An ultrasonic impact strengthening device and method based on reverse elastic preloading

Abstract

The application relates to an ultrasonic impact strengthening device and method based on reverse elastic preloading, and belongs to the technical field of metal surface treatment. The device comprises a rotary driving device for driving a shaft workpiece to rotate around an axis thereof; a clamping swing device for clamping the shaft workpiece; the clamping swing device comprises a base plate, a first swing assembly, a second swing assembly, a first clamping assembly and a second clamping assembly; a reverse pre-bending device for applying a reverse pre-bending load to both ends of the shaft workpiece; the reverse pre-bending device comprises a horizontal telescopic driving mechanism, a tension sensor, a first pull rod and a second pull rod, the first pull rod is used for pulling the first clamping assembly, and the second pull rod is used for pulling the second clamping assembly; and an ultrasonic impact device for performing ultrasonic impact strengthening on the shaft workpiece. The application can apply a reverse pre-bending opposite to the ultrasonic impact direction to the shaft workpiece, obtain a better residual compressive stress field, improve the overall stability of a surface strengthening layer, and prolong the fatigue life.

Description

Technical Field

[0001] This invention belongs to the field of metal surface strengthening technology, specifically relating to an ultrasonic impact strengthening device and method based on reverse elastic preloading. Background Technology

[0002] Ultrasonic impact testing is a highly efficient metal surface strengthening technology. Its core mechanism lies in using high-frequency mechanical impact to induce severe plastic deformation of the surface layer, thereby introducing a high-amplitude, deep residual compressive stress layer on the workpiece surface. This compressive stress layer is a key factor in improving the fatigue performance, stress corrosion resistance, and service life of metal components (especially welded structures, critical load-bearing components, and parts subjected to alternating loads).

[0003] Currently, to obtain deeper residual compressive stress layers or higher stress amplitudes, the industry commonly employs strategies that increase the output power and impact amplitude of ultrasonic impact equipment. While this approach can enhance the strengthening effect by driving more intense surface plastic deformation with higher energy input, it is limited by high equipment investment, maintenance costs, and potential quality risks. More importantly, simply relying on energy increases is no longer sufficient to overcome existing technological bottlenecks, necessitating more intelligent and efficient alternatives.

[0004] Traditional ultrasonic impact treatment methods introduce additional bending moments and pre-stress during the application of static pressure, and similarly remove these additional bending moments and pre-stress when the load is removed at the end of the process. This passively formed stress state severely weakens the modification effect of the surface alteration layer and restricts further improvement in fatigue life. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide an ultrasonic shock strengthening device and method based on reverse elastic preloading, so as to solve or improve the defects existing in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: an ultrasonic impact strengthening device based on reverse elastic preloading, comprising:

[0007] A rotary drive device for driving shaft-type workpieces to rotate about their axis;

[0008] A clamping and swinging device is used to clamp shaft-type workpieces. The clamping and swinging device includes a base plate, a first swinging component, a second swinging component, a first clamping component, and a second clamping component. The first clamping component is horizontally rotatably mounted on the base plate via the first swinging component, and the second clamping component is horizontally rotatably mounted on the base plate via the second swinging component. The first clamping component and the second clamping component are arranged facing each other, and the first clamping component and the second clamping component are respectively used to clamp the two ends of the shaft-type workpiece.

[0009] A reverse pre-bending device is used to apply a reverse pre-bending load to both ends of a shaft-like workpiece. The reverse pre-bending device includes a horizontal telescopic drive mechanism, a tension sensor, a first pull rod, and a second pull rod. One end of the horizontal telescopic drive mechanism is hinged to one end of the first pull rod, and the other end of the first pull rod is fixedly connected to a first clamping assembly. The first pull rod is used to pull the first clamping assembly to bend one end of the shaft-like workpiece. The other end of the horizontal telescopic drive mechanism is fixedly connected to one end of the tension sensor, and the other end of the tension sensor is hinged to one end of the second pull rod. The other end of the second pull rod is fixedly connected to a second clamping assembly, and the second pull rod is used to pull the second clamping assembly to bend the other end of the shaft-like workpiece.

[0010] An ultrasonic impact device is used to strengthen shaft-type workpieces through ultrasonic impact.

[0011] Preferably, the rotary drive device includes a spindle, a chuck, and a tailstock. The spindle is fixed on the frame, the chuck is fixedly installed on the output end of the spindle, the chuck and the tailstock are arranged opposite to each other, the tailstock is installed on the worktable of the frame, the chuck is used to drive the first clamping assembly to rotate the shaft-like workpiece, and the tailstock is used to hold the second clamping assembly.

[0012] Preferably, both the first clamping assembly and the second clamping assembly include a sleeve, a horizontal connecting shaft, and a spring clip. The inner circumferences of both ends of the sleeve are rotatably mounted on the horizontal connecting shaft via first bearings. One end of the horizontal connecting shaft is fixedly connected to a spring clip, which is used to fix and clamp the end of the shaft-type workpiece. The other end of the horizontal connecting shaft of the first clamping assembly is coaxially connected to the output end of the rotary drive device.

[0013] Preferably, both the first and second swing components include a swing element and a fixed base. The swing element is fixedly sleeved on the outer periphery of one end of the corresponding sleeve. A trunnion is provided at the center of both the upper and lower ends of the swing element. The fixed base includes a bottom plate, a top plate, a front plate, and a rear plate. The bottom plate is fixedly mounted on the base plate. The lower ends of the front and rear plates are fixedly connected to the front and rear ends of the bottom plate, respectively. The upper ends of the front and rear plates are fixedly connected to the front and rear ends of the top plate, respectively. A bearing seat hole is provided on both the bottom and top plates. The two trunnions are rotatably mounted in the corresponding bearing seat hole through a second bearing.

[0014] Preferably, the other end of the first pull rod is fixedly connected to the rear side of the other end of the sleeve of the first clamping assembly, and the other end of the second pull rod is fixedly connected to the rear side of the other end of the sleeve of the second clamping assembly.

[0015] Preferably, the horizontal telescopic drive mechanism is a pneumatic cylinder, a hydraulic cylinder, or an electric cylinder.

[0016] Preferably, the ultrasonic impact device includes an ultrasonic transducer, an ultrasonic amplitude transformer, and an ultrasonic impact head. The ultrasonic transducer is electrically connected to an ultrasonic generator. One end of the ultrasonic transducer is fixedly connected to one end of the ultrasonic amplitude transformer, and the other end of the ultrasonic amplitude transformer is fixedly connected to the ultrasonic impact head. The ultrasonic impact head is used to ultrasonically strengthen shaft-like workpieces. The end of the ultrasonic impact head is provided with a spherical groove, and a sphere for contacting the shaft-like workpiece is movably installed in the spherical groove.

[0017] Preferably, the other end of the ultrasonic transducer is fixedly connected to one end of the pressure sensor, and the other end of the pressure sensor is fixedly connected to a stop block. The stop block is connected to a fixed plate via a central shaft. A spring and a movable plate are slidably sleeved on the central shaft. The two ends of the spring abut against the stop block and the movable plate, respectively. A plurality of evenly distributed adjusting bolts are installed on the fixed plate, and the adjusting bolts cooperate with the threaded holes on the movable plate.

[0018] Preferably, the ultrasonic transducer is slidably mounted on the base plate, the base plate is fixedly mounted on the slider, the slider is slidably mounted on the guide rail, and the guide rail is fixedly mounted on the frame.

[0019] Meanwhile, the present invention also provides an ultrasonic impact strengthening method based on reverse elastic preloading, which uses the ultrasonic impact strengthening device based on reverse elastic preloading to fix the shaft workpiece to be processed between a first clamping assembly and a second clamping assembly, and includes the following steps:

[0020] S1. Control the horizontal telescopic drive mechanism to retract a first predetermined distance. The horizontal telescopic drive mechanism pulls the first clamping assembly and the second clamping assembly respectively through the first pull rod and the second pull rod. The first clamping assembly and the second clamping assembly rotate horizontally relative to the base plate through the first swing assembly and the second swing assembly respectively, so that the shaft workpiece is pre-bent in the reverse direction for the first time.

[0021] S2. Apply a predetermined static pressure to the shaft workpiece by making positive contact with the ultrasonic impact device;

[0022] S3. Control the horizontal telescopic drive mechanism to continue to retract the second predetermined distance. The horizontal telescopic drive mechanism continues to pull the first clamping assembly and the second clamping assembly through the first pull rod and the second pull rod respectively. The first clamping assembly and the second clamping assembly continue to rotate horizontally relative to the base plate through the first swing assembly and the second swing assembly respectively, so that the shaft workpiece is pre-bent in the reverse direction for the second time.

[0023] S4. The surface of shaft-type workpieces is subjected to ultrasonic impact treatment using an ultrasonic impact device.

[0024] S5. Control the horizontal telescopic drive mechanism to extend the second predetermined distance. The horizontal telescopic drive mechanism pushes the first clamping assembly and the second clamping assembly through the first pull rod and the second pull rod respectively. The first clamping assembly and the second clamping assembly rotate horizontally in opposite directions relative to the base plate through the first swing assembly and the second swing assembly respectively, so that the shaft workpiece returns to the first reverse pre-bending state.

[0025] S6. Control the ultrasonic impact device to move away from the shaft-like workpiece and remove the predetermined static pressure;

[0026] S7. Control the horizontal telescopic drive mechanism to extend the first predetermined distance. The horizontal telescopic drive mechanism continues to push the first clamping component and the second clamping component through the first pull rod and the second pull rod respectively. The first clamping component and the second clamping component continue to rotate horizontally in opposite directions relative to the base plate through the first swing component and the second swing component respectively, so that the shaft workpiece springs back to its natural state.

[0027] Preferably, in step S1, the pre-bending stress borne by the shaft workpiece during the first reverse pre-bending is controlled to not exceed 40% of the yield strength of the shaft workpiece material.

[0028] Preferably, in step S3, the pre-bending stress borne by the shaft workpiece during the second reverse pre-bending is controlled to not exceed 80% of the yield strength of the shaft workpiece material.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The device of the present invention, through the cooperation of a rotary drive device, a clamping swing device, a reverse pre-bending device and an ultrasonic impact device, can apply a reverse pre-bending to shaft-like workpieces in the opposite direction of ultrasonic impact, so that the surface of the shaft-like workpieces produces elastic tensile deformation and stores elastic strain energy. During ultrasonic impact, the pre-stored strain energy is released as an additional driving force, forming a "reverse pre-stretching-impact compensation" synergistic effect with the impact kinetic energy, promoting full plastic flow of the surface material, and obtaining a residual compressive stress field with higher amplitude, wider depth and more uniform distribution, overcoming the defects of shallow and unevenly distributed residual compressive stress layer of single ultrasonic impact.

[0031] This invention uses a tensile sensor to monitor the load in real time, which is beneficial for applying reverse pre-bending load in stages. This ensures that the shaft workpiece is always in the elastic deformation stage, avoids excessive loading at one time which would cause the shaft workpiece material to yield and be damaged, and balances the strengthening effect with the life of the shaft workpiece matrix.

[0032] The method of this invention employs a step-by-step loading strategy, first applying partial reverse pre-bending, then applying impact static pressure, and finally loading to the target pre-bending value. This precisely counteracts the non-uniform tensile stress interference introduced by static pressure in traditional ultrasonic impact, creating an ideal initial stress state for the impact region and suppressing crack initiation from the source. This solves the problem of stress concentration and fatigue crack initiation caused by static pressure in existing technologies. Furthermore, through combined strengthening with reverse pre-bending and ultrasonic impact, the surface hardness and roughness of shaft-type workpieces are simultaneously improved. Grain refinement increases hardness, and improved surface microstructure weakens stress concentration, effectively delaying fatigue crack initiation and early propagation, achieving a significant improvement in workpiece fatigue life. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on the drawings described below without creative effort.

[0034] Figure 1 This is a schematic diagram of the overall appearance of an ultrasonic impact strengthening device based on reverse elastic preloading according to an embodiment of the present invention.

[0035] Figure 2 This is a perspective view of the assembly structure of an ultrasonic impact strengthening device based on reverse elastic preloading, according to an embodiment of the present invention.

[0036] Figure 3 This is a top view of the assembly structure of an ultrasonic impact strengthening device based on reverse elastic preloading, according to an embodiment of the present invention.

[0037] Figure 4 This is a schematic diagram of the rotary drive device in an embodiment of the present invention.

[0038] Figure 5 This is a schematic diagram of the clamping and swinging device in an embodiment of the present invention.

[0039] Figure 6 This is a partial cross-sectional view of the clamping and swinging device in an embodiment of the present invention.

[0040] Figure 7 This is a schematic diagram showing the connection between the clamping swing device and the turret in an embodiment of the present invention.

[0041] Figure 8 This is a schematic diagram of the reverse pre-bending device in an embodiment of the present invention.

[0042] Figure 9 This is an assembly diagram of the clamping swing device and the reverse pre-bending device in an embodiment of the present invention.

[0043] Figure 10 This is a schematic diagram of the ultrasonic impact device in an embodiment of the present invention.

[0044] Figure 11 This is a diagram showing the bending moment variation of shaft-type workpieces in steps S1 to S3 of an ultrasonic impact strengthening method based on reverse elastic preloading according to the present invention.

[0045] Figure 12 A photograph of a shaft-type workpiece subjected to ultrasonic impact strengthening treatment based on reverse elastic preloading.

[0046] Figure 13 This is a schematic diagram comparing the results of conventional ultrasonic shock strengthening with the ultrasonic shock strengthening results based on reverse elastic preloading of the present invention.

[0047] Marked in the image:

[0048] 1. Frame; 2. Worktable; 3. Guide rail; 4. Turret;

[0049] 100. Rotary drive unit; 110. Chuck; 120. Tailstock;

[0050] 200. Clamping swing device; 201. Base plate; 210. First swing assembly; 211. Swing component; 2111. Trunnion; 212. Fixed seat; 2121. Base plate; 2122. Top plate; 2123. Front plate; 2124. Rear plate; 2125. Shaft seat hole; 2126. Connecting plate; 213. Second bearing; 220. Second swing assembly; 230. First clamping assembly; 231. Sleeve; 232. Horizontal connecting shaft; 233. Spring sleeve; 240. Second clamping assembly; 250. First bearing;

[0051] 300. Reverse pre-bending device; 310. Horizontal telescopic drive mechanism; 320. Tension sensor; 330. First tie rod; 340. Second tie rod; 350. Connecting rod; 360. Y-type connector.

[0052] 400. Ultrasonic impact device; 410. Ultrasonic transducer; 411. Substrate; 412. Slider; 420. Ultrasonic amplitude transformer; 430. Ultrasonic impact head; 431. Spherical groove; 432. Sphere; 440. Pressure sensor; 450. Stop; 460. Central shaft; 470. Fixing plate; 471. Adjusting bolt; 480. Spring; 490. Moving plate;

[0053] 500. Shaft-type workpieces;

[0054] 600. Cooling system. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. To make the above features and advantages of this invention more apparent and understandable, specific embodiments are provided below with reference to the accompanying drawings for detailed description.

[0056] like Figures 1 to 10 As shown, an embodiment of the present invention provides an ultrasonic shock strengthening device based on reverse elastic preloading, comprising:

[0057] A rotary drive device 100 is used to drive a shaft-type workpiece 500 to rotate about its axis.

[0058] A clamping swing device 200 is used to clamp a shaft-type workpiece 500. The clamping swing device 200 includes a base plate 201, a first swing component 210, a second swing component 220, a first clamping component 230, and a second clamping component 240. The first clamping component 230 is horizontally rotatably mounted on the base plate 201 via the first swing component 210, and the second clamping component 240 is horizontally rotatably mounted on the base plate 201 via the second swing component 220. The first clamping component 230 and the second clamping component 240 are arranged facing each other, and the first clamping component 230 and the second clamping component 240 are respectively used to clamp the two ends of the shaft-type workpiece 500.

[0059] A reverse pre-bending device 300 is used to apply a reverse pre-bending load to both ends of a shaft-type workpiece 500. The reverse pre-bending device 300 includes a horizontal telescopic drive mechanism 310, a tension sensor 320, a first pull rod 330, and a second pull rod 340. One end of the horizontal telescopic drive mechanism 310 is hinged to one end (e.g., the rear end) of the first pull rod 330, and the other end (e.g., the front end) of the first pull rod 330 is fixedly connected (e.g., by bolts) to a first clamping assembly 230. The first pull rod 330 is used to pull the first clamping assembly. 230 to bend one end of the shaft workpiece 500, the other end of the horizontal telescopic drive mechanism 310 (such as the telescopic rod end) is fixedly connected to one end of the tension sensor 320, the other end of the tension sensor 320 (such as the cylinder end) is hinged to one end (such as the rear end) of the second pull rod 340, the other end (such as the front end) of the second pull rod 340 is fixedly connected to the second clamping assembly 240 (such as by bolts), and the second pull rod 340 is used to pull the second clamping assembly 240 to bend the other end of the shaft workpiece 500;

[0060] An ultrasonic impact device 400 is used to perform ultrasonic impact strengthening on shaft-type workpieces 500.

[0061] In this embodiment, please refer to Figures 1 to 5 The rotary drive device 100 includes a spindle (not shown in the figure), a chuck 110, and a tailstock 120. The spindle is fixed on the frame 1, and the chuck 110 is fixedly mounted on the output end of the spindle. The chuck 110 and the tailstock 120 are arranged opposite to each other. The tailstock 120 is mounted on the worktable 2 of the frame 1. The chuck 110 is used to drive the first clamping assembly 230 to rotate the shaft-like workpiece 500, and the tailstock 120 is used to hold the second clamping assembly 240. The chuck 110 can be a three-jaw chuck, a four-jaw chuck, etc.

[0062] In this embodiment, please refer to Figures 1 to 6 Both the first clamping assembly 230 and the second clamping assembly 240 include a sleeve 231, a horizontal connecting shaft 232, and a spring clip 233. The inner circumferences of both ends of the sleeve 231 are rotatably mounted on the horizontal connecting shaft 232 via first bearings 250. The horizontal connecting shaft 232 can rotate freely relative to the sleeve 231 through the support of the two first bearings 250. One end of the horizontal connecting shaft 232 is fixedly connected (e.g., threaded) to a spring clip 233, which is used to fix and clamp the end of the shaft-like workpiece 500. The other end of the horizontal connecting shaft 232 of the first clamping assembly 230 is coaxially connected to the output end of the rotary drive device 100, specifically the first clamp... The other end of the horizontal connecting shaft 232 of the holding assembly 230 is clamped and fixed by the chuck 110. The chuck 110 drives the horizontal connecting shaft 232 of the first clamping assembly 230 to rotate synchronously. The horizontal connecting shaft 232 of the first clamping assembly 230 drives the shaft workpiece 500 to rotate synchronously through the spring sleeve 233 of the first clamping assembly 230. The shaft workpiece 500 drives the horizontal connecting shaft 232 of the second clamping assembly 240 to rotate synchronously through the spring sleeve 233 of the second clamping assembly 240. The horizontal connecting shaft 232 of the second clamping assembly 240 is held in place by the tailstock 120. The shaft workpiece 500, the two horizontal connecting shafts 232, and the two spring sleeves 233 form an assembly that can rotate freely relative to the sleeve 231. The first bearing 250 and the second bearing are positioned by steps or retaining rings (also called snap rings or retaining rings).

[0063] In this embodiment, please refer to Figures 1 to 7The first swing assembly 210 and the second swing assembly 220 both include a swing element 211 and a fixed base 212. The swing element 211 is fixedly sleeved on the outer periphery of one end of the corresponding sleeve 231. For example, the swing element 211 is fixedly connected to the flange of the sleeve 231 by a bolt and nut assembly. The upper and lower ends of the swing element 211 are each provided with a trunnion 2111. The fixed base 212 includes a base plate 2121, a top plate 2122, a front plate 2123, and a rear plate 2124. The base plate 2121 is fixed... The front plate 2123 and the rear plate 2124 are fixedly connected to the front and rear ends of the base plate 2121, respectively, and the upper ends of the front plate 2123 and the rear plate 2124 are fixedly connected to the front and rear ends of the top plate 2122, respectively. Both the base plate 2121 and the top plate 2122 have shaft seat holes 2125. Two trunnions 2111 are rotatably mounted in their respective shaft seat holes 2125 via second bearings 213, thus achieving hinged connection between the swing member 211 and the fixed seat 212. The two rear plates 2124 can be fixedly mounted on the turret 4 via connecting plates 2126. Alternatively, other parts of the fixed seat 212 or the base plate 201 can be fixedly mounted on the turret 4 or the frame 1 via connecting plates 2126.

[0064] In this embodiment, please refer to Figures 1 to 9The other end (e.g., the front end) of the first pull rod 330 is fixedly connected (e.g., by bolts) to the rear side of the other end (e.g., the left end) of the sleeve 231 of the first clamping assembly 230, and the other end (e.g., the front end) of the second pull rod 340 is fixedly connected (e.g., by bolts) to the rear side of the other end (e.g., the right end) of the sleeve 231 of the second clamping assembly 240. The other end of the horizontal telescopic drive mechanism 310 can be fixedly connected to one end of the tension sensor 320 via a connecting rod 350. The other end of the tension sensor 320 can be hinged to one end (rear end) of the second pull rod 340 via a Y-joint 360. The tension sensor 320 can monitor the reverse pre-bending load applied by the horizontal telescopic drive mechanism 310 in real time, thereby controlling the reverse pre-bending stress of the shaft workpiece 500. The horizontal telescopic drive mechanism 310 is preferably, but not limited to, a cylinder; hydraulic cylinders, electric cylinders, etc., are also acceptable. Initially, the horizontal telescopic drive mechanism 310 is in the extended state, and the shaft workpiece 500 is not bent. In use, under the contraction action of the horizontal telescopic drive mechanism 310, the first pull rod 330 and the second pull rod 340 transmit torque to the two sleeves 231, causing the sleeves 231, the swinging component 211, and its trunnion 2111 to deflect (i.e., swing) around the axis of the shaft seat hole 2125 of the fixed seat 212 at a certain angle. At the same time, the sleeves 231 drive the horizontal connecting shaft 232 and the spring clip 233 inside to deflect synchronously, ultimately applying a controllable reverse pre-bending load to the shaft workpiece 500. This embodiment adopts an assembly structure in which the horizontal connecting shaft 232 is threadedly connected to the spring clip 233 and the horizontal connecting shaft 232 passes through the inside of the sleeve 231. With the first pull rod 330 and the second pull rod 340 transmitting torque, precise loading of the shaft workpiece 500 is achieved. The spring clip 233 allows axial floating, avoiding over-constraint, ensuring precise load transmission and good process repeatability.

[0065] In this embodiment, please refer to Figures 1 to 10The ultrasonic impact device 400 can be disposed in front of the clamping swing device 200. The ultrasonic impact device 400 includes an ultrasonic transducer 410, an ultrasonic amplitude transformer 420, and an ultrasonic impact head 430. The ultrasonic transducer 410 is electrically connected to an ultrasonic generator (omitted in the figure). One end of the ultrasonic transducer 410 is fixedly connected to one end of the ultrasonic amplitude transformer 420, and the other end of the ultrasonic amplitude transformer 420 is fixedly connected to the ultrasonic impact head 430. The ultrasonic impact head 430 is used to ultrasonically strengthen the shaft workpiece 500. The end of the ultrasonic impact head 430 is provided with a spherical groove 431, and a ball 432 for contacting the shaft workpiece 500 is movably installed in the spherical groove 431. The ultrasonic impact strengthening device based on reverse elastic preloading may also include a cooling system 600. When the ultrasonic impact device 400 is working, the impact part of the shaft workpiece 500 is cooled by the cooling system 600. The cooling system 600 is existing technology and usually consists of a cooling pump, cooling medium, cooling pipe and nozzle, etc., which will not be described in detail here.

[0066] In this embodiment, the other end of the ultrasonic transducer 410 is fixedly connected to one end of the pressure sensor 440. The other end of the pressure sensor 440 is fixedly connected to a stop 450. The stop 450 is connected to a fixed plate 470 via a central shaft 460. A spring 480 and a moving plate 490 are slidably sleeved on the central shaft 460. The two ends of the spring 480 abut against the stop 450 and the moving plate 490, respectively. Multiple (e.g., four) evenly distributed adjusting bolts 471 are installed on the fixed plate 470. The adjusting bolts 471 cooperate with the threaded holes on the moving plate 490. By rotating the adjusting bolts 471, the moving plate 490 can be driven to move back and forth, thereby adjusting the tension of the spring 480 and changing the magnitude of the static pressure load. The ultrasonic transducer 410 is slidably mounted on the base plate 411, the base plate 411 is fixedly mounted on the slider 412, the slider 412 is slidably mounted on the guide rail 3, and the guide rail 3 is fixedly mounted on the frame 1. The ultrasonic impact device 400 can move horizontally left and right through the cooperation of the slider 412 and the guide rail 3, thereby performing ultrasonic impact treatment on the surface of the shaft workpiece 500 within a certain length range.

[0067] Please also refer to Figures 1 to 10 This embodiment also provides an ultrasonic impact strengthening method based on reverse elastic preloading. Using the aforementioned ultrasonic impact strengthening device based on reverse elastic preloading, the shaft workpiece 500 to be processed is fixedly clamped between the first clamping assembly 230 and the second clamping assembly 240, and includes the following steps:

[0068] S1. Control the horizontal telescopic drive mechanism 310 to retract a first predetermined distance. The horizontal telescopic drive mechanism 310 pulls the first clamping assembly 230 and the second clamping assembly 240 respectively through the first pull rod 330 and the second pull rod 340. The first clamping assembly 230 and the second clamping assembly 240 rotate horizontally relative to the base plate 201 through the first swing assembly 210 and the second swing assembly 220 respectively, so that the shaft workpiece 500 is pre-bent in the reverse direction for the first time. At this time, the surface of the shaft workpiece 500 generates elastic tensile deformation, and at the same time, elastic strain energy is stored in the subsurface layer.

[0069] S2. The ultrasonic impact device 400 makes positive contact with the shaft workpiece 500 and applies a predetermined static pressure to the shaft. Applying the predetermined static pressure will introduce non-uniform compressive stress, but since the shaft workpiece 500 has already been pre-bent in the opposite direction at this time, the two begin to produce a preliminary offsetting effect.

[0070] S3. Control the horizontal telescopic drive mechanism 310 to continue to retract the second predetermined distance. The horizontal telescopic drive mechanism 310 continues to pull the first clamping assembly 230 and the second clamping assembly 240 through the first pull rod 330 and the second pull rod 340 respectively. The first clamping assembly 230 and the second clamping assembly 240 continue to rotate horizontally relative to the base plate 201 through the first swing assembly 210 and the second swing assembly 220 respectively, so that the shaft workpiece 500 is pre-bent in the reverse direction for the second time, further stretching the surface of the shaft workpiece 500, accurately offsetting the local compressive stress concentration caused by static pressure, and creating an ideal and uniform stress state for the working area of ​​the ultrasonic impact head 430.

[0071] S4. The surface of the shaft workpiece 500 is subjected to ultrasonic impact treatment by ultrasonic impact device 400: the kinetic energy of ultrasonic impact causes plastic deformation of the surface of the shaft workpiece 500, and at the same time, the elastic strain energy stored in step S1 and step S2 is released as "additional driving force", which promotes more complete and uniform plastic flow; the surface of the shaft workpiece 500 changes from a pre-stretched state to a residual compressive stress state, and due to sufficient energy, the compressive stress layer is deeper and wider.

[0072] S5. Control the horizontal telescopic drive mechanism 310 to extend the second predetermined distance. The horizontal telescopic drive mechanism 310 pushes the first clamping assembly 230 and the second clamping assembly 240 respectively through the first pull rod 330 and the second pull rod 340. The first clamping assembly 230 and the second clamping assembly 240 rotate horizontally in opposite directions relative to the base plate 201 through the first swing assembly 210 and the second swing assembly 220 respectively, so that the shaft workpiece 500 returns to the first reverse pre-bending state. At this time, some elastic deformation is restored. At this time, the residual compressive stress field inside the shaft workpiece 500 will be finely adjusted according to the new equilibrium and tend to a more stable state.

[0073] S6. Control the ultrasonic impact device 400 to leave the shaft workpiece 500 and remove the predetermined static pressure. At this time, the shaft workpiece 500 completely releases the mechanical pressure applied by the ultrasonic impact device 400, leaving only the internal residual stress.

[0074] S7. Control the horizontal telescopic drive mechanism 310 to extend the first predetermined distance. The horizontal telescopic drive mechanism 310 continues to push the first clamping assembly 230 and the second clamping assembly 240 through the first pull rod 330 and the second pull rod 340 respectively. The first clamping assembly 230 and the second clamping assembly 240 continue to rotate horizontally in opposite directions relative to the base plate 201 through the first swing assembly 210 and the second swing assembly 220 respectively, so that the shaft workpiece 500 springs back to its natural state. Since strong plastic deformation has been generated in step S4, an ideal residual compressive stress field is formed on the surface after springback. Moreover, due to the reasonable stress history design, crack initiation is avoided.

[0075] In this embodiment, to optimize the effect of subsequent ultrasonic impact treatment on improving the fatigue life of the shaft workpiece 500, in step S1, the pre-bending stress borne by the shaft workpiece 500 during the first reverse pre-bending is controlled to not exceed 40% of the yield strength of the shaft workpiece 500 material, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc.; the pre-bending stress borne by the shaft workpiece 500 during the second reverse pre-bending (i.e., the cumulative total pre-bending stress) is controlled to not exceed 80% of the yield strength of the shaft workpiece 500 material, for example, 60%, 65%. The pre-bending stress is set at 70%, 75%, 80%, etc., to avoid inhibiting the strengthening effect due to excessive pre-bending stress. Through the above-mentioned graded reverse pre-bending, initial tensile stress is introduced into the surface layer of the shaft workpiece 500. Combined with ultrasonic impact to induce high-frequency loading and local plastic deformation, after the pre-bending load is removed, the shaft workpiece 500 transforms the original tensile stress zone into residual compressive stress under the combined action of geometric recovery and elastoplastic response, forming a "secondary strengthening" effect, which significantly increases the peak value of residual compressive stress. This "reverse pre-bending-ultrasonic impact-elastic recovery" synergistic mechanism provides mechanical support for improving the fatigue performance of the shaft workpiece 500. In this embodiment, the load magnitude can be monitored in real time by the tensile sensor 320 to ensure that the stress borne by the shaft workpiece 500 during the second reverse pre-bending never exceeds the yield limit of the shaft workpiece 500 material, thus avoiding plastic deformation of the shaft workpiece 500 and affecting the modification effect.

[0076] For a calibrated section of a shaft-type workpiece 500, denoted by diameter r and length I, the moment of inertia I of its cross-section is expressed as follows:

[0077] ;

[0078] Where I is the moment of inertia of the cross section;

[0079] The first stage involves fixing both ends of the shaft workpiece 500. The second stage involves applying a torque M of a certain magnitude to the shaft workpiece 500, causing it to bend in the opposite direction, ensuring that the shaft workpiece 500 does not undergo plastic deformation. At this point, the stress σ1 of the bent portion of the shaft workpiece 500 satisfies the following formula:

[0080] ;

[0081] Where, σ s Let y be the yield strength of the material, y be the distance from the calculated point on the cross section to the central axis, and M be the applied torque.

[0082] Under fixed ultrasonic impact parameters, the maximum stress amplitude generated on a workpiece of the same material is also fixed. This maximum stress amplitude is defined as σ. A For both cases with and without pre-bending, the effective driving stress is calculated as follows:

[0083] Without pre-bending:

[0084] ;

[0085] Where, Δσ no The stress is the stress without pre-bending;

[0086] When performing reverse pre-bending:

[0087] ;

[0088] Where, Δσ yes The stress during reverse pre-bending;

[0089] In a typical simplified plastic model, the amplitude of plastic strain is directly proportional to the excess stress exceeding the yield surface; therefore, the following relationship can be established:

[0090] ;

[0091] in, The value of plastic strain during reverse pre-bending. The value represents the plastic strain amplitude without pre-bending.

[0092] The above formula explains from a mechanistic perspective that reverse pre-bending produces better results. Since the value generated by reverse pre-bending is a positive tensile stress, for a fixed maximum stress amplitude σ... A The two steps of reverse pre-bending will generate greater effective driving stress, which in turn will lead to more intense plastic deformation, resulting in greater residual stress and ultimately a longer fatigue life.

[0093] In this embodiment, the specific method for ultrasonically impacting the surface of the shaft workpiece 500 using the ultrasonic impact device 400 in step S4 is as follows: the ultrasonic generator is started, and the ultrasonic impact head 430 performs ultrasonic impacting on the surface of the shaft workpiece 500 according to preset parameters (amplitude, frequency (e.g., 20KHz-40KHz), time); during the process, the elastic strain energy stored in steps S1 and S3 serves as an additional driving force, forming a "reverse pre-stretching-impact compensation" synergistic effect with the dynamic energy input by the ultrasonic impact, promoting full plastic flow of the surface material, improving the uniformity of residual stress distribution, and thus enhancing fatigue life.

[0094] like Figure 11 As shown, Figure 11 This is a diagram showing the bending moment variation of shaft-type workpieces in steps S1 to S3. Figure 11 In step S1, M1 represents the bending moment experienced by the shaft-like workpiece during its first reverse pre-bending; F S M2 is the static pressure applied by the ultrasonic impact device in step S2; M3 is the bending moment of the shaft workpiece under static pressure alone; M4 is the bending moment of the shaft workpiece under the first reverse pre-bending and static pressure simultaneously; M5 is the bending moment of the shaft workpiece under the second reverse pre-bending in step S3; M6 is the bending moment of the shaft workpiece under the second reverse pre-bending in step S3; M7 is the bending moment of the shaft workpiece under the second reverse pre-bending. max This represents the maximum bending moment corresponding to the yield limit of a shaft-type workpiece.

[0095] like Figure 12 and Figure 13 As shown, Figure 12 A photograph of a shaft-type workpiece subjected to ultrasonic impact strengthening treatment based on reverse elastic preloading. Figure 13 This diagram illustrates a comparison between existing conventional ultrasonic shock strengthening results and the ultrasonic shock strengthening results based on reverse elastic preloading of this invention. Figure 13 (a) shows the results of conventional ultrasonic impact strengthening. From the perspective of stress distribution uniformity, the residual stress of the conventional ultrasonic impact strengthened specimen along the test line fluctuates more, indicating that excessive static pressure exacerbates the difference between the bending of the impact head and the contact state. Figure 13(b) shows the ultrasonic impact strengthening results based on reverse elastic preloading of the present invention. The residual stress fluctuation on the surface of the ultrasonic impact strengthened specimen based on reverse elastic preloading is small, and the spatial non-uniformity is effectively suppressed. The specific test method is as follows: (1) Prepare the specimen: According to GB / T 4337-2015 "Metallic Materials Fatigue Test Rotation Bending Method", a 20CrNiMo steel carburized round shaft with a length of 140mm and a diameter of 12mm is processed into a shaft specimen with a middle section diameter of 6mm and a yield strength of 750MPa; (2) Existing ordinary ultrasonic impact strengthening method: one end of the shaft specimen is clamped with a chuck, and the other end is supported by a tailstock. The specimen is directly impacted with a static pressure of 400N. Finally, the axial residual compressive stress of the specimen is measured by an X-ray residual stress analyzer to be approximately -380MPa to -450MPa, and along the length of the specimen The residual stress is unevenly distributed in the direction of the degree, and the residual stress fluctuation difference exceeds 70 MPa; (3) The ultrasonic impact strengthening method based on reverse elastic preloading of the present invention: first, apply reverse pre-bending stress to the shaft sample to 262.5 MPa (35% of the yield limit), then apply 400 N static pressure, and then continue to apply reverse pre-bending load to 525 MPa (70% of the yield limit) and simultaneously ultrasonic impact. Finally, the axial residual compressive stress of the sample is measured by X-ray residual stress analyzer to be approximately -570 MPa to -612 MPa, and the residual stress fluctuation difference is less than 50 MPa. Experiments show that the reverse pre-bending process of the present invention can significantly improve the uniformity of the residual stress distribution of shaft workpieces and effectively increase the residual stress amplitude. The present invention is of great significance for optimizing the surface strengthening process of key components of high hardenability carburizing steel such as 20CrNiMo steel and extending their service life.

[0096] In the description of this invention, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0097] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "multiple" means two or more, unless otherwise explicitly specified.

[0098] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0099] All contents not described in detail in this invention are existing technologies, such as tension sensors and pressure sensors, and will not be elaborated here.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An ultrasonic impact strengthening device based on reverse elastic preloading, characterized in that, include: A rotary drive device for driving shaft-type workpieces to rotate about their axis; A clamping and swinging device is used to clamp shaft-type workpieces. The clamping and swinging device includes a base plate, a first swinging component, a second swinging component, a first clamping component, and a second clamping component. The first clamping component is horizontally rotatably mounted on the base plate via the first swinging component, and the second clamping component is horizontally rotatably mounted on the base plate via the second swinging component. The first clamping component and the second clamping component are arranged facing each other, and the first clamping component and the second clamping component are respectively used to clamp the two ends of the shaft-type workpiece. A reverse pre-bending device is used to apply a reverse pre-bending load to both ends of a shaft-like workpiece. The reverse pre-bending device includes a horizontal telescopic drive mechanism, a tension sensor, a first pull rod, and a second pull rod. One end of the horizontal telescopic drive mechanism is hinged to one end of the first pull rod, and the other end of the first pull rod is fixedly connected to a first clamping assembly. The first pull rod is used to pull the first clamping assembly to bend one end of the shaft-like workpiece. The other end of the horizontal telescopic drive mechanism is fixedly connected to one end of the tension sensor, and the other end of the tension sensor is hinged to one end of the second pull rod. The other end of the second pull rod is fixedly connected to a second clamping assembly, and the second pull rod is used to pull the second clamping assembly to bend the other end of the shaft-like workpiece. An ultrasonic impact device is used to strengthen shaft-type workpieces through ultrasonic impact.

2. The ultrasonic impact strengthening device based on reverse elastic preloading according to claim 1, characterized in that, The rotary drive device includes a spindle, a chuck, and a tailstock. The spindle is fixed on the machine frame, and the chuck is fixedly installed on the output end of the spindle. The chuck and the tailstock are arranged opposite to each other. The tailstock is installed on the worktable of the machine frame. The chuck is used to drive the first clamping assembly to rotate the shaft-type workpiece, and the tailstock is used to hold the second clamping assembly.

3. The ultrasonic impact strengthening device based on reverse elastic preloading according to claim 1, characterized in that, Both the first clamping assembly and the second clamping assembly include a sleeve, a horizontal connecting shaft, and a spring clip. The inner circumferences of both ends of the sleeve are rotatably mounted on the horizontal connecting shaft via first bearings. One end of the horizontal connecting shaft is fixedly connected to a spring clip, which is used to fix and clamp the end of the shaft-type workpiece. The other end of the horizontal connecting shaft of the first clamping assembly is coaxially connected to the output end of the rotary drive device.

4. The ultrasonic impact strengthening device based on reverse elastic preloading according to claim 3, characterized in that, Both the first and second swing components include a swing element and a fixed base. The swing element is fixedly sleeved on the outer periphery of one end of the corresponding sleeve. A trunnion is provided at the center of both the upper and lower ends of the swing element. The fixed base includes a base plate, a top plate, a front plate, and a rear plate. The base plate is fixedly mounted on the base plate. The lower ends of the front and rear plates are fixedly connected to the front and rear ends of the base plate, respectively. The upper ends of the front and rear plates are fixedly connected to the front and rear ends of the top plate, respectively. A bearing seat hole is provided on both the base plate and the top plate. The two trunnions are rotatably mounted in the corresponding bearing seat hole through a second bearing.

5. The ultrasonic impact strengthening device based on reverse elastic preloading according to claim 3, characterized in that, The other end of the first pull rod is fixedly connected to the rear side of the other end of the sleeve of the first clamping assembly, and the other end of the second pull rod is fixedly connected to the rear side of the other end of the sleeve of the second clamping assembly.

6. The ultrasonic impact strengthening device based on reverse elastic preloading according to claim 1, characterized in that, The horizontal telescopic drive mechanism is a pneumatic cylinder, a hydraulic cylinder, or an electric cylinder.

7. The ultrasonic impact strengthening device based on reverse elastic preloading according to claim 1, characterized in that, The ultrasonic impact device includes an ultrasonic transducer, an ultrasonic amplitude transformer, and an ultrasonic impact head. The ultrasonic transducer is electrically connected to an ultrasonic generator. One end of the ultrasonic transducer is fixedly connected to one end of the ultrasonic amplitude transformer, and the other end of the ultrasonic amplitude transformer is fixedly connected to the ultrasonic impact head. The ultrasonic impact head is used to ultrasonically strengthen shaft-like workpieces. The end of the ultrasonic impact head is provided with a spherical groove, and a ball for contacting the shaft-like workpiece is movably installed in the spherical groove.

8. The ultrasonic impact strengthening device based on reverse elastic preloading according to claim 7, characterized in that, The other end of the ultrasonic transducer is fixedly connected to one end of the pressure sensor. The other end of the pressure sensor is fixedly connected to a stop block. The stop block is connected to a fixed plate via a central shaft. A spring and a moving plate are slidably mounted on the central shaft. The two ends of the spring abut against the stop block and the moving plate, respectively. Multiple evenly distributed adjusting bolts are installed on the fixed plate. The adjusting bolts cooperate with the threaded holes on the moving plate. The ultrasonic transducer is slidably mounted on a base plate. The base plate is fixedly mounted on a slider. The slider is slidably mounted on a guide rail. The guide rail is fixedly mounted on a frame.

9. A method for ultrasonic shock strengthening based on reverse elastic preloading, using the ultrasonic shock strengthening device based on reverse elastic preloading as described in any one of claims 1 to 8, characterized in that, The shaft-type workpiece to be processed is fixedly clamped between the first clamping assembly and the second clamping assembly, and includes the following steps: S1. Control the horizontal telescopic drive mechanism to retract a first predetermined distance. The horizontal telescopic drive mechanism pulls the first clamping assembly and the second clamping assembly respectively through the first pull rod and the second pull rod. The first clamping assembly and the second clamping assembly rotate horizontally relative to the base plate through the first swing assembly and the second swing assembly respectively, so that the shaft workpiece is pre-bent in the reverse direction for the first time. S2. Apply a predetermined static pressure by making positive contact with the shaft-like workpiece using an ultrasonic impact device; S3. Control the horizontal telescopic drive mechanism to continue to retract the second predetermined distance. The horizontal telescopic drive mechanism continues to pull the first clamping assembly and the second clamping assembly through the first pull rod and the second pull rod respectively. The first clamping assembly and the second clamping assembly continue to rotate horizontally relative to the base plate through the first swing assembly and the second swing assembly respectively, so that the shaft workpiece is pre-bent in the reverse direction for the second time. S4. The surface of shaft-type workpieces is subjected to ultrasonic impact treatment using an ultrasonic impact device. S5. Control the horizontal telescopic drive mechanism to extend the second predetermined distance. The horizontal telescopic drive mechanism pushes the first clamping assembly and the second clamping assembly through the first pull rod and the second pull rod respectively. The first clamping assembly and the second clamping assembly rotate horizontally in opposite directions relative to the base plate through the first swing assembly and the second swing assembly respectively, so that the shaft workpiece returns to the first reverse pre-bending state. S6. Control the ultrasonic impact device to move away from the shaft-like workpiece and remove the predetermined static pressure; S7. Control the horizontal telescopic drive mechanism to extend the first predetermined distance. The horizontal telescopic drive mechanism continues to push the first clamping component and the second clamping component through the first pull rod and the second pull rod respectively. The first clamping component and the second clamping component continue to rotate horizontally in opposite directions relative to the base plate through the first swing component and the second swing component respectively, so that the shaft workpiece springs back to its natural state.

10. The ultrasonic shock strengthening method based on reverse elastic preloading according to claim 9, characterized in that, In step S1, the pre-bending stress borne by the shaft workpiece during the first reverse pre-bending is controlled to not exceed 40% of the yield strength of the shaft workpiece material; in step S3, the pre-bending stress borne by the shaft workpiece during the second reverse pre-bending is controlled to not exceed 80% of the yield strength of the shaft workpiece material.

Images