: The bending forming die comprises a rolling die, a bending center die, a pressing block and a heating device.

4. A method for controlling the quality of a micro heat pipe bending process according to claim 3, characterized in that: The micro heat pipe is clamped on the bending center mold, and the pressing block presses the micro heat pipe. According to whether the pipe section of the micro heat pipe changes relative to the initial position during the bending process, it is divided into a fixed end and a movable end. The pipe section of the micro heat pipe that has not changed is the fixed end, and the pipe section of the micro heat pipe that has changed is the movable end. The fixed end and the movable end are separated by the pressing block, and the heating device is located at the fixed end of the micro heat pipe during the bending process.

5. According to claim 4, a method for controlling the quality of a micro heat pipe bending process, characterized in that: The rolling die is located at the other side of the pressing block, namely the moving end side. The rolling die rolls along the bending center die, and the moving end of the micro heat pipe is bent and formed into a target shape under the driving action of the rolling die.

6. A method for controlling the quality of a micro heat pipe bending process according to claim 3, characterized in that: The rolling die, the bending center die and the pressing block are covered with a heat insulating coating on the surface in contact with the micro heat pipe, so as to reduce the heat loss of the pipe.

7. A method for controlling the quality of a micro heat pipe bending process according to claim 3, characterized in that: The heating device is an electromagnetic induction heater, and the micro heat pipe is passed through the heating coil of the electromagnetic induction heater for heating.

8. A method for controlling the quality of a micro heat pipe bending process according to claim 1, characterized in that: The maximum internal pressure that the micro heat pipe can withstand is calculated by the following calculation method: Among them, P is the maximum internal pressure that the micro heat pipe can withstand, t is the wall thickness of the pipe, D is the outer diameter of the pipe, σ s is the initial yield stress of the pipe, k is the correction factor, which corrects the decrease in the yield stress of the heat pipe due to temperature rise and other defects of the pipe.

9. A method for controlling the quality of bending of a micro heat pipe according to claim 8, characterized in that: According to the Antoine equation, the temperature value when the micro heat pipe reaches the maximum internal pressure is preliminarily calculated: Among them, A, B, and C are constants, which can be obtained according to "Chemical Thermodynamics" or other manuals on the physical properties of related substances according to different working fluids and temperature conditions. P is the maximum internal pressure that the micro heat pipe can withstand, and T is the temperature at which the heat pipe needs to be heated.

10. A method for controlling the quality of a micro heat pipe bending process according to claim 9, characterized in that: The temperature T that the heat pipe needs to heat and the maximum internal pressure P that the micro heat pipe can withstand are verified and corrected according to the following steps: Step 1), calculating the internal cavity volume V of the micro heat pipe according to the geometric dimensions of the micro heat pipe; Step 2), according to the mass m of the heat transfer medium contained in the micro heat pipe and the molar mass M of the heat transfer medium, the molar mass M of the heat transfer medium is converted into the molar number n: Step 3) Substituting the maximum internal pressure P that the micro heat pipe can withstand, the temperature T that the heat pipe needs to heat, the internal volume V of the micro heat pipe and the ideal gas constant R into the ideal gas equation, the number of moles of heat transfer medium required at the temperature and pressure can be calculated: Step 4): Compare the number of moles n of the heat transfer working fluid in the micro heat pipe in Step 2) with the required number of moles n' of the heat transfer working fluid at this temperature and atmospheric pressure. When n > n', it indicates that the calculated heating temperature T of the heat pipe meets the requirements. The maximum heating temperature of the micro heat pipe can be set to T, and the loop is exited. When n < n', it means that the maximum internal pressure P and temperature that the micro heat pipe can withstand at this time are too high, and go to Step 5). Step 5): When the internal pressure P is too high, risks such as heat pipe explosion will occur. It is necessary to reduce the internal pressure of the pipe material to within the range that the pipe material can withstand, and make the new internal pressure of the pipe material be P'. The new internal pressure of the pipe material is calculated according to the following method: Let P' = f * P, where the value range of f is (0, 1). Then substitute P' into the Antoine equation to calculate T', and then enter Step 3) for judgment and comparison.

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