Elliptical side wall hole pattern design method for controlling ovality of pipe based on stress-strain

Abstract

The invention relates to an elliptical side wall pass design method for controlling the ovality of a pipe based on stress-strain, which comprises the following steps of: inputting the outer diameter Dk and the wall thickness Sk of a pipe blank, the outer diameter Dj and the wall thickness Sj of a finished pipe, a roll gap SP, the length L of a deformation area, a pass opening angle alpha and an initial feeding amount t, and calculating a single-side initial opening value FCx of a pass side wall; a cyclic compression experiment is conducted on the pipe material, the initial opening value FCx is corrected according to stress-strain data of the pipe material, and the opening value Fx of the side wall of the hole pattern is calculated; meanwhile, necessary parameters of an oval side wall hole type opening are calculated; and finally, the maximum pipe feeding amount tmax is determined according to the critical point O of the elliptic curve. According to the stress-strain parameter characteristics of metal deformation, the pass opening is designed, stable rolling of the pipe is achieved, meanwhile, the ovality of the cold-rolled pipe in the rolling process can be controlled through uniform deformation of metal, the yield of the pipe is increased, and the production cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal pipe cold rolling, and particularly relates to an oval side wall pass design method for controlling pipe ovality based on stress and strain. BACKGROUND

[0002] As a key basic material of modern industry, seamless steel pipes play an irreplaceable role in many fields due to their hollow and weldless characteristics. In the field of energy transportation, seamless steel pipes are the preferred material for long-distance transportation of oil and natural gas. Their high strength and high sealing performance can ensure the safe and stable transportation of energy under complex geographical conditions and high pressure. In the field of mechanical manufacturing, seamless steel pipes are often used to manufacture parts with high precision and strength requirements, such as hydraulic cylinders and pneumatic elements, providing protection for the stable operation of mechanical equipment. In addition, seamless steel pipes are also indispensable in the construction, automobile, aerospace and other industries.

[0003] As an important process for producing high-precision seamless steel pipes, the design of roll pass plays a decisive role in the quality of pipes. At present, oval side wall pass rollers are widely used in the production of cold-rolled seamless steel pipes, but this type of roller has many drawbacks. The opening of the oval side wall pass is smaller than that of the straight side wall and the circular arc side wall, which limits the flow space of the metal during cold rolling and greatly increases the extrusion deformation. When the metal passes through the oval side wall pass, the deformation distribution in the circumferential direction is extremely uneven due to insufficient deformation space. This uneven deformation seriously affects the ovality of the pipe, making the ovality of the finished pipe exceed the standard range and making it difficult to meet the strict requirements of high-end application scenarios for the dimensional accuracy of the pipe. At the same time, the larger extrusion deformation causes the roller to bear higher pressure and friction, which in turn causes the roller to wear more quickly, shortens the service life of the roller, and increases production costs. In addition, due to the difficulty in controlling the quality of the pipe with the oval side wall pass, the waste rate is high during production, which not only reduces the production efficiency but also wastes resources.

[0004] In view of the above problems of the oval side wall pass roller in the production of cold-rolled seamless steel pipes, it is urgent to develop a new roller pass design or improve the process to overcome the shortcomings of the prior art and improve the production quality and efficiency of seamless steel pipes. SUMMARY

[0005] To solve the above problems, the present application provides an oval side wall pass design method for controlling pipe ovality based on stress and strain. Through a cyclic loading experiment on the material, the stress-strain curve data of the material is measured, and the mechanical properties of the material are combined with the pass opening design to design a pass opening that deforms the metal uniformly, which can accurately control the ovality of the pipe during cold rolling and improve the dimensional accuracy of the product.

[0006] The technical solutions adopted by the present application are as follows:

[0007] The elliptical side wall pass design method based on stress and strain control pipe ellipticity provided by the present application specifically comprises the following steps:

[0008] S1, determining the outer diameter D of the pipe blank k and the wall thickness S k , the outer diameter D of the finished pipe j and the wall thickness S j , the roll gap S of the roll P , the deformation zone length L, the opening angle α of the elliptical side wall pass, and the initial feed amount t;

[0009] S2, calculating the single-side initial opening value F of the pass side wall by the following first formula Cx ;

[0010]

[0011] Wherein: D x is the roll bottom groove diameter at the x section of the pipe deformation section; D x+t is the roll bottom groove diameter at the x+t section of the pipe deformation section;

[0012] S3, conducting a cyclic loading experiment on the material to measure the stress and strain curve data thereof;

[0013] S4, correcting the initial opening value F of the pass side wall Cx according to the stress and strain curve characteristics to obtain the opening value F of the pass side wall x ;

[0014] S5, calculating the opening width B of the elliptical side wall pass by the following second formula x :

[0015] B x = D x + 2F x

[0016] S6, calculating the eccentricity e of the pass center O1 and the elliptical curve center O2 by the following third formula:

[0017]

[0018] Wherein: θ is the ellipticity coefficient of the elliptical side wall pass;

[0019] S7, determining the major axis a and the minor axis b of the elliptical curve of the pass opening area;

[0020] S8, determining the critical point O of the elliptical curve of the elliptical side wall pass opening area;

[0021] S9, determining the maximum pipe feeding amount t from a critical point O of the elliptic curve max .

[0022] Further, in the step S1, the pipe is a small-diameter thin-walled seamless steel pipe, and the opening angle a of the elliptic side wall pass is 15°-40°; the roll gap is 1mm-2mm.

[0023] Further, in the step S2, x / L in the first formula represents the ratio of the distance from the rolling starting point to the x section to the total length of the deformation section, so the rolling starting point is 0 and the deformation section end point is 1.

[0024] Further, in the step S3, the cyclic loading experiment on the material is a compression experiment on the cylindrical pin-shaped material, the ratio of the compression length to the original length of the cylindrical pin is the same as the ratio of the pipe wall thickness change value to the initial pipe wall thickness, and the cycle number is the stroke number in the working period of the cold rolling pipe mill roll, and finally the stress-strain curve data of the material compression is obtained.

[0025] Further, in the step S4, the initial opening value F Cx of the pass side wall is corrected and calculated by the following fourth formula: x

[0026]

[0027] Where: σ max is the maximum stress of the material stress-strain curve; σ x is the stress corresponding to the x section of the pipe in the stress-strain curve; x M is the length corresponding to the maximum stress in the deformation section of the material stress-strain curve.

[0028] Further, in the step S6, the ellipticity coefficient θ of the elliptic side wall pass is calculated by the following fifth formula:

[0029]

[0030] Further, in the step S7, the major axis a of the elliptic curve of the pass opening area is calculated by the following sixth formula:

[0031]

[0032] The minor axis b of the elliptic curve of the pass opening area is calculated by the following seventh formula:

[0033]

[0034] Further, in the step S8, the critical point O of the elliptic curve of the elliptic side wall pass opening area is the intersection of the angle bisector of the pass opening angle and the elliptic curve.​

[0035] Further, in the step S9, the critical point O needs to be located on or outside the outer diameter profile line of the fed pipe, and when the critical point O is located on the outer diameter profile line of the fed pipe, the feeding amount is the maximum t max The maximum feeding amount t max is calculated by the following eighth formula:

[0036]

[0037] Wherein, K is the total reduction ratio of pipe deformation; R xO is the pass radius at the critical point.

[0038] Further, the total reduction ratio K of pipe deformation is calculated by the following ninth formula:

[0039]

[0040] The pass radius R xO at the critical point is calculated by the following tenth formula:

[0041]

[0042] Compared with the prior art, the present application has the following beneficial effects:

[0043] According to the above technical scheme, the present application calculates the single-side initial opening value F Cx of the pass side wall under the premise that the outer diameter D k and wall thickness S k of the pipe blank, the outer diameter D j and wall thickness S j of the finished pipe, the roll gap S P , the deformation zone length L, the opening angle α of the elliptical side wall pass and the initial feeding amount t are known; at the same time, the stress-strain data of the pipe material obtained by the cyclic compression experiment are corrected according to the experimental data, and the initial opening value F Cx of the pass side wall is corrected and the opening value F x of the pass side wall is calculated; the opening width B x of the elliptical side wall pass and various necessary parameters of the pass opening are calculated; and the maximum pipe feeding amount t max is determined by the critical point O of the elliptical curve. Compared with the traditional method, the stress-strain parameters of metal deformation are considered in the calculation of the pass opening in the present application, the pass opening of the deformation section in the early stage is larger, which is beneficial to the deformation flow of the metal, the pass opening in the later stage is smaller, which is beneficial to the forming of the finished pipe, the rolling efficiency can be effectively improved, the production cost is reduced, and the uniform deformation of the metal can control the ovality of the pipe during the rolling process and the finished pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the process of the present invention.

[0045] Figure 2 It is a schematic diagram of the longitudinal and elliptical hole cross section of the cold-rolled seamless steel pipe;

[0046] Figure 3 is a schematic diagram of the hole cross section at the deformation section x;

[0047] Figure 4 It is a schematic diagram of the cross-section of the hole at the deformation section x after the pipe is fed in. DETAILED DESCRIPTION

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0049] The pilger cold rolling mill is the main cold rolling equipment for producing seamless steel pipes. Its upper and lower rollers 1 and the middle mandrel 3 extrude and roll the pipe 2. Figure 2 As shown, the pipe 2 is a small-diameter, thin-walled, seamless steel tube. After the pipe 2 is fed, the upper and lower rollers 1 translate and roll from the initial position of the deformation section toward the end, reducing the diameter and wall thickness of the pipe 2. However, compared to straight and circular sidewalls, the elliptical sidewall pass opening is smaller, limiting the range of feed rate options. Furthermore, the ellipticity of the rolled pipe deformation cone is poor, due to the intense metal deformation. Excessive metal folding deformation in the pass opening area not only results in a large ellipticity but also creates significant defects on the pipe's inner wall, such as cracks and wrinkles.

[0050] Perform cyclic loading test on the material and measure its stress-strain curve data; at the same time, k and wall thickness S k , finished pipe outer diameter D j and wall thickness S j , Roller gap S P , deformation zone length L, elliptical side wall hole opening angle α and initial feed amount t are known, calculate the initial opening value F of the hole side wall Cx ; And according to the experimental data, the initial opening value F of the hole side wall Cx Make corrections and calculate the hole side wall opening value F x , and then calculate the various necessary parameters of the elliptical side wall hole opening, the specific parameters and position relationship are as follows Figure 3 shown.

[0051] Under the premise that the opening parameters of the elliptical side wall hole are known, the critical point O of the elliptical curve in the opening area of ​​the elliptical side wall hole is determined, and the maximum pipe feeding amount t is determined by the critical point O of the elliptical curve max ,,like Figure 4 shown.

[0052] The elliptical sidewall hole design method based on stress and strain control of the pipe ellipticity proposed in this invention is as follows: Figure 1 The specific implementation process is as follows:

[0053] S1. Determine the outer diameter D of the tube k and wall thickness S k , finished pipe outer diameter D j and wall thickness S j , Roller gap S P , deformation zone length L, elliptical side wall hole opening angle α and initial feed amount t;

[0054] The tube blank is a small-diameter thin-walled seamless steel tube, the opening angle α of the elliptical side wall hole is 15°-40°, and the roll gap is 1mm-2mm.

[0055] S2. Calculate the initial opening value F of the hole side wall using the following first formula Cx ;

[0056]

[0057] Where: D x D is the diameter of the roller bottom groove at the x section of the pipe deformation section; x+t is the diameter of the roller bottom groove at the x+t section of the pipe deformation section;

[0058] x / L represents the ratio of the distance from the rolling starting point to the x section to the total length of the rolling deformation section, so the rolling starting point is 0 and the deformation section end point is 1.

[0059] S3. Perform cyclic loading experiments on the material and measure its stress-strain curve data;

[0060] Among them, the cyclic loading test for the material is a compression test on the material in the shape of a cylindrical pin. The ratio of the compressed length to the original length of the cylindrical pin and the ratio of the change in pipe wall thickness to the initial wall thickness of the pipe are the same. The number of cycles is the number of strokes in the working cycle of the cold rolling mill roller, and finally the stress-strain curve data of the material compression is obtained.

[0061] S4. According to the characteristics of stress-strain curve, the initial opening value F of the hole side wall is Cx Make corrections to obtain the hole side wall opening value F x ;

[0062] Since the material will produce work hardening phenomenon under cyclic loading, the metal is softer in the early stage of deformation and harder in the later stage. Therefore, the hole opening in the early stage of deformation is larger, which is conducive to the deformation of the metal, and the opening is smaller in the later stage, which is conducive to the formation of the finished pipe. Therefore, the initial opening value F of the hole side wall is calculated by the following fourth formula: Cx Make corrections and calculate the hole side wall opening value F x :

[0063]

[0064] Where: max is the maximum stress of the material stress-strain curve; σ x is the stress corresponding to the x section of the pipe in the stress-strain curve; M It is the length corresponding to the maximum stress in the deformation section of the material stress-strain curve.

[0065] S5. Calculate the opening width B of the elliptical side wall hole by the following second formula x :

[0066] B x =D x +2F x

[0067] S6. Calculate the eccentricity e between the hole center O1 and the elliptical curve center O2 using the following third formula:

[0068]

[0069] Where: θ is the ellipticity coefficient of the elliptical sidewall hole;

[0070] The ellipticity coefficient θ of the elliptical sidewall hole is calculated by the following fifth formula:

[0071]

[0072] S7, determining the major axis a and minor axis b of the elliptical curve of the hole opening area;

[0073] The major axis a of the elliptical curve of the hole opening area is calculated by the following sixth formula:

[0074]

[0075] The minor axis b of the elliptical curve in the hole opening area is calculated using the following seventh formula:

[0076]

[0077] S8, determining the critical point O of the elliptical curve of the elliptical sidewall hole opening area;

[0078] The critical point O of the elliptical curve of the opening area of the elliptical side wall pass is the intersection of the angle bisector of the opening angle and the elliptical curve.

[0079] S9, determining the maximum pipe feeding amount t from the critical point O of the elliptical curve max ;

[0080] The critical point O needs to be located on the outer diameter contour line of the fed pipe or outside, and when the critical point O is located on the outer diameter contour line of the fed pipe, the feeding amount is the maximum t max The maximum feeding amount t is calculated by the following eighth formula max :

[0081]

[0082] Wherein: K is the total reduction ratio of pipe deformation; R xO is the pass radius at the critical point.

[0083] The total reduction ratio K of pipe deformation is calculated by the following ninth formula:

[0084]

[0085] The pass radius R at the critical point is calculated by the following tenth formula xO :

[0086]

[0087] The opening width of the pass side wall is designed to be larger in the early stage of the deformation section, which is beneficial to the deformation flow of the metal, and the opening is smaller in the later stage, which is beneficial to the forming of the finished pipe, can improve the rolling efficiency, and the uniform deformation of the metal can control the ovality of the pipe during the rolling process and the finished pipe.

[0088] The application will be further described through specific examples:

[0089] The elliptical side wall pass design method based on stress-strain control pipe ovality includes the following steps:

[0090] S1, determining the outer diameter D k =25.4mm and the wall thickness S k =2.5mm, the finished pipe outer diameter D j =12.7mm and the wall thickness S j =1.24mm, the roll gap S P =1mm, the deformation zone length L=280mm, the elliptical side wall pass opening angle a=25° and the initial feeding amount t=2mm;

[0091] S2, here let x = 10mm as an example of the calculation (the same below), the hole type side wall single edge initial opening value F is calculated by the following first formula C10 = 0.5865mm, the relevant calculation formula is:

[0092]

[0093] S3, the stress strain curve data is measured by cyclic loading experiment for the material;

[0094] S4, the hole type side wall initial opening value F is corrected according to the stress strain curve characteristics Cx , and the hole type side wall opening value F 10 = 1.2203mm is obtained;

[0095] S5, the elliptical side wall hole type opening width B is calculated by the following second formula 10 = 27.2195mm, the relevant calculation formula is:

[0096] B x = D x + 2F x

[0097] S6, the eccentricity e = 1.28mm between the hole type center O1 and the elliptical curve center O2 is calculated by the following third formula, and the relevant calculation formula is:

[0098]

[0099] S7, the major axis a = 13.67mm and the minor axis b = 12.66mm of the elliptical curve in the hole type opening area are determined;

[0100] S8, the critical point O of the elliptical curve in the elliptical side wall hole type opening area is determined;

[0101] S9, the maximum pipe feeding amount t max = 8.07mm is determined by the critical point O of the elliptical curve.

[0102] The cyclic loading experiment for the material is a compression experiment for the cylindrical pin shaped material, the ratio of the compression length to the original length of the cylindrical pin is the same as the ratio of the pipe wall thickness change value to the initial pipe wall thickness, the cycle number is the stroke number in the work period of the cold rolled pipe mill roller, and finally the stress strain curve data of the material compression is obtained, and the specific data is shown in Table 1:

[0103] Table 1 stress strain part data of material cyclic compression experiment

[0104] Strain Stress Strain Stress Strain Stress Strain Stress 0 0 0.1753 655.2 0.3506 908.92 0.5259 1037.16 0.0175 375.2 0.1928 681.96 0.3681 932.26 0.5434 1036.69 0.0351 406.66 0.2104 715.24 0.3856 944.02 0.5610 1036.46 0.0526 454.78 0.2279 730.3 0.4032 964.9 0.5785 1035.93 0.0701 480.1 0.2454 767.02 0.4207 984.55 0.5960 1035.25 0.0876 516.75 0.2629 789.21 0.4382 994.94 0.6135 1034.86 0.1052 553.7 0.2805 819.48 0.4558 1002.78 0.6311 1034.44 0.1227 574.55 0.2980 845.3 0.4733 1020.62 0.6486 1034.12 0.1402 601.52 0.3155 867.5 0.4908 1026.54 0.6661 1033.78 0.1578 625.13 0.3331 884.5 0.5084 1032.48 0.6836 1033.42

[0105] Since the material will produce work hardening phenomenon under cyclic loading, the metal in the early stage of deformation section is softer, and the metal in the later stage is harder, so the hole opening in the early stage of deformation section is larger, which is beneficial to the deformation of the metal, and the opening in the later stage is smaller, which is beneficial to the forming of the finished pipe; the initial opening value F of the hole side wall is calculated by the following fourth formula Cx The hole side wall opening value F is corrected and calculated 10 = 1.2203 mm, and the related calculation formula is:

[0106]

[0107] The ellipticity coefficient θ of the elliptical side wall hole is calculated by the following fifth formula: θ = 1.0985, and the related calculation formula is:

[0108]

[0109] The long axis a of the elliptical curve of the hole opening area is calculated by the following sixth formula: a = 13.67 mm, and the related calculation formula is:

[0110]

[0111] The short axis b of the elliptical curve of the hole opening area is calculated by the following seventh formula: b = 12.66 mm, and the related calculation formula is:

[0112]

[0113] The critical point O needs to be located on the outer diameter contour line of the pipe after feeding or outside. When the critical point O needs to be located on the outer diameter contour line of the pipe after feeding, the feeding amount is the maximum t max The maximum feeding amount t is calculated by the following eighth formula: max = 8.07 mm, and the related calculation formula is:

[0114]

[0115] The total reduction ratio K of the pipe deformation is calculated by the following ninth formula: K = 0.69315, and the related calculation formula is:

[0116]

[0117] The hole radius R at the critical point is calculated by the following tenth formula: xO = 12.4 mm, and the related calculation formula is:

[0118]

[0119] Table 2 Position of deformation section during pipe rolling process and ellipticity of finished pipe

[0120] Parameter Value / % Parameter Value / % Elongation at x = 2 mm position 0.595 Elongation at x = 200 mm position 0.459 Elongation at x = 50 mm position 0.574 Elongation at x = 230 mm position 0.427 Elongation at x = 100 mm position 0.547 Elongation at x = 260 mm position 0.401 Elongation at x = 150 mm position 0.498 Elongation of finished pipe 0.385

[0121] From the experimental measurement data, when the feed amount is 2mm and the opening angle is 25°, the difference between the long axis and the short axis of the initial position of the conical pipe is only 0.11mm, and with the progress of the rolling process, the ellipticity of the pipe gradually decreases, and the ellipticity of the finished pipe reaches 0.385%. Therefore, considering the stress-strain parameters of metal deformation in the calculation of the opening of the pass, the deformation flow of the metal and the forming of the pipe can be facilitated, and the uniform deformation of the metal can control the ellipticity of the pipe during the rolling process and the finished pipe.

[0122] The details of the application are all known technologies.

[0123] The above-described embodiments are merely preferred embodiments of the present application and are not intended to limit the scope of the present application. Various modifications and improvements to the technical solutions of the present application made by those of ordinary skill in the art without departing from the design spirit of the present application shall fall within the protection scope of the present application as defined by the claims.

Claims

1. The elliptical sidewall pass design method based on stress-strain control of pipe ellipticity is characterized by: The method comprises the following steps: S1. Determine the outer diameter D of the tube k and wall thickness S k , finished pipe outer diameter D j and wall thickness S j , Roller gap S P , deformation zone length L, elliptical side wall hole opening angle α and initial feed amount t; S2. Calculate the initial opening value F of the hole side wall using the following first formula Cx ; Where: D x D is the diameter of the roller bottom groove at the x section of the pipe deformation section; x+t is the diameter of the roller bottom groove at the x+t section of the pipe deformation section; S3. Perform cyclic loading experiments on the material and measure its stress-strain curve data; S4. According to the characteristics of stress-strain curve, the initial opening value F of the hole side wall is Cx Make corrections to obtain the hole side wall opening value F x ; S5. Calculate the opening width B of the elliptical side wall hole by the following second formula x : B x =D x +2F x S6. Calculate the eccentricity e between the hole center O1 and the elliptical curve center O2 using the following third formula: Where: θ is the ellipticity coefficient of the elliptical sidewall hole; S7, determining the major axis a and minor axis b of the elliptical curve of the hole opening area; S8, determining the critical point O of the elliptical curve of the elliptical sidewall hole opening area; S9. Determine the maximum pipe feed rate t by the critical point O of the elliptic curve max .

2. The method for designing an elliptical sidewall pass based on stress-strain control of the tubing ellipticity according to claim 1, characterized in that: In step S1, the pipe is a small-diameter thin-wall seamless steel pipe, the elliptical side wall hole opening angle α is 15°-40°, and the roller gap is 1mm-2mm.

3. The method for designing an elliptical sidewall pass based on stress-strain control of the tubing ellipticity according to claim 1, characterized in that: In step S2, x / L in the first formula represents the ratio of the distance from the rolling starting point to the x-section to the total length of the rolling deformation section, so the rolling starting point is 0 and the deformation section end point is 1.

4. The method for designing an elliptical sidewall pass based on stress-strain control of the tubing ellipticity according to claim 1, characterized in that: In step S3, the cyclic loading test for the material is a compression test on the cylindrical pin-shaped material. The ratio of the compressed length to the original length of the cylindrical pin and the ratio of the change in the pipe wall thickness to the initial wall thickness of the pipe are the same. The number of cycles is the number of strokes within the working cycle of the cold rolling mill roller, and finally the stress-strain curve data of the material compression is obtained.

5. The method for designing an elliptical sidewall pass based on stress-strain control of the tubing ellipticity according to claim 1, characterized in that: In step S4, the initial opening value F of the hole side wall is calculated by the following fourth formula: Cx Make corrections and calculate the hole side wall opening value F x : Where: max is the maximum stress of the material stress-strain curve; σ x is the stress corresponding to the x section of the pipe in the stress-strain curve; M It is the length corresponding to the maximum stress in the deformation section of the material stress-strain curve.

6. The method for designing an elliptical sidewall pass based on stress-strain control of the tubing ellipticity according to claim 1, characterized in that: In step S6, the ellipticity coefficient θ of the elliptical sidewall hole is calculated by the following fifth formula:

7. The method for designing an elliptical sidewall pass based on stress-strain control of the tubing ellipticity according to claim 1, characterized in that: In step S7, the major axis a of the elliptic curve of the hole opening area is calculated by the following sixth formula: The minor axis b of the elliptical curve in the hole opening area is calculated using the following seventh formula:

8. The method for designing an elliptical sidewall pass based on stress-strain control of the tubing ellipticity according to claim 1, characterized in that: In step S8, the critical point O of the elliptical curve of the elliptical sidewall hole opening area is the intersection of the angle bisector of the hole opening angle and the elliptical curve.

9. The method for designing an elliptical sidewall pass based on stress-strain control of the tubing ellipticity according to claim 1, characterized in that: In step S9, the critical point O needs to be located on or outside the outer diameter contour line of the pipe after feeding. When the critical point O is located on the outer diameter contour line of the pipe after feeding, the feeding amount is the maximum t max , calculate the maximum feed amount t by the following eighth formula max : Where: K is the total diameter reduction ratio of the pipe deformation; R xO is the hole radius at the critical point.

10. The method for designing an elliptical sidewall pass based on stress-strain control of the tube ellipticity according to claim 9, characterized in that: The total reduction ratio K of pipe deformation is calculated by the following ninth formula: The hole radius R at the critical point is calculated by the following tenth formula xO :

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