A design method for hollow drawn metal pipes based on conical dies

Abstract

The present invention belongs to the technical field of metal tube tapered die drawing, and specifically discloses a design method for hollow drawn metal pipes based on tapered dies. In the design method of the present invention, based on the yield strength and rheological stress model of metal pipes measured experimentally, the elementary plastic forming theory method and the computer programming iterative solution method are combined to perform the drawing process design calculation of hollow pipes, while maximizing the diameter reduction of the tapered die empty drawing, avoiding wire breakage and drawing instability caused by excessive deformation in a single pass, improving the efficiency and accuracy of the drawing process design, reducing the trial and error cost of implementing the drawing process production, and improving production efficiency.

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 a hollow drawn metal tube based on a tapered die. Background Art

[0002] The process of conical die hollow drawing is one of the important methods of metal plastic processing and forming. It can effectively reduce the diameter of metal pipe fittings, refine the internal grains of metal pipe fittings, and improve the toughness performance. Therefore, it is widely used in the drawing production of metal pipe fittings. In the existing production technology, the process parameters of conical die drawing of metal pipe fittings are mainly determined by empirical methods, and it takes a long time and continuous empirical trial and error to finally determine the process parameters on site. This empirical method usually makes the optimized design of the drawing process a long exploration process with a high trial and error cost. For example, in single-pass drawing, in order to obtain the maximum single-pass drawing reduction, thereby reducing the total number of product drawing passes and achieving the purpose of improving production efficiency, production line process personnel often use trial and error to explore and optimize the process. In this process, the metal pipe often becomes unstable or even breaks during drawing, and the yield rate is greatly reduced, resulting in a significant increase in production costs. Therefore, how to carry out process design based on engineering science to maximize the diameter reduction in drawing passes while ensuring the stability of the drawing process has become an urgent technical need. Summary of the invention

[0003] In view of the high cost of optimizing the drawing process by trial and error in the above-mentioned prior art, the present invention provides a design method for hollow drawn metal pipes based on a tapered die.

[0004] To achieve the above purpose, the following technical solutions are specifically included:

[0005] A design method for a hollow drawn metal pipe based on a tapered die comprises the following steps:

[0006] (1) Obtain the yield strength of metal pipes through tensile tests ;

[0007] (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;

[0008] (3) Obtaining the friction coefficient between the mold and the metal pipe surface under lubrication conditions ;

[0009] (4) Based on the preset conical die, the metal pipe is hollow-drawn to obtain a finished pipe, wherein the outer diameter of the preset metal pipe is , the wall thickness of the metal pipe is The outer diameter of the finished tube is , the wall thickness of the finished tube is ; During the drawing process, the inlet linear speed of the metal pipe is , the outlet linear speed of the metal pipe during drawing is , the drawing temperature is T, and the real-time drawing stress is , the taper angle is ;

[0010] Sure , , , , T, and Program iterative calculations for variables to obtain different value, combined with the friction coefficient , the rheological stress model of the metal pipe and the real-time drawing stress calculation formula, iteratively calculate the strain degree, strain rate, average rheological stress, optimal drawing cone angle and real-time drawing stress; when the real-time drawing stress Close to 0.75 times the yield strength of the metal pipe The iterative calculation terminates when , that is, the condition for the iterative calculation to terminate is:

[0011]

[0012] In the formula, Close to 0, is the metal yield strength;

[0013] After the calculation is terminated, the designed , , .

[0014] In the method of the present invention, the yield strength and rheological stress model of metal pipe fittings are obtained respectively through drawing test and mechanical detection test. Based on the yield strength and rheological stress model of metal pipe fittings, the engineering calculation of plastic mechanics principle and computer programming iterative solution technology are combined to carry out drawing process design calculation, and the drawing process parameters can be calculated. In the design method of the present invention, the size specifications of the metal pipe fittings fed, the drawing cone angle, the maximum tension, and the specifications of the finished pipe are all included in the calculation range. In the calculation process, the outer diameter and wall thickness of the target finished pipe are first preset, and then the outer diameter and wall thickness of the incoming metal pipe fittings are obtained through iterative calculation of the outer diameter and wall thickness of the finished pipe, the drawing cone angle, the drawing stress and the rheological stress model; the maximum tension refers to the mechanical state of making the drawing stress on the end face of the metal pipe fitting at the exit of the drawing die in a reasonable maximum tension, that is, the strength value of 0.75 times the yield strength of the metal pipe fitting. On the one hand, because in the method of the present invention, the process of calculating the outer diameter and wall thickness of the incoming metal pipe fittings is based on the state of maximum tension during the drawing process of the metal pipe fittings, the difference between the outer diameter of the incoming metal pipe fittings and the outer diameter of the finished pipe can be maximized, that is, the diameter reduction amount of a single drawing pass is maximized, and the purpose of obtaining the drawing process parameters through engineering scientific calculation is achieved; on the other hand, the method of the present invention ensures that the metal pipe is drawn under a reasonable maximum tension state from the perspective of process design, and ensures that the pipe fittings neither break nor enter a plastic state outside the drawing die from the perspective of process design, thereby reducing the drawing instability or even breaking accidents caused by excessive metal deformation during the drawing process, improving the product yield, reducing the loss during the drawing process, and saving costs.

[0015] The friction coefficient between the mold and the metal sample surface under lubricating oil lubrication conditions can be obtained through conventional friction test tests.

[0016] Preferably, in step (1), during the tensile test, multiple groups of tests are set up to obtain the metal yield strength taking into account the cumulative work hardening effect.

[0017] Preferably, in step (2), the rheological stress model of the metal pipe is a Johnson-Cook rheological stress model.

[0018] Preferably, in step (4), the real-time tensile stress calculation formula is:

[0019]

[0020] In the formula,

[0021] is the real-time tensile stress;

[0022] is the friction coefficient between the die and the metal pipe surface under lubrication conditions;

[0023] To draw the taper angle;

[0024] is the equivalent deformation degree of the metal in the deformation zone, and its value is calculated as follows:

[0025]

[0026] In the formula,

[0027]

[0028]

[0029]

[0030] is the average flow stress in the drawing deformation zone, which is calculated by combining the hole structure parameters and the metal pipe flow stress model. The equivalent strain degree is taken in the calculation process. The approximate value calculation formula is:

[0031]

[0032] Equivalent strain rate The calculation formula is:

[0033]

[0034] Where t is the deformation time of the metal passing through the deformation zone, and its calculation formula is:

[0035]

[0036] In the formula,

[0037] is the inlet linear velocity of the metal pipe;

[0038] is the outlet linear velocity of the metal pipe;

[0039] Based on the above-mentioned real-time drawing stress calculation formula, the optimal drawing taper angle corresponding to the minimum real-time drawing stress is calculated by an iterative extreme value method.

[0040] It is determined by the established drawing hole geometry parameters, metal deformation temperature, drawing speed and metal properties; Determined by the geometric parameters of the deformation zone.

[0041] Preferably, in step (4), the 55-80mm, 3-5mm.

[0042] Preferably, in step (4), the 35-50mm.

[0043] Preferably, in step (4), the 3.8-6mm.

[0044] Preferably, in step (4), the It is 100-300mm / s.

[0045] Preferably, in step (4), the 15-30℃.

[0046] Preferably, in step (4), the 5-20°.

[0047] Preferably, in step (4), the <1%, more preferably <0.1%.

[0048] In the present invention, the units of the parameters involved are as follows: , , , The unit is mm; and The unit of is mm / s; the unit of T is ℃, , The unit of is °; , , The unit is MPa.

[0049] In the method of the present invention, in step (4), the specification of the finished tube is first determined, and the maximum incoming tube specification and the corresponding optimized drawing taper angle are iteratively calculated as the process design parameters that meet the conditions.

[0050] Compared with the prior art, the present invention has the following beneficial effects: In the design method of the present invention, based on the yield strength and rheological stress model of metal pipe fittings, the elementary plastic forming theory method and the computer programming iterative solution method are combined to carry out the drawing process design, which can maximize the diameter reduction of the tapered die while avoiding the wire breakage and drawing instability caused by excessive deformation in a single pass, thereby improving the efficiency and accuracy of the drawing process design, reducing the trial and error cost of implementing the drawing process production, and improving the production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 The figure is a calculation flow chart of an embodiment of the present invention.

[0052] Figure 2 It is a schematic diagram of the metal tube tapered die drawing structure in an embodiment of the present invention. DETAILED DESCRIPTION

[0053] 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.

[0054] In the present invention, the units of the parameters involved are as follows: , , , The unit is mm; and The unit of is mm / s; the unit of T is ℃, , The unit is °, and the radian unit rad is used in the formula calculation; , , The unit is MPa.

[0055] Example 1

[0056] A design method for hollow drawn metal pipes based on a conical die, the calculation flow chart is as follows: Figure 1 As shown in the figure, the core structure diagram of the drawing die is shown in the attached figure. Figure 2 As shown, the specific steps include:

[0057] (1) The yield strength of the metal is tested by pulling out the test, and multiple sets of tests are set up to obtain the yield strength of the metal taking into account the cumulative work hardening effect. .

[0058] 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. .

[0059] (2) Through the Gleeble test, multiple sets of stress-strain curves applicable to the metal pipe fitting within the range of processing conditions are obtained. Data fitting processing is performed on the basis of the test data to obtain a rheological stress model applicable to the metal of the pipe fitting.

[0060] For example, taking the Johnson-Cook model as the deformation resistance model, the following formula is used:

[0061]

[0062] In the formula, is the average flow stress value 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:

[0063]

[0064] 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:

[0065]

[0066] In the formula, , , are respectively the average deformation temperature of the metal material currently being deformed by processing, the reference room temperature, and the melting point temperature of the material. The parameters involved in the above formula can be determined by conventional methods in the art.

[0067] (3) Obtain the friction coefficient between the mold and the metal sample surface under lubricating oil lubrication conditions by conventional friction test methods .

[0068] (4) The outer diameter of the preset metal pipe is , the wall thickness of the metal pipe is The outer diameter of the finished tube is , the wall thickness of the finished tube is ; During the drawing process, the inlet linear speed during drawing is , the exit line speed during drawing is , the drawing temperature is T, and the real-time drawing stress is , the taper angle is ; Based on the existing working conditions, first determine , , , , the specific value of T, and Undetermined;

[0069] In the case of tapered die drawing, the real-time drawing stress can be calculated according to the elementary plasticity theory by the following formula: :

[0070]

[0071] In the formula,

[0072] is the tensile stress;

[0073] is the friction coefficient between the die and the metal surface under the condition of lubricating oil lubrication;

[0074] To draw the taper angle;

[0075] is the equivalent deformation degree of the metal in the deformation zone, and its value is estimated by:

[0076]

[0077] In the formula,

[0078]

[0079]

[0080]

[0081] is the average flow stress value in the drawing deformation zone, which is calculated using the above-mentioned Johnson-Cook deformation resistance model. During the calculation process, the equivalent strain degree can be taken The approximate value calculation formula is:

[0082]

[0083] Equivalent strain rate The calculation formula is:

[0084]

[0085] Where t is the deformation time of the metal passing through the deformation zone, and its calculation formula is:

[0086]

[0087] In the formula, is the inlet linear velocity of the metal tube;

[0088] is the outlet linear velocity of the metal tube;

[0089] First, according to calculation formula 4, we can see that there is an optimal drawing taper angle that can make the drawing stress Minimize. That is, corresponding to the current Under the set value condition, an optimal drawing taper angle can be calculated by trial and error programming ;

[0090] Secondly, in the above calculation formula, the outer diameter of the incoming metal pipe has been set In the case of (The specific calculation process is a conventional calculation method in this field, such as the calculation process in the paper "Technology Research of Three-roller Micro-force Sizing Machine", pages 52-53, or the process calculation method of micro-tension sizing machine, Wang Lijun, Zhong Xihan, Tianjin University Metallurgical Branch, Steel Pipe, Issue 6, 1994);

[0091] Finally, combined with the friction coefficient , the rheological stress model of the metal pipe and the real-time tensile stress calculation formula, iterative calculation of the strain degree and strain rate , average flow stress , Optimal drawing taper angle And real-time tensile stress ; By continuously iteratively replacing the assumed outer diameter value of the incoming metal tube value, so that At nearly 0.75 times The calculation terminates at any time. That is, the condition for the termination of the iterative calculation is:

[0092]

[0093] In the formula, Close to 0.

[0094] In this way, the calculation is terminated to obtain the drawing process design parameters that meet the process design requirements: , , , , ,T, , The process parameters calculated in this embodiment are shown in Table 1. The process parameters were verified by drawing production of oxygen-free copper tubes, and it was confirmed that stable production can be achieved.

[0095] Table 1

[0096]

[0097] Comparative Example 1

[0098] The process table and working conditions of drawing oxygen-free copper tubes with tapered dies designed by traditional empirical methods are shown in Table 2 below.

[0099] Table 2

[0100]

[0101] By comparing the process results in Table 1 and Table 2, the effectiveness of the process design method of the present invention can be confirmed. The method of the present invention not only avoids the instability of metal tube drawing, but also further maximizes the incoming material diameter, increasing by 6.67% (incoming material diameter increase ratio % = (64-60) / 60×100). The design method of the present invention ensures that the process of metal tube empty drawing in the conical die uses the optimal drawing cone angle value and the maximum diameter reduction, improves the efficiency and accuracy of the process design, effectively reduces the process organization cost and process trial and error cost, improves production efficiency, and can improve the process control level in actual production, creating significant economic benefits.

[0102] 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 hollow drawn metal pipes based on a 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 friction coefficient between the mold and the metal pipe surface under lubrication conditions ; (4) Based on the preset conical die, the metal pipe is hollow-drawn to obtain a finished pipe, wherein the outer diameter of the preset metal pipe is , the wall thickness of the metal pipe is The outer diameter of the finished tube is , the wall thickness of the finished tube is ; During the drawing process, the inlet linear speed of the metal pipe is , the outlet linear speed of the metal pipe during drawing is , the drawing temperature is T, and the real-time drawing stress is , the taper angle is ; Sure , , , , T, and Program iterative calculations for variables to obtain different value, combined with the friction coefficient , the rheological stress model of the metal pipe and the real-time drawing stress calculation formula, iteratively calculate the strain degree, strain rate, average rheological stress, optimal drawing cone angle and real-time drawing stress; when the real-time drawing stress Close to 0.75 times the yield strength of the metal pipe The iterative calculation terminates when , that is, the condition for the iterative calculation to terminate is: In the formula, Close to 0, is the metal yield strength; After the calculation is terminated, the designed , , .

2. The design method of a conical die hollow drawn metal pipe according to claim 1, characterized in that: In step (1), during the tensile test, multiple groups of tests are set up to obtain the metal yield strength taking into account the cumulative work hardening effect.

3. The design method of a conical die hollow drawn metal pipe 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 of a conical die hollow drawn metal pipe according to claim 1, characterized in that: In step (4), the real-time tensile stress calculation formula is: In the formula, is the real-time tensile stress; is the friction coefficient between the die and the metal pipe surface under lubrication conditions; To draw the taper angle; is the equivalent deformation degree of the metal in the deformation zone, and its value is calculated as follows: In the formula, is the average flow stress in the drawing deformation zone, which is calculated by combining the hole structure parameters and the metal pipe flow stress model. The equivalent strain degree is taken in the calculation process. 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 outlet linear velocity of the metal pipe; Based on the above-mentioned real-time drawing stress calculation formula, the optimal drawing taper angle corresponding to the minimum real-time drawing stress is calculated by an iterative extreme value method.

5. The design method of a conical die hollow drawn metal pipe according to claim 1, characterized in that: In step (4), the 55-80mm, 3-5mm.

6. The design method of a conical die hollow drawn metal pipe according to claim 1, characterized in that: In step (4), the 35-50mm.

7. The design method of a conical die hollow drawn metal pipe according to claim 1, characterized in that: In step (4), the 3.8-6mm.

8. The design method of a conical die hollow drawn metal pipe according to claim 1, characterized in that: In step (4), the It is 100-300mm / s.

9. The design method of a conical die hollow drawn metal pipe according to claim 1, characterized in that: In step (4), the 15-30℃.

10. The design method of a conical die hollow drawn metal pipe according to claim 1, characterized in that: In step (4), the 5-20°.

Images