Method of bending tube forming with low reduction rate

Abstract

The present application provides a low thinning rate bending forming method, comprising the following steps: a hydraulic local expansion step, placing a straight pipe in a hydraulic thickening die and controlling the hydraulic thickening die to operate to form an expansion deformation of a target area of the straight pipe and ensure that the minimum wall thickness t1 after the expansion deformation is not less than the initial pipe wall thickness t0 of the straight pipe, the target area being a corresponding area of an outer wall of the straight pipe to be bent and formed; and a bending forming step, placing the expansion-deformed straight pipe in a numerical control bending die and controlling the numerical control bending die to operate to bend and thin the target area until the straight pipe is bent to a target bending radius. The present application only needs to perform expansion deformation on the target area of the straight pipe, the pipe quality is small, the material cost is low, and the working condition demand of small bending radius and low thinning rate is met, and the product quality and service performance are improved.

Description

Technical Field

[0001] This invention belongs to the field of tube forming technology, specifically relating to a tube bending forming method with low thinning rate. Background Technology

[0002] During the pipe bending process, the outer side experiences tangential stretching, resulting in wall thinning, while the inner side experiences tangential compression, leading to thickening. This stress characteristic causes defects such as excessive thinning on the outer side, wrinkling on the inner side, and cross-sectional distortion during bending. These defects affect the product quality and service performance of the bent pipe parts to varying degrees. In related technologies, to prevent the aforementioned pipe defects caused by excessively thin outer wall thickness after bending, one approach is to increase the overall wall thickness of the pipe to ensure that the outer wall thickness remains acceptable after bending. However, this method results in a bent pipe with excessive weight and high material costs. Another approach is to increase the bending radius, which obviously cannot meet the needs of scenarios requiring small bending radii. Summary of the Invention

[0003] Therefore, the present invention provides a pipe bending forming method with a low thinning rate, which can solve the technical problem in the prior art where the excessive thinning rate during pipe bending forming leads to excessive thinning of the outer side of the pipe after bending, resulting in reduced product quality and service performance.

[0004] To address the above problems, the present invention provides a method for forming a bent tube with a low thinning rate, comprising the following steps:

[0005] In the hydraulic local expansion step, the straight pipe is placed in the hydraulic thickening mold, and the operation of the hydraulic thickening mold is controlled to expand and deform the target area of ​​the straight pipe, ensuring that the minimum wall thickness t1 after expansion and deformation is not less than the initial wall thickness t0 of the straight pipe. The target area is the area corresponding to the outer wall of the straight pipe to be bent and formed.

[0006] In the bending forming step, the expanded and deformed straight pipe is placed in a CNC bending mold, and the CNC bending mold is controlled to bend and thin the target area until the straight pipe is bent to the target bending radius.

[0007] In some implementations, the target region after expansion and deformation is wavy and wrinkled.

[0008] In some embodiments, on the central axis section of the wave-like folds, the total length of the arc segments on the outer surface of each wave-like fold is not less than the total length of the arc segments on the outer surface of the curved portion formed after the bending forming step of the target region.

[0009] In some embodiments, the hydraulic thickening mold includes an upper mold and a lower mold that interlock, and a wave groove is formed at the position of the upper mold corresponding to the target area.

[0010] In some embodiments, during the hydraulic partial expansion step, the axial force on both ends of the straight pipe and the pressure of the hydraulic fluid flowing into the straight pipe are controlled such that 1.1t0≥t1>t0.

[0011] In some embodiments, the CNC bending die includes a bending die, wherein when the expanded and deformed straight tube is placed inside the CNC bending die, the rotation center of the bending die is placed in the radial plane of the straight tube passing through the midpoint of the length of the target region.

[0012] In some embodiments, the CNC bending die further includes a pressure die and a clamping die that rotates a preset angle following the bending die. The pressure die has a first clearance groove at the position corresponding to the target area, and the clamping die has a second clearance groove at the position corresponding to the target area.

[0013] In some embodiments, the CNC bending die further includes a chain mandrel, which is controlled to feed along the axial direction of the tube and support itself on the inner wall of the target area during the bending process of the bending die.

[0014] In some embodiments, after the bending forming step, the method further includes: introducing pressurized liquid into the formed bent pipe to shape the pipe wall corresponding to the target area.

[0015] The tube bending forming method with low thinning rate provided by the present invention has the following beneficial effects:

[0016] First, the target area of ​​the straight pipe, i.e. the section to be bent, is expanded and deformed. Then, traditional CNC bending control is used to bend the expanded and deformed target area. During the bending process, the wall thickness of the expanded and deformed target area will flatten. Since the expansion and deformation in the previous process provides sufficient deformation margin for the bending deformation in the next process, the reduction in pipe wall thickness during the bending process is minimal or even non-existent. Therefore, the thinning rate of the target area of ​​the finished bent pipe is extremely low. With sufficient expansion and deformation, it is even possible to achieve pipe bending with no thinning (i.e., a thinning rate of 0). Compared with the existing technology of increasing the overall pipe wall thickness, this invention only requires expansion and deformation of the target area of ​​the straight pipe. The pipe weight is small, the material cost is low, and it meets the working conditions of small bending radius and low thinning rate, thus improving product quality and service performance. Attached Figure Description

[0017] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the steps of a tube bending forming method with low thinning rate according to an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of the initial state of the straight pipe of the present invention placed in the hydraulic thickening mold;

[0020] Figure 3 yes Figure 2 A schematic diagram showing the state of the target area of ​​the straight pipe after the hydraulic thickening mold has expanded and deformed during operation.

[0021] Figure 4 This is a schematic diagram of the initial state of a straight pipe after expansion and deformation placed in a CNC bending mold;

[0022] Figure 5 yes Figure 4 A schematic diagram showing the state in which the wave-like folds of the CNC bending die are partially flattened during operation.

[0023] Figure 6 yes Figure 4 The diagram shows the state of the straight pipe after the CNC bending mold has completed its operation and bent it at a right angle.

[0024] The attached figures are labeled as follows:

[0025] 11. Upper die; 111. Wave groove; 12. Lower die; 13. Left punch; 14. Right punch; 21. Bending die; 22. Pressure die; 221. First clearance groove; 23. Clamping die; 231. Second clearance groove; 24. Chain mandrel; 100. Straight tube; 200. Bending tube. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0028] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90° or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0029] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0030] See Figure 1 and Figure 6 As shown in the embodiment of the present invention, a method for forming a bent tube with a low thinning rate is provided, comprising the following steps:

[0031] In the hydraulic local expansion step, the straight pipe 100 is placed in the hydraulic thickening mold, and the hydraulic thickening mold is controlled to expand and deform the target area of ​​the straight pipe 100, and to ensure that the minimum wall thickness t1 after expansion and deformation is not less than the initial wall thickness t0 of the straight pipe 100. The target area is the area corresponding to the outer wall of the straight pipe 100 to be bent and formed.

[0032] In the bending forming step, the expanded and deformed straight pipe 100 is placed in a CNC bending mold, and the CNC bending mold is controlled to bend and thin the target area until the straight pipe 100 is bent to the target bending radius.

[0033] It should be noted that the aforementioned initial pipe wall thickness refers to the total pipe wall thickness of the straight pipe 100 before expansion and deformation, rather than the local wall thickness. t1 is the minimum wall thickness of the straight pipe 100 in the target area after hydraulic thickening. The units of the aforementioned t0 and t1 can be in the International System of Units (SI).

[0034] In this technical solution, the target area of ​​the straight pipe 100, i.e. the section to be bent, is first expanded and deformed. Then, traditional CNC bending control is used to bend the expanded and deformed target area. During the bending operation, the wall thickness of the expanded and deformed target area will flatten. Since the expansion and deformation in the previous process provides sufficient deformation margin for the bending deformation in the next process, the wall thickness reduction of the pipe during the bending process is minimal or even non-existent. Therefore, the thinning rate of the target area of ​​the finished bent pipe 200 is extremely low. With sufficient expansion and deformation, it is even possible to achieve pipe bending with no thinning (i.e., a thinning rate of 0). Compared with the existing technology that increases the overall wall thickness of the pipe, this invention only requires expansion and deformation of the target area of ​​the straight pipe 100. The pipe weight is small, the material cost is low, and it meets the working conditions of small bending radius and low thinning rate, thus improving product quality and service performance.

[0035] In a preferred embodiment, the target area after expansion and deformation is wavy and wrinkled. As a more preferred implementation, the wavy and wrinkled areas have identical shapes and sizes across the same central cross-section. This technical solution, by designing the target area after expansion and deformation as wavy and wrinkled, ensures a relatively uniform wall thickness after expansion and deformation. Furthermore, it allows the expanded and deformed target area to flatten and bend more smoothly during subsequent bending steps, resulting in a more uniform wall thickness on the outer side of the bend. The aforementioned central cross-section refers to the plane passing through the center line of the straight pipe 100 and perpendicular to the closing plane of the hydraulic thickening mold. Figure 2 The cross-section shown is also the cross-section shown on the aforementioned central axis section.

[0036] In some embodiments, on the central axis section of the corrugated shape, the total length of the arc segments on the outer surface of each corrugated shape is not less than the total length of the arc segments on the outer surface of the curved portion formed in the target area after the bending forming step. Preferably, the total length of the arc segments on the outer surface of each corrugated shape is equal to the total length of the arc segments on the outer surface of the curved portion formed in the target area after the bending forming step. In this way, it can be theoretically ensured that after the corrugated shape is flattened after the bending forming step, the wall thickness of the outer wall of the bent pipe in the target area is not less than the initial wall thickness of the straight pipe 100, achieving the design objective of extremely low or even no thinning rate. It is understood that the determination of the aforementioned total arc length can be calculated and determined in advance using drawing software before forming.

[0037] In some embodiments, during the hydraulic local expansion step, the axial force on both ends of the straight pipe 100 and the pressure of the hydraulic fluid flowing into the straight pipe 100 are controlled to ensure that 1.1t0 ≥ t1 > t0. In this technical solution, the thickness of the pipe wall in the target area after expansion and deformation is designed to be greater than the initial thickness of the pipe, thus objectively achieving the purpose of local thickening of the pipe wall in the target area. This further ensures that the outer wall surface of the bent pipe does not thin after subsequent bending. See details... Figure 2 and Figure 3 As shown, axial thrust is applied simultaneously along the axis of the straight pipe 1 at both ends by left punch 13 and right punch 14. This process is also the feeding operation to the target area, thereby achieving local thickening of the pipe wall after expansion and deformation in the target area. Simultaneously, hydraulic fluid is introduced into the straight pipe 100 through the inlet holes of left punch 13 and right punch 14 to ensure controllable and stable expansion and deformation and prevent wrinkling of the pipe wall. It is understood that the left punch 13 and right punch 14 also simultaneously seal the pipe ends of the straight pipe 100. The magnitude of the axial thrust and the pressure of the hydraulic fluid can be determined using finite element analysis software.

[0038] Further refer to Figure 2 and Figure 3 As shown, the hydraulic thickening mold is similar in that it includes an upper mold 11 and a lower mold 12 that are interlocked. However, unlike traditional thickening molds, in this invention, a wave groove 111 is formed at the position of the upper mold 11 corresponding to the target area. This allows the pipe wall of the target area to expand and deform towards the wave groove 111 under the action of axial forces at both ends and hydraulic fluid inside the pipe during the operation of the hydraulic thickening mold. The wall then fits against the wall of the wave groove 111 to form a contour, thereby forming the aforementioned wave-like folded expansion deformation.

[0039] It is understandable that, in the circumferential direction of the aforementioned wave groove 111 on the straight pipe 100, the wave crest height of each wave segment gradually decreases smoothly from the aforementioned central axis section to both sides, and the wave crest height is 0 at the mold closing surface, forming a smooth connection with the profile of the semi-circular mold cavity on the lower mold 12.

[0040] See details Figure 4 As shown, in some embodiments, the CNC bending die includes a bending die 21. When the expanded and deformed straight tube 100 is placed inside the CNC bending die, the rotation center of the bending die 21 is placed within the radial plane of the straight tube 100 passing through the midpoint of the length of the target region, so as to... Figure 4 The orientation shown is for reference, and the aforementioned radial plane is also the vertical plane. In this technical solution, placing the rotation center of the bending die 21 within the aforementioned radial plane ensures that the corrugated pipe wall can be uniformly flattened along the length of the pipe during the bending operation, which ensures the uniformity of the wall thickness of the bent pipe 200 formed after bending.

[0041] For details, please refer to [link / reference]. Figures 4 to 6 As shown, the CNC bending die also includes a pressure die 22 and a clamping die 23 that rotates at a preset angle following the bending die 21. The preset angle is, for example, 90° when bending a right-angle pipe. The specific angle can be reasonably selected according to actual operation requirements. The pressure die 22 has a first clearance groove 221 at the position corresponding to the target area, and the clamping die 23 has a second clearance groove 231 at the position corresponding to the target area. It is understood that the groove depth of the first clearance groove 221 and the second clearance groove 231 should not be less than the maximum height of the pipe wall section after the expansion and deformation, so as to ensure reliable contact between the clamping die 23 and the pressure die 22 and the pipe, while preventing contact force from being applied to the target area.

[0042] The CNC bending die also includes a chain mandrel 24. During the bending process of the bending die 21, the chain mandrel 24 is controlled to feed along the axial direction of the tube and support the inner wall of the target area to form reliable support for the inner wall of the tube during the bending process, ensuring uniform deformation of the bent tube wall and preventing wrinkles from appearing on the wall.

[0043] As a preferred embodiment, in some implementations, after the bending forming step, the method further includes: introducing pressurized liquid into the formed bent pipe 200 to shape the pipe wall corresponding to the target area, so as to further shape the roundness of the pipe wall of the formed bent pipe 200 and further improve the quality of the formed bent pipe 200.

[0044] It will be readily understood by those skilled in the art that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A method for forming a bent tube with a low thinning rate, characterized in that, Includes the following steps: In the hydraulic local expansion step, the straight pipe (100) is placed in the hydraulic thickening mold, and the operation of the hydraulic thickening mold is controlled to expand and deform the target area of ​​the straight pipe (100) and ensure that the minimum wall thickness t1 after expansion and deformation is not less than the initial pipe wall thickness t0 of the straight pipe (100). The axial force on both ends of the straight pipe (100) and the pressure of the hydraulic fluid introduced into the straight pipe (100) are controlled so that 1.1t0≥t1>t0. The target area is the area corresponding to the outer wall of the straight pipe (100) to be bent and formed. In the bending forming step, the expanded and deformed straight tube (100) is placed in a CNC bending mold, and the CNC bending mold is controlled to bend and thin the target area until the straight tube (100) is bent to the target bending radius. The target area after expansion and deformation is a wavy fold shape. On the central axis section of the wavy fold shape, the total length of the arc segment of the outer surface of each wavy fold shape is not less than the total length of the arc segment of the outer surface of the curved part formed after the bending forming step of the target area. Each wavy fold shape is arranged sequentially along the length direction of the straight pipe (100). During the bending operation, the wall thickness of the target area after expansion and deformation will be flattened. The hydraulic thickening mold includes an upper mold (11) and a lower mold (12) that are interlocked. A wave groove (111) is formed at the position of the upper mold (11) corresponding to the target area.

2. The pipe bending forming method according to claim 1, characterized in that, The CNC bending die includes a bending die (21). When the expanded and deformed straight pipe (100) is placed in the CNC bending die, the rotation center of the bending die (21) is placed in the radial plane of the straight pipe (100) that passes through the midpoint of the length of the target area.

3. The pipe bending forming method according to claim 2, characterized in that, The CNC bending die also includes a pressure die (22) and a clamping die (23) that rotates a preset angle following the bending die (21). The pressure die (22) has a first clearance groove (221) at the position corresponding to the target area, and the clamping die (23) has a second clearance groove (231) at the position corresponding to the target area.

4. The pipe bending forming method according to claim 2, characterized in that, The CNC bending die also includes a chain mandrel (24). During the bending process of the bending die (21), the chain mandrel (24) is controlled to feed along the axial direction of the tube and support it on the inner wall of the target area.

5. The pipe bending forming method according to claim 1, characterized in that, Following the bending and forming step, the following is also included: Pressurized liquid is introduced into the formed curved pipe (200) to shape the pipe wall corresponding to the target area.

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