A spinning forming method for a large arc-shaped thin-walled shell with a variable semi-cone angle of φ400mm

Abstract

The spinning forming method of a large arc-shaped thin-walled shell with a variable half-cone angle of φ400mm belongs to the field of precision plastic forming technology, aiming to solve the problems existing in the prior art such as poor workpiece dimensional accuracy, obvious thinning effect, easy occurrence of wrinkles, cracking, etc. The present invention adopts the process of "sheet material - hot general spinning preforming - machining - multi-pass shear + general spinning composite spinning forming" for forming. The blank uses a sheet material with equal wall thickness and is formed by multiple spinning passes. The first spinning pass uses hot general spinning forming, and the second spinning pass to the last spinning pass all adopt the forming process of "shearing spinning + general spinning and strengthening composite spinning". In the parts where the blank thickness is less than the theoretical thickness requirement of shearing spinning, hot general spinning forming is adopted, and the thickness of all parts after the first spinning pass is greater than or equal to the theoretical thickness requirement of shearing spinning. For the corresponding parts with a thickness greater than the theoretical requirement of shearing spinning, machining is carried out, and the machining process can be carried out in any spinning pass after the first spinning pass.

Description

Technical Field

[0001] The present invention belongs to the technical field of precision plastic forming, and particularly relates to a spinning forming method for a large-sized arc-shaped thin-walled shell with a variable half-cone angle of φ400mm. Background Art

[0002] With the continuous development of high-tech manufacturing technologies and the continuous upgrading of industrial transformation, high-end equipment is also developing towards green manufacturing to achieve high-quality, high-efficiency, low-consumption, and low-cost production. As a major manufacturing country, China has not yet got rid of the development mode of high input, high consumption, and high emissions, and has an extremely urgent need for advanced processing technologies. By breaking through the bottleneck technologies that restrict the innovative development of equipment, building a green manufacturing system with high scientific and technological content, low resource consumption, and less environmental pollution, and accelerating the high-quality development of China's process technology system.

[0003] The arc-shaped thin-walled structure has a good aerodynamic shape, is thin and light, and has a small air resistance, and is widely used in core key structural parts in national defense and national economic fields such as weapons, aerospace, ships, and new energy vehicles. Adopting a large number of lightweight and integral design structures is an effective technical way to achieve light weight, high efficiency, high reliability, and green environmental protection.

[0004] The maximum variation range of the half-cone angle of the arc-shaped thin-walled structure is from 0° to 90°, and the forming difficulty is great. At present, the arc-shaped thin-walled structural parts mainly adopt the method of bar machining, which has problems such as low material utilization rate and low processing efficiency, and cannot meet the requirements of high-efficiency green manufacturing. While processes such as welding and casting cannot meet the high-performance requirements of the products, so there is a need for advanced integral manufacturing technologies for large-sized arc-shaped thin-walled shells.

[0005] Spinning forming is an energy-saving, material-saving, and high-efficiency advanced plastic forming process. It uses a spinning wheel, etc. as a forming tool, and applies an external force to the rotating blank to cause continuous local plastic deformation, and finally obtains a high-performance hollow rotary part. During the spinning process, its structural strength can be maximally improved, and at the same time, a good surface profile and dimensional accuracy can be obtained.

[0006] The main difficulty in direct multi-pass spinning of sheet metal is precision control. Stress relief heat treatment or full annealing is required between spinning passes to restore the plasticity of the material and avoid cracking of the blank caused by spinning hardening. Due to the synergistic effect of the deformation temperature and deformation, it will inevitably affect the dimensional accuracy of the workpiece. At the same time, as the circumferential diameter of the spun part increases, the initial thickness of the sheet metal can no longer meet the axial length requirements of the corresponding position of the spun part, that is, it cannot reach the theoretical thickness of shear spinning at the corresponding position of the spun part. At this time, the conventional spinning process needs to be used, but it will inevitably cause a thinning effect. The closer to the large port position, the more significant the thinning effect, and the probability of spinning defects such as wrinkling and cracking will also increase. The alternating change between shear spinning and conventional spinning processes makes it difficult to ensure the wall thickness accuracy of the workpiece, and even the situation where the component is directly scrapped due to not meeting the technical / tactical indicators may occur. The occurrence of spinning defects will also directly lead to the scrapping of the workpiece. Summary of the Invention

[0007] The object of the present invention is to provide a spinning forming method for a large arc-shaped thin-walled shell with a variable half-cone angle of φ400mm, which solves the problems of poor dimensional accuracy of workpieces, obvious thinning effect, and easy occurrence of wrinkles and cracks in the existing technology. By adopting a forming process combining multi-pass conventional spinning, strong-conventional spinning, multi-pass shear spinning, and cold-hot spinning, and precisely designing the forming trajectory of the sheet metal, the overall forming of the arc-shaped shell is realized, the forming quality and wall thickness accuracy of the spun part are improved, and the high-quality forming of the overall bottom of the box is realized. For the φ400mm spun part, the wall thickness difference in the same circumferential direction ≤0.1mm, the overall wall thickness difference ≤0.3mm, and the difference between the inner surface and the theoretical template ≤0.2mm.

[0008] A spinning forming method for a large arc-shaped thin-walled shell with a variable half-cone angle of φ400mm according to the present invention includes the following steps:

[0009] Step 1: Design the forming route of the large arc-shaped thin-walled shell. The forming route includes n spinning processes. The first spinning process is hot conventional spinning forming, and the second spinning process - the nth spinning process are all two-stage spinning, both including the first-stage shear spinning and the second-stage combined strong-conventional spinning.

[0010] Step 2: Select the spinning blank, and the spinning blank is a sheet metal with equal wall thickness.

[0011] Step 3: Calculate the dimensions of the spun parts in each spinning process, including the wall thickness of the spun parts in each spinning process and the inner surface shape and outer surface shape of the workpiece before spinning in each spinning process. The inner surface shape of the workpiece in each spinning process is used as the outer surface shape of the spinning mandrel.

[0012] Step 4: Determine the hot conventional spinning forming trajectory of the first spinning process.

[0013] Step 5: Determine the forming trajectories of the second spinning process - the nth spinning process.

[0014] Step Six: Clamp and fix the spinning blank selected in Step Two and the corresponding core mold determined in Step Three on the spinning machine, and perform spinning according to the forming route determined in Step One and the forming trajectory determined in Steps Four and Five;

[0015] Step Seven: Demold the spun part formed in Step Six;

[0016] Step Eight: Heat-treat the demolded workpiece, and perform machining on the small-size end and the large-size end to the required dimensions, thus completing the overall spinning forming of the arc-shaped thin-walled shell.

[0017] The starting point of the warm spinning forming in the first spinning process described in Step One is at the position where the thickness of the blank is less than the theoretical thickness requirement of shear spinning. The number of spinning passes is m, and the value range of m is 5 ≤ m ≤ 7; ensure that the thickness of the spun blank after spinning is greater than the theoretical thickness of shear spinning at the corresponding position.

[0018] There is also a machining process between the first spinning process and the second spinning process described in Step One. Remove the oxide scale on the surface after the first spinning process through machining; reach the thickness required by the shear theory.

[0019] For the described spinning forming method, anneal the workpiece after the end of the first spinning process - the nth spinning process.

[0020] The beneficial effects of the present invention are as follows: The spinning forming method of a φ400mm variable semi-cone angle large arc-shaped thin-walled shell of the present invention is aimed at large arc-shaped thin-walled structures and adopts the process of "sheet metal - warm spinning preforming - machining - multi-pass shear + conventional spinning composite spinning forming" for forming. During the forming process, through the reasonable design of the trajectory and spinning method, problems existing in the prior art such as poor workpiece dimensional accuracy, obvious thinning effect, easy occurrence of wrinkles and cracks are solved. By adopting the forming process of multi-pass conventional spinning, strong-conventional spinning, multi-pass shear spinning, and combination of cold-hot spinning, and precisely designing the forming trajectory of the sheet metal, the overall forming of the arc-shaped shell is realized, improving the forming quality and wall thickness accuracy of the spun part, achieving high-quality forming of the overall bottom of the box. For the Φ400mm spun part, the wall thickness difference in the same circumferential direction ≤ 0.1mm, the overall wall thickness difference ≤ 0.3mm, and the difference between the inner surface and the theoretical template ≤ 0.2mm, reducing the manufacturing cost, and improving the processing efficiency and material utilization rate. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the complete forming process of the spinning forming method of a φ400mm variable semi-cone angle large arc-shaped thin-walled shell of the present invention;

[0022] Figure 2Local enlarged view of the hot multi-point spinning process in the spinning forming method of a φ400mm large arc thin-walled shell with variable half-cone angle according to the present invention;

[0023] Figure 3 Schematic diagram of the spinning blank structure in the spinning forming method of a φ400mm large arc thin-walled shell with variable half-cone angle according to the present invention;

[0024] Figure 4 Schematic diagram of the calculation and design process of the spinning blank for each spinning process in the spinning forming method of a φ400mm large arc thin-walled shell with variable half-cone angle according to the present invention;

[0025] Figure 5 is Figure 4 local enlarged view of;

[0026] Wherein: 1. Spinning blank, 2. Blank part after the first spinning process, 201. Spinning track of the first pass, 202. Spinning track of the second pass, 203. Spinning track of the third pass, 204. Spinning track of the fourth pass, 205. Spinning track of the fifth pass, 3. Blank part after machining, 4. Blank part after the second spinning process, 401. First section of the second spinning process, 402. Second section of the second spinning process, 5. Blank part after the third spinning process, 501. First section of the third spinning process, 502. Second section of the third spinning process, 6. Blank part after the fourth spinning process, 601. First section of the fourth spinning process, 602. Second section of the fourth spinning process. Detailed implementation manners

[0027] The following further describes the implementation manners of the present invention with reference to the accompanying drawings.

[0028] See Figure 1 , the spinning forming method of a φ400mm large arc thin-walled shell with variable half-cone angle according to the present invention includes the following steps:

[0029] Step 1: Design the forming route of the large arc thin-walled shell. The forming route includes n spinning processes, wherein the first spinning process is hot multi-point spinning, and the second spinning process to the nth spinning process are both two-stage spinning, both including the first-stage shear spinning and the second-stage combined spinning of hot multi-point spinning and power spinning;

[0030] Step 2: Select the spinning blank, and the spinning blank is a plate with equal wall thickness;

[0031] Step 3: Calculate the dimensions of the spinning parts for each spinning process, including the wall thickness of the spinning parts for each spinning process and the inner surface shape and outer surface shape of the workpiece before each spinning process. The inner surface shape of the workpiece for each spinning process is used as the outer surface shape of the spinning mandrel;

[0032] Step 4: Determine the hot multi-point spinning track of the first spinning process;

[0033] Step Five: Determine the forming trajectories of the second to the nth spinning processes;

[0034] Step Six: Clamp and fix the selected spinning blank in Step Two and the corresponding core mold determined in Step Three on the spinning machine, and perform spinning according to the forming route determined in Step One and the forming trajectories determined in Steps Four and Five; the spinning blank is coaxially fixed at the small-dimension end of the core mold;

[0035] Step Seven: Demold the spun part formed in Step Six;

[0036] Step Eight: Heat-treat the demolded workpiece, and perform machining on the small-dimension end and the large-dimension end to the required dimensions to complete the overall spinning forming of the arc-shaped thin-walled shell. The heat treatment is vacuum annealing at 860 °C for 3 h.

[0037] The starting point of the hot spinning forming of the first spinning process described in Step One is at the part where the thickness of the blank is less than the theoretical thickness requirement of shear spinning. The number of spinning passes is m, and the value range of m is 5 ≤ m ≤ 7; so that the thickness of the spun blank after spinning is greater than the theoretical thickness of shear spinning at the corresponding position.

[0038] There is also a machining process between the first spinning process and the second spinning process described in Step One, and the oxide scale on the surface after the first spinning process is machined off through machining; to reach the thickness required by the shear theory.

[0039] For the spinning forming method described above, the workpiece is annealed after the end of the first to the nth spinning processes. Vacuum annealing is used at 860 °C for 3 h.

[0040] See Figures 3 - 5 , the wall thickness t0 of the spinning blank described in Step Two is calculated according to formula (1), specifically:

[0041] t0 = t f ÷ (1 - Ψ max ) ÷ S1 (1)

[0042] Where: t0 is the wall thickness of the spinning blank;

[0043] t f is the wall thickness of the final part;

[0044] Ψ max is the ultimate thinning rate of the material;

[0045] S1 is the drawing coefficient, and its value is 0.85 - 0.90;

[0046] The diameter D0 of the spinning blank is calculated according to the principle of constant volume.

[0047] The specific dimensions of the spun parts of each spinning process obtained by calculation described in Step Three are:

[0048] 1) Design and calculate the wall thickness of the spinning parts for each spinning process

[0049] The wall thickness of the spinning parts for each spinning process is calculated based on the thinning rate and the deviation rate of the wall thickness for each spinning process. In order to improve the mold fitting and ensure the accuracy of the spinning parts, the deviation rate is generally designed as a negative deviation, that is, the deviation rate of the actual wall thickness of the spinning part from the theoretical wall thickness. Based on the actual wall thickness of the spinning part, the theoretical blank wall thickness before spinning for each spinning process is deduced in turn; according to the formula as shown in formula (IV), formula (IV) is derived from formula (II) and formula (III):

[0050] The theoretical thinning rate Ψ of the i-th spinning process is calculated according to formula (II), and the value of Ψ is 15% - 50%;

[0051]

[0052] The deviation rate ε of the i-th spinning process is calculated according to formula (III), and the value of ε is -3% - -10%;

[0053]

[0054] Substitute formula (II) and formula (III) into formula (IV), and calculate the theoretical blank wall thickness of the workpiece before shear spinning for each spinning process according to formula (IV);

[0055]

[0056] Where: t 0(i) is the theoretical blank wall thickness before shear spinning for the i-th spinning process;

[0057] t f(i) is the actual blank wall thickness after shear spinning for the i-th spinning process;

[0058] t t(i) is the theoretical blank wall thickness after shear spinning for the i-th spinning process;

[0059] 2) Design and calculate the shape of the workpiece before spinning for each spinning process

[0060] First, based on the shear spinning forming theory formulas (V) and (VI), it is deduced to obtain formula (VII);

[0061]

[0062]

[0063]

[0064] Where: t0 is the theoretical blank wall thickness before spinning;

[0065] a0 / 2 is the semi-cone angle of the theoretical blank before spinning;

[0066] is the half-cone angle of the theoretical blank before the i-th pass of spin forming;

[0067] t t is the wall thickness of the theoretical blank after spin forming;

[0068] a t / 2 is the half-cone angle of the theoretical blank after spin forming;

[0069] is the half-cone angle of the theoretical blank after the i-th pass of spin forming;

[0070] (X i+1 -X i ) is the radial distance between the (i + 1)-th point and the i-th point;

[0071] (y i+1 -y i ) is the axial distance between the (i + 1)-th point and the i-th point;

[0072] t 0(i) is the wall thickness of the theoretical blank before the i-th pass of shear spin forming;

[0073] t t(i) is the wall thickness of the theoretical blank after the i-th pass of shear spin forming;

[0074] The average value of the tangent values of the half-cone angles corresponding to the i-th point and the (i + 1)-th point in formula (VII) is obtained to get formula (VIII), and the inner surface shape of the workpiece before each pass of spin forming is calculated according to formula (VIII);

[0075]

[0076] The wall thickness of the theoretical blank before each pass of spin forming is calculated through formula (III), and the outer surface shape of the workpiece before each pass of spin forming is obtained by equally offsetting the inner surface shape obtained according to formula (VIII), and finally the shape of the workpiece before each pass of spin forming is determined.

[0077] Formula (VIII) is only applicable to the calculation of the inner surface shape of the workpiece before each pass of shear spin forming.

[0078] See Figure 2 , the determination of the hot spinning forming trajectory described in step four specifically includes:

[0079] 1) The determination of the radial reduction per pass, specifically:

[0080] The total radial reduction of the spin blank is determined according to formula (IX);

[0081] h = H1 - t p -a (IX)

[0082] Where: h is the total radial reduction of the spinning blank;

[0083] H1 is the radial distance from the maximum outer diameter of the spinning blank to the core die;

[0084] t p is the wall thickness of the spinning blank after hot spinning;

[0085] a is the radial reduction reserved for the last pass of hot spinning, with a value of 2 - 5 mm;

[0086] The radial reduction in the first pass of hot spinning is h * 0.45, and the remaining h * 0.55 radial reduction is evenly distributed among the remaining passes;

[0087] 2) Determination of the end point of the axial pressing position for each pass, specifically:

[0088] The axial pressing amount for each pass is designed separately according to different spinning passes and the total deformation height H2. The total deformation height H2 is the radial distance from the maximum outer diameter of the spinning blank to the outer diameter of the tailstock;

[0089] When using 5 - pass spinning: The end point of the axial pressing position in the first pass is H2 * 35%, the end point of the axial pressing position in the second pass is H2 * 55%, the end point of the axial pressing position in the third pass is H2 * 75%, the end point of the axial pressing position in the fourth pass is H2 * 95%, and the end point of the axial pressing position in the fifth pass is the equal - volume calculation position;

[0090] When using 6 - pass spinning: The end point of the axial pressing position in the first pass is H2 * 35%, the end point of the axial pressing position in the second pass is H2 * 50%, the end point of the axial pressing position in the third pass is H2 * 65%, the end point of the axial pressing position in the fourth pass is H2 * 80%, the end point of the axial pressing position in the fifth pass is H2 * 95%, and the end point of the axial pressing position in the sixth pass is the equal - volume calculation position;

[0091] When using 7 - pass spinning: The end point of the axial pressing position in the first pass is H2 * 35%, the end point of the axial pressing position in the second pass is H2 * 47%, the end point of the axial pressing position in the third pass is H2 * 59%, the end point of the axial pressing position in the fourth pass is H2 * 71%, the end point of the axial pressing position in the fifth pass is H2 * 83%, the end point of the axial pressing position in the sixth pass is H2 * 95%, and the end point of the axial pressing position in the seventh pass is the equal - volume calculation position;

[0092] 3) Determination of the starting, lifting, and end positions of the spinning roller for each pass, specifically:

[0093] The starting position of the first pass is at H2 * 0.55 of the total deformation height, the lifting position is the same as the starting position, and the end position of the spinning roller is the equal - volume calculation position;

[0094] From the second pass to the (m - 1)-th pass, the starting and lifting positions divide the arc length L of the outer surface of the spun blank after hot spinning into m - 1 equal segments. Here, m is the number of spinning passes. Starting from each midpoint, the second pass to the (m - 1)-th pass start spinning and lift respectively, and the end position of the spinning wheel is the position calculated by equal volume;

[0095] The m-th pass starts spinning from the starting point of the first pass, and the end position of the spinning wheel is the position calculated by equal volume;

[0096] 4) Determination of the spinning gap and the transition method from the starting position to the end position of the axial pressing: Specifically:

[0097] From the starting position of the spinning wheel in the first pass to the end position of the axial pressing, a counterclockwise arc transition is adopted, and after the transition, it is a straight line segment parallel to the center line;

[0098] From the second pass to the (m - 1)-th pass, from the lifting position of the spinning wheel to the end position of the axial pressing, a clockwise arc + counterclockwise arc transition method is adopted to ensure that the tangent angle of the spinning trajectory at the lifting position and the tangent angle of the corresponding point on the core mold ≤ 15°;

[0099] From the second pass to the (m - 1)-th pass, at the starting position and the lifting position of the spinning wheel, the gap between the spinning wheel and the core mold is t0×S1, where t0 is the wall thickness of the spun blank; S1 is the thinning coefficient, with a value range of 0.85 - 0.90;

[0100] For the m-th pass, the gap between the spinning wheel and the core mold throughout the entire trajectory is t0×S1;

[0101] 5) Determination of the spinning process parameters for each pass: Specifically:

[0102] The spindle speed for each pass of spinning is 30 - 100 rpm, and the feed rate is 50 - 150 mm / min;

[0103] If the spun blank is aluminum alloy, the heating temperature is 200 - 350 °C; if the spun blank is steel, the heating temperature is 650 - 850 °C.

[0104] The determination of the forming trajectory of the second spinning process to the n-th spinning process in step five specifically includes:

[0105] 1) Determination of the shear spinning end position: Specifically:

[0106] Measure the axial length of the workpieces in different passes at the same height using contour lines. When the axial length of the conventional spinning blank is less than the axial length of the workpiece in the second pass, this point is the shear spinning end;

[0107] 2) Determination of the first spinning gap from the second spinning process to the n-th spinning process: Specifically:

[0108] Calculate the first-stage spinning gap in the second to the nth spinning process according to formula (X).

[0109] T i = t f(i) - B i (X)

[0110] Where: T i is the first-stage spinning gap in the ith spinning process;

[0111] t f(i) is the wall thickness actually required to be achieved in the ith spinning process;

[0112] B i is the retraction amount of the spinning machine tool;

[0113] 3) Determine the second-stage spinning gap in the second to the nth spinning process, specifically:

[0114] The second-stage spinning gap in the second to the nth spinning process is the same as the spinning gap at the end of the first-stage shear spinning;

[0115] 4) Determine the spinning process parameters for each pass, specifically:

[0116] The spindle speed for each pass of spinning is 30 - 80 rpm, and the feed rate is 30 - 80 mm / min;

[0117] When the thinning rate ≤ 35% or the radial runout at the maximum diameter after installation ≤ 0.3 mm, spinning is carried out at room temperature;

[0118] When the thinning rate > 35% or the radial runout at the maximum diameter after installation > 0.3 mm, hot spinning is carried out; during hot spinning, if the spinning blank is aluminum alloy, the heating temperature is 200 - 300 °C; when the spinning blank is steel, the heating temperature is 250 - 350 °C.

[0119] In this embodiment, taking the four-spin process as an example, the spinning blank 1 and the core die are clamped by the tail ejector rod and the pressing block, and the spinning blank 1 undergoes the first spin process, i.e., hot precision spinning. Under the restriction of the hot precision spinning core die, the blank part 2 after the first spin process is obtained according to the hot precision spinning forming trajectory. Among them, in this embodiment, the hot precision spinning adopts 5 passes, and the blank part after the first spin process is obtained successively according to the first-pass spinning trajectory 201, the second-pass spinning trajectory 202, the third-pass spinning trajectory 203, the fourth-pass spinning trajectory 204, and the fifth-pass spinning trajectory 205; the blank part 2 after the first spin process is machined to obtain the machined blank part 3. The machined blank part 3 is restricted by the second-spin core die and the blank part 4 after the second spin process is obtained according to the second-spin forming trajectory. The blank part 4 after the second spin process includes the first section 401 and the second section 402 of the second spin process. The blank part 4 after the second spin process is restricted by the third-spin core die and the blank part 5 after the third spin process is obtained according to the third-spin forming trajectory. The blank part 5 after the third spin process includes the first section 501 and the second section 502 of the third spin process. The blank part 5 after the third spin process is restricted by the fourth-spin core die and the blank part 6 after the fourth spin process is obtained according to the third-spin forming trajectory. The blank part 6 after the fourth spin process includes the first section 601 and the second section 602 of the fourth spin process.

Claims

1. A spinning forming method for a large-sized arc-shaped thin-walled shell with a variable semi-cone angle of φ400mm, characterized in that, It includes the following steps: Step 1: Design the forming route of the large arc thin-walled shell. The forming route includes n spinning processes, where the first spinning process is hot common spinning, and the second spinning process to the nth spinning process are both two-stage spinning, each including the first-stage shear spinning and the second-stage common-strengthening composite spinning; Step 2: Select the spinning blank, and the spinning blank is a sheet material with equal wall thickness; Step 3: Calculate the dimensions of the spinning parts in each spinning process, including the wall thickness of the spinning parts in each spinning process and the inner surface shape and outer surface shape of the workpiece before spinning in each spinning process. The inner surface shape of the workpiece in each spinning process is used as the outer surface shape of the spinning mandrel; Step 4: Determine the hot common spinning forming trajectory of the first spinning process; Step 5: Determine the forming trajectories of the second spinning process to the nth spinning process; Step 6: Clamp and fix the spinning blank selected in Step 2 and the corresponding mandrel determined in Step 3 on the spinning machine, and perform spinning according to the forming route determined in Step 1 and the forming trajectories determined in Step 4 and Step 5; Step 7: Demold the spinning part formed in Step 6; Step 8: Heat-treat the demolded workpiece, and perform machining on the small-size end and the large-size end to the required dimensions to complete the overall spinning forming of the arc thin-walled shell.

2. The spinning forming method of a large arc-shaped thin-walled shell with a variable semi-cone angle of φ400mm according to claim 1, characterized in that The starting point of the hot common spinning of the first spinning process described in Step 1 is at the part where the thickness of the blank is less than the theoretical thickness requirement of shear spinning. The number of spinning passes is m, and the value range of m is 5 ≤ m ≤ 7; so that the thickness of the spun blank after spinning is greater than the theoretical thickness of shear spinning at the corresponding position.

3. The spinning forming method of a large arc-shaped thin-walled shell with a variable semi-cone angle of φ400mm according to claim 1, characterized in that, There is also a machining process between the first spinning process and the second spinning process described in Step 1, and the oxide skin on the surface after the first spinning process is machined off through machining; to reach the thickness required by the shear theory.

4. A spinning forming method for a φ400mm large arc thin-walled shell with variable half-cone angle according to claim 1, characterized in that, For the spinning forming method described above, annealing is performed on the workpiece after each of the first spinning process to the nth spinning process.

5. A spinning forming method for a φ400mm large arc-shaped thin-walled shell with variable semi-cone angle according to any one of claims 1-4, characterized in that, The wall thickness t0 of the spinning blank described in Step 2 is calculated according to Formula (1), specifically: t0 = t f ÷(1 - Ψ max )÷S1(one) Where: t0 is the wall thickness of the spinning blank; t f is the wall thickness of the final part; Ψ max is the ultimate thinning rate of the material; S1 is the thinning coefficient, and its value is 0.85 - 0.90; The diameter D0 of the spinning blank is calculated according to the principle of volume invariance.

6. A spinning forming method for a φ400mm large arc thin-walled shell with variable half-cone angle according to any one of claims 1-4, characterized in that, The specific calculation of obtaining the dimensions of the spinning parts in each spinning process described in Step 3 is as follows: 1) Design and calculate the wall thickness of the spinning parts in each spinning process The theoretical thinning rate Ψ of the ith spinning process is calculated according to Formula (2), and the value of Ψ is 15% - 50%; The deviation rate ε of the ith spinning process is calculated according to Formula (3), and the value of ε is -3% - -10%; Substitute Formulas (2) and (3) into Formula (4), and calculate the theoretical blank wall thickness of the workpiece before shear spinning in each spinning process according to Formula (4); where: t 0(i) is the theoretical blank wall thickness before the i-th revolution shear spinning; t f(i) is the actual blank wall thickness after the i-th revolution shear spinning; t t(i) is the theoretical blank wall thickness after the i-th pass shear spinning; 2) Design and calculate the shape of the workpiece before spinning in each spinning process First, derive according to the shear spinning forming theoretical Formulas (5) and (6) to obtain Formula (7); Where: t0 is the theoretical blank wall thickness before spinning; a0 / 2 is the semi-cone angle of the theoretical blank before spinning; is the half-cone angle of the theoretical blank before the i-th spinning pass; t t is the theoretical blank wall thickness after spin forming; a t / 2 is the semi-cone angle of the theoretical blank after spinning; is the half-cone angle of the theoretical blank after the i-th spinning process; (X i+1 -X i ) is the radial distance between the (i + 1)-th point and the i-th point; (y i+1 -y i ) is the axial distance between the (i + 1)-th point and the i-th point; t 0(i) is the theoretical blank wall thickness before the i-th pass shear spinning; t t(i) is the theoretical blank wall thickness after the i-th revolution shear spinning; Calculate the average value of the tangent values of the semi-cone angles corresponding to the ith point and the (i + 1)th point in Formula (7) to obtain Formula (8), and calculate the inner surface shape of the workpiece before spinning in each spinning process according to Formula (8); The theoretical blank wall thickness before spinning for each spinning pass is calculated by formula (III). The outer surface shape of the workpiece before spinning for each spinning pass is obtained by equally offsetting the inner surface shape obtained according to formula (VIII). Finally, the shape of the workpiece before spinning for each spinning pass is determined.

7. A spinning forming method for a φ400mm large arc-shaped thin-walled shell with variable semi-cone angle according to any one of claims 1-4, characterized in that, The determination of the hot spinning forming trajectory described in step four specifically includes: 1) Determination of the radial reduction amount for each pass, specifically: Determine the total radial reduction amount of the spinning blank according to formula (IX); h = H1 - t p -a(nine) where: h is the total radial reduction amount of the spinning blank; H1 is the radial distance from the maximum outer diameter of the spinning blank to the core die; t p is the wall thickness of the hot spinning and backward spinning blank; a is the radial reduction amount reserved for the last pass of hot spinning, with a value of 2 - 5 mm; The radial reduction amount for the first pass of hot spinning is h * 0.45, and the remaining h * 0.55 radial reduction amount is evenly divided among the remaining passes; 2) Determination of the end point of the axial pressing position for each pass, specifically: The axial pressing amount for each pass is designed separately according to different spinning passes and the total deformation height H2. The total deformation height H2 is the radial distance from the maximum outer diameter of the spinning blank to the outer diameter of the tailstock; When 5 - pass spinning is adopted: the end point of the axial pressing position for the first pass is H2 * 35%, the end point of the axial pressing position for the second pass is H2 * 55%, the end point of the axial pressing position for the third pass is H2 * 75%, the end point of the axial pressing position for the fourth pass is H2 * 95%, and the end point of the axial pressing position for the fifth pass is the equal - volume calculation position; When 6 - pass spinning is adopted: the end point of the axial pressing position for the first pass is H2 * 35%, the end point of the axial pressing position for the second pass is H2 * 50%, the end point of the axial pressing position for the third pass is H2 * 65%, the end point of the axial pressing position for the fourth pass is H2 * 80%, the end point of the axial pressing position for the fifth pass is H2 * 95%, and the end point of the axial pressing position for the sixth pass is the equal - volume calculation position; When 7 - pass spinning is adopted: the end point of the axial pressing position for the first pass is H2 * 35%, the end point of the axial pressing position for the second pass is H2 * 47%, the end point of the axial pressing position for the third pass is H2 * 59%, the end point of the axial pressing position for the fourth pass is H2 * 71%, the end point of the axial pressing position for the fifth pass is H2 * 83%, the end point of the axial pressing position for the sixth pass is H2 * 95%, and the end point of the axial pressing position for the seventh pass is the equal - volume calculation position; 3) Determination of the starting, lifting, and end positions of the spinning wheel for each pass, specifically: The starting position for the first pass is at H2 * 0.55 of the total deformation height. The lifting position is the same as the starting position, and the end position of the spinning wheel is the equal - volume calculation position; For the starting and lifting positions of the second pass to the (m - 1) - th pass, the arc length L of the outer surface of the spinning blank after hot spinning is evenly divided into (m - 1) segments, where m is the number of spinning passes. The second pass to the (m - 1) - th pass start and lift from each equal - division point respectively, and the end position of the spinning wheel is the equal - volume calculation position; The m - th pass starts from the starting point of the first pass, and the end position of the spinning wheel is the equal - volume calculation position; 4) Determination of the spinning gap and the transition method from the starting position to the end point of the axial pressing position, specifically: From the starting position of the spinning wheel in the first pass to the end point of the axial pressing position, a counter - clockwise circular arc transition is adopted, and after the transition, it is a straight line segment parallel to the center line; From the second pass to the (m - 1)th pass, from the position where the roller is lifted to the end of the axially pressed-down position, a transition mode of clockwise arc + counterclockwise arc is adopted to ensure that the tangent angle of the spinning trajectory at the lifted position is ≤ 15° with the tangent of the corresponding point on the mandrel. From the second pass to the (m - 1)th pass, at the starting spinning position and the position where the roller is lifted, the gap between the roller and the mandrel is t0×S1, where t0 is the wall thickness of the spun blank; S1 is the thinning coefficient, and its value ranges from 0.85 to 0.

90. For the mth pass, the gap between the roller and the mandrel throughout the entire trajectory is t0×S1. 5) The determination of the spinning process parameters for each pass is specifically as follows: The spindle speed for spinning in each pass is 30 - 100 rpm, and the feed rate is 50 - 150 mm / min. If the spun blank is aluminum alloy, the heating temperature is 200 - 350 °C; if the spun blank is steel, the heating temperature is 650 - 850 °C.

8. A spinning forming method for a φ400mm large arc-shaped thin-walled shell with variable semi-cone angle according to any one of claims 1-4, characterized in that, The determination of the forming trajectories for the second to the nth spinning processes described in step five specifically includes: 1) The determination of the shear spinning end position, specifically as follows: The axial lengths of the workpieces in different passes at the same height are measured using contour lines. When the axial length of the conventional spinning blank is less than the axial length of the workpiece in the second pass, this point is the shear spinning end. 2) The determination of the first spinning gap from the second to the nth spinning processes, specifically as follows: The first spinning gap from the second to the nth spinning processes is calculated according to the following formula. T i = t f(i) - B i (Ten) Where: T i is the first spinning clearance of the i-th spinning process; t f(i) is the wall thickness actually required to reach for the i-th revolution; B i is the retraction amount of the spin forming machine tool; 3) The determination of the second spinning gap from the second to the nth spinning processes, specifically as follows: The second spinning gap from the second to the nth spinning processes is the same as the spinning gap at the end of the first shear spinning. 4) The determination of the spinning process parameters for each pass is specifically as follows: The spindle speed for spinning in each pass is 30 - 80 rpm, and the feed rate is 30 - 80 mm / min. When the thinning rate ≤ 35% or the radial runout at the maximum diameter after installation ≤ 0.3 mm, spinning is carried out at room temperature. When the thinning rate > 35% or the radial runout at the maximum diameter after installation > 0.3 mm, hot spinning is carried out; during hot spinning, if the spun blank is aluminum alloy, the heating temperature is 200 - 300 °C; when the spun blank is steel, the heating temperature is 250 - 350 °C.

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