A bending forming device and method suitable for forming a variable curvature metal thin-wall tube

Abstract

The present invention belongs to the technical field of tube bending and forming, and proposes a bending and forming device and method suitable for forming thin-walled metal tubes with variable curvature. The device includes a segmented upper die and a lower die, and a certain supporting internal pressure is filled inside the tube before the experiment; the height of the upper die and the lower die are adjustable to achieve earlier mold closing of the upper die and the lower die, which can increase the limit of the tube bending curvature; the relative height between the segmented molds is changed to achieve fine adjustment of the bending curvature radius of the metal tube; the upper die first contacts and closes the middle part of the lower die, and the outer surface of the metal tube will be subjected to the positive pressure and friction brought by the upper die and the lower die, which solves the problem that the inner side of the thin-walled metal tube is prone to wrinkling and the outer side of the tube is prone to thinning and cracking. The present invention can realize the bending of variable curvature multi-bend tubes and compensate and adjust the rebound of the tube after bending.

Description

Technical Field

[0001] The invention relates to the technical field of tube bending and forming, and in particular to a bending and forming device and method suitable for forming a variable curvature metal thin-wall tube. Background Art

[0002] Thin-walled hollow curved axis integral components are widely used in the automotive, aerospace and other fields because they have excellent bending and torsion resistance while reducing weight. Such components generally use thin-walled tubes as blanks, which are first bent into a space bending tube close to the final bending axis, and then formed into the final shape using processes such as internal high pressure, pressure pressing or hot air expansion. Therefore, the bending forming of thin-walled tubes is a very important step in forming such components. However, thin-walled tubes are prone to wrinkling on the inside of the bend and cracking on the outside during the bending process, and the unloading process after bending may also be accompanied by severe rebound.

[0003] At present, the methods for bending thin-walled metal pipes are mainly divided into press bending, CNC bending and push bending.

[0004] The CNC bending process and forming conditions of pipes are relatively complex, requiring strict coordination of multiple sets of dies and mandrels to control the deformation behavior of pipes. At the same time, CNC bending also has certain limitations: First, the price of CNC pipe bending machines is relatively high, suitable for mass production, not suitable for small batch production and experiments; second, the bending capacity is limited, and it is difficult to form pipes with larger diameters, thicker walls and higher material strength; third, flattening and wrinkling defects are prone to occur during bending.

[0005] The push-bending of pipes is done by using polyurethane rods and other supports inside the pipes, and applying thrust from the outside through a punch, so that the metal pipes can be bent. This bending method is only suitable for bending single-bend pipes, and cannot achieve multiple bends. It is not suitable for bending pipes with long straight sections at both ends. At the same time, the external axial thrust aggravates the axial compressive stress on the inside of the bent pipe, making it easy for the inside of the bent pipe to become unstable and wrinkled, reducing the forming accuracy.

[0006] Pipe bending is the earliest process used in pipe bending. It mainly refers to the process of bending metal pipes. A rigid bending die with a certain curved surface is directly in contact with the material in the deformation area of ​​the metal pipe on the outside of the metal pipe, and the rigidity of the die is used to bend and deform the metal pipe. Since bending can be performed on an ordinary press equipped with a bending die, the experimental cost is low and it is suitable for small-batch production and experiments.

[0007] The Chinese invention patent with the announcement number CN101616758A discloses a common tube bending processing device, and the main process of the bending forming is: first, the tube blank is placed in the lower die 2 of the forming die, and the upper die 1 moves downward, and the upper die 1 contacts the tube blank and continues to move downward until the bending forming of the metal tube is completed. The upper die 1 of this type of metal tube bending forming is a punch that matches the curvature of the formed part, and the lower die 2 is a group of rollers that match the outer surface of the tube. The three-point bending process of the tube is performed by the downward movement of the upper die 1. The contact mode between the tube blank and the lower die 2 is line contact, the contact load is concentrated, the local contact force of the tube blank is large, local collapse is prone to occur, the precision of the formed part is low, and it is often used for bending tubes with equal curvature; at the lowest point of the tube bending forming, there is no contact between the die and the metal tube, and the outer side of the metal tube is prone to material thinning or even cracking under the action of axial tensile stress, and the wall thickness of the inner side of the bend is thickened or even unstable and wrinkled under the action of axial compressive stress, which seriously affects the ultimate bending curvature radius of the tube bending, and thin-walled tubes with a large diameter-to-thickness ratio are more prone to wrinkling.

[0008] Even if the upper and lower molds 2 are molds that match the curvature of the shape of the formed part, the outer side of the lowest point of the tube bending forming process is the last to contact the tube. During the bending process, defects such as thinning cracking and unstable wrinkling are also prone to occur. It is difficult to form thin-walled metal tubes with a small bending radius.

[0009] In addition, springback will occur after the tube is bent, and the degree of springback varies for tubes made of different materials. Moreover, since the plastic constitutive relationship of thin-walled tubes is difficult to accurately establish, the bending springback results of thin-walled tubes predicted by finite element simulation will always have errors. The upper and lower molds 2 of the currently common tube bending molds are both integral, and the radius of curvature after bending is fixed and cannot be adjusted. Therefore, the springback of the tube after bending will cause the formed parts to fail to meet production requirements, and repeated mold repairs are required to finally obtain qualified bent tubes.

[0010] Therefore, in order to solve the problems in the existing variable curvature metal thin-walled tube press bending forming process, that the inner side of the thin-walled metal tube is prone to unstable wrinkling, the outer side of the thin-walled metal tube is prone to excessive thinning and cracking, the thin-walled metal tube has large springback after bending, and the metal thin-walled tube has a small bending forming limit curvature, a bending forming device and method suitable for forming variable curvature metal thin-walled tubes are proposed. Summary of the invention

[0011] The purpose of the present invention is to provide a bending forming device and method suitable for forming variable curvature metal thin-walled tubes, so as to solve the problems existing in the above-mentioned prior art, to realize the bending forming of variable curvature metal thin-walled tubes, and to provide a basis for the widespread application of the overall bending forming of thin-walled two-dimensional variable curvature axis tubes.

[0012] To achieve the above object, the present invention provides the following solutions:

[0013] A bending forming device suitable for forming a thin-walled metal tube with variable curvature comprises an upper die 1, a lower die 2, an upper base plate 3, a metal tube 4, a side baffle 5, bolts, a connecting plate 7, a support column 8, a lower base plate 9, a pressure mechanism, an adjustment mechanism and a high-pressure air pipe 14; the metal tube 4 is sealed at both ends and is located between the upper die 1 and the lower die 2, one end of which is connected to a high-pressure air pipe 14 for gas pressurization or filling the metal tube 4 with a gas-liquid mixture.

[0014] Both the upper mold 1 and the lower mold 2 are segmented structures, each divided into n segments; the 1st segment and the nth segment at both ends of the upper mold 1 are fixed on the upper base plate 3, respectively, and the remaining segments are fixed on the upper base plate 3 through adjustment mechanisms; the 1st segment, the 2nd segment, the n-1th segment and the nth segment at both ends of the lower mold 2 are fixed on the connecting plate 7 through adjustment mechanisms, respectively, and the remaining segments are in contact with the side baffle 5; the side baffle 5 is connected to the side ends of the 2nd segment and the n-1th segment of the lower mold 2; the connecting plate 7 is connected to the lower base plate 9 through a support column 8; n-4 through holes are provided in the middle of the connecting plate 7; circular grooves are provided on the lower surface of the remaining segments of the lower mold 2 and the upper surface in the middle of the lower base plate 9; one end of the pressure mechanism cooperates with the circular groove, and the other end passes through the through hole on the connecting plate 7 and contacts with the circular groove.

[0015] The adjusting mechanism is an adjusting pad 13 or a push rod 18 of different heights, which can fine-tune the height of the bending die in sections to achieve the bending of pipes with different axis shapes and different bending curvature radii.

[0016] The pressure mechanism is a hydraulic cylinder mechanism with different pressures or a nitrogen spring with different strokes. Nitrogen springs with different strokes are used to achieve different clamping heights between the upper die and the lower die 2, and the middle part is clamped in advance, which can significantly improve the forming limit of the tube bending. Hydraulic cylinders with different pressures are used to achieve the matching of the clamping force between the upper die and the lower die 2 in different sections. By controlling the stroke change of the hydraulic cylinder, different clamping heights between the upper die 1 and the lower die 2 are achieved, and the middle part is clamped in advance, which can significantly improve the forming limit of the tube bending.

[0017] The fixing method is bolt connection or keyway matching; when the fixing method is bolt connection, the upper base plate 3, the connecting plate 7, the side baffle plate 5 and the adjusting mechanism are provided with bolt holes, the upper surface of the upper mold 1 and the upper surfaces of the 1st, 2nd, n-1st and nth sections of the lower mold 2, and both sides of the 2nd and n-1st sections of the lower mold 2 are provided with threaded holes, the upper base plate 3 is connected to the 1st and nth sections at both ends of the upper mold 1 by bolts, and the upper base plate 3, the adjusting mechanism and the remaining sections of the upper mold 1 are connected by bolts in sequence; the connecting plate 7, the adjusting mechanism and the 1st, 2nd and nth sections of the lower mold 2 are connected to the upper base plate 3, the adjusting mechanism and the remaining sections of the upper mold 1 are connected in sequence by bolts. The first segment, the n-1th segment and the nth segment are connected by bolts; when the connection method is keyway matching, the lower surface of the upper base plate 3, the upper surface of the connecting plate 7 and the upper and lower surfaces of the adjusting mechanism, the upper mold 1 and the lower mold 2 are all provided with keyways; the upper base plate 3 and the 1st segment and the nth segment of the upper mold 1, the upper surface of the adjusting mechanism and the upper base plate 3, and the lower surface of the adjusting mechanism and the remaining segments of the upper mold 1 are respectively positioned by flat keys 20; the upper surface of the adjusting mechanism and the 1st segment, the 2nd segment, the n-1th segment and the nth segment of the lower mold 2, and the lower surface of the adjusting mechanism and the connecting plate 7 are positioned by flat keys 20.

[0018] The n is 7; the upper mold 1 includes the upper mold a1-1, the upper mold b1-2, the upper mold c1-3, the upper mold d1-4, the upper mold e1-5, the upper mold f1-6, and the upper mold g1-7; the lower mold 2 includes the lower mold a2-1, the lower mold b2-2, the lower mold c2-3, the lower mold d2-4, the lower mold e2-5, the lower mold f2-6, and the lower mold g2-7.

[0019] Both sides of each section of the upper mold 1 and the lower mold 2 are provided with lifting holes.

[0020] Before bending, the two ends of the pipe are sealed by welding end caps at both ends, one end of which is equipped with a high-pressure air pipe. After sealing, the sealed pipe is inflated through the high-pressure air pipe 14 to increase the internal support pressure inside the pipe, reduce the occurrence of defects such as wrinkling during the bending process of the pipe, and improve the accuracy of bending. The internal support pressure is applied to the inside of the pipe in the form of a gas-liquid mixture to reduce the occurrence of defects such as wrinkling during the bending process. Compared with gas pressurization, this method not only improves the accuracy of bending, but also has a faster pressurization speed and higher forming efficiency.

[0021] A bending forming method suitable for forming a metal thin-wall tube with variable curvature comprises the following steps;

[0022] Step 1, determining the axis shape of the metal pipe 4 for bending;

[0023] First, according to the shape and size requirements of the final formed component, the outer diameter, wall thickness and tube length of the original tube blank are determined, and the metal tube 4 is simulated by bending through finite element simulation software. After bending, the springback simulation of the formed part is performed to determine the bending axis shape of the metal tube 4 after springback compensation.

[0024] Step 2: According to the outer diameter, wall thickness, tube length and bending axis shape of the original tube blank determined in step 1, finite element simulation is performed to analyze the wrinkling of the cross section of the bent tube after bending. The area without wrinkling defects is not segmented, and the upper die 1 and the lower die 2 in the area with wrinkling defects are segmented along the axis direction of the metal tube 4; the segment length of the upper die 1 and the lower die 2 is determined according to the length of the wrinkled section of the bent tube, and the simulation results of different segmentation treatments are analyzed. The segmentation method of the upper die 1 and the lower die 2 is determined according to the segmentation simulation scheme with the best forming result, and the contour shape and size of the upper die 1 and the lower die 2 for bending the metal tube 4 are determined;

[0025] Step 3: According to the segmentation mode of the upper mold 1 and the lower mold 2 determined in step 2, a bending simulation with different mold clamping heights is performed to determine the segmented mold clamping heights, thereby determining the mold clamping height between the upper mold 1 and the lower mold 2;

[0026] Step 4, determine the elastic force and stroke of the pressure mechanism; according to the segmentation mode and segmented mold height determined in steps 2 and 3, determine the stroke of the pressure mechanism, under which the initial position of the segmented mold meets the corresponding segmented mold height requirements, and according to the finite element simulation in steps 2 and 3, analyze the mold reaction force received by each section of the lower mold 2 during segmented bending, so as to determine the elastic force parameters of the pressure mechanism, the elastic force of the pressure mechanism is greater than the reaction force received by the mold, so that the segmented lower mold 2 remains stationary when the pipe is bent, and after the upper mold 1 contacts the lower mold 2, the segmented lower mold 2 moves with the downward movement of the upper mold 1;

[0027] Step 5: Place the original tube blank;

[0028] Place the original tube blank determined in step 1 into the cavity of the lower die 2, and adjust the axial position of the metal tube 4 so that the margins at both ends of the metal tube 4 are equal;

[0029] Step 6: The cavity of the upper mold 1 contacts the metal pipe 4;

[0030] The upper mold 1 moves downward under the external force. After reaching the corresponding position, the cavity of the upper mold 1 contacts the outer surface of the metal tube 4. At this time, the metal tube has not yet deformed.

[0031] Step 7: The upper mold 1 and the lower mold 2 are molded together;

[0032] In step 6, the upper die 1 comes into contact with the surface of the metal tube 4, and the upper die 1 continues to move downward under the action of the external press. During the downward movement, the lower die 2 closest to the upper die 1 first realizes the clamping and clamping of the upper die 1; the outer surface of the metal tube 4 is subjected to the positive pressure and friction brought by the upper die 1 and the lower die 2, and the axial compressive stress on the inner side of the bending of the metal tube 4 is greatly reduced, which solves the problem that the inner side of the bending of the thin-walled metal tube is prone to wrinkling and the outer side of the bending is prone to thinning and cracking; the upper die 1 continues to move downward and is clamped with other lower dies 2 in turn until the upper die 1 and all the lower dies 2 are clamped, the press stops moving, and the upper die 1 stops moving downward;

[0033] Step 8: Separating the upper mold 1 from the lower mold 2;

[0034] The upper mold 1 moves upward, and the lower mold 2 that is the last to be molded in step seven is separated from the upper mold 1 first, and then the upper mold 1 continues to move upward and is separated from other lower molds 2 in turn, until it is separated from all lower molds 2;

[0035] Step 9: After the metal pipe is bent, take out the final bent pipe.

[0036] In the step 1, after the axial shape of the metal tube 4 is determined, a tube of the size required for the experiment is cut from the original tube blank by wire cutting.

[0037] The upward and downward movements of the upper die 1 are achieved by a double-action press or a single-action press.

[0038] The segment length of the upper die 1 and the lower die 2 is 1.2 to 1.5 times the length of the curved tube wrinkling section.

[0039] In step 4, before placing the pipe, for the pipe bending that requires application of supporting internal pressure, both ends of the pipe need to be sealed and pressurized; the sealing method can be a punch seal or a welded end cover seal, and the pressurized medium can be gas or a gas-liquid mixture.

[0040] Beneficial effects of the present invention:

[0041] 1) The forming method of the device of the present invention is segmented clamping forming. The upper die will first contact and close the middle part of the lower die, and the outer surface of the metal pipe will be subjected to the positive pressure and friction brought by the upper die and the lower die, which solves the problem that the inner side of the thin-walled metal pipe is prone to wrinkling and the outer side of the bent material is prone to thinning and cracking, ensures the shape and size accuracy of the formed part, and improves the surface quality of the formed part.

[0042] 2) The clamping height of the upper die and the lower die can be adjusted; by replacing nitrogen springs with different strokes, the height of each segment in the middle of the lower die can be changed, thereby changing the clamping height between the upper die and the lower die, so that the upper die and the lower die can be clamped earlier, the limit of the bending curvature of the pipe can be increased, and the bending forming of thin-walled pipes with small bending radius and thin walls can be achieved.

[0043] 3) Use segmented dies; by changing the relative height between segmented dies, the curvature radius of the metal pipe can be fine-tuned, and different axis shapes and different curvature radii can be bent without mold repair. In addition, the segmented dies can be replaced separately for the severely worn dies. The device is reasonably designed, has good versatility, low cost, convenient maintenance, simple and easy to implement.

[0044] 4) The springback after bending of the tube can be compensated and adjusted. By changing the radius of curvature, the springback after bending can be compensated, thereby solving the defects caused by the springback of the metal tube after bending and improving the forming accuracy of the metal tube bending; at the same time, when bending in sections, the axial stress of the tube part that the upper and lower dies hold in advance will change, and the axial compressive stress on the inner side of the bend and the axial tensile stress on the outer side of the bend will decrease. When the external load is removed, the springback of the tube will also decrease, thereby improving the forming accuracy of the metal tube bending.

[0045] 5) It can realize the bending of variable curvature multi-bend pipes. Compared with bending methods such as push bending and roll bending, this bending method can realize axis variable curvature multi-bend bending forming by only changing the shape of the upper mold and the lower mold cavity.

[0046] 6) Before the experiment, a certain supporting internal pressure is filled inside the tube. The pressurization method can be to fill gas or a certain proportion of gas and liquid. The tube is bent under this supporting internal pressure. When the tube is bent, the contact between the upper and lower molds and the tube is more uniform, and the stress distribution is more uniform. The interface distortion and flattening phenomenon during the metal tube forming process can be reduced. The volume change of the tube during the bending process will not have much effect on the pressure, and the tube bending forming quality is higher. Before the experiment, a certain supporting internal pressure is filled inside the tube. The tube is subjected to axial tension at both ends, and the axial compressive stress on the inner side of the tube is reduced, which increases the buckling limit of the tube when it is bent. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 The present invention is a schematic overall diagram of a bending forming device suitable for forming a variable curvature metal thin-wall tube.

[0048] Figure 2 for Figure 1 Schematic diagram of the cross-section structure.

[0049] Figure 3The present invention is a schematic diagram of the mold closing process of a bending forming device suitable for forming a variable curvature metal thin-walled tube.

[0050] Figure 4 The present invention is a schematic diagram of another mold closing process of a bending forming device suitable for forming a variable curvature metal thin-wall tube.

[0051] Figure 5 It is a schematic diagram of a fully mold-closed state of a bending forming device suitable for forming a variable-curvature metal thin-wall tube according to the present invention.

[0052] Figure 6 This is a schematic diagram of a bending forming device for forming a variable curvature metal thin-walled tube according to a second embodiment of the present invention.

[0053] Figure 7 This is a schematic diagram of a bending forming device for forming a variable curvature metal thin-walled tube according to Embodiment 3 of the present invention.

[0054] Figure 8 This is a schematic diagram of a bending forming device for forming a variable curvature metal thin-walled tube according to a fourth embodiment of the present invention.

[0055] Fig. 9 It is a schematic diagram of the cooperation mode between the nitrogen spring and the connecting plate in the present invention.

[0056] Fig.10 Schematic diagram of the connection and cooperation between the connecting plate and the lower mold in the present invention; (a) is a cross-sectional view; (b) is a CC cross-sectional diagram in (a).

[0057] Fig.11 It is a schematic diagram of the connection and cooperation between the support column, the connecting plate and the lower base plate in the present invention.

[0058] Fig.12 (a) is a schematic diagram of the connection and cooperation between the side baffle and the lower mold b2-2 and the lower mold f2-6 in the present invention, and (b) and (c) are cross-sectional views of AA and BB of (a).

[0059] Fig.13 It is a schematic diagram of a pipe fitting before and after adjustment of the bending curvature radius in a bending forming device suitable for forming a variable curvature metal thin-walled tube of the present invention.

[0060] In the figure: 1-upper die; 2-lower die; 3-upper base plate, 4-metal pipe, 5-side baffle, 6-bolt a, 7-connecting plate, 8-support column, 9-lower base plate, 10-nitrogen spring a, 11-nitrogen spring b, 12-nitrogen spring c, 13-adjusting pad, 14-high pressure air pipe, 15-hydraulic cylinder mechanism a, 16-hydraulic cylinder mechanism b, 17-hydraulic cylinder mechanism c, 18-elevator, 1 9-liquid, 20-flat key, 21-bolt b, 22-bolt c, 1-1-upper mold a; 1-2-upper mold b, 1-3-upper mold c, 1-4-upper mold d, 1-5-upper mold e, 1-6-upper mold f, 1-7-upper mold g, 2-1-lower mold a, 2-2-lower mold b, 2-3-lower mold c, 2-4-lower mold d, 2-5-lower mold e, 2-6-lower mold f, 2-7-lower mold g. DETAILED DESCRIPTION

[0061] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0062] The upper mold 1 includes an upper mold a1-1, an upper mold b1-2, an upper mold c1-3, an upper mold d1-4, an upper mold e1-5, an upper mold f1-6, and an upper mold g1-7; the lower mold 2 includes a lower mold a2-1, a lower mold b2-2, a lower mold c2-3, a lower mold d2-4, a lower mold e2-5, a lower mold f2-6, and a lower mold g2-7.

[0063] The upper base plate 3 and the adjustable pad 13 are provided with bolt connection through holes, and the upper surfaces of the upper mold a1-1, the upper mold b1-2, the upper mold c1-3, the upper mold d1-4, the upper mold e1-5, the upper mold f1-6 and the upper mold g1-7 are all provided with threaded holes. The upper base plate 3 is respectively connected to the upper mold a1-1 and the upper mold g1-7 by bolts b21; the upper base plate 3 and the adjustable pad 13 are respectively connected to the upper mold b1-2, the upper mold c1-3, the upper mold d1-4, the upper mold e1-5 and the upper mold f1-6 by bolts b21.

[0064] The lower surface of the upper base plate 3, the upper and lower surfaces of the adjustable pad 13, the upper mold a1-1, the upper mold b1-2, the upper mold c1-3, the upper mold d1-4, the upper mold e1-5, the upper mold f1-6, and the upper mold g1-7 are all provided with key slots. The upper base plate 3 is positioned with the upper mold a1-1 and the upper mold g1-7 by a flat key 20; the upper surface of the adjustable pad 13 is positioned with the upper base plate 3 by a flat key 20, and the lower surface of the adjustable pad 13 is positioned with the upper mold b1-2, the upper mold c1-3, the upper mold d1-4, the upper mold e1-5, and the upper mold f1-6 by a flat key 20.

[0065] Lifting holes are provided on both sides of the upper mold a1-1, upper mold b1-2, upper mold c1-3, upper mold d1-4, upper mold e1-5, upper mold f1-6, and upper mold g1-7 to facilitate device installation.

[0066] The side baffle 5 is provided with a bolt connection through hole, and threaded holes are provided on both sides of the lower mold b2-2 and the lower mold f2-6. The side baffle 5 is respectively connected to the lower mold b2-2 and the lower mold f2-6 through bolts a6.

[0067] The connecting plate 7 and the adjustable pad 13 are provided with bolt connection through holes, and the lower surfaces of the lower mold a2-1, the lower mold b2-2, the lower mold f2-6 and the lower mold g2-7 are all provided with threaded holes. The connecting plate 7 and the adjustable pad 13 are respectively connected to the lower mold a2-1, the lower mold b2-2, the lower mold f2-6 and the lower mold g2-7 by bolts b21.

[0068] The upper surface of the connecting plate 7, the upper and lower surfaces of the adjustable pad 13, the lower mold a2-1, the lower mold b2-2, the lower mold f2-6, and the lower mold g2-7 are all provided with key slots; the upper surface of the adjustable pad 13 and the lower mold a2-1, the lower mold b2-2, the lower mold f2-6, and the lower mold g2-7 are positioned by flat keys 20, and the lower surface of the adjustable pad 13 and the connecting plate 7 are positioned by flat keys 20.

[0069] The two sides of the lower mold a2-1, lower mold b2-2, lower mold c2-3, lower mold d2-4, lower mold e2-5, lower mold f2-6, and lower mold g2-7 are all provided with lifting holes to facilitate the installation of the device. The connecting plate 7 is provided with a bolt connection through hole, and the two ends of the support column 8 are provided with threaded holes. The support column 8 and the connecting plate 7 are connected by bolts c22. The lower mold c2-3, lower mold d2-4, and lower mold e2-5 are in contact with the side baffle 5 to achieve restraint and fixation in the front and rear directions.

[0070] Three through holes are provided in the middle of the connecting plate 7, and circular grooves are provided on the lower surfaces of the lower molds c2-3, d2-4 and e2-5. The nitrogen springs a10, b11 and c12 pass through the through holes in the middle of the connecting plate 7 and respectively cooperate with the circular grooves of the lower molds c2-3, d2-4 and e2-5.

[0071] The lower bottom plate 9 is provided with a bolt connection through hole, and the support column 8 is connected to the lower bottom plate 9 by bolts c22. A circular groove is provided on the upper surface of the middle position of the lower bottom plate 9, and the lower bottom plate 9 is matched with the nitrogen spring a10, nitrogen spring b11, and nitrogen spring c12 through the groove.

[0072] Embodiment 1: Combination Figures 1 to 5 It is explained that a bending forming device suitable for forming a thin-walled metal tube with a variable curvature in this embodiment is implemented according to the following steps:

[0073] Step 1: Determine the outer diameter, wall thickness and tube length of the original tube blank according to the shape and size requirements of the final formed component, cut the experimental tube from the original tube blank, and seal both ends of the tube.

[0074] Step 2: Use adjustment pads 13 of different heights between the upper mold 1 and the upper base plate 3, and between the lower mold 2 and the connecting plate 7 to fine-tune the bending radius of the mold during bending to achieve a change in the shape of the bending axis.

[0075] Step 3: Replace the nitrogen spring with suitable stroke and elastic force, change the initial height of the lower mold d2-4, lower mold e2-5, and lower mold f2-6, so that the upper mold 1 and lower mold 2 in the middle part are first clamped and closed, and the mold is closed from the middle to both ends in sequence.

[0076] Step 4: Place the metal tube 4 cut in step 1 on the lower die a2-1 and the lower die g2-7, and inflate the tube as required before bending so that the internal pressure of the tube meets the bending requirements.

[0077] Step 5. The external press slider moves downward, driving the upper base plate 3 downward, thereby driving the upper mold a1-1, upper mold b1-2, upper mold c1-3, upper mold d1-4, upper mold e1-5, upper mold f1-6, and upper mold g1-7 to move downward as a whole; the upper mold 1 first contacts the metal pipe 4, and the upper mold 1 continues to move downward. The metal pipe is bent and deformed under the action of the upper mold 1, and then the upper mold 1 contacts the lower mold d2-4. At this time, the upper mold 1 and the lower mold d2-4 completely wrap the metal pipe 4.

[0078] Step 6. The slider of the external press continues to move downward, the piston rod of the nitrogen spring b11 moves downward, the upper die 1 and the lower die d2-4 move downward together, the metal tube 4 continues to bend and deform, and then the upper die 1 contacts the lower die c2-3 and the lower die e2-5. At this time, the upper die 1 and the lower die c2-3, the lower die d2-4 and the lower die e2-5 completely wrap the metal tube 4.

[0079] Step seven, the external press slider continues to move downward, the piston rods of nitrogen spring a10 and nitrogen spring c12 move downward, the upper die 1 and the lower die c2-3, the lower die d2-4, and the lower die e2-5 move downward together, the metal tube blank continues to bend and deform, and then the upper die 1 contacts with the lower die a2-1, the lower die b2-2, the lower die f2-6, and the lower die g2-7 to achieve complete mold closing, and the bending of the metal tube is completed.

[0080] Step 8. The slider of the external press moves upward, driving the upper base plate 3 to move upward, the upper die 1 moves upward synchronously, the piston rods of the nitrogen spring a10 and the nitrogen spring c12 move upward, and the lower die c2-3 and the lower die e2-5 move upward with the nitrogen spring piston rod until they reach the nitrogen spring stroke and are separated from the upper die 1.

[0081] Step 9. The external press slide continues to move upward, the upper die 1 moves upward, the piston rod of the nitrogen spring b11 moves upward, and the lower die d2-4 moves upward with the nitrogen spring piston rod until it reaches the nitrogen spring stroke and is separated from the upper die 1.

[0082] Step 10: The slide block of the external press continues to move upward, and the upper die 1 moves upward until the upper die 1 returns to the initial position, and the metal pipe after the bending is taken out.

[0083] Embodiment 2: Hydraulic cylinder mechanism a15, hydraulic cylinder mechanism b16 and hydraulic cylinder mechanism c17 are used to replace nitrogen spring a10, nitrogen spring b11 and nitrogen spring c12 to realize the up and down movement of lower mold c2-3, lower mold d2-4 and lower mold e2-5.

[0084] The clamping positions of the lower mold c2-3, lower mold d2-4, lower mold e2-5 and upper mold 1 are controlled by telescopic hydraulic cylinder mechanism. After clamping, the upper mold 1 and the lower mold 2 are synchronously moved by the hydraulic cylinder mechanism to realize the bending deformation of the metal pipe. The steps are the same as those in Example 1.

[0085] Embodiment 3: A push rod 18 is used instead of the adjusting pad 13 to achieve fine adjustment of the bending radius of the metal pipe.

[0086] Combination Figure 7 It is explained that by replacing the adjusting pad 13 between the upper mold a1-1, upper mold b1-2, upper mold c1-3, upper mold d1-4, upper mold e1-5, upper mold f1-6, upper mold g1-7 and the upper base plate 3 with a push rod 18, and replacing the adjustable pad 13 between the lower mold a2-1, lower mold b2-2, lower mold c2-3, lower mold d2-4, lower mold e2-5, lower mold f2-6, lower mold g2-7 and the connecting plate 7 with a push rod 18, and changing the height of the mold by rotating the push rod 18, and changing the relative position relationship between the molds, the bending radius of the metal pipe can be adjusted to meet the requirements of bending of pipes with different bending radius and the adjustment of the springback of the pipe after bending.

[0087] Embodiment 4: internal pressure support is achieved by mixing gas and liquid 19.

[0088] In the first embodiment, the pipe needs to be inflated before bending according to the requirements. In this embodiment, the gas medium is changed into a gas-liquid mixed medium; in step 4, the liquid 19 and the gas mixed medium are filled into the pipe, and then the pipe is bent. For longer pipes, the pressurization rate is faster, and bending can be achieved under stable internal pressure support, reducing the occurrence of wrinkling defects in thin-walled pipes and improving the bending limit.

Claims

1. A bending forming device suitable for forming a thin-walled metal tube with variable curvature, characterized in that: The device comprises an upper die (1), a lower die (2), an upper base plate (3), a metal pipe (4), a side baffle (5), bolts, a connecting plate (7), a support column (8), a lower base plate (9), a pressure mechanism, an adjustment mechanism and a high-pressure gas pipe (14); the metal pipe (4) is sealed at both ends and is located between the upper die (1) and the lower die (2); one end of the metal pipe (4) is connected to a high-pressure gas pipe (14) for gas pressurization or filling the metal pipe (4) with a gas-liquid mixture; The upper die (1) and the lower die (2) are both segmented structures, each of which is divided into n segments; the first segment and the nth segment at both ends of the upper die (1) are respectively fixed to the upper base plate (3), and the remaining segments are respectively fixed to the upper base plate (3) through an adjustment mechanism; the first segment, the second segment, the n-1th segment and the nth segment at both ends of the lower die (2) are respectively fixed to the connecting plate (7) through an adjustment mechanism, and the remaining segments are in contact with the side baffle (5); the side baffle (5) is connected to the side ends of the second segment and the n-1th segment of the lower die (2); the connecting plate (7) is connected to the lower base plate (9) through a support column (8); n-4 through holes are provided in the middle of the connecting plate (7); the lower surface of the remaining segments of the lower die (2) and the upper surface of the middle of the lower base plate (9) are both provided with circular grooves; one end of the pressure mechanism cooperates with the circular groove on the upper surface of the middle of the lower base plate (9), and the other end passes through the through hole on the connecting plate (7) and cooperates with the circular groove on the lower surface of the remaining segments of the lower die (2) to contact.

2. The bending forming device suitable for forming a thin-walled metal tube with a variable curvature according to claim 1, characterized in that: The adjustment mechanism is an adjustment pad (13) or a push rod (18) of different heights.

3. The bending forming device suitable for forming a thin-walled metal tube with a variable curvature according to claim 1 or 2, characterized in that: The pressure mechanism is a hydraulic cylinder mechanism with different pressures or a nitrogen spring with different strokes.

4. The bending forming device suitable for forming a thin-walled metal tube with a variable curvature according to claim 1, characterized in that: The n is 7.

5. The bending forming device suitable for forming a thin-walled metal tube with a variable curvature according to claim 1, characterized in that: The fixing method is bolt connection or keyway matching; when the fixing method is bolt connection, the upper base plate (3), the connecting plate (7), the side baffle plate (5) and the adjusting mechanism are provided with bolt holes, the upper surface of the upper mold (1) and the upper surfaces of the first section, the second section, the n-1 section and the nth section of the lower mold (2), and both sides of the second section and the n-1 section of the lower mold (2) are provided with threaded holes, the upper base plate (3) is connected to the first section and the nth section at both ends of the upper mold (1) by bolts, and the upper base plate (3), the adjusting mechanism and the remaining sections of the upper mold (1) are connected in sequence by bolts; the connecting plate (7), the adjusting mechanism and the first section, the second section and the nth section of the lower mold (2) are connected to the upper base plate (3), the adjusting mechanism and the remaining sections of the upper mold (1) by bolts; The first and nth sections, the n-1th section and the nth section are connected by bolts; when the connection method is keyway matching, the lower surface of the upper base plate (3), the upper surface of the connecting plate (7) and the upper and lower surfaces of the adjusting mechanism, the upper die (1) and the lower die (2) are all provided with keyways; the upper base plate (3) and the first and nth sections of the upper die (1), the upper surface of the adjusting mechanism and the upper base plate (3), and the lower surface of the adjusting mechanism and the remaining sections of the upper die (1) are positioned by flat keys (20); the upper surface of the adjusting mechanism and the first, second, n-1th and nth sections of the lower die (2), and the lower surface of the adjusting mechanism and the connecting plate (7) are positioned by flat keys (20).

6. The bending forming device suitable for forming a thin-walled metal tube with a variable curvature according to claim 1, characterized in that: Both sides of each section structure of the upper die (1) and the lower die (2) are provided with lifting holes.

7. A bending forming method suitable for forming a thin-walled metal tube with a variable curvature, using the bending forming device according to any one of claims 1 to 6, characterized in that: The steps include: Step 1, determining the shape of the axis of the metal pipe (4) to be bent; First, according to the shape and size requirements of the final formed component, the outer diameter, wall thickness and tube length of the original tube blank are determined, and the bending of the metal tube (4) is simulated by finite element simulation software. After bending, the springback simulation of the formed part is performed to determine the bending axis shape of the metal tube (4) after springback compensation. Step 2: Based on the outer diameter, wall thickness, tube length and bending axis shape of the original tube blank determined in step 1, finite element simulation is performed to analyze the wrinkling of the cross section of the bent tube after bending. The area without wrinkling defects is not segmented, and the upper die (1) and the lower die (2) in the area with wrinkling defects are segmented along the axis direction of the metal tube (4); the segment length of the upper die (1) and the lower die (2) is determined according to the length of the wrinkled section of the bent tube, and the simulation results of different segmentation treatments are analyzed. The segmentation method of the upper die (1) and the lower die (2) is determined according to the segmentation simulation scheme with the best forming result, and the contour shape and size of the upper die (1) and the lower die (2) for bending the metal tube (4) are determined; Step 3: According to the segmentation method of the upper mold (1) and the lower mold (2) determined in step 2, a bending simulation with different mold clamping heights is performed to determine the segmented mold clamping heights, thereby determining the mold clamping height between the upper mold (1) and the lower mold (2); Step 4, determining the elastic force and stroke of the pressure mechanism; according to the segmentation mode and segmented mold height determined in steps 2 and 3, determining the stroke of the pressure mechanism, under which the initial position of the segmented mold meets the corresponding segmented mold height requirement, and according to the finite element simulation in steps 2 and 3, analyzing the mold reaction force received by each segment of the lower mold (2) during segmented bending, thereby determining the elastic force parameters of the pressure mechanism, the elastic force of the pressure mechanism is greater than the reaction force received by the mold, so that the segmented lower mold (2) remains stationary when the pipe is bent, and after the upper mold (1) contacts the lower mold (2), the segmented lower mold (2) moves with the downward movement of the upper mold (1); Step 5: Place the original tube blank; The original tube blank determined in step 1 is placed into the cavity of the lower die (2), and the axial position of the metal tube (4) is adjusted so that the margins at both ends of the metal tube (4) are equal; Step 6: The cavity of the upper mold (1) is in contact with the metal tube (4); The upper die (1) moves downward under the action of the external force, and after reaching the corresponding position, the cavity of the upper die (1) contacts the outer surface of the metal tube (4), and at this time, the metal tube has not yet deformed; Step 7: The upper mold (1) and the lower mold (2) are molded together; In step 6, the upper die (1) comes into contact with the surface of the metal pipe (4), and the upper die (1) continues to move downward under the action of the external press. During the downward movement, the lower die (2) closest to the upper die (1) first clamps and closes the upper die (1); the upper die (1) continues to move downward and closes with other lower dies (2) in turn until the upper die (1) and all lower dies (2) are closed, the press stops moving, and the upper die (1) stops moving downward; Step 8: The upper mold (1) and the lower mold (2) are separated; The upper mold (1) moves upward, and the lower mold (2) that is the last to be molded in step seven is separated from the upper mold (1) first, and then the upper mold (1) continues to move upward and is separated from other lower molds (2) in turn, until it is separated from all lower molds (2); Step 9: After the metal pipe is bent, take out the final bent pipe.

8. The bending forming method for forming a thin-walled metal tube with a variable curvature according to claim 7, characterized in that: In the step 1, after the axial shape of the metal tube (4) is determined, a tube of the size required for the experiment is cut from the original tube blank by wire cutting.

9. The bending forming method for forming a thin-walled metal tube with a variable curvature according to claim 7, characterized in that: The upward and downward movements of the upper die (1) are achieved by a double-action press or a single-action press.

10. The bending forming method for forming a thin-walled metal tube with a variable curvature according to claim 7, characterized in that: The segment lengths of the upper die (1) and the lower die (2) are 1.2 to 1.5 times the length of the curved tube wrinkling section.

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