Blank and method for making uniform wall thickness bent pipe

Abstract

The present invention relates to the technical field of pipe bending, and specifically to a blank and method for making a pipe bend with uniform wall thickness, wherein the blank includes a pipe bend section with a structure that gradually thickens from the inner wall to the outer wall, and is characterized in that the center point of the inner wall is the thinnest part of the inner wall, and the wall thickness of the inner wall gradually thickens from the center point of the inner wall toward the two end points of the inner wall; the pipe bend section is provided with a correction zone formed by the area outside the line between the center point of the inner wall and the two end points of the outer wall, and the wall thickness of the correction zone is the same as that of the inner wall at the same height in the circumferential direction. On the basis of the pipe bend section with a structure that gradually thickens from the inner wall to the outer wall, the correction zone is designed so that the stress on the blank during the bending process is more uniform, thus overcoming the problem of uneven wall thickness changes during the bending process.

Description

Technical Field

[0001] The invention relates to the technical field of pipe bending, and in particular to a blank and a method for manufacturing a pipe bending with uniform wall thickness. Background Art

[0002] High-pressure movable elbows are mostly used for liquid transportation under high-pressure conditions, so there are high requirements for their pressure resistance and wear resistance. Most high-pressure movable elbows are formed by bending tube billets. During the bending process of the tube billet, the outer wall is pulled and the inner wall is compressed, which forces the outer wall thickness of the elbow to decrease and the inner wall thickness to increase, affecting the forming effect.

[0003] In this regard, the existing patents propose an eccentric design scheme for the tube blank, that is, to form a structure in which the tube blank is gradually thickened from the inner wall to the outer wall, as shown in the existing patents CN108506588A-non-uniform wall thickness tube bending forming method, CN111842578A-a method for forming a bent tube structure to ensure uniform wall thickness, CN104407010B-subcritical energy reactor coolant bent single channel flow heat transfer characteristics experimental device and other schemes. However, in the actual production process, since the metal does not have uniform fluidity during the bending process, the stress distribution of each part is different, resulting in a simple eccentric design scheme that cannot achieve the effect of obtaining a uniform wall thickness bent tube after bending. Summary of the invention

[0004] In view of the above problems, an embodiment of the present invention provides a blank and a method for manufacturing a bent pipe with uniform wall thickness.

[0005] In one aspect of the present invention, a blank is provided for making a bent pipe with uniform wall thickness, the blank comprising a bent pipe section having a structure in which the thickness gradually increases from the inner wall to the outer wall, the inner wall having the thinnest wall thickness at the center point of the inner wall, and the inner wall thickness gradually increases from the center point of the inner wall toward the two end points of the inner wall; the bent pipe section is provided with a correction zone formed by the area outside the line between the center point of the inner wall and the two end points of the outer wall, and the wall thickness of the correction zone is the same as the thickness of the equal height part of the inner wall in the circumferential direction.

[0006] Another aspect of the present invention provides a method for making the above-mentioned blank, characterized in that the method comprises:

[0007] Determine the wall thickness of the inner wall and the outer wall of the curved pipe section in the blank, and determine the corrected wall thickness of the center point of the inner wall according to the wall thickness of the inner wall;

[0008] The three-dimensional modeling is performed in the simulation software using the blank outer dimensions, the wall thickness of the inner wall and the outer wall of the curved pipe section, and the corrected wall thickness. During the modeling process, the correction arc passing through the center point of the inner wall and the two end points of the inner wall is determined based on the corrected wall thickness, and the connecting line between the center point of the inner wall and the two end points of the outer wall is determined. The correction area is determined based on the correction principle that the wall thickness at the same height in the circumferential direction is the same between the correction arc and the connecting line, and finally the blank model is obtained;

[0009] Design a tube bending die in simulation software, and use the tube bending die to simulate the bending of the blank model. During the bending process, monitor the stress of each part of the blank model, and adjust the correction arc after the bending process is completed based on the wall thickness of the obtained tube bending model until a tube bending model with uniform wall thickness is obtained.

[0010] The blank is manufactured using the dimension information of the blank model corresponding to the uniform wall thickness bent pipe model.

[0011] Optionally, the process of determining the wall thickness of the inner and outer walls of the curved pipe section in the blank includes: using the inner diameter, outer diameter and bending radius of the curved pipe to be manufactured, and calculating the wall thickness of the inner and outer walls of the curved pipe section based on the principle of constant cross-sectional area.

[0012] Optionally, the pipe bending mold includes a left fixed part with the same height as the bent pipe section in the blank, and a right fixed part with the same height as the pipe section below the bent pipe section in the blank, and after the left fixed part and the right fixed part are molded together, a fixed cavity matched with the outer diameter of the lower pipe section is formed, and a guide core is coaxially arranged in the fixed cavity, and the outer diameter of the guide core is matched with the inner diameter of the blank and is at the same height as the left fixed part; a bending force applying part is arranged on the side of the right fixed part away from the left fixed part, and the bending force applying part has a bending groove matched with the outer diameter of the upper part of the bent pipe section in the blank, and the bending groove is engaged and fixed with the upper part of the bent pipe section in the blank during the bending process.

[0013] Optionally, the process of making the blank using the size information of the blank model corresponding to the uniform wall thickness elbow model includes:

[0014] A multi-directional die forging die is manufactured using the size information of the blank model, and the die forging blank is manufactured using the multi-directional die forging die, wherein the multi-directional die forging die includes: an upper die, a lower die, a left top core and a right top core. After the upper die and the lower die are closed, a mold cavity identical to the blank model is formed inside, as well as a left stamping channel and a right stamping channel connecting the left and right sides of the mold cavity with the outside world. The left top core is adapted to the left stamping channel, and the right top core is adapted to the right stamping channel.

[0015] The blank is obtained by axially opening a hole in the die forging blank according to the size information of the blank model.

[0016] Compared with the prior art, the beneficial effect of the present invention lies in that: on the basis of the bent pipe section with a structure that gradually thickens from the inner wall to the outer wall, a correction zone is designed to make the stress on the blank more uniform during the bending process, thus overcoming the problem of uneven wall thickness change during the bending process. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of the present application, and do not constitute a limitation of the present invention. In the drawings:

[0018] Figure 1 A schematic diagram of a three-dimensional structure of a blank provided in an embodiment of the present invention;

[0019] Figure 2 A schematic diagram of a front cross-sectional structure of a blank provided by an embodiment of the present invention;

[0020] Figure 3 A schematic diagram of wall thickness calculation provided in an embodiment of the present invention, FIG. a is a schematic diagram of the size of a bent pipe, FIG. b is a comparative schematic diagram, and FIG. c is a schematic diagram of the size of a blank;

[0021] Figure 4 A schematic diagram of the second wall thickness calculation provided in an embodiment of the present invention, FIG. d is a schematic diagram of the size of the bent pipe, FIG. e is a comparative schematic diagram, and FIG. f is a schematic diagram of the size of the blank;

[0022] Figure 5 A three-dimensional diagram of a pipe bending mold provided by an embodiment of the present invention;

[0023] Figure 6 A front cross-sectional view of a pipe bending die provided by an embodiment of the present invention;

[0024] Figure 7 A front and sectional view of a multi-directional forging die provided by an embodiment of the present invention;

[0025] Figure 8 Schematic diagram of the bending state of the blank during the simulation bending process provided by the embodiment of the present invention Figure 1 ;

[0026] Fig. 9 Schematic diagram of the bending state of the blank during the simulation bending process provided by the embodiment of the present invention Figure 2 ;

[0027] Fig.10 Schematic diagram of the bending state of the blank during the simulation bending process provided by the embodiment of the present invention Figure 3 ;

[0028] Fig.11 Schematic diagram of the bending state of the blank during the simulation bending process provided by the embodiment of the present invention Figure 4 .

[0029] Among them, there are an inner wall 1, an outer wall 2, a bent pipe section 3, a correction area 4, a left fixing part 5, a right fixing part 6, a guide core 7, a bending force applying part 8, an upper mold 9, a lower mold 10, a left top core 11, and a right top core 12. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0031] See also Figure 1 and Figure 2 The embodiment of the present invention provides a blank for making a uniform wall thickness bent pipe, the blank comprising a bent pipe section 3 with a structure gradually thickening from an inner wall 1 to an outer wall 2, the inner wall 1 having the thinnest wall thickness at the center point of the inner wall, and the wall thickness of the inner wall 1 gradually thickens from the center point of the inner wall toward the two end points of the inner wall 1; the bent pipe section 3 is provided with a correction zone 4 formed by an area outside a line between the center point of the inner wall and the two end points of the outer wall 2, and the wall thickness of the correction zone 4 is the same as that of the inner wall 1 at the same height in the circumferential direction.

[0032] Another aspect of the present invention provides a method for making the above-mentioned blank, comprising:

[0033] Step 1: determine the wall thickness of the inner wall and the outer wall of the curved pipe section in the blank, and determine the corrected wall thickness at the center point of the inner wall according to the wall thickness of the inner wall.

[0034] In practice, the inner wall and outer wall of the curved pipe section can be determined by using the existing patented technology. In addition, the inner diameter, outer diameter and bending radius of the curved pipe to be manufactured can be used to calculate the wall thickness of the inner wall and outer wall of the curved pipe section based on the principle of constant cross-sectional area. There are two specific calculation methods:

[0035] 1) See Figure 3 , the following calculation expression is obtained by geometric operation based on the principle of section invariance:

[0036] s1=[π×(Rd÷2)×(Rd÷2) ÷4-π×(RD÷2)×(RD÷2) ÷4] ÷(π×R÷2)

[0037] s2=[π×(R+D÷2)×(R+D÷2) ÷4-π×(R+d÷2)×(R+d÷2) ÷4] ÷(π×R÷2)

[0038] d=D-s1-s2

[0039] S = D ÷ 2 - s1 - (D - s1 - s2) ÷ 2

[0040] Among them, s1 represents the inner wall thickness, s2 represents the outer wall thickness, R represents the bending radius, D represents the outer diameter, d represents the inner diameter, and S represents the eccentricity.

[0041] 2) See Figure 4 , based on the principle of section invariance combined with synchronous changes, the following calculation expression is obtained:

[0042] s1=[π×(Rd÷2)×(Rd÷2) ÷4-π×(RD÷2)×(RD÷2) ÷4] ÷(π×R÷2)

[0043] s2=[π×(R+D÷2)×(R+D÷2) ÷4-π×(R+d÷2)×(R+d÷2) ÷4] ÷(π×R÷2)

[0044] t1=[(Dd)÷2-s1]÷2

[0045] t2=[s2- (Dd)÷2] ÷2

[0046] D1=D+t1-t2

[0047] d1=D1-s1-s2

[0048] S = D1÷2-s1-(D1-s1-s2)÷2

[0049] Among them, t1 is the synchronous change of the inner wall thickness, and t2 is the synchronous change of the outer wall thickness; it can be seen that the results of the two calculation methods are the same, which verifies the accuracy of the calculation.

[0050] In practice, the initial modified wall thickness may be set to half the thickness of the inner wall.

[0051] Step 2: Use the blank's outer dimensions, the wall thickness of the inner and outer walls of the curved pipe section, and the corrected wall thickness to perform three-dimensional modeling in the simulation software. During the modeling process, determine the correction arc at the inner wall passing through the center point of the inner wall and the two end points of the inner wall based on the corrected wall thickness, determine the connecting line between the center point of the inner wall and the two end points of the outer wall, and determine the correction area based on the correction principle that the wall thickness at the same height in the circumferential direction is the same from the correction arc to the connecting line, and finally obtain the blank model.

[0052] In practice, once the corrected wall thickness is determined, the outermost point A at the center point of the inner wall can be determined. Combining the two end points B and C of the inner wall, an arc can be determined, which is the initial correction line.

[0053] Step 3: Design a bending mold in the simulation software, and use the bending mold to simulate the bending of the blank model. Monitor the stress conditions of various parts of the blank model during the bending process, and adjust the correction arc after the bending is completed based on the wall thickness of the obtained bending model until a bending model with uniform wall thickness is obtained.

[0054] In implementation, see Figure 5 and Figure 6 The pipe bending mold includes a left fixing part 5 which is at the same height as the bent pipe section in the blank, and a right fixing part 6 which is at the same height as the pipe section below the bent pipe section in the blank. After the left fixing part 5 and the right fixing part 6 are molded together, a fixing cavity which is adapted to the outer diameter of the lower pipe section is formed. A guide core 7 is coaxially arranged in the fixing cavity. The outer diameter of the guide core 7 is adapted to the inner diameter of the blank and is at the same height as the left fixing part 5. A bending force applying part 8 is arranged on the side of the right fixing part 6 away from the left fixing part 5. The bending force applying part 8 has a bending groove which is adapted to the outer diameter of the upper part of the bent pipe section in the blank. During the bending process, the bending groove is engaged and fixed with the upper part of the bent pipe section in the blank.

[0055] CAE structural simulation analysis software can be used as simulation software to simulate the bending process of the blank model using its finite element method. Figure 8-Figure 11 The state changes of the blank during the simulation process are shown. The correction line is continuously optimized and adjusted by monitoring the stress of the blank model each time the bending simulation is performed and the results of the bending model obtained each time. Finally, when a bending model with uniform wall thickness is obtained, the corresponding blank model is the final required blank model.

[0056] Step 4: Make a blank using the size information of the blank model corresponding to the uniform wall thickness elbow model.

[0057] During implementation, multi-directional die forging technology can be used to make blanks. Specifically, the multi-directional die forging die can be first made using the size information of the blank model, and then the die forging blank is made using the multi-directional die forging die, wherein the multi-directional die forging die includes: an upper die 9, a lower die 10, a left top core 11 and a right top core 12. After the upper die 9 and the lower die 10 are combined, a mold cavity identical to the blank model is formed inside, as well as a left stamping channel and a right stamping channel connecting the left and right sides of the mold cavity with the outside world, the left top core 11 is adapted to the left stamping channel, and the right top core 12 is adapted to the right stamping channel; finally, an axial hole is opened in the die forging blank according to the size information of the blank model to obtain the blank.

[0058] The solution provided by the embodiment of the present invention designs a correction zone on the basis of the bending section with a structure that gradually thickens from the inner wall to the outer wall, so that the stress on the blank during the bending process is more uniform, breaking through the problem of uneven wall thickness change during the bending process; adopting the simulation technology, saving a lot of experimental time and cost, helping to solve the manufacturing problems of elbows with small diameters, large thicknesses, high pressures and long-term operation in harsh environments; applying the multi-directional die forging technology to the field of high-pressure elbow blank manufacturing, the bending tube blank is formed by multi-directional upsetting extrusion, the forging quality is excellent, the metal streamline is continuous, the structure is dense, and the stress corrosion resistance, fatigue strength and impact performance are greatly improved.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for making a blank, the blank is used to make a uniform wall thickness elbow, characterized in that: The blank comprises a curved pipe section with a structure that gradually thickens from the inner wall to the outer wall, the center point of the inner wall is the thinnest part of the inner wall, and the wall thickness of the inner wall gradually thickens from the center point of the inner wall to the two end points of the inner wall; the curved pipe section is provided with a correction zone formed by the area outside the line between the center point of the inner wall and the two end points of the outer wall, and the wall thickness of the correction zone is the same as the thickness of the equal height part of the inner wall in the circumferential direction; The method comprises: Determine the wall thickness of the inner wall and the outer wall of the curved pipe section in the blank, and determine the corrected wall thickness of the center point of the inner wall according to the wall thickness of the inner wall; The three-dimensional modeling is performed in the simulation software using the blank outer dimensions, the wall thickness of the inner wall and the outer wall of the curved pipe section, and the corrected wall thickness. During the modeling process, the correction arc passing through the center point of the inner wall and the two end points of the inner wall is determined based on the corrected wall thickness, and the connecting line between the center point of the inner wall and the two end points of the outer wall is determined. The correction area is determined based on the correction principle that the wall thickness at the same height in the circumferential direction is the same between the correction arc and the connecting line, and finally the blank model is obtained; Design a tube bending die in simulation software, and use the tube bending die to simulate the bending of the blank model. During the bending process, monitor the stress of each part of the blank model, and adjust the correction arc after the bending process is completed based on the wall thickness of the obtained tube bending model until a tube bending model with uniform wall thickness is obtained. The blank is manufactured using the dimension information of the blank model corresponding to the uniform wall thickness bent pipe model.

2. The method according to claim 1, characterized in that The process of determining the wall thickness of the inner and outer walls of the curved pipe section in the blank includes: using the inner diameter, outer diameter and bending radius of the curved pipe to be manufactured, and calculating the wall thickness of the inner and outer walls of the curved pipe section based on the principle of constant cross-sectional area.

3. The method according to claim 1, characterized in that The pipe bending mold includes a left fixed part with the same height as the bent pipe section in the blank, and a right fixed part with the same height as the pipe section below the bent pipe section in the blank, and after the left fixed part and the right fixed part are molded together, a fixed cavity adapted to the outer diameter of the lower pipe section is formed, and a guide core is coaxially arranged in the fixed cavity, and the outer diameter of the guide core is adapted to the inner diameter of the blank and is at the same height as the left fixed part; a bending force applying part is arranged on the side of the right fixed part away from the left fixed part, and the bending force applying part has a bending groove adapted to the outer diameter of the upper part of the bent pipe section in the blank, and the bending groove is clamped and fixed to the upper part of the bent pipe section in the blank during the bending process.

4. The method according to claim 3, characterized in that The process of making a blank using the size information of the blank model corresponding to the uniform wall thickness bending pipe model includes: A multi-directional die forging die is manufactured using the size information of the blank model, and a die forging blank is manufactured using the multi-directional die forging die, wherein the multi-directional die forging die comprises: an upper die, a lower die, a left top core and a right top core, a die cavity identical to the blank model is formed inside the upper die and the lower die after being closed, and a left punching channel and a right punching channel connecting the left and right sides of the die cavity with the outside, the left top core is adapted to the left punching channel, and the right top core is adapted to the right punching channel; The blank is obtained by axially opening a hole in the die forging blank according to the size information of the blank model.

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