Method for solving the stream line of the center boss of aluminum alloy wheel hub

Abstract

The application discloses a method for solving the problem of the streamline shape of the center boss of an aluminum alloy wheel hub, and belongs to the technical field of aluminum alloy forging. In view of the problem that the leakage of the streamline of the center boss of the wheel hub leads to low qualified rate of multiple batches of production, a distributed iterative optimization strategy is proposed, the whole process is iteratively optimized and finely controlled in sections, and the plastic deformation path of metal is dynamically controlled. The method comprises the following steps: selecting an extrusion rod, controlling the streamline angle through two fire times of large deformation upsetting, then designing the preform to show the boss feature and extruding the arc streamline into the cavity to prevent external leakage, and finally performing final forging forming. The method disclosed by the application realizes the accurate adaptation of the boss streamline along the profile of the forged piece, improves the load-carrying capacity and performance stability of the wheel hub, and can obtain a boss with good streamline.

Description

Technical Field

[0001] This application belongs to the field of aluminum alloy forging technology, specifically relating to a method for solving the problem of streamline conforming of the central boss of an aluminum alloy wheel hub. Background Technology

[0002] Aircraft landing gear is a critical system that supports the aircraft and facilitates ground movement during takeoff, landing, taxiing, and parking. Its performance directly affects the aircraft's operational safety and service life. The wheel hub, as the core load-bearing and rotating component of the landing gear, has a decisive impact on the overall performance and safety of the aircraft due to its structural design. The central boss of the wheel hub is the core part that is interference-fitted with the rotating shaft, and its working environment is subjected to enormous torque, bending moment, and high-frequency alternating loads.

[0003] To ensure the center boss possesses extremely high structural strength, fatigue resistance, and connection stability, existing technologies commonly employ a conformal metal streamline design. The core idea of ​​this design is to control the plastic flow of the metal material during the wheel hub forging process, ensuring that the orientation of the internal metal fibers (i.e., streamlines) is highly consistent with the three-dimensional geometry of the center boss. However, due to the inherent contradiction between the unique geometric characteristics of the wheel hub's center boss and the laws of metal plastic flow, metal converging at this point can easily lead to streamline leakage (also known as forging folding), resulting in a narrow process window and low yield rates and insufficient production efficiency in multiple batches of continuous production. Summary of the Invention

[0004] The purpose of this application is to provide a method for solving the problem of streamline following the shape of the center boss of aluminum alloy wheel hub. This method can fundamentally control the metal flow pattern in the center boss area, ensuring that the streamline perfectly follows the shape and is completely wrapped inside the part, thereby significantly improving the product qualification rate and reliability.

[0005] To achieve the above objectives, this application provides a method for solving the problem of streamlined conformal design of the central boss of an aluminum alloy wheel hub, comprising the following steps: A preform is obtained by bidirectional large deformation upsetting of aluminum alloy extruded bars of a predetermined specification to gradually increase the metal flow line angle of the aluminum alloy extruded bars and make the starting point of the metal flow line closer to the center of the preform. The preform is then extruded and formed through a boss cavity, and the boss flow line inside the boss cavity is controlled to conform to the shape of the structure to avoid metal leakage, thus obtaining a pre-forged part. After heat preservation treatment, the pre-forged part is placed in a final forging die for forging, and the metal flows in an orderly manner to obtain an aluminum alloy wheel hub. The heat preservation treatment temperature is 420℃~450℃, and the heat preservation treatment time is 5h~6h.

[0006] Furthermore, the preset specifications are designed based on the diameter of the hub's center hole and the diameter of the hub's outer contour. Even further, the preset specifications use aluminum alloy extruded bars with a diameter of 240mm~260mm and a height of 750mm~800mm.

[0007] Furthermore, when the diameter of the center hole of the wheel hub is 160mm~170mm and the outer contour diameter of the wheel hub boss is 265mm~275mm, the diameter of the aluminum alloy extruded bar material of the preset specifications is 240mm~260mm and the height is 750mm~800mm.

[0008] Furthermore, the large deformation upsetting process includes a first heat treatment using a billet upsetting fixture to obtain a heat-formed billet; wherein, the upper anvil of the billet upsetting fixture is a fixture with a drum shape, the lower anvil is a fixture with a cavity shape, and the aluminum alloy extruded bar is placed vertically between the fixture with the drum shape and the fixture with the cavity shape.

[0009] Furthermore, the cavity of the tooling with the cavity is provided with a rounded corner consistent with that of the aluminum alloy extruded bar, and the radius of the rounded corner is 25mm~35mm.

[0010] Furthermore, the radius of the drum of the tooling with the drum is 650mm~700mm, the radius of the fillet is 25mm~35mm, and the gap between the tooling with the cavity and the aluminum alloy extruded bar is 0.15mm~0.25mm.

[0011] Furthermore, the upsetting stroke of the first heat treatment is 590mm~610mm, and the upsetting ratio is 0.7~0.8.

[0012] Furthermore, the original streamline angle α of the aluminum alloy extruded bar is 90°, which is perpendicular to the horizontal direction. After the first heat treatment, the streamline angle increases to 90°~120°.

[0013] Furthermore, the large deformation upsetting process includes: inverting the fire-formed billet into the billet-forming fixture for a second fire treatment to further increase the streamline angle and obtain a preform; wherein, the lower anvil of the billet-forming fixture is a fixture with a drum shape, and the upper anvil is a punch fixture with a drum shape. The size of the punch matches the center hole of the preform, and while further deforming the streamline angle, it can also be used for pre-forging positioning.

[0014] Furthermore, the streamline angle of the preform is increased to 120°~180°.

[0015] Furthermore, the upsetting stroke of the second upsetting process is 180mm~210mm, and the upsetting ratio is 0.4~0.6.

[0016] Furthermore, the boss cavity includes a pressure upper die with a boss shape and a lower die supporting the blank. The pressure upper die and the lower die form a semi-enclosed space, which is an extrusion cavity used for extrusion molding of preforms.

[0017] Furthermore, the pressure-applying upper die includes an upper ejector block located at the center, boss cavities located on both sides of the upper ejector block, and rim cavities located on both sides of the boss cavities.

[0018] Furthermore, the lower mold includes a lower ejector block located at the center, concave cavities located on both sides of the lower ejector block, and hub cavities located on both sides of the concave cavities.

[0019] Furthermore, the heat preservation temperature is 420℃~450℃, the heat preservation time is 5h~6h, and the heat preservation coefficient of the aluminum alloy of the pre-forged part is 2.0.

[0020] Furthermore, the initial forging temperature is ≥370℃, and the final forging temperature is ≤470℃.

[0021] In summary, this application has the following advantages: This application provides a method for solving the problem of conforming the streamline of the central boss of an aluminum alloy wheel hub. Through large deformation upsetting, boss cavity extrusion and heat preservation final forging processes, the core logic is to dynamically control the metal plastic deformation path, thereby achieving precise conforming of the streamline of the central boss of the wheel hub to the structure.

[0022] Specifically: (1) To address the problem that the initial longitudinal streamline (angle 90°) of aluminum alloy extruded bar stock is difficult to adapt to the boss profile, a multi-stage large deformation upsetting design is adopted. First, the structural characteristics of small-diameter, high-height bar stock are combined with the constraint effect of the tooling with drum and the tooling with cavity. The streamline angle is increased from 90° to 90°~120° through the first stage of treatment. Then, the streamline angle is further increased to 120°~180° by using the billet inversion and the tooling with the punch with drum. This forms a streamline shape with the starting point close to the center of the billet and extending in an arc shape towards the upper end of the hole wall, providing a streamline basis for the subsequent boss cavity extrusion, thus breaking the bottleneck of insufficient streamline angle adjustment in the traditional process from the root.

[0023] (2) Based on the principle of metal flow and cavity contour adaptation, the preform after large deformation upsetting is extruded through customized design of the boss cavity. The cavity contour is consistent with the final structure of the boss. During the extrusion process, the curved streamline in the central area of ​​the preform will gradually fill the cavity space under the constraint of the cavity, avoiding disordered metal leakage. At the same time, the forced shaping effect of the cavity on the metal makes the streamlines fit and extend along the inner wall of the cavity, ensuring that the internal streamlines of the boss are completely matched with the height and contour shape of the boss, solving the problem of disordered boss streamlines and disconnection from the structure in traditional processes.

[0024] (3) Through heat preservation and final forging, the stability of the streamline and the integrity of the forming are ensured. Heat preservation of the pre-forged parts can eliminate the internal temperature gradient of the billet, ensure that the metal has uniform plasticity, and avoid the streamline breakage caused by local plasticity differences during final forging. The final forging stage relies on the material distribution optimization of the pre-formed billet (the metal volume has been accurately distributed in the early upsetting and extrusion), so that the metal flows in an orderly manner, and eliminates the streamline defects caused by backflow and pinching, and finally achieves the dual standard of hub forming and streamline conformity. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the left side cross-section of the central boss after final forging in this application; Figure 2 This is a schematic diagram showing the streamlined outward exposure of the central boss of the wheel hub; Figure 3 This is a flow chart of the first heat treatment in this application; Figure 4 This is a schematic diagram of the product after the first firing process of this application; in which, Figure 4 (a) in the diagram is a flow chart of the product. Figure 4 (b) in the diagram is a structural schematic of the product; Figure 5 This is a schematic diagram of the product after the second firing process of this application; in which, Figure 5 (a) in the diagram is a flow chart of the product. Figure 5 (b) in the diagram is a structural schematic of the product; Figure 6 This is a streamline diagram of the application before the use of the boss cavity extrusion. Figure 7 This is a streamline diagram of the boss cavity after the initial extrusion in this application; Figure 8 This is a streamline diagram of the cavity after re-extrusion using the boss in this application; Figure 9 This is a streamline diagram of the boss cavity after multiple extrusions in this application; Figure 10 This is a schematic diagram of the pre-forged part formed using the boss cavity in this application; wherein, Figure 10 (a) in the diagram is a streamline diagram of the pre-forged part. Figure 10 (b) is a schematic diagram of the pre-forged part; Figure 11 This is a streamline diagram of the central boss after final forging in this application; Figure 12 It is a theoretical streamline diagram of the center boss of a conformal radius wheel hub. Detailed Implementation

[0026] The principles and features of this application are described below with reference to embodiments. The examples are for illustrative purposes only and are not intended to limit the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0027] In theory, the streamline of the wheel hub center boss needs to have a conformal curvature, such as Figure 12 As shown, this conformal curvature has the following advantages: (1) It can optimize mechanical properties. The direction of the metal streamline coincides with the main stress direction (such as the torque transmission direction and the assembly compressive stress direction) that the part bears during operation. It can maximize the load-bearing capacity of the material, effectively transmit the load, and avoid stress concentration, microcrack initiation, or plastic deformation caused by material fiber disorder. (2) It can improve connection reliability. During the interference fit assembly process between the central boss and the rotating shaft, the conformal metal streamline can make the stress distribution more uniform, significantly reduce the stress concentration level during the assembly process, thereby delaying the initiation and propagation of fatigue cracks and extending the service life of the hub. (3) It can reduce assembly risks. The stable streamline structure ensures the dimensional stability and mechanical consistency of the connection part, which helps to reduce the risk of assembly error caused by internal material defects or uneven performance, and improve the assembly quality. Therefore, in the field of aerospace manufacturing, realizing the conformal design of the metal streamline of the hub's central boss has become an important indicator of the level of high-end hub manufacturing technology and a basic requirement for product delivery by mainstream airlines.

[0028] While conformal metal streamline design offers numerous theoretical advantages, its implementation in actual industrial production, especially in multi-batch continuous production, faces significant technical challenges. Existing technologies for manufacturing central bosses with conformal curved streamlines generally suffer from a fatal flaw: exposed metal streamlines (also known as "forging folds," such as...). Figure 2(As shown). This defect directly leads to serious consequences, such as low product yield: once the streamlines of the center boss are exposed, it is considered a serious product defect and must be scrapped. The huge scrap rate severely restricts production efficiency and increases manufacturing costs. For example, the process window is narrow: to avoid the formation of streamline exposure defects, existing processes have extremely stringent requirements on production parameters (such as billet shape, heating temperature, mold design, forging speed, and lubrication conditions), and the allowable range of parameter fluctuations (i.e., the process window) is very narrow. This makes the stability and controllability of the production process worse, highly dependent on the skills and experience of operators, and difficult to achieve large-scale, highly consistent automated production. For example, product performance and safety hazards: the essence of streamline exposure is the disruption of the continuity inside the material, forming a defect similar to a crack. This part is a natural stress concentration source, which is very likely to become the source of fatigue cracks during service, causing the hub to fail suddenly within a period far below the design life, posing a fatal threat to flight safety.

[0029] The fundamental reason for the leakage of streamlines in the hub center boss is the inherent contradiction between the unique geometric structure of this part and the plastic flow law of metal. The specific principles include: (1) Metal confluence characteristics: The hub center boss is usually the part with the largest volume and the most complex cross-section in its structure. During the forging process, the initial billet (usually cylindrical or square) needs to be squeezed by the die, and the metal needs to converge and fill from the periphery to the center area to finally form the shape of the boss. This flow pattern of multiple metal flows converging at one point is the innate condition for the generation of defects. (2) Poor front oxidation and welding: In the high temperature forging environment, an oxide film will quickly form on the surface of the metal billet. When the front of the metal flow from different directions meets in the center boss area, if the flow speed, temperature or pressure is not properly controlled, these metal surfaces with oxide films will not be able to achieve complete metallurgical welding. The subsequent metal flow will continue to advance, squeezing and folding the unwelded oxide scale and surface metal, and rolling it into the interior or near the surface of the part, thus forming leakage of streamlines or folding defects. (3) The conformal curvature increases complexity: The market requirement for the central boss streamline to have a conformal curvature means that the metal streamlines must not only converge, but also smoothly transition along the complex curved surface contour. This requires the metal to flow more precisely and in a more coordinated manner in three-dimensional space. However, any local flow instability, velocity difference or temperature gradient can easily cause turbulence, flow through or folding of the metal flow at bends or turns, making the difficulty of process control increase exponentially.

[0030] In summary, current technologies have failed to effectively address the issues of leading-edge welding and flow control during the metal convergence process of the central boss, leading to frequent defects such as exposed streamlines and an extremely narrow process window, which severely restricts the localization process and production efficiency of high-performance aircraft wheel hubs. Therefore, this application develops a new wheel hub forging process that can fundamentally control the metal flow pattern in the central boss area, ensuring that the streamlines perfectly conform to the shape and are completely enclosed within the part, thereby significantly improving product yield and reliability.

[0031] Specifically, this application provides a method for solving the problem of streamlined conformal design of the central boss of an aluminum alloy wheel hub, including the following steps: S1. The aluminum alloy extruded bar of the preset specifications is subjected to bidirectional large deformation upsetting to obtain a preform, so as to gradually increase the metal flow line angle of the aluminum alloy extruded bar and make the starting point of the metal flow line closer to the center of the preform.

[0032] This application modifies the angle of the original longitudinal streamlines through step-by-step upsetting, gradually bringing them closer to a "conformal" shape, achieving iterative optimization in two upsetting processes. The first upsetting process adjusts the original longitudinal streamlines (angle α = 90°, relative to the horizontal direction) to 90° < α < 120°, causing the streamlines to move towards the center, fixing the starting point at the center, and creating a tendency for them to flow in an arc towards the upper end of the hole wall. The cavity of the lower anvil simultaneously positions the billet center, ensuring uniform upsetting. The second upsetting process further increases the streamline angle to 120° < α ≤ 180°, bringing the streamline starting point even closer to the billet center, and upsetting the exposed streamlines to a shape that extends along the center and has an arc, laying the foundation for subsequent conformal shaping.

[0033] As some optional embodiments of this application, the preset specifications are designed based on the diameter of the hub center hole and the diameter of the outer contour of the hub boss. This application does not recommend selecting extruded bar stock with a large diameter. Because the streamline angle changes first in the two side regions during the upsetting process, while the center position is often the least likely to change, for the same hub forging, with the same bar stock volume, according to V=πR... 2 ×H, a larger radius R and a smaller height H mean a smaller upsetting stroke, resulting in less change in streamline angle. This application achieves a larger upsetting ratio by selecting a smaller diameter aluminum alloy bar, thus allowing for greater change in streamline angle. Furthermore, a smaller bar diameter results in a narrower range of streamlines with smaller angle changes at the center position, which is more conducive to subsequent streamline control.

[0034] As some optional embodiments of this application, the diameter of the aluminum alloy extruded bar is 240mm~260mm, and the height is 750mm~800mm. The diameter of the hub center hole is 160mm~170mm, and the outer contour diameter of the hub boss is 265mm~275mm. Preferably, when the diameter of the hub center hole is 160mm and the outer contour diameter of the hub boss is 268mm, the diameter of the aluminum alloy extruded bar of the preset specifications is 250mm, and the height is 790mm.

[0035] As some optional embodiments of this application, in actual production, the commonly used diameter specifications of aluminum alloy bars include Φ500, Φ300, Φ250, and Φ150, etc. For most precision forgings of aluminum alloy wheel hubs, the weight ranges from tens of kilograms to hundreds of kilograms, and the feed ratio is generally less than 1.05. According to the principle of mass conservation, this applies to Φ300 and Φ250 bars. The diameter and height of the bar are variables, while the diameter of the wheel hub center boss is fixed. The higher the bar height, the greater the deformation during upsetting, and the greater the angular deformation of the metal fibers (streamlines), which is closer to the horizontal (180°) direction. Through subsequent pre-forging tooling, the horizontal streamlines can be pressed into streamlines that conform to the shape of the center boss, such as... Figure 10 As shown, this application therefore prioritizes Φ250 bar stock with a smaller diameter and higher height, i.e., bar stock with a diameter of 250mm.

[0036] As some optional embodiments of this application, the large deformation upsetting process includes a first heat treatment using a billet upsetting fixture to obtain a heat-formed billet; wherein, the upper anvil of the billet upsetting fixture is a fixture with a drum shape, and the lower anvil is a fixture with a cavity shape, and the aluminum alloy extruded bar is vertically placed between the fixture with the drum shape and the fixture with the cavity shape. The cavity of the fixture with the cavity shape has a rounded corner consistent with that of the aluminum alloy extruded bar, and the radius of the rounded corner is 25mm~35mm, preferably 30mm. The drum shape radius of the fixture with the drum shape is 650mm~700mm, preferably 700mm, and the gap between the fixture with the cavity shape and the aluminum alloy extruded bar is 0.15mm~0.25mm, preferably 0.25mm. In this application, the drum-shaped arc structure exerts a central compressive force on the surface metal of the bar stock during the upsetting process, preventing the metal from spreading randomly in the radial direction. This causes the originally longitudinally distributed streamlines (initial 90°) to gradually deflect in the horizontal direction, laying the structural foundation for the subsequent increase of the streamline angle to 90°~120°. At the same time, it ensures that the streamlines are concentrated in the central area required for the boss formation, reducing the consumption of useless streamlines at the edges. The fit design between the lower anvil cavity and the bar stock can effectively constrain the bottom metal of the bar stock, preventing the bottom metal from flowing irregularly due to lack of constraint during upsetting. This ensures that the bottom streamlines fit the cavity contour, avoiding the problem of bottom streamline breakage or wrinkling during subsequent preform forming. Both the bulging fixture and the cavity fixture use 30mm rounded corners, matching the rounded corners of the aluminum alloy extruded bar stock. This serves two purposes: firstly, it prevents stress concentration at the fixture's edges during upsetting, preventing metal cracking or streamline breakage due to excessive localized stress; secondly, the rounded corner transition makes metal flow smoother, reducing streamline disturbance at transition points and ensuring a continuous and stable streamline shape, providing a complete streamline foundation for subsequent boss conformal shaping. The 0.25mm gap between the cavity fixture and the bar stock ensures smooth insertion into the cavity and precisely positions the bar stock at the fixture's center through the gap's limiting effect, preventing uneven stress caused by bar stock misalignment during upsetting. If the bar stock misaligns, it will cause excessive stretching of the streamline on one side and compression and accumulation on the other, ultimately leading to asymmetrical boss streamlines. Precise centering ensures uniform metal flow from the center outwards, resulting in consistent streamline angle changes and improving the symmetry and consistency of the boss streamline conformal shaping.

[0037] As some optional embodiments of this application, the upsetting stroke of the first heat treatment is 590mm~610mm, preferably 610mm, and the upsetting ratio is 0.7~0.8, preferably 0.77. The original streamline angle α of the aluminum alloy extruded bar is 90°, which is perpendicular to the horizontal direction, and the streamline angle increases to 90°~120° after the first heat treatment.

[0038] In this application, the upsetting ratio refers to the ratio of the reduction in height during upsetting to the height before upsetting. The reduction in height is the quantification of the upsetting stroke. Upsetting can change the streamline angle, and aluminum alloys are soft and easily deformable, thus their upsetting ratio is relatively large, with the maximum upsetting ratio ranging from 0.7 to 0.8. Therefore, a larger upsetting ratio is more conducive to the deformation of the streamline angle. In addition, the specifications of the hub center boss are fixed. By adjusting the size of the bar stock and the shape of the billet, the conformal streamline of the hub can be obtained. The smaller the diameter of the bar stock, the more metal will flow towards the direction of the bulge during upsetting. The metal streamline within 160mm to 275mm of the center, which is also the location of the center boss, will have a large amount of angular deformation, ultimately obtaining the target streamline. By controlling the holding temperature, the forging process can be kept within the recrystallization deformation temperature range, preventing overheating of the microstructure due to excessive deformation.

[0039] As some optional embodiments of this application, the large deformation upsetting process includes: inverting the fire-formed billet in the billet-forming fixture for a second fire treatment to further increase the streamline angle to obtain a preform; wherein, the lower anvil of the billet-forming fixture is a fixture with a drum shape, and the upper anvil is a punch fixture with a drum shape, and the size of the punch matches the center hole of the preform. After the fire-formed billet is inverted, its bottom fits against the drum-shaped lower anvil. During upsetting, the arc-shaped drum structure of the lower anvil generates a centripetal extrusion force on the metal at the bottom of the billet, preventing the metal from spreading radially in a disordered manner. At the same time, it supports the 90°~120° streamline formed in the first fire, providing stable bottom support for its further deflection. The size of the punch matches the center hole of the preformed billet. During upsetting, the punch applies axial pressure to the center area of ​​the billet. On the one hand, it squeezes the metal in the center area to flow towards the boss cavity (reserving metal for subsequent boss forming). On the other hand, through the drum-shaped arc surface of the punch, it guides the surface and middle layers of metal in the billet to flow along an arc trajectory, causing the original "90°~120° streamline" to further deflect to "120°~180°", ultimately forming an ideal streamline shape with "the starting point close to the center of the billet and extending arc-shaped towards the upper end of the hole wall", which fits the conformal requirements of the boss contour. Furthermore, after the first firing process, the upper and lower ends of the billet may exhibit slight unevenness in streamline distribution due to differences in temperature and stress in contact with the tooling. By inverting the fire-formed billet, the original "upper end (the end in contact with the upper anvil in the first firing)" becomes the "lower end (the end in contact with the lower anvil in the second firing)," and the original "lower end (the end in contact with the lower anvil in the first firing)" becomes the "upper end (the end in contact with the punch in the second firing)," thus balancing the deformation conditions at the upper and lower ends of the billet. This avoids localized accumulation or breakage of streamlines caused by continuous stress / heat on one side, ensuring uniform and consistent streamline angle changes throughout the entire billet cross-section. This application employs a punch tooling, which first further compresses the billet in the middle, causing it to flow to both sides, leaving the streamline endpoints in the center. The flow trend is outward, thereby forming large-angle grain streamlines on both the upper and lower surfaces of the middle section, such as... Figure 5The punch fixture can also be used for positioning the pre-forging die, such as... Figure 6 The constraints of the lower mold cavity can also limit the movement of the blank, ultimately making the streamline flow uniform.

[0040] As some optional embodiments of this application, the upsetting stroke of the second heat treatment is 180mm~210mm, preferably 206mm, and the upsetting ratio is 0.4~0.6, preferably 0.46. The streamline angle of the preform increases from 90°~120° after the first heat treatment to 120°~180°. In this application, compared with the streamline angle of "90°~120°" in the first heat treatment, the second heat treatment, through the synergistic effect of the punch and the lower anvil, raises the streamline angle to "120°~180°", realizing the key transformation of the streamline from "near horizontal" to "near longitudinal (along the height direction of the boss)". With an increased angle, the streamline starting point is closer to the center of the billet, providing a streamline foundation that extends "from the center to the cavity" for subsequent precast billet filling of the boss cavity. This avoids "streamline breakage" or "metal leakage" caused by misalignment of streamline direction during cavity filling, fundamentally ensuring the conformity of the boss's streamline to the structure. Furthermore, a streamline angle of 120°~180° allows the metal fibers in the boss area to be distributed along the height of the boss, significantly improving the boss's load-bearing capacity (such as tensile and shear resistance), thus solving the performance instability problem caused by disordered streamline direction in traditional processes.

[0041] S2. The preform is extruded and formed using a boss cavity, and the streamlines and structure of the boss inside the boss cavity are controlled to conform to the shape to avoid metal leakage, thus producing a pre-forged part. In this application, the boss cavity is the cavity of the pre-forging mold. Through its boss cavity and material distribution design, the central boss features and thin-walled hub structure of the preform can be initially formed. Specifically, the curved streamlines in the central region of the preform are extruded into the boss cavity, allowing the streamlines and structure within the cavity to conform to the shape; the starting point of non-conforming streamlines is limited to the middle connecting skin position to avoid metal leakage or streamline defects (such as backflow or pinching) caused by flow turbulence.

[0042] As some optional embodiments of this application, the boss cavity includes a pressure upper die with a boss shape and a lower die supporting the blank. The pressure upper die and the lower die form a semi-enclosed space, which is an extrusion cavity used for extruding and forming the preform. The pressure upper die includes a centrally located upper ejector block, boss cavities on both sides of the upper ejector block, and rim cavities on both sides of the boss cavities. The lower die includes a centrally located lower ejector block, concave cavities on both sides of the lower ejector block, and hub cavities on both sides of the concave cavities.

[0043] S3. After heat preservation treatment, the pre-forged part is placed in the final forging mold and forged into shape, and the metal flows in an orderly manner to obtain an aluminum alloy wheel hub; wherein, the heat preservation treatment temperature is 420℃~450℃ and the heat preservation treatment time is 5h~6h.

[0044] As one of the optional embodiments of this application, the heat treatment temperature is 430℃, and the heat preservation coefficient is 2.0. The combination of a heat preservation temperature of 430℃ and a heat preservation coefficient of 2.0 before final forging ensures the overall temperature uniformity of the pre-forged part, avoids uneven metal flow velocity caused by local temperature differences, and ultimately achieves the ideal state of "non-turbulent and defect-free" final forging metal, thus ensuring the consistency and stability of the streamline conformal effect of the wheel hub boss. The heat preservation coefficient refers to the heating rate, typically the heat preservation time required to heat through 1mm, measured in min / mm. The heat preservation coefficient indicates the time required for the metal to be fully heated through at the heat preservation temperature. Once the material is fully heated through, forging can begin. There are no intermediate processes during the heating and heat preservation of aluminum alloy wheel hubs, such as heating with insulating cotton, commonly known as "wrapping." Therefore, there is only a single-stage heating process. Forging can begin once the material is thoroughly heated. There is no cooling stage in the furnace. After exiting the furnace, the material will transfer heat with the air, resulting in a brief temperature drop. Therefore, this application requires an initial forging temperature ≥370℃; otherwise, the material is prone to surface cracking due to temperature drop, increasing deformation resistance. The final forging temperature ≤470℃ is required because the forging temperature cannot exceed the solution temperature; otherwise, it can easily lead to over-aging or microstructural degradation within the material, thus affecting its mechanical properties. Based on this, this application uses a large upsetting ratio to press the bar stock and a specific tooling with a radius-angle bevel to control the streamline deformation in real time, while strictly adhering to the forging thermal characteristics of the aluminum alloy itself, in order to obtain wheel hub forgings that meet both the requirements for streamline and performance.

[0045] As some optional embodiments of this application, the initial forging temperature is ≥370℃ and the final forging temperature is ≤470℃. By setting the initial forging temperature T1≥370℃ and the final forging temperature T2≤470℃, this application can ensure that the metal has sufficient plasticity (avoiding flow line fracture caused by cold brittleness) and prevent the coarse grains at high temperatures from affecting the performance of the forged material.

[0046] The technical solutions described above in this application will be explained in detail below with reference to specific embodiments.

[0047] Example 1 This embodiment provides a method for solving the problem of streamlined conformity of the central boss of an aluminum alloy wheel hub, including the following steps: (1) Prepare raw materials Based on the hub center hole diameter D1=160mm and the boss outer contour D2=268mm, a 2014 aluminum alloy extruded bar with a diameter D=250mm and a height H=790mm is selected. The metal flow lines distributed longitudinally (L direction) (parallel to the central axis) are controlled within the central region, such as... Figure 3 As shown, the yellow-green part is the aluminum alloy extruded bar, and the dense fine lines on its surface are its metal flow lines, which are parallel to the central axis.

[0048] (2) Production of precast billets By gradually changing the streamline angle through a distributed iterative optimization strategy, the angle of the originally longitudinally distributed metal streamlines is gradually increased. A preform is obtained by large-deformation upsetting of 2014 aluminum alloy extruded bars to alter the metal streamline angle. This includes a first and second upsetting process, using two sets of tooling to upset the cylindrical 2014 aluminum alloy extruded bars into preforms.

[0049] The tooling for the first heat treatment is a billet upsetting tooling, and the aluminum alloy extruded bar is placed vertically between the drum tooling and the cavity tooling, such as... Figure 3 and Figure 4 As shown, the anvil is a drum-shaped fixture with a platform on the upper surface and a protrusion on the lower surface. The lower surface contacts the upper surface of the 2014 aluminum alloy extruded bar, and the protrusion extrudes the 2014 aluminum alloy extruded bar. Figure 4 As shown in (b) of the diagram. The drum radius of the drum fixture is R1=700mm. Upsetting with a large rounded corner drum fixture can change the direction of the original streamline from the original longitudinal direction to the horizontal direction (perpendicular to the central axis), and the streamline will move closer to the center position, further controlling the streamline in the central area. The starting point of the streamline is fixed at the center position, so that the streamline flows from the center to the upper end of the hole wall in an arc shape. Through the design of the cavity, the shape-following effect is finally achieved. The lower anvil is a tooling with a cavity. Its internal cavity is used to accommodate the lower part of the 2014 aluminum alloy extruded bar. The bottom has the same rounded corner R2=30mm as the bar, and the gap between the bottom and the bar is 0.25mm, which can position the bar in the center position, so that the upsetting process is uniform. Furthermore, the cavity positioning ensures that the initial streamlines are controlled within the central region. The streamline angle is gradually increased through the upsetting process. The first upsetting stroke is 610mm, with an upsetting ratio of 0.77. The streamline angle is altered through large deformation upsetting. The initial bar stock streamline angle α = 90° (compared to the horizontal direction), and the upsetting completed streamline angle is 90° < α < 120°, thus gradually approaching the conformal streamlines of subsequent pre-forging. Figure 4 As shown in (a) of the diagram.

[0050] After the first firing process, a fire-formed billet is obtained. This billet is then inverted and subjected to a second upsetting process using a billet-forming fixture to obtain a preform. For example... Figure 5As shown in (a), the upper anvil of the billet-making fixture is a punch fixture with a drum shape, and the lower anvil is a punch fixture with a drum shape, consistent with the upper anvil of the first heat treatment. This allows for conformal fitting, saving the need for new fixtures and facilitating center positioning. The punch design allows the originally exposed streamlines to be upset into curved streamlines extending along the center, thus placing the starting point of the streamlines at the center of the billet. The second heat upsetting stroke is 206mm, and the upsetting ratio is 0.46. Upsetting further alters the streamline angle. Therefore, after the second heat upsetting, the streamline angle increases further to 120°<α≤180°, with the streamline starting point closer to the center of the billet, which is beneficial for the pre-formed billet's streamlines to conform to the shape, resulting in a product as shown in the image. Figure 5 As shown in (b) of the diagram.

[0051] (3) Extrusion to obtain pre-forged parts Use such as Figure 6 The boss cavity shown is used to extrude and form the preform, controlling the flow lines and structural conformity within the boss cavity to produce a pre-forged part. The boss cavity allows for the design of the central boss and the thin-walled structure of the hub. This means that by dividing the preform into portions, the final forging is uniform, the metal flow is turbulent, and flow defects caused by metal backflow or flow pinching are avoided. Figures 7-9 As shown, by applying a force in the V direction, the originally curved streamlines at the center of the preform can be gradually squeezed into each sub-cavity (including the rim cavity, boss cavity, concave cavity, and hub cavity), leaving the starting point of the non-conforming streamlines at the middle connecting skin position. Then, the streamlines in the boss cavity conform to the structure, as shown... Figure 10 As shown in (a), this avoids the situation of metal leakage.

[0052] The boss-shaped cavity includes a pressure-applying upper die with a boss shape and a lower die supporting the billet. The upper and lower dies form a semi-enclosed space, which is the extrusion cavity used for extruding and forming the preform. The pressure-applying upper die includes a central upper ejector block, boss-shaped cavities on both sides of the upper ejector block, and rim cavities on both sides of the boss-shaped cavities. The lower die includes a central lower ejector block, concave cavities on both sides of the lower ejector block, and hub cavities on both sides of the concave cavities. It can be understood that the preform itself does not fill each sub-cavity; it is filled step by step through the material distribution effect of the boss-shaped cavities. Then, the hollow structure of the boss-shaped cavities fixes the final shape of the pre-forged part. Figure 10 As shown in (b) of the diagram.

[0053] (4) Final forging After holding the pre-forged part at 430℃ for 5 hours (ensuring a holding coefficient of 2.0), it is placed in a conventional final forging die for aluminum alloy wheels for forging. The initial forging temperature T1 > 370℃, and the final forging temperature T2 < 470℃. Through the pre-formed billet's material distribution design, the final forging metal flow is non-turbulent, preventing flowline defects caused by metal backflow or clamping, resulting in excellent final flow lines. Figure 11 As shown.

[0054] In this application, Figure 12 This is a theoretical diagram showing the streamlined distribution of the central boss on an aluminum alloy wheel hub. Figure 11 This is a streamline diagram obtained after forging improvements according to this application; its streamlines and the outline of the central boss are conformal. (And...) Figure 2 In contrast, the streamlined shape of the center boss in aluminum alloy wheel hubs produced by traditional one-fire blanking is difficult to achieve. The metal flow deformation at this location is significant, making it highly susceptible to streamline defects. Furthermore, due to… Figure 2 It can be seen that the streamlines at the boss position extend vertically upwards, posing a risk of streamline leakage. Tensile tests conducted on the central boss yielded a tensile strength of 380 MPa, while the samples produced in this application have an average tensile strength of 450 MPa. Figure 2 Significant improvements were achieved based on experimental results. Upsetting with a fixture featuring a 700mm drum angle clearly showed an angular shift in the top streamline, an effect unattainable with flat anvil upsetting. Flat anvils, lacking drum angle, experience minimal metal movement in the center, with deformation occurring only on the sides of the drum. However, the drum fixture, due to the centripetal force at the center, draws the metal from the center to the sides during upsetting, causing the top streamline to move closer to the center. Simultaneously, the metal flows towards the sides of the drum, resulting in the effect described above. Figure 4 The angled streamlines shown are... Figure 2 The result of upsetting with a flat anvil shows that the center streamline angle of the pre-forged part has not changed. This is a change brought about by the use of the drum tooling in this application. Secondly, in order to allow the central metal to flow better to both sides, this application prioritizes the use of large-angle tooling, that is, R700 (combined according to the billet size specifications). After the first upsetting, the drum tooling can still be used for positioning under the second upsetting. Through experiments, the metal streamline will not be disordered within the drum radius range of this application. The drum radius cannot be increased further because, firstly, the material has reached the limit of upsetting, with an upsetting ratio of 0.7~0.8; and secondly, it cannot meet the positioning requirements of the tooling under the second upsetting, thus reducing the consumption of unnecessary tooling.

[0055] In summary, this application has at least the following advantages: (1) In view of the structural features of the hub center hole (D1=160mm) and the outer contour of the boss (D2=268mm), 250mm×790mm 2014 aluminum alloy extruded bar stock was innovatively selected, which has two major advantages compared with large diameter short bar stock. First, it increases the upper limit of the upsetting ratio, with the maximum upsetting ratio reaching 0.77 (far higher than the conventional parameter), which allows the streamline angle to be significantly adjusted from the initial 90° (horizontal direction), providing sufficient adjustment space for subsequent conformal control; Second, it reduces the range of low-variable streamlines in the center, and the metal flow in the central area of ​​the small diameter bar stock is more uniform, and the distribution range of streamlines with smaller angle changes is narrower, which effectively reduces the difficulty of controlling streamline defects in subsequent processes and improves the conformal accuracy of streamlines from the source.

[0056] (2) Breaking through the traditional single billet preparation mode, a dual-fire iterative optimization strategy is adopted. The metal plastic deformation path is dynamically controlled through customized tooling design to achieve step-by-step optimization of the streamline angle. In the first fire, the streamline direction can be adjusted directionally. A combination tooling with a drum-shaped upper anvil and a cavity-shaped lower anvil is used. After large-stroke upsetting, the streamline angle increases from 90° to 90°~120°. At the same time, the drum structure guides the streamline towards the center, initially realizing the transformation of the longitudinal flow direction to the horizontal direction. In the second fire, the conformal feature can be deepened. After inverting the billet, a lower anvil matching the upper anvil of the first fire and a tooling with a drum-shaped punch are used. The stroke further increases the streamline angle to 120°~180°, so that the streamline starting point is concentrated at the center of the billet, forming an ideal path of arc flow from the center to the upper end of the hole wall, laying the key streamline shape for the conformal boss. In contrast, the traditional single-fire billet preparation mode is prone to microstructural damage to the product due to large deformation at one time, such as cracks and eddies, and the streamline is also prone to disorder. While single-fire upsetting is commonly used in the market to save energy and reduce costs, it is prone to aluminum alloy forming problems, resulting in a low pass rate in mass production. Furthermore, when using drum upsetting, the aluminum alloy tends to flow towards the center. Only when the center streamline reaches 150°~180° can the center boss achieve a conforming streamline effect by back-extending this portion of metal during pre-forging. Only through the two-fire upsetting method described in this application can the streamline angle of the center boss achieve maximum deformation, thus being back-extended into the cavity. Statistics show that the highest pass rate for domestic aluminum alloy wheel production is only 60%~70%. The method described in this application can effectively reduce the streamline disorder and structural damage caused by the intense metal flow during single-fire large deformation, as well as the risk of strain concentration. Simultaneously, the two-fire tooling deformation can mitigate the one-time drastic deformation of the streamline and iteratively allow the center boss streamline to undergo sufficient angular deformation, thus being extruded into the pre-forging cavity, forming a uniformly distributed streamline, ultimately increasing the production pass rate to approximately 90%.

[0057] (3) The preform design integrates the dual functions of boss cavity preforming and material distribution optimization, solving problems such as metal leakage and streamline disorder in traditional processes. In particular, through the progressive filling design of the boss cavity, the curved streamline in the central area is gradually squeezed into the cavity, so that the internal streamline of the boss completely fits the structural contour, completely avoiding the problem of metal leakage and ensuring the continuity of the overall streamline of the boss. The preform preforms the wheel hub sidewall and boss features, and the material distribution design achieves uniform distribution of metal volume, effectively avoiding defects such as streamline breakage and folding caused by metal backflow and flow pinching in the final forging stage. At the same time, it improves the load-bearing capacity and performance stability of the forging (reduced fluctuation of mechanical properties), and the stress corrosion resistance can reach 30N / mm. 2 above.

[0058] While specific embodiments of this application have been described in detail, this should not be construed as limiting the scope of protection of this application. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims still fall within the scope of protection of this application.

Claims

1. A method for solving the problem of streamlined conformity of the central boss in an aluminum alloy wheel hub, characterized in that, Includes the following steps: A preform is obtained by bidirectional large deformation upsetting of aluminum alloy extruded bar material of preset specifications, so as to gradually increase the metal flow line angle of the aluminum alloy extruded bar material and make the starting point of the metal flow line closer to the center of the preform. The preform is extruded and formed by the boss cavity, and the streamline of the boss inside the boss cavity is controlled to conform to the shape of the structure in order to avoid metal leakage, so as to obtain a pre-forged part. After the pre-forged part is heat-insulated, it is placed in the final forging mold and forged into shape, with the metal flowing in an orderly manner to obtain an aluminum alloy wheel hub; wherein, the heat-insulation temperature is 420℃~450℃ and the heat-insulation time is 5h~6h. The large deformation upsetting process includes a first upsetting process using a billet upsetting fixture to obtain a fire-formed billet, and a second upsetting process where the fire-formed billet is inverted in the billet fixture to further increase the streamline angle and obtain a preform. The billet upsetting fixture has an upper anvil with a bulging shape and a lower anvil with a cavity shape. The aluminum alloy extruded bar is placed vertically between the bulging shape and the cavity shape. The lower anvil of the billet fixture is the bulging shape, and the upper anvil is a punch fixture with a bulging shape. The size of the punch matches the center hole of the preform.

2. The method for solving the problem of streamlined conformity of the central boss of an aluminum alloy wheel hub according to claim 1, characterized in that, The aluminum alloy extruded bar material of the preset specifications has a diameter of 240mm~260mm and a height of 750mm~800mm.

3. The method for solving the problem of streamlined conformity of the central boss of an aluminum alloy wheel hub according to claim 2, characterized in that, The diameter of the center hole of the hub is 160mm~170mm, and the outer diameter of the hub boss is 265mm~275mm.

4. The method for solving the problem of streamlined conformity of the central boss of an aluminum alloy wheel hub according to claim 1, characterized in that, The cavity of the tooling with the cavity is provided with a rounded corner that is consistent with the aluminum alloy extruded bar, and the radius of the rounded corner is 25mm~35mm.

5. The method for solving the problem of streamlined conformity of the central boss of an aluminum alloy wheel hub according to claim 1, characterized in that, The radius of the drum of the tooling with the drum is 650mm~700mm, and the gap between the tooling with the cavity and the aluminum alloy extruded bar is 0.15mm~0.25mm.

6. The method for solving the problem of streamlined conformity of the central boss of an aluminum alloy wheel hub according to claim 1, characterized in that, The upsetting stroke of the first heat treatment is 590mm~610mm, and the upsetting ratio is 0.7~0.

8.

7. The method for solving the problem of streamlined conformity of the central boss of an aluminum alloy wheel hub according to claim 6, characterized in that, The original streamline angle α of the aluminum alloy extruded bar is 90°, which is perpendicular to the horizontal direction. After the first heat treatment, the streamline angle increases to 90°~120°.

8. The method for solving the problem of streamlined conformity of the central boss of an aluminum alloy wheel hub according to claim 1, characterized in that, The streamline angle of the preform is increased to 120°~180°.

9. The method for solving the problem of streamlined conformity of the central boss of an aluminum alloy wheel hub according to claim 1, characterized in that, The upsetting stroke of the second heat treatment is 180mm~210mm, and the upsetting ratio is 0.4~0.

6.

10. The method for solving the problem of streamlined conformity of the central boss of an aluminum alloy wheel hub according to claim 1, characterized in that, The boss cavity includes a pressure upper die with a boss shape and a support lower die for the blank. The pressure upper die and the lower die form a semi-enclosed space, which is an extrusion cavity used for extrusion molding of the preform.

11. The method for solving the problem of streamlined conformity of the central boss of an aluminum alloy wheel hub according to claim 10, characterized in that, The pressure-applying upper die includes an upper top block located at the center, boss cavities located on both sides of the upper top block, and rim cavities located on both sides of the boss cavities.

12. The method for solving the problem of streamlined conformity of the central boss of an aluminum alloy wheel hub according to claim 10, characterized in that, The lower mold includes a lower top block located at the center, concave cavities located on both sides of the lower top block, and hub cavities located on both sides of the concave cavities.

13. The method for solving the problem of streamlined conformity of the central boss of an aluminum alloy wheel hub according to claim 1, characterized in that, The heat preservation temperature of the pre-forged part is 420℃~450℃, the heat preservation time is 5h~6h, and the aluminum alloy heat preservation coefficient of the pre-forged part is 2.

0.

14. The method for solving the problem of streamlined conformity of the central boss of an aluminum alloy wheel hub according to claim 1, characterized in that, The initial forging temperature is ≥370℃, and the final forging temperature is ≤470℃.

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