A process optimization method to prevent instability in multi-pass spinning of thin-walled pipe fittings

Abstract

The present invention belongs to the technical field of material plastic processing, and specifically relates to a process optimization method for preventing instability in multi-pass spinning of thin-walled pipe fittings, comprising the following steps: S1, determining the maximum radial feed amount of each pass based on a thin-walled shell instability mechanical model; S2, calculating the total number of passes required for multi-pass spinning of thin-walled pipe fittings based on the radial feed amount, and recording the total number of passes and the feed amount of each pass; S3, generating the motion trajectory of a spinning wheel during multi-pass spinning based on the total number of passes and the feed amount of each pass; S4, establishing a finite element model for spinning of thin-walled pipe fittings, simulating the spinning process based on the motion trajectory of the spinning wheel, and obtaining spinning process parameters based on the simulation results; the present invention can effectively avoid the occurrence of instability in the spinning process of thin-walled pipe fittings, obtain optimized closing values ​​for each pass, realize efficient planning of the spinning wheel trajectory, greatly reduce the R&D cost and time cost of the enterprise, and have obvious economic benefits.

Description

Technical Field

[0001] The invention belongs to the technical field of material plastic processing, and in particular relates to a process optimization method for preventing instability in multi-pass spinning of thin-walled pipe fittings. Background Art

[0002] Launch vehicle fuel tanks, deep-sea manned submersible hulls, nuclear power plant containment heads, and most gas cylinders are all thin-walled shell components with complex curved surfaces and high forming precision requirements. Currently, the most advanced manufacturing process utilizes multi-pass neck-spinning. Due to the weak overall rigidity and inherent instability of thin-walled shell components, the unconstrained end of the multi-pass neck-spinning process is prone to instability defects. This results in wasted manufacturing costs and, due to the unique material properties of thin-walled shell components, significant economic losses.

[0003] Prior art, such as Chinese patent application CN113695449A, discloses a hot spinning method for gas cylinders based on finite element modeling. This method uses a three-dimensional thermomechanical coupling model to calculate the hot spinning process. The heat transfer coefficients of the inner and outer surfaces of the tube blank are optimized based on the difference between the calculated and actual temperatures, resulting in hot spinning process parameters and providing guidance for practical application. The material constitutive equations employed in this technical solution are relatively generalized, considering too few influencing factors. Furthermore, the model accuracy can only be assessed through feedback from the surface temperature of the spun tube blank, making it ineffective in preventing instability in thin-walled tube fittings.

[0004] Separately, Chinese patent application publication number CN108838265A discloses a method for constructing a multi-pass spinning process trajectory for curved components. This method first predicts flange wrinkling to determine the maximum spin-out angle for each pass of the curved component. The method then determines the number of passes required for the multi-pass spinning process, and finally plots the involute trajectory of the spinning wheel for each pass. This technical solution can only prevent unstable wrinkling during the spinning process of thin-plate parts; it cannot guide the end-spinning process of thin-walled pipes, nor can it guide the selection of spinning process parameters.

[0005] Therefore, there is an urgent need for a method that can prevent the instability of thin-walled pipe end spinning to solve the above technical problems. Summary of the Invention

[0006] The purpose of the present invention is to provide a process optimization method for preventing instability in multi-pass spinning of thin-walled pipe fittings, which can effectively avoid the occurrence of instability during the spinning process of thin-walled pipe fittings, obtain optimized process parameters, and realize efficient planning of the spinning wheel trajectory.

[0007] The present invention proposes a process optimization method to prevent the instability of multi-pass spinning of thin-walled pipe fittings.

[0008] The following steps are involved:

[0009] S1. Determine the maximum radial feed rate for each pass based on the thin-walled shell instability mechanical model; the thin-walled shell instability mechanical model is constructed based on formula (14) and formula (19):

[0010] (14),

[0011] (19),

[0012] in, is the minimum bending strain energy required for deformation; is the neutral surface radius of the shell before closing deformation; is the radius of the neutral surface of the shell after the deformation; θ is the circumferential angular coordinate; is the shell wall thickness; E is Young's modulus; is Poisson's ratio; is the axial strain; is the circumferential strain; is the shear strain; is the radial coordinate variable; ΔT is the work done by the external force; is the differential force; ΔL is the differential displacement; L is the closing length, in meters; l is the axial coordinate variable, ranging from 0 to L, in meters; is the absolute value of the circumferential stress; is the absolute value of radial stress;

[0013] S2. Calculate the total number of passes required for multi-pass spinning of thin-walled pipe fittings based on the radial feed rate, and record the total number of passes and the feed rate for each pass;

[0014] S3, generating a motion trajectory of the spinning wheel during the multi-pass closing spinning process according to the total number of passes and the feed rate of each pass;

[0015] S4. Establish a finite element model for the thin-walled pipe necking spinning, simulate the necking spinning process according to the motion trajectory of the spinning wheel, and obtain the spinning process parameters based on the simulation results.

[0016] Specifically, step S1 includes the following steps:

[0017] S11, initialize the radial feed of each pass, within the range of wall thickness to between;

[0018] S12, obtaining the shell shape parameters before and after the closing deformation, wherein the shell shape parameters include the radius of the shell neutral surface before the closing deformation , the neutral surface radius of the shell after the deformation , closing length L, shell wall thickness ;

[0019] S13, obtaining basic material parameters, wherein the material parameters include Young's modulus E, Poisson's ratio ν, and equivalent true stress-true strain curve;

[0020] S14, based on the shell shape parameters and basic material parameters, calculate the work done by the external force during the shell deformation process through the thin-walled shell instability mechanical model Minimum bending strain energy required for deformation ;

[0021] S15. Work done by external force Minimum bending strain energy required for deformation Determine whether the predetermined instability criterion conditions are met. If so, determine the radial feed amount for each pass.

[0022] Specifically, the predetermined instability criterion condition in step S15 is the work done by the external force. Less than or equal to the minimum bending strain energy required for deformation And the radial feed amount for each pass does not need to be increased.

[0023] Specifically, the total number of passes required for the multi-pass spinning of the thin-walled pipe in step S2 is calculated according to formula (20):

[0024] ,

[0025] Where N is the total number of passes required for multi-pass spinning of thin-walled pipe fittings. is the total radial feed of multi-pass spinning of thin-walled pipe fittings, is the radial feed for each pass.

[0026] Specifically, step S3 specifically includes: the feed trajectory of the spinning wheel in each spinning process adopts a straight trajectory, and a multi-pass spinning process is performed using a pulling and pressing reciprocating spinning method to plan the trajectory as the motion trajectory of the spinning wheel, and the coordinates of the spinning wheel reference point relative to the geometric center of the blank are calculated.

[0027] Specifically, step S4 includes the following steps:

[0028] S41. Create a three-dimensional model of the thin-walled pipe, the rotating wheel, and the fixture based on the finite element software. Set the thin-walled pipe as a shell and set the mesh type to hexahedral SC8R elements.

[0029] S42, setting a working angle α between the rotating wheel and the thin-walled pipe, and setting a penalty contact;

[0030] S43, coupling constraining the thin-walled tube and the fixture through a reference point, and applying a rotation boundary condition to the fixture to drive the thin-walled tube to rotate;

[0031] S44. Assign material parameters required for thermal-mechanical coupling calculation to thin-walled pipe fittings;

[0032] S45, assigning the finite element model with spinning process parameters and performing a simulation calculation of the closing spinning process according to the motion trajectory of the spinning wheel, and optimizing the spinning process parameters according to the simulation results.

[0033] Specifically, the method further includes: S5, performing actual spinning on the thin-walled pipe according to the spinning process parameters and the motion trajectory of the spinning wheel.

[0034] Specifically, the working angle α in step S42 is calculated by formula (21):

[0035] ,

[0036] in, L is the closing length, in millimeters; The radial feed of each pass is in millimeters.

[0037] Specifically, the material parameters required for the thermomechanical coupling calculation in step S44 include Young's modulus, Poisson's ratio, constitutive equation, initial temperature, specific heat capacity, thermal conductivity, thermal expansion coefficient, heat transfer coefficient and frictional heat generation coefficient.

[0038] Specifically, the spinning process parameters in step S44 include spindle speed, feed ratio, and wheel fillet radius.

[0039] Specifically, the thin-walled pipe fitting refers to a metal pipe fitting that can be used for spinning processing and has a tube blank wall thickness of 0.5 mm to 15 mm and an outer diameter of the tube blank greater than or equal to 50 times the wall thickness.

[0040] The present invention provides a process optimization method for preventing instability in multi-pass necking spinning of thin-walled pipe fittings, comprising: S1, determining the maximum radial feed rate of each pass based on a thin-walled shell instability mechanical model; S2, calculating the total number of passes required for multi-pass necking spinning of thin-walled pipe fittings based on the radial feed rate; S3, generating the motion trajectory of a spinning wheel during the multi-pass necking spinning process based on the total number of passes; S4, establishing a finite element model for necking spinning of thin-walled pipe fittings, simulating the necking spinning process based on the motion trajectory of the spinning wheel, and obtaining spinning process parameters based on the simulation results. The present invention achieves an optimized design of the necking spinning process of thin-walled pipe fittings by establishing a thin-walled shell instability mechanical model and combining it with thermal-mechanical coupling finite element analysis, and has the following beneficial effects:

[0041] 1. The process optimization method for preventing instability in multi-pass spinning of thin-walled pipe fittings provided by the present invention can effectively avoid the occurrence of instability during the spinning process of thin-walled pipe fittings, obtain optimized closing values ​​for each pass, and realize efficient planning of the spinning wheel trajectory.

[0042] 2. The present invention utilizes a method combining finite element technology and instability mechanics criteria to optimize the design of thin-walled pipe necking spinning process parameters, thereby achieving accurate planning of the multi-pass necking spinning process for thin-walled pipes.

[0043] 3. The present invention establishes an instability criterion based on energy balance by calculating the relationship between the work done by the external force and the minimum bending strain energy required for deformation, and provides a method for optimizing spinning process parameters by combining theory with numerical simulation. Compared with traditional empirical methods or large-scale experimental methods, it greatly reduces the R&D costs and time costs of enterprises, and has obvious economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Flowchart of a process optimization method for preventing instability in multi-pass spinning of thin-walled pipe fittings according to an embodiment of the present invention;

[0045] Figure 2 This is a flow chart for optimizing the closing value of each pass in an embodiment of the present invention;

[0046] Figure 3 Schematic diagram of the basic mechanical model of instability in cylindrical shell coordinates according to an embodiment of the present invention;

[0047] Figure 4 1 is a spinning wheel trajectory curve during a multi-pass necking spinning process in an embodiment of the present invention;

[0048] Figure 5 A diagram illustrating the setting of geometric constraints of a finite element model in an embodiment of the present invention;

[0049] Figure 6 This is a simulation result diagram obtained by the process optimization method for preventing instability in multi-pass spinning of thin-walled pipes in an embodiment of the present invention (the single-pass spinning wheel feed rate is 8 mm);

[0050] Figure 7 This is a simulation result diagram of multi-pass neck spinning instability when the feed rate of the spinning wheel is increased to 10 mm in an embodiment of the present invention. DETAILED DESCRIPTION

[0051] Please refer to the attached Figure 1-5 , the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] like Figure 1 As shown, the present invention provides a process optimization method for preventing instability in multi-pass spinning of thin-walled pipe fittings, comprising the following steps:

[0053] S1. Determine the radial feed rate for each pass based on the instability mechanics model of thin-walled shells;

[0054] like Figure 2 As shown, the S1 specifically includes the following steps:

[0055] S11, initialize the radial feed of each pass, within the range of wall thickness to between;

[0056] In one embodiment of the present invention, the initial feed rate setting is critical and can typically be started from a low value and gradually increased. For example, for a thin-walled pipe with a wall thickness of 2 mm, the initial feed rate can be set to 3 mm for the first calculation. This ensures processing efficiency while preventing an excessively high initial feed rate, which could lead to unstable calculation results.

[0057] S12, obtaining the shell shape parameters before and after the closing deformation, wherein the shell shape parameters include the radius of the shell neutral surface before the closing deformation , the neutral surface radius of the shell after the deformation , closing length L, shell wall thickness ;

[0058] These shape parameters describe the geometric characteristics of thin-walled tubing before and after neck spinning. The shell neutral plane refers to the ideal surface at the middle of the wall thickness where stress is zero during deformation. The neck length, L, represents the axial distance from the necking start to the necking end. These parameters can be obtained from design drawings or initial measurements and directly influence the stress distribution during the necking process.

[0059] S13, obtaining basic material parameters, wherein the material parameters include Young's modulus E, Poisson's ratio ν, and equivalent true stress-true strain curve;

[0060] Material parameters are crucial for accurately calculating instability conditions. Young's modulus E represents the material's stiffness during elastic deformation and is typically expressed in GPa. Poisson's ratio ν describes the ratio of the material's lateral to axial deformation and is typically a dimensionless number. For example, the Poisson's ratio for aluminum alloys is approximately 0.33. The equivalent true stress-true strain curve describes the material's mechanical behavior during plastic deformation. This curve is typically obtained through tensile testing and is input into the calculation model as a table or curve.

[0061] S14, based on the shell shape parameters and basic material parameters, calculate the work done by the external force during the shell deformation process through the thin-walled shell instability mechanical model Minimum bending strain energy required for deformation ;

[0062] The instability mechanical model of the thin-walled shell in this embodiment is established based on the energy balance principle. The work done by the external force during the shell deformation process is calculated by the instability mechanical model of the thin-walled shell. Minimum bending strain energy required for deformation Determine the radial feed for each pass;

[0063] The energy method proposed by Senior is an important theoretical analysis method for predicting wrinkling in sheet metal plastic forming. Reference: BW Senior, Flange wrinkling in deep-drawing operations, Journal of the Mechanics and Physics of Solids, 1956, 4(4). This method uses the energy method to calculate the bending strain energy ΔU and uses analytical or numerical methods to calculate the external force work ΔT. If ΔT < ΔU, the blank is stable; otherwise, the blank is in an unstable state. Wang et al. used this method to establish a thin plate bending instability model, which has since been gradually improved and applied to many plate and shell instability problems. Reference: X. Wang, J. Cao, On the prediction of side-wallwrinkling in sheet metal forming processes[J]. International journal ofmechanical sciences, 2000. 42: 2369-2394.

[0064] The spinning process may cause wrinkles to appear. This embodiment simplifies the appearance of wrinkles to the problem of instability of a cylindrical shell under the action of a normal concentrated force.

[0065] This embodiment draws on the process of establishing the thin plate bending instability criterion, and can still use the expression of deformation energy U containing displacement and external force work T to establish a numerical optimization model, that is, the thin-walled shell instability mechanical model described in this embodiment, and then use a computer to solve it.

[0066] The following is the derivation and establishment process of the thin-walled shell instability mechanical model described in this embodiment:

[0067] Establish as Figure 3 The orthogonal curvilinear coordinates of the shell shown in the figure are based on the curvature line and normal of the mid-surface. In the orthogonal curvilinear coordinate system of the microelement in the figure, the two curved surface directions α and β are axial and circumferential, α and β are the two curvature directions, R1 is the axial curvature radius, which is used to mark the general curved cylindrical shell, R2 is the circumferential curvature radius, γ points to the convex direction of the mid-surface, MM1 and MM2 are the neutral axes of the axial section and the radial section respectively, and PP1 is the curved layer at a certain distance from the neutral surface.

[0068] During the spinning process, the wrinkle displacement on the blank is linearly distributed along the axial direction and cosine distributed along the circumferential direction. Based on this, the two-dimensional deflection equation is established as shown in formula (1):

[0069] ,

[0070] in, w is the deflection in radians; s is the fold height in meters; m is the number of folds; θ is the circumferential angle, ranging from 0 to 2π, in radians (rad); l is the closing length, in millimeters; L is the axial length in millimeters;

[0071] During the closing process, the circumferential change ∆ l As shown in formula (2):

[0072] ,

[0073] in, Indicates Deflection w Circumferential angle θ The partial derivative of d Compute symbols for differentials; Compute signs for partial derivatives;

[0074] From the geometric relationship, we can see that:

[0075] ,

[0076] Where R0 is the radius of the neutral surface of the shell before the deformation of the closing, in millimeters; R2 is the radius of the neutral surface of the shell after the deformation of the closing, in millimeters;

[0077] It is worth noting that R2 is the circumferential curvature radius and R2 is the radius of the neutral plane of the shell after the end deformation, which have the same meaning. R2 is the circumferential curvature radius for the general derivation;

[0078] Therefore, the fold height s can be deduced as:

[0079] ,

[0080] Right now , which is equivalent to the equivalent radius;

[0081] Substituting equation (4) into equation (1), we can get the deflection w for:

[0082] ,

[0083] The neutral surface geometric equation is established as shown in formula (6):

[0084] ,

[0085] in, u , v ,w correspond α 、 γ, β The displacement of the three coordinate axes is in meters; , , Respectively represent α 、 γ, β Normal strain in the three coordinate axis directions, dimensionless; , , Respectively represent α 、 γ, β Shear strain in the three coordinate axis directions, dimensionless; A, B They are all structural constants. Here, A=B=1 can be taken for cylindrical shells;

[0086] Therefore, the geometric equation of the entire cylindrical shell is shown in formula (7):

[0087] ,

[0088] in, e 1, e 2, e 12 Respectively represent α 、 γ, β The principal strains in the three coordinate axes are dimensionless;

[0089] Establish the bending strain energy per unit area of ​​the shell U 0 As shown in formula (8):

[0090] ,

[0091] in, v is Poisson's ratio, dimensionless; E is the elastic modulus, is the shell thickness in meters;

[0092] It is worth noting that the elastic modulus in metal materials refers to Young's modulus;

[0093] The total bending strain energy can be obtained by integrating over the entire shell surface U As shown in formula (9):

[0094] ,

[0095] Taking into account:

[0096] ,

[0097] In formula (9), A1, A2, and A3 are as shown in formula (11):

[0098] ,

[0099] A 1 、 A 2 、 A 3 is the coefficient of each term after integration of formula (8), R is the expression of the axial diameter of the tube, the diameter of the tube at different axial positions is different, and the maximum end is R 0 , the minimum end is R 2 ;

[0100] Formula (9) can be regarded as a double-check function (ax+b / x), which takes its minimum value at ax=b / x, that is, , in formula (9) take There is a minimum value when m is called the critical fold number m c .

[0101] Therefore, from the mathematical relationship, we can know that there is a critical number of folds m c The total bending strain energy U Minimum, critical number of folds m c As shown in formula (12):

[0102] ,

[0103] The theoretical minimum bending strain energy is U min As shown in formula (13):

[0104] ,

[0105] Substitute formulas (7), (9), and (10) into formula (8) and take the infinitesimal element to obtain the minimum bending strain energy required for deformation: , its expression is shown in formula (14):

[0106] (14),

[0107] in, is the minimum bending strain energy required for deformation, in joules (J); θ is the circumferential angle coordinate, ranging from 0 to 2π, in radians (rad); is the shell wall thickness, in millimeters (mm); E is Young's modulus, in megapascals (MPa); is Poisson's ratio, dimensionless; is the axial strain, dimensionless; is the circumferential strain, dimensionless; is the shear strain, dimensionless; is the radial coordinate variable, and its value range is - / 2 to / 2, unit is millimeter (mm);

[0108] The first integral of this formula represents the integral along the axial direction, the second integral represents the integral along the circumferential direction, and the third integral represents the integral along the radial direction. The result of the triple integral is the bending strain energy of the entire deformation area.

[0109] The expression of external force work is established as shown in formula (15):

[0110] ,

[0111] Where T is the theoretical total external work, is the mean stress; is the material yield stress, which is the stress component in the three coordinate axis directions ( 、 、 ) vector sum; R is the expression of the axial diameter, the diameters of the tubes at different axial positions are different, and the maximum end is R 2 , the minimum end is R 0 ;

[0112] The stress components in each coordinate axis direction are shown in formula (17):

[0113] ,

[0114] in, is the axial stress, representing α Stress components in the axial direction; is the radial stress, representing γ Stress components in the axial direction; is the circumferential stress, representing β Stress components in the axial direction; K and n is the material constant;

[0115] Substituting equation (10) into equation (15), considering that there is no axial force doing work, the work done by the external force is Calculate according to formula (19):

[0116] ,

[0117] in, ΔT The work done by internal and external forces in each pass, in joules (J); is the infinitesimal element of force, in Newton (N); ΔL is the differential displacement, in millimeters (mm); Lis the closing length, in millimeters (mm); π is a mathematical constant, approximately equal to 3.14159; l is the axial coordinate variable, ranging from 0 to L , the unit is millimeter (mm); is the absolute value of the circumferential stress, in megapascals (MPa); is the absolute value of radial stress, in megapascals (MPa); is the neutral surface radius of the shell before closing deformation, in millimeters (mm); The radius of the neutral surface of the shell after the deformation of the closing, in millimeters (mm);

[0118] For example, the average stress of 7075 aluminum alloy is ,

[0119] ,

[0120] in, is the Mises equivalent strain;

[0121] The full name of Mises equivalent strain is von Mises equivalent strain, also known as equivalent strain or equivalent total strain. Mises equivalent strain can be calculated from the partial strains, and its formula can be found in books. This basic concept is existing in the art and will not be repeated here.

[0122] Then the expression of external force work is shown in formula (18):

[0123] ,

[0124] In summary, the instability condition is .

[0125] Therefore, when the work done by the external force in each closing spinning process Greater than the minimum bending strain energy required for deformation When the system energy cannot be balanced, it will lead to instability and wrinkling.

[0126] The instability mechanical model of the thin-walled shell in this embodiment is ultimately constructed based on formula (14) and formula (19). The comparison of the energy values ​​of these two formulas constitutes the core of the instability criterion. Formula (14) calculates the minimum bending strain energy required for the elastic deformation of the thin-walled tube, which is the energy required to prevent instability; Formula (19) calculates the work done by the external force on the thin-walled tube during the spinning process, taking into account the circumferential stress. and radial stress contribution;

[0127] S15, determine whether the predetermined instability criterion conditions are met, if so, determine the radial feed amount for each pass .

[0128] The predetermined instability criterion condition is the work done by the external force Less than or equal to the minimum bending strain energy required for deformation The radial feed rate in each pass is the maximum value. This is a reflection of energy balance, that is, the deformation energy provided by the system is sufficient to resist the work done by external forces, thereby maintaining structural stability, and the radial feed rate in each pass is the maximum value without instability.

[0129] Calculate the work done by the external force based on the initial radial feed of each pass Minimum bending strain energy required for deformation ,judge Is it less than or equal to If yes, then increase the radial feed of each pass according to the preset feed increment and recalculate the work done by the external force. Minimum bending strain energy required for deformation , judge again Is it less than or equal to Otherwise, reduce the radial feed of each pass according to the preset feed reduction amount and recalculate the work done by the external force. Minimum bending strain energy required for deformation , judge again Is it less than or equal to ; Iterate in sequence until the predetermined instability criterion is met, that is, the work done by the external force Less than or equal to the minimum bending strain energy required for deformation And the radial feed amount of each pass is the maximum value.

[0130] Specifically, the preset feed increase is [5%, 10%] of the radial feed of each pass in the previous pass. Preferably, in this example, 10% of the radial feed of each pass in the previous pass is taken; the preset feed decrease is half of the preset feed increase; thereby quickly determining the maximum radial feed of each pass;

[0131] The method for determining the preset increase amount and the preset decrease amount can be adjusted according to different processing stages to meet the processing requirements of different stages.

[0132] S2. Calculate the total number of passes required for multi-pass spinning of thin-walled pipe fittings based on the radial feed rate, and record the total number of passes and the feed rate for each pass;

[0133] The total number of passes required for multi-pass spinning of thin-walled pipe fittings is calculated according to formula (20):

[0134] ,

[0135] Where N is the total number of passes required for multi-pass spinning of thin-walled pipe fittings, a dimensionless integer; The total radial feed of multi-pass spinning of thin-walled pipe fittings, in millimeters (mm); The radial feed of each pass is in millimeters (mm).

[0136] Calculating feed rates using the instability mechanics model for thin-walled shells reveals that the radial feed limit for subsequent passes (such as the second and third passes) to avoid instability is smaller than that of the preceding passes. This means that the smaller the billet diameter, the greater the radial feed limit. To efficiently estimate the total number of feed passes and consider the surface quality requirements of actual forming parts, the total number of passes is estimated by using the same feed rate for each pass as for the first. This calculation method is straightforward: simply divide the total closing amount by the feed rate for each pass to obtain the required number of passes.

[0137] For example, if the total radial dimension of a thin-walled pipe required for closing is 60 mm, and the safe feed per pass is 8 mm, the total number of passes is 60 / 8 = 7.5, rounded up to 8. In practice, the feed of the last pass may be adjusted to make the total number of passes an integer. For example, the feed for the first seven passes is 8 mm, and the feed for the eighth pass is 4 mm. The total number of passes and the feed for each pass are recorded.

[0138] In another possible embodiment, step S2 can also be performed after the spinning is completed according to the radial feed amount calculated according to the thin-walled shell instability mechanical model, and the radial feed amount of the next pass of the current thin-walled tube structure is recalculated according to the thin-walled shell instability mechanical model, and the feed amount of each pass and the corresponding number of passes are recorded, and the radial feed amount of each pass is repeatedly calculated and superimposed until the total radial feed amount of the superimposed calculation is greater than or equal to , if greater than Then adjust the feed amount of the last pass appropriately and record the total number of passes and the feed amount of each pass.

[0139] S3, generating a motion trajectory of the spinning wheel during the multi-pass closing spinning process according to the total number of passes and the feed rate of each pass;

[0140] Preferably, if Figure 4 As shown in the figure, according to the total number of passes and the feed amount of each pass, the feed trajectory of the spinning wheel in each pass of spinning forming adopts a straight trajectory, and the multi-pass spinning forming trajectory planning is performed using a pulling and pressing reciprocating spinning method as the motion trajectory of the spinning wheel, and the coordinates of the spinning wheel reference point relative to the geometric center of the blank are calculated based on the geometric coordinate conversion.

[0141] Compared with curved trajectories, straight-line trajectories are easier to control and implement, reducing programming complexity. At the same time, the use of a reciprocating spinning method of tension and compression can fully utilize the reciprocating motion of the rotary wheel and improve processing efficiency. In actual operation, the coordinate calculation of the rotary wheel reference point usually takes into account the geometric characteristics of the rotary wheel and the way the coordinate system of the workpiece is established to ensure that the rotary wheel can move accurately along the predetermined trajectory. For example, for a thin-walled pipe with a diameter of 200 mm, in each processing pass, the starting position of the rotary wheel may be set at a position outside the center axis of the workpiece, and then move along the radial direction according to the predetermined feed amount.

[0142] S4. Establish a finite element model for the thin-walled pipe necking spinning, simulate the necking spinning process according to the motion trajectory of the spinning wheel, and obtain the spinning process parameters based on the simulation results;

[0143] Preferably, the thin-walled pipe fittings described in the present invention refer to metal pipe fittings with a wall thickness of 0.5 mm to 15 mm and an outer diameter of 50 times or more of the wall thickness that can be used for spinning. This definition clarifies the scope of application of the present invention, and is particularly suitable for thin-walled structural parts commonly used in aerospace, deep-sea exploration and other fields. Figure 5 As shown, the steps of establishing the finite element model of thin-walled pipe necking spinning in S4 specifically include:

[0144] S41. Create a three-dimensional model of the thin-walled pipe, the rotating wheel, and the fixture based on the finite element software. Set the thin-walled pipe as a shell and set the mesh type to hexahedral SC8R elements.

[0145] In actual modeling, commercial finite element software such as ABAQUS or ANSYS can be used to create the model. The hexahedral SC8R element is a continuous shell element with reduced integration functionality, effectively reducing the computational effort while maintaining high accuracy. For thin-walled components, shell elements are more suitable than solid elements because they significantly reduce computational costs while maintaining accuracy.

[0146] S42, setting a working angle α between the rotating wheel and the thin-walled pipe, and setting a penalty contact;

[0147] The working angle α refers to the angle between the axis of the wheel and the axis of the thin-walled tube, which is calculated by formula (21):

[0148] ,

[0149] in, L is the closing length, in millimeters (mm); The radial feed of each pass is in millimeters (mm);

[0150] Penalty contact is a commonly used contact algorithm that applies a penalty factor to the contact surfaces to prevent excessive penetration without overly constraining their relative motion. For complex contact problems like spinning, the penalty contact method ensures computational stability while effectively simulating actual contact behavior.

[0151] In this example, the penalty factor is 0.05;

[0152] S43, coupling constraining the thin-walled tube and the fixture through a reference point, and applying a rotation boundary condition to the fixture to drive the thin-walled tube to rotate;

[0153] The reference point will be the geometric center of the bottom of the pipe diameter, that is, the clamping center of the fixture;

[0154] Reference point coupling is a common technique in finite element modeling. It links the motion of a reference point with the motion of a set of nodes or surfaces, simplifying the application of boundary conditions. In this invention, by coupling a fixture to a reference point and then applying rotational boundary conditions to the reference point, the self-rotation of a thin-walled tube can be easily achieved, which is consistent with the rotational motion of the workpiece during actual machining. For example, the fixture can be set to rotate around its axis at 300 rpm, which will cause the thin-walled tube to rotate at the same speed.

[0155] S44. Assign the material parameters required for thermal-mechanical coupling calculations to thin-walled pipe fittings, including Young's modulus, Poisson's ratio, constitutive equation, initial temperature, specific heat capacity, thermal conductivity, thermal expansion coefficient, heat transfer coefficient, and frictional heat generation coefficient;

[0156] Thermal coupling analysis takes into account the mutual influence of temperature and deformation fields, which is crucial for accurately simulating the spinning process. The initial temperature is usually set to the ambient temperature, such as 20°C. The specific heat capacity describes the amount of heat required to increase the unit temperature of a material per unit mass, and the unit is J / (kg·K). The thermal conductivity coefficient indicates the ability of a material to conduct heat, and the unit is W / (m·K). The thermal expansion coefficient describes the degree to which a material expands with temperature changes, and the unit is K⁻¹. The heat transfer coefficient describes the rate of heat exchange between the material and the environment, and the unit is W / (m²·K). The frictional heat generation coefficient describes the proportion of frictional work converted into heat, and is usually a dimensionless number.

[0157] S45. Assign the finite element model spinning process parameters and perform a simulation calculation of the closing spinning process according to the motion trajectory of the spinning wheel, and obtain the spinning process parameters according to the simulation results; the spinning process parameters include the spindle speed, feed ratio and the rounded radius of the spinning wheel.

[0158] S5. Perform actual spinning on the thin-walled pipe according to the spinning process parameters and the motion trajectory of the spinning wheel.

[0159] In a typical embodiment, the spindle speed can be set within the range of 300-600 rpm, the feed ratio can be set within the range of 0.2-1.0 mm / rpm, and the wheel corner radius can be selected based on the workpiece wall thickness, typically 5-10 times the wall thickness. The selection of these parameters requires a comprehensive consideration of factors such as material properties, workpiece geometry, and equipment capabilities. Finite element simulation can predict the stress distribution, deformation, and potential instability risk under different parameter combinations, thereby selecting the optimal parameter combination.

[0160] The application of the present invention is described below with a specific embodiment:

[0161] In this embodiment, a 7075-O aluminum alloy thin-walled pipe with an outer diameter of 72 mm and a wall thickness of 1.2 mm is used for the simulation calculation and processing of the end-spinning, which specifically includes the following steps:

[0162] Initialization stage: Initialize the radial feed of each pass to δd = 7 mm.

[0163] Extract the shape parameters of the shell with closed deformation, and use MATLAB software to calculate the work done by the external force during the shell deformation process under the current radial feed amount δd according to the instability mechanical model of the thin-walled shell. =1.1359×10 6 J and the minimum bending strain energy required for deformation =1.6228×10 6 J, that is .

[0164] First iteration: Due to , indicating that instability will not occur under the current circumstances.

[0165] Feed adjustment: Increase the radial feed of each pass according to the preset feed increment. The preset feed increment is 10% of the previous (initial) radial feed of each pass, so the new radial feed δd1 = δd + δd × 10% = 7 + 7 × 0.1 = 7.7 mm.

[0166] Recalculate and judge: Use MATLAB software to calculate the work done by the external force under the new radial feed δd1 =1.5327×10 6 J and the minimum bending strain energy required for deformation =1.9451×10 6 J, that is ;

[0167] Second iteration: Due to , indicating that instability will not occur under the current circumstances.

[0168] Feed adjustment: Increase the radial feed again according to the preset feed increase (10% of the previous radial feed δd1). The new radial feed δd1==δd1+δd1×10%=7.7+7.7×0.1=8.47 mm.

[0169] Recalculate and judge: Use MATLAB software to calculate the work done by external force under δd2 =1.9236×10 6 J and the minimum bending strain energy required for deformation =1.8215×10^6 J, that is ;

[0170] Third iteration: Due to , indicating that instability will occur in the current situation.

[0171] Feed adjustment: Reduce the radial feed according to the preset feed reduction (half of the preset feed increase, i.e. 5% of the previous radial feed δd1). The new radial feed δd3 = δd2 − δd1 × 5% = 8.47 − 7.7 × 0.05 = 8.47 − 0.385 = 8.085 mm.

[0172] Recalculate and judge: Use MATLAB software to calculate the work done by external force under δd3 =1.9752×10 6 J and the minimum bending strain energy required for deformation =1.8764×10 6 J, continue to judge and The size relationship;

[0173] Repeat the above process of feed adjustment, recalculation and judgment. , and continue to adjust the feed rate according to the growth rate will appear If the situation is not favorable, then the feed rate is gradually fine-tuned to make it close to meeting the predetermined instability criterion (the work done by the external force is less than or equal to the minimum bending strain energy required for deformation and the radial feed rate of each pass is the maximum value).

[0174] Finally, after several iterations, the maximum radial feed of each pass was determined to be 8 mm, which satisfies the requirement that the work done by the external force is less than or equal to the minimum bending strain energy required for deformation. Therefore, the radial feed of each pass can be set to =8 mm;

[0175] Step 2: The total closing value of the thin-walled pipe spinning =56 mm, then the number of closing spinning passes N=ΔD / Δd=7;

[0176] Step 3: Select a straight line trajectory and use the tension and pressure reciprocating spinning method to plan the multi-pass spinning process. Draw the spinning wheel trajectory as shown in the figure. Figure 4 As shown, it is then converted into the coordinates of the reference point of the rotating wheel relative to the geometric center of the blank;

[0177] Step 4: Create a simplified 3D model of thin-walled pipe, roller and fixture, set the thin-walled pipe as shell, set the mesh type to hexahedron SC8R unit; set the roller fillet radius r = 10 mm, the closing length L =60mm, the working angle α between the spinning wheel and the thin-walled tube is 52.6°, and the penalty contact friction coefficient is set to 0.05; the thin-walled tube and the fixture are coupled and constrained through the reference point, and a rotational boundary condition is applied to the fixture to drive the thin-walled tube to rotate; the required material constants are assigned to the finite element model, including Young's modulus, Poisson's ratio, constitutive equation, initial temperature, specific heat capacity, thermal conductivity, thermal expansion coefficient, heat transfer coefficient, and friction heat generation coefficient; the finite element model is used to simulate the closing spinning process according to the motion trajectory of the spinning wheel, specifically including:

[0178] (1) Determination of the wheel trajectory based on the third step: In the finite element simulation, the wheel trajectory needs to be converted into a mathematical expression or discrete motion points so that the corresponding displacement load can be applied during the simulation process;

[0179] (2) Applying motion load: In the finite element software, the motion trajectory of the spinning wheel is applied to the spinning wheel model as a displacement load; for axial feed motion, the feed amount of the spinning wheel along the axis of the core mold is defined; for radial motion, the feed speed of the spinning wheel in the direction perpendicular to the axis of the core mold is defined to ensure that the application of the motion load is consistent with the actual spinning wheel motion in the processing, so as to accurately simulate the spinning process;

[0180] (3) Perform simulation calculations: Select a suitable solver (such as an explicit solver or an implicit solver), and set the solver parameters according to the characteristics of the spinning process and the calculation scale; start the finite element simulation calculation, and the software will calculate the distribution and change law of the physical fields such as stress, strain, displacement, and temperature of the blank during the spinning process based on the established model, the assigned spinning process parameters (including spindle speed, feed ratio, and wheel fillet radius) and the applied motion load; during the calculation process, it is necessary to monitor the stability and convergence of the calculation. If there is any abnormality, adjust the spinning process parameters in time to finally obtain the simulation calculation results;

[0181] After observing the simulation calculation results and confirming that the blank is deformed evenly and has no unstable wrinkles during the spinning process, the actual spinning can be carried out after adjusting the spinning process parameters and the motion trajectory of the spinning wheel.

[0182] like Figure 7As shown, this embodiment also provides a simulation result diagram of the instability of multi-pass necking spinning when the wheel feed rate is increased to 10mm. It can be seen that there are many wrinkles on the top. The more wrinkles, the more serious the instability of the necking process of the thin-walled tube. The results of necking spinning of thin-walled tubes using the necking spinning process optimization method for thin-walled tubes (single-pass wheel feed rate is 8mm) are shown in the final simulation results. Figure 6 As shown, it can be seen that the surface is smooth and continuous, which means that there is no instability in the spinning process of the thin-walled pipe fitting, and the spinning forming effect is very good.

[0183] Through the above steps, the narrowing spinning process for thin-walled pipe fittings was successfully optimized, effectively avoiding instability and achieving optimal process parameters. Furthermore, compared to traditional empirical methods or extensive testing, the inventive method significantly reduces development costs and time, offering significant economic benefits.

[0184] The above description is only a preferred embodiment of the present invention and does not limit the scope of patent protection of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A process optimization method for preventing instability in multi-pass spinning of thin-walled pipe fittings, characterized in that: The following steps are involved: S1. Determine the maximum radial feed rate for each pass based on the thin-walled shell instability mechanical model; the thin-walled shell instability mechanical model is constructed based on formula (14) and formula (19): （14）， （19）， in, is the minimum bending strain energy required for deformation; is the neutral surface radius of the shell before closing deformation; is the radius of the neutral surface of the shell after the deformation; θ is the circumferential angular coordinate; is the shell wall thickness; E is Young's modulus; is Poisson's ratio; is the axial strain; is the circumferential strain; is the shear strain; is the radial coordinate variable; ΔT is the work done by the external force; is the differential force; ΔL is the differential displacement; L is the closing length, in meters; l is the axial coordinate variable, ranging from 0 to L, in meters; is the absolute value of the circumferential stress; is the absolute value of radial stress; Calculate the work done by the external force based on the initial radial feed of each pass Minimum bending strain energy required for deformation ,like , then the radial feed of each pass is increased according to the preset feed increase amount; if , the radial feed of each pass is reduced according to the preset feed reduction amount; then the work done by the external force is recalculated. Minimum bending strain energy required for deformation , and judge again Is it less than or equal to ; Iterate in sequence until And the radial feed of each pass is the maximum value; S2. Calculate the total number of passes required for multi-pass spinning of thin-walled pipe fittings based on the radial feed rate, and record the total number of passes and the feed rate for each pass; S3, generating a motion trajectory of the spinning wheel during the multi-pass closing spinning process according to the total number of passes and the feed rate of each pass; S4. Establish a finite element model for the thin-walled pipe necking spinning, simulate the necking spinning process according to the motion trajectory of the spinning wheel, and obtain the spinning process parameters based on the simulation results.

2. The process optimization method for preventing instability of multi-pass spinning of thin-walled pipe fittings according to claim 1 is characterized in that: Step S1 specifically includes the following steps: S11, initialize the radial feed of each pass, within the range of wall thickness to between; S12, obtaining the shell shape parameters before and after the closing deformation, wherein the shell shape parameters include the radius of the shell neutral surface before the closing deformation , the neutral surface radius of the shell after the deformation , closing length L, shell wall thickness ; S13, obtaining basic material parameters, wherein the material parameters include Young's modulus E, Poisson's ratio ν, and equivalent true stress-true strain curve; S14, based on the shell shape parameters and basic material parameters, calculate the work done by the external force during the shell deformation process through the thin-walled shell instability mechanical model Minimum bending strain energy required for deformation ; S15. Work done by external force Minimum bending strain energy required for deformation Determine whether the predetermined instability criterion is met. If so, determine the radial feed amount for each pass. The predetermined instability criterion is the work done by the external force. Less than or equal to the minimum bending strain energy required for deformation And the radial feed amount for each pass does not need to be increased.

3. The process optimization method for preventing instability of multi-pass spinning of thin-walled pipe fittings according to claim 1 is characterized in that: The total number of passes required for the multi-pass spinning of the thin-walled pipe in step S2 is calculated according to formula (20): ， Where N is the total number of passes required for multi-pass spinning of thin-walled pipe fittings. is the total radial feed of multi-pass spinning of thin-walled pipe fittings, is the radial feed for each pass.

4. The process optimization method for preventing instability of multi-pass spinning of thin-walled pipe fittings according to claim 1 is characterized in that: Step S3 specifically includes: the feed trajectory of the roller in each spinning pass adopts a straight trajectory, and the multi-pass spinning forming trajectory planning is performed using a tensile and compressive reciprocating spinning method as the motion trajectory of the roller, and the coordinates of the roller reference point relative to the geometric center of the blank are calculated.

5. The process optimization method for preventing instability of multi-pass spinning of thin-walled pipe fittings according to claim 1 is characterized in that: Step S4 specifically includes the following steps: S41. Create a three-dimensional model of the thin-walled pipe, the rotating wheel, and the fixture based on the finite element software. Set the thin-walled pipe as a shell and set the mesh type to hexahedral SC8R elements. S42, setting a working angle α between the rotating wheel and the thin-walled pipe, and setting a penalty contact; S43, coupling constraining the thin-walled tube and the fixture through a reference point, and applying a rotation boundary condition to the fixture to drive the thin-walled tube to rotate; S44. Assign material parameters required for thermal-mechanical coupling calculation to thin-walled pipe fittings; S45, assigning the finite element model with spinning process parameters and performing a simulation calculation of the closing spinning process according to the motion trajectory of the spinning wheel, and optimizing the spinning process parameters according to the simulation results.

6. The process optimization method for preventing instability of multi-pass spinning of thin-walled pipe fittings according to claim 1 is characterized in that: The method further includes: S5, performing actual spinning on the thin-walled pipe according to the spinning process parameters and the motion trajectory of the spinning wheel.

7. The process optimization method for preventing instability in multi-pass spinning of thin-walled pipes according to claim 5 is characterized in that: The working angle α in step S42 is calculated by formula (21): ， in, L is the closing length, in millimeters; The radial feed of each pass is in millimeters.

8. The process optimization method for preventing instability of multi-pass spinning of thin-walled pipe fittings according to claim 5 is characterized in that: The material parameters required for the thermomechanical coupling calculation in step S44 include Young's modulus, Poisson's ratio, constitutive equation, initial temperature, specific heat capacity, thermal conductivity, thermal expansion coefficient, heat transfer coefficient and frictional heat generation coefficient.

9. The process optimization method for preventing instability of multi-pass spinning of thin-walled pipe fittings according to claim 1 is characterized in that: The thin-walled pipe fittings are metal pipe fittings that can be used for spinning processing and have a tube blank wall thickness of 0.5 mm to 15 mm and an outer diameter of the tube blank greater than or equal to 50 times the wall thickness.

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