A device and method for processing microstructure on surface of a curved thin-walled part

Abstract

In order to solve the technical problem that the existing roll forming method and device cannot process the drag reduction microstructure on the surface of the curved thin-walled part made of high-hardness material, the application provides a device and method for processing microstructure on the surface of a curved thin-walled part.The device comprises a numerical control machine tool, an ultrasonic vibration unit and a microstructure roll forming unit, wherein the microstructure roll forming unit comprises a roller with a whole-circle microstructure protrusion, and the roller is extruded in the area on the surface of the curved thin-walled part where the microstructure needs to be processed under the combined action of the numerical control machine tool and the ultrasonic vibration unit in the application, so that uniform plastic flow is generated, thereby forming a microstructure matching the shape and size of the microstructure protrusion on the roller, realizing the microstructure processing on the surface of the difficult-to-machine metal curved thin-walled part, and having the advantages of simple operation and high precision.

Description

Technical Field

[0001] This invention relates to an apparatus and method for machining microstructures on the surface of curved thin-walled parts. Background Technology

[0002] The fabrication of surface functional microstructures has become a new research topic in the manufacturing field in recent years. Fabricating different microstructures on the surface of parts can endow them with various superior properties, such as anti-fogging, anti-icing, corrosion resistance, drag reduction, and anti-fouling properties. Among these, microstructures for drag reduction have become one of the focal points in the aerospace manufacturing industry.

[0003] Currently, the methods for fabricating surface functional microstructures can be mainly divided into surface material removal methods and plastic forming methods. Surface material removal methods include special processing (high precision), ultra-precision machining (high efficiency), and etching (good structural uniformity and simple equipment). These methods have drawbacks such as high cost, long processing time, and difficulty in fabricating microstructures on a large area, and cannot meet the requirements of continuous production of microstructures. Plastic forming methods include surface imprinting, biomimetic replication, and roll forming. Among them, surface imprinting and biomimetic replication have certain limitations, such as small forming area, low forming efficiency, and large forming force required, which are not conducive to the large-area continuous fabrication of microstructures.

[0004] In comparison, roll forming is an effective method for processing surface functional microstructures, offering advantages such as low production cost and high efficiency. Roll forming mainly involves two processes: roll-to-roll forming and roll-to-flat forming. These processes are primarily used for flat materials with low hardness and good plasticity, such as flat aluminum and copper plates. With the development of aerospace technology, the demand for surface drag-reducing microstructures in curved, thin-walled parts made of high-hardness materials is increasing, and the existing two roll forming processes can no longer meet this demand. Summary of the Invention

[0005] To address the technical problem that existing roll forming methods and equipment cannot process drag-reducing microstructures on the surface of curved thin-walled parts made of high-hardness materials, this invention proposes a device and method for processing microstructures on the surface of curved thin-walled parts.

[0006] The technical solution of this invention is:

[0007] A device for machining microstructures on the surface of curved thin-walled parts is characterized by comprising a CNC machine tool, an ultrasonic vibration unit, and a microstructure rolling unit.

[0008] The microstructure rolling unit is connected to the machine tool spindle in the CNC machine tool through the ultrasonic vibration unit, and moves on the surface of the thin-walled curved part to be processed according to the set trajectory under the drive of the machine tool spindle;

[0009] The ultrasonic vibration unit is used to generate mechanical vibration signals and transmit them to the microstructure rolling unit, so that it presses down on the surface of the thin-walled curved part to be processed, causing it to produce plastic flow.

[0010] The microstructure rolling unit includes a first support, a roller, and a second support arranged in sequence; both the first support and the second support are provided with bearing mounting holes; the roller includes a roller and support shafts on both sides of the roller, and the support shafts are installed in the bearing mounting holes of the first support and the second support through bearings;

[0011] The roller has a wheel-shaped symmetrical structure, and its diameter gradually decreases from the middle to both sides; on the largest outer circumference surface in the middle of the roller, a full circle of micro-structure protrusions is provided in the center, and the edges of the micro-structure protrusions are rounded.

[0012] Preferably, on the largest outer circumference surface in the middle of the roller, two sets of secondary microstructure protrusions with a certain distance are provided in the center, and the cross-sectional shape and size of the two sets of secondary microstructure protrusions are the same; the pits formed by the two sets of secondary microstructure protrusions are rounded.

[0013] Preferably, the included angle between the two secondary microstructure protrusions is 30-60°, and the radius of the rounded corner is 0.005-0.007mm.

[0014] Preferably, the radial height of a single microstructure protrusion is equal to half the distance between two secondary microstructure protrusions.

[0015] Preferably, the radius of the rounded corners at the edges of the microstructure protrusions is 0.007-0.012 mm.

[0016] Preferably, the cross-sectional shape of the microstructure protrusion is trapezoidal, triangular, or rectangular.

[0017] Preferably, the roller and its two side supports are manufactured by integral precision grinding with a forming error within 10μm, and the material is cemented carbide; the first support and the second support are both made of high-strength titanium alloy.

[0018] The present invention also provides a method for machining microstructures on the surface of curved thin-walled parts based on the above-described apparatus, wherein the method is characterized by:

[0019] Step 1: Clamp the curved thin-walled part to be processed onto the worktable of the CNC machine tool;

[0020] Step 2: Connect the ultrasonic transducers in the microstructure rolling unit and ultrasonic vibration unit to the machine tool spindle of the CNC machine tool, turn on the ultrasonic transmitter in the ultrasonic vibration unit, and set different ultrasonic frequencies and amplitudes;

[0021] Step 3: Set different pressing depths and feed speeds in the Z direction. According to the pre-generated curved surface forming toolpath using the line projection method, the rollers in the microstructure rolling unit are displaced in the Y-axis direction to control the length and depth of the formed microstructure. During the processing, turn on the cooling and lubrication system of the CNC machine tool and keep its universal joint aligned with the contact area between the curved thin-walled part to be processed and the roller until the rolling is finished.

[0022] Step 4: The roller moves slowly upward along the Z-axis to separate from the curved thin-walled part to be processed, and the surface of the curved thin-walled part to be processed is formed with the microstructure required by the design.

[0023] The beneficial effects of this invention are:

[0024] 1. The microstructure rolling unit of the present invention includes a roller with a full circle of microstructure protrusions. Under the combined action of the CNC machine tool and the ultrasonic vibration unit in the present invention, the roller is squeezed in the area on the surface of the curved thin-walled part that needs to be processed to generate uniform plastic flow, thereby forming a microstructure that matches the shape and size of the microstructure protrusions on the roller. This realizes the microstructure processing of the surface of difficult-to-machine metal curved thin-walled parts, and has the advantages of simple operation and high precision.

[0025] 2. Compared with traditional methods that can only manufacture microstructures on a plane, the device of the present invention does not require a complex control system. It can roll and manufacture various microstructures that improve surface properties on free-form metal parts by relying on the line projection path planning of CNC machine tools.

[0026] 3. For surface functional microstructure requirements of different sizes and shapes, the present invention only needs to design and replace the rollers in the microstructure rolling unit according to the shape and size of the microstructure to meet the processing requirements.

[0027] 4. The cooling, lubrication, and ultrasonic-assisted rolling method used in this invention helps reduce roller wear.

[0028] 5. The rollers in this invention are made of WC cemented carbide, which has high hardness and is not easily deformed. It can roll hard materials that are difficult to process, such as titanium alloys and nickel alloys.

[0029] 6. This invention can process workpieces of different thicknesses by adjusting the position of the rollers, pressure and feed speed, and has a wide range of applications.

[0030] 7. The surface microstructure size obtained by roll forming using this invention can reach the 30μm level (e.g., Figure 10 As shown), the surface residual compressive stress value is improved to over 400 MPa (e.g. Figure 11 As shown in the figure, the workpiece surface is made to have a complete and defect-free microstructure without deformation.

[0031] 8. The rollers obtained by the present invention through integrated precision grinding will not deviate during the rolling process, and the processing error is small, making it suitable for surface microstructure forming with micron-level requirements.

[0032] 9. The bracket made of titanium alloy in this invention ensures low-friction rotation of the rollers. The overall size of the rollers can be as small as 93mm in length and 23mm in width. The smaller size also reduces tool interference in the forming and machining of thin-walled parts with large torsion, such as blades. Long-term service only requires replacement of bearings and rollers. The simple and easy-to-install and control characteristics of the device can ensure interference-free vertical downward pressure contact between the rollers and the workpiece, which greatly improves the accuracy and processing efficiency in microstructure machining.

[0033] 10. In this invention, the curved surface rolling tool path is generated by the line projection method. The tool contact point trajectory is offset onto the curved surface along the normal direction of the curved surface. Then, the shortest distance from the tool point to the curved surface is used for interference detection and adjustment to ensure that the roller makes just contact with the curved surface during rolling, thereby reducing contact error and improving forming accuracy.

[0034] 11. Existing microstructure rolling tools commonly use ball bearings or long rollers with microstructure protrusions. Ball bearings have good adaptability and can be used for surface strengthening of curved surfaces, but the shape formed by the ball bearing is uncontrollable. Long rollers with microstructure protrusions can control the shape formed, but the processing conditions are suitable for flat surface rolling, and the length of the front rolling roller is relatively long. In contrast, the roller with microstructure protrusions used in this invention is not only suitable for processing curved surfaces, but also has high forming accuracy and good controllability.

[0035] 12. In this invention, two microstructure protrusions with a certain spacing are centrally arranged on the outermost circumference of the roller, and the cross-sectional shape and size of the two microstructure protrusions are the same, which ensures the controllability and consistency of the formed microstructure, and at the same time, the forming efficiency is high.

[0036] 13. In this invention, the pits formed by the two secondary microstructure protrusions on the roller are rounded with a radius of 0.005mm-0.007mm. This reduces stress concentration and avoids deformation of the microstructure protrusions on one side (one side of the raceway), thus delaying the wear of the microstructure protrusions on the roller.

[0037] 14. In this invention, the included angle between the two microstructure protrusions on the roller is 30-60°, which is beneficial to the deformation and flow of materials during processing and helps to improve the quality of microstructure forming; the radial height (rib height) of a single microstructure protrusion is equal to 1 / 2 of the distance (rib spacing) between two secondary microstructure protrusions, resulting in optimal aerodynamic drag reduction performance. Attached Figure Description

[0038] Figure 1 This is a three-dimensional structural diagram of the device of the present invention.

[0039] Figure 2 This is a schematic diagram of the microstructure rolling unit in this invention.

[0040] Figure 3 for Figure 2 Exploded view.

[0041] Figure 4 This is a structural diagram of the roller in the microstructure rolling unit.

[0042] Figure 5 This is an enlarged view of the microstructure protrusions with different cross-sectional shapes on the roller.

[0043] Figure 6 This is a schematic diagram of the first support in the microstructure rolling unit.

[0044] Figure 7 This is a schematic diagram of the ultrasonic vibration unit in this invention.

[0045] Figure 8 This is a schematic diagram of the projection trajectory of the machining line on the curved surface.

[0046] Figure 9 Based on Figure 8 The microstructure morphology obtained from the surface rolling trajectory is shown in the figure.

[0047] Figure 10 for Figure 9 Dimensional measurement of cross-sections of microstructures.

[0048] Figure 11 The results are from the surface residual stress test.

[0049] Explanation of reference numerals in the attached figures:

[0050] 1-CNC machine tool; 11-Worktable; 12-Universal joint; 13-Machine tool spindle;

[0051] 2-Ultrasonic vibration unit; 21-Ultrasonic transmitter; 22-Energy transfer head connecting rod; 23-Ultrasonic transducer; 24-Holding ring;

[0052] 3-Microstructure rolling unit; 31-First bracket; 311-Bolt through hole; 312-Locking pin hole; 313-Bearing mounting hole; 32-Roller; 321-Roller; 3211-Microstructure protrusion; 322-Support shaft; 33-Second bracket; 331-Connecting rod; 34-Bolt; 35-Nut; 36-Bearing; 37-Locking pin; 38-Washer;

[0053] 4-Workpiece;

[0054] 6-Clamp;

[0055] 7-Force measuring table. Detailed Implementation

[0056] The present invention will be further described in detail below with reference to the accompanying drawings.

[0057] like Figure 1-7 As shown, the device for machining microstructures on the surface of curved thin-walled parts provided by the present invention includes a CNC machine tool 1, an ultrasonic vibration unit 2, and a microstructure rolling unit 3.

[0058] The CNC machine tool 1 is an existing device, mainly comprising a bed, a machine spindle 13, a worktable 11, a CNC system, a drive system, a transmission system, and a cooling and lubrication system. The worktable 11 is used to hold the workpiece 4 to be processed. The machine spindle is used to move some components of the ultrasonic vibration unit 2 and the microstructure rolling unit 3. The universal joint 12 in the cooling and lubrication system, used to deliver coolant, is always aligned with the contact area between the workpiece 4 and the microstructure rolling unit 3, providing cooling and lubrication to this area. Furthermore, a force gauge can be installed on the worktable 11 to detect the contact state between the workpiece 4 and the microstructure rolling unit 3. Before the pressing begins, the force gauge controls the force in the Z direction to be 0N, ensuring that the initial contact state between the workpiece and the microstructure rolling unit 3 is just contact, thus guaranteeing rolling accuracy.

[0059] like Figure 7 As shown, the ultrasonic vibration unit 2 is used to generate mechanical vibration signals and transmit them to the microstructure rolling unit 3. The ultrasonic vibration unit 2 includes an ultrasonic transmitter 21, a power transmission magnetic head connecting rod 22, an ultrasonic transducer 23, and a retaining ring 24, which are arranged sequentially from top to bottom. The ultrasonic transmitter 21 is used to generate a high-frequency electrical signal with a set frequency and amplitude (the frequency can be adjusted between 18kHz and 27kHz, and the amplitude can be adjusted between 1.5 and 5μm). This high-frequency electrical signal is then transmitted to the ultrasonic transducer 23 through the power transmission magnetic head connecting rod 22. The ultrasonic transducer 23 converts the high-frequency electrical signal into a mechanical vibration signal and transmits it to the microstructure rolling unit 3, causing the microstructure rolling unit 3 to vibrate. The retaining ring 24 is used to connect the power transmission magnetic head connecting rod 22 to the machine tool spindle 13.

[0060] The microstructure rolling unit 3, under the combined action of the ultrasonic vibration unit 2 and the CNC machine tool 1, compresses the surface of the workpiece 4 in areas where microstructures need to be machined, causing plastic flow and thus forming the desired microstructures on the surface of the workpiece 4. For example... Figure 2-6As shown, the microstructure rolling unit 3 includes a first support 31, a roller 32, and a second support 33 arranged sequentially. Both the first support 31 and the second support 33 are provided with bolt 34 through holes 311, positioning pin 37 holes 312, and bearing mounting holes 313. The first support 31 and the second support 33 are positioned by installing positioning pins 37 at the positioning pin holes 312, and connected by installing bolt 34 nut 35 assemblies at the bolt 34 through holes 311. The roller 32 includes a roller 321 and support shafts 322 on both sides of the roller 321. The support shafts 322 on both sides of the roller 32 are installed in the bearing mounting holes 313 of the first support 31 and the second support 33 through bearings 36, thereby installing the roller 32 between the first support 31 and the second support 33. The present invention uses positioning pin 37 to position the first bracket 31 and the second bracket 33. This is because relying solely on the bolt 34 and nut 35 assembly for positioning is insufficient to limit the degree of freedom of the first bracket 31 and the second bracket 33 during processing, which may easily cause misalignment between the first bracket 31 and the second bracket 33 and affect the processing and forming structure.

[0061] like Figure 3 As shown, to achieve the connection between the microstructure rolling unit 3, the ultrasonic vibration unit 2, and the CNC machine tool 1, a connecting rod 331 is provided at the upper end of the second bracket 33. This connecting rod 331 is used to connect the entire microstructure rolling unit 3 to the ultrasonic transducer 23 in the ultrasonic vibration unit 2. Specifically, it can be connected to the ultrasonic transducer 23 through a spring clip, thereby receiving the mechanical vibration signal output by the ultrasonic transducer 23. In addition, to reduce the weight of the bracket and ensure that the bracket is not easily deformed, the first bracket 31 and the second bracket 33 are preferably made of high-strength titanium alloy.

[0062] like Figure 4-5 As shown, the roller 321 in the roller 32 has a wheel-shaped symmetrical structure, and its diameter gradually decreases from the middle to both sides. On the largest outer circumference surface in the middle of the roller 321, a full circle of microstructure protrusions 3211 is provided in the center. The cross-section of the microstructure protrusions 3211 is trapezoidal, triangular or rectangular, and the edges of the microstructure protrusions 3211 are all rounded to reduce stress concentration. Considering that it is difficult to process if the rounded corners are too small, and the effect of relieving stress concentration is poor if the rounded corners are too large, the radius of the rounded corners is preferably 0.007mm-0.012mm.

[0063] Considering the low forming efficiency of single-pass microstructure protrusions 3211, and the fact that the microstructure morphology obtained after three or more passes of microstructure protrusions 3211 is destroyed by the plastic flow of the material on both sides after rolling, resulting in a poor final forming effect, this invention preferably uses two passes of microstructure protrusions 3211 with a certain spacing, centered on the maximum outer circumference of the roller 321, that is, two complete circles of microstructure protrusions 3211, and the cross-sectional shape and size of the two passes of microstructure protrusions 3211 are the same; the cross-sectional shape of the two passes of microstructure protrusions 3211 is the same. The identical shape and size ensure the controllability and consistency of the formed microstructure. Similarly, to reduce stress concentration, the recesses formed by the two secondary microstructure protrusions 3211 also need to be rounded. Considering that the recesses are the intersection of two material flows, if the rounded corners are too large, the stress concentration during rolling will be more obvious, which will easily cause deformation on one side of the microstructure protrusion (one side of the raceway) and aggravate the wear of the microstructure protrusions on the roller. Therefore, the preferred range of the rounded corner radius at the recesses formed by the two secondary microstructure protrusions 3211 is 0.005mm-0.007mm. An included angle of 30-60° between the two microstructure protrusions 3211 is beneficial to the deformation and flow of materials during processing, which is conducive to improving the quality of microstructure forming. The aerodynamic drag reduction performance is optimal when the radial height (rib height) of a single microstructure protrusion 3211 is equal to 1 / 2 of the distance (rib spacing) between the two secondary microstructure protrusions 3211.

[0064] Meanwhile, the shape and dimensions of the roller 321 in the roller 32 should also be adapted to the surface shape and dimensions of the curved thin-walled part to be processed. The cross-sectional shape, axial width, and radial height of the single-turn microstructure protrusion 3211 on the roller 321 should be adapted to the microstructure shape and dimensions required to be formed on the surface of the workpiece 4 to be processed, thereby effectively controlling the forming shape of the microstructure during the rolling process of the roller 321 on the curved thin-walled part and improving the surface performance of the curved thin-walled part. In addition, in order to ensure and improve the strength of the roller 32, the roller 32 is made entirely of cemented carbide material, such as WC-Co cemented carbide.

[0065] To further improve machining accuracy, in addition to the roller 321 with microstructure protrusions, the supports on both sides of the roller 321 are also precision ground together with the roller 321. The part forming error is within 10μm, and the overall dimensional accuracy is high.

[0066] During processing, the workpiece 4 to be processed is placed on the worktable 11 of the CNC machine tool 1. The microstructure rolling unit 3, driven by the machine tool spindle, moves on the surface of the workpiece 4 according to a pre-set curved toolpath trajectory. The roller 32 in the microstructure rolling unit 3 contacts the surface of the workpiece 4, and under the action of the mechanical vibration signal transmitted to the roller 32 by the ultrasonic vibration unit 2, it squeezes the surface of the workpiece 4 to produce plastic flow, thereby forming a microstructure on the surface of the workpiece 4 that matches the shape and size of the microstructure protrusion 3211 on the largest circumference surface in the middle of the roller 32. The pre-set curved toolpath trajectory can be generated by UG based on the line projection method. First, the tool position trajectory (the movement trajectory of the roller) is planned. Then, the tool position trajectory is offset onto the curved surface along the normal of the surface of the workpiece to be processed. Then, interference detection and adjustment are performed using the shortest distance from the tool position to the curved surface, and finally, an interference-free curved toolpath trajectory is generated.

[0067] In this embodiment:

[0068] In the microstructure rolling unit 3, the total axial length of the roller 32 is 23mm, the thickness of the roller 321 is 5mm, the maximum outer diameter of the roller 321 is 20mm, the axial width of the circumferential surface where the microstructure protrusion 3211 is located is 1mm, the diameter of the support shafts 322 on both sides of the roller 321 is 5mm, the distance between the two passes of the microstructure protrusion 3211 is 0.07mm, the radius of the fillet at the edge of the single pass of the microstructure protrusion 3211 is 0.007mm, and the chamfer of the pit between the two passes is 0.005mm.

[0069] The microstructure protrusion 3211 has two levels, and the cross-sectional shape can be trapezoidal, triangular or rectangular; the included angle and dimensions of the microstructure protrusion 3211 with different cross-sectional shapes are shown in Table 1 below.

[0070] Table 1. Angles and dimensions of different microstructural protrusions 3211

[0071]

[0072] Processing effect verification:

[0073] The metal curved surface part to be processed is placed horizontally and fixed on the worktable 11 of the CNC machine tool 1 by a fixture, with the metal curved surface part positioned below the roller 32 in the microstructure rolling unit 3; the CNC system of the CNC machine tool 1 is then imported. Figure 9 The rolling trajectory of the curved surface shown is obtained using the line projection method. The feed speed and pressing depth are set, the ultrasonic vibration unit 2 is adjusted, and the frequency and amplitude are set. The cooling and lubrication system of the CNC machine tool 1 is turned on. Driven by the machine tool spindle of the CNC machine tool 1, the roller 32 rolls along the metal curved surface. The upper surface of the metal curved surface contacts and is pressed by the microstructure protrusions 3211 of the roller 32. After the rolling process is completed, a trapezoidal microstructure is obtained on the surface of the metal curved surface. Figure 9 The overall morphology of the obtained microstructure shows that the raceway is smooth and without defects. Figure 10 for Figure 9 The cross-sectional dimensions of microstructures, from Figure 10 It can be seen that the depth of the obtained trapezoidal microstructure is 32μm and the width is 72μm (close to the design requirements), and the rolling forming effect on both sides of the raceway is good. From Figure 11 It can be seen that after processing trapezoidal microstructures on the surface of a metal curved part using the device and method of the present invention, the value of the residual compressive stress on the surface can be improved to more than 400 MPa.

[0074] The method for fabricating microstructures on the surface of curved thin-walled parts using the device of the present invention is as follows:

[0075] Step 1: Clamp and fix the curved workpiece 4 on the worktable 11;

[0076] Step 2: Connect the microstructure rolling unit 3 and the ultrasonic transducer 23 to the machine tool spindle 13, turn on the ultrasonic transmitter 21, and set different ultrasonic frequencies and amplitudes;

[0077] Step 3: Set different pressing depths and feed speeds in the Z direction. According to the curved tool path generated in advance using the line projection method, make the roller 32 in the microstructure rolling unit 3 move in the Y-axis direction to control the length and depth of the formed microstructure. During the processing, turn on the cooling and lubrication system of the CNC machine tool 1 and keep its universal joint aligned with the contact area between the workpiece 4 and the roller 32 until the rolling is finished.

[0078] Step 4: After the rolling is completed, the roller 32 moves slowly upward along the Z direction to separate from the workpiece 4, and the surface of the workpiece 4 is formed with the microstructure required by the design.

Claims

1. A device for machining microstructures on the surface of curved thin-walled parts, characterized in that: Includes CNC machine tools, ultrasonic vibration units, and microstructure rolling units; The microstructure rolling unit is connected to the machine tool spindle in the CNC machine tool through the ultrasonic vibration unit, and moves on the surface of the thin-walled curved part to be processed according to a set trajectory under the drive of the machine tool spindle; the set trajectory is generated according to the line projection method. The ultrasonic vibration unit is used to generate mechanical vibration signals and transmit them to the microstructure rolling unit, so that it presses down on the surface of the thin-walled curved part to be processed to induce plastic flow. The microstructure rolling unit includes a first support, a roller, and a second support arranged in sequence; the first support and the second support are positioned by locating pins and connected by bolt and nut assemblies to restrict the degree of freedom of the first support and the second support during processing; both the first support and the second support are provided with bearing mounting holes; the roller includes a roller and support shafts on both sides of the roller, and the support shafts are installed in the bearing mounting holes of the first support and the second support through bearings; The roller has a wheel-type symmetrical structure, and its diameter gradually decreases from the middle to both sides; on the largest outer circumference surface in the middle of the roller, there are two rows of secondary microstructure protrusions with a certain distance between them, and the edges of the microstructure protrusions are rounded with a radius of 0.007-0.012mm. The two secondary microstructure protrusions have the same cross-sectional shape and size, and the included angle between the two secondary microstructure protrusions is 30-60°; the pits formed by the two secondary microstructure protrusions are rounded with a radius of 0.005-0.007mm. The radial height of a single microstructure protrusion is equal to half the distance between two secondary microstructure protrusions.

2. The apparatus for machining microstructures on the surface of curved thin-walled parts according to claim 1, characterized in that: The cross-sectional shape of the microstructure protrusions is trapezoidal, triangular, or rectangular.

3. The apparatus for machining microstructures on the surface of curved thin-walled parts according to claim 1, characterized in that: The roller and its two side supports are manufactured by precision grinding in one piece with a forming error within 10μm, and the material is cemented carbide; the first support and the second support are both made of high-strength titanium alloy.

4. A method for machining microstructures on the surface of a curved thin-walled part based on the apparatus for machining microstructures on the surface of a curved thin-walled part according to any one of claims 1-3, characterized in that, Including the following steps: Step 1: Clamp the curved thin-walled part to be processed onto the worktable of the CNC machine tool; Step 2: Connect the ultrasonic transducers in the microstructure rolling unit and ultrasonic vibration unit to the machine tool spindle of the CNC machine tool, turn on the ultrasonic transmitter in the ultrasonic vibration unit, and set different ultrasonic frequencies and amplitudes; Step 3: Set different pressing depths and feed speeds in the Z direction. According to the pre-generated curved surface forming toolpath using the line projection method, the rollers in the microstructure rolling unit are displaced in the Y-axis direction to control the length and depth of the formed microstructure. During the processing, turn on the cooling and lubrication system of the CNC machine tool and keep its universal joint aligned with the contact area between the curved thin-walled part to be processed and the roller until the rolling is finished. Step 4: The roller moves slowly upward along the Z-axis to separate from the curved thin-walled part to be processed, and the surface of the curved thin-walled part to be processed is formed with the microstructure required by the design.

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