Cold roll forming method for three-dimensional bent pipe

Abstract

The invention relates to the technical field of large elbow bending forming, in particular to a three-dimensional elbow cold bending forming method which comprises the following steps that S1, the bending center position is theoretically determined, the central axis of a 180-degree arc pipe section of a three-dimensional elbow is theoretically divided into three arc sections, and each arc section corresponds to a set cold bending forming angle; setting the center of each arc section as a bending center; s2, a bending center is delimited, and the position of the bending center is determined by scribing on the pipe blank; s3, the pipe shape is formed through cold bending, a lower forming die is adopted for supporting the pipe blank, an upper forming die is adopted for conducting cold bending on the bending center in the axis direction of the pipe blank according to the sequence from the two ends to the middle, and a 180-degree plane bent pipe is formed; and S4, a deflection angle is formed through bending, specifically, a forming die is adopted to apply pressure to the 180-degree plane bent pipe, and the deflection angle of the spiral bent section and the deflection angle of the straight pipe sections at the two ends are formed. The formed three-dimensional bent pipe is uniform in bending radius, uniform in ascending gradient and high in shape precision, the correction workload is reduced, and the preparation efficiency and the preparation precision are improved.

Description

Technical Field

[0001] This invention relates to the field of large-scale pipe bending and forming technology, and specifically to a three-dimensional pipe cold bending forming method. Background Technology

[0002] like Figures 1-3 As shown, a section of the waveguide in the primary loop of third-generation nuclear power technology is a three-dimensional bend made of 316LN or X2CrNiMo18.12 nitrogen-controlled austenitic stainless steel. The three-dimensional bend includes a 180° spiral bend section and straight pipe sections at both ends of the spiral bend section. The three-dimensional bend rotates upward in a spiral shape with an overall skew angle of 2.5°. The outer diameter of the three-dimensional bend is ≥φ360mm, the wall thickness is ≥36mm, the skew angle tolerance is required to be (0, 0.3º), and the opening length tolerance is ±3mm. It has the characteristics of large outer diameter, large wall thickness and high dimensional accuracy requirements.

[0003] Currently, this three-dimensional bent pipe is mainly prepared by hot molding or cold molding. The cold molding process mainly uses a 180° upper die and an integral forming lower die for one-time cold bending. Then, the spiral bending section and one end of the straight pipe section are fixed, and a hydraulic device is used to apply force to the other end of the straight pipe section, causing the two straight pipe sections to shift in opposite directions and form a skew angle.

[0004] However, during production, it was found that when the 180° upper die and the integral forming lower die were cold-bent in one go, the bend could only be formed to 165-170°, and the workpiece was in a forked state. If the bending continued, the workpiece would be stuck in the die and could not be removed. In addition, there was a noticeable peach-point phenomenon at the bending center in the middle of the bend. At the same time, when the hydraulic device applied force to form the skew angle, the overall slope of the formed bend was uneven. In order to obtain a 180° three-dimensional bend that meets the design requirements, it is necessary to use a step-by-step bending method to correct the angle in the range of 10-15° after cold bending. The correction workload is large and the bending radius is uneven, which affects the dimensional accuracy of the three-dimensional bend. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing three-dimensional bending tube manufacturing method, which uses one-time cold bending and hydraulic force to deflect the tube, resulting in uneven bending radius, large amount of correction work, and uneven overall slope of the three-dimensional bending tube, affecting dimensional accuracy. This invention provides a cold bending forming method for three-dimensional bending tubes.

[0006] This invention provides a method for cold bending and forming of three-dimensional tubes, comprising the following steps: S1. Theoretically determine the location of the bending center. The theoretical division of the spiral bending section of the three-dimensional pipe into three arc segments is used. Each arc segment corresponds to a set cold bending forming angle, and the center of each arc segment is set as the bending center. S2. Determine the bending center by marking the arc length corresponding to the cold bending forming angle on the tube blank; S3. Cold bending forming of the tube shape: The lower forming die supports the tube blank, and the upper forming die cold bends the bending center along the axial direction of the tube blank in the order of first the two ends and then the middle to form a 180° planar bent tube. S4. Pressing and bending to form the skew angle: The forming mold is used to apply pressure to the 180° planar bend to form the skew angle of the spiral bend section and the straight pipe sections at both ends. The forming mold is provided with a cavity that is consistent with the shape of the three-dimensional bend.

[0007] Preferably, the cold bending forming angle includes 60°±5°, the three arc segments are arranged symmetrically, and adjacent arc segments are arranged continuously or at intervals.

[0008] Preferably, the bending center includes a first bending center, a third bending center, and a second bending center arranged sequentially along the axis of the tube blank in the cold bending sequence. In S3, cold bending is performed sequentially in the order of the first bending center, the second bending center, and the third bending center.

[0009] Preferably, in S3, the tube blank is slid along the axial direction within the lower forming die to adjust the relative positional relationship between the bending center and the upper forming die.

[0010] Preferably, the material hardness of the forming lower die is at least 20 HB greater than the material hardness of the tube blank.

[0011] Preferably, the upper forming die is provided with an arc forming surface, the arc angle of the forming surface is 60-80°, and the upper forming die matches the lower forming die.

[0012] Preferably, the lower forming die is provided with two support positions, and the support spacing between the two support positions satisfies 1 / 3πr+2(1.25~1.45)D; In the formula, r is the theoretical bending radius of the three-dimensional bend, in mm; D is the outer diameter of the three-dimensional curved pipe, in mm.

[0013] Preferably, the forming mold includes a top mold and a bottom mold, the top mold and the bottom mold are respectively provided with a spiral segment groove, the two ends of the spiral segment groove are respectively connected to a straight segment groove, and the top mold and the bottom mold are engaged to form the cavity.

[0014] Preferably, a pad is provided at the port position corresponding to the straight section groove of the cavity, and the thickness of the pad is positively correlated with the deflection angle of the three-dimensional bent tube.

[0015] Preferably, the tube blank has extension sections reserved at both ends, the extension sections are detachably connected to lifting fixtures, and the extension sections are cut off after bending and forming the skew angle.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a method for cold bending forming of three-dimensional tubes. By first theoretically determining the bending center position and then cold bending multiple times, a three-dimensional tube is obtained. This method can accurately determine the bending center position and improve the cold bending accuracy. 2. This invention provides a three-dimensional cold bending forming method for pipe bending, which achieves uniform bending radius and high shape accuracy by multiple small-range bending to form a 180° planar pipe, thereby reducing the amount of correction work. 3. This invention provides a method for cold bending of three-dimensional tubes, which uses a forming mold to bend a 180° planar tube in one step to form an accurate skew angle, reducing the preparation steps of three-dimensional tubes and improving preparation efficiency and accuracy. Attached Figure Description

[0017] Figure 1 This is a top view of the three-dimensional curved pipe described in the background art.

[0018] Figure 2 This is a schematic diagram of the end of the three-dimensional bent pipe described in the background art.

[0019] Figure 3 This is a side view of the three-dimensional curved pipe described in the background art.

[0020] Figure 4 This is a schematic flowchart of a three-dimensional tube bending cold bending forming method according to Example 1.

[0021] Figure 5 This is a schematic diagram of the tube blank corresponding to S2 in Example 1.

[0022] Figure 6 This is a schematic diagram of the first bending forming in Example 1.

[0023] Figure 7 This is a schematic diagram of the second bending forming in Example 1.

[0024] Figure 8 This is a schematic diagram of the third bending forming in Example 1.

[0025] Figure 9 This is a schematic diagram of the forming mold described in Example 1.

[0026] Marked in the image: 1-Three-dimensional pipe bend, 11-Helical bending section, 12-Straight pipe section, 2-Pipe blank, 31-First bending center, 32-Second bending center, 33-Third bending center, 4-Upper forming die, 41-Forming surface, 5-Lower forming die, 51-Support position, 6-Forming mold, 61-Top die, 62-Bottom die, 63-Helical section groove, 64-Straight section groove, 5-Plate, 6-Extension section, 7-Lifting fixture. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0028] Unless otherwise specified, the terms "upper," "lower," "left," "right," "center," "inner," and "outer," etc., used in the description of specific embodiments of the present invention to indicate orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationship in which the product / equipment / device is usually placed during use. These terms are merely for the purpose of facilitating the description of the present invention or simplifying the description in specific embodiments, and for enabling those skilled in the art to quickly understand the solution, and do not indicate or imply that a particular device / component / element must have a specific orientation, or be constructed and operated in a specific positional relationship. Therefore, they should not be construed as limitations on the present invention.

[0029] Furthermore, the use of terms such as "horizontal," "vertical," "suspended," "parallel," and "coaxial" does not imply that the corresponding device / component / element must be absolutely horizontal, vertical, suspended, parallel, or coaxial. Slight tilt or deviation is permissible, as long as it does not affect the normal function of the relevant component. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," not that the structure must be perfectly horizontal; a slight tilt is acceptable. "Coaxial" means that two components are arranged as coaxially as possible, allowing them to move coaxially or approximately coaxially when their relative positions change. Alternatively, it can be simplified to mean that the corresponding device / component / element, when arranged in "horizontal," "vertical," "suspended," "parallel," or "coaxial" directions, can have an error / deviation of ±10% relative to the corresponding direction, more preferably within ±8%, more preferably within ±6%, more preferably within ±5%, and more preferably within ±4%. For example, the deviation in the "coaxial" direction is controlled within 0.2-1mm, preferably within 0.2-0.5mm. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its function in the solution of the present invention.

[0030] Furthermore, the use of terms such as "first," "second," and "third" in terminology is merely for distinguishing descriptions of identical or similar components and should not be interpreted as emphasizing or implying the relative importance of a particular component.

[0031] Furthermore, in the description of the embodiments of the present invention, "several", "more than", and "a number of" represent at least two. The number can be any number, such as two, three, four, five, six, seven, eight, or nine, and can even exceed nine.

[0032] Furthermore, in the description of the technical solution of this invention, unless otherwise explicitly specified / limited / restricted, the terms "set up," "install," "connect," "link," "provided with," "laid out," and "arranged" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to connection methods commonly used in the art, such as welding, riveting, bolting, and threaded connections. Such connections can be mechanical, electrical, or communication connections; they can be direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components.

[0033] Example 1 like Figures 4-9 As shown, a three-dimensional tube bending cold bending forming method includes the following steps: S1. Theoretically determine the location of the bending center. The central axis of the spiral bending segment 11 of the three-dimensional bending pipe 1 is divided into three arc segments. Each arc segment corresponds to a set cold bending forming angle, and the center of each arc segment is set as the bending center.

[0034] S1 is used to determine the theoretical bending center on the tube blank 2. By dividing it into three arc segments, multiple bending centers are determined, so that the tube blank 2 can gradually form the required tube shape during multiple bending processes.

[0035] In an optional implementation, the cold bending forming angle corresponding to each arc segment is preferably 60°, the three arc segments are arranged in an axisymmetric state, and adjacent arc segments are arranged continuously.

[0036] In an optional implementation, the cold bending forming angle can be adjusted within a small range according to the actual situation, so that the adjacent arc segments can be adjusted within a small range according to the size of the three-dimensional bent tube 1 and the cold bending forming angle. The three corresponding arc segments can be set at intervals according to the corresponding size matching. For example, the cold bending forming angles corresponding to the three arc segments can be 50°, 65° and 50° respectively, and the corresponding interval distance between adjacent arc segments can be determined according to the theoretical marking.

[0037] S2. Mark the bending center. Mark the position of the bending center on the tube blank 2 according to the arc length corresponding to the cold bending forming angle.

[0038] S2 is used to determine the position of the bending center on the straight tubular blank 2 based on the theoretically determined bending center position, providing guidance for the bending position in cold bending forming.

[0039] In an optional implementation, S2 can project the arc length dimension determined by the angle onto the tube blank 2, thereby determining the position of the bending center.

[0040] S3. Cold bending to form a tube shape: The lower forming die 5 supports the tube blank 2, and the upper forming die 4 cold bends the bending center along the axial direction of the tube blank 2 in the order of first the two ends and then the middle to form a 180° planar bent tube.

[0041] S3 is used to perform multiple bending operations on the straight tubular blank 2 to obtain a 180° planar bent tube with high forming dimensional accuracy, which can ensure that the bending radius of the three-dimensional bent tube 1 is uniform.

[0042] In an optional embodiment, the bending center includes a first bending center 31, a third bending center 33 and a second bending center 32 arranged sequentially along the axis of the tube blank 2. In S3, cold bending can be performed sequentially in the order of the first bending center 31, the second bending center 32 and the third bending center 33.

[0043] In an optional embodiment, in step S3, the tube blank 2 slides along the axial direction within the lower forming die 5 to adjust the relative position of the bending center with the upper forming die 4. Both ends of the tube blank 2 can be connected to lifting fixtures 7. By connecting the lifting fixtures 7 to the lifting equipment, the position of the tube blank 2 relative to the lower forming die 5 during the bending process can be quickly adjusted to allow different bending centers to correspond with the upper forming die 4.

[0044] In an optional embodiment, the lifting fixture 7 can be welded to both ends of the tube blank 2 to ensure stable lifting and lifting safety. The lifting fixture 7 can also partially extend into the tube blank 2 to provide internal support, which helps to avoid the influence of the cold bending process on the shape of the inner cavity of the tube blank 2.

[0045] In an optional embodiment, the material hardness of the forming lower die 5 is at least 20 HB greater than the material hardness of the tube blank 2. This is to achieve stable support for the tube blank 2. An appropriate material hardness difference can be set according to the actual situation to avoid scratches on the surface of the tube blank 2 when the tube blank 2 moves relative to the forming lower die 5.

[0046] In an optional embodiment, the upper forming die 4 is provided with an arc forming surface 41, the arc angle of the forming surface 41 being 60-80°, and the upper forming die 4 matches the lower forming die 5. The width of the upper forming die 4 is smaller than the width of the three-dimensional bent tube 1. The upper forming die 4 uses a specific arc forming surface 41, which can form point contact with the bending center, ensuring stable bending of the bending center and improving the dimensional accuracy after bending.

[0047] In an optional embodiment, the forming surface 41 of the forming upper die 4 can be configured to fit against the outer surface arc of the 180° spiral bending segment 11 of the three-dimensional bent tube 1 after a single bending is completed, so as to improve the bending accuracy.

[0048] In an optional embodiment, the lower forming die 5 is provided with two support positions 51, and the support spacing between the two support positions 51 satisfies 1 / 3πr+2(1.25~1.45)D; In the formula, r is the theoretical bending radius of the three-dimensional bend 1, in mm; D is the outer diameter of the three-dimensional bent tube 1, in mm. This allows for fixed-point support of the tube blank 2, aligning with the bending center, and enabling rapid cold pressing forming of the tube blank 2 into a 180° planar bend.

[0049] S4. Press bending to form the skew angle: The forming mold 6 applies pressure to the 180° planar bend to form the skew angle of the spiral bend section 11 and the straight pipe sections 12 at both ends. The forming mold 6 is provided with a cavity that is consistent with the shape of the three-dimensional bend 1.

[0050] S4 is used to apply pressure to the 180° planar bend through the forming mold 6 to achieve cold pressing forming of the 180° planar bend into the three-dimensional bend 1.

[0051] In one or more embodiments, the forming mold 6 can be a mold structure independent of the forming upper mold 4 and the forming lower mold 5. The forming mold 6 is provided with a cavity that is consistent with the shape of the three-dimensional bent tube 1. The three-dimensional bent tube 1 is formed by applying pressure through the cavity, which can make the rising slope of the formed three-dimensional bent tube 1 uniform and the shape accuracy high, thereby improving the preparation efficiency and preparation accuracy.

[0052] In an optional embodiment, the forming mold 6 can be composed of two parts, a top mold 61 and a bottom mold 62, which are fastened together. The top mold 61 and the bottom mold 62 are respectively provided with a spiral segment groove 63 corresponding to the 180° spiral bending segment 11 of the three-dimensional bent pipe and a straight segment groove 64 corresponding to the straight pipe segments 12 at both ends of the spiral bending segment 11. The spiral segment groove 63 and the straight segment groove 64 are connected, and a cavity is formed by fastening the top mold 61 and the bottom mold 62.

[0053] In an optional embodiment, a pad 5 is provided at the port position of the corresponding straight section groove 64 in the cavity, and the thickness of the pad 5 is positively correlated with the deflection angle of the three-dimensional bent tube 1.

[0054] In an optional embodiment, the pad 5 can be a steel structural component with the same material hardness as the forming mold 6.

[0055] In one or more embodiments, extension sections 6 can be reserved at both ends of the tube blank 2. The extension sections 6 can be detachably connected to the lifting fixture 7. The extension sections 6 are cut off after the bending and forming of the skew angle, so that the end of the three-dimensional bent tube 1 after the extension sections 6 are cut off has higher precision.

[0056] The above description is only 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.

Claims

1. A method for cold bending and forming a three-dimensional tube, characterized in that, Includes the following steps: S1. Theoretically determine the position of the bending center and theoretically divide the spiral bending segment (11) of the three-dimensional bent pipe (1) into three arc segments. Each arc segment corresponds to a set cold bending forming angle, and the center of each arc segment is set as the bending center. S2. Determine the bending center by marking the arc length corresponding to the cold bending forming angle on the tube blank (2). S3. Cold bending to form a tube shape: the lower forming die (5) supports the tube blank (2), and the upper forming die (4) cold bends the bending center along the axial direction of the tube blank (2) in the order of first the two ends and then the middle to form a 180° planar bent tube. S4. Press and bend to form the skew angle. The forming mold (6) is used to apply pressure to the 180° planar bend to form the skew angle of the spiral bend section (11) and the straight pipe sections (12) at both ends. The forming mold (6) is provided with a cavity that is consistent with the shape of the three-dimensional bend (1).

2. The method for cold bending and forming of a three-dimensional tube according to claim 1, characterized in that, The cold bending forming angle includes 60°±5°, and the three arc segments are arranged symmetrically, with adjacent arc segments being continuous or spaced apart.

3. The method for cold bending and forming of a three-dimensional tube according to claim 2, characterized in that, The bending center includes a first bending center (31), a third bending center (33), and a second bending center (32) arranged sequentially along the axis of the tube blank (2) in the cold bending sequence. In S3, cold bending is performed sequentially in the order of the first bending center (31), the second bending center (32), and the third bending center (33).

4. The method for cold bending and forming of a three-dimensional tube according to claim 4, characterized in that, In S3, the tube blank (2) adjusts the relative position of the bending center and the upper forming die (4) by sliding along the axial direction within the lower forming die (5).

5. The method for cold bending and forming of a three-dimensional tube according to claim 5, characterized in that, The material hardness of the forming lower die (5) is at least 20 HB greater than the material hardness of the tube blank (2).

6. A method for cold bending and forming a three-dimensional tube according to any one of claims 1-5, characterized in that, The upper forming mold (4) is provided with an arc forming surface (41), the arc angle of the forming surface (41) is 60-80°, and the upper forming mold (4) matches the lower forming mold (5).

7. The method for cold bending and forming of a three-dimensional tube according to claim 6, characterized in that, The forming lower die (5) is provided with two support positions (51), and the support distance between the two support positions (51) satisfies 1 / 3πr+2(1.25~1.45)D; In the formula, r is the theoretical bending radius of the three-dimensional bent pipe (1), in mm; D is the outer diameter of the three-dimensional bent pipe (1), in mm.

8. The method for cold bending and forming of a three-dimensional tube according to claim 1, characterized in that, The forming mold (6) includes a top mold (61) and a bottom mold (62). The top mold (61) and the bottom mold (62) are respectively provided with a spiral segment groove (63). The two ends of the spiral segment groove (63) are respectively connected to a straight segment groove (64). The top mold (61) and the bottom mold (62) are engaged to form the cavity.

9. A method for cold bending and forming a three-dimensional tube according to claim 8, characterized in that, The cavity is provided with a pad (5) at the port position corresponding to the straight section groove (64), and the thickness of the pad (5) is positively correlated with the deflection angle of the three-dimensional bent tube (1).

10. A method for cold bending and forming a three-dimensional tube according to claim 8, characterized in that, The tube blank (2) has extension sections (6) reserved at both ends. The extension sections (6) are detachably connected to the lifting fixture (7). The extension sections (6) are cut off after being bent and formed at an angle.

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