Precise manufacturing method of high-precision low-residual-stress C-shaped section ring piece

Abstract

The invention discloses a precise manufacturing method of a high-precision low-residual-stress C-shaped section ring piece, which comprises the following steps of: firstly, upsetting and punching a bar material, then performing ring rolling to obtain a rectangular ring with a reasonable size, and then adopting expansion and shrinkage integrated equipment to enlarge or reduce the diameter of a central area in the height direction of the rectangular ring under the combined action of an expansion mold and a diameter shrinkage mold; the size of the C-shaped section ring meets the conditions that d0 is larger than or equal to 0.88 d and smaller than or equal to 1.04 d, D0 is larger than or equal to 0.86 D and smaller than or equal to D, meanwhile, the wall thickness t0 is larger than or equal to 0.96 t and smaller than or equal to 1.18 t, the deformation delta ranges of single bulging and hole shrinkage are 02% and 01.5% respectively, and compared with a rolled rectangular ring, the average value of the residual stress reduction rate of the C-shaped section special-shaped ring obtained through the method is about 0.350.77 (100 delta / t0) 0.15. And the error between the actual geometric dimension and the target dimension is not more than 0.1%, and compared with a rolled rectangular ring, the residual stress reduction rate is 60%-90%, so that the precision manufacturing of the low-residual-stress C-shaped section ring piece is favorably realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the precision plastic forming of metal ring parts, and in particular to a precision manufacturing method for a high-precision low-residual-stress C-section ring part. BACKGROUND

[0002] Existing C-section ring parts, as key functional components, such as stepped, concave outer circumferential surface, convex inner circumferential surface, and other special-shaped sections, are widely used in the fields of wind power generation, aerospace, energy equipment, etc., and usually need to withstand extreme working conditions such as high load, high temperature, or strong corrosion. For example, in wind power bearing rings, C-section stepped ring parts need to have excellent wear resistance and fatigue resistance, while in aero-engines, C-section ring parts made of cobalt-based alloy or 2219 aluminum alloy need to meet the requirements of high-temperature strength and corrosion resistance. However, the existing manufacturing technology still faces many challenges. In the existing technology, the main processing methods are as follows.

[0003] (1) Cutting: ① Simplify the C-section ring part into a rectangular ring part by designing with an increased allowance for ring rolling forming, and then obtain the target shape through subsequent mechanical processing, resulting in a large amount of material waste and a prolonged processing cycle; ② Mechanical processing will cut off the original complete metal flow line of the ring part, greatly reducing its mechanical properties, and cannot meet the stringent requirements of the aerospace field for high specific strength and high fatigue life components; ③ The hardening layer (thickness about 0.1-0.3mm) formed on the processed surface is extremely prone to micro-cracks under alternating loads, leading to early failure and posing a major safety hazard to key load-bearing components.

[0004] (2) Welding: Free forging combined with segmented welding or plate rolling can manufacture large components, but still has the following key problems: ① For Haynes188 and other difficult-to-deform high-temperature alloys and 2219 aluminum alloys, the metal flow is uneven during free forging due to poor material plasticity and large deformation resistance, which easily causes local strain concentration and leads to micro-cracks or even macro-cracks; ② Low forming precision, free forging is difficult to accurately control the size, and a large amount of subsequent machining is required, not only causing material waste, but also possibly damaging the flow line of the forged part and reducing the mechanical properties; ③ Poor welding performance, high-temperature alloys are prone to hot cracks and liquid cracks, and aluminum alloy weld zones have grain growth and precipitated phase dissolution, all of which lead to deterioration of the heat-affected zone structure, significantly reducing strength, corrosion resistance, and high-temperature durability; ④ Residual stress problem is prominent, residual stress formed by uneven heat input is prone to cause subsequent processing deformation or service warping; ⑤ Low structural reliability, the weld as a weak zone of structure and performance is easily a crack source under cyclic load or corrosion environment, greatly reducing the fatigue life of the component, and difficult to meet the requirements of severe working conditions such as aero-engines.

[0005] (3) Ring rolling: The manufacture of C-shaped cross-section ring by ring rolling process conforms to the current trend of overall forming of large structural parts, but its process is more complex than the traditional rectangular ring rolling. The main difficulties are as follows: ① The deformation process is complex. When rolling the ring with special cross-section, the cavity needs to be filled while the wall thickness is reduced and the diameter is expanded, and the metal flow is characterized by three-dimensional non-uniformity; ② Due to the interaction of cross-section mutation (such as wall thickness difference at the step) and roller movement, the core roller and the blank often have point / line contact, resulting in the characteristics of asymmetric, non-isothermal and multi-pass dynamic changes in the deformation process; ③ Complex metal flow is prone to cause defects such as instability, folding and disc-shaped warping, which reduces the dimensional accuracy; ④ The ring is unevenly stressed during rolling, resulting in large residual stress after forming, which directly affects the service performance of the component; ⑤ In order to alleviate the negative impact of cross-section mutation, the design allowance usually needs to be increased to make the transition area smooth, which reduces the material utilization and the process adaptability; ⑥ The mold (especially the core roller) is severely worn due to local stress concentration, and needs to be replaced frequently, increasing the production cost.

[0006] (4) Direct bulging and shrinking forming, which has large residual stress and affects service life, as shown in Figure 1 A method for grain homogenization of a nickel-based high-temperature alloy cartridge, as disclosed in Chinese Patent No. CN114318193A, includes the following steps: Step S1: preparing a blank, which is pre-formed into a ring shape; Step S2: first bulging, heating the blank to 1080-1100°C, placing the blank on the outer edge of the bulging die, and moving the die radially from the inside to the outside along the circumference to make the blank deform radially; Step S3: second bulging, keeping the blank temperature at 1080-1100°C, resetting the bulging die, rotating the blank, and moving the die radially from the inside to the outside along the circumference to make the blank deform radially. The advantages of the present invention lie in that, through specific bulging methods and heat treatment, part of the coarse grains in the radial direction obtains certain deformation energy, the deformation is synchronous and cumulative, and the microstructure uniformity is ensured.

[0007] In summary, the existing methods generally have the problems of high material consumption, low forming efficiency, long manufacturing cycle and insufficient control of residual stress. The existing technology cannot simultaneously consider dimensional accuracy and residual stress control, resulting in deformation or even failure of the ring during subsequent processing or service. Therefore, it is urgent to develop a precision manufacturing method that takes into account high precision, low residual stress and high efficiency forming, in order to improve the performance consistency and production economy of C-shaped cross-section rings. SUMMARY

[0008] The purpose of this invention is to propose a precision manufacturing method for high-precision, low-residual-stress C-shaped cross-section rings. This method organically combines mature rectangular ring rolling technology with an integrated expansion and contraction forming / straightening process, leveraging their respective advantages to address the shortcomings of existing C-shaped cross-section irregular ring manufacturing methods, such as low material utilization, high production costs, and difficulty in guaranteeing microstructure and properties. Specifically, the ring rolling process for rectangular rings is simple, the rectangular ring forging design allowance is small, and the overall stress is uniform. In the expansion and contraction forming of C-shaped cross-section irregular rings, not only can rings of the target size be precisely formed, but also, through the synergistic and interactive action of the expansion and contraction dies, the inner and outer circumferential surfaces of the C-shaped cross-section ring undergo appropriate deformation times and values, effectively controlling its residual stress, thereby obtaining high-precision, low-residual-stress C-shaped cross-section rings.

[0009] The technical solution of this invention: a precision manufacturing method for a high-precision, low-residual-stress C-shaped cross-section ring, characterized by comprising the following steps: Step S1: Rectangular ring blank size design. Based on the dimensions of the target C-shaped cross-section ring, calculate the size range of the rectangular ring blank according to the principle of constant volume. It should meet the following conditions: inner diameter d0 satisfies 0.88d ≤ d0 ≤ 1.04d, outer diameter D0 satisfies 0.86D ≤ D0 ≤ D, wall thickness t0 satisfies 0.96t ≤ t0 ≤ 1.18t, and height h0 satisfies h0 = h, where D represents the maximum outer diameter of the target C-shaped ring, d represents the maximum inner diameter, h represents the height, and t represents the maximum wall thickness; D0, d0, h0, and t0 represent the outer diameter, inner diameter, height, and wall thickness of the rectangular ring blank, respectively. Step S2: Rectangular ring billet rolling. The heated and held bar stock is upset, punched and ring rolled to obtain a rectangular ring billet. Step S3: Equipment loading and initial setup. Place the obtained rectangular ring blank into the expansion and contraction integrated equipment. The diameter reduction mold is arranged on the outer circumference of the rectangular ring, and its inner diameter is equal to the outer diameter of the rectangular ring. The expansion mold is arranged on the inner circumference of the rectangular ring, and its outer diameter is equal to the inner diameter of the rectangular ring. In the initial state, no load is applied to either the expansion or contraction mold. Step S4: Alternate deformation treatment, following the process route of "expansion-pressure holding-unloading-rotating ring-resetting-diameter reduction-pressure holding-unloading" for n cycles; after each expansion or diameter reduction, select stress monitoring points on the ring to perform residual stress testing, and dynamically adjust the number of deformation cycles according to the relationship between the residual stress reduction rate η and the number of cycles n. Step S5: After deformation is complete, all molds are returned to their initial positions, and the workpiece is removed for cooling; Step S6: Inspect the geometry and residual stress level of the finally obtained C-shaped cross-section ring.

[0010] Furthermore, in step S4, for workpieces with low residual stress levels, a process route of "bulging-diameter reduction-pressure holding-unloading-rotating ring-diameter reduction-bulging-cycle" can be adopted.

[0011] Furthermore, step S4 specifically includes the following sub-steps: Step S41: Perform bulging-holding-unloading-rotating ring. The diameter reduction die keeps the outer diameter limit, the bulging die extrudes the inner wall of the ring blank to achieve local bulging, unload after holding pressure, and rotate the ring by 45°. Step S42: Mold reset, the bulging mold returns to the position before deformation in step S41, at this time both the bulging and shrinking molds are in an unloaded state; Step S43: Perform diameter reduction-pressure holding-unloading. The expansion mold keeps the inner diameter limit, the diameter reduction mold extrudes the outer wall of the ring blank inward to achieve local diameter reduction, pressure holding is followed by unloading, and the ring is rotated 45°. Step S44: The mold is reset, and the shrinking mold returns to the position before deformation in step S43. At this time, both the expansion and contraction molds are in an unloaded state. Step S45: Repeat steps S41 to S44, looping n times.

[0012] Furthermore, in step S41, the amount of single bulging deformation δ is controlled between 0% and 2%, and in step S43, the amount of single diameter reduction deformation δ is controlled between 0% and 1.5%.

[0013] Furthermore, in steps S41 and S43, the single-time reduction rate η of the residual stress equivalent value of the rectangular ring after rolling, compared with the single-time local deformation, satisfies the following relationship: 0.35~0.77 (100δ / t0). 0.15 δ is the amount of deformation in a single operation, and t0 is the initial wall thickness of the rectangular ring blank.

[0014] Furthermore, the number of cycles n is 2, 3, 4, or 5.

[0015] Furthermore, in step S3, the rectangular ring blank needs to be heated to a temperature 50-100°C below the recrystallization temperature, and then kept at that temperature before being loaded into the equipment.

[0016] Furthermore, the bulging mold and the reducing mold are each composed of 8 or 12 fan-shaped modules, and the combined structure formed by them matches the inner and outer contours of the rectangular ring blank.

[0017] Furthermore, the residual stress reduction rate η of the C-shaped cross-section ring obtained by this method is related to the number of cycles n according to the following formula: , where k is a material constant, εa and εb are the true plastic strains of bulging and shrinking, respectively, and α is the strain sensitivity coefficient.

[0018] Furthermore, the C-shaped cross-section ring manufactured using this method has an actual geometric dimension error of no more than 0.1% compared to the target dimension, and the residual stress is reduced by 60% to 90% compared to the rolled rectangular ring blank. The beneficial effects of this invention are: 1. The material utilization rate of the present invention is significantly improved: The present invention first rolls an easy-to-form rectangular ring blank, and then forms it into a C-shaped cross section through local expansion and contraction composite forming, which avoids reserving a large amount of allowance for the transition of large cross section during irregular ring rolling.

[0019] 2. The controllability of residual stress and the reliability of components are improved by this invention: By establishing a quantitative relationship between deformation parameters (single deformation amount δ, number of cycles n) and residual stress reduction rate, active control of the stress state of the ring component is achieved. The stress reduction rate after a single deformation is approximately 0.35~0.77×(100δ / t0). 0.15 The total reduction rate η and the number of cycles n satisfy the following relationship: This method avoids the subsequent stress-relief annealing process, shortens the process, and improves production efficiency and microstructure stability.

[0020] 3. The present invention has high forming accuracy: Since the deformation process is always constrained by the mold surface and the stress is uniform, the deformation is stable and there is no local load impact phenomenon in traditional irregular rolling. The final part geometric dimension error does not exceed 0.1% of the target dimension, and the residual stress is reduced by 60%~90% compared with the rectangular ring blank.

[0021] 4. The forming process of this invention is stable and efficient: there is no sudden load change caused by the local contact between the irregular core roller and the ring during the irregular ring rolling process. During the expansion and contraction deformation process, the inner and outer sides of the ring are supported by the mold at the same time, avoiding defects such as instability and folding. The process has good repeatability and is suitable for the efficient and precise forming of high-performance alloy rings. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the residual stress distribution when a C-shaped cross-section ring is directly formed by expansion and contraction. Figure 2 This is a schematic diagram of the C-shaped cross-section ring of TC4 titanium alloy of the present invention, which is concave from the outer circumference to the inner circumference. Figure 3 This is a schematic diagram of the residual stress distribution after the rectangular ring rolling process in Example 1. Figure 4This is a schematic diagram of the residual stress distribution of the C-shaped cross-section ring obtained in Example 1; Figure 5 This is a schematic diagram of the residual stress distribution after the rectangular ring rolling process in Example 2; Figure 6 This is a schematic diagram of the residual stress distribution of the C-shaped cross-section ring obtained in Example 2; Figure 7 This is a schematic diagram of the residual stress distribution after the rectangular ring rolling process in Example 3; Figure 8 This is a schematic diagram of the residual stress distribution of the C-shaped cross-section ring obtained in Example 3; Figure 9 This is a schematic diagram of the ring forging formed using this method and the target forging; Figure 10 This is a schematic diagram of the cross-section of a C-shaped irregular ring; Figure 11 This is a schematic diagram of the residual stress of the C-shaped ring obtained in Example 4. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, it should not be construed that the scope of the subject matter of the present invention is limited to the following embodiments. All modifications, substitutions and alterations made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention are included within the scope of the present invention.

[0025] This invention provides a precision manufacturing method for high-precision, low-residual-stress C-shaped cross-section rings. Addressing the problems of low material utilization, difficulty in controlling residual stress, and the challenge of balancing forming accuracy in existing technologies, this method optimizes blank design and employs a unique alternating expansion and contraction deformation process to actively regulate and reduce residual stress while achieving precision forming. The method specifically includes the following steps: Step S1: Rectangular Ring Blank Dimension Design and Calculation Based on the dimensions of the target C-shaped cross-section ring (including maximum outer diameter D, maximum inner diameter d, height h, and maximum wall thickness t), the dimensions of the rectangular ring blank (outer diameter D0, inner diameter d0, height h0, and wall thickness t0) are accurately calculated based on the principle of constant volume. To improve material flow, increase utilization, and reduce machining allowance, a rectangular ring blank design with equal or similar height and wall thickness is preferred. For C-shaped rings with an inwardly concave outer circumference, the blank dimensions must meet the following requirements: 0.88d ≤ d0 ≤ 1.04d, 0.86D ≤ D0 ≤ D, and the wall thickness must meet the requirement of 0.96t ≤ t0 ≤ 1.18t (while t0 must be greater than the minimum wall thickness of the C-shaped ring); the design principle for C-shaped rings with an outwardly convex inner circumference is similar. This design can significantly improve material utilization and reduce subsequent processing costs.

[0026] Step S2: Rolling and forming of the rectangular ring billet After heating the alloy bar to the forging temperature and holding it at that temperature for a sufficient period, it is then upsetting, punching, and ring rolling to form a rectangular ring billet. This step uses a conventional ring rolling process, which has high forming efficiency and avoids the problems of process instability and excessive allowance caused by the complexity of the shape when rolling irregularly shaped rings.

[0027] Step S3: Billet loading and equipment initialization After heating the rectangular ring blank to 50-100°C below its recrystallization temperature and holding it there, it is placed into an expansion and contraction forming device. This device is equipped with several (usually 8 or 12) expansion and contraction molds, the shape of which matches the inner and outer contours of the rectangular ring blank. During initialization, the contraction molds are distributed around the outer circumference of the ring blank, with their inner diameter equal to the outer diameter D0; the expansion molds are distributed around the inner circumference of the ring blank, with their outer diameter equal to the inner diameter d0; all molds are initially unloaded. This temperature setting and mold layout lay the foundation for subsequent uniform deformation and stress control.

[0028] Step S4: Alternating Expansion and Contraction Deformation Process The deformation process employs a cycle of "bulging-holding-unloading-rotating ring-resetting-reducing diameter-holding-unloading" for n alternating deformations, as follows: Step S41: In the bulging stage, the reducing die maintains its outer diameter limit, and the bulging die moves radially outward to compress the inner wall of the ring blank to achieve local bulging. The deformation amount δ in a single operation is controlled within 0~2%. After holding pressure, the die is unloaded, and the ring is rotated 45°. This process effectively reduces residual rolling stress. Step S412: The die is reset, and the bulging die returns to its initial inner diameter position. All dies return to the unloaded state. Step S43: In the reducing diameter stage, the bulging die maintains its inner diameter limit, and the reducing die moves radially inward to compress the outer wall of the ring blank to achieve local diameter reduction. The diameter reduction amount δ in a single operation is controlled within 0~1.5%. After holding pressure, the die is unloaded, and the ring is rotated 45° again to further promote stress uniformity. Step S44: The die is reset, and the reducing die returns to its initial outer diameter position. All dies return to the unloaded state. Step S45: Repeat steps S41 to S4 a total of n times, where n is typically 2 to 5, and the number of cycles can be dynamically adjusted based on stress monitoring. For ring blanks with low residual stress levels, a simplified path of "expansion-diameter reduction-pressure holding-unloading-rotating ring-diameter reduction-expansion-cycle" can be adopted, improving efficiency while ensuring stress reduction. This alternating deformation strategy effectively avoids local stress concentration and deformation instability problems in irregular rolling. Step S5: Workpiece removal and cooling After deformation, all molds are returned to their initial positions, the formed ring is removed, and it is air-cooled or controlled-cooled. Since residual stress has been effectively controlled in the previous process, additional annealing is usually unnecessary, shortening the production cycle.

[0029] Step S6: Geometric Dimensions and Residual Stress Detection Finally, precision measurement methods were used to inspect the geometric dimensions of the C-shaped cross-section ring and measure the residual stress. Practice shows that the dimensional error of the ring formed by this invention does not exceed 0.1%, and the residual stress is reduced by 60% to 90% compared to the rolled rectangular ring blank, achieving a synergistic manufacturing process of high precision and low residual stress. (Refer to...) Figure 10 The diagram shows the ring forging and the target forging formed using this method.

[0030] Example 1: The following uses a C-shaped cross-section ring made of TC4 titanium alloy with the outer circumference facing inwards to the inner circumference as an example to illustrate the specific implementation of the present invention.

[0031] Concave C-shaped cross-section irregular ring forgings, such as Figure 2 As shown, its maximum outer diameter D=1657mm, minimum inner diameter d=1536mm, height h=260mm, maximum wall thickness t=34mm, and weight is approximately 175kg. Step S1: Calculate the dimensions of the rectangular ring, based on... Figure 1 The concave C-shaped cross-section ring shown is used to calculate the required rectangular ring size based on the principle of constant volume. Its outer diameter D0 = 1628 mm (≈0.98D), inner diameter d0 = 1560 mm (≈1.02d), height h0 = 260 mm, thickness t0 = 34 mm (=1.0t), and weight is approximately 200 kg.

[0032] Step S2: Rolling of rectangular ring billets. Using Φ270mm×800mm bars, after rounding the end faces, heat to 955℃ and hold for 90~100min, then upset to a height of 260mm in two passes, punch holes and ring roll to obtain rectangular ring billets. Refer to... Figure 3 This represents the residual stress distribution after the rectangular ring rolling process is completed. Step S3: Start the equipment. The billet is ready. Heat the obtained rectangular ring billet to 930℃ and keep it at that temperature for 30 minutes. Then put it into the expansion and shrinkage integrated equipment and start the expansion and shrinkage integrated forming device. This device is equipped with 8 expansion molds and 8 shrinking molds. The shrinking molds are distributed on the outer circumference of the rectangular ring. The inner diameter of the molds at the location is the outer diameter of the rectangular ring. At this time, the expansion molds are distributed on the inner circumference of the rectangular ring. The outer diameter of the molds at the location is the inner diameter of the rectangular ring. At this time, neither the expansion nor shrinking molds are loaded.

[0033] Step S4: Alternating deformation, the process route is "expansion-pressure holding-unloading-rotating ring-resetting-diameter reduction-pressure holding-unloading-cycle", as detailed below. Step S41: The reducing die maintains the outer diameter limit, while the expanding die radially extrudes the inner circumference of the rectangular ring to achieve local bulging deformation. The single bulging amount δ is 0.53%. After holding the pressure, the pressure is released, and the ring is rotated 45°. Six nodes with high stress are selected on the rectangular ring to track the changes. The stress values ​​before bulging are 192.2 MPa, 203.8 MPa, 212.5 MPa, 230.1 MPa, 237.1 MPa, and 256.3 MPa. The equivalent stress values ​​after unloading are 113.3 MPa, 120.6 MPa, 125.4 MPa, 136.9 MPa, 139.7 MPa, and 151.2 MPa. The residual stress reduction rate is approximately 40.9% on average, which is approximately equal to 0.77 × (0.53 / 34). 0.15 ; Step S42: The bulging mold is reset to the deformation position of the process in S41. At this time, the bulging mold is in the same state as in step S3, which is unloaded. Step S43: The bulging die maintains the inner diameter limit, while the shrinking die radially presses the outer circumference of the rectangular ring to achieve local shrinkage deformation. The single shrinkage deformation amount δ is 0.58%. After holding the pressure, the pressure is released, and the ring is rotated 45°. The corresponding residual stress values ​​are 72.3 MPa, 80.7 MPa, 85.0 MPa, 92.5 MPa, 96.3 MPa, and 103.4 MPa, respectively. The average residual stress reduction rate is approximately 33.5%, which is approximately equal to 0.63 × (0.58 / 34). 0.15 ; Step S44: The reducing mold is reset to the deformation position of the process in S43. At this time, the expanding and shrinking mold is in the same state as in step S3, which is unloaded. Step S45: Repeat the alternating deformation process steps S41 to S44, repeating 3 times.

[0034] Step S5: After deformation is complete, the mold is reset and the workpiece is removed and cooled; Step S6: Refer to Figure 4 The geometric dimensions and residual stress of the deformed C-shaped cross-section ring were measured, with a dimensional error of ±1 mm. The residual stress of the C-shaped cross-section ring generally did not exceed 75 MPa, mostly falling below 50 MPa. The overall residual stress reduction rate was approximately 50.2%. .

[0035] Example 2: Taking the target ring forging from Example 1 as an example, its maximum outer diameter D=1657mm, minimum inner diameter d=1536mm, height h=260mm, maximum wall thickness t=34mm, and weight is approximately 175kg. Step S1: Calculate the size of the rectangular ring—based on Figure 2The concave C-shaped cross-section ring shown is used to calculate the required rectangular ring size using the principle of constant volume. Its outer diameter D0 = 1657 mm (=D), inner diameter d0 = 1592 mm (≈1.04d), height h0 = 260 mm, wall thickness t0 = 32.5 mm (≈0.95t), and weight is approximately 197 kg.

[0036] Step S2: Rectangular Ring Billet Rolling—Using Φ270mm×810mm bar stock, after rounding the end faces, heat to 955℃ and hold for 90~100min, then upset to a height of 260mm in two passes, punch holes and ring roll to obtain a rectangular ring billet, refer to... Figure 5 A schematic diagram of the stress distribution for a rectangular ring blank obtained by ring rolling; Step S3: Start the equipment and prepare the billet—Heat the obtained rectangular ring billet to 935℃ and hold it for 30 minutes, then place it into the expansion and shrinkage integrated equipment and start the expansion and shrinkage integrated forming device. This device is equipped with 8 expansion molds and 8 shrinking molds. The shrinking molds are distributed on the outer circumference of the rectangular ring, and the inner diameter of the molds at the location is the outer diameter of the rectangular ring. At this time, the expansion molds are distributed on the inner circumference of the rectangular ring, and the outer diameter of the molds at the location is the inner diameter of the rectangular ring. At this time, neither the expansion nor shrinking molds are loaded.

[0037] Step S4: Alternating Deformation—The process route is “diameter reduction-expansion-pressure holding-unloading-repetition”, as detailed below. Step S41: The bulging mold maintains the inner diameter limit, and the diameter reduction deformation δ=0; Step S42: The diameter reduction die maintains the outer diameter limit, while the bulging die radially extrudes the inner circumference of the rectangular ring to achieve local bulging deformation. The single diameter reduction deformation amount δ is 0.88%. After holding the pressure, the pressure is released, and the ring is rotated 45°. Six nodes with relatively high stress are selected on the rectangular ring to track their value changes. The stress values ​​before bulging are 396.5 MPa, 334.3 MPa, 269.3 MPa, 233.9 MPa, 227.6 MPa, and 198.4 MPa. The equivalent stress values ​​after unloading are 270.8 MPa, 226.6 MPa, 183.2 MPa, 158.0 MPa, 155.5 MPa, and 128.1 MPa. The residual stress reduction rate is approximately 32.3% on average, which is approximately equal to 0.56 × (0.88 / 32.5). 0.15 ; Step S43: Repeat the deformation process step S42, repeating 4 times.

[0038] Step S5: After deformation is complete, the mold is reset and the workpiece is removed and cooled; Step S6: Measure the geometric dimensions and residual stress of the deformed C-shaped cross-section ring. The outer diameter should match the target ring size, while the inner diameter should be 0.6 mm smaller on one side (error 0.7‰). Refer to... Figure 6The vast majority of residual stresses are below 80-90 MPa, and the overall residual stress reduction rate is approximately 65.8%. .

[0039] Example 3: Taking the target forging from the above embodiment as an example, its maximum outer diameter D=1657mm, minimum inner diameter d=1536mm, height h=260mm, maximum wall thickness t=34mm, and weight is approximately 175kg.

[0040] Step S1: Calculate the dimensions of the rectangular ring, based on... Figure 2 The concave C-shaped cross-section ring shown is used to calculate the required rectangular ring size using the principle of constant volume. Its outer diameter D0 = 1430mm (≈0.86D), inner diameter d0 = 1350mm (≈0.88d), height h0 = 255mm, thickness t0 = 40mm (≈1.18t), and weight is approximately 198kg.

[0041] Step S2: Rolling of rectangular ring billets. Using Φ270mm×815mm bars, after rounding the end faces, heat to 945℃ and hold for 90~100min, then upset to a height of 255mm in two passes, punch holes and ring roll to obtain rectangular ring billets. Refer to... Figure 7 This is a schematic diagram of the stress distribution in a rectangular ring blank; Step S3: Start the equipment and prepare the billet—Heat the obtained rectangular ring billet to 935℃ and hold it for 30 minutes, then place it into the expansion and shrinkage integrated equipment and start the expansion and shrinkage integrated forming device. This device is equipped with 8 expansion molds and 8 shrinking molds. The shrinking molds are distributed on the outer circumference of the rectangular ring, and the inner diameter of the molds at the location is the outer diameter of the rectangular ring. At this time, the expansion molds are distributed on the inner circumference of the rectangular ring, and the outer diameter of the molds at the location is the inner diameter of the rectangular ring. At this time, neither the expansion nor shrinking molds are loaded.

[0042] Step S4: Alternating deformation, the process route is "expansion-pressure holding-unloading-rotating ring-resetting-diameter reduction-pressure holding-unloading-cycle", as detailed below. Step S41: The reducing die maintains the outer diameter limit, while the expanding die radially extrudes the inner circumference of the rectangular ring to achieve local bulging deformation. The single bulging amount δ is 2%. After holding the pressure, the pressure is released, and the ring is rotated 45°. Six nodes with high stress are selected on the rectangular ring to track the changes. The stress values ​​before bulging are 202.2 MPa, 290.1 ​​MPa, 367.3 MPa, 416.9 MPa, 512.8 MPa, and 573.6 MPa. The equivalent stress values ​​after unloading are 149.1 MPa, 213.8 MPa, 266.6 MPa, 308.5 MPa, 380.2 MPa, and 430.5 MPa. The residual stress reduction rate is approximately 26.7% on average, which is approximately equal to 0.41 × (2 / 40). 0.15 ; Step S42: The bulging mold is reset to the deformation position of the process in S41. At this time, the bulging mold is in the same state as in step S3, which is unloaded. Step S43: The bulging die maintains the inner diameter limit, while the shrinking die radially presses the outer circumference of the rectangular ring to achieve local shrinkage deformation. The single shrinkage deformation amount δ is 1.5%. After holding the pressure, the ring is unloaded and rotated 45°. Corresponding to the above nodes, the equivalent stress values ​​after deformation and unloading are 118.3 MPa, 167.5 MPa, 207.3 MPa, 249.1 MPa, 293.2 MPa, and 335.7 MPa. The residual stress reduction rate is approximately 21.3% on average, which is approximately equal to 0.35 × (1.5 / 40). 0.15 ; Step S44: The diameter reduction mold is reset to the deformation position of the process in step S43. At this time, the expansion and contraction mold is in the same state as in step S3, which is unloaded. Step S45: Repeat the alternating deformation process steps S41 to S44, repeating 5 times.

[0043] Step S5: After deformation is complete, the mold is reset and the workpiece is removed and cooled; Step S6: Refer to Figure 8 The geometric dimensions and residual stress of the deformed C-shaped cross-section ring were measured, with a dimensional error of ±1 mm. The overall average residual stress was 150~160 MPa, and the overall residual stress reduction rate was approximately... Although there was a good reduction in residual stress, the final residual stress value was still relatively high. This was because the initial rectangular ring dimensions were too small: the outer diameter (1430mm ≈ 0.86D) and inner diameter (1350mm ≈ 0.88d) were much smaller than the target part size. Significant bulging was required to expand it to the target size, and the wall thickness (40mm ≈ 1.18t) was also relatively thick. This caused the rectangular ring to undergo additional thinning and diameter expansion during the precision forming of the C-shaped ring, resulting in severe plastic deformation. For example, to achieve the target size, the amount of deformation per cycle increased (bulging 2%, diameter reduction 1.5%). Large deformation introduces significant residual stress, resulting in a significant work hardening effect and making stress relaxation more difficult. Although five cycles of bulging and shrinking were performed, the diameter expansion and thinning deformation simultaneously introduced residual stress, leading to a still high level of residual stress after final forming.

[0044] On the one hand, although a smaller wall thickness (as in Example 2) can be locally thickened under the constrained deformation of the expansion and contraction die to achieve the target thickness locally, this approach is rarely used in actual production to avoid scrapping. On the other hand, for rectangular ring blanks with thicker walls and smaller diameters, although rolling is easier and the residual stress reduction effect is better, the final residual stress is higher (lower than the residual stress of directly expanding and contracting to form C-shaped rings and irregularly shaped rings), which may not meet the requirements in special application scenarios. Therefore, in this invention, a rectangular ring with the same thickness as the target C-shaped ring is preferred, as in Example 1.

[0045] Since residual stress reduction essentially involves redistributing internal stress through plastic deformation to achieve relaxation or homogenization, when a ring undergoes bulging, the external load causes plastic deformation (an increase in equivalent plastic strain). This process disrupts the original residual stress equilibrium, leading to plastic flow in high-stress areas (such as dislocation slip and grain boundary migration), thereby consuming residual stress energy (converting it into heat or microstructural changes). Larger plastic strain implies more thorough microscopic plastic adjustment (such as grain refinement and dislocation reorganization), which can more effectively eliminate residual stress (for example, continued deformation after the yield point can reduce the stress peak). The mathematical expressions in this application, besides being verified by simulation data, also conform to this theoretical principle.

[0046] In this invention, the rectangular ring blank is easy to form and the expansion and contraction mold design is simple, which can significantly shorten the design and manufacturing cycle. The part weighs 113kg, reducing the allowance design of the ring forging (in the example, the forging is 133kg, the above-mentioned bar stock is about 160kg, and the material utilization rate is 70.6%). Compared with irregular ring rolling (with an 8mm allowance on one side and a smooth transition, the forging is about 272kg, the bar stock is about 294kg, and the material utilization rate is about 38.4%), the material utilization rate can be increased by about 83.3%. Moreover, compared with the direct expansion and contraction forming of C-shaped rings, due to the repeated process of deformation-unloading-reverse deformation, the residual stress can be released to a certain extent under the low residual stress state of the original small deformation, thereby realizing the low residual stress, high precision and high efficiency manufacturing of C-shaped cross-section rings.

[0047] Example 4: Taking a C-shaped cross-section ring of 30Si2MnCrMoVE alloy as an example, the specific implementation of the present invention is illustrated.

[0048] Concave C-shaped cross-section irregular ring forgings, such as Figure 10 As shown, its maximum outer diameter D=1454mm, minimum inner diameter d=1185mm, height h=239mm, maximum wall thickness t=80mm, and weight is approximately 506kg. Step S1: Calculate the dimensions of the rectangular ring, based on... Figure 1The concave C-shaped cross-section ring shown is used to calculate the required rectangular ring size based on the principle of constant volume. Its outer diameter D0 = 1390 mm (≈0.96D), inner diameter d0 = 1215 mm (≈1.02d), height h0 = 239 mm, thickness t0 = 87.5 mm (=1.09t), and weight is approximately 531 kg.

[0049] Step S2: Rolling of rectangular ring billet. Use Φ300mm×1000mm bar stock, about 563kg. After rounding the end face, heat to 980℃ and hold for 100~110min. Then, upset to a height of 239mm in two heats. After punching and ring rolling, obtain rectangular ring billet. Step S3: Start the equipment. The billet is ready. Heat the obtained rectangular ring billet to 980℃ and keep it at that temperature for 50 minutes. Then put it into the expansion and shrinkage integrated equipment and start the expansion and shrinkage integrated forming device. This device is equipped with 8 expansion molds and 8 shrinking molds. The shrinking molds are distributed on the outer circumference of the rectangular ring. The inner diameter of the molds at the location is the outer diameter of the rectangular ring. At this time, the expansion molds are distributed on the inner circumference of the rectangular ring. The outer diameter of the molds at the location is the inner diameter of the rectangular ring. At this time, neither the expansion nor shrinking molds are loaded.

[0050] Step S4: Alternating deformation, the process route is "expansion-pressure holding-unloading-rotating ring-resetting-diameter reduction-pressure holding-unloading-cycle", as detailed below. Step S41: The reducing die maintains its outer diameter limiting function, while the bulging die radially extrudes the inner circumference of the rectangular ring to achieve local bulging. The single bulging amount δ is 2%. After holding the pressure, the pressure is released, and the ring is rotated 45°. Six stress nodes with high stress are selected on the rectangular ring to track the stress changes. The stress values ​​before bulging are 195.3 MPa, 205.8 MPa, 215.1 MPa, 232.5 MPa, 241.8 MPa, and 259.6 MPa; the corresponding values ​​after deformation and unloading are 142.1 MPa, 150.8 MPa, 157.6 MPa, 170.9 MPa, 176.2 MPa, and 190.3 MPa. The average residual stress reduction rate is approximately 38.6%, which is approximately equal to 0.68 × (2 / 87.5). 0.11 ; Step S42: The bulging mold is reset to the deformation position of the process in S41. At this time, the bulging mold is in the same state as in step S3, which is unloaded. Step S43: The bulging die maintains the inner diameter limit, while the shrinking die radially presses the outer circumference of the rectangular ring inward to achieve local shrinkage deformation. The single shrinkage deformation amount δ is 1.5%. After holding the pressure, the pressure is released, and the ring is rotated 45°. The corresponding residual stress values ​​are 99.8 MPa, 106.1 MPa, 110.9 MPa, 120.5 MPa, 124.3 MPa, and 134.2 MPa, respectively. The average residual stress reduction rate is approximately 31%, which is approximately equal to 0.57 × (1.5 / 87.5).0.15 ; Step S44: The reducing mold is reset to the deformation position of the process in S43. At this time, the expanding and shrinking mold is in the same state as in step S3, which is unloaded. Step S45: Repeat the alternating deformation process steps S41 to S44, repeating 4 times.

[0051] Step S5: After deformation is complete, the mold is reset and the workpiece is removed and cooled; Step S6: Measure the geometric dimensions and residual stress of the deformed C-shaped cross-section ring, with a dimensional error of ±1mm, referring to... Figure 11 The residual stress values ​​for the C-shaped cross-section rings are 46.3 MPa, 51.7 MPa, 58.2 MPa, 62.9 MPa, 68.4 MPa, and 70.7 MPa, respectively, generally not exceeding 75 MPa, with most areas below 50 MPa. The overall residual stress reduction rate is approximately 71.3%. .

[0052] The foregoing has provided a detailed description of a precision manufacturing method for a high-precision, low-residual-stress C-shaped cross-section ring provided by this invention. Specific examples have been used to illustrate the structure and working principle of this invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims of this invention.

Claims

1. A precision manufacturing method for a high-precision, low-residual-stress C-shaped cross-section ring, characterized in that: Includes the following steps, Step S1: Rectangular ring blank size design. Based on the dimensions of the target C-shaped cross-section ring, calculate the size range of the rectangular ring blank according to the principle of constant volume. It should meet the following conditions: inner diameter d0 satisfies 0.82d ≤ d0 ≤ 1.04d, outer diameter D0 satisfies 0.86D ≤ D0 ≤ D, wall thickness t0 satisfies 0.96t ≤ t0 ≤ 1.18t, and height h0 is equal to the height h of the C-shaped cross-section ring; where D represents the maximum outer diameter of the C-shaped cross-section ring, d represents the maximum inner diameter, h represents the height, and t represents the maximum wall thickness; D0, d0, h0, and t0 represent the outer diameter, inner diameter, height, and wall thickness of the rectangular ring blank, respectively. Step S2: Rectangular ring billet rolling. The heated and held bar stock is upset, punched and ring rolled to obtain a rectangular ring billet. Step S3: Equipment loading and initial setup. Place the obtained rectangular ring blank into the expansion and contraction integrated equipment. The diameter reduction mold is arranged on the outer circumference of the rectangular ring, and its inner diameter is equal to the outer diameter of the rectangular ring. The expansion mold is arranged on the inner circumference of the rectangular ring, and its outer diameter is equal to the inner diameter of the rectangular ring. In the initial state, no load is applied to either the expansion or contraction mold. Step S4: Alternate deformation treatment, following the process route of "expansion-pressure holding-unloading-rotating ring-resetting-diameter reduction-pressure holding-unloading" for n cycles; after each expansion or diameter reduction, select stress monitoring points on the ring to perform residual stress testing, and dynamically adjust the number of deformation cycles according to the relationship between the residual stress reduction rate η and the number of cycles n. Step S5: After deformation is complete, all molds are returned to their initial positions, and the workpiece is removed for cooling; Step S6: Inspect the geometry and residual stress level of the finally obtained C-shaped cross-section ring.

2. The precision manufacturing method for the high-precision, low-residual-stress C-shaped cross-section ring according to claim 1, characterized in that: In step S4, for workpieces with low residual stress levels, a process route of "bulging-diameter reduction-pressure holding-unloading-rotating ring-diameter reduction-bulging-cycle" is adopted.

3. The precision manufacturing method for the high-precision, low-residual-stress C-shaped cross-section ring according to claim 1, characterized in that: Step S4 specifically includes the following sub-steps: Step S41: Perform the bulging-holding-unloading-rotating ring process. The diameter reduction die keeps the outer diameter limit, the bulging die extrudes the inner wall of the ring blank to achieve local bulging, and after holding the pressure, unload and rotate the ring by 45°. Step S42: Mold reset, the bulging mold returns to the position before deformation in step S41, at this time both the bulging and shrinking molds are in an unloaded state; Step S43: Perform the diameter reduction-pressure holding-unloading process. The expansion mold keeps the inner diameter limit, the diameter reduction mold extrudes the outer wall of the ring blank inward to achieve local diameter reduction, and after pressure holding, unload and rotate the ring part by 45°. Step S44: The mold is reset, and the shrinking mold returns to the position before deformation in step S43. At this time, both the expansion and contraction molds are in an unloaded state. Step S45: Repeat steps S41 to S44, looping n times.

4. The precision manufacturing method for the high-precision, low-residual-stress C-shaped cross-section ring according to claim 3, characterized in that: In step S41, the amount of single bulging deformation δ is controlled between 0 and 2%, and in step S43, the amount of single diameter reduction deformation δ is controlled between 0 and 1.5%.

5. The precision manufacturing method for the high-precision, low-residual-stress C-shaped cross-section ring according to claim 3, characterized in that: In steps S41 and S43, the single-time reduction rate η of the residual stress equivalent value of the rectangular ring after rolling, compared with the single-time local deformation, satisfies the following relationship: 0.35~0.77(100δ / t0). 0.15 δ is the amount of deformation in a single operation, and t0 is the initial wall thickness of the rectangular ring blank.

6. The precision manufacturing method for the high-precision, low-residual-stress C-shaped cross-section ring according to claim 3, characterized in that: The number of cycles n is 2, 3, 4 or 5.

7. The precision manufacturing method for the high-precision, low-residual-stress C-shaped cross-section ring according to claim 1, characterized in that: In step S3, the rectangular ring blank needs to be heated to a temperature 50-100°C below the recrystallization temperature, and then kept at that temperature before being loaded into the equipment.

8. The precision manufacturing method of the high-precision, low-residual-stress C-shaped cross-section ring according to claim 1, characterized in that: The bulging mold and the reducing mold are each composed of 8 or 12 fan-shaped modules, and the combined structure formed by them matches the inner and outer contours of the rectangular ring blank.

9. The precision manufacturing method of the high-precision, low-residual-stress C-shaped cross-section ring according to claim 1, characterized in that: The residual stress reduction rate η of the C-shaped cross-section ring obtained by this method is related to the number of cycles n according to the following formula: , where k is a material constant, εa and εb are the true plastic strains of bulging and shrinking, respectively, and α is the strain sensitivity coefficient.

10. The precision manufacturing method of the high-precision, low-residual-stress C-shaped cross-section ring according to claim 1, characterized in that: The C-shaped cross-section ring manufactured by this method has an actual geometric dimension error of no more than 0.1% compared with the target dimension, and the residual stress is reduced by 60% to 90% compared with the rolled rectangular ring blank.

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