A method for precision forming of large-scale ribbed shell segments

Abstract

The present application relates to the technical fields of precision plastic forming manufacturing, in particular to a precision forming method for large-scale ribbed shell segment, comprising: rectangular ring blank preparation: preparing a rectangular ring blank through multi-directional forging, mandrel expanding, rectangular ring rolling and skinning; in-die forging-rolling composite preforming: restraining the rectangular ring blank through L-shaped ring die and pre-rolling core roller with grooves to obtain a preformed blank; the preformed blank has an initial forming middle inner ring rib and an initial forming bottom inner ring rib; in-die forging-rolling composite final forming: restraining the preformed blank through in-die ring rolling and in-die forging-rolling composite forming mode of final rolling core roller with resistance groove to obtain a ribbed shell segment precision forming piece. The above method has high forming precision and high material utilization rate.

Description

Technical Field

[0001] This invention relates to the field of precision plastic forming manufacturing technology, specifically to a method for precision forming of large-size ribbed shell segments. Background Technology

[0002] Shell sections are critical load-bearing components of weapon systems. To meet the demands for lightweight, high-performance, and high-reliability development in weapon systems, shell sections are evolving towards larger diameters, thinner walls, integral designs, and greater complexity. They typically consist of highly ribbed end frames, thin-walled shells, and internal rectangular grid reinforcements to meet complex service load requirements. Materials are generally lightweight alloys such as aluminum and magnesium.

[0003] Currently, weapon and equipment shell sections are mainly manufactured by using methods such as reverse extrusion, ring rolling, and spinning to form straight / conical cylinders, followed by machining for integral forming. This method has problems such as severe damage to the flow lines of component forging, low overall performance and poor uniformity, low material utilization, and long processing cycles.

[0004] Existing single forming technologies such as reverse extrusion, ring rolling, and spinning are all insufficient for achieving near-net-shape plastic forming of large-scale ribbed shell sections. Reverse extrusion is suitable for forming small to medium-sized straight / conical shell sections, but it has a high forming load and is difficult to demold, making it unsuitable for forming large-scale ribbed shell sections and difficult to achieve high aspect ratio ring ribs. Ring rolling is suitable for forming large-scale shell sections integrally, but due to the rotary forming method, the metal flow varies greatly in all directions, making it difficult to accurately control the forming stability and shape and size accuracy of large-scale ribbed shell sections. It is usually used for simple symmetrical structures, and the material utilization rate is usually only 7%. Spinning is suitable for forming thin-walled shell sections integrally, but due to the point-by-point forming method, the forming load is small, the filling capacity is weak, and it cannot achieve high aspect ratio ring ribs. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the shortcomings and defects mentioned in the background art above, and to provide a precision forming method for large-size ribbed shell segments with high forming accuracy and high material utilization. To solve the above technical problem, the technical solution proposed by this invention is as follows:

[0006] A method for precision forming of large-size ribbed shell segments includes:

[0007] Rectangular ring billet preparation: Rectangular ring billets are prepared by multi-directional forging, frame reaming, rectangular ring rolling, and rolling mill.

[0008] In-mold forging and rolling composite preforming: A rectangular ring billet is constrained by an L-shaped ring die and a grooved pre-rolling core roll to obtain a preform; the preform has an inner ring rib in the middle of the initial forming and an inner ring rib at the bottom of the initial forming.

[0009] In-mold forging and rolling composite final forming: The preform is subjected to confined ring rolling and final rolling mandrel with resistance groove in-mold forging and rolling composite forming method to obtain a precision formed part with rib shell section by confined ring rolling.

[0010] In one embodiment, during in-die forging and rolling composite preforming, a rectangular ring blank is placed in an L-shaped ring die at room temperature. The L-shaped ring die is heated to the forging temperature and then lifted out to a ring mill. On the ring mill, the L-shaped ring die is rotated by a drive roller, and the pre-rolled core roller is fed radially. Utilizing the constraint effect of the L-shaped ring die and the pre-rolled core roller, the outer diameter of the ring remains unchanged in the later stage of forming. Under the action of open die forging, the cross section of the rectangular ring blank stably and gradually fills the cavity. The height of the inner ring rib in the middle of the initial forming of the preform is 30-40% of the height of the inner ring rib in the middle of the final forming, and the height of the inner ring rib at the bottom of the initial forming is 80-90% of the height of the inner ring rib at the bottom of the final forming.

[0011] In one embodiment, during the in-mold forging and rolling composite final forming, high-temperature forming is adopted. The mold and the preform are heated to a preset temperature. After the preform is kept warm, under the high temperature of the preform and the thermal compensation of the mold, the constraint effect of the L-shaped annular mold and the final rolling core roll with resistance groove is used to achieve stable forging and rolling composite final forming of the ribbed shell section.

[0012] In one embodiment, during the in-mold forging and rolling composite preforming and in-mold forging and rolling composite final forming, when demolding is required, air cooling is first performed to separate the preform or the precision formed part with ribbed shell section from the L-shaped ring mold and form a gap. During demolding, the preform or the precision formed part with ribbed shell section is taken out as a whole along the axial direction.

[0013] In one embodiment, during the preparation of the rectangular ring blank,

[0014] The forging process includes: heating the billet to 480±5℃, holding it at that temperature, and then forging the billet in multiple directions to obtain a solid cylindrical billet. A hole is punched in the center of the solid cylindrical billet to obtain a hollow cylindrical billet. The final forging temperature is above 380℃.

[0015] The process of expanding the hole using a frame includes: heating a hollow cylindrical billet to 480±5℃, holding it at that temperature, and then expanding the hole in the hollow cylindrical billet using a frame process to obtain a rectangular cross-section ring billet, with a final forging temperature of 380℃ or higher.

[0016] Rectangular ring rolling includes: heating a rectangular cross-section ring billet to 255±5℃, holding it at that temperature, and then using a ring rolling process to reduce the wall thickness, height, and diameter of the rectangular cross-section ring billet, with a final forging temperature of 380℃ or higher.

[0017] The process of rolling a car includes machining the billet after it has been rolled into a rectangular ring to obtain a rectangular ring billet that meets the dimensional requirements.

[0018] In one embodiment, during in-mold forging and rolling composite preforming, the rectangular ring billet is heated to 480±5℃ and held for 4~6 hours, with a forming time of ≤10min and a final forging temperature of 380℃ or higher.

[0019] In one embodiment, the in-mold forging and rolling composite preform is heated to 480±5℃, held for 2~4 hours, formed for ≤8min, and the final forging temperature is above 380℃.

[0020] In one embodiment, the rib height-to-thickness ratio of the precision-formed ribbed shell segment is >3, and the rib height is >50mm.

[0021] In one embodiment, the blank of the precision-formed part with ribbed shell section is an aluminum alloy.

[0022] Compared with the prior art, the beneficial effects of this invention are as follows: Through the constraint of the L-shaped annular die and the grooved pre-rolling mandrel, an open die forging section is formed. During the forming process, the outer diameter of the ribbed shell section remains unchanged, achieving a combined forging and rolling forming. The billet cross-section is rolled and then die-forged, providing the possibility for forming complex structural ring parts. Using the L-shaped annular die and the grooved pre-rolling mandrel, the axial rolling force is balanced by the grooved pre-rolling mandrel, allowing the billet to fall directly to the bottom of the L-shaped annular die, improving the forming stability of complex thin-walled ribbed shell sections. The L-shaped annular die is made of die steel with a specific wall thickness and heat capacity. The large-volume process, supplemented by temperature replenishment through annular molds, improves the temperature and uniformity of thin-walled ribbed shell sections, enhancing material plasticity and the ability to fill complex components. A composite forming method combining in-mold constrained ring rolling and in-mold forging with a final rolling mandrel featuring resistance grooves regulates the vertical flow resistance of the ribbed shell section, achieving precise control of metal rheology in large-size ribbed shell sections. This solves the problem of easy upward flow but difficult downward flow in asymmetric structures, facilitating high-rib filling. Near-net-shape plastic forming of large-size ribbed shell sections is achieved, with post-forming accuracy reaching ±1mm and material utilization more than doubled. Its contour closely approximates the final part shape. This process avoids forging flowline damage, improves shell section performance, reduces machining removal by 70%, increases material utilization more than doubled, and shortens the processing cycle by 50%. Simultaneously, it ensures sufficient axial flow and improved axial performance, solving the problem of low axial performance commonly encountered in conventional rectangular ring rolling processes.

[0023] The stepped surface of the L-shaped ring die matches the bottom rib shape of the product, guiding the orderly flow of metal in the early stages of rolling and playing a role in local pre-forming. This effectively ensures the fullness and clarity of the bottom rib filling, improving component quality. Dual-purpose die for cost reduction and efficiency improvement: This design allows for the sharing of pre-rolling and final rolling ring dies. A single set of constraint ring dies can complete the entire process from billet pre-forming to final finishing, eliminating the cost of a dedicated die and significantly reducing die changeover time, thus substantially lowering overall manufacturing costs. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a process flow diagram of a precision forming method for a ribbed shell segment according to one embodiment.

[0026] Figure 2 This is a schematic diagram of the pre-rolling forming die structure for a reinforced shell section according to one embodiment;

[0027] Figure 3 This is a schematic diagram of the final rolling forming die structure for a ribbed shell section according to one embodiment.

[0028] Figure 4 This is a schematic cross-sectional view of a pre-rolling and final rolling die and forging of a ribbed shell section according to one embodiment, wherein (a) is a schematic cross-sectional view before forming, (b) is a schematic cross-sectional view after pre-rolling, and (c) is a schematic cross-sectional view after final rolling.

[0029] Figure 5 This is a schematic diagram of near-net-net plastic forming of a ribbed shell section forging according to one embodiment, wherein (a) is a diagram of the filling situation after final rolling forming, and (b) is a diagram of the equivalent strain at the end of final rolling forming.

[0030] Figure 6 This is a physical drawing of a forging with ribbed shell section near net plastic forming according to one embodiment, wherein (a) is a perspective view and (b) is a side view of the cut surface of the forging;

[0031] Figure 7 This is a schematic diagram of the rolling instability of the ribbed shell section of the unconstrained die in Comparative Example 1.

[0032] Figure 8 This is a schematic diagram of near-net-net plastic forming of a shell section forging without pre-rolling ribs in Comparative Example 2, where (a) is a schematic diagram of the cross section before rolling begins, and (b) is a schematic diagram of the cross section after rolling.

[0033] Figure 9 This is a schematic diagram of the near-net-net plastic forming of the pre-rolled short rib shell section forging of Comparative Example 3, where (a) is a schematic diagram of the cross section before the start of pre-rolling, (b) is a schematic diagram of the cross section before the start of final rolling, and (c) is a schematic diagram of the cross section after final rolling. Detailed Implementation

[0034] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0035] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0036] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0037] Please see Figure 1-9 One embodiment of the method for precision forming of large-size ribbed shell segments includes:

[0038] S10. Rectangular ring billet preparation: Rectangular ring billets are prepared by multi-directional forging, frame reaming, rectangular ring rolling, and rolling mill.

[0039] Specifically, the forging process includes: heating the billet to 480±5℃, holding it at that temperature, and then performing multi-directional forging to obtain a solid cylindrical billet. A hole is then punched in the center of the solid cylindrical billet to obtain a hollow cylindrical billet. The final forging temperature is above 380℃. Preferably, burrs on the billet are removed, and a release agent is uniformly coated onto the surface of the ingot. Multi-directional forging of the billet eliminates casting defects. The billet for the precision-formed part with ribbed shell section is made of aluminum alloy, more preferably 2A14 aluminum alloy.

[0040] The process of expanding the hole using a frame includes: heating a hollow cylindrical billet to 480±5℃, holding it at that temperature, and then expanding the hole in the hollow cylindrical billet using a frame process to obtain a rectangular cross-section ring billet, with a final forging temperature of 380℃ or higher.

[0041] Rectangular ring rolling includes: heating a rectangular cross-section ring billet to 255±5℃, holding it at that temperature, and then using a ring rolling process to reduce the wall thickness, height, and diameter of the rectangular cross-section ring billet, with a final forging temperature of 380℃ or higher.

[0042] The process of rolling a car includes machining the billet after it has been rolled into a rectangular ring to obtain a rectangular ring billet that meets the dimensional requirements.

[0043] S20, In-mold forging and rolling composite preforming: Using an L-shaped ring die and a grooved pre-rolling core roll to constrain the ring rolling of a rectangular ring blank to obtain a preform blank; the preform blank has an inner ring rib in the middle of the initial forming and an inner ring rib at the bottom of the initial forming.

[0044] More specifically, in the in-die forging and rolling composite preforming process, a rectangular ring billet is placed in an L-shaped ring die at room temperature. The L-shaped ring die heats the billet to the forging temperature, and the billet is then lifted to a ring mill. On the ring mill, the ring die rotates via a drive roller, and the mandrel is radially fed. Utilizing the constraints of the L-shaped ring die and the pre-rolled mandrel, the outer diameter of the ring remains unchanged in the later stages of forming. The billet cross-section steadily fills the cavity under the action of open die forging. The height of the inner ring rib in the middle of the initial forming is 30-40% of the height of the inner ring rib in the final forming, and the height of the inner ring rib at the bottom of the initial forming is 80-90% of the height of the inner ring rib at the bottom of the final forming. The rectangular ring billet is pre-rolled using a pre-rolled ring die for constraint and heated to obtain a ribbed shell section preform forging. This ribbed shell section preform forging has an inner ring rib in the middle and an inner ring rib at the bottom. The ribs have a small height-to-thickness ratio, making forming easier. Large-size precision-formed shell sections with ribs refer to precision-formed shell sections with rib height-to-thickness ratio > 3 and rib height > 50mm.

[0045] More specifically, in the in-mold forging and rolling composite preforming process, the rectangular ring billet is heated to 480±5℃, held for 4~6 hours, formed for ≤10min, and the final forging temperature is above 380℃.

[0046] Specifically, the pre-rolling forming die includes an outer ring die 20, and a grooved pre-rolling core roll 30, a main roll 40, a guide roll 50, and a tapered roll 60 used in conjunction with the outer ring die 20.

[0047] S30, In-mold forging and rolling composite final forming: The preform is subjected to confined ring rolling and final rolling mandrel with resistance groove in-mold forging and rolling composite forming method to obtain a precision formed part with ribbed shell section.

[0048] More specifically, in the in-mold forging and rolling composite final forming, high-temperature forming is adopted. The mold and the preform are heated to the preset temperature. After the preform is kept at the temperature, under the high temperature of the preform and the thermal compensation of the mold, the hot forging billet with thin wall characteristics is always in a high temperature state during the forming process. Under the constraint of the L-shaped ring mold and the final rolling core roll with resistance groove, the stable forging and rolling composite final forming of the ribbed shell section is achieved.

[0049] More specifically, the in-mold forging and rolling composite final preform is heated to 480±5℃, held for 2~4 hours, formed for ≤8min, and the final forging temperature is above 380℃.

[0050] Specifically, during the in-mold forging and rolling composite preforming and in-mold forging and rolling composite final forming, when demolding is required, air cooling is first performed to separate the preform or the precision formed part with ribbed shell section from the L-shaped ring mold and form a gap. When demolding, the preform or the precision formed part with ribbed shell section is taken out as a whole along the axial direction.

[0051] Preferably, the process further includes machining the precision-formed ribbed shell segment. The single-sided allowance of the precision-formed ribbed shell segment is 6-8mm, and the material utilization rate is approximately 16%. Compared with the existing rectangular ring rolling + machining forming method, the material utilization rate is increased by more than 2 times, the processing cycle is shortened by 50%, and the manufacturing cost is reduced by more than 30%.

[0052] Specifically, the final rolling forming die includes an outer ring die 20, a final rolling core roll 70 with resistance grooves, a main roll 40, a guide roll 50, and a tapered roll 60 used in conjunction with the outer ring die 20.

[0053] The pre-roll forming die and the final rolling forming die are only different in the pre-rolling core roll 30 and the final rolling core roll 70; the other structures are the same.

[0054] Example 1

[0055] A method for precision forming of a ribbed shell segment by forging and rolling includes the following steps:

[0056] Multi-directional forging: The 2A14 aluminum alloy billet is heated to 480℃ and held for 20 hours, then subjected to seven upsetting and six drawing operations, with a single upsetting of 60%, and a final forging temperature of 380℃. Burrs on the billet are removed, and a release agent is evenly applied to the surface of the ingot. Multi-directional forging of the billet eliminates casting defects.

[0057] Hole reaming using a frame: The cast billet is heated to 480℃ and held for 4 hours. Holes are then reamed using a frame process to obtain a rectangular cross-section ring billet. The final forging temperature is 380℃.

[0058] Rectangular ring rolling: The rectangular cross-section ring billet is heated to 255℃ and held for 3 hours. The ring rolling process is used to reduce the wall thickness, height and diameter of the rectangular cross-section ring billet. The final forging temperature is 380℃.

[0059] Roller: The billet after rectangular ring rolling is machined to obtain a rectangular ring billet that meets the dimensional requirements.

[0060] In-mold forging and rolling composite preforming: The rectangular ring billet after the car body is placed on the bottom end frame of the pre-rolling ring die at room temperature. It is heated to 480°C with the pre-rolling ring die, held for 4 hours, formed for 8 minutes, and finally forged at 380°C. The pre-rolling ring die is then lifted out to the ring rolling mill for ring rolling. On the ring rolling mill, the pre-rolling ring die is rotated by the drive roller and the pre-rolling core roller is radially fed, so that the billet gradually fills the cavity to obtain the preformed billet with ribbed shell section.

[0061] In-die forging and rolling composite final forming: The pre-rolled ribbed shell section preform is placed on the bottom end frame of the final rolling annular die at room temperature. The die heats the preform to a forging temperature of 480℃, holds it at that temperature for 2 hours, and forms it for 6 minutes, reaching a final forging temperature of 380℃. The final rolling annular die is then lifted to a ring mill for ring rolling. On the ring mill, the drive rollers rotate the final rolling annular die, and the final rolling mandrel feeds radially, gradually filling the cavity with the preform, thus forming the ribbed shell section final rolled forging. The ribbed shell section final rolled forging has an inner ring rib in the middle position and a bottom inner ring rib with a large height-to-thickness ratio (rib height-to-thickness ratio > 3, rib height > 50mm).

[0062] The single-sided allowance in the forming of the ribbed shell section is 8mm, and the material utilization rate is about 16%. Compared with the existing forming method of rectangular ring rolling + machining, the material utilization rate is increased by more than 2 times, the processing cycle is shortened by 50%, and the manufacturing cost is reduced by more than 30%.

[0063] In the embodiments of this invention, the core lies in the introduction of a constrained ring die, transforming open and semi-open rolling into closed in-die forming, fundamentally changing the stress on the workpiece and the material flow. It has the following advantages: 1. Three-dimensional full-domain constraint: eliminating instability at its source. The constrained ring die provides radial, axial, and circumferential rigid support to the workpiece, eliminating all "free regions" and preventing material buckling. This completely eliminates radial distortions such as "saddle-shaped" and "fishtail-shaped" and axial deformations such as "trumpet-shaped" deformations, ensuring that the ring maintains a near-perfect circular shape and regular cross-section throughout the process. Ribs are protected within the cavity, preventing twisting and tilting, thus being completely and accurately filled with a clear outline. 2. Controllable material flow for precise forming. The cavity of the constrained ring die acts as a "passive mold," precisely guiding material flow. Under the action of rolling force, the material is confined within the die cavity for controllable "volume transfer," ensuring uniform web thinning and full filling of ribs. This enables a qualitative leap in product dimensional and shape accuracy, with extremely high cross-sectional repeatability, allowing for minimized machining allowances or even net-shape forming, significantly improving material utilization. 3. Smooth rolling, enhancing process and equipment stability. Rigid die cavity constraints ensure workpiece geometric stability and uniform rotational inertia, fundamentally eliminating severe vibrations and noise caused by shape distortion. This makes the rolling process smooth, significantly reducing equipment impact loads. Simultaneously, the stable process provides a reliable environment for online measurement, enabling precise closed-loop control based on real-time feedback, with control accuracy of critical dimensions far exceeding that of unconstrained conditions.

[0064] Comparative Example 1: Unconstrained Ring Rolling

[0065] Multi-directional forging: The 2A14 aluminum alloy billet is heated to 480℃ and held for 20 hours, then subjected to seven upsetting and six drawing operations, with a single upsetting of 60%, and a final forging temperature of 380℃. Burrs on the billet are removed, and a release agent is evenly applied to the surface of the ingot. Multi-directional forging of the billet eliminates casting defects.

[0066] Hole reaming using a frame: The cast billet is heated to 480℃ and held for 4 hours. Holes are then reamed using a frame process to obtain a rectangular cross-section ring billet. The final forging temperature is 380℃.

[0067] Rectangular ring rolling: The rectangular cross-section ring billet is heated to 255℃ and held for 3 hours. The ring rolling process is used to reduce the wall thickness, height and diameter of the rectangular cross-section ring billet. The final forging temperature is 380℃.

[0068] Roller: The billet after rectangular ring rolling is machined to obtain a rectangular ring billet that meets the dimensional requirements.

[0069] Unrestrained ring rolling: The rectangular ring billet behind the car body is heated to 480℃, held for 4 hours, formed for 8 minutes, and finally forged at 380℃. The rectangular ring billet is then lifted out to the ring rolling mill for ring rolling. On the ring rolling mill, the billet is gradually formed by the rotation of the drive roller and the radial feeding of the pre-rolling core roller, thus obtaining the forging with ribbed shell section.

[0070] In unrestrained ring rolling, the core roll applies rotational and radial feed motion, the mandrel acts as a passive support, and the guide roll provides centering. For thin-walled, ribbed shell sections, this "open" rolling environment leads to instability throughout the rolling process under extreme conditions of high temperature and pressure. Specifically, this manifests as follows: 1. Radial instability: "Saddle-shaped" and "fishtail-shaped" defects. Due to insufficient radial stiffness in thin-walled parts, under rolling force, the free ends not in contact with the rolls buckle due to compressive stress, forming a "saddle-shaped" (concave in the middle, convex at both ends) or, conversely, a "fishtail-shaped" (inverted). This results in severely out-of-tolerance roundness of the ring and introduces harmful residual stress. 2. Axial instability: Rib twisting and "trumpet-mouth" deformation. Under the axial component of the rolling force and uneven material flow, the ribs are prone to twisting, tilting, or even collapse. Macroscopically, the entire shell section becomes unstable, changing from a rectangle to a "trumpet-mouth" shape with one end larger than the other. 3. Cross-sectional shape distortion: Uneven rib height and web thickness, coupled with unrestrained material flow, make it difficult for the material to be fully and evenly squeezed into the rib grooves, resulting in incomplete filling and inconsistent rib heights. Simultaneously, stress concentration due to web instability leads to localized excessive thinning or material accumulation, resulting in uneven thickness. 4. Process dynamic instability: Vibration, impact, and dimensional instability. Geometric distortion of the ring component causes uneven rotational inertia, generating strong vibrations and noise, and impacting and damaging the equipment. Vibration also causes inaccurate online measurement signals, rendering the closed-loop control system ineffective, ultimately resulting in out-of-tolerance product dimensions or forced increases in machining allowances, leading to extremely low yield and high production costs.

[0071] Comparative analysis table of Example 1 and Comparative Example 1

[0072]

[0073] Comparative Example 2

[0074] The difference from Example 1 is that the in-mold forging and rolling composite preforming process is omitted, and the final core roll is not equipped with a resistance groove.

[0075] Results Analysis: In the constrained ring rolling process without preforming and without resistance grooves in Comparative Example 2, the metal mainly flows upward to the free zone due to the "law of least resistance," resulting in severe underfilling of the bottom rib grooves. Specifically: 1. Upward escape of metal dominates. When using uniform thickness cylindrical billets for direct forming, in the constrained ring die without preforming and without resistance grooves, although the workpiece is constrained, the material flow path is not optimized. The uniform thickness cylindrical billet (without preforming) is placed directly into the die. At this time, the gap between the billet and the die cavity (especially the rib groove part) is large and the contact surface is small. In vertical ring rolling, the upper end of the workpiece is the weakest constrained area, and the resistance of axial flow of metal in this direction is much less than that of radial filling of the rib grooves. Therefore, most of the plastic flow will choose to escape upward. 2. Poor rib filling, with the bottom rib filling being the worst: due to the longest flow path, the greatest resistance, and severe material diversion, the bottom rib height is usually only 60%-80% of the design value, the outline is unclear, and the filling rate is extremely low. This defect directly weakens the structural stiffness and load-bearing capacity of the outermost edge of the shell section. Poor filling of the intermediate ribs: Affected by the upward flow "siphon" effect and insufficient initial billet thickness, the filling height and fullness are substandard, and the state is uneven, exhibiting performance gradients and becoming potential fatigue crack initiation zones. Excessive thinning and flash in the upper region: The large amount of metal accumulating upwards causes excessive thinning of the web in this region, forming flash, which needs to be removed by subsequent machining, increasing time and material waste, and causing material waste and demolding difficulties. 3. Part failure and process instability: Based on the above factors, although the final part has a ring shape, the rib function is lost. Insufficient rib height significantly reduces structural stiffness and load-bearing capacity, resulting in a high risk of stress concentration. To barely fill the gaps, the billet weight often needs to be increased, which in turn exacerbates flash and material waste, leading to low material utilization. This process is extremely sensitive to parameter fluctuations, has a low yield, and is difficult to achieve stable production.

[0076] Comparative analysis table of Example 1 and Comparative Example 2

[0077]

[0078] Comparative Example 3

[0079] The difference from the embodiment is that the pre-rolling core roll in the pre-forming process does not have a pre-forming blank intermediate rib forming groove, and the final rolling core roll has a protrusion in the middle.

[0080] In Comparative Example 3, Figure 9 Image (a) shows the inner contour of the pre-rolled mandrel as it is pre-rolled. Figure 9(b) shows the preform forming diagram. The preform design is unreasonable: the initial height of its bottom rib is too low, only 60%-70% of the target height, and the root fillet is too large; the preform has no protrusions or thickenings except in the bottom area, and still maintains a simple cylindrical surface that is basically flush with the web, that is, the initial height of the middle rib is almost zero.

[0081] In the ring rolling process, the filling of multiple rows of ribs should ideally resemble a relay race, with a sequential and smooth progression. The defective design in Comparative Example 3 disrupts this sequence. The first pass of bottom rib filling is weak: the excessively short bottom ribs have a small contact area with the die, resulting in high flow resistance and difficulty in initiating effective filling in the early stages of rolling, leading to insufficient subsequent growth momentum. The second pass is interrupted: because the middle rib area is completely flat, filling requires overcoming a significant "starting energy barrier." Before the bottom ribs can form effective extrusion, the material in the middle area falls into a "flow dead zone" due to insufficient radial compressive stress, unable to fill the rib grooves. This ultimately results in insufficient bottom rib height and severely incomplete filling of the middle ribs. The bottom rib height only reaches 80%-90% of the design value, with excessively large top radii and unclear outlines. Severely incomplete filling of the middle ribs: This is the most fatal defect; their height may be only 70% or lower of the design value, with blurred shapes and the upper half of the rib grooves mostly being cavities.

[0082] Due to the discontinuity of the metal flow lines, the above-mentioned defects cause severe stress concentration at the root of the rib, and the grains in this area are coarse, which will seriously affect the fatigue performance and structural integrity of the part.

[0083] Comparative analysis table of Example 1 and Comparative Example 3

[0084]

[0085] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method of precision forming large scale ribbed shell segments, characterised in that, include: Rectangular ring billet preparation: Rectangular ring billets are prepared by multi-directional forging, frame reaming, rectangular ring rolling, and rolling mill. In-die forging and rolling composite preforming: An L-shaped annular die and a grooved pre-rolling mandrel are used to constrain the ring rolling of a rectangular ring billet to obtain a preformed billet. The preformed billet has an inner ring rib in the middle of the initial forming and an inner ring rib at the bottom of the initial forming. The in-die forging and rolling composite preforming uses a pre-rolling forming die, which includes an L-shaped annular die, a grooved pre-rolling mandrel, a main roll, a guide roll, and a tapered roll used in conjunction with the L-shaped annular die. The stepped surface of the L-shaped annular die matches the shape of the bottom rib of the product, guiding the orderly flow of metal in the early stage of rolling and playing a local preforming role. This effectively ensures the fullness of the bottom rib filling and the clarity of the outline, improving the quality of the component. The pre-rolling forming die and the final rolling forming die are only different in terms of the pre-rolling mandrel and the final rolling mandrel, while the other structures are shared. In-dip forging and rolling composite final forming: In-dip forging and rolling composite forming method is used to constrain the preform into a ring, obtaining a precision formed part with a ribbed shell section. During in-dip forging and rolling composite preforming, the rectangular ring blank is placed in an L-shaped ring die at room temperature and heated to the forging temperature by the L-shaped ring die. It is then lifted out to the ring rolling mill. On the ring rolling mill, the L-shaped ring die is rotated by the drive roller and the pre-rolled mandrel is fed radially. With the constraint of the L-shaped ring die and the pre-rolled mandrel, the outer diameter of the ring part remains unchanged in the later stage of forming. The cross section of the rectangular ring blank stably and gradually fills the cavity under the action of open die forging. The height of the inner ring rib in the middle of the initial forming of the preform is 30-40% of the height of the inner ring rib in the middle of the final forming, and the height of the inner ring rib at the bottom of the initial forming is 80-90% of the height of the inner ring rib at the bottom of the final forming. In the in-dip forging and rolling composite final forming, high-temperature forming is adopted. The mold and preform are heated to the preset temperature. After the preform is held at the temperature, under the high temperature of the preform and the thermal compensation of the mold, the constraint effect of the L-shaped ring mold and the final rolling core roll with resistance groove is used to achieve stable forging and rolling composite final forming of the ribbed shell section. The preform of the in-dip forging and rolling composite final is heated to 480±5℃, held at the temperature for 2~4 hours, the forming time is ≤8min, and the final forging temperature is above 380℃. After forming, the accuracy can reach ±1mm, and the material utilization is more than twice that of the forming method of rectangular ring rolling combined with machining; its outline is close to the shape of the final part; the rib height-to-thickness ratio of the precision formed part with ribs is >3 and the rib height is >50mm.

2. The method for precision forming of large-size ribbed shell segments according to claim 1, characterized in that, When the in-mold forging and rolling composite preforming and in-mold forging and rolling composite final forming are required to demold, air cooling is first performed to separate the preform or the precision formed part with ribbed shell section from the L-shaped ring mold and form a gap. When demolding, the preform or the precision formed part with ribbed shell section is taken out as a whole along the axial direction.

3. The method for precision forming of large-size ribbed shell segments according to claim 1, characterized in that, In the preparation of rectangular ring blanks, The forging process includes: heating the billet to 480±5℃, holding it at that temperature, and then forging the billet in multiple directions to obtain a solid cylindrical billet. A hole is punched in the center of the solid cylindrical billet to obtain a hollow cylindrical billet. The final forging temperature is above 380℃. The process of expanding the hole using a frame includes: heating a hollow cylindrical billet to 480±5℃, holding it at that temperature, and then expanding the hole in the hollow cylindrical billet using a frame process to obtain a rectangular cross-section ring billet, with a final forging temperature of 380℃ or higher. Rectangular ring rolling includes: heating a rectangular cross-section ring billet to 255±5℃, holding it at that temperature, and then using a ring rolling process to reduce the wall thickness, height, and diameter of the rectangular cross-section ring billet, with a final forging temperature of 380℃ or higher. The process of rolling a car includes machining the billet after it has been rolled into a rectangular ring to obtain a rectangular ring billet that meets the dimensional requirements.

4. The method for precision forming of large-size ribbed shell segments according to claim 1, characterized in that, In the in-mold forging and rolling composite preforming process, when the rectangular ring billet is heated to 480±5℃ and held for 4~6 minutes, the forming time is ≤10 minutes and the final forging temperature is above 380℃.

5. The method for precision forming of large-size ribbed shell segments according to claim 1, characterized in that, The blank for the precision-formed part with ribbed shell section is an aluminum alloy.

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