Method for improving free bending forming quality of thin-walled pipe
Through the anisotropic magnetorheological elastomer-supported thin-walled tube forming method, the forming defects of thin-walled tubes with small bending radius are solved, and high-quality forming effect is achieved, which is suitable for engineering fields such as aerospace.
Patent Information
- Application Number
- CN202510898915.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-01
- Publication Date
- 2025-08-15
AI Technical Summary
When forming a thin-walled pipe with a small bending radius, the existing three-dimensional free bending forming technology has defects such as cross-section collapse in the transition section, thickening the inner side of the forming section and excessive thinning and cracking on the outer side. The traditional mandrel support process cannot solve these problems at the same time.
The anisotropic magnetorheological elastomer supports thin-walled tube forming method is adopted. By planning the forming length in sections and configuring magnetorheological elastomers with different iron powder contents, the mechanical properties are regulated by magnetic fields to achieve support effect on different forming areas.
It effectively solves the defects of cross-section collapse of thin-walled pipe transition section, thickening of the inner side of the forming section and excessive thinning and rupture of the outer side, improves the forming quality, reduces production costs, and has a wide range of engineering application value.
Smart Images
Figure CN120480022A_ABST
Abstract
Description
Technical Field
[0001] The invention discloses a method for improving the free bending forming quality of a thin-walled tube, and belongs to the technical field of tube bending forming. Background Art
[0002] Due to its lightweight advantages and high specific strength, thin-walled pipes have become core structural components of high-end equipment such as aerospace fuel delivery pipelines, new energy vehicle chassis load-bearing components, and building curtain wall connection systems, significantly reducing manufacturing costs while achieving system weight reduction.
[0003] When forming small bending radius pipes with existing three-dimensional free bending forming technology, the material deformation gradient changes sharply in the transition section due to the sudden change in the pipe geometry, resulting in local stress concentration and cross-sectional collapse. Currently, the industry generally uses rigid metal core rods or thermosetting resin core rods as internal support media, but there are still technical bottlenecks: (1) Although rigid core rods can provide high-strength support, their excessive hardness and poor flexibility lead to cracks on the outer side of the bend when forming small bending radii; (2) Although resin core rods have a certain degree of flexibility, their low elastic modulus and poor creep resistance cannot effectively restrain the circumferential flow of the material during the bending process, resulting in uncontrolled wall thickness distribution.
[0004] In view of the above problems, the present invention provides a method for forming a thin-walled tube by supporting an anisotropic magnetorheological elastomer. Summary of the Invention
[0005] The traditional core rod support process has great limitations in forming thin-walled tubes with a small curvature radius and cannot simultaneously solve the forming defects in the background. The purpose of the present invention is to provide a method for forming thin-walled tubes with support by anisotropic magnetorheological elastomers. By changing the iron powder content in the segmented areas of the anisotropic magnetorheological elastomer, the magnetic field size in each area is controlled, and the mechanical properties of the anisotropic magnetorheological elastomer are regulated in real time, so that the core rod can produce different support effects on the thin-walled tube in different forming areas.
[0006] A method for improving the free bending forming quality of a thin-walled tube comprises the following steps:
[0007] The first step is to plan the forming length according to the forming radius of the thin-walled tube and divide it into sections, including transition section S1, bending section S2, and transition section S3;
[0008] The second step is to customize the mold according to the outer diameter and inner diameter of the thin-walled tube and the length of each section, including two sets of transition section forming molds and upper and lower molds for the stable forming section;
[0009] The third step is to pour the prepared liquid magnetorheological elastomer into the mold and place the mold in a magnetic field generator to fix the mold.
[0010] Step 4: Sequentially place the solidified magnetorheological elastomer into the tube, and then install the thin-walled tube into the three-dimensional free bending equipment. Finally, transfer it to the equipment according to the established process parameters to perform actual bending forming. The process parameters include bending radius R, tube feeding speed v, moving distance x of the spherical bearing, moving time t, distance A from the center of the bending die to the guide, and magnitude H of the magnetic field strength.
[0011] In the described method, the diameter of the thin-walled tube is 8 to 20 mm, the wall thickness is 0.5 to 2 mm, and the ratio of the bending radius of the pipe fitting to the outer diameter is more than 1.5.
[0012] In the described method, the forming die for the transition section is cylindrical, with an inner diameter the same as that of the formed thin-walled tube and a length equal to the forming length of the transition section. The forming die for the forming section is semi-cylindrical, with a length equal to the forming length of the forming section.
[0013] In the described method, the anisotropic magnetorheological elastomer is composed of addition-type silicone rubber, micron-sized iron powder, and a vulcanizing agent. Mix the addition-type silicone rubber, iron powder, and vulcanizing agent in a certain proportion and stir at high speed for 10 - 15 min. Then, place it in a vacuum pump to extract the air in the liquid magnetorheological elastomer. When no bubbles emerge on the surface, turn off the vacuum pump. Finally, place it in a magnetic field generator with a magnetic field strength of 0.5 T and let it stand still, and fix the die, so that the iron powder is arranged in the direction of the magnetic induction line under the action of the magnetic field to form a chain structure, improving the mechanical properties of the magnetorheological elastomer. After the magnetorheological elastomer solidifies, take it out. Compared with directly pouring in segments into the tube, it not only reduces the time cost but also realizes the zoning regulation of the magnitude of the supporting forces on the inner and outer sides of the bending of the forming section.
[0014] In the described method, the iron powder content in the magnetorheological elastomer is configured according to the forming radius of the thin-walled tube. When the bending radius R ≤ 2D, the iron powder content in the magnetorheological elastomer filled in the first and second transition sections is 50%, the iron powder content in the magnetorheological elastomer on the outer side of the stable forming section is 40%, and the iron powder content in the magnetorheological elastomer on the inner side of the stable forming section is 30%. When 2D < R ≤ 3D, the iron powder content in the magnetorheological elastomer filled in the first and second transition sections is 40%, the iron powder content in the magnetorheological elastomer on the outer side of the stable forming section is 35%, and the iron powder content in the magnetorheological elastomer on the inner side of the stable forming section is 25%. When R > 3D, the iron powder content in the magnetorheological elastomer filled in the first and second transition sections is 30%, the iron powder content in the magnetorheological elastomer on the outer side of the stable forming section is 30%, and the iron powder content in the magnetorheological elastomer on the inner side of the stable forming section is 20%.
[0015] In the described method, for the direction of placing the anisotropic magnetorheological elastomer in the thin-walled tube, it is required that the arrangement direction of the iron powder therein is consistent with the magnetic field direction.
[0016] In the method, the relationship between the geometric parameters of the first transition section, the forming section, and the second transition section, such as length, bending radius R, and the tube feed speed v, the spherical bearing movement distance u, the movement time t, the distance A from the bending die center to the guide, and the magnetic field strength H is as follows, where the tube speed v moves at a uniform speed along the Z-axis:
[0017] During the first transition period t1:
[0018] When the center of the bending die deviates from the origin by x, it can be deduced that the central angle of the arc at this time is θ1 = arcsin(A / R);
[0019] The length of the transition section axis is the length of the magnetorheological elastomer in the transition section
[0020] Spherical bearing movement distance
[0021] During the forming section movement time t2:
[0022] As the pipe is fed, the central angle of the arc corresponding to the transition section is θ2
[0023] The axial length of the transition section is the length of the magnetorheological elastomer in the forming section Spherical bearing movement distance x = 0;
[0024] During the movement time t3 of the second transition section, the axial length of the transition section, i.e., the length of the magnetorheological elastomer of the transition section, S3 = A.
[0025] Magnetic field strength at each stage Where E is the elastic modulus of the pipe, C vis is the velocity-dependent damping coefficient, μ0 is the magnetic permeability, χ is the magnetic susceptibility, A contact is the contact area between the pipe and MRE, and I is the moment of inertia of the pipe section.
[0026] Beneficial effects:
[0027] 1. The present invention provides a method for improving forming quality, which can simultaneously solve the problems of cross-sectional collapse in the transition section of thin-walled tubes, thickening on the inside of the forming section, and cracking due to excessive thinning on the outside;
[0028] 2. The present invention provides a mandrel of smart materials that can regulate the mechanical properties of anisotropic magnetorheological elastomers in real time according to the curvature radius of a bent thin-walled tube;
[0029] 3. The present invention is simple and feasible, has low production cost, and has important engineering application value and obvious economic benefits in engineering fields such as aviation and aerospace. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Figure 1 is a schematic diagram of a bending model of the present invention;
[0031] Figure 2 A top view of a magnetorheological elastomer forming die according to the present invention;
[0032] Figure 3 This is a positive triaxial drawing of the magnetorheological elastomer forming die of the present invention;
[0033] Figure 4 Schematic diagram of the solidification process of the anisotropic magnetorheological elastomer of the present invention;
[0034] Figure 5 FIG. 1 is a diagram of a thin-walled tube filled with anisotropic magnetorheological elastomer in each section of the present invention;
[0035] Figure 6 This is a diagram of the anisotropic magnetorheological elastomer-assisted thin-walled tube forming process of the present invention;
[0036] Figure 7 This is a typical "U"-shaped sample diagram of the present invention.
[0037] Figure numerals: first transition section forming die 1, stable forming section forming upper die 2, stable forming section forming lower die 3, second transition section forming die 4, magnetic field generator 5, anisotropic magnetorheological elastomer 6, aluminum alloy thin-walled tube 7, three-dimensional free bending forming equipment 8, "U"-shaped tube typical sample 9, first transition section 10, stable forming section 11, second transition section 12 DETAILED DESCRIPTION
[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.
[0039] Example 1
[0040] The first step is to determine the target as a 16×0.5mm 5a06 aluminum alloy thin-walled tube 7, a "U"-shaped tube 9 with a bending radius R of 32mm, R / D = 2, a distance A from the guide to the center of the bending die = 30mm, and the axial feed speed of the thin-walled tube 7 is maintained at 10mm / s;
[0041] The second step is to calculate the required forming length of the thin-walled tube 7, the first transition section 10 Stable forming section 11 The second transition section 12S3 = A = 30 mm.
[0042] The third step is to customize the forming molds for each section: the first transition section forming mold cylinder 1 has an outer radius of 8mm, an inner radius of 7.5mm, and a cylinder height of 38.89mm; the stable forming section forming mold semi-cylinder has an outer radius of 8mm, an inner radius of 7.5mm, and a cylinder height of 61.64mm (upper mold 2 and lower mold 3); the second transition section forming mold cylinder 4 has an outer radius of 8mm, an inner radius of 7.5mm, and a cylinder height of 30mm.
[0043] In the fourth step, anisotropic magnetorheological elastomers 6 with iron powder mass fractions of 30%, 40% and 50% are respectively configured, wherein the magnetorheological elastomer 6 with an iron powder mass fraction of 50% is poured into the first transition section mold 1 and the second transition section mold 4, respectively, the magnetorheological elastomer 6 with an iron powder mass fraction of 40% is poured into the upper mold 2 of the stable forming section, and the magnetorheological elastomer 6 with an iron powder mass fraction of 30% is poured into the lower mold 3 of the stable forming section. The molds are placed in a magnetic field generator 5 and allowed to stand, the molds are fixed, the magnetic field strength is set to 0.5 T, and the magnetorheological elastomer 6 is taken out after solidification;
[0044] The fifth step is to put the solidified magnetorheological elastomer 6 into the tube in sequence, and then install the thin-walled tube 7 into the three-dimensional free bending equipment 8. Figure 1 As shown, where E = 75 GPa, C vis =30N·s / m, I=2.945mm 4 .
[0045] First transition section 10: forming time Bending die movement distance μ0=5.8,χ=0.17,A contact =1710.47mm 2
[0046] Stable forming section 11: forming time x=0mm, μ0=5.2, χ=0.15, A contact =2711.69mm 2 ,
[0047] Second transition section 12: forming time x=-3.633mm, μ0=5.8, χ=0.17, A contact =1319.47mm 2 ,
[0048] Finally, the established process parameters are transmitted to the equipment to perform the actual bending forming.
[0049] During the thin-walled tube bending process, different forming sections are filled with anisotropic magnetorheological elastomers containing varying iron powder mass fractions. The magnetic field modifies their mechanical properties, ensuring the quality of the tube. Compared to rigid / flexible mandrels, which can only address forming defects in a single section, anisotropic magnetorheological elastomer mandrels address the problem of transition section depression by regulating mechanical properties in real time. This also significantly improves forming defects such as wrinkling on the inside of the forming section and thinning and cracking on the outside. This invention effectively suppresses the occurrence of forming defects in thin-walled tubes, providing a strong guarantee for high-quality forming of thin-walled tubes and possesses promising application prospects.
[0050] 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, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.
Claims
1. A method for improving the quality of free bending of thin-walled tubes, characterized by: It includes the following steps: In the first step, plan the forming length according to the forming radius of the thin-walled tube and segment it, including a transition section S1, a bending section S2, and a transition section S3; In the second step, customize the molds according to the outer diameter, inner diameter of the thin-walled tube, and the lengths of each segment, including two sets of transition section forming molds, an upper mold and a lower mold for the stable forming section; In the third step, pour the configured liquid magnetorheological elastomer into the mold, place the mold in a magnetic field generator and let it stand still to fix the mold; In the fourth step, sequentially place the solidified magnetorheological elastomer into the tube in order, load the thin-walled tube into a three-dimensional free bending equipment, and finally transfer it to the equipment according to the established process parameters to perform actual bending and forming.
2. The method for improving the free bending forming quality of thin-walled tubes according to claim 1, characterized in that: The diameter of the thin-walled tube is 8 to 20 mm, and the wall thickness is 0.5 to 2 mm. The ratio of the bending radius of the pipe fitting to the outer diameter is more than 1.
5.
3. The method for improving the free bending forming quality of thin-walled tubes according to claim 1, characterized in that: The transition section forming mold is cylindrical, with an inner diameter the same as that of the formed thin-walled tube and a length equal to the forming length of the transition section; the forming section mold is semi-cylindrical, with a length equal to the forming length of the forming section.
4. The method for improving the free bending forming quality of thin-walled tubes according to claim 1, characterized in that: The iron powder content in the magnetorheological elastomer is configured according to the size of the forming radius of the thin-walled tube.
5. The method for improving the free bending forming quality of thin-walled tubes according to claim 4, characterized in that: When the bending radius R ≤ 2D, the iron powder content of the magnetorheological elastomer filled in the first and second transition sections is 50%, the iron powder content of the magnetorheological elastomer on the outer side of the stable forming section is 40%, and the iron powder content of the magnetorheological elastomer on the inner side of the stable forming section is 30%; when 2D < R ≤ 3D, the iron powder content of the magnetorheological elastomer filled in the first and second transition sections is 40%, the iron powder content of the magnetorheological elastomer on the outer side of the stable forming section is 35%, and the iron powder content of the magnetorheological elastomer on the inner side of the stable forming section is 25%; when R > 3D, the iron powder content of the magnetorheological elastomer filled in the first and second transition sections is 30%, the iron powder content of the magnetorheological elastomer on the outer side of the stable forming section is 30%, and the iron powder content of the magnetorheological elastomer on the inner side of the stable forming section is 20%. The direction of the anisotropic magnetorheological elastomer placed in the thin-walled tube, where the arrangement direction of the iron powder is consistent with the magnetic field direction.
6. The method for improving the free bending forming quality of thin-walled tubes according to claim 1, characterized in that: The specific bending in step four is as follows: The geometric shape parameters of the first transition section, forming section, and second transition section, such as length, bending radius R, and the relationships with the tube feeding speed v, the moving distance u of the spherical bearing, the moving time t, the distance A from the center of the bending die to the guide, and the magnetic field strength H, are as follows. The tube speed v advances uniformly along the Z-axis direction: During the moving time t1 of the first transition section: When the center of the bending die deviates from the origin position by x, the corresponding central angle θ1 of the arc at this time can be deduced as θ1 = arcsin(A / R); The length of the transition section axis is the length of the magnetorheological elastomer in the transition section Spherical bearing movement distance During the moving time t2 of the forming section: As the tube feeds, the corresponding central angle of the arc for the transition section at this time is θ2 The axial length of the transition section is the length of the magnetorheological elastomer in the forming section Spherical bearing movement distance x = 0; During the moving time t3 of the second transition section: the axial length of the transition section, that is, the length S3 of the magnetorheological elastomer in the transition section = A.
7. The method for improving the free bending forming quality of thin-walled tubes according to claim 6, characterized in that: Magnetic field strength at each stage Where E is the elastic modulus of the pipe, C vis is the velocity-dependent damping coefficient, μ0 is the magnetic permeability, χ is the magnetic susceptibility, A contact is the contact area between the pipe and MRE, and I is the moment of inertia of the pipe section.