Method for multi-wheel rolling and integral forming of thin-wall metal expansion joint

Abstract

The thin-wall metal expansion joint multi-wheel rolling integral forming method relates to the field of plastic forming of thin-wall metal parts, and aims to solve the problems of high process control requirement, high equipment cost, low efficiency, many welds and poor reliability in the manufacture of expansion joints by the existing method. Main steps are as follows: step one, calculating the width and length of the required sheet; step two, curling and welding the sheet into a cylinder blank; step three, the roller group inside the cylinder blank is pressed against the cylinder blank on the flat die surface, the roller group is continuously pushed to press the cylinder blank against the position of different section features of the flat die surface, and the corrugation is gradually formed on the cylinder blank under the action of the roller group and the flat die; and step four, removing the constraint to obtain the expansion joint. The large-size multi-corrugated thin-wall expansion joint is manufactured in a high-efficiency, accurate, simple, low-cost and low-equipment requirement manner.

Description

Technical Field

[0001] This invention pertains to plastic forming methods for thin-walled metal parts, specifically relating to a multi-roll rolling integral forming method for thin-walled metal expansion joints. Background Technology

[0002] A metal expansion joint is a thin-walled cylindrical body with a corrugated shape along its axial direction (such as...). Figure 3 and Figure 4 As shown, it includes a corrugated section in the middle and straight sections at both ends, and is a type of elastic component. It can change shape and size under relatively small external loads, and can return to its original shape and size after unloading, thus possessing functions such as displacement compensation, vibration reduction and noise reduction, stress release caused by structural thermal deformation, and sealing. Expansion joints can be used between air intake sections of hypersonic aircraft, and also in shipbuilding, transportation, petrochemicals, nuclear energy, and other fields. The expansion joints used have large diameters and thin walls, very low overall rigidity, and the corrugated features are often small in size, making the forming of metal expansion joints quite difficult. Currently, there are five main forming methods for metal expansion joints: hydroforming, sheet welding forming, roll forming, spinning forming, and mechanical bulging.

[0003] Hydraulic forming involves placing a cylindrical blank or thin sheet rolled and welded into a mold, injecting a pressurized medium into the blank or cylinder, and applying a load to both ends of the blank or cylinder with a punch to replenish material. Under this combined action, the blank undergoes plastic deformation and gradually conforms to the mold. This method can form all the corrugated features of the expansion joint in one pass, resulting in high forming efficiency. However, this method places extremely high demands on the precise and coordinated control of two key parameters: internal pressure and axial material replenishment. Excessive internal pressure or insufficient axial material replenishment can easily lead to excessive thinning or even cracking of the blank, while excessive axial material replenishment can cause local wrinkling or overall buckling instability. For expansion joints with larger diameters, the thrust required by the end punch and the mold locking force during hydraulic forming are very large, placing high demands on the equipment. Thin sheet welding forming involves first plastically deforming a thin sheet into annular corrugated diaphragms, and then welding the diaphragms sequentially into a whole expansion joint. This method is relatively simple and easy to implement, has high wall thickness uniformity, and can be applied to the manufacture of expansion joints with various irregular cross-sectional shapes. Because it requires welding a large number of diaphragms together sequentially, production efficiency is low, labor costs are high, and material utilization is low; there are also many weld seams, resulting in relatively low reliability. Roll forming typically involves the simultaneous radial movement of a driving roller placed inside the tube blank or cylinder and multiple driven rollers placed outside, gradually pressing out corrugations. During forming, the driven rollers on both sides of the corrugations need to move axially. For expansion joints with multiple corrugation features, each corrugation needs to be formed individually, resulting in low efficiency. Because forming corrugations requires radial and axial movement of the rollers, the drive mechanism on the rollers results in a large roller-to-roll spacing, making it unsuitable for forming expansion joints with small corrugation spacing. Relative sliding exists between the blank and the rollers, making the surface of the expansion joint parts prone to mechanical damage. The motion control accuracy of the rollers directly affects the forming accuracy of the expansion joint. Spin forming is a continuous forming method that uses a roller with a helical surface to rotate outside the tube blank, causing the tube blank to be compressed and deformed axially and radially to form corrugations. This method is more efficient but only suitable for forming slender expansion joints with a diameter of less than 50mm and a small corrugation depth. Mechanical bulging utilizes a conical core that moves axially under axial force. The inclined surfaces between the core and the segmented punches allow the punches to expand radially, pressing the blank from the inside out into a mold placed outside the tube blank. Mechanical bulging is a single-wave, sequential forming process, which is inefficient. As each wave is formed, the already formed waves are also affected, reducing product quality. Because the blank is expanded, the wall thickness at the top of the waves is reduced, with higher waves experiencing more severe thinning. During forming, the segmented punches are expanded, creating gaps that affect the inner surface quality of the expansion joint. Multiple components, such as the conical core, outer mold, and segmented punches, require precise positioning and repositioning, resulting in a complex device structure. While these methods each have their advantages, forming large-size, multi-wave, thin-walled expansion joints all have limitations: high requirements for process control, high equipment costs, low efficiency, numerous welds, and poor reliability. Summary of the Invention

[0004] This invention addresses the problems of high process control requirements, high equipment costs, low efficiency, and poor reliability caused by numerous welds in existing methods for manufacturing expansion joints. It proposes a multi-round rolling integral forming method for thin-walled metal expansion joints, and its key technology is the development of a special device.

[0005] A method for integral forming of thin-walled metal expansion joints by multi-wheel rolling, the integral forming method comprising the following steps:

[0006] Step 1: Prepare an integral forming mold, which includes a flat mold 4, a roller assembly 3, and a wrinkle-suppressing unit 6.

[0007] The flat mold 4 is generally elongated, with multiple grooves machined along its length on its upper surface. The number of grooves matches the number of corrugations on the target expansion joint 2. These grooves form the flat mold profile 4-3. The two ends of the flat mold 4 are the flat mold forming start section 4-2 and the flat mold forming end section 4-1, respectively. The cross-sectional shape of the flat mold profile 4-3 varies at different positions between the flat mold forming start section 4-2 and the flat mold forming end section 4-1. Specifically, from the flat mold forming start section 4-2 to the flat mold forming end section 4-1... The groove spacing between the forming termination section 4-1 gradually decreases and the groove depth gradually increases until the groove spacing and groove depth of the flat mold forming termination section 4-1 no longer change, and the shape, size and spacing of the grooves are consistent with the cross-section of the corrugated outer surface of the target expansion joint 2. The groove depth of the flat mold forming start section 4-2 approaches zero. The total width of the groove at the flat mold forming start section 4-2 is the same as the generatrix length of the corrugated section of the target expansion joint 2. The length of the flat mold profile 4-3 is not less than 3πD, where D is the outer diameter of the straight section at the end of the target expansion joint 2.

[0008] The roller assembly 3 includes multiple rollers 3-2 with identical structures and a shaft 3-1. The number of rollers 3-2 is consistent with the number of corrugations on the target expansion joint 2. The rollers 3-2 are axially inserted into the shaft 3-1 through holes and can move axially along the shaft 3-1. The cross-sectional shape and size of the rollers 3-2 are consistent with the inner surface cross-section of the corrugations of the target expansion joint 2. The radius of the rollers 3-2 is greater than the corrugation height H of the target expansion joint 2 and less than the outer diameter D of the straight section at the end of the target expansion joint 2, and is between 1.5H and 0.25D. When the rollers 3-2 press the cylindrical blank 1 against the flat mold surface 4-3, their position corresponds to the groove position. The spacing of the rollers 3-2 changes adaptively with the change of the groove spacing of the flat mold surface 4-3.

[0009] The initial distance P between rollers 3-2 is calculated according to the following formula:

[0010] P=2H+(π-2)(R1+R2) (1)

[0011] In the formula, R1 is the radius of the fillet at the crest of the expansion joint corrugation, R2 is the radius of the fillet at the trough of the expansion joint corrugation, and H is the height of the expansion joint corrugation.

[0012] The wrinkle-suppressing unit 6 consists of two sets, respectively arranged on both sides of the roller group 3. The wrinkle-suppressing unit 6 includes a fixing block 6-1, an elastic element 6-2, and a pressing block 6-3. The fixing block 6-1 is a block-shaped structure with through holes, which is inserted into both ends of the shaft 3-1. The lower end of the fixing block 6-1 and the upper end of the pressing block 6-3 are connected by the elastic element 6-2, which is a helical spring or a gas spring. The distance between the axis of the through hole of the fixing block 6-1 and the bottom surface of the pressing block 6-3 is greater than the radius of the roller 3-2. The pressing block 6-3 is used to press down the blanks at both ends of the cylindrical blank 1 during forming to prevent the blanks at both ends of the cylindrical blank 1 from wrinkling or lifting. The wrinkle-suppressing unit 6 can rotate around the shaft 3-1 and move axially along the shaft 3-1. As the distance between the rollers 3-2 decreases, the wrinkle-suppressing unit 6 moves inward along the shaft 3-1, always keeping the pressing block 6-3 acting on the cylindrical blank 1.

[0013] The integral forming mold can also use a ring mold 5 instead of a flat mold 4, specifically:

[0014] The annular mold 5 is generally circular. The bottom of the inner surface of the annular mold 5 has an annular mold forming start section 5-2 and an annular mold forming end section 5-1. Multiple grooves are machined along the circumferential direction of the inner surface of the annular mold 5 between the two. The number of grooves is the same as the number of corrugations on the target expansion joint 2. These grooves form the annular mold profile 5-3. The cross-sectional shape of the profile is different at different positions between the annular mold forming start section 5-2 and the annular mold forming end section 5-1. The groove spacing gradually decreases and the groove depth increases from the annular mold forming start section 5-2 to the annular mold forming end section 5-1. The groove spacing and groove depth no longer change at the annular mold forming end section 5-1. The shape, size and spacing of the grooves are consistent with the outer surface of the corrugations of the target expansion joint 2. The groove depth of the annular mold forming start section 5-2 tends to zero. The total width of the grooves is the same as the generatrix length of the corrugated section of the target expansion joint 2. The length of the annular mold profile 5-3 along the circumferential direction is not less than 3πD.

[0015] Optionally, current-assisted heating is used for forming. The DC power supply 7 is connected to the roller assembly 3, the flat mold 4, or the ring mold 5 through wires. The current-assisted heating makes the blank 1 at the contact position with the roller assembly 3 reach a stress relief temperature of 20-50°C above the stress relief temperature. The output voltage range of the DC power supply 7 is 0-15V, and the output current range is 0-10000A. This eliminates the stress on the blank during the forming process and avoids springback problems.

[0016] Step 2: Calculate the required width and length of the thin plate: Length L is the perimeter of the straight segment at the end of target expansion joint 2, and width W is the total length of the generatrix of target expansion joint 2, calculated according to the following formula:

[0017] L=D·π (2)

[0018] W=2S+(R3-R2)π+2N·H+N(π-2)(R1+R2) (3)

[0019] In the formula, D is the outer diameter of the straight section at the end of the target expansion joint 2, S is the length of the straight section at the end of the target expansion joint 2, R3 is the radius of the transition fillet between the expansion joint corrugations and the straight section, and N is the number of corrugations in the expansion joint.

[0020] Step 3: Roll and weld the thin plate into a cylindrical blank: Cut the thin plate according to the dimensions calculated in Step 2, bend the thin plate into a straight cylinder along the width direction, and weld the seam to obtain cylindrical blank 1. The difference between the maximum outer diameter and the minimum outer diameter of cylindrical blank 1 is no greater than 0.1D.

[0021] Step 4, forming the cylindrical blank 1 by rolling with multiple rollers: The cylindrical blank 1 prepared in step 3 is placed on the flat mold 4, and the roller group 3 consisting of multiple rollers 3-2 is placed inside the cylindrical blank 1. A force is applied to make the roller group 3 press the cylindrical blank 1 against the flat mold surface 4-3, and push the roller group 3 to roll from the forming start section 4-2 of the flat mold to the forming end section 4-1 of the flat mold. The roller group 3 continuously presses the cylindrical blank 1 against different positions on the flat mold surface 4-3, and always keeps the pressing block 6-3 acting on the blanks at both ends of the cylindrical blank 1 to prevent the blanks at both ends of the cylindrical blank 1 from wrinkling or lifting. Under the action of the roller group 3 and the flat mold 4, ripples gradually form on the cylindrical blank 1 until the roller group 3 rolls to the forming end section 4-1 of the flat mold.

[0022] In this step, an annular mold 5 can be used instead of a flat mold 4. The cylindrical blank 1 prepared in step two is placed on the annular mold 5, and a roller group 3 consisting of multiple rollers 3-2 is placed inside the cylindrical blank 1. A force is applied to make the roller group 3 press against the cylindrical blank 1 against the annular mold surface 5-3, and push the roller group 3 to roll from the forming start section 5-2 of the annular mold to the forming end section 5-1 of the annular mold. The roller group 3 continuously presses the cylindrical blank 1 against different positions on the annular mold surface 5-3, and always keeps the pressing block 6-3 acting on the blanks at both ends of the cylindrical blank 1 to prevent the blanks at both ends of the cylindrical blank 1 from wrinkling or warping. Under the action of the roller group 3 and the annular mold 5, ripples gradually form on the cylindrical blank 1 until the roller group 3 rolls to the forming end section 5-1 of the annular mold.

[0023] Step 5, remove constraints to obtain target expansion joint 2: remove roller assembly 3 and remove target expansion joint 2 from flat mold 4 or ring mold 5.

[0024] Furthermore, in step two, the thin plate is made of titanium alloy, high-temperature alloy, aluminum alloy, copper, or stainless steel.

[0025] Furthermore, in step three, thin plates with a wall thickness of less than or equal to 0.3 mm are bent into a straight cylindrical shape by hand, while thin plates with a wall thickness greater than 0.3 mm are bent into a straight cylindrical shape by three-axis roller bending.

[0026] Furthermore, in step four, the surface of the blank 1 is coated with a conductive lubricating coating, which is graphite.

[0027] Furthermore, the integral forming method can be used to form multi-layer expansion joints. In step two, prefabricate cylindrical blanks of corresponding specifications. The length of the blank used for the inner cylindrical blank is 2π·t shorter than the length of the blank used for the adjacent outer cylindrical blank, where t is the thickness of the blank used for the adjacent outer cylindrical blank. Then, multiple cylindrical blanks are assembled together in sequence according to their size to form a multi-layer cylindrical blank.

[0028] The beneficial effects of this invention are:

[0029] First, the integral forming mold used in this invention has a simple structure, and the position of the rollers does not require special control during the forming process but is guided by the grooves on the mold surface, which is easy to implement and has low cost.

[0030] Second, the present invention can form all the corrugations in one step, with good corrugation uniformity, and the forming process is relatively simple and efficient.

[0031] Third, the forming process of this invention is a localized gradual forming process, which is relatively labor-saving.

[0032] Fourth, in this invention, the groove spacing gradually decreases from the forming start section to the forming end section. Through the interaction between the roller and the groove on the mold surface, the billet in the length direction of the cylindrical blank is gradually gathered to form ripples. It does not require the billet to be stretched and deformed to form ripples, and the wall thickness uniformity is high.

[0033] V. This invention can form expansion joints with different diameters of corrugations of the same size without changing the mold and roller assembly. Attached Figure Description

[0034] Figure 1 Flowchart of the multi-round rolling integral forming process for thin-walled metal expansion joints;

[0035] Figure 2 Axonometric drawing of the cylindrical blank;

[0036] Figure 3 The figure shows the front view of the target expansion joint. In the figure, R1 is the radius of the rounded corner of the corrugation peak of the expansion joint, R2 is the radius of the rounded corner of the corrugation trough of the expansion joint, R3 is the radius of the rounded corner of the transition between the corrugation and the straight section of the expansion joint, H is the height of the corrugation of the expansion joint, and S is the length of the straight section at the end of the expansion joint.

[0037] Figure 4 An axonometric view of the target expansion joint after it has been sectioned along its axis.

[0038] Figure 5 Isometric drawing of the roller assembly;

[0039] Figure 6 This is a top view of a flat mold.

[0040] Figure 7 This is a schematic diagram showing the initial stage of forming an expansion joint using a flat mold.

[0041] Figure 8 This is a schematic diagram illustrating the process of forming an expansion joint using a flat mold.

[0042] Figure 9 Axonometric drawing of a ring-shaped mold;

[0043] Figure 10 This is a front view of a ring-shaped mold;

[0044] Figure 11 A schematic diagram of forming an expansion joint using a ring-shaped mold;

[0045] Figure 12(a) shows Figure 6 AA or Figure 10 A cross-sectional diagram of the EE;

[0046] Figure 12(b) shows Figure 6 BB or Figure 10 A cross-sectional schematic diagram of FF;

[0047] Figure 12(c) is Figure 6 CC or Figure 10 A cross-sectional schematic diagram of GG;

[0048] Figure 13(a) is a schematic diagram of the contact relationship between the blank, rollers and integral forming mold in the final stage of forming;

[0049] Figure 13(b) is a schematic diagram of the contact relationship between the blank, rollers and integral forming mold in the intermediate stage of forming;

[0050] Figure 13(c) is a schematic diagram of the contact relationship between the blank, roller and integral forming mold in the initial stage of forming;

[0051] Figure 14 Axonometric view of the wrinkle-suppressing unit;

[0052] Figure 15 This is a schematic diagram of the integral forming of an expansion joint using current-assisted heating through multi-wheel rolling.

[0053] In the diagram: 1. Cylindrical blank; 2. Target expansion joint; 3. Roller assembly; 4. Flat mold; 5. Ring mold; 6. Wrinkle suppression unit; 7. DC power; 3-1. Shaft; 3-2. Roller; 4-1. Flat mold forming termination section; 4-2. Flat mold forming start section; 4-3. Flat mold profile; 5-1. Ring mold forming termination section; 5-2. Ring mold forming start section; 5-3. Ring mold profile; 6-1. Fixing block; 6-2. Elastic element; 6-3. Clamping block. Detailed Implementation

[0054] Example 1

[0055] The target expansion joint 2 has a circular cross-section and is made of GH4169 high-temperature alloy. Its specific dimensions are as follows: outer diameter of the straight section at the end of the expansion joint D = 350 mm, number of corrugations N = 11, corrugation height H = 15 mm, trough fillet radius R1 = 2.5 mm, crest fillet radius R2 = 2.5 mm, length of the straight section at both ends of the expansion joint S = 30 mm, fillet radius of the expansion joint cross-section R3 = 10 mm, wall thickness t = 0.3 mm, and total axial length of the expansion joint 132.5 mm. Figure 3 and Figure 4 As shown.

[0056] A method for integral forming of thin-walled metal expansion joints by multi-roll rolling, the process flow is as follows: Figure 1 As shown, it includes the following steps:

[0057] Step 1: Prepare an integral forming mold, which includes a flat mold 4, a roller assembly 3, and a wrinkle-suppressing unit 6.

[0058] The flat mold 4 is generally elongated, with 11 grooves machined along its length on its upper surface. These grooves form the flat mold profile 4-3. The two ends of the flat mold 4 are the forming start section 4-2 and the forming end section 4-1, respectively. The cross-sectional shape of the flat mold profile 4-3 varies at different positions between the forming start section 4-2 and the forming end section 4-1. Specifically, the groove spacing gradually decreases and the groove depth gradually increases from the forming start section 4-2 to the forming end section 4-1 (e.g., ...). Figures 12(a) to 12(c) As shown), the groove spacing and groove depth no longer change at the end section 4-1 of the flat mold forming process, and the shape, size, and spacing of the grooves are consistent with the cross-section of the corrugated outer surface of the target expansion joint 2 (as shown). Figure 6 As shown in Figure 13, the groove depth of the initial forming section 4-2 of the flat mold approaches zero. The total width of the groove at the initial forming section 4-2 of the flat mold is the same as the length of the generatrix of the corrugated section of the target expansion joint 2. The length of the flat mold surface 4-3 is 4000mm.

[0059] like Figure 5As shown, the roller group 3 includes 11 rollers 3-2 with the same structure and a shaft 3-1. The rollers 3-2 are inserted into the shaft 3-1 through holes in the axial direction and can move along the shaft 3-1 in the axial direction. The cross-sectional shape and size of the rollers 3-2 are consistent with the inner surface cross-section of the corrugation of the target expansion joint 2. The radius of the rollers 3-2 is 50mm. When the rollers 3-2 press the cylindrical blank 1 against the flat mold surface 4-3, their position corresponds to the groove position. The spacing of the rollers 3-2 changes adaptively with the change of the groove spacing of the flat mold surface 4-3. The initial spacing P between the rollers 3-2 is calculated to be 35.7mm according to formula (1).

[0060] like Figure 14 As shown, the wrinkle-suppressing unit 6 consists of two sets, respectively arranged on both sides of the roller group 3. The wrinkle-suppressing unit 6 includes a fixing block 6-1, an elastic element 6-2, and a pressing block 6-3. The fixing block 6-1 is a block-shaped structure with through holes, which is inserted into both ends of the shaft 3-1. The lower end of the fixing block 6-1 and the upper end of the pressing block 6-3 are connected by the elastic element 6-2, which is a helical spring or a gas spring. The pressing block 6-3 is used to press down the blanks at both ends of the cylindrical blank 1 during forming to prevent the blanks at both ends of the cylindrical blank 1 from wrinkling or lifting. The wrinkle-suppressing unit 6 can rotate around the shaft 3-1 and move axially along the shaft 3-1. As the distance between the rollers 3-2 decreases, the wrinkle-suppressing unit 6 moves inward along the shaft 3-1, always keeping the pressing block 6-3 acting on the cylindrical blank 1.

[0061] Step 2, calculate the required length L and width W of the thin plate (e.g., ...). Figure 2 As shown):

[0062] L = D·π = 1099.6 mm,

[0063] W=2S+(R3-R2)π+2N·H+N(π-2)(R1+R2)=476.3mm.

[0064] Step 3: Roll and weld the thin plate into a cylindrical blank: Cut GH4169 high-temperature alloy plate with a thickness of 0.3mm and a diameter of 1099.6mm×476.3mm, and prepare cylindrical blank 1 by manual bending. The difference between the maximum and minimum outer diameter of cylindrical blank 1 is no more than 35mm. Weld the seam using laser welding.

[0065] Step four, forming the cylindrical blank by rolling with multiple rollers: The cylindrical blank 1 prepared in step two is placed on the flat mold 4, and the roller assembly 3 is placed inside the cylindrical blank 1, as shown in the figure. Figure 7As shown, a force is applied to press the roller assembly 3 against the cylindrical blank 1 on the flat mold surface 4-3, pushing the roller assembly 3 from the forming start section 4-2 of the flat mold to the forming end section 4-1. The roller assembly 3 continuously presses the cylindrical blank 1 against different positions on the flat mold surface 4-3, always maintaining the pressure block 6-3 acting on the blank at both ends of the cylindrical blank 1 to prevent wrinkling or warping of the blank at both ends. Under the action of the roller assembly 3 and the flat mold 4, ripples gradually form on the cylindrical blank 1 until the roller assembly 3 rolls to the forming end section 4-1 of the flat mold (e.g., ...). Figure 8 (as shown in Figure 13).

[0066] Step 5, Remove constraints to obtain expansion joint: Remove roller assembly 3 and remove target expansion joint 2 from flat mold 4.

[0067] Example 2

[0068] This embodiment is basically the same as Embodiment 1, except that in step four of Embodiment 1, a ring-shaped mold 5 is used instead of a flat mold 4, such as... Figure 9 and Figure 10 As shown.

[0069] The annular mold 5 is generally circular in shape. Eleven grooves are machined circumferentially on the inner surface of the annular mold 5. These grooves form the annular mold profile 5-3. The cross-sectional shape of the profile is different at different positions between the forming start section 5-2 and the forming end section 5-1 of the annular mold. The groove spacing gradually decreases and the groove depth increases from the forming start section 5-2 to the forming end section 5-1. The groove spacing and groove depth no longer change at the forming end section 5-1. The shape, size and spacing of the grooves are consistent with the outer surface of the corrugated outer surface of the target expansion joint 2. The groove depth of the forming start section 5-2 of the annular mold approaches zero. The total width of the grooves is the same as the generatrix length of the corrugated section of the target expansion joint 2. The length of the annular mold profile 5-3 along the circumferential direction is 4000 mm.

[0070] Step four, as Figure 11 As shown, the cylindrical blank 1 prepared in step two is placed on the annular mold 5, and the roller assembly 3 is placed inside the cylindrical blank 1. A force is applied to press the roller assembly 3 against the annular mold surface 5-3, pushing the roller assembly 3 from the forming start section 5-2 of the annular mold to the forming end section 5-1. The roller assembly 3 continuously presses the cylindrical blank 1 against different positions on the annular mold surface 5-3, always maintaining the pressure block 6-3 acting on the blanks at both ends of the cylindrical blank 1 to prevent wrinkling or warping. Under the action of the roller assembly 3 and the annular mold 5, ripples gradually form on the cylindrical blank 1 until the roller assembly 3 rolls to the forming end section 5-1 of the annular mold; other steps are the same as in Example 1. This setup can greatly reduce the space occupied by the overall forming mold.

[0071] Example 3

[0072] like Figure 15 As shown, this embodiment is basically the same as Embodiment 1, except that: current-assisted heating is used for forming. A DC power supply 7 is connected to the roller assembly 3, the flat mold 4, or the ring mold 5 via wires. The output voltage range of the DC power supply 7 is 0–15V, and the output current range is 0–10000A. Current-assisted heating raises the cylindrical blank 1 at the contact point with the roller assembly 3 to 30°C above the stress-relief temperature of the blank. Other steps are the same as in Embodiment 1. This configuration reduces the residual stress in the cylindrical blank 1 during forming and minimizes springback.

[0073] Example 4

[0074] This embodiment is basically the same as Embodiment 1, except that: for the expansion joint with a three-layer structure, the thicknesses of the cylindrical blank 1 from the outer layer to the inner layer are 1.0mm, 0.5mm, and 0.3mm, respectively, and the materials from the outer layer to the inner layer are stainless steel, titanium alloy, and high-temperature alloy, respectively. In step two, the required length L and width W of the thin plate are calculated, and the blank dimensions L×W from the outer layer to the inner layer are 1099.6mm×476.3mm, 1093.3mm×476.3mm, and 1090.2mm×476.3mm, respectively. In step three, the thin plate is bent into a straight cylindrical shape along the width direction and the seam is welded. Multiple cylindrical blanks are then assembled together according to their size to form a multi-layer cylindrical blank. Other steps are the same as in Embodiment 1. This configuration can simultaneously achieve multiple functions such as heat insulation and corrosion prevention.

[0075] Example 5

[0076] This embodiment is basically the same as Embodiment 1, except that: in step four, the surface of the cylindrical blank 1 is sprayed with a conductive lubricating coating, which is graphite. The other steps are the same as in Embodiment 1. This arrangement reduces friction between the integral forming device and the cylindrical blank 1, preventing scratches, abrasions, and other defects from appearing on the cylindrical blank 1.

[0077] The present invention has been disclosed above with reference to preferred embodiments, but it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed structure and technical content to create equivalent implementation cases without departing from the scope of the present invention. However, any simple modifications, equivalent changes and alterations made to the above implementation cases based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for integral forming of thin-walled metal expansion joints by multi-wheel rolling, characterized in that, The integral forming method includes the following steps: Step 1: Prepare an integral forming mold, which includes a flat mold (4), a roller assembly (3), and a wrinkle-suppressing unit (6); The flat mold (4) is elongated in shape, and its upper surface has multiple grooves along its length. The number of grooves is the same as the number of corrugations on the target expansion joint (2). These grooves form the flat mold profile (4-3). The two ends of the flat mold (4) are the flat mold forming start section (4-2) and the flat mold forming end section (4-1), respectively. The cross-sectional shape of the flat mold profile (4-3) is different at different positions between the flat mold forming start section (4-2) and the flat mold forming end section (4-1). The roller assembly (3) includes multiple rollers (3-2) with the same structure and a shaft (3-1). The number of rollers (3-2) is consistent with the number of corrugations on the target expansion joint (2). The rollers (3-2) are axially inserted into the shaft (3-1) through holes and can move axially along the shaft (3-1). The cross-sectional shape and size of the rollers (3-2) are consistent with the inner surface cross-section of the corrugations of the target expansion joint (2). The radius of the rollers (3-2) is greater than the corrugation height H of the target expansion joint (2) and less than the outer diameter D of the straight section at the end of the target expansion joint (2). When the rollers (3-2) press the cylindrical blank (1) against the flat mold surface (4-3), their position corresponds to the groove position. The spacing of the rollers (3-2) changes adaptively with the change of the groove spacing of the flat mold surface (4-3). The wrinkle-suppressing unit (6) is provided in two sets, which are respectively arranged on both sides of the roller group (3). The wrinkle-suppressing unit (6) includes a fixed block (6-1), an elastic element (6-2) and a pressing block (6-3). The fixed block (6-1) is a block structure with through holes, which is inserted into both ends of the shaft (3-1). The lower end of the fixed block (6-1) and the upper end of the pressing block (6-3) are connected by the elastic element (6-2). The distance between the axis of the through hole of the fixed block (6-1) and the bottom surface of the pressing block (6-3) is greater than the radius of the roller (3-2). The pressing block (6-3) is used to press down the blanks at both ends of the cylindrical blank (1) during forming. The wrinkle-suppressing unit (6) can rotate around the shaft (3-1) and move along the shaft (3-1) axially. As the distance between the rollers (3-2) decreases, the wrinkle-suppressing unit (6) moves inward along the shaft (3-1) and always keeps the pressing block (6-3) acting on the cylindrical blank (1). Step 2, calculate the required width and length of the thin plate: the length L is the perimeter of the straight segment at the end of the target expansion joint (2), and the width W is the total length of the generatrix of the target expansion joint (2), calculated according to the following formula: L=D·π (2) W=2S+(R3-R2)π+2N·H+N(π-2)(R1+R2) (3) In the formula, D is the outer diameter of the straight section at the end of the target expansion joint (2), S is the length of the straight section at the end of the target expansion joint (2), R1 is the radius of the rounded corner of the corrugation peak of the expansion joint, R2 is the radius of the rounded corner of the corrugation valley of the expansion joint, R3 is the radius of the rounded corner of the transition between the corrugation and the straight section of the expansion joint, and N is the number of corrugations in the expansion joint. Step 3, roll and weld the thin plate into a cylindrical blank: cut the thin plate according to the dimensions calculated in Step 2, bend the thin plate into a straight cylinder along the width direction, and weld the seam to obtain the cylindrical blank (1); Step 4, forming the cylindrical blank (1) by rolling it with multiple rollers: The cylindrical blank (1) prepared in step 3 is placed on the flat mold (4) and the roller group (3) composed of multiple rollers (3-2) is placed inside the cylindrical blank (1). The roller group (3) is applied to press the cylindrical blank (1) against the flat mold surface (4-3) and push the roller group (3) to roll from the forming start section (4-2) of the flat mold to the forming end section (4-1) of the flat mold. The roller group (3) continuously presses the cylindrical blank (1) against different positions on the flat mold surface (4-3) and always keeps the pressing block (6-3) acting on the blanks at both ends of the cylindrical blank (1) until the roller group (3) rolls to the forming end section (4-1) of the flat mold. Step 5, remove constraints to obtain target expansion joint (2): remove roller assembly (3) and remove target expansion joint (2) from flat mold (4).

2. The method for integral forming of a thin-walled metal expansion joint by multi-wheel rolling according to claim 1, characterized in that, In step one, the groove spacing between the integral forming mold from the forming start section (4-2) of the flat mold to the forming end section (4-1) of the flat mold gradually decreases and the groove depth gradually increases. When the groove spacing and groove depth at the forming end section (4-1) of the flat mold no longer change, the shape, size and spacing of the groove are consistent with the cross-section of the corrugated outer surface of the target expansion joint (2). The groove depth at the forming start section (4-2) of the flat mold approaches zero. The total width of the groove at the forming start section (4-2) of the flat mold is the same as the generatrix length of the corrugated section of the target expansion joint (2). The length of the flat mold profile (4-3) is not less than 3πD, where D is the outer diameter of the straight section at the end of the target expansion joint (2).

3. The method for integral forming of a thin-walled metal expansion joint by multi-wheel rolling according to claim 1, characterized in that, In step one, the radius of the roller (3-2) of the integral forming mold is between 1.5H and 0.25D.

4. The method for integral forming of a thin-walled metal expansion joint by multi-wheel rolling according to claim 1, characterized in that, In step one, the initial distance P between the rollers (3-2) of the integral forming mold is calculated according to the following formula: P=2H+(π-2)(R1+R2) (1) In the formula, R1 is the radius of the fillet at the crest of the expansion joint corrugation, R2 is the radius of the fillet at the trough of the expansion joint corrugation, and H is the height of the expansion joint corrugation.

5. The method for integral forming of a thin-walled metal expansion joint by multi-wheel rolling according to claim 1, characterized in that, A ring-shaped mold (5) is used instead of a flat mold (4). Specifically: The annular mold (5) is generally circular. The bottom of the inner surface of the annular mold (5) has an annular mold forming start section (5-2) and an annular mold forming end section (5-1). Multiple grooves are machined circumferentially along the inner surface of the annular mold (5) between these two sections. The number of grooves is consistent with the number of corrugations on the target expansion joint (2). These grooves form the annular mold profile (5-3). The cross-sectional shape of the profile differs at different positions between the annular mold forming start section (5-2) and the annular mold forming end section (5-1). The groove spacing between the mold forming start section (5-2) and the ring mold forming end section (5-1) gradually decreases and the groove depth increases. The groove spacing and groove depth no longer change at the ring mold forming end section (5-1). The shape, size and spacing of the groove are consistent with the outer surface of the corrugated surface of the target expansion joint (2). The groove depth of the ring mold forming start section (5-2) approaches zero. The total width of the groove is the same as the generatrix length of the corrugated section of the target expansion joint (2). The length of the ring mold profile (5-3) along the circumferential direction is not less than 3πD.

6. A method for integral forming of a thin-walled metal expansion joint by multi-wheel rolling according to claim 1 or 5, characterized in that, The forming process is achieved by using current-assisted heating. A DC power supply (7) is connected to a roller assembly (3), a flat mold (4), or a ring mold (5) via wires. The current-assisted heating causes the cylindrical blank (1) at the contact position with the roller assembly (3) to reach a stress-relief temperature of 20 to 50°C above the temperature. The DC power supply (7) has an output voltage range of 0 to 15V and an output current range of 0 to 10000A, which eliminates the stress on the cylindrical blank during the forming process.

7. The method for integral forming of a thin-walled metal expansion joint by multi-wheel rolling according to claim 1, characterized in that, In step two, the thin plate is made of titanium alloy, high-temperature alloy, aluminum alloy, copper, or stainless steel.

8. The method for integral forming of a thin-walled metal expansion joint by multi-wheel rolling according to claim 1, characterized in that, In step three, thin plates with a wall thickness of less than or equal to 0.3 mm are bent into a straight cylindrical shape by hand, while thin plates with a wall thickness greater than 0.3 mm are bent into a straight cylindrical shape by three-axis roller bending.

9. The method for integral forming of a thin-walled metal expansion joint by multi-wheel rolling according to claim 1, characterized in that, In step four, the surface of the cylindrical blank (1) is coated with a conductive lubricating coating.

10. The method for integral forming of a thin-walled metal expansion joint by multi-wheel rolling according to claim 1, characterized in that, The integral forming method is used to form an expansion joint with a multi-layer structure. In step two, a cylindrical blank of the corresponding specification (1) is prefabricated. The length of the blank used for the inner cylindrical blank is 2π·t shorter than the length of the blank used for the adjacent outer cylindrical blank, where t is the thickness of the blank used for the adjacent outer cylindrical blank. Then, multiple cylindrical blanks are assembled together in sequence according to their size to form a multi-layer cylindrical blank.

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