Ultrasonic assisted microbulge hole extrusion strengthening device and method

Abstract

The application discloses an ultrasonic-assisted micro-bulge hole extrusion strengthening device and method, which is used for strengthening a hole to be processed. The device comprises a transducer for converting a high-frequency electric signal into mechanical vibration; a variable amplitude rod, one end of the variable amplitude rod being connected with the transducer, the variable amplitude rod being used for amplifying the amplitude of the mechanical vibration and transmitting the mechanical vibration in the axial direction; and an extrusion rod, one end of the extrusion rod being connected with the other end of the variable amplitude rod, and the other end of the extrusion rod being provided with a working section. The surface of the working section is provided with a plurality of micro-bulge rings in the axial direction, and the outer diameters of at least part of the micro-bulge rings are gradiently increased in the reverse direction of the feeding direction of the extrusion rod. The application can solve a series of problems caused by the overall extrusion mainly relying on a large static load in the existing hole extrusion strengthening process, for example, large extrusion force, high energy consumption, easy micro-damage of the hole wall surface, and difficulty in accurately controlling the distribution depth and uniformity of the residual compressive stress field.

Description

Technical Field

[0001] This application relates to the field of surface strengthening technology, and in particular to an ultrasonic-assisted micro-bulging hole extrusion strengthening device and method. Background Technology

[0002] Currently, passenger aircraft fuselages are primarily assembled using riveting and bolting connections. During flight cycles, these connection holes continuously bear alternating loads, becoming weak points in the structure due to fatigue. To improve the fatigue performance of these connection holes, hole extrusion strengthening technology has become an important manufacturing process in the aerospace industry. This technology inhibits the initiation and propagation of fatigue cracks by inducing plastic deformation and residual compressive stress in the material surrounding the hole wall.

[0003] In existing technologies, hole extrusion strengthening techniques employ a rigid mandrel for integral extrusion or drawing of the hole to be processed. This method introduces residual compressive stress into the hole wall through forced macroscopic deformation. However, due to the intense and continuous nature of the process, the material is subjected to extremely high shear stress instantaneously, easily leading to microscopic tearing, scratches, and other damage on the hole wall surface and subsurface. These microscopic damages may become new fatigue crack initiations, thus weakening the strengthening effect. Furthermore, the plastic deformation generated by existing methods is concentrated on the surface layer, resulting in a shallow residual compressive stress layer, which is insufficient to meet the deep strengthening requirements of thick-walled components or high-load-bearing conditions.

[0004] Furthermore, the implementation process requires overcoming enormous static friction, relies on high-tonnage pressure equipment, and results in high energy consumption and costs. Due to the inability to precisely guide and control the plastic flow within the material, existing technologies still fall short in terms of the uniformity, depth, and surface integrity of the reinforcement effect. Summary of the Invention

[0005] This application provides an ultrasonic-assisted micro-bulging hole extrusion strengthening device and method, which aims to solve a series of problems commonly found in existing hole extrusion strengthening processes, which mainly rely on large static load overall extrusion, such as large extrusion pressure, high energy consumption, easy generation of micro-damage on the hole wall surface, and difficulty in accurately controlling the depth and uniformity of the residual compressive stress field distribution.

[0006] To achieve the above objectives, this application provides the following technical solution.

[0007] According to a first aspect of this application, this application provides an ultrasonic-assisted micro-bulging hole extrusion strengthening device for strengthening holes to be processed, the device comprising: A transducer for converting high-frequency electrical signals into mechanical vibrations; An amplitude transformer, one end of which is connected to the transducer, is used to amplify the amplitude of the mechanical vibration and transmit it axially. An extrusion rod, one end of which is connected to the other end of the amplitude transformer, and the other end of the extrusion rod is provided with a working section; wherein, the surface of the working section is provided with a plurality of micro-protruding rings along the axial direction, and at least some of the micro-protruding rings have an outer diameter that increases in a gradient in the opposite direction to the feed direction of the extrusion rod.

[0008] In some possible implementations, the cross-sectional profile of the micro-protruding ring along the axial direction is one of an arc shape, a semi-circle, and a streamlined shape.

[0009] In some possible implementations, the plurality of micro-protruding rings are sequentially arranged along the axial direction of the extrusion rod; including at least a first micro-protruding ring that enters the hole to be processed, a second micro-protruding ring that enters the hole to be processed, and a third micro-protruding ring that enters the hole to be processed; based on the hole diameter d0, the diameter of the first micro-protruding ring is d1 = d0 + 0.015 mm; the diameter of the second micro-protruding ring is d2 = d0 + 0.030 mm; and the diameter of the third micro-protruding ring is d3 = d0 + 0.045 mm.

[0010] In some possible implementations, the axial span H of the micro-protrusion ring and the wall thickness T of the hole to be processed satisfy the relationship: H≥T.

[0011] In some possible implementations, the extrusion rod has a front conical end connected to the front side of the extrusion rod in the feed direction and a rear conical end connected to the rear side of the feed direction; the outer surface of the rear conical end is a conical surface that gradually tapers in the opposite direction of the feed direction.

[0012] In some possible implementations, the ultrasonic-assisted micro-bulge hole extrusion strengthening device further includes a connecting end cap, through which the extrusion rod is connected to the amplitude transformer; the extrusion rod and the connecting end cap are connected by a thread.

[0013] In some possible implementations, the base material of the extrusion rod is cemented carbide.

[0014] According to a second aspect of this application, this application provides an ultrasonic-assisted micro-bulge hole extrusion strengthening method using the ultrasonic-assisted micro-bulge hole extrusion strengthening device as described in any embodiment of this application, the method comprising the following steps: Align the front conical end of the extrusion rod with the center of the hole to be machined; Start the transducer to cause the extrusion rod to vibrate at high frequency; The extrusion rod is driven to rotate uniformly around its axis while simultaneously applying an axial feed force. Multiple micro-protruding rings on the working section of the extrusion rod pass sequentially through the hole wall of the hole to be processed, performing sequential micro-area incremental forming of the hole wall material; After the working section has completely passed through the hole to be processed, the outlet of the hole to be processed is shaped by the rear cone end, and the extrusion rod is moved out of the hole to be processed.

[0015] In some possible implementations, the process parameters in the method are set as follows: ultrasonic frequency of 25 kHz to 40 kHz, rotational speed of 55 r / min to 75 r / min, and feed rate of 4.8 mm / min to 7.2 mm / min.

[0016] In some possible implementations, the steps are repeated 6 to 10 times for the same hole to be machined; and tapping oil is continuously applied to the hole wall during the machining process.

[0017] This application provides an ultrasonic-assisted micro-bulge hole extrusion strengthening device and method. By setting micro-bulge rings with at least partially gradient-increasing outer diameters in the opposite direction of the feed direction on the working section surface of the extrusion rod, and generating ultrasonic vibrations through a transducer and amplitude transformer, the traditional integral strong extrusion is transformed into sequential micro-area incremental forming. The micro-bulge rings with smaller diameters at the front end of the device can smoothly cut into the hole wall with lower loads. Subsequent micro-bulge rings with increasing diameters extrude in stages, and the high-frequency vibrations and acoustic softening effect generated by the ultrasonic waves reduce the deformation resistance and interfacial friction of the material. This avoids microscopic tearing or scratches on the hole wall surface caused by excessive instantaneous shear stress, and allows the material to undergo ordered plastic flow, thereby forming a deeper and more uniformly distributed residual compressive stress field inside the hole wall. It should be noted that ordered plastic flow refers to the controlled, regular, directional, and predictable permanent deformation of the metallic material; deeper refers to the range of influence of the strengthening effect; and more uniform gradient distribution refers to the stress change trend from the surface to the depth.

[0018] Furthermore, the cross-sectional profile of the micro-protruding ring adopts an arc shape or a streamlined shape, and the axial span of the micro-protruding ring and the wall thickness of the hole to be processed meet a specific proportional relationship, improving the contact stress distribution during processing. Moreover, under the continuous action of high-frequency micro-forging, the micro-protruding ring can refine the surface grains of the hole wall, improving fatigue performance while enhancing the surface integrity and process adaptability of the hole wall. In addition, this device adopts a threaded connection and a rigid connection method with axial pre-tightening in the assembled state, ensuring a tight fit between the connected end faces. This maintains the stability of the connection under the combined action of high-frequency vibration and rotational torque, avoiding connection loosening and ensuring the transmission of ultrasonic energy. Furthermore, this application employs a multi-pass low-load cumulative strengthening method, achieving an improvement in the fatigue life of the connecting hole with lower equipment energy consumption. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0020] Figure 1 This is a schematic diagram of the overall structure of the ultrasonic-assisted micro-bulge hole extrusion strengthening device provided in the embodiments of this application.

[0021] Figure 2 This is a schematic diagram of the extrusion rod provided in the embodiment of this application after it has been aligned and is in its initial positioning state.

[0022] Figure 3 This is a schematic diagram of the working section of the extrusion rod provided in the embodiment of this application, which extrudes and strengthens the hole wall of the hole to be processed.

[0023] Figure 4 A flowchart illustrating the steps of the ultrasonic-assisted micro-bulge hole extrusion strengthening method provided in this application embodiment.

[0024] Figure 5 This is a schematic diagram comparing the fatigue life of the unstrengthened specimen and the specimen strengthened by this application under different loads in Example 2 of this application.

[0025] Explanation of reference numerals in the attached figures: 1. Front cone end; 20. Working section; 2. Micro-protruding ring; 21. First micro-protruding ring; 22. Second micro-protruding ring; 23. Third micro-protruding ring; 24. Fourth micro-protruding ring; 25. Fifth micro-protruding ring; 3. Rear conical end; 4. Extrusion rod; 5. Connecting end cap; 6. Flange; 7. Amplifier rod; 8. Transducer; 100. Workpiece to be processed; 101. Hole to be processed; 102. Hole wall. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] Currently, passenger aircraft fuselages are primarily assembled using riveting and bolting connections. During flight cycles (including takeoff, cruise, and landing), these connection holes continuously bear alternating loads, making them weak points prone to structural fatigue fracture. Aircraft failures during service are a major concern, with fatigue fracture being a primary form of damage, and overall structural fractures caused by damage to connection holes being particularly common. Therefore, improving the fatigue life of connection holes has become a crucial issue in the aerospace industry. Hole structures, as important mechanical connections, are areas of significant stress concentration, making them highly susceptible to fatigue crack initiation and severely impacting the overall structural fatigue life. To improve the fatigue performance of holes, hole extrusion strengthening technology has become an important manufacturing process. This technology inhibits the initiation and propagation of fatigue cracks by inducing plastic deformation and residual compressive stress in the material surrounding the hole wall.

[0028] In existing technologies, hole extrusion strengthening technology uses a rigid mandrel to integrally extrude or pull the hole to be processed. This method introduces residual compressive stress into the hole wall through forced macroscopic deformation. However, due to its relatively violent and continuous process, it has the following problems: First, the integral extrusion causes the hole wall material to be subjected to extremely high shear stress instantaneously, which can easily produce microscopic tears, scratches and other damage on the surface and subsurface of the hole wall. These microscopic damages may become new fatigue crack sources, thus weakening the strengthening effect. Second, the plastic deformation generated by the existing method is concentrated on the surface layer, and the residual compressive stress influence layer is shallow, which is difficult to meet the deep strengthening requirements of thick-walled components or high load-bearing conditions. Third, the process is relatively rigid and has poor adaptability to different materials and hole diameters, which can easily cause hole shape distortion and uneven distribution of residual compressive stress, resulting in insufficient stability of the strengthening effect. In addition, it is necessary to overcome huge static friction during implementation and rely on high-tonnage pressure equipment, resulting in high energy consumption and cost. Ultimately, the shortcomings of existing methods lie in their reliance on forced deformation, which makes it impossible to precisely guide and control the plastic flow inside the material, resulting in limitations in the uniformity, depth, and surface quality of the strengthening effect.

[0029] To address the above issues, this application provides an ultrasonic-assisted micro-bulging hole extrusion strengthening device and method. The device includes a transducer, an amplitude transformer, and an extrusion rod. The working section surface of the extrusion rod has multiple micro-bulging rings arranged axially, and at least some of the micro-bulging rings have outer diameters that increase in a gradient opposite to the feed direction of the extrusion rod. This device reduces the material's deformation resistance through axial high-frequency vibration generated by the transducer and amplitude transformer. With the assistance of this vibration, the micro-bulging rings, in conjunction with the hole walls to be processed, perform sequential micro-area incremental forming and high-frequency micro-forging. Because the smaller-diameter micro-bulging rings at the front end smoothly cut into the hole wall during this process, followed by extrusion with subsequent rings of increasing diameter, not only does this allow for orderly material flow, but it also reduces extrusion pressure and frictional damage during processing. This reduces extrusion pressure while simultaneously creating a deep, uniform residual compressive stress field within the hole wall, effectively protecting surface integrity. It should be noted that high-frequency micro-forging refers to the application of high-frequency, low-amplitude indentation periodic loading to a local micro-area of ​​the hole wall by a micro-protruding ring under ultrasonic vibration, causing the material to undergo micro-plastic deformation during repeated compression and gradually accumulate strengthening.

[0030] refer to Figures 1 to 3 This application provides an ultrasonic-assisted micro-bulge hole extrusion strengthening device. The device includes a transducer 8, an amplitude transformer 7, and an extrusion rod 4.

[0031] Specifically, in this embodiment, the transducer 8 is used to receive high-frequency electrical signals generated by an external ultrasonic generator (not shown in the figure) and convert them into mechanical vibrations. One end of the amplitude transformer 7 is connected to the transducer 8 to amplify the amplitude of the mechanical vibrations and transmit them axially.

[0032] In some embodiments, the connecting end cover 5 is provided with a flange 6. The flange 6 is used to connect to an external drive device (e.g., a CNC machine tool spindle, a robotic arm end effector, or a drive head of a reinforcement device), enabling the entire device to perform rotational and / or axial feed movements under the drive of the external drive device. As an optional implementation, the connecting end cover 5 and the flange 6 are an integral structure to improve the structural rigidity of the device and maintain the stability of the connection under the combined action of high-frequency vibration and rotational torque. Of course, in other embodiments, the flange 6 can also be a separate component, fixedly connected to the connecting end cover 5 by welding or bolting.

[0033] In this embodiment, one end of the extrusion rod 4 is connected to the other end (i.e., the output end) of the amplitude transformer 7 via a connecting end cap 5, and the other end of the extrusion rod 4 is provided with a working section 20. The extrusion rod 4 uses high-hardness cemented carbide as the base material to ensure wear resistance and rigidity under high-frequency impact and severe friction conditions.

[0034] In some embodiments, the connection between the extrusion rod 4 and the connecting end cap 5 employs a threaded connection and forms an axially pre-tightened connection in the assembled state. This ensures that the opposing end faces of the extrusion rod 4 and the connecting end cap 5 are tightly fitted, thereby maintaining connection stability under the combined action of high-frequency vibration and rotational torque, and preventing connection loosening. Specifically, the connection between the extrusion rod 4 and the connecting end cap 5 is provided with a threaded connection. During assembly, the extrusion rod 4 and the connecting end cap 5 are axially tightened through the threaded connection, ensuring that the opposing end faces of the extrusion rod 4 and the connecting end cap 5 are tightly fitted, thereby forming a rigid connection. During this process, the threaded connection provides axial pre-tightening force in the assembled state, ensuring tight contact of the connecting surfaces, thereby maintaining connection stability under the action of high-frequency vibration and rotational torque, and achieving effective transmission of ultrasonic vibration.

[0035] Furthermore, the compression rod 4 and the connecting end cap 5 are preferably made of materials with similar or identical acoustic impedance characteristics to reduce the impedance discontinuity of the sound wave at the connection point, thereby reducing the attenuation of ultrasonic vibration at the connection interface and ensuring the stability of ultrasonic energy transmission.

[0036] In this embodiment of the application, along the feed direction of the extrusion rod 4, such as Figure 2 As shown in the top-to-bottom direction, the extrusion rod 4 is connected to a front conical end 1 on the front side of the feed direction and a rear conical end 3 on the rear side of the feed direction. Multiple micro-protruding rings 2 are axially arranged on the surface of the working section 20 of the extrusion rod 4, and these micro-protruding rings 2 are located between the front conical end 1 and the rear conical end 3 along the feed direction. Furthermore, the outer diameters of these micro-protruding rings 2 are distributed in a stepped manner in the opposite direction to the feed direction of the extrusion rod 4, and at least some of the micro-protruding rings 2 have an increasing outer diameter. That is, at least some of the micro-protruding rings 2 have an increasing outer diameter from the front conical end 1 to the rear conical end 3.

[0037] In the embodiment of the present application, the front conical end 1 is a guiding conical surface with a small taper, which is used to smoothly guide the extrusion rod 4 into the hole to be machined 101 at the initial stage of machining, playing a role of centering and guiding, ensuring that the extrusion rod 4 is accurately aligned with the hole, and avoiding damage caused by initial deflection. Following the front conical end 1 are multiple micro-protrusion rings 2 arranged axially. These micro-protrusion rings 2 are not arranged with equal diameters, but their outer diameters are distributed in a stepped manner in the opposite direction of the feeding direction, and the outer diameters of at least some of the micro-protrusion rings 2 increase in a gradient manner. In this embodiment, taking the hole to be machined 101 with a hole diameter of d0 as an example, multiple micro-protrusion rings 2 are sequentially arranged along the axis of the extrusion rod 4, specifically including at least the first micro-protrusion ring 21 that enters the hole to be machined 101 first, the second micro-protrusion ring 22 that enters the hole to be machined 101 second, the third micro-protrusion ring 23 that enters the hole to be machined 101 third, the fourth micro-protrusion ring 24 that enters the hole to be machined 101 fourth, and the fifth micro-protrusion ring 25 that enters the hole to be machined 101 fifth. Based on the hole diameter d0 of the hole to be machined 101, the diameter gradients of each micro-protrusion ring 2 are set as follows: the diameter d1 of the first micro-protrusion ring 21 = d0 + 0.015 mm; the diameter d2 of the second micro-protrusion ring 22 = d0 + 0.030 mm, and the diameters of the third micro-protrusion ring 23, the fourth micro-protrusion ring 24, and the fifth micro-protrusion ring 25 are the same, and d3 = d4 = d5 = d0 + 0.045 mm. Of course, in some other embodiments, it is also possible to set that the outer diameters of all micro-protrusion rings 2 increase in a gradient manner in the opposite direction of the feeding direction (i.e., d1 < d2 < d3 < d4 < d5), to achieve continuous step-by-step hole expansion.

[0038] With such a setting, by using the gradually increasing micro-protrusion radii (whether it is partial increase or full increase), the overall extrusion is decomposed into multiple local micro-forging presses, forming a gradient plastic deformation field of "pilot cutting in first and then relay expansion": the small-radius protrusions at the front end (such as the first micro-protrusion ring 21) establish guidance on the surface layer; the subsequent increasing large-radius protrusions (such as the second micro-protrusion ring 22 and the third micro-protrusion ring 23) smoothly introduce plastic flow into the deep layer of the material in a relay manner. Thus, while reducing the single-point peak load, sequential plastic deformation from the surface to the inside and from the pilot to the main is achieved, and then the residual compressive stress is introduced deeper and more evenly into the material interior.

[0039] In the embodiment of the present application, the axial cross-sectional profile of the micro-protrusion ring 2 is one of circular arc, semi-circular, and streamline, so as to optimize the contact stress distribution and prevent scratching the hole wall 102 of the hole to be machined 101. In this embodiment, the axial cross-sectional profile of the micro-protrusion ring 2 is semi-circular.

[0040] In some embodiments, such as Figure 2As shown, the axial span H of the multiple micro-protruding rings 2 and the hole depth T of the hole 101 to be processed satisfy the relationship: H≥T. This setting ensures that the hole wall 102 is always stably supported in the thickness direction during the processing.

[0041] In this embodiment, the rear conical end 3 is located at the end of the working section 20, and its outer surface is a tapered surface that gradually contracts in the opposite direction of the feed direction. After all the micro-protruding rings 2 have been extruded, the rear conical end 3 presses and shapes the orifice that has contracted due to elastic rebound, and ensures that the surface of the orifice wall 102 will not be scratched when the device withdraws or reciprocates.

[0042] This application also provides an ultrasonic-assisted micro-bulging pore extrusion strengthening method, which utilizes the ultrasonic-assisted micro-bulging pore extrusion strengthening device described in any embodiment of this application. The specific structure and function of the ultrasonic-assisted micro-bulging pore extrusion strengthening device are detailed above and will not be repeated here.

[0043] refer to Figure 4 The ultrasonic-assisted micro-bulge pore compression strengthening method includes the following steps: Step S100: Align the front conical end of the extrusion rod with the center of the hole to be machined. Specifically, fix the workpiece 100 to be machined on the worktable and adjust the position of the machine tool spindle so that the front conical end 1 of the extrusion rod 4 is aligned with the center of the hole 101 to be machined in the workpiece 100. The front conical end 1 has a guide conical surface for smooth introduction and centering, ensuring the alignment of the extrusion rod 4 with the hole 101 to be machined, avoiding damage caused by initial misalignment, and ensuring a gradual transition.

[0044] Step S200: Activate the transducer to generate high-frequency vibration in the extrusion rod. Specifically, turn on the transducer 8 to generate high-frequency vibration, which is amplified by the amplitude transformer 7 and transmitted to the extrusion rod 4. In this embodiment, the ultrasonic frequency is set to 25kHz to 40kHz, and the amplitude range is 8μm to 30μm.

[0045] Step S300: Drive the extrusion rod to perform a uniform rotational motion around the axis, while simultaneously applying an axial feed force. Specifically, drive the machine tool spindle to rotate, and the spindle drives the extrusion rod 4 to perform a uniform rotational motion around the axis through the connecting end cover 5. At the same time, axial ultrasonic vibration is applied to the extrusion rod 4 through the transducer 8 and the amplitude transformer 7. The rotational speed is set to 55 r / min to 75 r / min. Simultaneously, an axial feed force is applied, causing the extrusion rod 4 to move downward along the hole axis at a speed of 4.8 mm / min to 7.2 mm / min. At this time, the extrusion rod 4 superimposes three motions: high-frequency vibration, axial feed, and circumferential rotation, to achieve the synergistic effect of ultrasonic high-frequency micro-forging, axial extrusion, and rotational shearing on the hole wall 102 material.

[0046] Step S400: Multiple micro-protruding rings on the working section of the extrusion rod sequentially pass through the hole wall of the hole to be processed, performing sequential micro-area incremental forming on the hole wall material. Here, sequential micro-area incremental forming refers to decomposing the traditional large deformation amount extrusion into multiple, localized micro-deformation accumulations, and completing the forming and strengthening through a step-by-step superposition method.

[0047] Specifically, the high-frequency vibration characteristics of ultrasound are utilized for sequential micro-area forging. That is, in the above-mentioned step-by-step superposition process, the micro-protruding rings impact the tiny area in contact with the hole wall at high frequency, and as micro-protruding rings of different diameters are fed, the high-frequency impact is progressively advanced along the axial direction.

[0048] Step S400 includes pilot cutting and relay expansion. Pilot cutting refers to the smooth entry of the smaller-diameter micro-protrusion ring 2 (i.e., the first micro-protrusion ring 21) into the hole wall 102 with a low load, establishing a precise guiding path on the surface. Relay expansion refers to the subsequent sequential passage of the second micro-protrusion ring 22 and the third micro-protrusion ring 23, etc., with increasing diameters, gradually expanding the contact area and deformation depth along the guiding path, thus smoothly introducing plastic flow into the deeper layers of the material in a relay manner. Each micro-protrusion ring 2 undergoes a small amount of plastic deformation based on the previous one. This avoids sudden and drastic deformation of the material. Simultaneously, the circumferential shear force generated by the rotational motion and the axial high-frequency micro-forging force and acoustic softening effect of the ultrasonic vibration work synergistically to refine the material grains, forming a reinforced layer with good fatigue performance.

[0049] Step S500: After the working section has completely passed through the hole to be processed, the rear conical end is used to shape the outlet of the hole to be processed, and the extrusion rod is removed from the hole to be processed. Specifically, after all the micro-protruding rings 2 on the working section 20 have completely passed through the hole to be processed 101, the rear conical end 3 is used to press and shape the slight deformation caused by elastic rebound at the outlet of the hole to be processed 101 to prevent burrs from forming. Then, the extrusion rod 4 is removed from the hole to be processed 101, completing this processing step.

[0050] In some embodiments, steps S100 to S500 are repeated 6 to 10 times for the same hole 101 to be machined, to achieve multi-pass low-load cumulative strengthening. During the machining process, tapping oil is continuously applied to the hole wall 102 for lubrication and cooling. Therefore, this process achieves "replacing single-pass strong rough pressing with multi-pass rapid micro-forging", and through the stress accumulation effect, achieves a significant performance improvement with a slightly increased single-hole time.

[0051] The apparatus and method described in this application will be further illustrated below through two embodiments.

[0052] Example 1: The ultrasonic-assisted micro-bulging hole extrusion strengthening process of this embodiment begins with the preparation and alignment stage. First, the workpiece to be strengthened (such as an aerospace structural component) is fixed on the worktable. The extrusion rod 4 is rigidly connected to the amplitude transformer 7 through the connecting end cap 5 at its rear end, ensuring that ultrasonic vibration and rotational torque can be transmitted simultaneously during subsequent processing. Subsequently, the position of the machine tool spindle is adjusted so that the front conical end 1 of the extrusion rod 4 is precisely aligned with the hole 101 to be processed on the workpiece, and the guide cone surface of the front conical end 1 is used to complete the initial positioning and alignment.

[0053] It should be noted that positioning refers to using the guide cone surface to quickly align the extrusion rod 4 with the center of the hole 101 to be processed; guiding refers to guiding the extrusion rod 4 smoothly into the hole 101 to be processed, avoiding scratches and deviation.

[0054] During the extrusion stage, transducer 8 is activated, generating high-frequency vibrations that are transmitted to extrusion rod 4 via amplitude transformer 7. Simultaneously, the machine tool spindle drives extrusion rod 4 downwards under a constant axial feed force and rotates uniformly around its own axis. During this process, multiple micro-protruding rings 2 on the working section 20 surface of extrusion rod 4 work synergistically in a composite energy field of axial extrusion, rotational shearing, and ultrasonic vibration to strengthen the material of the hole wall 102. Rotational shearing and ultrasonic vibration are two independent modes of action with different physical sources and complementary effects. The machine tool spindle provides circumferential motion to achieve rotational shearing, ensuring a uniform distribution of strengthening action on the hole wall 102 through the generated circumferential shearing force. This also ensures that the extrusion point moves uniformly along the circumference of the hole wall 102, guaranteeing uniform coverage of the entire hole wall and avoiding local overpressure or weakening. Ultrasonic vibration generates axial high-frequency micro-amplitude vibrations, utilizing the acoustic softening effect to reduce the material's deformation resistance and achieve micro-forging. Because the outer diameter of the micro-protruding ring 2 increases gradually in the opposite direction of the feed direction, the strengthening process is more stable. This process transforms the overall strong extrusion in traditional processes into sequential micro-area incremental forming along a spiral trajectory. This reduces the extrusion pressure while creating a uniform residual compressive stress field deep within the hole wall 102, effectively protecting the integrity of the hole wall 102 surface. After the working section 20 of the extrusion rod 4 has completely passed through the hole 101 to be processed, the rear conical end 3, located behind the micro-protruding ring 2, begins to function. While the extrusion rod 4 continues to rotate, the conical surface of the rear conical end 3 guides and regulates the deformation of the orifice material as it retracts, preventing it from flanging or tearing, and also performs ironing and shaping on the orifice. This eliminates burrs at the orifice, stabilizes the hole shape, and obtains a smooth and regular exit morphology, thereby mitigating stress release and preventing damage such as tearing at the orifice. After the entire process is completed, the ultrasonic and rotary drives are turned off, the extrusion rod 4 is removed, and the device is reset. In Embodiment 1 of this application, a reinforced layer with good fatigue performance is obtained on the hole wall through a continuous process of mechanical motion and energy field control, achieving the processing goals of high quality, high efficiency and high consistency.

[0055] Example 2: In Embodiment 2 of this application, the ultrasonic-assisted micro-bulging hole extrusion strengthening device described above is used to conduct extrusion strengthening and low-cycle fatigue verification tests on a titanium alloy TC4 specimen with holes, in order to verify the actual effect of the device and method of this application. In the test, the thickness of the specimen with holes was 4 mm, and the initial hole diameter was 8.5 mm. The working section 20 of the extrusion rod 4 used is provided with three micro-bulging rings 2, whose outer diameters are set sequentially along the feed direction as 8.515 mm, 8.530 mm, and 8.545 mm.

[0056] During the strengthening process, the process parameters were set as follows: the ultrasonic frequency was controlled within 25kHz to 40kHz, the rotational speed of the device was set to 55r / min to 75r / min, and the axial feed speed was 4.8mm / min to 7.2mm / min. For the same hole 101 to be processed, a multi-pass cumulative strengthening method was adopted, with the number of processing passes set to 6 to 10 (defined as one pass of the extrusion rod 4 reciprocating through the hole along the axial direction). Tapping oil was continuously added during the processing to provide lubrication and cooling. Measurements showed that the average hole diameter after extrusion strengthening was 8.538mm, and the surface quality of the hole wall 102 was good.

[0057] Low-cycle fatigue tests were conducted on three unstrengthened original specimens and three specimens strengthened using the method described in this application. The test conditions were set as follows: ambient temperature, maximum load of 650 MPa, stress ratio of 0.1, and frequency of 10 Hz. The fatigue test results showed that the average fatigue life of the three unstrengthened specimens was 114,283 cycles; while the average fatigue life of the three specimens strengthened using the method described in this application increased to 426,589 cycles. Figure 5 As shown. Therefore, compared with the unstrengthened state, the fatigue life of the connecting hole treated with the ultrasonic-assisted micro-bulging hole extrusion strengthening technology of this application is increased by 2.73 times, which proves that the device and method have significant advantages in improving the fatigue performance of aerospace structural components.

[0058] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The features, structures, or characteristics described above can be combined in any suitable manner in one or more embodiments.

[0059] It is understood that those skilled in the art can combine various implementation methods in the above embodiments under the guidance of the above examples to obtain technical solutions with multiple implementation methods. The above descriptions are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An ultrasonic-assisted micro-bulging hole extrusion strengthening device, used to strengthen holes to be processed, characterized in that, The device includes: A transducer for converting high-frequency electrical signals into mechanical vibrations; An amplitude transformer, one end of which is connected to the transducer, is used to amplify the amplitude of the mechanical vibration and transmit it axially. An extrusion rod, one end of which is connected to the other end of the amplitude transformer, and the other end of the extrusion rod is provided with a working section; wherein, the surface of the working section is provided with a plurality of micro-protruding rings along the axial direction, and at least some of the micro-protruding rings have an outer diameter that increases in a gradient in the opposite direction to the feed direction of the extrusion rod.

2. The ultrasonic-assisted micro-bulge pore extrusion strengthening device as described in claim 1, characterized in that, The cross-sectional profile of the micro-protruding ring along the axial direction is one of the following: arc shape, semi-circular shape, and streamlined shape.

3. The ultrasonic-assisted micro-bulge hole extrusion strengthening device as described in claim 1, characterized in that, The plurality of micro-protruding rings are arranged sequentially along the axial direction of the extrusion rod; including at least a first micro-protruding ring that enters the hole to be processed, a second micro-protruding ring that enters the hole to be processed, and a third micro-protruding ring that enters the hole to be processed; based on the hole diameter d0 of the hole to be processed, the diameter d1 of the first micro-protruding ring is d0 + 0.015 mm; the diameter d2 of the second micro-protruding ring is d0 + 0.030 mm; and the diameter d3 of the third micro-protruding ring is d0 + 0.045 mm.

4. The ultrasonic-assisted micro-bulge hole extrusion strengthening device as described in claim 1, characterized in that, The axial span H of the micro-protruding ring and the wall thickness T of the hole to be processed satisfy the following relationship: H≥T.

5. The ultrasonic-assisted micro-bulge hole extrusion strengthening device as described in claim 1, characterized in that, Along the feed direction of the extrusion rod, the extrusion rod is connected to a front conical end on the front side of the feed direction and a rear conical end on the rear side of the feed direction; the outer surface of the rear conical end is a conical surface that gradually contracts in the opposite direction of the feed direction.

6. The ultrasonic-assisted micro-bulge hole extrusion strengthening device as described in claim 1, characterized in that, It also includes a connecting end cap, through which the extrusion rod is connected to the amplitude transformer; the extrusion rod and the connecting end cap are connected by a thread.

7. The ultrasonic-assisted micro-bulge hole extrusion strengthening device as described in claim 1, characterized in that, The base material of the extrusion rod is cemented carbide.

8. A method for ultrasonic-assisted micro-bulging hole extrusion strengthening using the ultrasonic-assisted micro-bulging hole extrusion strengthening device as described in any one of claims 1 to 7, characterized in that, The method includes the following steps: Align the front conical end of the extrusion rod with the center of the hole to be machined; Start the transducer to cause the extrusion rod to vibrate at high frequency; The extrusion rod is driven to rotate uniformly around its axis while simultaneously applying an axial feed force. Multiple micro-protruding rings on the working section of the extrusion rod pass sequentially through the hole wall of the hole to be processed, performing sequential micro-area incremental forming of the hole wall material; After the working section has completely passed through the hole to be processed, the outlet of the hole to be processed is shaped by the rear cone end, and the extrusion rod is moved out of the hole to be processed.

9. The ultrasonic-assisted micro-bulge pore extrusion strengthening method as described in claim 8, characterized in that, The process parameters in the method are set as follows: ultrasonic frequency of 25kHz to 40kHz, rotational speed of 55r / min to 75r / min, and feed speed of 4.8mm / min to 7.2mm / min.

10. The ultrasonic-assisted micro-bulge pore extrusion strengthening method as described in claim 8, characterized in that, For the same hole to be machined, the above steps are repeated 6 to 10 times; and tapping oil is continuously applied to the hole wall during the machining process.

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