Processing method of ultra-thin copper tube for micro heat pipe

Abstract

The present application belongs to the field of heat pipe, and particularly relates to a processing method of ultra-thin copper pipe for micro heat pipe. The method comprises the following steps: 1) taking a preformed tubular copper material as a base material, and performing cold deformation processing on the base material to obtain a pre-processed carrier; 2) performing intermediate annealing treatment on the pre-processed carrier to obtain a heat pipe; 3) taking the heat pipe obtained in step 2) as a base material to replace the tubular copper material, and repeating the above steps 1) and 2) until the heat pipe reaches a preset specification, and then performing final annealing treatment to obtain an ultra-thin copper pipe for micro heat pipe. The processing method can effectively realize the processing and preparation of the ultra-thin copper pipe, can effectively produce and prepare the ultra-thin copper pipe with a thickness of 55-60 microns, and can effectively guarantee the strength and yield of the ultra-thin copper pipe.

Description

Technical Field

[0001] This invention belongs to the field of heat pipes, and particularly relates to a method for processing ultrathin copper tubes for micro heat pipes. Background Technology

[0002] Heat pipes are a very common and frequently used heat-conducting element. Compared with traditional air-cooling and water-cooling heat conduction, they have the advantage of portability. Furthermore, they achieve heat conduction through phase change, which has the characteristics of efficient and safe heat conduction and dissipation.

[0003] Micro heat pipes are a type of heat pipe that are smaller in size and specifications than conventional heat pipes. Their outer diameter is typically 1.5 mm or even less than 1.0 mm, and they are used for heat conduction and dissipation in some small and precision devices.

[0004] However, despite its superior performance, its manufacturing process remains challenging. For instance, common heat pipe copper tube manufacturing processes are largely inadequate for producing ultra-thin copper tubes for micro heat pipes. Our company has previously conducted research and development on this topic. For example, the segmented floating drawing process described in ZL202011121677.2 can achieve the fabrication of micron-level ultra-thin copper tubes, and under extreme process conditions, it can almost achieve a wall thickness of only about 75–80 μm (i.e., 0.075–0.080 mm). However, with the increasing demands for performance and usability in the market, even thinner copper tubes are required in some conditions. Existing processing technologies are insufficient for large-scale production, necessitating methods such as electrochemical forming, which are difficult to industrialize and extremely costly. Furthermore, the ultra-thin-walled copper tubes with a thickness of less than 0.12 mm prepared by traditional multi-segment floating drawing process and electrochemical deposition method have poor strength and very limited performance during use, and are prone to wall breakage, collapse and breakage. Summary of the Invention

[0005] To address the challenges of existing processes in effectively fabricating ultrathin-walled copper tubes, and the fact that ultrathin-walled copper tubes produced by existing methods suffer from poor strength and are prone to breakage during use, this invention provides a processing method for ultrathin copper tubes used in micro heat pipes.

[0006] The purpose of this invention is:

[0007] I. It can achieve the fabrication of ultra-thin-walled copper tubes with a wall thickness of approximately 55–60 μm;

[0008] II. The preparation method is simple, effective, and suitable for industrial production.

[0009] Third, ensure that the produced ultra-thin-walled copper tube has good mechanical properties.

[0010] To achieve the above objectives, the present invention adopts the following technical solution.

[0011] A method for fabricating ultrathin copper tubes for micro heat pipes.

[0012] The method includes:

[0013] 1) Take the pre-formed tubular copper material as the base material and perform cold deformation processing on it to obtain the pre-processed carrier;

[0014] 2) The pre-processed carrier is subjected to intermediate annealing to obtain an annealed hose;

[0015] 3) Using the annealed hose obtained in step 2) as the substrate, repeat steps 1) and 2) until the ultrathin tube reaches the preset specifications, and then perform final annealing to obtain an ultrathin copper tube for micro heat pipes.

[0016] As a preferred option

[0017] Step 1) The cold deformation processing is cold deformation drawing;

[0018] The cold deformation drawing is carried out under conditions where the ambient temperature is ≤60 ℃.

[0019] As a preferred option

[0020] During the cold deformation drawing process, a core with an outer diameter greater than or equal to the inner diameter of the substrate is inserted into the substrate.

[0021] As a preferred option

[0022] The core is a heat-conducting medium, which is preheated to 180-220°C before use.

[0023] As a preferred option

[0024] Step 1) The cold deformation processing procedure controls the deformation amount per cycle to be... Def The Def The calculation is performed using the following formula:

[0025] ;

[0026] In the formula: Def This represents the deformation amount in a single instance, and has no unit. A This is the draw ratio, which has no unit. Def c The critical deformation of the selected copper material, without units; F The number of pulls is not specified.

[0027] As a preferred option

[0028] The number of pulls F Should be controlled F ≤20.

[0029] As a preferred option

[0030] The pull-out coefficient A Based on the critical deformation of the selected copper material Def c The following adjustments will be made:

[0031] When 10%≤ Def c When <12%, A Take 0.915;

[0032] When 12%≤ Def c When <16%, A Take 0.930;

[0033] When 16%≤ Def c When ≤20%, A Take 0.945.

[0034] As a preferred option

[0035] Step 2) The intermediate annealing process is controlled with an annealing temperature of 120-150 ℃ and a single annealing time of 30-60 min.

[0036] As a preferred option

[0037] Step 3) The final annealing process controls the annealing temperature to be 260–320 °C and the annealing time to be 1–2 h.

[0038] The core of the technical solution of this invention lies in improving the influence of the drawing process of ultra-thin copper tubes for micro heat pipes on their microstructure morphology.

[0039] In the processing of heat pipes, the focus for the base copper tube is typically on its purity and grain size. Because the copper tube requires continuous drawing, it is usually necessary to select copper tubes with a grain size of 5-12 to improve yield and prevent breakage during drawing. In particular, it is crucial to ensure that the oxygen-free copper base material obtained from continuous casting has fine and uniform grains, while ensuring that the phosphorus and oxygen content in the copper is less than 5 ppm. Furthermore, during the continuous drawing process, it is necessary to control the deformation of each drawing and the annealing temperature after drawing to ensure that the copper tube maintains its fine-grained state after each drawing.

[0040] Previous technical studies have found that the critical deformation of copper is typically 10-20%, with variations depending on the copper composition and original texture coefficient. During the drawing process, it's crucial to ensure that the single-step deformation is less than or equal to the lower limit of the critical deformation. When the critical deformation is reached, uneven deformation leads to significant localized stress concentration in the copper tube, making it highly susceptible to breakage during processing and accumulating substantial radial residual stress. This radial residual stress makes the copper tube extremely prone to breakage during use. While this defect doesn't directly affect the use of copper tubes with a wall thickness ≥1.0 mm, in the fabrication of ultra-thin-walled copper tubes, the radial residual stress can cause internal and external cracking when subjected to bending or radial impact, necessitating extreme caution when using ultra-thin-walled tubes. Therefore, existing ultra-thin-walled micro heat pipe copper tubes require repeated drawing-annealing processes during manufacturing.

[0041] Some heat pipes, however, undergo the opposite process, employing supercritical processing. Supercritical processing accelerates grain deformation and dislocation accumulation. Residual stress lowers the recrystallization temperature, refining the grains. Furthermore, stress reduction is typically achieved through low-temperature tempering at 320–360°C, ensuring the mechanical properties of the copper tube. However, this process also introduces defects and more grain boundaries. In ultra-thin-walled applications, the extremely small wall thickness of the copper tube makes it prone to fracture. Moreover, supercritical processing cannot be repeated multiple times; otherwise, the yield rate will drastically decrease.

[0042] To address this, the researchers of this invention established a pre-copper tube drawing model based on the optimal drawing model selected through analysis of the deformation law of the pre-copper tube.

[0043] The Finite Element Analysis model for drawing deformation was used to analyze the dimensional changes before and after drawing using ANSYS, and to perform grain characterization and texture analysis. The deformation variation law of drawing deformation was analyzed, and the deformation variation law of typical pre-copper tubes was obtained, i.e., the finite element analysis results. In this process, it was found that there are significant differences in grain characterization and texture analysis results between ultra-thin-walled copper tubes with actual wall thickness ≤0.15 mm and conventional copper tubes with thickness ≥1.0 mm, especially on the inner and outer walls of ultra-thin-walled copper tubes, where there are very obvious differences that have not been found in conventional thickness copper tubes.

[0044] Further research revealed that under low-critical or supercritical processing conditions, the grain size and texture of the inner and outer walls of ultra-thin-walled copper tubes tend to be consistent. However, in the near-critical state, the grains on the outer wall are significantly coarser, while the grains on the inner wall break prematurely during the floating drawing process. The broken fine grains are embedded in the coarse grains to some extent, which also causes some breakage. New crystal nuclei will be generated at defects and grain boundaries, resulting in a difference in grain size between the inner and outer walls, forming a "gradient grain size". The resulting gradient grain size ensures the strength and toughness of the copper tube and can also alleviate its residual stress to a certain extent.

[0045] In response, researchers re-established control over copper tube processing by combining near-critical machining with core floating drawing and internal heating, reducing defects, dislocations, and excessive grain boundaries. Based on this phenomenon, they re-established and validated the Finite Element Analysis model, deriving the optimal processing conditions and corresponding parameter control methods.

[0046] In particular, by adjusting the fixed parameters based on the critical deformation of the selected copper material, a calculation model suitable for industrial production is derived through fitting analysis. ;

[0047] In the formula: Def This represents the deformation amount in a single instance, and has no unit. A This is the draw ratio, which has no unit. Def c The critical deformation of the selected copper material, without units; F This refers to the number of pull-out cycles, without units.

[0048] By combining the above model with the copper material with different critical deformation, the variable drawing coefficient is further adjusted to finally determine the optimal calculation model.

[0049] The beneficial effects of this invention are:

[0050] The processing method of this invention can very effectively realize the processing and preparation of ultra-thin-walled copper tubes, and can effectively produce ultra-thin-walled copper tubes with a thickness of 55-60 μm, while effectively ensuring the strength and yield of the copper tubes. Detailed Implementation

[0051] The present invention will be further described clearly and in detail below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0052] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0053] Unless otherwise specified, the copper materials used in the embodiments of the present invention are all industrial pure copper, and the copper materials used in the embodiments of the present invention are all high-quality copper materials purchased on December 29, 2021 from the same batch. Random sampling experiments were conducted to record the copper materials of this batch. The critical deformation amount of this batch of copper materials is 15.8% to 15.9%, which is highly consistent. Before each experiment, a small amount of the experimental material is sampled and re-characterized.

[0054] Unless otherwise specified, the copper drawing process in the embodiments of the present invention is carried out by floating drawing. Tubular copper material is taken as the base copper tube blank, and the copper tube blank is subjected to pre-forming treatments such as polishing, descaling, degreasing, three-roll planetary rolling and clamping three-stage drawing to obtain pre-copper tube. Example 1

[0055] A method for processing ultrathin copper tubes for micro heat pipes, characterized in that,

[0056] The method includes:

[0057] 1) Take the pre-formed copper tube as the substrate and perform cold deformation processing on it. During the cold deformation processing, the pre-copper tube is installed using an outer mold and a core made of Ti(CN) metal ceramic material. Lubricating oil is applied to the inner and outer walls of the pre-copper tube. The outer diameter of the core is equal to the inner diameter of the pre-copper tube. The processing environment temperature is controlled at 50 ℃. After preheating the core to 200 ℃, the tube is drawn by floating to obtain an ultra-thin-walled copper tube, thus obtaining a pre-processed carrier.

[0058] 2) The pre-processed carrier is subjected to intermediate annealing at 135 °C for 45 min to obtain the heat pipe;

[0059] 3) Using the heat pipe obtained in step 2) as a substitute for the tubular copper material as the substrate, repeat steps 1) and 2) until the heat pipe reaches the preset specifications, and then perform a final annealing treatment at 300 °C for 1.5 h to obtain an ultra-thin copper tube for micro heat pipes.

[0060] Characterization experiments were conducted on the copper material before processing, and the results showed its critical deformation amount. Def c Approximately 15.8%, until the grains reach their maximum size, without significant grain breakage. Therefore, the pull-out coefficient... A The value is 0.930.

[0061] Calculate the single deformation amount using the deformation amount formula. Def The calculation formula is as follows:

[0062] ;

[0063] In the formula: Def This represents the deformation amount in a single instance, and has no unit. A This is the draw ratio, which has no unit. Def c The critical deformation of the selected copper material, without units; F The number of pulls is not specified.

[0064] Based on the calculated values, a drawing process was performed until the tube wall thickness reached approximately 58 μm, involving a total of 16 drawing operations. F The number of pull-out cycles ranges from 1 to 16.

[0065] The single drawing amount and the resulting wall thickness are calculated. The wall thickness is controlled using a high-precision micrometer, with the minimum distance between the outer die and the mandrel as specified. See the table below for details.

[0066]

[0067] Table: Pull-out sequence F When the value is 0, it is not included in the calculation of single deformation. Def .

[0068] The final copper tube was sampled and characterized. The wall thickness of the tube was between 0.0579 and 0.0582 mm at ten sampling points. The average value was calculated to be approximately 0.058 mm, indicating extremely high processing accuracy.

[0069] In addition, the obtained copper tube was characterized by its mechanical properties, including tensile strength and elongation at break, to indirectly demonstrate its toughness and brittleness. It was compared with an ultra-thin-walled copper tube with the same outer diameter and wall thickness of 0.08 mm produced by segmented drawing with a spiral core as described in ZL202011121677.2, serving as a control sample.

[0070] The characterization results are shown in the table below.

[0071]

[0072] The characterization results above show that the copper tubes produced by this invention exhibit significantly improved tensile strength and elongation at break compared to existing technologies, and the yield rate can be effectively maintained above 98% during the manufacturing process. The overall product quality is effectively guaranteed. Example 2

[0073] A method for processing ultrathin copper tubes for micro heat pipes, characterized in that,

[0074] The method includes:

[0075] 1) Take the pre-formed copper tube as the substrate and perform cold deformation processing on it. During the cold deformation processing, the pre-copper tube is installed using an outer mold and a core made of Ti(CN) metal ceramic material. Lubricating oil is applied to the inner and outer walls of the pre-copper tube. The outer diameter of the core is equal to the inner diameter of the pre-copper tube. The processing environment temperature is controlled at 50 ℃. After preheating the core to 200 ℃, the tube is drawn by floating to obtain an ultra-thin-walled copper tube, thus obtaining a pre-processed carrier.

[0076] 2) The pre-processed carrier is subjected to intermediate annealing at 135 °C for 45 min to obtain the heat pipe;

[0077] 3) Using the heat pipe obtained in step 2) as a substitute for the tubular copper material as the substrate, repeat steps 1) and 2) until the heat pipe reaches the preset specifications, and then perform a final annealing treatment at 300 °C for 1.5 h to obtain an ultra-thin copper tube for micro heat pipes.

[0078] Characterization experiments were conducted on copper samples taken before processing. The results showed that its critical deformation was approximately 15.8%, reaching its maximum grain growth without significant grain breakage. Therefore, the pull-out coefficient... A The value is 0.930.

[0079] Calculate the single deformation amount using the deformation amount formula. Def The calculation formula is as follows:

[0080] ;

[0081] In the formula: Def This represents the deformation amount in a single instance, and has no unit. A This is the draw ratio, which has no unit. Def c The critical deformation of the selected copper material, without units; F The number of pulls is not specified.

[0082] Based on the calculated values, a drawing process was performed until the tube wall thickness reached approximately 55 μm, involving a total of 15 drawing operations. F The number of pull-out cycles ranges from 1 to 15.

[0083] The single drawing amount and the resulting wall thickness are calculated. The wall thickness is controlled using a high-precision micrometer, with the minimum distance between the outer die and the mandrel as specified. See the table below for details.

[0084]

[0085] Table: Pull-out sequence F When the value is 0, it is not included in the calculation of single deformation. Def .

[0086] The final copper tube was sampled and characterized. Ten sampling results showed that the tube wall thickness was between 0.0550 and 0.552 mm, and the average measurement result was approximately 0.055 mm, indicating extremely high processing accuracy.

[0087] In addition, the obtained copper tube was characterized by its mechanical properties, including tensile strength and elongation at break, to indirectly demonstrate its toughness and brittleness. It was compared with an ultra-thin-walled copper tube with the same outer diameter and wall thickness of 0.075 mm produced by segmented drawing with a spiral core as described in ZL202011121677.2, serving as a control sample.

[0088] The characterization results are shown in the table below.

[0089]

[0090] The characterization results above show that the copper tubes produced by this invention exhibit significantly improved tensile strength and elongation at break compared to existing technologies, and the yield rate can be effectively maintained above 98% during the manufacturing process. The overall product quality is effectively guaranteed. Comparative Example 1

[0091] Based on Example 1, the process and parameters of Example 1 were used to prepare copper tubes with a wall thickness of 0.058–0.062 mm, focusing only on the single deformation. Def Adjustments were made to the single deformation. Def The pull-out coefficient substituted during the calculation A Adjustments were made. The copper material was then subjected to characterization experiments before the same treatment, and the results showed that its critical deformation was approximately 15.8%.

[0092] The results of this comparative experiment were also used to validate and / or refine the Finite Element Analysis model.

[0093] The experimental results are shown in the table below.

[0094]

[0095] Among them, the pull-out coefficient A Frequent fractures occurred during sample preparation at values ​​of 0.945 and 0.950. The fractures were concentrated in the intermediate processing stage where the tube wall thickness was approximately 0.08–0.09 mm, and therefore no data were available.

[0096] The above experimental results clearly show that the pull-out coefficient has a significant impact on the performance of the final sample. This is because the pull-out coefficient of this invention exhibits a certain regularity in experiments and model components. Substituting the pull-out coefficient into the model should result in a single deformation amount during the initial pull-out process. Def As close as possible to the material's critical deformation. Def c However, when the pull-out coefficient deviates from this value, although the tensile strength can still be retained to some extent, the elongation at break decreases significantly, such as the pull-out coefficient. A At a pull-out coefficient of 0.915, the elongation at break decreased by approximately 5% compared to Example 1. Furthermore, when the pull-out coefficient was too high, it was observed that the tensile strength of the sample was higher, but the decrease in elongation at break was more significant, even affecting the pull-out coefficient. A When the values ​​are 0.945 and 0.950, fracture occurs directly during the processing.

[0097] It can be seen that for the critical deformation amount Def c For a copper material with 15.8% content, the optimal draw factor should be 0.930 to 0.935.

[0098] Therefore, through model construction and analysis, models with different critical deformation amounts are selected. Def c Orthogonal experiments were conducted on copper materials with different drawdown coefficients to verify different critical deformation amounts. Def c The optimal drawing coefficient range for the copper material is shown in the table below.

[0099]

[0100] Based on the above experiments and calculations, and to facilitate industrial-scale processing, the intersection value is taken, i.e., the value is determined when 10% ≤ Def c When <12%, the draw coefficient A Take 0.915, when 12% ≤ Def c When <16%, the draw coefficient A Take 0.930, when 16% ≤ Def c When ≤20%, the draw ratio A Take 0.945. Comparative Example 2

[0101] Based on Example 1, the only difference is:

[0102] The same preparation experiment was conducted using different core tip preheating temperatures. The experimental results are shown in the table below.

[0103]

[0104] The experimental results above show that, in the drawing process of this invention, the use of a spiral core combined with internal heating can effectively improve the mechanical properties of the resulting copper tube samples, significantly enhancing both tensile strength and elongation at break. This is because, during spiral core drawing, preheating of the core tip effectively achieves dynamic heat treatment of the copper tube's interior. The main purpose of this heat treatment is to effectively break and grow the grains on the inner wall of the copper tube during near-critical deformation processing, thereby compressing the grains on the outer wall and causing them to fracture. Meanwhile, the outer wall is under low-temperature conditions, essentially undergoing a continuous "cooling" process. Combined with critical deformation drawing, this achieves dynamic "breaking" and "growth," preventing excessive grain refinement that would limit the drawing process and avoiding excessive grain coarsening that would lead to brittleness and cracks. Therefore, the control of the core tip preheating temperature during spiral core drawing has a significant impact on the actual production process.

Claims

1. A method for processing ultrathin copper tubes for micro heat pipes, characterized in that, The method includes: 1) Take the pre-formed tubular copper material as the base material and perform cold deformation processing on it to obtain the pre-processed carrier; Step 1) The cold deformation processing is cold deformation drawing; The cold deformation drawing is carried out under conditions where the ambient temperature is ≤60 ℃; 2) The pre-processed carrier is subjected to intermediate annealing to obtain an annealed hose; 3) Using the annealed hose obtained in step 2) as the substrate, repeat steps 1) and 2) until the copper tube reaches the preset specifications, and then perform final annealing to obtain an ultra-thin copper tube for micro heat pipes. Step 1) The cold deformation processing procedure controls the deformation amount per cycle to be... Def The Def The calculation is performed using the following formula: ； In the formula: Def This represents the deformation amount in a single instance, and has no unit. A This is the draw ratio, which has no unit. Def c The critical deformation of the selected copper material, without units; F This refers to the number of pull-out cycles, without units. The number of pulls F Should be controlled F ≤20; The pull-out coefficient A Based on the critical deformation of the selected copper material Def c The following adjustments will be made: When 10%≤ Def c When <12%, A Take 0.915; When 12%≤ Def c When <16%, A Take 0.930; When 16%≤ Def c When ≤20%, A Take 0.

945.

2. The processing method of an ultra-thin copper tube for a micro heat pipe according to claim 1, characterized in that, During the cold deformation drawing process, a core with an outer diameter greater than or equal to the inner diameter of the substrate is inserted into the substrate.

3. The processing method of an ultra-thin copper tube for a micro heat pipe according to claim 2, characterized in that, The core is a heat-conducting medium, which is preheated to 180-220°C before use.

4. The processing method of an ultra-thin copper tube for a micro heat pipe according to claim 1, characterized in that, Step 2) The intermediate annealing process is controlled with an annealing temperature of 120-150 ℃ and a single annealing time of 30-60 min.

5. The processing method of an ultra-thin copper tube for a micro heat pipe according to claim 1, characterized in that, Step 3) The final annealing process controls the annealing temperature to be 260–320 °C and the annealing time to be 1–2 h.

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