Hollow heat pipe integrated ball screw and design method thereof

Abstract

The invention discloses a hollow heat pipe integrated ball screw and a design method thereof, and belongs to the technical field of ball screws. The ball screw comprises a hollow screw body, one end of a hollow cavity in the hollow screw body is a closed end, the other end of the hollow cavity is an open end, the open end forms a condensation end, and the inner wall of the hollow cavity directly forms the outer wall of a heat pipe; the liquid absorption core is of a wave-shaped porous capillary structure formed by additive manufacturing and is tightly attached to the inner wall of the hollow cavity; the hollow cavity is filled with the working medium; and the heat dissipation fins are arranged at the condensation end and are of a lattice structure manufactured by additive materials. A thermal interface between the heat pipe and the lead screw is omitted, and thermal resistance is reduced; a hydrophilic coating and a hydrophobic coating are arranged on the wave trough and the wave crest of the wick respectively and are matched with centrifugal force generated when the lead screw rotates to enhance working medium backflow; the radiating fins form forced convection through rotation of the lead screw. The ball screw has the advantages of being good in temperature uniformity, short in heat balance time and simple in structure, and the precision retentivity of the ball screw can be improved.

Description

Technical Field

[0001] This invention belongs to the field of ball screw technology, and particularly relates to a hollow heat pipe integrated ball screw and its design method. Background Technology

[0002] A ball screw is a mechanical device that converts rotary motion into linear motion. It boasts advantages such as high transmission efficiency, high precision, and long service life, and is widely used in CNC machine tools. The precision of the ball screw is a crucial factor affecting the machining accuracy of CNC machine tools. However, during operation, the ball screw is subjected to uneven heat sources, creating a complex temperature field. Under the influence of this temperature field, deformation occurs, thereby reducing the machining accuracy of the machine tool.

[0003] In precision machining, a common practice to avoid machining errors caused by thermal deformation of the ball screw is to perform a warm-up process for half an hour to several hours to allow the ball screw to reach thermal equilibrium before machining. This approach reduces machine tool utilization and machining efficiency, while increasing workpiece manufacturing costs. Therefore, how to regulate the temperature field during ball screw operation, thereby controlling thermal deformation and achieving high thermal stability ball screw design, is an urgent need in the field of ball screw manufacturing and design.

[0004] Currently, existing technologies propose the design of hollow water-cooled lead screws, which involves hollowing out the inside of the lead screw and designing water channels to pump water in and remove the heat generated by the heat source during processing, thus maintaining the stability of the lead screw temperature. Although this approach can reduce the operating temperature of the lead screw, the contact area between the water flow and the inner wall is small, resulting in poor heat exchange efficiency. In addition, this design increases the need for water channels, chillers, and other mechanisms and equipment, significantly increasing the cost and complexity of the machine tool.

[0005] Heat pipes are highly efficient heat transfer elements, with thermal conductivity tens of thousands of times that of copper. Applying heat pipes to lead screws can effectively conduct away the heat generated during operation, thereby improving temperature uniformity and showing great application potential in CNC machine tools. However, simply stuffing a heat pipe into a hollow lead screw does not achieve the best results because a thermal interface exists between the outer wall of the heat pipe and the inner wall of the hollow lead screw, increasing thermal resistance and hindering the heat exchange process. Therefore, achieving efficient heat exchange between the heat pipe and the hollow lead screw is key to designing a lead screw with high thermal stability.

[0006] Therefore, there is an urgent need in this field for a ball screw design that can solve the problems of poor heat exchange capacity and complex structure of hollow water-cooled ball screws, and achieve efficient heat exchange between heat pipes and hollow ball screws. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a hollow heat pipe integrated ball screw and its design method. By directly using the inner wall of the hollow screw as the outer wall of the heat pipe, efficient heat exchange is achieved through the phase change process of the working fluid, and the heat generated by the screw is conducted to the air through heat dissipation fins, thereby improving the temperature stability of the screw and thus enhancing the precision retention of the ball screw.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides an integrated hollow heat pipe ball screw, comprising: The hollow screw body has an axially extending hollow cavity inside. One end of the hollow cavity is a closed end and the other end is an open end. The open end constitutes the condensing end of the heat pipe, and the inner wall of the hollow cavity directly constitutes the outer wall of the heat pipe. A liquid-absorbing core is disposed in the hollow cavity. The liquid-absorbing core is an additively manufactured wavy porous capillary structure with a wavy longitudinal section. The liquid-absorbing core is tightly attached to the inner wall of the hollow cavity. The working medium is filled into the hollow cavity, and the hollow cavity is filled with the working medium after being evacuated. Heat dissipation fins are disposed on the condensation end, and the heat dissipation fins are additively manufactured lattice structures.

[0010] Furthermore, the wave-shaped structure of the liquid-absorbing core has 6 to 9 peaks and troughs along the axial direction, with the wave height value being 1 / 10 to 1 / 8 of the inner diameter of the hollow cavity. The troughs are set to correspond to the heat source position, and the peaks are set to correspond to the condensation position.

[0011] Furthermore, a hydrophobic coating is provided on the surface of the liquid absorption core at the crest, and a hydrophilic coating is provided on the surface of the liquid absorption core at the trough. The hydrophobic coating is a fluorosilane composite material deposited by physical vapor deposition, and the hydrophilic coating is an alumina-based composite material deposited by atomic layer deposition. The thickness of both the hydrophobic coating and the hydrophilic coating is 80-120 μm.

[0012] Furthermore, the liquid-absorbing core has a porosity of 70%–80%, a pore size distribution of 30–60 μm, and a permeability of 10. 10 ~10 11 m 2 .

[0013] Furthermore, the two ends of the liquid suction core are rigidly fixed to the hollow screw body by mechanical clamping, and the mechanical clamping method includes setting a threaded set plug at the end of the hollow screw body.

[0014] Furthermore, the working fluid is a mixture of liquid ammonia and Freon-like working fluid, with a mass ratio of liquid ammonia to Freon-like working fluid of 5:1 to 2:1, the liquid volume of the working fluid accounting for 15% to 30% of the volume of the hollow cavity, and the gas pressure of the hollow cavity being 10 to 40 kPa.

[0015] Furthermore, the heat dissipation fins are connected to the hollow lead screw body by an interference fit. The heat dissipation fins are designed with optimized flow resistance and are shaped as a triangle, a paddle, or a streamline to form forced convection heat dissipation when the lead screw rotates.

[0016] Secondly, this invention provides a design method for an integrated hollow heat pipe ball screw, comprising the following steps: Step 1: Process a hollow lead screw body with a hollow cavity. The hollow cavity extends axially. One end of the hollow cavity is a closed end and the other end is an open end. The open end constitutes the condensing end of the heat pipe. The inner wall of the hollow cavity directly constitutes the outer wall of the heat pipe. Step 2: Using additive manufacturing technology, a wave-shaped porous capillary structure liquid-absorbing core is formed on the inner wall of the hollow cavity. The longitudinal section of the liquid-absorbing core is wave-shaped and closely fits the inner wall of the hollow cavity. Step 3: Vacuum the hollow cavity and fill it with working fluid; Step four: Use additive manufacturing to form heat dissipation fins with a dot matrix structure, and install the heat dissipation fins on the condenser end.

[0017] Furthermore, in step two, the molding parameters of the wavy porous capillary core include: porosity of 70%–80%, pore size distribution of 30–60 μm, and permeability of 10. 10 ~10 11 m 2 After molding, a fluorosilyl hydrophobic coating is physically vapor deposited on the surface at the crest, and an alumina-based hydrophilic coating is atomically deposited on the surface at the trough. The thickness of both the hydrophobic and hydrophilic coatings is 80–120 μm.

[0018] Further, in step three, the working fluid is a mixture of liquid ammonia and Freon-like working fluid, with a mass ratio of liquid ammonia to Freon-like working fluid of 5:1 to 2:1, the liquid volume of the working fluid accounting for 15% to 30% of the volume of the hollow cavity, and the air pressure of the hollow cavity being 10 to 40 kPa; in step four, the heat dissipation fins are designed with optimized flow resistance, and their shape is one of triangular, paddle-shaped, or streamlined, so as to form forced convection heat dissipation when the lead screw rotates.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. By integrating the design and manufacturing of the hollow screw and heat pipe, the inner wall of the hollow screw is directly used as the outer wall of the heat pipe, eliminating the thermal interface between the heat pipe and the screw, realizing efficient thermal contact between the screw and the heat pipe, significantly improving the heat extraction capacity of the heat pipe screw, thereby improving the temperature uniformity and precision retention of the screw.

[0020] 2. By applying heat pipe technology to the lead screw and utilizing the principle of phase change heat transfer, the thermal conductivity of the lead screw is significantly improved, the temperature gradient during the operation of the heat pipe is effectively reduced, the accuracy retention and temperature uniformity of the lead screw are improved, the thermal equilibrium time of the lead screw is reduced, and the processing efficiency and utilization rate of the machine tool are improved.

[0021] 3. Through innovative additive manufacturing of a wave-shaped liquid wick design, the troughs are placed at the heat source and the crests at the condensation point. Hydrophilic and hydrophobic coatings are sprayed on the troughs and crests respectively. The centrifugal force of the screw rotation enhances the recirculation of the working fluid, forming a push-pull effect, which significantly enhances the phase change heat transfer effect of the heat pipe.

[0022] 4. By optimizing the design of the additive manufacturing lattice structure heat dissipation fins and utilizing the rotational motion of the lead screw, air convection is enhanced, changing the heat exchange between the fins and the air from natural convection to forced convection. This effectively transfers the heat generated by the system to the air, eliminating the need for cooling water and reducing the complexity and cost of machine tool design. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the overall structure of the hollow heat pipe integrated ball screw in an embodiment of the present invention; Figure 2 This is a schematic diagram of the additive manufacturing lattice heat sink fins in an embodiment of the present invention; Figure 3 This is a schematic diagram of the wavy liquid-absorbing core in an embodiment of the present invention.

[0025] In the diagram: 1. Hollow screw body; 11. Hollow cavity; 2. Liquid suction core; 21. Peak; 22. Trough; 3. Heat dissipation fins; 4. Working fluid. Detailed Implementation

[0026] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0027] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] Example 1 like Figures 1-3 As shown, this embodiment provides a hollow heat pipe integrated ball screw, including a hollow screw body 1, a liquid wick 2, a working fluid 4, and heat dissipation fins 3.

[0029] The hollow lead screw body 1 is a shaft-like component with an axially extending hollow cavity 11 inside. One end of the hollow cavity is closed, and the other end is open. The closed end is fixed by a bearing and connected to the motor via a coupling. The open end is supported by a bearing and forms the condenser end of the heat pipe, extending beyond the bearing by a certain distance. The exposed portion is used to install the heat dissipation fins 3. The inner wall of the hollow cavity directly serves as the outer wall of the heat pipe, eliminating the need for an additional heat pipe shell.

[0030] The liquid-absorbing core 2 is disposed within the hollow cavity 11. It is an additively manufactured, wave-shaped porous capillary structure with a wave-shaped longitudinal section and 6-9 peaks 21 and troughs 22 along the axial direction (the number of peaks and troughs can be adjusted within the range of 6-9 according to the length of the lead screw). The wave height is 1 / 10 to 1 / 8 of the inner diameter of the hollow cavity. The troughs 22 are set at the heat source location (such as bearings or ball nuts), and the peaks 21 are set at the condensation location. The liquid-absorbing core 2 is tightly fitted to the inner wall of the hollow cavity by mechanical compression, and both ends are rigidly fixed by threaded set plugs set at the ends of the hollow lead screw body 1. The porosity of the liquid-absorbing core 2 is 70%-80%, the pore size distribution is 30-60μm, and the permeability is 10. 10 ~10 11 m 2 .

[0031] A fluorosilane-based hydrophobic coating is deposited on the surface of the suction core 2 at the peak 21 via physical vapor deposition (PVD), and an alumina-based hydrophilic coating is deposited on the surface of the trough 22 via atomic layer deposition (ALD). The thickness of both the hydrophobic and hydrophilic coatings is 80–120 μm, with a preferred coating thickness of 100 μm. The combination of the hydrophilic and hydrophobic coatings creates a push-pull effect, which, combined with the centrifugal force during screw rotation, significantly enhances the reflux capability of the working fluid.

[0032] The working medium 4 is a mixture of liquid ammonia and Freon-like substances, with a mass ratio of liquid ammonia to Freon-like substances of 5:1 to 2:1. The liquid volume of the working medium accounts for 15% to 30% of the volume of the hollow cavity. The hollow cavity is evacuated to a pressure of 10 to 40 kPa (preferably 15 kPa) and then filled with the working medium. After filling, the open end is sealed by welding.

[0033] The heat dissipation fins 3 are disposed at the condensation end (i.e., outside the open end) of the hollow lead screw body 1, such as... Figure 2 As shown, the heat dissipation fins 3 are additively manufactured lattice structures, and their shape is one of triangular, paddle-shaped, or streamlined. The heat dissipation fins 3 are connected to the hollow lead screw body 1 by an interference fit. The heat dissipation fins 3 are optimized by CFD flow resistance design, with capillary suction performance index as the target. When the lead screw rotates, it can fan out air to form forced convection, which significantly enhances the heat dissipation effect.

[0034] In this embodiment, when the integrated hollow heat pipe ball screw is working, the bearings and ball nuts generate heat, causing the working fluid to evaporate. The phase change of the working fluid absorbs heat, lowering the temperature at the heating end. The gaseous working fluid moves towards the condensing end under pressure, where it cools and condenses, causing the temperature at the low-temperature end to rise. Figure 3 As shown, the liquid working fluid is transferred to the evaporation end through the wick 2 under capillary action, forming a working cycle. During this process, the heat transfer efficiency is significantly improved because the thermal interface between the heat pipe and the lead screw is eliminated. Simultaneously, the trough 22 of the corrugated wick 2 is located at the heat source, and the crest 21 is located at the condensation point. When the lead screw rotates, centrifugal force causes the working fluid to move towards the trough 22, enhancing the reflux of the working fluid. The push-pull effect of the hydrophilic and hydrophobic coatings further enhances the reflux capability. The heat dissipation fins 3 at the condensation end utilize the rotation of the lead screw to form forced convection, efficiently transferring heat to the air. Tests show that, under the same operating conditions, the maximum surface temperature difference of the lead screw in this embodiment does not exceed 1.2℃, and the thermal equilibrium time is shortened to within 8-10 seconds. Compared to traditional hollow water-cooled lead screws and ordinary heat pipe lead screws, both temperature uniformity and thermal response speed are significantly improved.

[0035] Example 2 This embodiment provides a design method for an integrated hollow heat pipe ball screw, including the following steps: Step 1: Process a hollow lead screw body 1 with a hollow cavity. The hollow cavity extends axially, with one end closed and the other end open. The open end forms the condensing end of the heat pipe, and the inner wall of the hollow cavity serves as the outer wall of the heat pipe.

[0036] Step two: Using additive manufacturing technology, a wave-shaped porous capillary structure liquid-absorbing core 2 is formed on the inner wall of the hollow cavity. The longitudinal section of the liquid-absorbing core 2 is wave-shaped, with 6-9 peaks and troughs along the axial direction. The peak height is 1 / 10 to 1 / 8 of the inner diameter of the hollow cavity, and it is tightly fitted to the inner wall of the hollow cavity. The forming parameters are controlled as follows: porosity 70%-80%, pore size distribution 30-60 μm, and permeability 10. 10 ~10 11 m 2 After molding, a fluorosilyl hydrophobic coating is deposited on the surface at the crests by physical vapor deposition, and an alumina-based hydrophilic coating is deposited on the surface at the troughs by atomic layer deposition. The thickness of both the hydrophobic and hydrophilic coatings is 80–120 μm, with a preferred coating thickness of 100 μm.

[0037] Step 3: Vacuum the hollow cavity to a pressure of 10-40 kPa, preferably 15 kPa, and fill it with a working fluid, which is a mixture of liquid ammonia and Freon-like fluid (mass ratio 5:1-2:1). The amount of working fluid filling the hollow cavity is 15%-30% of its volume.

[0038] Step four: Heat dissipation fins 3 with a dot matrix structure are formed by additive manufacturing and installed on the condensation end of the hollow lead screw body. The shape of the heat dissipation fins 3 is one of triangular, paddle-shaped or streamlined. It is optimized by CFD flow resistance optimization with the capillary suction performance index as the target, so as to form forced convection heat dissipation when the lead screw rotates. The heat dissipation fins 3 and the hollow lead screw body 1 are connected by interference fit.

[0039] The design method of this embodiment enables the efficient manufacturing of integrated hollow heat pipe ball screws, and the resulting products have good temperature uniformity and rapid thermal response characteristics.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the embodiments of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A hollow heat pipe integrated ball screw, characterized in that, include: The hollow screw body has an axially extending hollow cavity inside. One end of the hollow cavity is a closed end and the other end is an open end. The open end constitutes the condensing end of the heat pipe, and the inner wall of the hollow cavity directly constitutes the outer wall of the heat pipe. A liquid-absorbing core is disposed in the hollow cavity. The liquid-absorbing core is an additively manufactured wavy porous capillary structure with a wavy longitudinal section. The liquid-absorbing core is tightly attached to the inner wall of the hollow cavity. The working medium is filled into the hollow cavity, and the hollow cavity is filled with the working medium after being evacuated. Heat dissipation fins are disposed on the condensation end, and the heat dissipation fins are additively manufactured lattice structures.

2. The hollow heat pipe integrated ball screw according to claim 1, characterized in that, The wavy structure of the liquid-absorbing core has 6 to 9 peaks and troughs along the axial direction. The wave height is 1 / 10 to 1 / 8 of the inner diameter of the hollow cavity. The troughs are set to correspond to the heat source position, and the peaks are set to correspond to the condensation position.

3. The hollow heat pipe integrated ball screw according to claim 2, characterized in that, The surface of the liquid-absorbing core is provided with a hydrophobic coating at the crest and a hydrophilic coating at the trough. The hydrophobic coating is a fluorosilane composite material deposited by physical vapor deposition, and the hydrophilic coating is an alumina-based composite material deposited by atomic layer deposition. The thickness of both the hydrophobic and hydrophilic coatings is 80-120 μm.

4. The hollow heat pipe integrated ball screw according to claim 1, characterized in that, The liquid absorption core has a porosity of 70%–80%, a pore size distribution of 30–60 μm, and a permeability of 10. 10 ~10 11 m 2 .

5. The hollow heat pipe integrated ball screw according to claim 1, characterized in that, The two ends of the liquid suction core are rigidly fixed to the hollow screw body by mechanical clamping, and the mechanical clamping method includes setting a threaded set plug at the end of the hollow screw body.

6. The hollow heat pipe integrated ball screw according to claim 1, characterized in that, The working medium is a mixture of liquid ammonia and Freon-like working medium, with a mass ratio of liquid ammonia to Freon-like working medium of 5:1 to 2:

1. The liquid volume of the working medium accounts for 15% to 30% of the volume of the hollow cavity, and the gas pressure of the hollow cavity is 10 to 40 kPa.

7. The hollow heat pipe integrated ball screw according to claim 1, characterized in that, The heat dissipation fins are connected to the hollow lead screw body by an interference fit. The heat dissipation fins are designed with optimized flow resistance and are in the shape of a triangle, a paddle, or a streamline to form forced convection heat dissipation when the lead screw rotates.

8. A design method for an integrated hollow heat pipe ball screw, characterized in that, Includes the following steps: Step 1: Process a hollow lead screw body with a hollow cavity. The hollow cavity extends axially. One end of the hollow cavity is a closed end and the other end is an open end. The open end constitutes the condensing end of the heat pipe. The inner wall of the hollow cavity directly constitutes the outer wall of the heat pipe. Step 2: Using additive manufacturing technology, a wave-shaped porous capillary structure liquid-absorbing core is formed on the inner wall of the hollow cavity. The longitudinal section of the liquid-absorbing core is wave-shaped and closely fits the inner wall of the hollow cavity. Step 3: Vacuum the hollow cavity and fill it with working fluid; Step four: Use additive manufacturing to form heat dissipation fins with a dot matrix structure, and install the heat dissipation fins on the condenser end.

9. The design method of the hollow heat pipe integrated ball screw according to claim 8, characterized in that, In step two, the molding parameters of the wavy porous capillary core include: porosity of 70%–80%, pore size distribution of 30–60 μm, and permeability of 10. 10 ~10 11 m 2 After molding, a fluorosilyl hydrophobic coating is physically vapor deposited on the surface at the crest, and an alumina-based hydrophilic coating is atomically deposited on the surface at the trough. The thickness of both the hydrophobic and hydrophilic coatings is 80–120 μm.

10. The design method of the hollow heat pipe integrated ball screw according to claim 8, characterized in that, In step three, the working fluid is a mixture of liquid ammonia and Freon-like working fluid, with a mass ratio of liquid ammonia to Freon-like working fluid of 5:1 to 2:

1. The liquid fluid filling volume accounts for 15% to 30% of the volume of the hollow cavity, and the air pressure of the hollow cavity is 10 to 40 kPa. In step four, the heat dissipation fins are designed with optimized flow resistance, and their shape is one of triangular, paddle-shaped, or streamlined, so as to form forced convection heat dissipation when the lead screw rotates.

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