A drive shaft friction welding apparatus and method

Abstract

The application relates to a transmission shaft friction welding device and method, and belongs to the technical field of transmission shaft machining. The device comprises a contact die assembly arranged on one side of a friction interface of a welding part; the contact die assembly is installed on the friction welding device through a moving device, so that the contact die assembly can at least move in the radial direction and the axial direction of the welding part; when the contact die assembly is close to the welding part in a welding state, the flowing direction of the flash in the flash forming process of the welding part is constrained. Through the application, the technical problems that the flash forming process of the welding part is uncontrollable and the flash cannot be effectively utilized in the prior art are solved.

Description

Technical Field

[0001] This invention relates to a friction welding device and method for transmission shafts, belonging to the technical field of transmission shaft processing. Background Technology

[0002] As a typical friction welding process, inertia friction welding boasts advantages such as high quality, high efficiency, energy saving, and environmental friendliness, and is widely used in aerospace, automotive, and energy industries. During friction welding, the workpieces rotate at relatively high speeds under axial pressure, and the friction interface and its surrounding area reach a plastic state due to frictional heat. As the welding process progresses, some of the ductile metal is extruded from the friction interface, forming flash. Flash is a typical macroscopic morphological feature of inertia friction welding, and its morphology has a significant impact on the performance of the welded joint.

[0003] In existing technologies, flash is generally considered a byproduct of the welding process. Its formation lacks effective control, resulting in flash often extending irregularly radially. This not only fails to contribute positively to the strength of the welded joint but also negatively impacts the appearance and assembly performance of the weldment due to its irregular shape and excessive length. It often requires subsequent machining for removal, increasing production steps and costs. Furthermore, the disordered flow of flash can easily lead to stress concentration and uneven microstructure, further weakening the mechanical properties of the joint.

[0004] Therefore, a new solution is needed to address this problem. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a friction welding device and method for a transmission shaft, which solves the technical problems of uncontrollable flash forming process and ineffective utilization of flash in the prior art.

[0006] The technical problem to be solved by this invention is achieved by the following technical solution:

[0007] A friction welding device for a drive shaft includes a contact mold assembly disposed on one side of the friction interface of the workpiece.

[0008] The contact mold assembly is mounted on the friction welding device via a moving device to drive the contact mold assembly to move at least in the radial and axial directions of the weldment;

[0009] When the contact mold assembly approaches the weldment in the welding state, it constrains the flow direction of the weldment during the flash forming process.

[0010] The present invention is further configured such that: the contact mold assembly includes a V-shaped seat with an opening facing the weldment, and elastic plates with both ends slidably connected to both ends of the V-shaped seat;

[0011] The curvature of the elastic plate is variable on the inner side of the V-shaped seat.

[0012] The present invention is further configured such that: the V-shaped seat includes a base, a first support block and a second support block, both the first support block and the second support block being hinged to the base to adjust the included angle at the opening of the V-shaped seat.

[0013] The invention is further configured to include a sound wave generator to propagate vibrations on the portion of the elastic plate inside the V-shaped seat, causing the metal to flow rapidly to both sides of the friction interface.

[0014] A friction welding method for a drive shaft involves clamping the shaft tube workpiece and the shaft fork workpiece to be welded in the spindle box and the moving fixture of a friction welding equipment, respectively, while keeping them coaxial.

[0015] Adjust the included angle of the V-shaped seat according to the diameter of the workpiece, and adjust the initial curvature of the elastic plate in the opening of the V-shaped seat according to the diameter of the workpiece and the feed rate.

[0016] The contact mold assembly is brought radially closer to the welding interface, so that the arc-shaped part of the elastic plate maintains a gap with the friction welding area.

[0017] The spindle box is driven to rotate the shaft tube workpiece, while the moving fixture is controlled to feed towards the spindle box, so that the shaft fork workpiece contacts the end face of the rotating shaft tube workpiece and rubs under axial pressure;

[0018] When the temperature of the friction interface reaches the plastic state of the material, the contact mold assembly is controlled to move to the vicinity of the welding interface, so that its opening faces the area where the flash of the weldment is formed.

[0019] The contact mold assembly provides contact constraint on the flash forming process of plastic metal in both the radial and axial directions, restricting its radial flow and guiding the plastic metal to flow axially, thereby forming a structurally reinforced sloping flash.

[0020] Maintain the position of the contact mold assembly until the end of the upsetting stage, and the flash is shaped;

[0021] Remove the mold assembly, stop rotation, and welding is complete.

[0022] The present invention is further configured such that: in the initial stage of flash forming, the elastic plate is controlled to maintain a first curvature state, so that its inner constraint surface forms an approximately planar constraint interface, which generates a radial constraint force on the extruded plastic metal, forcing the plastic metal to flow directionally along the workpiece axis toward both sides of the V-shaped seat opening, forming the basic width of the flash;

[0023] As the welding process proceeds, when the axial metal flow reaches a predetermined distribution state, the curvature of the elastic plate is increased to transform it into a second curvature state.

[0024] In the second curvature state, the inner constraint surface of the elastic plate transforms into an arc-shaped guide surface with a specific curvature, guiding the axial metal flow on both sides to change its flow direction, converge towards the outer periphery of the friction interface, and form superimposed bulges.

[0025] By precisely controlling the timing and rate of the transition of the elastic plate from the first curvature state to the second curvature state, the morphology control of the flash forming process can be achieved.

[0026] The final result is a reinforced flash structure with a specific sloping cross-sectional morphology and a smooth transition with the workpiece body.

[0027] The present invention is further configured to: simultaneously control the change in the included angle of the V-shaped seat opening during the process of dynamically adjusting the curvature of the elastic plate, so as to coordinately control the flash morphology.

[0028] In the early stage of flash forming, the V-shaped seat is controlled to maintain a large opening angle, while the elastic plate maintains a small curvature, forming a flash expansion control mode with radial constraint as the main factor, guiding the plastic metal to be fully diverted along the axial direction.

[0029] During the mid-stage of flash forming, the included angle of the V-slot opening is reduced and the curvature of the elastic plate is increased simultaneously, so that the sidewall of the V-slot and the elastic plate form a gradually narrowing forming channel, guiding the subsequent metal flow extruded from the friction interface to converge in the central area.

[0030] In the later stage of flash forming, by precisely controlling the ratio between the convergence rate of the V-shaped seat opening angle and the rate of change of the elastic plate curvature, the converging metal flow generates axial superposition and radial compaction effects in the confined space, forming a reinforced flash structure with high density and controllable slope.

[0031] A pressure sensor is installed at the end of the contact mold assembly to monitor the pressure changes during the flash forming process in real time. By adjusting the motion parameters of the V-shaped seat and the elastic plate based on the pressure changes during the flash forming process, the flash forming quality is ensured.

[0032] The present invention is further configured to: establish a flash forming control method based on acoustic vibration, wherein an acoustic generator is provided in the central region inside the V-shaped seat to directionally emit acoustic waves of a specific frequency toward the central region of the elastic plate;

[0033] In the early stage of flash forming, the sound wave generator is controlled to output low-frequency high sound pressure level sound waves. The sound wave energy is transferred to the plastic metal through the elastic plate to promote the initial flow and axial diversion of the metal material.

[0034] During the mid-stage of flash forming, the acoustic parameters are dynamically adjusted based on the pressure change characteristics fed back by the pressure sensor: when the pressure value reaches the first threshold, the acoustic frequency is increased and the sound pressure level is adjusted, and the acoustic vibration effect promotes the rearrangement of metal particles and their convergence toward the central region.

[0035] In the later stage of flash forming, based on the density signal monitored by the pressure sensor, a high-frequency low sound pressure level acoustic wave mode is used to perform micro-structure conditioning treatment on the flash to improve the density and uniformity of the internal structure of the flash.

[0036] By utilizing the cavitation and acoustic flow effects generated by acoustic vibration, the uniformity of metal flow during flash forming is improved, the density of the internal structure of the flash is enhanced, and finally a sloping flash structure with excellent mechanical properties is obtained.

[0037] The present invention is further configured to: evaluate the quality of the burr edge region based on image recognition, including the following steps:

[0038] Obtain a digital image of the flash area of ​​the welded part;

[0039] The digital image is preprocessed to enhance the morphological features of the flash;

[0040] Extract the image features of the fringe region, the image features including:

[0041] Texture features, including gray-level co-occurrence matrix features and / or local binary pattern features;

[0042] Contour features, including the continuity, curvature, and contour defect detection results of the flash edges;

[0043] Based on the image features, the type of flash shape is determined using a classification model:

[0044] If the flash surface is smooth, continuous and without breaks, it is judged as a smooth morphology;

[0045] If the surface of the flash has an arc-shaped texture and no obvious cracks, it is judged to be an arc-shaped texture.

[0046] If the surface of the flash has obvious cracks or fractures, it is judged as a cracked morphology.

[0047] The quality of the joint is evaluated based on the morphology of the flash: a smooth morphology corresponds to a high-quality joint, a wavy morphology corresponds to a medium-quality joint, and a cracked morphology corresponds to a substandard joint.

[0048] The beneficial effects of this invention are:

[0049] By setting up contact mold components to constrain and guide the flow of plastic metal in the radial and axial directions, a structurally reinforced sloping flash is formed, which avoids stress concentration at the flash and improves the mechanical properties of the joint.

[0050] By adjusting the curvature of the elastic plate and the opening angle of the V-shaped seat, the metal flow path is controlled, the disorderly expansion of the flash is avoided, and a flash morphology structure with controllable slope is formed, reducing the need for subsequent processing.

[0051] By combining acoustic vibration to promote metal flow and microstructure densification, and through real-time monitoring using an image recognition system, the quality assessment of flash morphology can be achieved. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the friction welding process between the shaft fork and the shaft tube in the prior art.

[0053] Figure 2 This is a top view of the contact mold assembly in this invention.

[0054] Figure 3 This is a bottom view of the contact mold assembly in this invention.

[0055] Figure 4 This is a schematic diagram of the contact mold assembly and the weldment in this invention.

[0056] Figure 5 This is a schematic diagram of the structure of the weldment after the flash is formed in this invention.

[0057] Figure 6 This is a flowchart of the method in this invention.

[0058] In the diagram: 1. Shaft fork; 2. Shaft tube; 3. Contact mold assembly; 4. V-shaped seat; 5. Elastic plate; 6. Base; 7. First support block; 8. Second support block; 9. Electric cylinder; 10. Rewinding roller; 11. Through groove; 12. Guide roller; 13. Limiting block; 14. Acoustic wave generator. Detailed Implementation

[0059] To facilitate a clear understanding of the technical means, creative features, objectives, and effects of this invention, the invention will be further described below in conjunction with specific illustrations.

[0060] Friction welding, as a solid-state joining technology, has been widely used and continuously developed in the field of drive shaft manufacturing. This process utilizes the heat generated by mechanical friction to locally plasticize the material, achieving a connection under pressure; the entire process requires no filler material. For drive shafts, friction welding is mainly used for connecting components such as the shaft tube 2 to the shaft fork 1 and spline sleeves.

[0061] like Figure 1As shown, during the friction welding process of shaft fork 1 and shaft tube 2, due to the frictional heat generation, the interface metal undergoes dynamic recrystallization and gradually softens. When the interface temperature reaches the material welding window, the metal enters a plastic state. Under continuous axial pressure, the plastic metal is squeezed out from the friction interface and accumulates around the workpiece to form flash. The formation of flash is a natural phenomenon in the friction welding process, but its morphological characteristics directly affect the mechanical properties and reliability of the joint.

[0062] Due to the lack of effective constraint and control over the flow path of the plastic metal, the extruded high-temperature metal usually extends radially freely and forms curls, and in most cases forms an M-shaped flash that is thin in the middle and thick on both sides.

[0063] In the transition area of ​​the flash (i.e., the junction between the flash and the base material), especially in the thin-walled recessed area of ​​the M-shaped flash, the geometry changes abruptly, which leads to a significant increase in the stress level at this point, forming a stress concentration point. Under alternating loads, fatigue cracks are very likely to be generated at the stress concentration point. The cracks will gradually extend and extend into the interior of the welded joint, severely reducing the fatigue strength and life of the joint.

[0064] like Figures 2-3 As shown, a friction welding device for a drive shaft includes a spindle box for clamping the workpiece, a movable clamp, and a contact mold assembly 3. The workpiece includes a shaft fork 1 and a shaft tube 2. The spindle box is used to clamp and rotate the shaft tube 2. The movable clamp is used to clamp the shaft fork 1 and apply axial movement. The contact mold assembly 3 is mounted on the friction welding device via a moving device and is located on one side of the friction interface of the workpiece. Since the spindle box, movable clamp, and moving device are all prior art, they will not be described in detail here.

[0065] The contact mold assembly 3 is driven by a moving device to move at least radially and axially toward the weldment, thereby enabling it to move radially toward or away from the weldment and to move synchronously with the weldment axially. When the contact mold assembly 3 approaches the weldment in the welding state, it constrains the flow direction of the weldment during the flash forming process.

[0066] Furthermore, the contact mold assembly 3 includes a V-shaped seat 4 with its opening facing the weldment and elastic plates 5 with their ends slidably connected to both ends of the V-shaped seat, wherein the curvature of the elastic plates 5 inside the V-shaped seat 4 is variable.

[0067] To facilitate control of the curvature of the elastic plate 5, the V-shaped seat 4 includes a base 6, a first support block 7, and a second support block 8. The first support block 7 and the second support block 8 are claw-shaped and are respectively hinged to the two ends of the base 6. An electric cylinder 9 is provided on the top of the base 6, and the two ends of the electric cylinder 9 are respectively hinged to the top of the first support block 7 and the second support block 8 to adjust the included angle at the opening of the V-shaped seat 4. A winding roller 10 is provided on the inner side of the first support block 7 and the second support block 8. The winding roller 10 is driven to rotate by a servo motor. A through slot 11 is provided on the outer side of the first support block 7 and the second support block 8. A guide roller 12 is provided at the bottom of the first support block 7 and the second support block 8. A limiting block 13 is provided at the bottom of the first support block 7 and the bottom of the second support block 8 to limit the elastic plate 5 to adhere to the surface of the guide roller 12.

[0068] The elastic plate 5 can be made of high-temperature spring steel. It is set as a strip, with both ends passing around the guide roller 12 and through the through groove 11, and one end is fixedly connected to the take-up roller 10. The take-up roller 10 is driven to rotate by a servo motor, which controls the length of the elastic plate 5 between the first support block 7 and the second support block 8, thereby changing its curvature.

[0069] To promote metal flow, a sound wave generator 14 is provided at the bottom of the base 6. The sound wave generating end corresponds to the middle position of the elastic plate 5 in the V-shaped seat 4. The sound wave propagates the vibration of the vibrating plate, causing the metal to flow quickly to both sides of the friction interface.

[0070] like Figures 4-6 As shown, a friction welding method for a transmission shaft involves clamping the shaft fork 1 and shaft tube 2 of the workpiece in the spindle box and moving fixture of the friction welding equipment, respectively. The centering mechanism ensures that the two remain coaxial, and the coaxiality error is controlled within 0.03mm to ensure uniform force distribution and avoid uneven loading during the welding process.

[0071] The first support block 7 and the second support block 8 of the V-shaped seat 4 are driven to rotate around the hinge point according to the diameter of the workpiece, thereby adjusting the included angle at the opening of the V-shaped seat 4 to match the specifications of the workpiece; and according to the diameter of the workpiece and the preset feed amount, the initial curvature of the elastic plate 5 in the opening of the V-shaped seat 4 is adjusted to initially form an arc-shaped guide surface.

[0072] Based on the diameter of the weldment and the preset feed amount, the initial curvature of the elastic plate 5 in the opening of the V-shaped seat 4 is adjusted by the curvature adjustment mechanism so that it initially forms an arc-shaped guide surface that adapts to the expected flash shape.

[0073] The contact mold assembly 3 is moved radially towards the welding interface by a moving device, maintaining an initial gap of 2.0–5.0 mm with the friction welding area to avoid interfering with the friction process while reserving operating space for subsequent constraints.

[0074] Then, drive the spindle box to rotate the shaft tube 2 workpiece, and at the same time control the moving fixture to feed towards the spindle box, so that the shaft fork 1 workpiece contacts the end face of the rotating shaft tube 2 workpiece and rubs under axial pressure. When the temperature of the friction interface reaches the plastic state of the material, control the contact mold assembly 3 to move to the vicinity of the welding interface, so that its opening faces the area where the weldment flash is formed.

[0075] In the initial stage of flash forming, the elastic plate 5 is controlled to maintain the first curvature state, so that its inner constraint surface forms an approximately planar constraint interface, which generates a radial constraint force on the extruded plastic metal, forcing the plastic metal to flow directionally along the workpiece axis toward both sides of the V-shaped seat 4 opening, forming the basic width of the flash.

[0076] As the welding process proceeds, when the axial metal flow reaches the predetermined distribution state, the curvature of the elastic plate 5 is increased to transform it into a second curvature state. In the second curvature state, the inner constraint surface of the elastic plate 5 transforms into an arc-shaped guide surface with a specific curvature, guiding the axial metal flow on both sides to change its flow direction, converge towards the outer periphery of the friction interface, and form a superimposed bulge.

[0077] By precisely controlling the timing and rate of the transition of the elastic plate 5 from the first curvature state to the second curvature state, the morphology control of the flash forming process is achieved, and finally a reinforced flash structure with a specific slope cross-sectional morphology and a smooth transition with the workpiece body is obtained.

[0078] Furthermore, during the dynamic adjustment of the curvature of the elastic plate 5, the change in the opening angle of the V-shaped seat 4 is simultaneously controlled to achieve coordinated control of the flash morphology:

[0079] In the early stage of flash forming, the V-shaped seat 4 is controlled to maintain a large opening angle, while the elastic plate 5 is kept with a small curvature, forming a flash expansion control mode with radial constraint as the main factor, guiding the plastic metal to be fully diverted along the axial direction.

[0080] During the mid-stage of flash forming, the included angle of the opening of the V-shaped seat 4 is reduced and the curvature of the elastic plate 5 is increased simultaneously, so that the side wall of the V-shaped seat 4 and the elastic plate 5 form a gradually narrowing forming channel, guiding the subsequent metal flow extruded from the friction interface to converge in the central area.

[0081] In the later stage of flash forming, by precisely controlling the ratio between the convergence rate of the opening angle of the V-shaped seat 4 and the curvature change rate of the elastic plate 5, the converged metal flow generates axial superposition and radial compaction effects in the confined space, forming a reinforced flash structure with high density and controllable slope.

[0082] Maintain the position of contact mold assembly 3 until the end of the forging stage, and the flash is shaped;

[0083] Remove the mold assembly, stop rotation, and welding is complete.

[0084] To achieve precise pressure control of the contact mold assembly 3, a high-precision pressure sensor is integrated at the end of the contact mold assembly 3, specifically at the base 6 connected to the drive device. This pressure sensor is preferably a high-temperature piezoelectric or thin-film pressure sensor, used to monitor in real time the change in the reaction force of the plastic metal on the mold during flash forming. It has good high-temperature stability and dynamic response characteristics, and can capture instantaneous pressure fluctuations during flash forming. Based on the pressure changes during flash forming, the motion parameters of the V-shaped seat 4 and the elastic plate 5 are adjusted.

[0085] When the pressure value is detected to be lower than the preset lower limit, it indicates that the metal flow is insufficient or the constraint is too loose. The control system should appropriately reduce the opening angle of the V-slot 4 to increase the radial constraint force and promote the axial flow of the metal. When the pressure value exceeds the preset upper limit or the pressure gradient increases abnormally, it indicates that the flash is accumulating too quickly or may be blocked. In this case, the opening angle of the V-slot 4 should be appropriately increased or the spindle speed should be reduced to ensure the flash forming quality.

[0086] Furthermore, to promote metal flow and microstructure densification, a flash forming control method based on acoustic vibration is established. This involves using an acoustic generator 14 located in the central region of the V-shaped base 4 to directionally emit acoustic waves of a specific frequency towards the central region of the elastic plate 5.

[0087] In the early stage of flash forming, the sound wave generator 14 is controlled to output low-frequency high sound pressure level sound waves. The sound wave energy is transferred to the plastic metal through the elastic plate 5 to promote the initial flow and axial diversion of the metal material.

[0088] During the mid-stage of flash forming, the acoustic parameters are dynamically adjusted based on the pressure change characteristics fed back by the pressure sensor: when the pressure value reaches the first threshold, the acoustic frequency is increased and the sound pressure level is adjusted, and the acoustic vibration effect promotes the rearrangement of metal particles and their convergence towards the central region.

[0089] In the later stage of flash forming, based on the density signal monitored by the pressure sensor, a high-frequency low sound pressure level acoustic wave mode is used to perform micro-structure conditioning treatment on the flash to improve the density and uniformity of the internal structure of the flash.

[0090] By utilizing the cavitation and acoustic flow effects generated by acoustic vibration, the uniformity of metal flow during flash forming is improved, the density of the internal structure of the flash is enhanced, and finally a sloping flash structure with excellent mechanical properties is obtained.

[0091] After welding is completed, the quality of the flash area is evaluated based on image recognition. The system includes an image acquisition unit, an image processing unit, a feature extraction and analysis unit, and a quality judgment unit, and includes the following steps:

[0092] First, a clear digital image of the flash area of ​​the welded part is obtained by using an industrial CCD or CMOS camera installed on the side of the welding station in conjunction with a highly uniform light source. To ensure imaging consistency, the camera axis is perpendicular to the weldment axis to highlight the height and shape of the flash, and a high-temperature resistant glass lens is used to isolate the welding heat radiation.

[0093] After acquiring the image, the digital image is preprocessed to enhance the morphological features of the flash and eliminate noise: Gaussian filtering is performed for noise reduction, histogram equalization is used for contrast enhancement, and Canny operator is used for preliminary edge enhancement to improve the signal-to-noise ratio of defects and feature regions.

[0094] Extract image features of the flash edge region. Image features include:

[0095] Texture features are extracted using the gray-level co-occurrence matrix (GLCM) to obtain its energy, contrast, correlation, and homogeneity parameters, which are used to quantify the uniformity and fineness of the texture of the flash surface. At the same time, local binary mode (LBP) features are combined to describe local texture patterns, effectively identifying surface anomalies such as micro-cracks and wrinkles.

[0096] Contour features are extracted using a sub-pixel edge detection algorithm to determine the external contour of the flash, and its edge continuity, curvature distribution, and degree of defect-free characteristics are evaluated. In particular, the contour is segmented and fitted and subjected to curvature analysis to identify any abrupt changes, depressions, or breaks in the contour.

[0097] Based on the extracted image features, a classification model trained on samples is imported to intelligently determine the type of flyedge shape:

[0098] If the flash surface is smooth, continuous and without breaks, it is judged as a smooth morphology;

[0099] If the surface of the flash has an arc-shaped texture and no obvious cracks, it is judged to be an arc-shaped texture.

[0100] If the surface of the flash has obvious cracks or fractures, it is judged as a cracked morphology.

[0101] Finally, the joint quality is automatically evaluated based on the flash morphology type, and the results are output:

[0102] "Smooth morphology" corresponds to high-quality joints, indicating that the flash is uniformly formed and the structure is dense, requiring no post-processing;

[0103] "Arc pattern morphology" corresponds to medium-quality joints, and it is recommended to conduct subsequent macroscopic inspection or local grinding.

[0104] "Crack morphology" corresponds to a defective joint, requiring an alarm and isolation of the weldment;

[0105] This system enables non-contact, automated, and traceable evaluation of burr quality, reducing human error.

[0106] The implementation principle of this invention is as follows:

[0107] By using a contact mold assembly 3, which is movable radially and axially and is located on one side of the friction interface of the weldment, active contact constraints are applied to the metal in a plastic state during the flash forming process. The flow path and accumulation pattern of the plastic metal are controlled by the composite structure formed by its V-shaped seat 4 and the elastic plate 5 with adjustable curvature.

[0108] In the early stage of forming, radial constraint is mainly used to guide the axial flow of metal to form the base width. In the middle stage, the curvature is increased and the included angle of the V-shaped seat is reduced to guide the metal to converge towards the center. In the later stage, the axial superposition and radial compaction of the metal flow are achieved through coordinated control.

[0109] Furthermore, through pressure sensor feedback, acoustic vibration to promote flow and densification, and image recognition quality assessment, we can jointly ensure the formation of a reinforced sloping flash that is smooth to the workpiece body, has high density, and is free of stress concentration, thereby improving the overall performance of the welded joint.

[0110] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention, all of which fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for friction welding of a drive shaft, comprising a friction welding apparatus, characterized in that: The friction welding device includes a contact mold assembly (3) and an acoustic wave generator (14) disposed on one side of the friction interface of the workpiece. The contact mold assembly (3) is mounted on the friction welding device by a moving device to drive the contact mold assembly (3) to move at least in the radial and axial directions of the weldment; When the contact mold assembly (3) approaches the weldment in the welding state, it constrains the flow direction of the weldment during the flash forming process; The contact mold assembly (3) includes a V-shaped seat (4) with its opening facing the weldment, and elastic plates (5) with their ends slidably connected to both ends of the V-shaped seat (4). The curvature of the elastic plates (5) inside the V-shaped seat (4) is variable. The sound wave generator (14) propagates vibrations to the portion of the elastic plates (5) inside the V-shaped seat (4), causing the metal to flow rapidly to both sides of the friction interface. The V-shaped seat (4) includes a base (6), a first support block (7) and a second support block (8). The first support block (7) and the second support block (8) are both hinged to the base (6) to adjust the included angle at the opening of the V-shaped seat (4). The shaft tube (2) workpiece and the shaft fork (1) workpiece to be welded are respectively clamped in the spindle box and the moving fixture of the friction welding equipment, keeping them coaxial; Adjust the included angle of the V-shaped seat (4) according to the diameter of the workpiece, and adjust the initial curvature of the elastic plate (5) in the opening of the V-shaped seat (4) according to the diameter of the workpiece and the feed rate; The contact mold assembly (3) is brought radially closer to the welding interface so that the arc-shaped part of the elastic plate (5) maintains a gap with the friction welding area; Drive the spindle box to rotate the shaft tube (2) workpiece, and at the same time control the moving fixture to feed towards the spindle box, so that the shaft fork (1) workpiece contacts the end face of the rotating shaft tube (2) workpiece and rubs under axial pressure; When the temperature of the friction interface reaches the plastic state of the material, the contact mold assembly (3) is controlled to move to the vicinity of the welding interface so that its opening faces the flash formation area of ​​the weldment; The contact mold assembly (3) provides contact constraint on the flash forming process of plastic metal in the radial and axial directions, restricting its radial flow and guiding the plastic metal to flow in the axial direction, thereby forming a structurally reinforced sloping flash. Maintain the position of the contact mold assembly (3) until the end of the upsetting stage, and the flash is shaped; Remove the mold assembly, stop rotation, and welding is complete.

2. The friction welding method for a transmission shaft according to claim 1, characterized in that: In the initial stage of flash forming, the elastic plate (5) is controlled to maintain the first curvature state, so that its inner constraint surface forms an approximately planar constraint interface, which generates a radial constraint force on the extruded plastic metal, forcing the plastic metal to flow directionally along the workpiece axis toward both sides of the V-shaped seat (4) opening, forming the basic width of the flash. As the welding process proceeds, when the axial metal flow reaches a predetermined distribution state, the curvature of the elastic plate (5) is increased to transform it into a second curvature state. In the second curvature state, the inner constraint surface of the elastic plate (5) is transformed into an arc-shaped guide surface with a specific curvature, which guides the axial metal flow on both sides to change the flow direction, converge towards the outer periphery of the friction interface and form superimposed bulges. By precisely controlling the timing and rate of the transition of the elastic plate (5) from the first curvature state to the second curvature state, the morphology control of the flash forming process is achieved. The final result is a reinforced flash structure with a specific sloping cross-sectional morphology and a smooth transition with the workpiece body.

3. The friction welding method for a transmission shaft according to claim 2, characterized in that, During the process of dynamically adjusting the curvature of the elastic plate (5), the change of the opening angle of the V-shaped seat (4) is controlled synchronously to coordinate the control of the flash morphology: In the early stage of flash forming, the V-shaped seat (4) is controlled to maintain a large opening angle, while the elastic plate (5) is kept with a small curvature, forming a flash expansion control mode with radial constraint as the main feature, guiding the plastic metal to be fully diverted along the axial direction; During the mid-stage of flash forming, the opening angle of the V-shaped seat (4) is reduced and the curvature of the elastic plate (5) is increased simultaneously, so that the side wall of the V-shaped seat (4) and the elastic plate (5) form a gradually narrowing forming channel, guiding the subsequent metal flow extruded from the friction interface to converge in the central area. In the later stage of flash forming, by precisely controlling the ratio of the convergence rate of the opening angle of the V-shaped seat (4) to the curvature change rate of the elastic plate (5), the converged metal flow generates axial superposition and radial compaction effects in the confined space, forming a reinforced flash structure with high density and controllable slope. A pressure sensor is installed at the end of the contact mold assembly (3) to monitor the pressure changes during the flash forming process in real time. The motion parameters of the V-shaped seat (4) and the elastic plate (5) are adjusted by the pressure changes during the flash forming process to ensure the quality of flash forming.

4. The friction welding method for a transmission shaft according to claim 1, characterized in that: A method for controlling the forming of flash based on acoustic vibration is established. A sound wave generator (14) is set in the central region inside the V-shaped seat (4) to directionally emit sound waves of a specific frequency to the central region of the elastic plate (5). In the early stage of flash forming, the sound wave generator (14) outputs low-frequency high sound pressure level sound waves. The sound wave energy is transferred to the plastic metal through the elastic plate (5) to promote the initial flow and axial diversion of the metal material. During the mid-stage of flash forming, the acoustic parameters are dynamically adjusted based on the pressure change characteristics fed back by the pressure sensor: when the pressure value reaches the first threshold, the acoustic frequency is increased and the sound pressure level is adjusted, and the acoustic vibration effect promotes the rearrangement of metal particles and their convergence toward the central region. In the later stage of flash forming, based on the density signal monitored by the pressure sensor, a high-frequency low sound pressure level acoustic wave mode is used to perform micro-structure conditioning treatment on the flash to improve the density and uniformity of the internal structure of the flash. The cavitation and acoustic flow effects generated by acoustic vibration improve the uniformity of metal flow during flash forming and enhance the density of the internal structure of the flash.

5. The friction welding method for a transmission shaft according to claim 1, characterized in that, The quality assessment of the flash area based on image recognition includes the following steps: Obtain a digital image of the flash area of ​​the welded part; The digital image is preprocessed to enhance the morphological features of the flash; Extract the image features of the graffiti region, the image features including: Texture features, including gray-level co-occurrence matrix features and / or local binary pattern features; Contour features, including the continuity, curvature, and contour defect detection results of the flash edges; Based on the image features, the type of flash shape is determined using a classification model: If the flash surface is smooth, continuous and without breaks, it is judged as a smooth morphology; If the surface of the flash has an arc-shaped texture and no obvious cracks, it is judged to be an arc-shaped texture. If the surface of the flash has obvious cracks or fractures, it is judged as a cracked morphology. The quality of the joint is evaluated based on the morphology of the flash: a smooth morphology corresponds to a high-quality joint, a wavy morphology corresponds to a medium-quality joint, and a cracked morphology corresponds to a substandard joint.

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