Design method for drawing metal pipe fitting based on fixed core rod conical die

Abstract

The invention belongs to the technical field of metal pipe conical die drawing, and particularly discloses a design method for drawing a metal pipe fitting based on a fixed core rod conical die. According to the design method, the yield strength and the flow stress model of metal pipe fitting drawing are obtained firstly, the outer diameter of an incoming pipe fitting is used as a variable based on the known incoming pipe fitting wall thickness, the outer diameter and wall thickness of a finished pipe, the drawing rate, the drawing temperature and the flow stress model, and the total drawing stress is calculated; during calculation, the optimal compression angle value is determined under the condition that the minimum value of the drawing stress is obtained, calculation is terminated under the condition that the maximum drawing tension degree is obtained, and finally key process parameters such as the maximum outer diameter of the incoming metal pipe fitting and the optimal compression angle of the drawing hole are determined, so that process optimization is achieved. According to the design method, the process design efficiency is improved, and the trial and error cost of the production field process is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of metal tube tapered die drawing, and in particular relates to a design method for drawing a metal tube based on a fixed mandrel tapered die. Background Art

[0002] The metal pipe deformation process by drawing with a fixed mandrel cone die is one of the methods of metal plastic forming. It can not only reduce the diameter and wall of the metal pipe to achieve the target product size, but also refine the metal material grains and improve the mechanical properties. Therefore, it is widely used in the drawing production of metal pipes. In this drawing deformation process, maximizing the deformation amount of each pass can make the metal grains finer, the structure more uniform, and the surface quality better, but it also brings the risk of instability or even breaking of the pipe drawing. Therefore, how to maximize the drawing deformation amount of each pass while avoiding excessive drawing force through reasonable process design has always been a technical problem that has plagued the on-site production of enterprises. At present, the use of finite element simulation technology has made certain progress in the study of the deformation law of the drawing process. Although it can help to design the drawing process to a certain extent, its simulation calculation is large and time-consuming, and it cannot meet the real-time and high-efficiency requirements of process formulation and optimization on the production line. How to research and develop a method that can scientifically, reasonably, quickly and efficiently realize the design and calculation of the drawing process, so as to maximize the deformation of the pass in the fixed mandrel conical die drawing process while avoiding the instability of the drawing process has become an urgent technical need. Summary of the invention

[0003] In view of the above-mentioned prior art problems involving maximizing the deformation amount per pass and avoiding instability of the drawing process during the drawing process with a fixed mandrel conical die, as well as the problems of design and calculation, the present invention will provide a design method for drawing metal pipes based on a fixed mandrel conical die.

[0004] To achieve the above purpose, the following technical solutions are specifically included: A design method for drawing a metal pipe based on a fixed mandrel tapered die comprises the following steps: (1) Obtain the yield strength of metal pipes through tensile tests ; (2) Obtain stress-strain curves of multiple groups of metal pipe fittings through Gleeble test, and obtain the rheological stress model of metal pipe fittings through the stress-strain curves of multiple groups of metal pipe fittings; (3) Obtain processing deformation temperature T and drawing exit line speed , Wall thickness of finished pipe , Outer diameter of finished pipe , Wall thickness of incoming metal pipe fittings , the friction coefficient between the metal pipe and the inner wall of the mold And the friction coefficient between the metal pipe and the mandrel ; (4) A fixed mandrel conical die is preset to draw the incoming metal pipe to obtain a finished pipe, and the deformation zone of the metal pipe during the drawing process is divided into a diameter reduction zone and a wall reduction zone. Based on the rheological stress model of the metal pipe in step (2), the parameters obtained in step (3) and the calculation formula in the energy method, the outer diameter of the incoming metal pipe is calculated. and the compression angle of the drawing hole As a variable, the average drawing stress of the outlet end face of the drawn pipe is iteratively calculated. , the condition for the termination of iterative calculation is: In the formula, is the error value; after the calculation is terminated, the corresponding design , .

[0005] The present invention divides the strategy of maximizing the deformation of the metal pipe into two parts: maximizing the outer diameter of the incoming metal pipe under the condition that the wall thickness of the incoming metal pipe is fixed. The present invention combines the outer diameter and wall thickness of the incoming metal pipe and the finished pipe, the optimized compression angle of the drawing hole and the maximum tension of the drawing, and performs design calculations to make the pipe outside the drawing die in a reasonable maximum tension mechanical state, that is, when the average drawing stress of the outlet end face of the drawn pipe is Close to 0.75 times the yield strength of metal pipes The iterative calculation is terminated when the drawing process is realized to maximize the deformation of each pass while ensuring the process safety and stability, that is, the drawn workpiece neither breaks nor enters a plastic state outside the drawing die. The present invention can improve the efficiency of process design, effectively reduce the cost of process trial and error, and improve production efficiency.

[0006] In the design method of the present invention, the yield strength and rheological stress model of the metal pipe drawing are first obtained, the outer diameter of the incoming metal pipe is preset as a fixed value, and then the compression angle of the drawing hole is used as a variable, and the optimized compression angle of the drawing hole is iteratively calculated by the energy method calculation formula. Then, based on the known optimized compression angle of the drawing hole, the outer diameter and wall thickness of the finished pipe, the drawing rate, the drawing temperature and the rheological stress model, the outer diameter of the incoming metal pipe is used as a variable, and the real-time theoretical drawing stress of the drawing is iteratively calculated. During the iterative calculation, the real-time theoretical drawing stress is made close to 0.75 times the yield strength of the metal pipe drawing, so as to include the maximum tension mechanical state of the drawn metal pipe into the calculation scope. After terminating the iterative calculation, the outer diameter and other process parameters of the corresponding incoming metal pipe can be determined. The design method of the present invention comprehensively applies modeling technology based on metal mechanics test data and material constitutive model, analytical calculation based on the principle of plastic mechanics, and computer programming iterative solution technology, which improves the efficiency of process design and reduces the trial and error cost of production site processes, thereby creating economic benefits.

[0007] Preferably, in step (1), during the tensile test, a plurality of tensile pause points are set so that the yield strength of the metal pipe is the yield strength of the metal pipe with the cumulative work hardening effect.

[0008] Preferably, in step (2), the rheological stress model of the metal pipe is the Johnson-Cook rheological stress model. Preferably, in step (4), the calculation formula in the energy method includes the following calculation formula: In the formula, is the work done by the pulling force at the pulling outlet corresponding to unit volume, and the calculation formula is: In the formula, is the average drawing stress of the outlet end face of the drawn pipe; Metal flow occurs during drawing The corresponding length of the pipe after drawing; Metal flow occurs during drawing The corresponding length of the pipe before drawing; is the ideal unit volume strain energy of the reduced diameter area, and its calculation formula is: In the formula, is the average flow stress corresponding to the diameter reduction deformation zone; is the equivalent strain value of the metal pipe in the diameter reduction deformation zone, and its calculation formula is: In the formula, The above Substitute into the rheological stress model of the metal pipe in step (2) and calculate the average rheological stress in the drawing reduction zone: , and in the calculation process, the equivalent strain degree is taken The approximate value calculation formula is: Equivalent strain rate The calculation formula is: Where t is the deformation time of the metal passing through the deformation zone, and its calculation formula is: In the formula, is the inlet linear velocity of the metal pipe; is the instantaneous linear velocity of the metal pipe when it enters the wall reduction zone; , The value of the known metal pipe drawing outlet line speed Under the premise of , it is calculated according to the law of constant metal volume; is the ideal unit volume strain energy of the wall reduction area, and its calculation formula is: In the formula, is the average flow stress corresponding to the wall reduction deformation zone; is the equivalent strain value of the pipe fittings in the wall deformation zone, and its calculation formula is: In the formula, The above Substitute into the rheological stress model of the metal pipe in step (2) and calculate the average rheological stress in the drawing and wall reduction zone: ; In the calculation process, take the equivalent strain degree The approximate value calculation formula is: Equivalent strain rate The calculation formula is: Where t is the deformation time of the metal passing through the deformation zone, and its calculation formula is: In the formula, is the linear speed of the metal pipe drawing outlet, is the instantaneous linear velocity of the metal pipe when it enters the wall reduction zone, , The value of the known metal pipe drawing outlet line speed Under the premise of , it is calculated according to the law of constant metal volume; is the shear strain energy per unit volume in the deformation zone, and its calculation formula is: In the formula, The compression angle of the drawing hole; is the friction work per unit volume in the deformation zone, and its calculation formula is: In the formula, is the friction coefficient between the metal pipe and the inner hole wall of the mold; is the friction coefficient between the metal pipe and the mandrel; The radial component of the pressure of the die on the metal pipe in the diameter reduction area; It is the radial component of the pressure of the die on the metal pipe in the wall reduction area; To reduce the pressure of the core rod in the wall area on the inner wall of the metal pipe; The length of work done by the metal per unit volume flow to overcome friction in the diameter reduction area; It is the length of work done by metal per unit volume flow to overcome friction in the wall reduction area.

[0009] Preferably, in step (3), the 0.5-4mm.

[0010] Preferably, in step (3), the 20-40mm.

[0011] Preferably, in step (3), the 0.5-4mm.

[0012] Preferably, in step (3), the 400-800mm / s.

[0013] Preferably, in step (3), the 15-30℃.

[0014] Preferably, in step (4), the 30-80mm.

[0015] Preferably, in step (4), the 8-20°.

[0016] Preferably, in step (4), the <1%, more preferably <0.1%.

[0017] The closer the error value is to 0, the higher the average drawing stress of the outlet end face of the drawn pipe. The closer it is to 0.75 times the yield strength of the metal pipe , which can avoid the instability of pipe drawing caused by large deformation in a single pass.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The design method of the present invention is based on scientific engineering calculation to carry out process design. While obtaining the maximum deformation of the fixed mandrel conical die drawing pass, it can avoid the instability of the pipe drawing caused by large deformation in a single pass; (2) The design method of the present invention improves the efficiency of process design and reduces the process trial and error cost at the production site due to the comprehensive application of modeling technology based on metal mechanics test data and material constitutive model, analytical calculation based on the principle of plastic mechanics, and computer programming iterative solution technology, thereby creating economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a calculation flow chart in an embodiment of the present invention.

[0020] Figure 2 It is a schematic structural diagram of the drawing deformation zone of the fixed mandrel cone die in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below through specific examples. The test methods used in the examples and / or comparative examples are conventional methods unless otherwise specified; the materials, reagents, etc. used can be obtained from commercial channels unless otherwise specified.

[0022] In the present invention, the units of the parameters involved are as follows: , , , The unit is mm; The unit of is mm / s; the unit of T is ℃, , The unit is °, and the radian unit rad is used in the calculation; , The unit is MPa.

[0023] Example 1 A design method for drawing metal pipes based on a fixed mandrel conical die, the calculation flow chart is as follows: Figure 1 As shown, the mold structure diagram is as shown in the attached Figure 2 As shown, the specific steps include: (1) Obtaining metal yield strength: The yield strength of metal pipes taking into account work hardening is obtained through tensile tests on metal pipes. Specific value.

[0024] For example, the as-cast drawn specimen is regarded as a tensile specimen without work hardening, the tensile specimen obtained after the as-cast specimen is cold drawn with an equivalent strain degree of 0.4 is regarded as a medium-hardened specimen, and the tensile specimen obtained after the as-cast specimen is cold drawn with an equivalent strain degree of 0.85 is regarded as a highly work-hardened specimen. The corresponding metal yield strength values ​​are obtained by drawing the samples separately. In this way, the actual metal yield strength in the drawing deformation can be estimated by interpolation method. .

[0025] (2) Obtaining JC model coefficients: Use a Gleeble testing machine to perform tensile tests under different temperatures and strain rates. Use the deformation resistance model to fit the stress-strain curve obtained from the test to obtain the material constants in the deformation resistance model of the metal for subsequent calculations.

[0026] Taking the Johnson-Cook model as an example of the deformation resistance model, the following formula is used: In the formula, is the average flow stress in the drawing deformation zone; A, B, C, n and m are all material constants; is the equivalent strain degree; is the dimensionless equivalent strain rate, and the calculation formula is: In the formula, is the equivalent strain rate; is the reference value of equivalent strain rate; is the dimensionless temperature coefficient, and its calculation formula is: In the formula, , , They are respectively the average deformation temperature of the metal material currently being deformed, the reference room temperature, and the melting point temperature of the material.

[0027] (3) Obtain working condition parameters: preset processing deformation temperature T and drawing exit line speed , Wall thickness of finished pipe , Wall thickness of incoming metal pipe fittings .

[0028] (4) Obtain mold related parameters: Preset the finished tube diameter (including the outer diameter of the finished tube) ), core rod diameter, friction coefficient between the pipe and the inner wall of the mold and the friction coefficient between the pipe and the mandrel .

[0029] (5) The outer diameter of the incoming metal pipe is preset to be , the wall thickness of the incoming metal pipe is The outer diameter of the finished tube is , the wall thickness of the finished tube is ; During the drawing process, the drawing outlet line speed , the processing deformation temperature is T, and the average drawing stress (referred to as drawing stress) at the outlet end of the drawn pipe is , the compression angle of the drawing hole is ; (5-1) During the drawing process, the total length of the deformation zone of the metal pipe can be determined by the feed pipe specifications and the geometric parameters of the drawing die, and it can be divided into a diameter reduction zone and a wall reduction zone.

[0030] The length of the diameter reduction zone is determined by programming iterative calculation of the wall thickness change of the pipe in the diameter reduction zone as the pipe is deformed in the diameter reduction zone according to the principle of elementary plastic mechanics, that is, calculating the real-time outer diameter of the pipe when it moves in the diameter reduction zone. and wall thickness , when the real-time wall thickness When the gap between the die wall and the core rod can be filled, the position is identified as the end point of the diameter reduction zone, and the area corresponding to the thinning of the wall thickness in the subsequent deformation zone is the wall reduction zone. When the outer diameter and wall thickness of the pipe at the end of the diameter reduction zone are known, the outer diameter and wall thickness of the pipe before drawing can be combined. and And the pipe after drawing and According to the elementary plasticity theory of pipe deformation, the compressive stress on the outer surface of the pipe in the diameter reduction zone and the compressive stress on the inner and outer surfaces of the pipe in the wall reduction zone can be calculated. In this way, according to the principle of energy method, the ideal work of drawing deformation can be easily calculated. According to the ideal work, the average rheological stress value of the metal in the deformation zone can be estimated, and the friction work and shear work can be further calculated. The specific relationship includes the following formula: Average drawing stress at the outlet end of drawn pipe fittings It can be calculated according to the energy method: In the formula, is the work done by the pulling force at the pulling outlet corresponding to unit volume, and its calculation formula is: In the formula, is the average drawing stress of the outlet end face of the drawn pipe, Metal flow occurs during drawing The corresponding length of the pipe after drawing, Metal flow occurs during drawing The corresponding length of the pipe before drawing; is the ideal unit volume strain energy of the reduced diameter area, and its calculation formula is: In the formula, is the average flow stress corresponding to the diameter reduction deformation zone; is the equivalent strain value of the pipe fitting in the diameter reduction deformation zone, and its estimated calculation formula is: In the formula, Substituting the above strain degree and strain rate values ​​into the flow stress model, the average flow stress in the drawing reduction zone can be calculated: .

[0031] In the calculation process, the equivalent strain degree can be taken The approximate value calculation formula is: Equivalent strain rate The calculation formula is: Where t is the deformation time of the metal passing through the deformation zone, and its calculation formula is: In the formula, is the inlet linear velocity of the metal tube; is the instantaneous linear velocity of the metal tube when it enters the wall reduction zone. Its value can be determined by the known metal tube drawing outlet velocity. Under the premise of , it is calculated according to the law of metal volume constancy.

[0032] is the ideal unit volume strain energy of the wall reduction area, and its calculation formula is: In the formula is the average flow stress corresponding to the wall reduction deformation zone; is the equivalent strain value of the pipe fittings in the wall deformation zone, and its estimation formula is: In the formula, Substituting the above strain degree and strain rate values ​​into the flow stress model, the average flow stress in the drawing wall reduction zone can be calculated. ; In the calculation process, the equivalent strain degree can be taken The approximate value calculation formula is: Equivalent strain rate The calculation formula is: Where t is the deformation time of the metal passing through the deformation zone, and its calculation formula is: In the formula, is the linear speed of the metal tube’s drawing outlet; It is the instantaneous linear velocity of the metal tube when it enters the wall reduction zone.

[0033] is the shear strain energy per unit volume in the deformation zone, and its calculation formula is: is the friction work per unit volume in the deformation zone, and its calculation formula is: In the formula, is the friction coefficient between the pipe and the inner hole wall of the mold; is the friction coefficient between the pipe and the mandrel; The radial component of the pressure of the die on the pipe in the diameter reduction area; The radial component of the pressure of the die on the pipe in the wall reduction area; is the pressure of the core rod on the inner wall of the pipe in the wall reduction area (here, , , The calculation method of can be obtained by conventional methods, for example: please refer to the theoretical calculation method of Toyohiko Okamoto recorded on page 163 of "Theory of Continuous Rolling of Steel Pipe"); It is the length of friction work overcome by the metal per unit volume flow in the diameter reduction area; It is the length of friction work overcome by unit volume flow of metal in the wall reduction area.

[0034] (5-3) As mentioned above, shear strain energy And the friction work value As shown in the estimation formula, the compression angle of the drawing hole during the drawing process It has opposite effects on friction work and shear deformation work. Therefore, based on the principle of energy method, the outer diameter of the incoming metal pipe is calculated by trial and error method of computer programming. and the compression angle of the drawing hole As a variable, the compression angle is obtained by iterative calculation is the optimal compression angle , the compression angle value Make the average drawing stress value of the outlet end face of the drawn pipe The average drawing stress value of the outlet end face of the minimum drawn pipe is achieved , and then the average drawing stress value of the outlet end face of the minimum drawing pipe is and 0.75 times compare; when Close to 0.75 times , the obtained real-time tension has only a small deviation from the reasonable maximum tension allowed by the process design, and the iterative calculation is terminated. The conditions for the termination of the iterative calculation are: In the formula, The value is close to 0.

[0035] The specific process is: S1: In steps (3) and (4), the conditions of the incoming metal pipe fittings and the finished pipe have been determined. The outer diameter of the incoming metal pipe fittings Unknown, so preset the outer diameter of the incoming metal pipe For a certain value, preset the compression angle of the drawing hole is a certain value; S2: Calculate the diameter reduction and thickening to determine the diameter reduction area and wall reduction area, and calculate the shear stress (including shear strain energy) corresponding to the diameter reduction area based on the above formula. ) and tensile stress, shear stress corresponding to the wall reduction zone (including shear strain energy ) and drawing stress; then calculate the total real-time drawing stress on the pipe at the exit of the drawing hole ; S3: Re-preset the compression angle of the drawing hole For a new value, recalculate the diameter reduction and thickening to determine the diameter reduction area and wall reduction area, and recalculate the shear stress (including shear strain energy) corresponding to the diameter reduction area based on the above formula ) and tensile stress, shear stress corresponding to the wall reduction zone (including shear strain energy ) and drawing stress; then recalculate the total real-time drawing stress on the pipe at the exit of the drawing hole ; S4: Iterate the above process to obtain a compression angle is the optimal compression angle , the compression angle value Make the average drawing stress value of the outlet end face of the drawn pipe The average drawing stress value of the outlet end face of the minimum drawn pipe is achieved , and then the average drawing stress value of the outlet end face of the minimum drawing pipe is and 0.75 times compare; when Not even close to 0.75 times When the above-mentioned iterative calculation termination condition cannot be met, the process of the above-mentioned steps S1-S4 is iterated until the previous iterative calculation is terminated.

[0036] S5: Terminate the calculation and sort out the corresponding , , , , ,T, , .

[0037] The strategy for maximizing the deformation of the metal pipe in this embodiment is to maximize the wall thickness of the incoming metal pipe. Under given circumstances, pursue the outer diameter of incoming metal pipe fittings maximization.

[0038] The design method of this embodiment is applied to the process table and working condition results of drawing oxygen-free copper tubes with a fixed mandrel tapered die as shown in Table 1 below.

[0039] Table 1 Comparative Example 1 The process table and working conditions of drawing oxygen-free copper tubes with a tapered die designed using the traditional empirical method are shown in Table 2 below.

[0040] Table 2 After production verification, production can be organized normally according to the process table 1 of the present invention. By comparing the process data of Table 1 and Table 2, the effectiveness of the process design method of the present invention can be confirmed. The design method of the present invention not only solves the frequent problem of drawing instability in the original process, but also increases the pass reduction rate of the fixed mandrel tapered die by about 9.5% (pass reduction rate increment % = (43.2-30) / 43.2-(38-30) / 38), realizing the maximization of the outer diameter or wall thickness of the incoming material.

[0041] The present invention ensures the use of an optimized compression angle, maximum deformation, and reasonable maximum tension in the drawing process through a process design method to ensure the safety and stability of the process, thereby maximizing the production potential of the production equipment, reducing the process organization cost, and improving production efficiency. In actual production, the process technology level can be improved to create economic benefits.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A design method for drawing metal pipes based on a fixed mandrel tapered die, characterized in that: The steps include: (1) Obtain the yield strength of metal pipes through tensile tests ; (2) Obtain stress-strain curves of multiple groups of metal pipe fittings through Gleeble test, and obtain the rheological stress model of metal pipe fittings through the stress-strain curves of multiple groups of metal pipe fittings; (3) Obtaining the processing deformation temperature T and the metal pipe drawing outlet line speed , Wall thickness of finished pipe , Outer diameter of finished pipe , Wall thickness of incoming metal pipes , the friction coefficient between the metal pipe and the inner wall of the mold And the friction coefficient between the metal pipe and the mandrel ; (4) A fixed mandrel conical die is preset to draw the incoming metal pipe to obtain a finished pipe, and the deformation zone of the metal pipe during the drawing process is divided into a diameter reduction zone and a wall reduction zone. Based on the rheological stress model of the metal pipe in step (2), the parameters obtained in step (3) and the calculation formula in the energy method, the outer diameter of the incoming metal pipe is calculated. and the compression angle of the drawing hole As a variable, the average drawing stress of the outlet end face of the drawn pipe is iteratively calculated. , the condition for the termination of iterative calculation is: In the formula, is the error value; after the calculation is terminated, the corresponding design , .

2. The design method for drawing a metal pipe based on a fixed mandrel tapered die according to claim 1, characterized in that: During the tensile test, a plurality of tensile pause points are set so that the yield strength of the metal pipe is the yield strength of the metal pipe with the cumulative work hardening effect.

3. The design method for drawing a metal pipe based on a fixed mandrel tapered die according to claim 1, characterized in that: In step (2), the rheological stress model of the metal pipe is the Johnson-Cook rheological stress model.

4. The design method for drawing a metal pipe based on a fixed mandrel tapered die according to claim 1, characterized in that: In step (4), the calculation formula in the energy method includes the following calculation formula: In the formula, is the work done by the pulling force at the pulling outlet corresponding to unit volume, and the calculation formula is: In the formula, is the average drawing stress of the outlet end face of the drawn pipe; Metal flow occurs during drawing The corresponding length of the pipe after drawing; Metal flow occurs during drawing The corresponding length of the pipe before drawing; is the ideal unit volume strain energy of the reduced diameter area, and its calculation formula is: In the formula, is the average flow stress corresponding to the diameter reduction deformation zone; is the equivalent strain value of the metal pipe in the diameter reduction deformation zone, and its calculation formula is: In the formula, The above Substitute into the rheological stress model of the metal pipe in step (2) and calculate the average rheological stress in the drawing reduction zone: , and in the calculation process, the equivalent strain degree is taken The approximate value calculation formula is: Equivalent strain rate The calculation formula is: Where t is the deformation time of the metal passing through the deformation zone, and its calculation formula is: In the formula, is the inlet linear velocity of the metal pipe; is the instantaneous linear velocity of the metal pipe when it enters the wall reduction zone; , The value of the known metal pipe drawing outlet line speed Under the premise of , it is calculated according to the law of constant metal volume; is the ideal unit volume strain energy of the wall reduction area, and its calculation formula is: In the formula, is the average flow stress corresponding to the wall reduction deformation zone; is the equivalent strain value of the pipe fittings in the wall deformation zone, and its calculation formula is: In the formula, The above Substitute into the rheological stress model of the metal pipe in step (2) and calculate the average rheological stress in the drawing and wall reduction zone: ; In the calculation process, the equivalent strain degree is taken The approximate value calculation formula is: Equivalent strain rate The calculation formula is: Where t is the deformation time of the metal passing through the deformation zone, and its calculation formula is: In the formula, is the linear speed of the metal pipe drawing outlet, is the instantaneous linear velocity of the metal pipe when it enters the wall reduction zone, , The value of the known metal pipe drawing outlet line speed Under the premise of , it is calculated according to the law of constant metal volume; is the shear strain energy per unit volume in the deformation zone, and its calculation formula is: In the formula, The compression angle of the drawing hole; is the friction work per unit volume in the deformation zone, and its calculation formula is: In the formula, is the friction coefficient between the metal pipe and the inner hole wall of the mold; is the friction coefficient between the metal pipe and the mandrel; The radial component of the pressure of the die on the metal pipe in the diameter reduction area; It is the radial component of the pressure of the die on the metal pipe in the wall reduction area; To reduce the pressure of the core rod in the wall area on the inner wall of the metal pipe; The length of work done by the metal per unit volume flow to overcome friction in the diameter reduction area; It is the length of work done by metal per unit volume flow to overcome friction in the wall reduction area.

5. The design method for drawing a metal pipe based on a fixed mandrel tapered die according to claim 1, characterized in that: In step (3), the 0.5-4mm.

6. The design method for drawing a metal pipe based on a fixed mandrel tapered die according to claim 1, characterized in that: In step (3), the 20-40mm.

7. The design method for drawing a metal pipe based on a fixed mandrel tapered die according to claim 1, characterized in that: In step (3), the 0.5-4mm.

8. The design method for drawing a metal pipe based on a fixed mandrel tapered die according to claim 1, characterized in that: In step (3), the is 400-800mm / s; in step (3), the 15-30℃.

9. The design method for drawing a metal pipe based on a fixed mandrel tapered die according to claim 1, characterized in that: In step (4), the 30-80mm.

10. The design method for drawing a metal pipe based on a fixed mandrel tapered die according to claim 1, characterized in that: In step (4), the 8-20°.

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