Pipe forming method based on perimeter equalization and flange cutting

Abstract

The present application relates to the technical field of pipe forming, and discloses a pipe forming method based on perimeter equalization and flange cutting, which comprises the following steps: analyzing and designing the cross-section structural features of a target part to obtain a blank configuration in which the cross-section perimeter is basically equal to the maximum perimeter of the target part; designing a forming die according to the blank configuration; selecting a pipe blank and obtaining a pre-formed part: selecting a circular or elliptical pipe blank with a cross-section perimeter of (0.95-1) L, placing the pipe blank into the forming die, filling high-pressure gas into the pipe blank, and then performing compression forming on the pipe blank by the forming die, taking out the pre-formed part after pressure maintaining, and obtaining a pre-formed part with a compression zone; cutting off the excess material at the flange edge of the pre-formed part according to the size of the target part, welding the cutting part, and obtaining the target part. The flange pipe is directly hot formed by using a common pipe blank, and the number of molds and the process are reduced, and the manufacturing cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of pipe forming technology, and specifically to a pipe forming method based on perimeter equalization and flange removal. Background Technology

[0002] Closed-section pipe fittings are widely used in the automotive and aerospace industries due to their high bending strength, integrity, impact resistance, and high material utilization. Flange pipes are a special type of structural component, characterized by a flange edge formed through a folding process. Compared to traditional round or square pipes, the flat flange edge formed by the folding provides an ideal lap surface for spot welding. This design gives them unique advantages in welding assembly, especially suitable for lapping automotive body panels and appliance housings.

[0003] Flange pipes often use high-strength steel or hot-formed high-strength steel to achieve lightweight design. To ensure complete filling of the flange area, the pipe blank often needs to undergo significant bulging deformation, with its local cross-sectional perimeter needing to be significantly expanded from the original value to the target value. This directly results in extremely high internal pressure required during the forming process, generally requiring a gas pressure of greater than or equal to 50MPa. At the same time, the clamping force also increases dramatically, forcing companies to use large-tonnage hydraulic presses, resulting in huge equipment investment and high production energy consumption. Furthermore, during the edge folding process, the material is under complex tensile and compressive stress, making it prone to micro-cracks and fissures at the bending radius, leading to high manufacturing costs. On the other hand, the currently used air forming technology for steel pipes involves filling the mold with gas during mold opening and closing, relying on high-pressure gas to "blow" a portion of the pipe wall into the flange cavity of the mold. After being blown into the flange area of ​​the mold, part of the pipe wall is pressed together, and the area of ​​the pipe blank entering the flange cannot be precisely controlled, resulting in unstable flange edge width.

[0004] Therefore, the high manufacturing cost of flange pipes and the inability to control the flange width have become urgent technical problems that need to be solved. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides a pipe forming method based on perimeter equalization and flange removal. The aim is to achieve efficient and high-quality forming of flanged pipes and pipe fittings with different cross-sections through constant cross-sectional perimeter design, local pressing, and precise edge cutting processes.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a pipe forming method based on perimeter equalization and flange removal, comprising the following steps: S10. Analyze the cross-sectional structural features of the target part: Obtain the perimeter of the maximum cross-section of the target part and record it as the reference perimeter L; The target part undergoes cross-sectional perimeter equalization and pressing zone design: A blank configuration is designed based on the shape of the target part, wherein at least one side of the blank configuration is a flange edge with a pressing zone, and the perimeter of each cross-section of the blank configuration is (0.95). 1.02)L; S20. Obtain the forming mold based on the design results of the blank configuration; S30. Selecting a tube blank and obtaining a pre-formed part: Select a circular or elliptical tube blank with a cross-sectional perimeter of (0.95-1)L, place the tube blank into the forming mold, fill the tube blank with high-pressure gas, and then the forming mold presses and shapes the tube blank. After holding the pressure, the tube blank is taken out to obtain a pre-formed part with a pressing area. S40. Based on the dimensions of the target part, cut off the excess material at the flange edge of the preformed part and weld the cut area to obtain the target part.

[0007] Preferably, the pressing area at the flange edge of the blank configuration is concave on one side or both sides, and the thickness of the pressing area is less than or equal to twice the wall thickness of the tube blank.

[0008] Preferably, the pressing zones are continuously or intermittently distributed in the axial direction.

[0009] Preferably, the pressing area has a pressing surface for spot welding, and the minimum inscribed circle diameter of the pressing surface is ≥6mm.

[0010] Preferably, in step S40, spot welding, laser welding, or arc welding is used to weld the cut area.

[0011] Preferably, in step S30, when the tube blank is made of hot-formed steel, the austenitized tube blank is placed into the forming mold.

[0012] Preferably, in step S30, the heating temperature for austenitizing the tube blank is 890-950℃, and the heating time is 4-10 minutes.

[0013] Preferably, the forming mold includes a mating upper mold and a lower mold. The lower mold has a receiving cavity for accommodating the tube blank, and the side wall height of the receiving cavity is higher than the height of the flange edge of the target part. The upper mold includes a support plate, a central insert, a flange insert, and an elastic element. The central insert is connected to the support plate, and two flange inserts are disposed on both sides of the central insert. The flange inserts are connected to the support plate through the elastic element. The upper mold and the lower mold cooperate to form a forming cavity.

[0014] Preferably, the target part is a variable cross-section pipe or a flange pipe.

[0015] The present invention has the following beneficial effects: 1. Based on the maximum cross-sectional perimeter of the target part, a blank configuration with all cross-sectional perimeters approximately equal to the maximum perimeter of the target part is designed. This eliminates the need for significant bulging during the forming process, significantly reducing the required gas pressure and clamping force, thereby lowering the tonnage requirements of the hydraulic press and reducing energy consumption and equipment costs. Simultaneously, flanges are obtained directly from ordinary tube blanks through thermoforming. Since pre-forming is unnecessary, the number of molds and process steps are reduced, achieving integrated forming and quenching, significantly shortening the process chain and lowering manufacturing costs.

[0016] 2. By designing a locally recessed pressing zone on the lap surface of the flange edge, the bending radius of the non-pressed area at the flange edge is larger, which effectively avoids stress concentration and material cracking, improves the yield, and reduces manufacturing costs; at the same time, the thickness of the pressing zone is reduced (not exceeding twice the wall thickness), which is beneficial to the penetration and connection strength during subsequent spot welding.

[0017] 3. In the mold design, the side wall of the lower mold cavity is higher than the flange edge, which can precisely control the flow of pipe wall material to the flange area during the forming process, thereby stabilizing the lateral width of the flange and ensuring the consistency of product dimensions.

[0018] 4. For ordinary variable cross-section pipe fittings without flanges, by adding temporary flange edges to make the perimeter of each cross-section consistent, and then completely cutting off and welding the flange edges after forming, it is possible to form pipe fittings with large cross-section differences with extremely low bulging rate, which greatly improves the forming limit, avoids cracking defects, and expands the application range of pipe forming technology. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the target part to be formed in Embodiment 1 of the present invention; Figure 2 For the present invention Figure 1 Schematic diagram of the cross section at point AA; Figure 3 This is a schematic diagram of the blank configuration in Embodiment 1 of the present invention; Figure 4 For the present invention Figure 3 Schematic diagram of the cross section at point BB; Figure 5 This is a schematic diagram of the cutting of the pre-formed part in Embodiment 1 of the present invention; Figure 6 For the present invention Figure 5 Schematic diagram of cross-section at CC; Figure 7 This is a schematic diagram of the forming mold of the present invention; Figure 8 This is a schematic diagram of the forming process of the variable cross-section tube in Embodiment 2 of the present invention.

[0020] The reference numerals in the attached drawings are as follows: 1. Target part; 2. Blank configuration; 21. Partial pressing area; 22. Continuous pressing area; 31. Lower mold; 32. Middle insert; 33. Flange insert; 34. Elastic element; 4. Preformed part; 41. Cutting line; 5. Variable cross-section pipe fitting; 5.1. Maximum cross-section; 5.2. Minimum cross-section. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0022] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. The terms "vertical," "upper," "lower," "horizontal," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention.

[0023] Example 1: like Figures 1 to 7 As shown, this embodiment takes target part 1 with double-sided flanges as an example for explanation, that is, target part 1 in this embodiment is a flange pipe.

[0024] This invention discloses a pipe forming method based on perimeter equalization and flange removal, comprising the following steps: S10. Analyze and design the cross-sectional structural features of target part 1: Measure the perimeter of each cross-section of target part 1 along its length direction, find the maximum cross-sectional perimeter, and record it as the reference perimeter L.

[0025] Then, the flange structure of the target part 1 is optimized: a blank configuration 2 is designed according to the shape of the target part 1, wherein at least one side of the blank configuration 2 is a flange edge with a pressing area. In this embodiment, one flange edge of the blank configuration 2 has a continuous pressing area 22, and the other flange edge has a partial pressing area 21. The inner walls of the pipes at the pressing areas are in close contact with each other, and the perimeter of each section of the blank configuration 2 reaches or basically reaches the maximum perimeter of the target part 1. In this embodiment, the perimeter of each section of the blank configuration 2 is controlled within the range of (0.95-1.02)L, that is, basically consistent with the original perimeter of the pipe blank. In this embodiment, the partial pressing area 21 is concave on one side and is distributed at intervals in the axial direction. Both the partial pressing area 21 and the continuous pressing area 22 have pressing surfaces for spot welding, and the minimum inscribed circle diameter of the pressing surface is ≥6mm. In this embodiment, the minimum inscribed circle diameter of the pressing surface is designed to be 8mm, which is 6mm larger than the diameter of the spot welding electrode, facilitating the subsequent lap spot welding of the target part 1 to the plate. The thickness of the pressing zone is 1.9 times the wall thickness of the tube blank, and less than or equal to twice the wall thickness of the tube blank. Specifically, when the wall thickness of the tube blank is 1.8mm, the thickness of the pressing zone is 3.4mm to ensure the strength of the subsequent lap welding.

[0026] S20. Design the forming mold according to the blank configuration 2: such as Figure 7 As shown, the forming die includes a lower die 31, a central insert 32, a flange insert 33, and an elastic element 34. The central insert 32 and the flange insert 33 together constitute the upper die. The flange insert 33 is located on both sides of the central insert 32 and is pushed downwards by the elastic element 34 (such as a spring). The lower die 31 has a receiving cavity for accommodating the tube blank, and the sidewall height of the receiving cavity of the lower die 31 is higher than the final flange height of the target part 1, in order to guide material flow during the forming process and limit the width of the part.

[0027] After completing the above design steps, the target part 1 is manufactured using a forming mold, as follows: S30. Selecting a tube blank and obtaining a pre-formed part: Select a circular or elliptical tube blank with a cross-sectional perimeter of (0.95-1)L. If the tube blank is made of non-hot-formed steel, place it directly into the forming mold for forming. When the tube blank is made of hot-formed steel, place the austenitized tube blank into the forming mold. The heating temperature for austenitization is 890-950℃, and the heating time is 4-10 minutes. In this embodiment, the tube blank material is 22MnB5 hot-formed steel. The tube blank is placed in a heating furnace, heated to 930℃, and held for 5 minutes to fully austenitize it. Then, the austenitized tube blank is quickly transferred to the forming mold. Before closing the mold, high-pressure gas (such as nitrogen) is injected into the tube blank to establish an initial internal pressure. The gas pressure is less than or equal to 20MPa. As the hydraulic press lowers the upper mold, the flange insert 33 first contacts the tube blank. Under the action of the elastic element 34, the two sides of the tube wall are pressed together to form the flange edge. A partial pressing zone 21 and a continuous pressing zone 22 are formed on the flange edges on both sides, respectively. As the mold continues to close, the middle insert 32 presses the tube blank body until the upper and lower molds 31 are completely closed. Pressure holding and quenching are then performed, allowing the tube to obtain high strength and a good shape during the martensitic transformation process. After the pressure holding is completed, the mold is opened and the pre-formed part 4 is removed.

[0028] S40. Using the flange edge line of target part 1 as the cutting line 41, excess material at the flange edge of preformed part 4 is removed using laser cutting. Then, spot welding, laser welding, or arc welding is performed on the cut area to finally obtain target part 1, i.e., the flange pipe. Depending on the dimensions of the preformed part and the flange edge of target part 1, excess material on one or both sides of the preformed part 4 can be removed and welded to obtain the target part. In this embodiment, excess material at one flange edge of the preformed part 4 is removed and then welded to obtain target part 1.

[0029] This embodiment targets pipe fittings with double-sided flanges. By designing a pre-formed cross-section that is essentially the same as the reference perimeter of the target part 1, the internal pressure required for forming is significantly reduced. The forming process only requires an internal pressure of less than or equal to 20MPa, far lower than the 50-70MPa internal pressure required by traditional hot air expansion processes. This results in lower pressure requirements for equipment and a significant reduction in equipment and energy costs. Simultaneously, the sidewall height of the lower mold cavity is higher than the flange edge height, precisely limiting the excessive flow of pipe wall material into the flange area during forming. This ensures that the final flange edge width error is controlled within ±0.3mm, exhibiting dimensional stability far superior to traditional processes. The pressing zone allows for a larger bending radius at the flange edge, effectively preventing cracking defects at the bending radius and increasing the yield to over 98%.

[0030] Example 2 This embodiment uses a common variable cross-section pipe fitting 5 as the target part, such as Figure 8 As shown.

[0031] The perimeter of the variable cross-section pipe fitting 5 at its maximum cross-section 5.1 is L1, and the perimeter at its minimum cross-section 5.2 is 0.7L1. If internal high pressure or hot gas expansion forming is used directly, and the pipe blank diameter is 0.7L1 / π, then the expansion ratio of the maximum cross-section needs to reach 42%, which exceeds the elongation rate of common metal materials, making it very easy to crack. In addition, the forming pressure is high and the power consumption is large.

[0032] To reduce the forming difficulty, this embodiment performs forming analysis on the variable cross-section pipe 5. In areas with smaller cross-sectional perimeters (such as the area where the smallest cross-section 5.2 is located), temporary flange edges are designed and added. By widening the flange edges, the perimeter of each cross-section of the designed formed part is equal to L1. Specifically, in areas where the cross-sectional perimeter needs to be increased, the pipe wall is extended outward and folded to form temporary flange edges, and a pressing zone is set near the pipe cavity.

[0033] The same mold structure as in Example 1 is used, wherein the dimensions of the upper and lower molds 31 are adjusted according to the specific dimensions of the final formed part, thereby adjusting the cavity dimensions. A circular tube blank with a circumference of L is selected and formed according to the heating, forming, pressure holding and quenching process of Example 1 to obtain an intermediate part with a temporary flange edge.

[0034] After forming, the temporary flange edge of the intermediate part is completely removed by laser cutting, that is, the cutting is carried out according to the outline of the desired variable cross-section pipe fitting 5. Since the pipe fitting forms an opening after cutting, the cut edge is arc welded to seal the weld, and the final part is obtained.

[0035] Through the above method, the forming of the variable cross-section tube 5 with a large cross-sectional difference (cross-sectional perimeter ratio of 0.7) was achieved with a near-zero bulging process, avoiding cracking defects, reducing forming pressure, and improving process feasibility.

[0036] 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 within the protection scope of the present invention.

Claims

1. A method for forming pipe fittings based on perimeter equalization and flange removal, characterized in that, Includes the following steps: S10. Analyze the cross-sectional structural features of the target part: Obtain the perimeter at the maximum cross-section of the target part and record it as the reference perimeter L; The target part is subjected to cross-sectional perimeter equalization and pressing zone design: the blank configuration is designed according to the shape of the target part, at least one side of the blank configuration is a flange edge with a pressing zone, and the perimeter of each cross section of the blank configuration is (0.95-1.02)L; S20. Obtain the forming mold based on the design results of the blank configuration; S30. Selecting a tube blank and obtaining a pre-formed part: Select a circular or elliptical tube blank with a cross-sectional perimeter of (0.95-1)L, place the tube blank into the forming mold, fill the tube blank with high-pressure gas, and then the forming mold presses and shapes the tube blank. After holding the pressure, the tube blank is taken out to obtain a pre-formed part with a pressing area. S40. Based on the dimensions of the target part, remove excess material from the flange edge of the preformed part and weld the cut area to obtain the target part.

2. The pipe forming method based on perimeter equalization and flange removal according to claim 1, characterized in that, The pressing area at the flange edge of the blank configuration is concave on one side or both sides, and the thickness of the pressing area is less than or equal to twice the wall thickness of the tube blank.

3. The pipe forming method based on perimeter equalization and flange removal according to claim 2, characterized in that, The pressing zones are distributed continuously or intermittently in the axial direction.

4. The pipe forming method based on perimeter equalization and flange removal according to claim 2, characterized in that, The pressing zone has a pressing surface for spot welding, and the minimum inscribed circle diameter of the pressing surface is ≥6mm.

5. The pipe forming method based on perimeter equalization and flange removal according to claim 1, characterized in that, In step S40, spot welding, laser welding, or arc welding is used to weld the cut area.

6. The pipe forming method based on perimeter equalization and flange removal according to claim 1, characterized in that, In step S30, when the tube blank is made of hot-formed steel, the austenitized tube blank is placed into the forming mold.

7. The pipe forming method based on perimeter equalization and flange removal according to claim 6, characterized in that, In step S30, the heating temperature for austenitizing the tube blank is 890-950℃, and the heating time is 4-10 minutes.

8. The pipe forming method based on perimeter equalization and flange removal according to claim 1, characterized in that, The forming mold includes a mating upper mold and a lower mold. The lower mold has a receiving cavity for accommodating the tube blank. The side wall height of the receiving cavity is higher than the height of the flange edge of the target part. The upper mold includes a support plate, a central insert, a flange insert, and an elastic element. The central insert is connected to the support plate. Two flange inserts are disposed on both sides of the central insert. The flange inserts are connected to the support plate through the elastic element. The upper mold and the lower mold cooperate to form a forming cavity.

9. The pipe forming method based on perimeter equalization and flange removal according to claim 1, characterized in that, The target part is a variable cross-section pipe or flange.

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