A method for integral hydraulic forming of small radius elbows

Abstract

This invention provides a method for integral hydraulic forming of small-radius elbows, relating to the field of hydraulic forming technology. The method includes: obtaining an elbow blank with a straight section; performing a pre-forming operation on the elbow blank with the straight section to obtain a pre-formed elbow, wherein the inner sidewall bending region of the pre-formed elbow includes multiple smooth bulge regions; placing the pre-formed elbow in a hydraulic forming mold for hydraulic bulging to obtain the final target formed elbow. This invention can achieve integral forming of small-radius elbows while reducing hydraulic forming pressure, obtaining higher forming quality, meeting the needs of mass production, and reducing production costs.

Description

Technical Field

[0001] This invention relates to the field of hydraulic forming technology, and more specifically, to a method for integral hydraulic forming of small-radius elbows. Background Technology

[0002] In recent years, metal elbows have been widely used in aerospace, automotive, and shipbuilding industries as important components for fuel transportation. Most metal elbows (small radius elbows) are produced using hydroforming technology. This involves using a right-angle elbow with a small diameter and a large bending radius (r / d>1.5) as a blank, placing it in a forming mold (hydraulic forming mold), and then using hydraulic bulging to expand the pipe diameter and reduce the relative bending radius (r / d<1), thereby obtaining a small radius elbow.

[0003] However, in existing hydroforming processes, a small fillet transition section needs to be designed to facilitate the deformation and mold application of the tube blank. Firstly, due to the limited deformation capacity of the material, the diameter D0 of the tube blank with the straight section is not significantly different from the diameter D1 of the bulging elbow. This results in a small fillet size in the transition area during mold design. According to the empirical formula for pressure and fillet size during hydroforming, the smaller the fillet, the greater the pressure required for forming. Therefore, the existing technology requires a large liquid pressure for elbow hydroforming and mold application, which increases the tonnage of the forming equipment, exacerbates mold wear, and leads to an increase in overall production costs. Secondly, the high forming pressure required during liquid filling and bulging increases the friction between the tube and the mold, making it difficult for material to flow outside the fillet area. This prevents material from replenishing the fillet area, increasing the deformation of the material in the fillet area and causing defects such as wall thinning or even cracking. Summary of the Invention

[0004] The problem addressed by this invention is how to reduce forming pressure during the hydraulic forming process of elbows, thereby saving production costs, improving production efficiency, and mitigating issues such as excessive deformation or even cracking in characteristic areas of the tube blank. To solve the above problems, this invention provides a method for integral hydraulic forming of small-radius elbows, comprising the following steps:

[0005] Obtain a pipe blank with a straight section;

[0006] The elbow blank with a straight section is pre-formed to obtain a pre-formed elbow. The inner wall bending area of ​​the pre-formed elbow includes multiple bulge areas.

[0007] The preformed elbow is placed in a hydraulic forming mold for hydraulic bulging to obtain the final target formed elbow.

[0008] Optionally, obtaining the elbow blank with a straight section includes:

[0009] Obtain an original elbow tube blank with a bending radius of R0 and a diameter of D0, and obtain a matching straight tube blank based on the original elbow tube blank;

[0010] Weld one of the straight section billets to each of the two ends of the original elbow pipe billet to obtain the elbow pipe billet with straight sections.

[0011] Optionally, the preforming operation on the elbow pipe billet with straight sections to obtain a preformed elbow includes:

[0012] Place the elbow pipe billet with straight sections in a preforming die to obtain the preformed elbow;

[0013] Among them, the preforming die includes an upper backing plate, a lower backing plate, a sealing punch (5), a fluid-filled punch (7) provided with a liquid inlet channel, an upper female die, and a lower female die (6). The upper backing plate is used to fix the upper female die, and the lower backing plate is used to fix the lower female die (6); the upper female die and the lower female die (6) are designed to be mirror-symmetrical. The upper female die and the lower female die (6) form a preforming inner cavity; the sealing punch (5) is placed at one end of the preforming inner cavity; the fluid-filled punch (7) is placed at the other end of the preforming inner cavity. The sealing punch (5) and the fluid-filled punch (7) can slide and advance along the straight section area of the preforming inner cavity.

[0014] Optionally, the inner side of the preforming inner cavity includes multiple smooth bulge areas and a straight section area; the outer bending radius of the preforming inner cavity is r, where (R1 + D1 / 2) < r < (R0 + D0 / 2); the radius at the center of the inner curve of the preforming inner cavity and the radius at the center of the inner curve of the inner cavity of the hydroforming die are both R1 - D1 / 2. Among them, R1 is the bending radius of the target formed elbow, D1 is the diameter of the target formed elbow, R0 is the bending radius of the original right-angle elbow pipe billet, and D0 is the diameter of the original right-angle elbow pipe billet.

[0015] Optionally, the placing the elbow pipe billet with straight sections in a preforming die to obtain the preformed elbow includes:

[0016] Place the elbow pipe billet with straight sections in the preforming die, and perform a sealing operation through the sealing punch and the fluid-filled punch;

[0017] Advance the sealing punch and the fluid-filled punch according to a preset displacement amount, and maintain the hydraulic pressure of the elbow pipe billet according to a preset threshold to obtain the preformed elbow.

[0018] Optionally, the outer bending radius of the preforming inner cavity is:

[0019] r = 1.45R0 - 0.08D0 - 0.04R1 + 0.34D1.

[0020] Optionally, the preset displacement amount is:

[0021] s=0.078×(R1-R0)+1.85×(D1-D0);

[0022] Wherein, R1 is the bending radius of the target formed elbow, D1 is the diameter of the target formed elbow, R0 is the bending radius of the original right-angle elbow blank, D0 is the diameter of the original right-angle elbow blank, and s is the preset displacement.

[0023] Optionally, the bulge area includes at least two rounded bulges, which are respectively located on both sides of the center of the inner curve of the preformed cavity, and the radius r of the rounded bulges is... a The inner corner radius r of the hydraulic forming die is greater than that of the die. c .

[0024] The advantages of the integral hydraulic forming method for small radius elbows described in this invention compared to existing technologies are as follows:

[0025] Elbow blanks with straight sections can be obtained by welding 20-50mm straight sections to both ends of the original elbow blank. This provides material for the bulges formed during the preforming process, helps maintain the internal pressure of the pipe during preforming, and reduces the sealing difficulty during hydraulic bulging.

[0026] Through preforming, a smooth, high-curvature bulge is formed on the inner wall of the tube. Firstly, the material storage in the bulge facilitates localized tube blank adhesion during the hydraulic bulging process. By reducing the contact area between the material and the mold, friction is reduced, which facilitates material flow and adhesion in the rounded corner areas, effectively reducing forming pressure. At the same time, the bulge storage reduces deformation concentration in the rounded corner areas, providing more metal to the deformation zone, effectively reducing deformation and avoiding defects such as excessive thinning or even breakage.

[0027] By reducing the forming pressure based on the above principles, cracking defects can be avoided, the tonnage of forming equipment can be reduced, mold production losses can be decreased, forming quality can be improved, and the yield rate can be increased. In this way, the overall forming cost can be reduced from both the equipment and forming quality aspects, and production efficiency can be improved.

[0028] Therefore, this invention divides the overall forming process, namely the large circumferential deformation at both ends of the elbow, into two stages: preforming and bulging, through a preforming process. This avoids cracking defects, reduces the maximum expansion rate during bulging, and lowers the material performance requirements for liquid-filled bulging processing of elbows with small bending radii. In other words, by using the forming method of this invention, we can obtain the beneficial effects of higher forming quality, higher efficiency, and reduced production costs. Attached Figure Description

[0029] Figure 1This is a schematic flowchart of the integral hydraulic forming method for small-radius elbows in an embodiment of the present invention;

[0030] Figure 2 This is a cross-sectional schematic diagram of the hydroforming mold in an embodiment of the present invention;

[0031] Figure 3 This is a cross-sectional schematic diagram of the preforming mold in an embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram illustrating the shape changes of the original elbow tube blank in an embodiment of the present invention;

[0033] Figure 5 This is a cross-sectional schematic diagram of a bend tube blank with a straight section placed in a preforming mold in an embodiment of the present invention;

[0034] Figure 6 This is a cross-sectional schematic diagram of a preformed elbow placed in a hydroforming mold in an embodiment of the present invention.

[0035] Explanation of reference numerals in the attached figures:

[0036] 1-Sealing punch of hydraulic forming die; 2-Lower die of hydraulic forming die; 3-Filling punch of hydraulic forming die; 4-Filling port of hydraulic forming die; 5-Sealing punch; 6-Lower die; 7-Filling punch; 8-Filling port; 9-Weld. Detailed Implementation

[0037] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0038] like Figure 1 As shown, in one embodiment, a method for integral hydraulic forming of a small-radius elbow is provided, specifically including the following steps:

[0039] Step S1: Obtain the elbow blank with a straight section.

[0040] Specifically, the process begins by obtaining a tube blank with a straight section as raw material through mandrel bending technology, CNC bending technology, or hydraulic bending technology. This tube blank is usually made of metal materials, such as stainless steel or aluminum alloy. Due to limitations of traditional technology, tube blanks with straight sections are often selected as pre-bent tube blanks with a smaller diameter and a relatively larger bending radius. The desired shaped elbow is obtained by performing a hydraulic forming operation on the tube blank with a straight section.

[0041] Step S2: The elbow blank with straight section is pre-formed to obtain a pre-formed elbow. The inner wall bending area of ​​the pre-formed elbow includes multiple bulge areas.

[0042] Specifically, the tube blank is placed in a preforming mold and bent through preforming to obtain a preformed elbow. Multiple bulges will form on the inner bending area of ​​the preformed elbow. These bulges are formed to store material, reduce the expansion rate during the second forming, avoid cracking, and thus improve forming quality and production efficiency. At the same time, the bulges can reduce the friction between the mold and the tube blank, which is conducive to material flow and mold adhesion, and reduces forming pressure.

[0043] Step S3: Place the preformed elbow in the hydraulic forming mold for hydraulic expansion to obtain the final target formed elbow.

[0044] Specifically, the pre-formed elbow is placed in a hydraulic forming mold, and further shaped by hydraulic pressure to obtain a temporary formed elbow. This temporary elbow is then cut and processed to obtain the target formed elbow. Hydraulic forming is a method of plastically processing metal materials using hydraulic pressure. By controlling the pressure and flow rate of the hydraulic system, the pre-formed elbow is finally shaped under the action of the mold, forming a small-radius elbow, such as... Figure 2 The diagram shown is a schematic of the hydraulic forming mold.

[0045] The small-radius elbow integral hydraulic forming method described in this embodiment can obtain an elbow blank with straight sections by welding 20-50mm straight sections to both ends of the original elbow blank. This provides material for the bulge formed during the preforming process, and is also beneficial for maintaining the internal pressure of the pipe during the preforming process. Furthermore, the straight section will reduce the sealing difficulty during forming when hydraulically expanding.

[0046] Through preforming, a material storage bulge with a large curvature and smooth shape is formed on the inner wall of the tube. Firstly, the material storage in the bulge facilitates the mold bonding during the hydraulic forming process of the hydraulic mold. By reducing the contact area between the material and the mold, the friction is reduced, which facilitates the flow of material and the bonding of the rounded corner area, effectively reducing the forming pressure. At the same time, the material storage in the bulge can reduce the deformation concentration in the rounded corner area, providing more metal to the deformation zone to reduce the amount of deformation, effectively reducing the amount of deformation and avoiding defects such as excessive thinning or even cracking.

[0047] By reducing forming pressure based on the above principles, defects can be avoided, the tonnage of forming equipment can be reduced, mold production losses can be decreased, forming quality can be improved, and the yield rate can be increased. In this way, the overall forming cost can be reduced from both the equipment and forming quality aspects, and production efficiency can be improved.

[0048] Therefore, this embodiment divides the overall forming process, namely the large circumferential deformation at both ends of the elbow, into two stages: preforming and bulging, through a preforming process. This avoids cracking defects, reduces the maximum expansion rate during bulging, and lowers the material performance requirements for liquid-filled bulging processing of elbows with small bending radii. In other words, by using the forming method of this invention, we can obtain the beneficial effects of higher forming quality, higher efficiency, and reduced production costs.

[0049] In some embodiments, obtaining the elbow blank with a straight section includes:

[0050] Obtain an original elbow tube blank with a bending radius of R0 and a diameter of D0, and obtain a matching straight tube blank based on the original elbow tube blank;

[0051] Connect a straight section of the tube blank to each end of the original elbow tube blank to obtain the elbow tube blank with the straight section.

[0052] Specifically, the original elbow pipe blank is often selected from pre-bent pipe blanks with a smaller diameter and a relatively larger bending radius. This can be achieved by cutting the two ends of the original elbow pipe blank together, welding a straight section of pipe blank to each end, and then aligning the weld seam 9 (e.g. Figure 5 The weld seam 9 shown is ground smooth, and a straight section of pipe blank is welded to each end. The straight section of pipe blank has the same diameter and thickness as the original elbow pipe blank. The length of the straight section of pipe blank can be set according to the actual situation, for example, the length can be selected as 20-50mm. This avoids the situation in the traditional forming process where the pipe blank used does not have a straight section, so that after the punches on both sides are sealed, the pipe blank cannot be pushed into the mold cavity, and thus the material cannot be replenished. That is, during the preforming process, the pipe end sealing of the elbow pipe blank with the straight section and the material being pushed into the mold cavity by the punch are achieved.

[0053] This involves welding 20-50mm straight sections to both ends of the original right-angle tube blank to provide material for the bulges formed during the preforming process. This also helps maintain the internal pressure of the tube during preforming, and the straight sections also reduce the sealing difficulty during hydraulic bulging.

[0054] In some embodiments, the pre-forming operation of the elbow blank with a straight section to obtain a pre-formed elbow includes:

[0055] The elbow blank with a straight section is placed in a preforming mold to obtain the preformed elbow;

[0056] Among them, such as Figure 3As shown, the preforming die includes an upper backing plate, a lower backing plate, a sealing punch 5, a fluid-filled punch 7 provided with a liquid inlet channel, an upper female die and a lower female die 6. The upper backing plate is used to fix the upper female die, and the lower backing plate is used to fix the lower female die 6. The upper female die and the lower female die 6 are designed to be mirror-symmetrical. The upper female die and the lower female die 6 form a preforming inner cavity, and the inner side of the preforming inner cavity includes the bulging area and the straight section area. The curvature radius of the bulge is r a , the diameter of the straight section is slightly larger than R0. The straight section areas of the upper and lower female dies form a cylindrical cavity, which provides space for the feeding of the punches 5 and 7. The outer bending radius of the preforming inner cavity is r, where (R1 + D1 / 2) < r < (R0 + D0 / 2). The radius at the center of the inner curve of the preforming inner cavity and the radius at the center of the inner curve of the inner cavity of the hydroforming die are both R1 - D1 / 2. Here, R1 is the bending radius of the target formed elbow, D1 is the diameter of the target formed elbow, R0 is the bending radius of the original right-angle elbow tube blank, and D0 is the diameter of the original right-angle elbow tube blank. The sealing punch 5 is placed at one end of the preforming inner cavity. The fluid-filled punch 7 is placed at the other end of the preforming inner cavity. The sealing punch 5 and the fluid-filled punch 7 can slide and feed along the straight section area of the preforming inner cavity

[0057] Place the elbow tube blank with a straight section into the preforming die to obtain the preformed elbow

[0058] Specifically, as Figure 3 shown, the preforming die includes an upper backing plate, a lower backing plate, a sealing punch 5, a fluid-filled punch 7, and the fluid-filled punch 7 is provided with a liquid inlet channel; an upper female die and a lower female die 6. The upper backing plate is used to fix the upper female die, and the lower backing plate is used to fix the lower female die 6. The upper female die and the lower female die 6 are designed to be mirror-symmetrical. The upper female die and the lower female die 6 form a preforming inner cavity, and the inner side of the preforming inner cavity includes multiple bulging areas and a straight section area. The curvature radius of the bulge is r a , the diameter of the straight section is slightly larger than R0. The straight section areas of the upper and lower female dies (the upper female die and the lower female die 6) form a cylindrical cavity, which provides space for the feeding of the sealing punch 5 and (7). The outer bending radius of the preforming inner cavity is r, where (R1 + D1 / 2) < r < (R0 + D0 / 2). The radius at the center of the inner curve of the preforming inner cavity and the radius at the center of the inner curve of the inner cavity of the hydroforming die are both R1 - D1 / 2. Here, R1 is the bending radius of the target formed elbow, and D1 is the diameter of the target formed elbow. The sealing punch 5 is placed at one end of the preforming inner cavity. The fluid-filled punch 7 is placed at the other end of the preforming inner cavity. The sealing punch 5 and the fluid-filled punch 7 can slide and feed along the straight section cavity formed by the upper and lower female die cavities

[0059] Specifically, such as Figure 3 As shown, the preforming mold also includes two hydraulic cylinders and two cylinder seats. The backing plate includes an upper backing plate and a lower backing plate. The upper backing plate can be fixed to the upper mold base of the hydraulic press via a T-slot. The upper die can be fixed to the upper backing plate with bolts. The lower die 6 can be fixed to the lower backing plate with bolts. The hydraulic cylinders can be fixed to the cylinder seats with bolts. The cylinder seats can be fixed to the lower backing plate with bolts. The lower backing plate can be fixed to the lower mold base of the hydraulic press via a T-slot. Both the sealing punch 5 and the filling punch 7 can move within the preforming cavity to achieve pipe end sealing. The filling port 8 of the filling punch 7 changes the hydraulic pressure within the preforming cavity.

[0060] The upper die and the lower die 6 form a pre-formed inner cavity, and the center of the inner shape curve of the pre-formed inner cavity has the same radius as the center of the inner curve of the hydraulic forming mold, and the radius is R1-D1 / 2, with an angle of 90 degrees, so that the pre-formed elbow can be assembled into the hydraulic forming mold; and the inner ends of the pre-formed inner cavity are provided with smooth bulge-shaped curves (see the bulge area). Figure 3 (Dashed box) The bulge area causes a smooth bulge to form on the inside of the tube blank under the action of internal pressure and punch during preforming, which stores material for subsequent deformation and effectively reduces hydraulic pressure during hydraulic expansion forming.

[0061] The hydraulic pressure during the forming process using a preforming die is lower than that during the forming process using a traditional hydraulic forming die. In other words, the preforming die is a low-pressure preforming die, and its forming process is a low-pressure preforming process. For example, the hydraulic pressure inside the tube blank is often maintained at 2-30 MPa during the preforming process, while the hydraulic pressure inside the tube blank may need to be maintained at a higher level, such as 140 MPa, during the forming process using a traditional hydraulic forming die. The reduced hydraulic pressure during the forming process decreases the required forming pressure, which in turn reduces the expansion rate during the second forming, avoiding cracking and thus improving forming quality and production efficiency.

[0062] In some embodiments, placing the elbow blank with the straight section in a preforming mold to obtain the preformed elbow includes:

[0063] The elbow blank with a straight section is placed in the pre-forming mold, and the sealing operation is performed by the sealing punch 5 and the liquid filling punch 7.

[0064] The sealing punch 5 and the liquid filling punch 7 are advanced according to a preset displacement, and the hydraulic pressure of the elbow blank is maintained according to a preset threshold to obtain the preformed elbow.

[0065] Specifically, the liquid filling punch 7 is provided with a liquid inlet channel. When the sealing punch 5 and the liquid filling punch 7 are pushed forward, they form an integral closed pressurization space with the pipe material. When pressurizing, the liquid filling punch 7 feeds high-pressure liquid.

[0066] In some embodiments, the outer bending radius of the preformed inner cavity is:

[0067] r=1.45R0-0.08D0-0.04R1+0.34D1.

[0068] In some embodiments, the preset displacement is:

[0069] s=0.078×(R1-R0)+0.925×(D1-D0);

[0070] Wherein, R1 is the bending radius of the target formed elbow, D1 is the diameter of the target formed elbow, R0 is the bending radius of the original right-angle elbow blank, D0 is the diameter of the original right-angle elbow blank, and s is the preset displacement.

[0071] In some embodiments, the bulge region includes at least two rounded bulges, which are respectively positioned on both sides of the center of the inner curve of the preformed cavity, and the radius r of the rounded bulges is... a The inner corner radius r of the hydraulic forming die is smaller than that of the die. c For example, the radius r of the rounded corner bulge can be selected. a The radius of the inner corner of the hydraulic forming mold is 30mm, which is 80mm.

[0072] Specifically, the rounded bulges are smoothly connected, and the radius of the center of the inner curve of the preformed inner cavity is consistent with the radius of the center of the inner curve of the inner cavity of the hydraulic forming mold. The purpose is to deform only the tube material stored in the bulge part during subsequent bulging, so as to avoid cracking. It should be noted that there is no specific limit to the number of rounded bulges, which can be limited according to the actual situation. According to the small rounded bulging pressure formula p=tσ / r, the smaller the rounded corner, the greater the forming pressure. In order to reduce the forming pressure, the radius of curvature of the rounded bulge should be greater than the radius of the rounded corner of the forming mold.

[0073] Specifically, during the preforming process, the elbow blank with a straight section is placed in the preforming mold. After the mold is closed, the punches on both sides (sealing punch 5 and liquid filling punch 7) are pushed forward to achieve pipe end sealing. When both punches are in contact with both ends of the elbow blank with a straight section, the punches on both sides (sealing punch 5 and liquid filling punch 7) are pushed forward into the preforming cavity again according to the preset displacement. While the punches at both ends are pushed forward, the elbow blank with a straight section is kept under low hydraulic support (e.g., 2-30MPa). Hydraulic pressure has a supporting effect, which can prevent the elbow of the pipe from bending excessively when the punches are pushed forward. Under hydraulic support, the punches push the pipe material at both ends to feed at the same time, forming a small number of smooth bulges in the bending area inside the pipe blank, which can avoid the formation of dead wrinkles.

[0074] It should be noted that the bending angles of the original elbow blank and the final target elbow are not specifically limited and can be determined according to the actual situation. For example, in this embodiment, the bending angle of the blank is 90 degrees. Small-radius elbows with different angle requirements can also be formed using the aforementioned small-radius elbow hydraulic forming method.

[0075] In this embodiment, as Figures 4-6 Taking the example shown, the initial elbow blank has a bending radius R0 of 240mm and a diameter D0 of 160mm. The target formed elbow (target pipe fitting) has a bending radius R1 of 150mm and a diameter D1 of 200mm. The pre-formed fillet radius is r. a The radius of the hydraulically bulged fillet is 95.5mm. c The forming pressure is 40mm. The forming pressure in existing technologies is no less than 90MPa, while in this embodiment, the forming pressure is reduced to between 45 and 50MPa.

[0076] The implementation process of hydroforming of small-radius elbows in this example is as follows:

[0077] Step A1, take the initial elbow blank (such as...) Figure 4 The tube blank shown in Figure a has a bending radius of 240mm and a diameter of 160mm. Both sides are trimmed, and straight sections of the same diameter and thickness, 30mm in length, are welded to both sides of the trimmed initial elbow tube blank to obtain a right-angle elbow (e.g., ...). Figure 4 (The tube blank shown in b).

[0078] Step A2: Grind the two sides of the right-angle elbow and the weld seam 9 to make them smooth, then put the right-angle elbow into the pre-forming mold and close the mold.

[0079] Step A3: Advance the two punches (pre-sealing punch 5 and filling punch 7) to both ends of the right-angle bend to achieve a seal, while simultaneously replenishing the fluid. Continue advancing the two punches to maintain the hydraulic pressure inside the pipe. Record the stroke from when the punch just contacts the right-angle bend to its final advanced position. The following conditions must be met:

[0080] s=0.078×(R1-R0)+0.925×(D1-D0)=29.98mm;

[0081] Where s is the preset displacement.

[0082] Step A4, apply a liquid pressure of 20 MPa (e.g., Figure 5 The pressure P shown causes the right-angle bend to be shaped into a pre-formed bend (such as...). Figure 4 The tube blank shown in Figure c has a radius of r for the rounded corner bulge. aAfter the outer curve radius of the preformed elbow is r), the hydraulic pressure inside the preformed elbow is released, the two end punches (the sealing punch 1 of the hydraulic forming mold and the filling punch 3 of the hydraulic forming mold) are retracted, and the mold is opened to take out the preformed elbow.

[0083] Step A5: Place the preformed elbow into the lower cavity of the hydraulic forming mold, and after closing the mold, push the two punches on both sides of the hydraulic forming mold (the sealing punch 1 and the filling punch 3 of the hydraulic forming mold) into the seal, and replenish the liquid through the filling port 4 of the hydraulic forming mold to pressurize and expand the inner side of the preformed elbow.

[0084] Step A6, apply a liquid pressure of 45-50 MPa (e.g., Figure 6 The pressure P shown in the figure causes the preformed elbow to become a temporary formed elbow (such as...). Figure 4 The tube blank shown in d has an inner corner radius r. c With a bending radius of R1, the hydraulic pressure on the tube blank in the hydraulic forming die is unloaded, the punch is retracted, and the die is opened to remove the part. The removed tube blank is then cut (trimmed) to obtain the target tube part (such as...). Figure 4 The tube blank shown in Figure e has a bending radius of R1, a diameter of D1, and an angle of θ.

[0085] It should be noted that the implementation process of this invention can be adapted to perform hydraulic forming on small-radius bends at different angles.

[0086] The small-radius elbow integral hydraulic forming method described in this embodiment obtains an elbow blank with straight sections by welding 30mm straight sections to both ends of the original elbow blank. This provides material for the bulge formed during the preforming process and helps maintain the internal pressure of the pipe during preforming. Furthermore, the straight sections reduce the sealing difficulty during hydraulic bulging. Through preforming, a smooth, high-curvature bulge is formed on the inner wall of the pipe. The material storage in the bulge facilitates mold adhesion during the hydraulic forming process. By reducing the contact area between the material and the mold, friction is reduced, facilitating material flow and adhesion to the rounded corner areas, effectively reducing forming pressure. Simultaneously, the bulge reduces deformation concentration in the rounded corner areas, providing more metal to the deformation zone to reduce deformation, effectively minimizing deformation and avoiding excessive thinning or even breakage. By reducing forming pressure, avoiding defects, reducing the tonnage of forming equipment, reducing mold production wear, improving forming quality, and increasing yield, the overall forming cost is reduced and production efficiency is improved from both equipment and forming quality perspectives.

[0087] Therefore, this embodiment divides the overall forming process, namely the large circumferential deformation at both ends of the elbow, into two stages: preforming and bulging, through a preforming process. This avoids cracking defects, reduces the maximum expansion rate during bulging, and lowers the material performance requirements for liquid-filled bulging processing of elbows with small bending radii. In other words, by using the forming method of this invention, we can obtain the beneficial effects of higher forming quality, higher efficiency, and reduced production costs.

[0088] It should be noted that, in this document, terms such as "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0089] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

[0090] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for integral hydraulic forming of a small-radius elbow, characterized in that, Including: Obtain an elbow pipe blank with a straight section; Perform a pre-forming operation on the elbow pipe blank with a straight section to obtain a pre-formed elbow, and the inner wall bending area of the pre-formed elbow includes multiple smooth bulge areas; Place the pre-formed elbow in a hydroforming die for hydroforming to obtain a final target formed elbow; Among them, the obtaining of the elbow pipe blank with a straight section includes: Obtain an original right-angle elbow pipe blank with a bending radius of R0 and a diameter of D0, and obtain a matching straight section pipe blank according to the original right-angle elbow pipe blank; Weld a straight section pipe blank to each end of the original right-angle elbow pipe blank to obtain the elbow pipe blank with a straight section; The performing of the pre-forming operation on the elbow pipe blank with a straight section to obtain a pre-formed elbow includes: Place the elbow pipe blank with a straight section in a pre-forming die to obtain the pre-formed elbow; The preforming mold includes an upper die and a lower die (6), which are mirror-symmetrically designed. The upper die and the lower die (6) form a preforming cavity. The inner side of the preforming cavity includes multiple smooth bulge regions, each smooth bulge region including at least two rounded bulges. The rounded bulges are respectively located on both sides of the center of the inner curve of the preforming cavity, and the radius of curvature r of the rounded bulges is... a The inner corner radius r of the hydraulic forming die is greater than that of the die. c ; Among them, the inner side of the pre-formed inner cavity also includes a straight section area; the outer bending radius of the pre-formed inner cavity is r, where (R0 + D0 / 2) < r < (R1 + D1 / 2); the radius at the center of the inner curve of the pre-formed inner cavity and the radius at the center of the inner curve of the inner cavity of the hydroforming die are both R1 - D1 / 2, where R1 is the bending radius of the target formed elbow, D1 is the diameter of the target formed elbow, R0 is the bending radius of the original right-angle elbow pipe blank, and D0 is the diameter of the original right-angle elbow pipe blank.

2. The method for integral hydraulic forming of a small-radius elbow according to claim 1, characterized in that, The pre-forming die further includes an upper backing plate, a lower backing plate, a sealing punch (5), a fluid-filled punch (7) provided with a liquid inlet channel, an upper female die and a lower female die (6). The upper backing plate is used to fix the upper female die, and the lower backing plate is used to fix the lower female die (6); the sealing punch (5) is placed at one end of the pre-formed inner cavity; the fluid-filled punch (7) is placed at the other end of the pre-formed inner cavity, and the sealing punch (5) and the fluid-filled punch (7) can slide and advance along the straight section area of the pre-formed inner cavity.

3. The method for integral hydraulic forming of a small-radius elbow according to claim 1, characterized in that, The outer bending radius of the pre-formed inner cavity is: 。 4. The method for integral hydraulic forming of a small-radius elbow according to claim 2, characterized in that, Placing the elbow pipe blank with a straight section in a pre-forming die to obtain the pre-formed elbow includes: Place the elbow pipe blank with a straight section in the pre-forming die, and perform a synchronous pushing and sealing operation through the sealing punch (5) and the fluid-filled punch (7); Push the sealing punch (5) and the fluid-filled punch (7) according to a preset displacement amount, and maintain the hydraulic pressure of the elbow pipe blank according to a preset threshold to obtain the pre-formed elbow.

5. The method for integral hydraulic forming of a small-radius elbow according to claim 4, characterized in that, The preset displacement amount is: ； Among them, R1 is the bending radius of the target formed elbow, D1 is the diameter of the target formed elbow, R0 is the bending radius of the original right-angle elbow pipe blank, D0 is the diameter of the original right-angle elbow pipe blank, and s is the preset displacement amount.

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