An asymmetric spinning method for the middle part of pipe fittings based on a universal spinning wheel

Abstract

A method for asymmetric spinning of the middle part of a pipe fitting based on a universal spinning wheel, comprising the following steps: Select a numerically controlled spinning machine, and clamp two identical cylindrical mandrels at both ends of the pipe fitting to be spun; Install the universal spinning wheel on a spinning wheel frame perpendicular to the main shaft of the spinning machine, and the central axis of the universal spinning wheel is parallel to the main shaft of the pipe fitting to be spun; Derive and solve the non-axisymmetric spinning deformation path equation along the radial direction of the pipe fitting during the processing of the universal spinning wheel to obtain the pressing amount of the universal spinning wheel at each moment in a single pass; Derive and solve the trajectory equation of the axial feed during the processing of the universal spinning wheel; Set the spinning forming method according to the difference in the spinning wheel path; Calculate the pressing amount of the universal spinning wheel at each moment in all passes; Compile a numerically controlled code program according to the pressing amount of the universal spinning wheel at each moment in all passes, and a preformed avoidance groove can be machined through the numerical control system. The present invention greatly saves the process cost and time of manufacturing a profiling spinning wheel, and more embodies the characteristics of high efficiency and energy saving of the spinning process.

Description

Technical Field

[0001] The present invention belongs to the technical field of asymmetric spinning of metal pipe materials, and particularly relates to a method for asymmetric spinning in the middle part of a pipe fitting based on a universal spinning wheel. Background Art

[0002] With the rapid development of the aerospace industry, the manufacturing technology of various aircraft has become quite mature today. However, the control of the weight of the aircraft itself remains a key issue. Data shows that for some aircraft, if the mass is reduced by 1%, its performance can be improved by 3% - 5%. Using new materials with high strength on the premise of ensuring the performance of the aircraft is an important means to reduce the weight of the aircraft. In addition to material lightweighting, structural lightweighting is another important way to reduce the weight of the aircraft.

[0003] A large number of pipelines with various functions are applied on the aircraft, used for transporting fuel, lubricating oil, compressed air, and wrapping cables, etc. The crossing of pipelines is inevitable. The traditional way to deal with pipeline crossing is the "completely bypass" method, that is, there is no overlap between the cross-sections of the two pipe fittings. Usually, the pipe joint or the "vertical and horizontal adjacent" method is adopted, which will inevitably increase the vertical height of the overlapping position of the pipeline crossing. When installing the outer casing, the material consumption of the casing will increase due to the increase in the height of some pipeline crossing positions, and the internal cavity of the aircraft will increase, resulting in a decrease in space utilization rate. If a relief groove is opened on the surface of the middle part of the pipe fitting by means of spinning forming without damaging the pipe wall, so that the two crossed pipelines pass along the groove, the spatial layout of the pipeline can be greatly optimized, and the pipe fitting with the relief groove can be used to replace the pipe joint directly to achieve weight reduction of parts, which will make an important contribution to the structural lightweighting of the aircraft.

[0004] Regarding the non-axisymmetric spinning in the middle part of the pipe fitting, relevant research has been done in "Numerical simulation and experimental study on non axisymmetric spinning with a groove at the middle of the tube" by Jia Zhen et al. However, the non-axisymmetric spinning of the pipe fitting based on the profiling spinning wheel has obvious limitations. The radius and axial width of the profiling spinning wheel need to match the width and depth of the required relief groove, which requires designing and processing different specifications of profiling spinning wheels to meet the actual needs, and this goes against the characteristics of the spinning process with high efficiency and low cost. Therefore, a method for non-axisymmetric spinning in the middle part of the pipe fitting based on a universal spinning wheel is proposed. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention proposes an asymmetric spinning method for the middle part of a pipe fitting based on a universal spinning wheel to solve the problems of obvious limitations, low efficiency and high cost existing in the existing asymmetric spinning method for the middle part of a pipe fitting with a universal spinning wheel in the above-mentioned background art.

[0006] To achieve the above object, the present invention provides an asymmetric spinning method for the middle part of a pipe fitting based on a universal spinning wheel, including the following steps:

[0007] Step 1: Select a numerically controlled spinning machine, and respectively clamp two cylindrical mandrels at both ends of the pipe fitting to be spun. When clamping, reserve the position of the part to be spun.

[0008] Step 2: Install the universal spinning wheel on the spinning wheel frame of the main shaft of the spinning machine.

[0009] Step 3: Deduce and solve the non-axisymmetric spinning deformation path equation along the radial direction of the pipe fitting during the processing of the universal spinning wheel, and obtain the pressing amount of the universal spinning wheel at each moment in a single pass.

[0010] Step 4: Deduce and solve the trajectory equation of the universal spinning wheel along the axial feed during processing.

[0011] Step 5: Set the spinning forming method according to the difference in the spinning wheel path.

[0012] Step 6: According to the depth h and width d of the preformed avoidance groove, set the total number of passes to be processed, the relative feed rate of the universal spinning wheel, and the maximum trajectory curvature radius of the universal spinning wheel. According to the non-axisymmetric spinning deformation path equation, calculate the pressing amount of the universal spinning wheel at each moment in all passes.

[0013] Step 7: Write a numerically controlled code program according to the pressing amount of the universal spinning wheel at each moment in all passes.

[0014] Further, the said Step 3 includes:

[0015] Step 3.1: Define the center of the cross-sectional circle of the cylindrical pipe fitting (2) to be spun as point C, and the radius of the cross-sectional circle as R.

[0016] Step 3.2: Calculate the pressing amount of the universal spinning wheel (3) in the current pass, including:

[0017] Step 3.2.1: Define the radius of curvature of the trajectory of the universal wheel (3) in the current pass as r, the center of the trajectory of the universal wheel (3) as point O, the distance between the center O of the trajectory of the universal wheel (3) and the center C of the cross-section circle of the spun tube (2) as L, point P is the point on the spun tube (2) closest to the universal wheel (3) in the initial state, and is also the point where the outer periphery of the spun tube (2) and the universal wheel (3) are farthest relative to each other during the current spinning process. Point P is defined as the position corresponding to the starting time of the current pass, i.e., t=0, the center of the cross-section circle of the universal wheel (3) at the tth time is recorded as point A, then the distance between the center C of the cross-section circle of the spun tube (2) in the current pass and the center A of the cross-section circle of the universal wheel (3) is s, Φ is the radius of the universal wheel, let θ be the supplementary angle of ∠ACO, calculate the cosine value of θ, cosθ is expressed as:

[0018]

[0019] Step 3.2.2: Taking the spun pipe (2) as a reference, define the relative angle value of the universal wheel (3) rotating within the time period t in the current pass as θ, ω represents the rotational angular velocity of the spun pipe, t represents time, and θ is expressed as:

[0020] θ=π-ωt (2)

[0021] Step 3.2.3: Solve for s by combining formulas (1) and (2), then s is expressed as:

[0022]

[0023] Step 3.2.4: Define δ as the feed depth of the universal rotary wheel (3) at time t in the current pass. δ is expressed as:

[0024] δ=Φ+Rs (4)

[0025] Step 3.2.5: In order to more accurately represent the position of the universal rotating wheel (3) at different times, the inverse of δ f(t) is taken to represent the non-axisymmetric spinning deformation path equation. By combining formulas (3) to (4), the feed amount of the universal rotating wheel (3) at each time in a single pass can be obtained. Then, the non-axisymmetric spinning deformation path equation f(t) is expressed as:

[0026]

[0027] Furthermore, the step 4 comprises:

[0028] Step 4.1: To improve the stability of the lap joint in practical applications, it is required that the avoidance groove formed on the pipe fitting to be lapped is consistent with the outer shape of the lapping pipe fitting. According to the diameter of the lapping pipe fitting and the overlapping position height required for lapping, set the depth h and width d of the preformed avoidance groove, that is, the profile of the preformed avoidance groove on the longitudinal section is an arc of the cross-sectional circle of the lapping pipe fitting, and determine the trajectory equation of the circle where the arc is located;

[0029] Step 4.1.1: Taking the plane where the longitudinal section of the preformed avoidance groove is located as the reference plane, establish an appropriate plane rectangular coordinate system, such as Figure 3 , define (0, y0) as the coordinate origin, r′ as the radius of the circle to be found, x and y are respectively the abscissa and ordinate of any point on the trajectory of the circle, and the trajectory equation of the circle can be expressed as:

[0030] x 2 +(y - y0) 2 =r′ 2 (6)

[0031] Step 4.1.2: According to formula (6), y can be expressed as:

[0032]

[0033] Step 4.1.3: According to the geometric relationship, y0 can be expressed as:

[0034] y0 = r′ - h (8)

[0035] Step 4.1.4: Since the value of y is negative within the range of the arc of the circle in the longitudinal section of the preformed avoidance groove, according to its actual meaning, take the opposite number of y, h n represents the maximum depth formed when the universal roller (3) feeds axially to different positions. Substitute y0 in formula (8) into formula (7), then h n can be expressed as:

[0036]

[0037] where x can be expressed by formula (10), Δx represents the step size of the universal roller (3) during axial feeding. For each rotation of the pipe fitting, the universal roller (3) feeds axially by one step size, and n represents the number of rotations of the pipe fitting;

[0038] x = n△x (10)

[0039] Step 4.1.5: According to the geometric relationship, the geometric relationship among the depth, width and radius of the circle where the preformed avoidance groove is located can be expressed as:

[0040]

[0041] Step 4.1.6: r′ in formula (11) can be expressed as:

[0042]

[0043] Step 4.1.7: According to the non-axisymmetric spinning deformation path along the radial direction of the tube during processing by the universal wheel (3), there exists a geometric relationship as shown in formula (13), where r is the radius of curvature of the trajectory of the universal wheel (3) at the current pass. Combining formulas (9), (10), and (12), the radius of curvature of the universal wheel (3) at different passes can be expressed by formula (14):

[0044] r=L+Rh n (13)

[0045]

[0046] Substituting r in formula (14) into formula (5), we can obtain the feed amount of each pass at each moment when the universal rotary wheel (3) is at different positions during the axial feed process;

[0047] Step 4.2: Define F as the axial feed rate of the universal wheel (3), which means the displacement of the universal wheel (3) along the axial direction for each rotation of the spun tube (2). Δα is the angle of rotation of the tube. When the tube rotates at any angle, the displacement of the universal wheel (3) along the main axis can be expressed by formula (15). The spindle speed of the spinning machine is set to f. The displacement of the universal wheel (3) along the main axis at each moment can be expressed by formula (16);

[0048]

[0049]

[0050] Furthermore, the central axis of the universal rotating wheel (3) in step 2 is parallel to the main axis of the spun pipe (2).

[0051] Furthermore, in the step 7, the preformed avoidance groove can be processed by a numerical control system.

[0052] The beneficial effects of the present invention are:

[0053] The present invention provides a method for asymmetric spinning of the middle part of a pipe fitting based on a universal spinning wheel. By using the method of spin forming without a die, it completely relies on the cooperation of the translational motion of the universal spinning wheel in the radial and axial directions, the rotation of the spinning wheel, and the rotation of the pipe fitting to be spun for spin forming. It is a new spin forming method in the field of asymmetric spinning of pipe fittings. By using a universal spinning wheel for spin forming, avoidance grooves with arbitrary depths and widths can be formed. Compared with using a profiling spinning wheel, it greatly saves the process cost and time for manufacturing the profiling spinning wheel, and further reflects the characteristics of high efficiency and energy saving of the spin forming process. The tubular parts processed by the present invention can save space when used at the places where the pipelines of the aircraft are arranged in a crosswise manner, which helps to reduce the weight of the aircraft and promotes the solution of the technical problems of the utilization of the internal space of the aircraft and weight reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a schematic installation diagram of the pipe fitting to be spun in the present invention;

[0055] Figure 2 It is a schematic diagram of the derivation process of the non-axisymmetric spin forming deformation path equation in the radial direction in the present invention;

[0056] Figure 3 It is a schematic diagram of the movement trajectory of the universal spinning wheel in the axial direction in the present invention;

[0057] Figure 4a It is a schematic diagram of the first spin forming method of the universal spinning wheel in the present invention;

[0058] Figure 4b It is a schematic diagram of the second spin forming method of the universal spinning wheel in the present invention;

[0059] Figure 5 It is a result diagram of the formed part of the embodiment of the asymmetric spinning of the middle part of the pipe fitting based on the universal spinning wheel in the present invention;

[0060] In combination with the attached drawings, the reference numerals in the embodiments of the present invention are as follows:

[0061] 1 - cylindrical mandrel, 2 - pipe fitting to be spun, 3 - universal spinning wheel. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0062] In order to enable those skilled in the art of the present technology to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with the attached drawings and specific implementation examples.

[0063] In this embodiment, the model of the numerically controlled spinning machine is PS-CNCSXY-5. The numerically controlled spinning machine is built-in with a Siemens numerical control system, and the spindle speed is set at 10 r / min. In this embodiment, a spun tube 2 made of 6063-T state aluminum alloy with a diameter of 30 mm and a wall thickness of 2 mm is used. The depth of the preformed notch is 8 mm and the width is 26 mm. After the forming is completed, a test piece with dimensional and shape accuracy within 0.05 mm can be obtained.

[0064] A method for asymmetric spinning of the middle part of a tube based on a universal spinning wheel, comprising the following steps:

[0065] Step 1: Select a numerically controlled spinning machine. As Figure 1 shown, assemble the spun tube 2. Clamp two identical cylindrical mandrels 1 at both ends of the spun tube 2 respectively. When clamping, reserve the position of the spun part, that is, keep it hollow at the processing position of the preformed avoidance groove.

[0066] Step 2: Select a universal spinning wheel 3. Install the universal spinning wheel 3 on a spinning wheel frame perpendicular to the spindle of the spinning machine. As Figure 1 shown, the spinning wheel frame has been omitted in the figure. The central axis of the universal spinning wheel 3 is parallel to the spindle of the spun tube 2. The universal spinning wheel 3 rotates with the spindle. In the working state, the rotation center of the universal spinning wheel 3 and the rotation center of the spun tube 2 are on the same horizontal plane. During the spinning operation, the universal spinning wheel 3 not only needs to move reciprocally in the radial direction and rotate around its own rotation center, but also move axially along the spindle direction of the spinning machine. The universal spinning wheel 3 periodically contacts and presses down on the spun tube 2. On the basis of precise control of the radial displacement of the universal spinning wheel 3, by cooperating with the rotational movement of the spun tube 2, the effect of always pressing down on a certain local position of the spun tube 2 is achieved. At the same time, the universal spinning wheel 3 makes continuous axial movement according to the machine tool program under the control of the servo motor, and the two move synchronously, thereby realizing a complete spinning process.

[0067] Step 3: As Figure 2 shown, deduce and solve the non-axisymmetric spinning deformation path equation of the universal spinning wheel 3 along the radial direction of the spun tube 2 to obtain the pressing amount of the universal spinning wheel 3 at each moment in a single pass. Since the spun tube 2 rotates on its own axis during actual spinning, the universal spinning wheel 3 only moves back and forth in the radial direction. In the process of deducing the non-axisymmetric spinning deformation path equation, when taking the spun tube 2 as a reference, the universal spinning wheel 3 revolves around the spun tube 2. Under this reference, the path equation is deduced. The difference in the spinning trajectory between each spinning pass lies only in the radius of the trajectory circle. The specific deduction process includes:

[0068] Step 3.1: Define the center of the cross-sectional circle of the cylindrical spun tube 2 as point C, and the radius of the cross-sectional circle as R.

[0069] Step 3.2: Calculate the downward pressure of the universal roller 3 in the current pass, including:

[0070] Step 3.2.1: Define the radius of curvature of the trajectory of the universal roller 3 in the current pass as r, the center of the trajectory of the universal roller 3 as point O, the distance between the center O of the trajectory of the universal roller 3 and the center C of the cross-sectional circle of the tube to be spun 2 as L, point P as the point on the tube to be spun 2 closest to the universal roller 3 in the initial state, and also the point with the farthest relative position between the outer periphery of the tube to be spun 2 and the universal roller 3 during the spinning process of the current pass. Define point P as the position corresponding to the starting moment t = 0 in the current pass. The center of the cross-sectional circle of the universal roller 3 at the t-th moment is denoted as point A. Then the distance between the center C of the cross-sectional circle of the tube to be spun 2 and the center A of the cross-sectional circle of the universal roller 3 in the current pass is s, Φ is the radius of the universal roller 3, let θ be the supplementary angle of ∠ACO, calculate the cosine value of θ, and cosθ is expressed as:

[0071]

[0072] Step 3.2.2: Taking the tube to be spun 2 as a reference object, define the relative angular value of the rotation of the universal roller 3 in the t time period in the current pass as θ, ω represents the rotational angular velocity of the tube to be spun, and t represents time. Then θ is expressed as:

[0073] θ = π - ωt (2)

[0074] Step 3.2.3: Solve s by combining formula (1) - formula (2). Then s is expressed as:

[0075]

[0076] Step 3.2.4: Define δ as the feed depth of the universal roller 3 at the t-th moment in the current pass. δ is expressed as:

[0077] δ = Φ + R - s (4)

[0078] Step 3.2.5: To more accurately represent the position of the universal roller 3 at different moments, take the opposite number f(t) of δ to represent the non-axisymmetric spinning deformation path equation. By combining formula (3) - formula (4), the feed amount of the universal roller 3 at each moment in a single pass can be obtained. Then the non-axisymmetric spinning deformation path equation f(t) is expressed as:

[0079]

[0080] Step 4: Derive and solve the trajectory equation of the axial feed when the universal roller 3 is processed;

[0081] Step 4.1: As Figure 3As shown, to improve the stability of the lap joint in practical applications, it is required that the avoidance groove formed on the lap joint pipe fitting be consistent with the outer shape of the overlapping pipe fitting. According to the diameter of the overlapping pipe fitting and the height of the overlapping position required for the lap joint, the depth h and width d of the preformed avoidance groove are set. That is, the contour of the preformed avoidance groove in the longitudinal section is an arc of the cross-sectional circle of the overlapping pipe fitting, and the trajectory equation of the circle where the arc is located is determined;

[0082] Step 4.1.1: Taking the plane where the longitudinal section of the preformed avoidance groove is located as the reference plane, establish an appropriate plane rectangular coordinate system, such as Figure 3 , define (0, y0) as the coordinate origin, r′ as the radius of the circle to be found, x and y are respectively the abscissa and ordinate of any point on the trajectory of the circle, and the trajectory equation of the circle can be expressed as:

[0083] x 2 +(y - y0) 2 =r′ 2 (6)

[0084] Step 4.1.2: According to formula (6), y can be expressed as:

[0085]

[0086] Step 4.1.3: According to the geometric relationship, y0 can be expressed as:

[0087] y0 = r′ - h (8)

[0088] Step 4.1.4: Since the value of y is negative within the range of this arc of the longitudinal section of the preformed avoidance groove for the circle to be solved, according to its actual meaning, take the opposite number h of y n , which represents the maximum depth formed when the universal roller 3 feeds axially to different positions. Substitute y0 in formula (8) into formula (7), then h n can be expressed as:

[0089]

[0090] Among them, x can be expressed by formula (10), Δx represents the step size of the universal roller 3 during axial feeding. For each rotation of the tube to be spun 2, the universal roller 3 feeds axially by one step size, and n represents the number of rotations of the tube;

[0091] x = n△x (10)

[0092] Step 4.1.5: According to the geometric relationship, the geometric relationship among the depth, width of the preformed avoidance groove and the radius of the circle where it is located can be expressed as:

[0093]

[0094] Step 4.1.6: r′ in formula (11) can be expressed as:

[0095]

[0096] Step 4.1.7: According to the non-axisymmetric spinning deformation path along the radial direction of the spun tube 2 during the processing of the universal wheel 3, it can be known that there is a geometric relationship shown in formula (13), where r is the curvature radius of the trajectory of the universal wheel 3 in the current pass. Combining formulas (9), (10), and (12), the curvature radius of the universal wheel 3 in different passes can be expressed by formula (14):

[0097] r=L+Rh n (13)

[0098]

[0099] Substituting r in formula (14) into formula (5), we can obtain the feed amount of each pass at each moment when the universal rotary wheel 3 is at different positions during the axial feeding process;

[0100] Step 4.2: Define F as the axial feed rate of the universal wheel 3, that is, the displacement of the universal wheel 3 along the axial direction for each rotation of the spun tube 2. Δα is the angle of rotation of the spun tube 2. When the spun tube 2 rotates at any angle, the displacement of the universal wheel 3 along the main axis can be expressed by formula (15). The spindle speed of the spinning machine is set to f, and the displacement of the universal wheel 3 along the main axis at each moment can be expressed by formula (16);

[0101]

[0102]

[0103] Step 5: Figure 4a and Figure 4b As shown, two different spinning forming methods are set according to the difference in the paths of the universal spinning wheel 3. Figure 4a As shown, in method 1, the universal roller 3 performs feeding motion according to the pre-forming width in each pass, that is, the width of the avoidance groove remains unchanged in each depth forming process of the spinning process; Figure 4b As shown, in method 2, when forming at different depths, the forming experiment is carried out according to the width corresponding to the depth, that is, during the forming process, the width of the avoidance groove increases with the increase of its depth. At the same time, the bidirectional spinning method can also ensure the symmetry of the preformed avoidance groove in the axial direction;

[0104] Step 6: Based on the depth h and width d of the preformed relief groove, set the total number of passes to be machined, the relative feed rate of the universal roller 3, and the maximum trajectory curvature radius of the universal roller 3. According to the non-axisymmetric spinning deformation path equation, calculate the downward pressure of the universal roller 3 at each moment in all passes; in this embodiment, MATLAB software is used for programming calculation and the data is exported in the form of Excel.

[0105] Step 7: Import the data in the Excel generated in Step 6 into the numerical control machine tool, compile it into a Siemens numerical control code program according to the downward pressure at each moment in all passes, start the numerical control spinning machine, and execute the spin forming process without a die according to the processing program until the tube to be spun 2 is processed into a non-axisymmetric formed part, as Figure 5 shown. After actual measurement, the dimensional and shape accuracies of the formed part are both within 0.05 mm.

Claims

1. A method for asymmetric spinning of the middle part of a pipe fitting based on a universal spinning wheel, characterized in that, The steps include: Step 1: Select a CNC spinning machine, and clamp two cylindrical mandrels (1) at the two ends of the spun pipe (2) respectively, leaving a space for the spun part when clamping; Step 2: Install the universal rotary wheel (3) on a rotary wheel frame perpendicular to the main axis of the spinning machine; Step 3: derive and solve the equation of the non-axisymmetric spinning deformation path along the radial direction of the pipe during the processing of the universal spinning wheel (3), and obtain the downward pressure of the universal spinning wheel (3) at each moment in a single pass; Step 4: derive and solve the trajectory equation of the universal rotary wheel (3) during axial feeding; Step 5: Set the spinning method according to the difference in the spinning wheel path; Step 6: according to the depth h and width d of the preformed avoidance groove, the total number of passes required for processing, the relative feed rate of the universal wheel (3), and the maximum trajectory curvature radius of the universal wheel (3) are set, and according to the non-axisymmetric spinning deformation path equation, the downward pressure of the universal wheel (3) at each moment in all passes is calculated; Step 7: Write the NC code program according to the pressing amount at each moment in all passes; The step 3 comprises: Step 3.1: Define the center of the cross-section circle of the cylindrical spun pipe (2) as point C, and the radius of the cross-section circle as R; Step 3.2: Calculate the downward pressure of the universal rotary wheel (3) in the current pass, including: Step 3.2.1: Define the radius of curvature of the trajectory of the universal wheel (3) in the current pass as r, the center of the trajectory of the universal wheel (3) as point O, the distance between the center O of the trajectory of the universal wheel (3) and the center C of the cross-section circle of the spun tube (2) as L, point P is the point on the spun tube (2) closest to the universal wheel (3) in the initial state, and is also the point where the outer periphery of the spun tube (2) and the universal wheel (3) are farthest relative to each other during the current spinning process. Point P is defined as the position corresponding to the starting time of the current pass, i.e., t=0, the center of the cross-section circle of the universal wheel (3) at the tth time is recorded as point A, then the distance between the center C of the cross-section circle of the spun tube (2) in the current pass and the center A of the cross-section circle of the universal wheel (3) is s, Φ is the radius of the universal wheel, let θ be the supplementary angle of ∠ACO, calculate the cosine value of θ, cosθ is expressed as: Step 3.2.2: Taking the spun pipe (2) as a reference, define the relative angle value of the universal wheel (3) rotating within the time period t in the current pass as θ, ω represents the rotational angular velocity of the spun pipe, t represents time, and θ is expressed as: θ=π-ωt (2) Step 3.2.3: Solve for s by combining formulas (1) and (2), then s is expressed as: Step 3.2.4: Define δ as the feed depth of the universal rotary wheel (3) at time t in the current pass. δ is expressed as: δ=Φ+Rs (4) Step 3.2.5: In order to more accurately represent the position of the universal rotating wheel (3) at different times, the inverse of δ f(t) is taken to represent the non-axisymmetric spinning deformation path equation. By combining formulas (3) to (4), the feed amount of the universal rotating wheel (3) at each time in a single pass can be obtained. Then, the non-axisymmetric spinning deformation path equation f(t) is expressed as: The step 4 comprises: Step 4.1: To improve the stability of the lap joint in practical applications, it is required that the relief groove formed on the tube to be lapped be consistent with the outer shape of the lapping tube. According to the diameter of the lapping tube and the height of the overlapping position required for lapping, set the depth h and width d of the preformed relief groove, that is, the contour of the preformed relief groove in the longitudinal section is an arc of the cross-sectional circle of the lapping tube, and determine the trajectory equation of the circle where the arc is located; Step 4.1.1: Taking the plane where the longitudinal section of the preformed relief groove is located as the reference plane, establish an appropriate plane rectangular coordinate system, define (0, y0) as the coordinate origin, r′ as the radius of the circle to be found, x and y as the abscissa and ordinate of any point on the trajectory of the circle respectively, and the trajectory equation of the circle can be expressed as: x 2 +(y - y0) 2 = r' 2 (6) Step 4.1.2: According to formula (6), y can be expressed as: Step 4.1.3: According to the geometric relationship, y0 can be expressed as: y0 = r′ - h (8) Step 4.1.4: Since the y values are all negative within the arc range of the circle to be solved in the longitudinal section of the preformed avoidance groove, according to its actual meaning, take the opposite number h of y n represents the maximum depth formed when the universal roller (3) advances axially to different positions. Substitute y0 in formula (8) into formula (7), then h n can be expressed as: Where x can be expressed by formula (10), Δx represents the step size of the universal roller (3) during axial feeding. When the tube rotates one week, the universal roller (3) feeds axially by one step size, and n represents the number of rotations of the tube; x = nΔx (10) Step 4.1.5: According to the geometric relationship, the geometric relationship among the depth, width and radius of the circle where the preformed relief groove is located can be expressed as: Step 4.1.6: r′ in formula (11) can be expressed as: Step 4.1.7: According to the non-axisymmetric spinning deformation path of the universal roller (3) along the radial direction of the tube during processing, there is a geometric relationship shown in formula (13), where r is the curvature radius of the trajectory of the universal roller (3) in the current pass. Combining formulas (9), (10) and (12), the curvature radius of the universal roller (3) in different passes can be expressed by formula (14): r = L + R - h n (13) Substitute r in formula (14) into formula (5), and the feed rate of each pass at each moment when the universal roller (3) is axially fed can be obtained; Step 4.2: Define F as the feed rate of the universal roller (3) in the axial direction, that is, it represents the displacement of the universal roller (3) along the axial direction when the tube to be spun (2) rotates one week. Δα is the angle through which the tube rotates, then when the tube rotates through any angle, the displacement of the universal roller (3) in the main axis direction can be expressed by formula (15). If the spindle speed of the spinning machine is set to f, the displacement of the universal roller (3) in the main axis direction at each moment can be expressed by formula (16); 2. The asymmetric spinning method for the middle part of a pipe fitting based on a universal spinning wheel according to claim 1, characterized in that The central axis of the universal roller (3) in step 2 is parallel to the main axis of the tube to be spun (2).

3. The asymmetric spinning method for the middle part of a pipe fitting based on a universal spinning wheel according to claim 1, characterized in that In step 7, the preformed relief groove can be machined by a numerical control system.

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