A method for plastic forming of a large aspect ratio shell with linearly varying radial dimension

Abstract

The application provides a plastic forming design method for a large-length-diameter-ratio shell with linearly changed radial size, and belongs to the technical field of metal plastic forming. In view of the problems that a punch is prone to breakage in overall punch cold extrusion forming, and a center boss and an edge boss are difficult to be fully filled and prone to fold vortex defects in split punch forming, the bottom of a blank is divided into a center boss area, an edge boss area and a large-length-diameter-ratio wall area, a dynamic correlation model of volume transfer amount of each characteristic cross section and geometric parameters of the blank is established, based on the volume conservation constraint, the volume transfer amount of the large-length-diameter-ratio wall area is minimized as an optimization target, and the geometric parameters of the blank are solved. Through the cooperation of region decomposition, dynamic modeling and partition optimization, the change from experience trial and error to quantitative calculation of the blank design is realized, the three areas are filled in sequence and do not interfere with each other, the vortex and fold defects are fundamentally eliminated, and the maximum equivalent stress of the punch is reduced by about 26%.

Description

Technical Field

[0001] This application belongs to the field of metal plastic forming technology, specifically relating to a design method for plastic forming of shells with large aspect ratios and linearly varying radial dimensions. Background Technology

[0002] High-precision and high-efficiency manufacturing of large aspect ratio shells with linearly varying radial dimensions is a common requirement supporting the development of high-end equipment. Taking copper alloy shells as an example, they are currently mainly formed using cold extrusion and cold drawing processes. Because the bottom of the shell has a deep blind hole structure with straight walls or at a certain angle to the generatrix, if an integral punch cold extrusion forming method is used, the punch has a large load-bearing capacity and is prone to breakage, affecting the punch life and shell production efficiency.

[0003] Meanwhile, process tests were conducted on the shell using a split punch method. It was found that the bottom center boss and the side bosses were difficult to fill fully, resulting in material waste and increased load, and even affecting the geometry of the shell and causing product scrap. When the loading sequence and orientation of the split punch are inappropriate or the shell opening is closed during extrusion, defects such as folding, eddy currents, holes, and damage are easily introduced.

[0004] Therefore, the bottom structure of the shell blank needs to be designed and optimized. Due to the large deformation of the shell, it is necessary to master the coordinated process of shell deformation and heat treatment to improve the manufacturing accuracy and performance of the shell. Summary of the Invention

[0005] In view of this, this application provides a plastic forming design method for large aspect ratio shells with linearly varying radial dimensions, in order to solve the problems of easy breakage and short service life of punches when cold extruding large aspect ratio shells with integral punches, and the difficulty in filling the bottom center boss and side bosses with full shape when forming split punches, and the easy generation of defects such as folding and eddy currents.

[0006] To solve the above problems, the technical solution adopted in this application is as follows: In a first aspect, this application proposes a design method for a large aspect ratio shell blank with linearly varying radial dimensions. The bottom of the shell includes a central boss and side bosses. The method includes the following steps: Step 1: Based on the geometry of the target shell, the bottom of the blank is divided into a central boss region, a side boss region, and a large aspect ratio wall region, and the characteristic cross-sections representing material transfer in each region are determined; Step 2: A dynamic correlation model is established between the volume transfer amount of each characteristic cross-section and the geometric parameters of the blank during the forming process; Step 3: Based on the volume conservation constraint, the geometric parameters of the blank are solved with the minimization of the volume transfer amount of the large aspect ratio wall region as the optimization objective.

[0007] Preferably, in step 1, the characteristic cross-section includes a first cross-section representing material transfer in the central boss region, a second cross-section representing material transfer in the edge boss region, and a third cross-section representing material transfer in the high aspect ratio wall region.

[0008] Preferably, in step 2, the dynamic association model includes: (1) (2) (3) (4) Where R1 is the distance from the endpoint of the first section to the central axis, R 2a R 2b R represents the distance from the two endpoints of the second section to the central axis. 2m R1 is the distance from the bisector of the second section to the central axis; R2 and R4 are the distances from the two ends of the third section to the central axis, respectively; a is the angle between the second section and the horizontal plane; H0 is the distance between the two ends of the blank corresponding to the contact surfaces of the punches; v0 is the punch loading speed; v1, v2, and v3 are the instantaneous velocities in the Y direction of the first section, the X direction of the second section, and the Y direction of the third section, respectively; Δt is the unit time of deformation; and t is the forming time.

[0009] Preferably, in step 3, the solution process includes: establishing a correspondence between the instantaneous velocity of each feature section and time according to the time stage of the forming process; The partitioning includes: the first stage of filling the central boss area, the second stage of filling the side boss areas, the third stage of filling the large aspect ratio wall area, and the fourth stage of making the skin thickness reach the design value.

[0010] Preferably, in step 3, the optimization objective is achieved through the following objective function: (5) (6) (7) (8) The first equation represents the volume conservation constraint for the first stage [0, t1], where the total volume of the billet transfer is equal to the sum of the transfer volumes of the three regions: the first section, the second section, and the third section, ensuring that the edge boss region is basically filled in this stage. The second equation represents the volume conservation constraint for the second stage [t1, t2], ensuring that the central boss region is basically filled in this stage. The third equation represents the optimization objective for the third stage [t2, t3], minimizing the volume transfer amount of the third section to ensure that the material flow in the large aspect ratio wall opening region is most stable during the filling process in this stage. The fourth equation represents the total volume transfer amount of the billet within a unit time Δt.

[0011] Preferably, the obtained geometric parameters of the billet include: the angle α between the second cross section and the horizontal plane, and the distance R from the two endpoints of the second cross section to the central axis. 2a and R 2b The distance H0 between the two ends of the blank corresponding to the contact surfaces of the punches.

[0012] Preferably, the design method uses the absence of eddy currents and folding defects as the verification criteria for forming quality, and the minimum forming load of the punch as the engineering effect of the optimization objective. The engineering effect is naturally achieved by minimizing the volume transfer amount of the large aspect ratio wall region to obtain the optimal billet geometry parameters.

[0013] Secondly, this application also proposes a forming process for a shell with a large aspect ratio whose radial dimensions change linearly. One side of the bottom skin of the shell includes a central boss and an edge boss, and the other side includes a wall with a large aspect ratio whose radial dimensions change linearly. The blank is obtained using the design method described in the first aspect. The forming process includes the following steps: Shaping step: The blank is placed in the mold cavity. The first punch is stationary, and the second punch moves downward to cause plastic deformation of the blank until the geometry of the central boss area, the edge boss area, and the wall area meets the design requirements; Thickness setting step: The first punch and the second punch move downward synchronously and at the same speed until the thickness of the bottom skin reaches the design value.

[0014] Preferably, before forming, the contour of the first punch fits into the corresponding mating surface of the blank without interference, and the contour of the second punch fits into the corresponding mating surface of the blank without interference.

[0015] Preferably, in the shaping step, the second punch moves downward at a speed of 70-90 mm / s.

[0016] Preferably, in the thickness determination step, the design thickness of the bottom skin is 0.7-1.5 times the wall thickness.

[0017] Thirdly, this application also proposes a shell with a large aspect ratio whose radial dimensions change linearly, obtained by processing a blank using the shell forming process described in the second aspect and / or by processing a blank designed using the design method described in the first aspect. The shell with a large aspect ratio whose radial dimensions change linearly includes a straight-walled shell and a sloping-walled shell. The central boss has an arc shape, and the side bosses have sloping shapes.

[0018] In summary, due to the adoption of the above technical solution, the beneficial effects of this application are: This application decomposes complex forming problems into controllable units through region division and characteristic section determination, providing a physical basis for establishing a dynamic correlation model. The dynamic correlation model couples the billet geometric parameters with material flow in real time, making the optimization objective function computable. The zonal velocity characterization and the four-stage objective function work together to achieve precise temporal control of material flow, ensuring that the edge bosses, center bosses, and wall openings are filled sequentially and without interference. The optimal billet parameters obtained by optimization minimize the volume transfer of the third section, fundamentally suppressing material flow turbulence and eliminating eddies and folding defects. The optimal billet parameters work in conjunction with the two-step forming process of shaping and thickness determination, with the first punch stationary and the second punch moving independently. The current geometric shape precision control and synchronous movement of the two punches achieve precise skin thickness, and their cooperation reduces the maximum equivalent stress of the punch from 539MPa to 399MPa. The synergistic effect of heat treatment annealing and cold extrusion deformation ensures uniform deformation by achieving a grain size of less than 45μm after annealing. After stress-relief annealing, the tensile strength is ≥300MPa and the elongation is ≥40%, achieving a balance between high-precision forming and excellent mechanical properties. In this synergistic mechanism, design method optimization, forming process control, and heat treatment microstructure regulation are mutually supportive and indispensable: without optimal billet parameters, the process cannot eliminate defects; without a two-step forming strategy, die life cannot be guaranteed; and without heat treatment synergy, mechanical properties cannot meet standards. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application 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 only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1-1 The geometry of the shell blank; Figure 1-2 The final geometry of the shell; Figure 2 This is a schematic diagram showing the defect state of incomplete filling of the central boss and side bosses at the bottom of the shell when using a split punch forming process. Figure 3-1This is a schematic diagram of the folding defects that occur at the bottom of the housing when the loading sequence and orientation of the split punch are inappropriate or the opening of the housing is closed during extrusion. Figure 3-2 This is a schematic diagram of the eddy current defects generated inside the shell when the loading sequence and orientation of the split punch are inappropriate or the shell opening is closed during extrusion. Figure 4-1 This is a structural schematic diagram of the shell blank; the diagram shows the positions of the first section (section AB, representing material transfer in the central boss area), the second section (section CD, representing material transfer in the edge boss area), and the third section (section EF, representing material transfer in the high aspect ratio wall area); it also indicates the blank's geometric parameters: the angle α between the second section and the horizontal plane, and the distance R from the two endpoints of the second section to the central axis. 2a and R 2b The distance H0 between the two ends of the blank corresponding to the contact surfaces of the punches; Figure 4-2 A schematic diagram of the fit analysis of the shell extrusion molding die; Figure 5-1 A schematic diagram of a pre-designed shell blank with an angle α of 68° between the second cross section and the horizontal plane; Figure 5-2 To pre-design the folding and hole defects that appear in the edge boss area when the angle α between the second section of the shell blank and the horizontal plane is 68°; Figure 6-1 A schematic diagram of a pre-designed shell blank with an angle α of 88° between the second cross section and the horizontal plane; Figure 6-2 A schematic diagram of the defect state of incomplete filling in the central boss area when the angle α between the second section of the shell blank and the horizontal plane is 88°. Figure 7-1 This is a schematic diagram of billet transfer in the region of 15 nodes, including 6 analysis nodes (P1-P6) selected in the central boss region (first section) and 9 analysis nodes (P7-P15) selected in the side boss region (second section). Figure 7-2 A schematic diagram of billet transfer in a region of 20 nodes, with 10 nodes selected from P16 to P25 for the third section and 10 nodes selected from P26 to P35 for the shell wall region. Figure 7-3 A schematic diagram of billet transfer in the region of 10 nodes from P16 to P25 selected for the third section; Figure 8 The velocity distribution curves along the x-axis are for each node in the central boss region (first section) and the wall opening region (third section); Figure 9The velocity distribution curves along the x-axis are shown for each node in the edge boss region (second section). Figure 10 The velocity distribution curves of each node in the central boss region (first section) along the y-axis are shown. Figure 11 The velocity distribution curves along the y-axis are shown for each node in the opening region of the wall (third section). Figure 12 The velocity distribution curves of each node in the lower region of the wall along the y-axis are shown. Figure 13 The curves showing the relationship between the volume transfer at different times between the third section and the first section; Figure 14-1 This is a schematic diagram of a shell structure formed by extrusion molding of a shell using optimized billet geometry parameters. Figure 14-2 A magnified view of the filling effect of the central boss at the bottom of the shell after process optimization; Figure 14-3 This is a rendering showing the defect effect of the bottom edge boss of the housing after process optimization. Figure 14-4 A magnified view of the forming effect of the shell wall area after process optimization; Figure 14-5 To analyze the flatness of the connection area between the bottom of the shell and the wall after process optimization; Figure 14-6 Equivalent stress distribution cloud map during the shell forming process after process optimization.

[0020] Among them, 100 is the shell; 110 is the side boss; 120 is the central boss; 130 is the wall; and 140 is the skin. 210, First punch; 220, Second punch; 230, First die; 240, Second die. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The components of the embodiments of this application described and shown in the accompanying drawings can be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0024] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0025] In this application, unless otherwise expressly specified and limited, "above" or "below" a second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of a second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" a second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature. The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and do not limit the number of objects; for example, a first object can be one or more. Furthermore, "and / or" in the specification and claims indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0026] The high-precision and high-efficiency manufacturing of large aspect ratio shells with linearly varying radial dimensions is a common requirement supporting the development of high-end equipment. Taking copper alloy shells as an example, they are currently mainly formed using cold extrusion and cold drawing processes. Due to the deep blind hole structure with straight walls or a certain angle with the generatrix at the bottom of the shell, if the integral punch cold extrusion method is used, the punch has a large load-bearing capacity and is prone to breakage, affecting the punch life and shell production efficiency. At the same time, process tests on shells using the split punch method have found that the bottom center boss and side bosses are difficult to fill fully, resulting in material waste and increased load, and even affecting the geometry of the shell and causing product scrap. When the loading sequence and orientation of the split punch are inappropriate or the shell opening is closed during extrusion, defects such as folding, eddy currents, holes, and damage are easily introduced.

[0027] This application decomposes complex forming problems into controllable units through region division and characteristic section determination, providing a physical basis for establishing a dynamic correlation model. The dynamic correlation model couples the billet geometric parameters with material flow in real time, making the optimization objective function computable. The zonal velocity characterization and the four-stage objective function work together to achieve precise temporal control of material flow, ensuring that the edge bosses, center bosses, and wall openings are filled sequentially and without interference. The optimal billet parameters obtained by optimization minimize the volume transfer of the third section, fundamentally suppressing material flow turbulence and eliminating eddies and folding defects. The optimal billet parameters work in conjunction with the two-step forming process of shaping and thickness determination, with the first punch stationary and the second punch moving independently. The current geometric shape precision control and synchronous movement of the two punches achieve precise skin thickness control. The combination of these two techniques reduces the maximum equivalent stress of the punches from 539 MPa to 399 MPa. The synergistic effect of heat treatment annealing and cold extrusion deformation ensures uniform deformation by achieving a grain size of less than 45 μm after annealing. After stress-relief annealing, the tensile strength is ≥300 MPa and the elongation is ≥40%, achieving a balance between high-precision forming and excellent mechanical properties. In this synergistic mechanism, design method optimization, forming process control, and heat treatment microstructure regulation are mutually supportive and indispensable: without optimal billet parameters, the process cannot eliminate defects; without a two-step forming strategy, die life cannot be guaranteed; and without the synergistic effect of heat treatment, the mechanical properties cannot meet the standards.

[0028] The following is a reference to Figures 1 to 2. Figure 14-6 The technical solutions provided in this application will be described in detail through specific embodiments and application scenarios.

[0029] A shell with a large length-to-diameter ratio and linearly varying radial dimensions is made of H70 copper alloy. It has an outer diameter of φ11.92 mm, a total length of 48 mm, a straight outer wall, and an inner wall with a 1° inclination angle to the generatrix. The inner diameter at the opening is φ9.84 mm, and the inner diameter at the bottom is φ5.42 mm. The bottom of the shell includes a central boss and side bosses. The central boss has an arc shape, and the side bosses have a beveled shape. During cold extrusion forming, the shell with the above geometry and material presents challenges due to the deep blind hole structure at the bottom. If an integral die is used, the die has a high load-bearing capacity and is prone to breakage. If a split die is used, the central and side bosses are difficult to fill fully and are prone to defects such as folding and eddy currents.

[0030] Based on the geometry of the target shell, the bottom of the billet is divided into a central boss region, an edge boss region, and a high aspect ratio wall region, and characteristic sections representing material transfer in each region are determined. These characteristic sections include a first section representing material transfer in the central boss region, a second section representing material transfer in the edge boss region, and a third section representing material transfer in the high aspect ratio wall region. The distance R1 from the endpoint of the first section to the central axis is 1.2 mm; the distances from the two endpoints of the third section to the central axis are R3 = 5.96 mm and R4 = 4.92 mm, respectively. By dividing the region and determining the characteristic sections, the complex shell bottom forming problem is decomposed into three relatively independent material flow problems, facilitating the establishment of separate mathematical models for precise control.

[0031] Establish a dynamic correlation model between the volume transfer amount of each of the aforementioned feature sections and the geometric parameters of the billet during the forming process: (1) (2) (3) (4) Where R1 is the distance from the endpoint of the first section to the central axis, R 2a R 2b R represents the distance from the two endpoints of the second section to the central axis. 2m R1 is the distance from the bisector of the second section to the central axis; R2 and R3 are the distances from the two endpoints of the third section to the central axis, respectively; a is the angle between the second section and the horizontal plane; H0 is the distance between the two ends of the blank corresponding to the contact surfaces of the punches; v0 is the punch loading speed; v1, v2, and v3 are the instantaneous velocities in the Y direction of the first section, the X direction of the second section, and the Y direction of the third section, respectively; Δt is the unit time of deformation; and t is the forming time. Through the above dynamic correlation model, the geometric parameters of the blank (a, R4, ..., R5) are... 2a R 2b The model (H0) is linked in real time with the material flow during the forming process, realizing the transformation of billet design from experience-based trial and error to quantitative calculation.

[0032] Based on the time stages of the forming process, a corresponding relationship between the instantaneous velocity of each characteristic section and time is established by dividing the process into zones. The zones include: a first stage [0, t1] for filling the central boss area; a second stage [t1, t2] for filling the edge boss areas; a third stage [t2, t3] for filling the high aspect ratio wall areas; and a fourth stage [t3, t4] for achieving the designed thickness of the connecting skin. Specifically, the first stage is [0, 0.00582s], i.e., steps 0-20; the second stage is (0.00582s, 0.00819s], i.e., steps 21-45; the third stage is (0.00819s, 0.00926s], i.e., steps 46-63; and the fourth stage is (0.00926s, 0.0107s], i.e., steps 64-77. By establishing the correspondence between velocity and time through these zones, precise control of the material flow sequence is achieved, ensuring that each area is filled sequentially without interference.

[0033] The optimization objective is achieved through the following objective function: (5) (6) (7) (8) The first equation represents the volume conservation constraint for the first stage [0, t1], where the total volume of the billet transfer is equal to the sum of the transfer volumes of the three regions: the first section, the second section, and the third section, ensuring that the edge boss region is basically filled in this stage. The second equation represents the volume conservation constraint for the second stage [t1, t2], ensuring that the central boss region is basically filled in this stage. The third equation represents the optimization objective for the third stage [t2, t3], minimizing the volume transfer amount of the third section to ensure the smoothest material flow during the filling process of the large aspect ratio wall opening region in this stage. The fourth equation represents the total volume transfer amount of the billet within a unit time Δt. Through iterative optimization of the above objective function, when the angle α between the second section of the shell billet and the horizontal plane is 83.1°, and the distance R from the two ends of the second section to the central axis is... 2a 3.36mm, R 2b When the diameter is 2.90mm and the distance H0 between the two ends of the blank corresponding to the contact surfaces of the punches is 3.83mm, V3 has a minimum value of 28.49mm. 3 .

[0034] The design method uses the absence of eddy currents and folding defects as the verification criteria for forming quality, and the minimum forming load of the punch as the engineering effect of the optimization objective. This engineering effect is naturally achieved by minimizing the volume transfer in the large aspect ratio wall region to obtain the optimal billet geometry parameters. After adopting the above optimization parameters, compared to the tendency for folding and hole defects to occur on the edge bosses when a=68°, and the maximum equivalent stress of the first punch being 539MPa and the central boss not being fully filled when a=88°, the optimized billet achieves coordinated filling in three regions.

[0035] The optimized blank is placed in the mold cavity. The first punch 210 remains stationary, while the second punch 220 moves downward along the Y-axis at a speed of 80 mm / s, causing plastic deformation of the blank until the geometry of the central boss area, the side boss area, and the wall area meets the design requirements. Before forming, the contour of the first punch 210 fits without interference with the corresponding mating surface of the blank, and the contour of the second punch 220 fits without interference with the corresponding mating surface of the blank. Through the shaping step of the first punch 210 remaining stationary and the second punch 220 moving independently, the geometric accuracy of the central boss 120, the side boss 110, and the wall 130 areas of the shell is ensured, avoiding the problem of the entire punch breaking due to excessive load.

[0036] The first punch 210 and the second punch 220 move downwards synchronously and at the same speed of 80 mm / s until the bottom skin thickness reaches the designed value of 1.23 mm. The designed thickness of the bottom skin 140 is 0.7-1.5 times the thickness of the wall 130, and in this embodiment it is 0.72-1.18 times. Through the synchronous and speed-driven thickness determination step, the designed thickness of the shell skin 140 is achieved, realizing a smooth transition between the bottom and the wall.

[0037] Using the above forming process, the three areas of the shell bottom center boss, side boss, and high aspect ratio wall are fully filled, the bottom and wall are flat, the flow is smooth, and there are no defects such as eddies or folds. The punch load is effectively reduced, and the maximum equivalent stress is reduced from 539MPa to 399MPa, a reduction of about 26%.

[0038] Before forming, the billet undergoes heat treatment annealing at 500-600℃ for 1 hour, resulting in a grain size of less than 45μm. After forming, stress-relief annealing is performed at a temperature below 200℃ for 3 hours, resulting in a shell tensile strength ≥300MPa and elongation ≥40%. Through a combined heat treatment process, the problem of controlling the microstructure and properties of the shell under large deformation was solved, achieving a balance between high-precision forming and excellent mechanical properties.

[0039] Region division and characteristic section determination decompose complex forming problems into controllable units, providing a physical basis for establishing a dynamic correlation model. The dynamic correlation model couples billet geometric parameters with material flow in real time, making the optimization objective function computable. The zonal velocity characterization and the four-stage objective function work together to achieve precise temporal control of material flow, ensuring that the edge bosses, center bosses, and wall openings are filled sequentially and without interference. The optimal billet parameters obtained by optimization minimize the volume transfer of the third section, fundamentally suppressing material flow turbulence and eliminating eddies and folding defects. The optimal billet parameters work together with the two-step forming process of shaping and thickness determination, with the first punch stationary and the second punch moving independently, achieving several... The precise control of shape accuracy and the synchronous movement of the two punches ensure accurate achievement of the skin thickness. Their combined action reduces the maximum equivalent stress of the punches from 539 MPa to 399 MPa. The synergistic effect of heat treatment annealing and cold extrusion deformation ensures uniform deformation by achieving a grain size of less than 45 μm after annealing. Stress-relief annealing results in tensile strength ≥300 MPa and elongation ≥40%, achieving a balance between high-precision forming and excellent mechanical properties. In this synergistic mechanism, design optimization, forming process control, and heat treatment microstructure regulation are mutually supportive and indispensable: without optimal billet parameters, the process cannot eliminate defects; without a two-step forming strategy, die life cannot be guaranteed; and without synergistic heat treatment, mechanical properties cannot meet standards.

[0040] Example 1 The final shape of the shell is shown in Figure 1. It is made of H70 copper alloy, with an outer diameter of φ11.92mm and a total length of 48mm. The outer diameter of the wall is a straight wall type, and the inner diameter of the wall has a 1° inclination angle with the generatrix. The inner diameter of the opening is φ9.84mm, and the inner diameter of the bottom is φ5.42mm. R... b =1.2mm, R e =4.92mm, R f =5.96mm. To improve mold life and prevent punch breakage during forming, the shell blank structure needs to be optimized (as shown in Figure 4). Specifically, this includes the angle α between the shell blank's CD section and the horizontal plane, and the distance R from the two ends of the CD section to the central axis. c and R d The distance H0 between the CF end face and the BD end face.

[0041] The extrusion process includes: first, designing the geometry of the shell blank; then, placing the shell blank in the mold cavity, with the first punch stationary and the second punch moving downwards to ensure the geometric accuracy of areas such as the central boss, side bosses, and walls of the shell; next, the first and second punches move downwards synchronously and at the same speed to achieve the designed thickness of the shell skin.

[0042] The shell blank geometry design process includes: First, the outer contours of the first punch 210, the second punch 220, the first die 230, and the second die 240 are fitted with the outer contours of the corresponding areas of the blank of the shell 100. Target filling areas are formed in the three areas of the central boss 120, the side boss 110, and the large length-to-diameter ratio wall 130, respectively. At the same time, the AB section (first section), the CD section (second section), and the EF section (third section) represent the unit area of ​​material transfer in the three areas, respectively.

[0043] Secondly, before forming, the first punch 210 contour BD surface is non-interferingly attached to the shell 100 blank BD surface, and the second punch 220 contour CF surface is non-interferingly attached to the shell blank CF surface; during forming, the second punch 230 applies a load to the blank along the Y-axis at a speed v0=80mm / s and promotes the plastic deformation of the blank.

[0044] Third, let's assume a time t during the plastic deformation process, where the unit time of deformation is Δt, and the volume transfer of section AB within that unit time Δt. The volume transfer of section EF within a unit time Δt The volume transfer of section CD within a unit time Δt The downward movement of the second punch promotes the volume transfer of the billet within a unit time Δt. ,in Here R b R c R d R e R f R represents the distances from the endpoints B, C, D, E, and F of sections AB, CD, and EF to the central axis, respectively. cd denoted by , where 'a' represents the distance from the bisector of section CD to the central axis; 'a' represents the angle between section CD and the horizontal plane; 'H0' represents the distance between the end faces of CF and BD; 'v0' represents the downward Y-axis velocity of the second punch loaded on the end face of the shell blank CF; and 'v' represents the velocity of the second punch loaded on the CF end face of the shell blank. ab v cd v ef These represent the instantaneous velocities in the Y direction at section AB, the X direction at section CD, and the Y direction at section EF, respectively.

[0045] First, the angle α between the cross section CD of the shell blank and the horizontal plane is pre-designed to be 68° and 88° respectively. When the angle α is 68°, the life of the first punch can be improved, but the height of the metal volume that needs to be transferred at the edge boss is longer, and defects such as folds and holes are prone to occur during filling of the edge boss area (as shown in Figure 5). When the angle α is 88°, the axial load on the first punch is larger, affecting the life of the first punch. At the same time, the material transfer to the shell opening is accelerated, which can easily cause incomplete filling of the central boss area (as shown in Figure 6).

[0046] Therefore, the initial design places the angle α between the cross section CD of the shell blank and the horizontal plane between 68° and 88°. According to the principle of equal volume, i.e., the total volume V of the blank transfer... 总 =V 1区 +V 2区 +V 3区 (As shown in Figure 7), regions V1, V2, and V3 represent the transfer amounts in the three regions: the edge boss, the central boss, and the opening of the wall with a large aspect ratio, respectively, thus initially obtaining the range of height H0. Simultaneously, analysis is performed at nodes P1-P6 in section AB, nodes P7-P15 in section CD, nodes P16-P25 in section EF, and nodes P26-P35 in the shell wall region (as shown in Figure 7). It can be observed that the velocity along the x-axis is very small, close to zero, in the central boss region (e.g., section AB), the wall region, and the opening region (e.g., section EF). Figure 8 The x-axis velocity of the nodes at the CD section in the edge boss region decreases from the CF loading surface downwards (e.g., Figure 9 This is mainly due to the decrease in the instantaneous height H0 of the billet.

[0047] In the central boss region (e.g., section AB), the wall and opening regions (e.g., section EF), the velocities of each node along the y-axis are basically the same (e.g. Figure 10 , 11 (12), indicating that the average velocity of the cross-section nodes can be used for analysis.

[0048] Meanwhile, in the first stage: from time 0 to t1 [0, 0.00582s], i.e., 0-20 steps, region 1 is basically filled, corresponding to the velocity v. ab1 v cd1 v ef1 Second stage: From time t1 to t2 (0.00582s, 0.00819s), i.e., steps 21-45, region 2 is basically filled, corresponding to velocity v. ab2 v cd2 v ef2 The third stage: From time t2 to t3, [0.00819s, 0.00926s], i.e., steps 46-63, region 3 is basically filled, corresponding to the velocity v. ab3 v cd3 v ef3 Fourth stage: From time t3 to t4 (0.00926s, 0.0107s), i.e., 64-77 steps, the skin thickness reaches the design requirement, corresponding to the speed v. ab4 v cd4 v ef4 This partitioning creates v ab v cd v ef The relationship between velocity and time t.

[0049] by , , Using V as the objective function, the values ​​at different times are calculated. AB V EF The interrelationship of volume conversion (e.g.) Figure 13 Then iteratively optimize V. CD Volume conversion amount, when the angle α between the shell blank CD section and the horizontal plane is 83.1°, and the distance R from the two ends of the CD section to the central axis. c 3.36mm, R d When the diameter is 2.90mm and the distance H0 between the CF end face and the BD end face is 3.83mm, V EF The minimum value is 28.49 mm. 3 .

[0050] Next, the first and second punches move downwards synchronously at a speed of 80 mm / s, reaching a thickness of 1.23 mm including the skin, which is approximately 0.72-1.18 of the shell wall thickness. The three areas of the shell bottom center boss, side boss, and large length-to-diameter ratio wall are fully filled, the bottom and wall are flat, the flow is smooth, and there are no defects such as eddies or folds (as shown in Figure 14). The punch load is effectively reduced, and the maximum equivalent stress is reduced from 539 MPa (as shown in Figure 6) to 399 MPa (as shown in Figure 14).

[0051] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0052] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0053] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0054] Furthermore, it should be noted that the scope of the methods and apparatus in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. In addition, features described with reference to certain examples may be combined in other examples.

Claims

1. A method for designing a large aspect ratio shell blank with linearly varying radial dimensions, wherein the bottom of the shell (100) includes a central boss (120) and an edge boss (110), characterized in that, Includes the following steps: Step 1: Based on the geometry of the target shell (100), the bottom of the billet is divided into a central boss area, an edge boss area, and a large aspect ratio wall area, and the characteristic cross sections representing material transfer in each area are determined. Step 2: Establish a dynamic correlation model between the volume transfer amount of each characteristic section and the geometric parameters of the billet during the forming process; Step 3: Based on the volume conservation constraint, with the optimization objective of minimizing the volume transfer in the large aspect ratio wall region, solve for the geometric parameters of the billet.

2. The design method according to claim 1, characterized in that, In step 1, the characteristic cross-sections include a first cross-section representing material transfer in the central boss region, a second cross-section representing material transfer in the edge boss region, and a third cross-section representing material transfer in the high aspect ratio wall region.

3. The design method according to claim 1 or 2, characterized in that, In step 2, the dynamic association model includes: ， ， ， ， Where R1 is the distance from the endpoint of the first section to the central axis, R 2a R 2b R represents the distance from the two endpoints of the second section to the central axis. 2m R1 is the distance from the bisector of the second section to the central axis, R2 and R4 are the distances from the two ends of the third section to the central axis, a is the angle between the second section and the horizontal plane, H0 is the distance between the two ends of the blank corresponding to the contact end faces of the punch, v0 is the punch loading speed, v1, v2, and v3 are the instantaneous velocities in the Y direction of the first section, the X direction of the second section, and the Y direction of the third section, respectively, Δt is the unit time of deformation, and t is the forming time.

4. The design method according to claim 1, characterized in that, In step 3, the solution process includes: establishing the correspondence between the instantaneous velocity of each feature section and time according to the time stage of the forming process; The partitioning includes: a first stage of filling the central boss area, a second stage of filling the side boss area, a third stage of filling the large aspect ratio wall area, and a fourth stage of making the thickness of the skin (140) reach the design value.

5. The design method according to claim 1, characterized in that, In step 3, the optimization objective is achieved through the following objective function: ， ， ， ， The first formula is the volume conservation constraint for the first stage [0, t1]. The total volume of the billet transfer is equal to the sum of the transfer volumes of the three regions of the first section, the second section and the third section, ensuring that the edge boss (110) region is basically filled in this stage. The second equation is the volume conservation constraint for the second stage [t1, t2], ensuring that the central boss (120) area is basically filled in this stage; The third equation is the optimization objective for the third stage [t2, t3], which minimizes the volume transfer of the third section and ensures that the material flow in the opening region of the large aspect ratio wall is the most stable during the filling process in this stage. The fourth formula represents the total volume transfer of the billet within a unit time Δt.

6. The design method according to claim 1, characterized in that, The obtained geometric parameters of the billet include: the angle α between the second section and the horizontal plane, and the distance R from the two endpoints of the second section to the central axis. 2a and R 2b The distance H0 between the two ends of the blank corresponding to the contact surfaces of the punches; And / or, the design method uses the absence of eddy currents and folding defects as the verification criteria for forming quality, and the minimum forming load of the punch as the engineering effect of the optimization objective. The engineering effect is naturally achieved by minimizing the volume transfer amount of the large aspect ratio wall region to obtain the optimal billet geometry parameters.

7. A forming process for a shell with a large aspect ratio and linearly varying radial dimensions, wherein one side of the bottom skin (140) of the shell (100) includes a central boss (120) and an edge boss (110), and the other side includes a wall (130) with a large aspect ratio and linearly varying radial dimensions, characterized in that, The blank is obtained using the design method described in any one of claims 1-6; the forming process includes the following steps: Shaping steps: Place the blank in the mold cavity, the first punch (210) is stationary, and the second punch (220) moves downward to cause the blank to undergo plastic deformation until the geometry of the central boss (120), the side boss (110) and the wall (130) meets the design requirements; Thickness determination step: The first punch (210) and the second punch (220) move downward synchronously and at the same speed until the thickness of the bottom skin (140) reaches the design value.

8. The forming process according to claim 7, characterized in that, Before forming, the outline of the first punch (210) fits into the corresponding mating surface of the blank without interference, and the outline of the second punch (220) fits into the corresponding mating surface of the blank without interference. And / or, in the shaping step, the second punch (220) moves downward at a speed of 70-90 mm / s.

9. The forming process according to claim 7, characterized in that, In the thickness determination step, the designed thickness of the skin (140) is 0.7-1.5 times the thickness of the wall (130).

10. A large aspect ratio shell (100) with linearly varying radial dimensions, obtained by processing a blank using the shell forming process according to any one of claims 7-9 and / or designing it using the design method according to any one of claims 1-6, characterized in that... The large aspect ratio shell with linearly varying radial dimensions includes straight-walled shells and inclined-walled shells, the central boss (120) has an arc shape, and the side bosses (110) have an inclined shape.

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