Precise forming method for large-specification ribbed shell section

Abstract

The invention relates to the technical field of precision plastic forming manufacturing, in particular to a large-specification ribbed shell section precision forming method which comprises the steps that a rectangular ring blank is prepared, specifically, the rectangular ring blank is prepared through multi-direction forging cogging, trestle reaming, rectangular ring rolling and wagon turning; in-mold forging rolling composite preforming is conducted, specifically, an L-shaped annular mold and a pre-rolling core roller with a groove are adopted for restraining ring rolling of the rectangular ring blank, and a prefabricated blank is obtained; the prefabricated blank is provided with a pre-formed middle inner ring rib and a pre-formed bottom inner ring rib; and in-mold forging and rolling composite final forming: carrying out constraint ring rolling on the prefabricated blank by adopting an in-mold constraint ring rolling and in-mold forging and rolling composite forming mode of a final rolling core roller with a resistance groove, so as to obtain a precision forming part with a ribbed shell section. The method is high in forming precision and high in material utilization rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of precision plastic forming manufacturing, in particular to a precision forming method for large-scale shell segment with ribs. BACKGROUND

[0002] The shell segment is a key load-bearing component of weapon equipment. In order to meet the development requirements of lightweight, high performance and high reliability of weapon equipment, the shell segment develops towards large diameter, thin wall, integration and complexity, and is usually composed of high rib end frame, thin wall shell and internal rectangular grid ribs to meet the requirements of complex service load. The material is usually light alloy such as aluminum magnesium.

[0003] At present, the shell segment of weapon equipment is mainly manufactured by reverse extrusion, ring rolling, spinning and other methods to form a straight cylinder / cone cylinder + machining mode, which has problems such as serious damage to the flow line of the component, low overall performance and poor uniformity, low material utilization rate, long processing cycle and so on.

[0004] The existing single forming technologies such as reverse extrusion, ring rolling and spinning are difficult to realize near-net plastic forming manufacturing of large-scale shell segment with ribs. Reverse extrusion is suitable for forming and manufacturing of medium and small scale straight cylinder / cone cylinder shell segment, and has large forming load and high demolding difficulty, which is difficult to be used for forming and manufacturing of large-scale shell segment with ribs, and difficult to realize large height-to-thickness ratio ring forming. Ring rolling is suitable for overall forming manufacturing of large-scale shell segment. Due to the rotary forming mode, the difference of metal flow in each direction is large, the forming stability and shape size precision of large-scale shell segment with ribs are difficult to control, it is usually used for simple symmetrical structure, and the material utilization rate is usually only 7%. Spinning is suitable for overall forming manufacturing of thin-walled shell segment. Due to the point-by-point forming mode, the forming load is small, the filling capacity is weak, and it is difficult to realize large height-to-thickness ratio ring forming. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the deficiencies and defects mentioned in the above background technology, and to provide a precision forming method for large-scale shell segment with ribs, which has high forming precision and high material utilization rate. In order to solve the above technical problems, the technical scheme provided by the present application is as follows: A precision forming method for large-scale shell segment with ribs, comprising: Rectangular ring blank preparation: preparing a rectangular ring blank through multi-directional forging, mandrel expanding, rectangular ring rolling and car skin preparation; In-mold forging and rolling composite preforming: using an L-shaped ring die and a pre-rolling core roller with grooves to constrain the ring rolling of the rectangular ring blank to obtain a preformed blank; the preformed blank has an initial forming inner ring rib in the middle and an initial forming inner ring rib at the bottom; In-mold forging and rolling composite final forming: using the in-mold forging and rolling composite forming mode of in-mold constrained ring rolling and a final rolling core roller with resistance grooves to constrain the ring rolling of the preformed blank to obtain a shell segment with ribs.

[0006] In an embodiment, in the process of preparing the rectangular ring blank, the rectangular ring blank is heated to 480±5℃, and the rectangular ring blank is kept at the temperature for 4-6 hours, and the final forging temperature is above 380℃.

[0007] In an embodiment, in the process of the final forming of the forging-rolling composite, high-temperature forming is adopted, the mold and the preform are heated to a preset temperature, and after the preform is kept at the temperature, the preform is stably forged and rolled to form the shell segment with ribs under the constraint of the L-shaped ring mold and the final rolling core roll with resistance grooves.

[0008] In an embodiment, in the process of the preforming of the forging-rolling composite and the final forming of the forging-rolling composite, when demolding is needed, air cooling is performed first to separate the preform or the shell segment with ribs from the L-shaped ring mold and form a gap, and the preform or the shell segment with ribs is taken out as a whole along the axial direction.

[0009] In an embodiment, in the process of preparing the rectangular ring blank, the rectangular ring blank is heated to 480±5℃, and the rectangular ring blank is kept at the temperature for 4-6 hours, and the final forging temperature is above 380℃. The forging roughing includes: heating the cast blank to 480±5℃, and after keeping the cast blank at the temperature, performing multi-directional forging on the cast blank to obtain a solid cylindrical blank, and punching a hole in the center of the solid cylindrical blank to obtain a hollow cylindrical blank, and the final forging temperature is above 380℃. The horse frame hole expanding includes: heating the hollow cylindrical blank to 480±5℃, and after keeping the hollow cylindrical blank at the temperature, expanding the hole of the hollow cylindrical blank by the horse frame process to obtain a rectangular cross-section ring blank, and the final forging temperature is above 380℃. The rectangular ring rolling includes: heating the rectangular cross-section ring blank to 255±5℃, and after keeping the rectangular cross-section ring blank at the temperature, reducing the wall thickness and the height of the rectangular cross-section ring blank and increasing the diameter of the rectangular cross-section ring blank by the ring rolling process, and the final forging temperature is above 380℃. The wagon includes: machining the blank after the rectangular ring rolling to obtain a rectangular ring blank meeting the size requirements.

[0010] In an embodiment, in the process of the preforming of the forging-rolling composite, the rectangular ring blank is heated to 480±5℃, and the rectangular ring blank is kept at the temperature for 4-6 hours, the forming time is less than or equal to 10 minutes, and the final forging temperature is above 380℃.

[0011] In an embodiment, in the process of the final forming of the forging-rolling composite, the preform is heated to 480±5℃, and the preform is kept at the temperature for 2-4 hours, the forming time is less than or equal to 8 minutes, and the final forging temperature is above 380℃.

[0012] In an embodiment, the ribbed shell segment precision forming piece has a rib height thickness ratio > 3 and a rib height > 50 mm.

[0013] In an embodiment, the blank of the ribbed shell segment precision forming piece is an aluminum alloy.

[0014] Compared with the prior art, the present application has the following beneficial effects: through the constraint effect of the L-shaped ring die and the pre-rolling core roller with grooves, an open die forging section is formed, the outer diameter of the ribbed shell segment does not change during the forming process, the forging and rolling composite forming is realized, the cross section of the blank is rolled and formed, the cross section of the blank is die forged, and the complex structure ring forming is possible; the L-shaped ring die and the pre-rolling core roller with grooves are adopted, the axial rolling force is balanced by the pre-rolling core roller with grooves, the blank can directly fall on the bottom of the L-shaped ring die, and the forming stability of the complex thin-walled ribbed shell segment is improved; the L-shaped ring die is made of die steel, has a large wall thickness and heat capacity, the temperature of the thin-walled ribbed shell segment and its uniformity are improved through the temperature compensation of the ring die, and the material plasticity and the filling capacity of the complex component are improved; the in-die constrained ring rolling and the in-die forging composite forming mode of the final rolling core roller with resistance grooves are adopted, the up and down flow resistances on the cross section of the ribbed shell segment are regulated, the accurate control of the metal flow of the large-size ribbed shell segment is realized, the problem that the asymmetric structure is easy to flow upward and difficult to flow downward is solved, and it is beneficial to high rib filling; the near-net plastic forming of the large-size ribbed shell segment is realized, the precision after forming can reach ±1 mm, the material utilization is improved by more than 2 times, and the profile is close to the final part shape. The forging streamline is avoided to be damaged, the performance of the shell segment is improved, the machining removal amount is reduced by 70%, the material utilization is improved by more than 2 times, the machining cycle is shortened by 50%, meanwhile, the axial flow is sufficient, the axial performance is improved, and the problem of low axial performance usually faced in the conventional rectangular ring rolling process is solved.

[0015] The stepped surface of the L-shaped ring die matches the rib shape at the bottom of the product, can guide the metal to flow orderly at the initial stage of rolling, plays a role of local preforming, effectively ensures the filling fullness and profile clarity of the bottom rib, and improves the component quality; one die for two purposes, cost reduction and efficiency increase: the design realizes the sharing of the pre-rolling and final rolling ring dies. The same set of constraint ring die can complete the whole process from blank preforming to final finishing, saves the cost of a set of special die, greatly reduces the die changing time, and significantly reduces the comprehensive manufacturing cost. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0017] Figure 1Process flow chart of the precision forming method of the ribbed shell segment of an embodiment; Figure 2 Structure schematic diagram of the pre-rolling forming die of the ribbed shell segment of an embodiment; Figure 3 Structure schematic diagram of the finish-rolling forming die of the ribbed shell segment of an embodiment; Figure 4 Cross-sectional schematic diagram of the pre-rolling forming and finish-rolling forming die and the forged piece of the ribbed shell segment of an embodiment, wherein (a) is a cross-sectional schematic diagram before forming, (b) is a cross-sectional schematic diagram after pre-rolling forming, and (c) is a cross-sectional schematic diagram after finish-rolling forming; Figure 5 Schematic diagram of the near-net plastic forming of the forged piece of the ribbed shell segment of an embodiment, wherein (a) is a filling situation diagram after finish-rolling forming, and (b) is an equivalent strain diagram at the end of finish-rolling forming; Figure 6 Actual diagram of the near-net plastic forming of the forged piece of the ribbed shell segment of an embodiment, wherein (a) is a perspective view, and (b) is a cut surface side view of the forged piece; Figure 7 Schematic diagram of the rolling instability of the ribbed shell segment of the unconstrained die of Comparative Example 1; Figure 8 Schematic diagram of the near-net plastic forming of the forged piece of the ribbed shell segment without pre-rolling of Comparative Example 2, wherein (a) is a cross-sectional schematic diagram before rolling, and (b) is a cross-sectional schematic diagram after rolling forming; Figure 9 Schematic diagram of the near-net plastic forming of the forged piece of the ribbed shell segment with pre-rolled short ribs of Comparative Example 3, wherein (a) is a cross-sectional schematic diagram before pre-rolling, (b) is a cross-sectional schematic diagram before finish-rolling, and (c) is a cross-sectional schematic diagram after finish-rolling forming. DETAILED DESCRIPTION

[0018] In order to facilitate the understanding of the present application, the present application will be described in more detail and in a more complete, specific manner below in conjunction with the drawings of the specification and the preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0019] Unless otherwise defined, all the professional terms used below have the same meaning as generally understood by those skilled in the art. The professional terms used in the present application are only for the purpose of describing the specific embodiments and are not intended to limit the scope of protection of the present application.

[0020] Unless otherwise specified, various raw materials, reagents, instruments and equipment, etc. used in the present application can be purchased from the market or can be prepared by existing methods.

[0021] Please refer to Figures 1-9 The precision forming method of the large-scale ribbed shell segment of an embodiment comprises: S10, rectangular ring blank preparation: the rectangular ring blank is prepared by multi-directional forging, mandrel hole expansion, rectangular ring rolling and skinning.

[0022] Specifically, the forging breakdown includes: heating the casting blank to 480±5℃, after holding, the casting blank is subjected to multi-directional forging to obtain a solid cylindrical blank, a hole is punched in the center of the solid cylindrical blank to obtain a hollow cylindrical blank, and the final forging temperature is above 380℃. Preferably, the blanking burr of the casting blank is removed, and the surface of the ingot is uniformly coated with a release agent. Casting defects are eliminated by multi-directional forging of the casting blank. The blank of the ribbed shell segment precision formed part is an aluminum alloy, more preferably 2A14 aluminum alloy.

[0023] The mandrel hole expansion includes: heating the hollow cylindrical blank to 480±5℃, after holding, the hollow cylindrical blank is subjected to hole expansion by the mandrel process to obtain a rectangular cross-section ring blank, and the final forging temperature is above 380℃.

[0024] The rectangular ring rolling includes: heating the rectangular cross-section ring blank to 255±5℃, after holding, the wall thickness of the rectangular cross-section ring blank is reduced, the height is reduced, and the diameter is increased by the ring rolling process, and the final forging temperature is above 380℃.

[0025] The skinning includes: machining the blank after rectangular ring rolling to obtain a rectangular ring blank that meets the size requirements.

[0026] S20, in-die forging and rolling composite preforming: the rectangular ring blank is constrained by an L-shaped ring die and a pre-rolling core roller to obtain a preformed blank; the preformed blank has an initially formed middle inner ring rib and an initially formed bottom inner ring rib.

[0027] More specifically, during the in-die forging and rolling composite preforming, the rectangular ring blank is placed in the L-shaped ring die at room temperature, the L-shaped ring die is heated to the forging temperature, and then it is lifted out to the ring rolling machine. On the ring rolling machine, the ring die is rotated by the driving roller and the core roller is fed radially. By using the characteristics of the L-shaped ring die and the pre-rolling core roller, the outer diameter of the ring part remains unchanged during the later forming stage, and the blank cross-section is gradually filled into the cavity under the action of open die forging. The initially formed middle inner ring rib is 30-40% of the height of the finally formed middle inner ring rib, and the height of the initially formed bottom inner ring rib is 80-90% of the height of the finally formed bottom inner ring rib. The rectangular ring blank is pre-rolled by using a pre-rolling ring die, heated to obtain a ribbed shell segment preformed blank, which has a middle inner ring rib and a bottom inner ring rib, and the rib has a small height-thickness ratio, making the forming difficulty small. Large-scale ribbed shell segment precision formed parts refer to ribbed shell segment precision formed parts with a rib height-thickness ratio > 3 and a rib height > 50mm.

[0028] More specifically, in the in-die forging and rolling composite preforming, the rectangular ring blank is heated to 480±5℃, held for 4-6 hours, the forming time is ≤10min, and the final forging temperature is above 380℃.

[0029] Specifically, the pre-rolling forming die includes an outer ring die 20, a grooved pre-rolling core roller 30 matched with the outer ring die 20, a main roller 40, a guide roller 50 and a taper roller 60.

[0030] S30, the combined final forming of die forging and rolling: the preformed blank is subjected to combined forming of die constraint ring rolling and die forging with a resistance groove to obtain a precisely formed part with a shell segment.

[0031] More specifically, in the combined final forming of die forging and rolling, the die and the preformed blank are heated to a preset temperature by high-temperature forming. After the preformed blank is kept warm, the hot-forged blank with a thin-wall feature is always in a high-temperature state during the forming process under the high temperature of the preformed blank and the thermal compensation of the die. The combined final forming of the shell segment with ribs is realized by the constraint action of the L-shaped ring die and the final rolling core roller with a resistance groove.

[0032] More specifically, the preformed blank is heated to 480±5℃ and kept warm for 2-4 hours, and the forming time is ≤8min, and the final forging temperature is above 380℃.

[0033] Specifically, in the combined pre-forming of die forging and rolling and the combined final forming of die forging and rolling, when demolding is needed, air cooling is performed first to separate the preformed blank or the precisely formed part with a shell segment from the L-shaped ring die and form a gap. The preformed blank or the precisely formed part with a shell segment is taken out as a whole during demolding.

[0034] Preferably, the precisely formed part with a shell segment taken out is further machined. The single-side allowance of the precisely formed part with a shell segment is 6-8mm, 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%.

[0035] Specifically, the final rolling forming die includes an outer ring die 20, a grooved final rolling core roller 70 matched with the outer ring die 20, a main roller 40, a guide roller 50 and a taper roller 60.

[0036] The pre-rolling forming die and the final rolling forming die only differ in the pre-rolling core roller 30 and the final rolling core roller 70, and the other structures are shared.

[0037] Example 1 A forging and rolling combined precision forming method for a shell segment with ribs includes the following steps: Multi-directional forging breakdown: a 2A14 aluminum alloy ingot is heated to 480℃, the holding time is 20h, seven upsetting and six drawing, the single upsetting is 60%, and the final forging temperature is 380℃. The blanking burr of the ingot is removed, and the demolding agent is uniformly coated on the surface of the ingot. The casting defects are eliminated by multi-directional forging of the ingot.

[0038] Horse frame reaming: the blank billet is heated to 480℃ and kept for 4h, and the hollow cylindrical blank is reamed by horse frame process to obtain a rectangular cross-section ring blank, and the final forging temperature is 380℃.

[0039] Rectangular ring rolling: the rectangular cross-section ring blank is heated to 255℃ and kept for 3h, and the wall thickness of the rectangular cross-section ring blank is thinned, the height is reduced, and the diameter is increased by ring rolling process, and the final forging temperature is 380℃.

[0040] Carriage: the blank after rectangular ring rolling is machined to obtain a rectangular ring blank that meets the size requirements.

[0041] Die forging and rolling composite preforming: the carriage rectangular ring blank is placed on the bottom end frame of the pre-rolling ring die at room temperature, and the pre-rolling ring die is heated to 480℃ and kept for 4h, the forming time is 8min, the final forging temperature is 380℃, and the pre-rolling ring die is lifted out of the ring rolling machine for ring rolling. On the ring rolling machine, the pre-rolling ring die is driven by the driving roller to rotate, and the pre-rolling core roller is radially fed, so that the blank gradually fills the cavity, and a ribbed shell segment preform is obtained.

[0042] Die forging and rolling composite final forming: the pre-rolled ribbed shell segment preform is placed on the bottom end frame of the final rolling ring die at room temperature, and the final rolling ring die is heated to the forging temperature of 480℃ and kept for 2h, the forming time is 6min, the final forging temperature is 380℃, and the final rolling ring die is lifted out of the ring rolling machine for ring rolling. On the ring rolling machine, the final rolling ring die is driven by the driving roller to rotate, and the final rolling core roller is radially fed, so that the blank gradually fills the cavity, and the ribbed shell segment final rolling forging is formed. The ribbed shell segment final rolling 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).

[0043] The single-side allowance in the ribbed shell segment forming is 8mm, and the material utilization rate is about 16%. Compared with the existing rectangular ring rolling + mechanical 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%.

[0044] The core of the embodiment of the present application is to introduce a constraint ring die, which changes open or semi-open rolling into closed in-die forming, and fundamentally changes the stress of the workpiece and the material flow. It has the following advantages: 1. Three-dimensional global constraint: fundamentally eliminates instability. The constraint ring die provides the workpiece with radial, axial and circumferential rigid support, eliminates all "free areas", and makes the material unable to buckle. This completely eliminates the "saddle-shaped", "fish tail-shaped" radial distortion and "bell mouth" axial deformation, and ensures that the ring remains nearly perfect circular shape and regular cross section throughout the process. The rib is protected in the cavity and will not be twisted and tilted, so it is completely and accurately filled, and the profile is clear. 2. Controllable material flow, accurate forming. The cavity of the constraint ring die acts as a "negative die" to accurately guide the material flow. Under the action of rolling force, the material is limited in the die cavity for controllable "volume transfer", ensuring that the web is uniformly thinned and the rib is fully filled. This makes the product size and shape accuracy leap forward, with high cross section repeatability, and can achieve minimum machining allowance or even net forming, greatly improving material utilization. 3. Smooth rolling, improve process and equipment stability. The rigid cavity constraint ensures the stability of the workpiece geometry and uniform moment of inertia, fundamentally eliminating the violent vibration and noise caused by shape distortion. This makes the rolling process smooth, significantly reducing the impact load of the equipment. At the same time, the stable process provides a reliable environment for online measurement, making precise closed-loop control based on real-time feedback possible, and the control accuracy of key dimensions far exceeds that of unconstrained conditions.

[0045] Comparative Example 1: Unconstrained ring rolling Multi-directional forging breakdown: heat the 2A14 aluminum alloy casting blank to 480℃, and keep for 20h, seven upsetting and six drawing, single upsetting 60%, and final forging temperature 380℃. The casting blank is cut to remove the burr, and the surface of the casting ingot is evenly coated with a release agent. The casting defects are eliminated by multi-directional forging of the casting blank.

[0046] Horse frame hole expansion: heat the casting blank to 480℃, and keep for 4h, expand the hollow cylindrical blank by horse frame process to obtain a rectangular cross-section ring blank, and the final forging temperature is 380℃.

[0047] Rectangular ring rolling: heat the rectangular cross-section ring blank to 255℃, and keep for 3h, use ring rolling process to reduce the wall thickness and height of the rectangular cross-section ring blank, and increase the diameter, and the final forging temperature is 380℃.

[0048] Truck skin: machine the blank after rectangular ring rolling to obtain a rectangular ring blank that meets the size requirements.

[0049] Unconstrained ring rolling: the rectangular ring blank after the wagon is heated to 480℃, and the holding time is 4h, the forming time is 8min, the final forging temperature is 380℃, the rectangular ring blank is hung out to the ring rolling mill for ring rolling. On the ring rolling mill, the blank is gradually formed by the rotation of the driving roller and the radial feeding of the pre-rolling core roller, and the shell segment with ribs is obtained.

[0050] The core of unconstrained ring rolling is that the driving roller applies rotation and radial feeding motion, the core roller is a passive support, and the guide roller plays a centering role. For this special workpiece of thin-walled shell segment with ribs, this "open" rolling environment is unstable throughout the rolling under extreme conditions of high temperature and high pressure. The specific performance is as follows: 1. Radial instability: "saddle-shaped" and "fish tail-shaped" defects. Due to the insufficient radial stiffness of the thin-walled part, the free end part not in contact with the roller is bulged due to the buckling of the compressive stress under the action of the rolling force, forming a "saddle-shaped" with the middle concave and the ends convex, or a "fish tail-shaped" in the opposite direction. This leads to a serious deviation of the roundness of the ring piece and introduces harmful residual stress. 2. Axial instability: rib twisting and "bell mouth" deformation. The rib is prone to twisting, tilting and even collapsing under the axial component of the rolling force and the uneven flow of the material. Macroscopically, the entire shell segment section is unstable, changing from a rectangle to a "bell mouth" shape with one end large and the other end small. 3. Cross-sectional shape distortion: uneven rib height and uneven web thickness. Under the unconstrained state, the material flow is arbitrary, and it is difficult to be fully and uniformly extruded into the rib groove, resulting in uneven filling of the rib and uneven height. At the same time, the web produces stress concentration due to instability, resulting in local excessive thinning or material accumulation, leading to uneven thickness. 4. Process dynamic instability: vibration impact and size out of control. The geometric distortion of the ring piece causes uneven moment of inertia, resulting in strong vibration and noise, impacting the equipment. Vibration also causes the online measurement signal to be misaligned, causing the closed-loop control system to fail, ultimately causing the product size to be out of tolerance or being forced to increase the processing allowance, resulting in a very low finished product rate and high production cost.

[0051] Table of comparative analysis of example 1 and comparative example 1

[0052] Comparative example 2 The difference from example 1 is that the in-die forging and rolling composite preforming process is omitted, and the final rolling core roller is not provided with a resistance groove.

[0053] Result analysis: In the no-preforming process and the no-resistance groove final rolling core roller of Comparative Example 2, the metal mainly flows to the upper end free area due to the "minimum resistance law", resulting in serious deficiency of the bottom rib groove filling. Specifically, 1. Metal upward escape dominates. When using an equal-thickness cylindrical blank to directly form, in the no-preforming and no-resistance groove constrained ring die, although the workpiece is constrained, the material flow path is not optimized. The equal-thickness cylindrical blank (no preforming) is directly placed into the die. At this time, the gap between the blank and the die cavity (especially the rib groove part) is large, and the contact area is small. In the vertical ring rolling, the upper end of the workpiece is the weakest constraint area, and the resistance of the metal flowing in this direction is much smaller than that of filling the rib groove in the radial direction. Therefore, most of the plastic flow will choose to escape upward. 2. Poor rib filling, with the worst bottom rib filling: due to the longest flow path and the largest resistance, and the material is severely diverted, the height of the bottom rib is usually only 60%-80% of the design value, the profile is not clear, and the filling rate is extremely low. This defect directly weakens the structural stiffness and load-carrying capacity of the most marginal shell segment. The middle rib is not well filled: affected by the "siphon" effect of upward flow and insufficient initial blank thickness, its filling height and fullness are not up to standard, and the state is not uniform, there is a performance gradient, which becomes a potential fatigue crack initiation area. Over-thinning and flash at the upper end area: a large amount of metal gathers upward, causing the web at this area to be excessively thinned and forming a flash, which needs to be removed by subsequent mechanical processing, increasing the labor and material waste, causing material waste and demolding difficulty. 3. Part failure and process instability, based on the above factors, the final part has a ring shape but the rib function is lost. The insufficient rib height greatly reduces the structural stiffness and load-carrying capacity, and the risk of stress concentration is high. In order to fill it, the blank weight often needs to be increased, which in turn aggravates the flash and material waste, resulting in low material utilization. This process is extremely sensitive to parameter fluctuations, has low yield, and is difficult to achieve stable production.

[0054] Table of comparative analysis of Example 1 and Comparative Example 2

[0055] Comparative Example 3 The difference from the example is that the pre-rolling core roller in the pre-forming process is not provided with a pre-forming blank middle rib forming groove, and a protrusion is provided in the final rolling core roller.

[0056] In this comparative example 3, Figure 9 (a) in the figure shows the inner profile of the pre-rolling core roller for pre-rolling forming, Figure 9 (b) in the figure shows the pre-formed blank forming diagram. The pre-formed blank design is unreasonable: the initial height of the bottom rib is too low, only 60%-70% of the target height, and the root roundness is too large; the pre-formed blank has no any protrusion or thickening except the bottom area, still maintaining a simple cylindrical surface basically flush with the web, that is, the initial height of the middle rib is almost zero.

[0057] In the ring rolling process, the filling of multiple rows of ribs should be like a relay race with a smooth and orderly transfer. The defect design of Comparative Example 3 disrupts this order. The first bar of the bottom rib filling is weak: the short bottom rib has a small contact area with the die, resulting in large flow resistance, making it difficult to start effective filling at the beginning of rolling, and the subsequent growth power is insufficient. The second bar is interrupted: the middle rib area is completely flat, and filling needs to overcome a huge "activation energy barrier". Before the bottom rib can form effective extrusion, the middle area material falls into a "flow dead zone" due to insufficient radial pressure stress, and cannot fill the rib groove. Ultimately, the bottom rib is insufficient in height and the middle rib is severely underfilled. The height of the bottom rib can only reach 80-90% of the design value, and the top corner is too large, with unclear contours. The middle rib is severely underfilled: this is the most fatal defect, its height may be only 70% or less of the design value, the shape is blurred, and the upper half of the rib groove is mostly hollow.

[0058] Due to the discontinuity of the metal flow line, the above defects cause severe stress concentration at the rib root, and the grains in this area are coarse, which will seriously affect the fatigue performance and structural integrity of the part.

[0059] Comparison analysis table of Example 1 and Comparative Example 3

[0060] The above is only an embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation using the content of the present application specification and drawings, or direct or indirect application in other related technical fields, is also included in the patent protection scope of the present application.

Claims

1. A method of precision forming large scale ribbed shell segments, characterised in that, The application relates to a method for preparing a precision formed piece with a ribbed shell section. The method comprises the following steps: Rectangular ring blank preparation: preparing a rectangular ring blank through multi-directional forging, horse frame hole expanding, rectangular ring rolling and skinning; In-die forging-rolling composite preforming: adopting an L-shaped ring die and a pre-rolling core roller with grooves to constrain the rectangular ring blank to obtain a preformed blank; the preformed blank has an initial forming middle inner ring rib and an initial forming bottom inner ring rib; 2. The precision forming method of large-size ribbed shell segments according to claim 1, characterized in that, In-die forging-rolling composite final forming: adopting an in-die constrained ring rolling and a final rolling core roller with resistance grooves to constrain the preformed blank to obtain the precision formed piece with the ribbed shell section.

3. The precision forming method of large-size ribbed shell segments according to claim 1, characterized in that, In the in-die forging-rolling composite preforming, the rectangular ring blank is placed in the L-shaped ring die at room temperature, the L-shaped ring die is heated to a forging temperature, and then is hung out to a ring rolling machine; on the ring rolling machine, the L-shaped ring die is driven to rotate by a driving roller, the pre-rolling core roller is radially fed, the L-shaped ring die and the pre-rolling core roller are used for constraint, the outer diameter of the ring piece is unchanged in the later forming stage, the cross section of the rectangular ring blank is steadily filled into the cavity under the open die forging action, the initial forming middle inner ring rib of the preformed blank is 30-40% of the height of the final forming middle inner ring rib, and the height of the initial forming bottom inner ring rib is 80-90% of the height of the final forming bottom inner ring rib.

4. The precision forming method of large-size ribbed shell segments according to claim 1, characterized in that, In the in-die forging-rolling composite final forming, the die and the preformed blank are heated to a preset temperature, the preformed blank is kept warm, and then the preformed blank is stably forged and rolled to form the ribbed shell section under the high-temperature forming of the preformed blank and the heat compensation of the die.

5. The precision forming method of large-size ribbed shell segments according to claim 1, characterized in that, When demoulding is needed, the preformed blank or the precision formed piece with the ribbed shell section is first air-cooled to separate the preformed blank or the precision formed piece with the ribbed shell section from the L-shaped ring die and form a gap, and then the preformed blank or the precision formed piece with the ribbed shell section is integrally taken out along the axial direction. In the rectangular ring blank preparation, The forging blanking comprises the following steps: heating a casting blank to 480+ / -5 DEG C, keeping warm, and then multi-directionally forging the casting blank to obtain a solid cylindrical blank, punching a hole in the center of the solid cylindrical blank to obtain a hollow cylindrical blank, and final forging temperature being above 380 DEG C; The horse frame hole expanding comprises the following steps: heating the hollow cylindrical blank to 480+ / -5 DEG C, keeping warm, and then expanding the hole of the hollow cylindrical blank through a horse frame process to obtain a rectangular cross-section ring blank, and final forging temperature being above 380 DEG C; The rectangular ring rolling comprises the following steps: heating the rectangular cross-section ring blank to 255+ / -5 DEG C, keeping warm, and then adopting a ring rolling process to reduce the wall thickness, height and diameter of the rectangular cross-section ring blank, and final forging temperature being above 380 DEG C; 6. The precision forming method of large-size ribbed shell segments according to claim 1, characterized in that, The skinning comprises the following steps: machining the blank after the rectangular ring rolling to obtain a rectangular ring blank meeting the size requirements.

7. The precision forming method of large-size ribbed shell segments according to claim 1, characterized in that, In the in-die forging-rolling composite preforming, the rectangular ring blank is heated to 480+ / -5 DEG C, kept warm for 4-6 hours, the forming time is less than or equal to 10 minutes, and the final forging temperature is above 380 DEG C.

8. The precision forming method of large-size ribbed shell segments according to claim 1, characterized in that, In the in-die forging-rolling composite final preformed blank, the preformed blank is heated to 480+ / -5 DEG C, kept warm for 2-4 hours, the forming time is less than or equal to 8 minutes, and the final forging temperature is above 380 DEG C.

9. The precision forming method of large-size ribbed shell segments according to claim 1, characterized in that, The rib height thickness ratio of the precision formed piece with the ribbed shell section is greater than 3, and the rib height is greater than 50 mm. The blank of the precision formed piece with the ribbed shell section is an aluminum alloy.

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