A rubber bag hydraulic forming die and forming method for a large-depth multi-rib sheet metal part

Abstract

This invention discloses a rubber bladder hydroforming mold and forming method for sheet metal parts with large depth and multiple reinforcing ribs. The forming method includes: Step 1, fabricating a rubber bladder hydroforming mold; Step 2, placing the unfolded blank on a transition punch and fixing the unfolded blank around the perimeter with a limiting frame, performing the first rubber bladder hydroforming; Step 3, sequentially installing the pre-formed sheet metal part obtained in Step 2 and the limiting frame on a forming die 1, performing the second rubber bladder hydroforming to obtain a shaped sheet metal part; Step 4, placing structurally matching rubber strips at the positions of each reinforcing rib of the shaped sheet metal part, performing the third rubber bladder hydroforming, so as to correct the shape of each reinforcing rib position through the rubber strips and the forming grooves in the forming surface of the forming die. This invention solves the problem of poor material flowability and insufficient local elongation in existing forming methods, which easily leads to tearing of the reinforcing rib area during hydroforming.

Description

Technical Field

[0001] This invention relates to sheet metal rubber bladder forming technology in the field of aircraft manufacturing, specifically a hydraulic forming mold and forming method for rubber bladders of sheet metal parts with large depth and multiple reinforcing ribs. Background Technology

[0002] Sheet metal reinforcing ribs are a type of stiffening plate structure designed on sheet metal parts. Their main functions include increasing the rigidity of the sheet metal parts, making them more robust and durable; improving load-bearing capacity, allowing the reinforcing ribs to share the load and reduce deformation when bearing loads; and improving stability, enhancing the stability and seismic resistance of the sheet metal parts when subjected to external forces, making them safer and more reliable. Therefore, reinforcing ribs are widely used in the aerospace industry.

[0003] "M"-shaped ring-shaped sheet metal parts with large-depth reinforcing ribs are difficult to form. In aircraft manufacturing, sheet metal rubber bladder forming is a common forming process for multi-ribbed panel parts. For sheet metal parts with multiple reinforcing ribs, a single die forming is currently used. Due to the large amount of deformation and the fact that the reinforcing ribs cover the parts, the material flow is further restricted, resulting in insufficient local elongation. When using hydroforming, it is easy to cause tearing at the reinforcing ribs. In addition, finite element analysis of the die forming also shows that there is a lot of stress when the reinforcing ribs are deformed, the material deforms violently, and there are multiple tearing points. Summary of the Invention

[0004] The purpose of this invention is to provide a hydraulic forming mold and forming method for a rubber bladder of sheet metal parts with large depth and multiple reinforcing ribs, so as to solve the problem that the existing forming method for sheet metal parts with multiple reinforcing ribs is prone to tearing in the reinforcing rib area during hydraulic forming due to the poor material fluidity and insufficient local elongation caused by the reinforcing ribs being full of reinforcing ribs in the part structure.

[0005] The technical solution of the present invention is as follows: In the first aspect, the present invention provides a hydraulic forming mold for a rubber bladder of a sheet metal part with a large depth and multiple reinforcing ribs, comprising: a forming die 1, a transition punch 10 and a limiting frame 6; The upper end face of the forming die 1 serves as the die forming surface 2. The die forming surface 2 is configured to match the theoretical shape of the multi-rib sheet metal part 9. Based on the multi-rib structure in the multi-rib sheet metal part 9, the die forming surface 2 is provided with a die forming groove 5 for forming each rib. The die forming surface 2 of the forming die 1 is provided with a die annular process edge 3 around its periphery. A positioning hole 4 is provided on the die annular process edge 3 so that a positioning pin 8 can be used to fix the limiting frame 6 on the die annular process edge 3. The upper end face of the transition punch 10 serves as the punch forming surface 14. The punch forming surface 14 is provided with reinforcing rib transition bosses 15 corresponding to the positions of each reinforcing rib in the theoretical surface of the multi-reinforcing rib sheet metal part 9. Each reinforcing rib transition boss 15 is obtained by modifying the reinforcing rib surface at the corresponding position in the theoretical surface. The punch forming surface 14 of the transition punch 10 is provided with a punch annular process edge 16 around its periphery. A positioning hole 4 is provided on the punch annular process edge 16 to fix the limiting frame 6 on the punch annular process edge 16 using a positioning pin 8. The position of the positioning hole on the punch annular process edge 16 is consistent with the position of the positioning hole 4 on the die annular process edge 3. The limiting frame 6 is provided with an annular frame structure that matches both the annular process edge 3 of the concave die and the annular process edge 16 of the convex die. The limiting frame 6 is provided with a connecting hole 7 corresponding to the positioning hole 4. During the forming process, the positioning pin 8 is used to connect with the positioning hole 4 to fix the tooling.

[0006] Optionally, in the rubber bladder hydroforming mold for a sheet metal part with large depth and multiple reinforcing ribs as described above, the dimensions of the forming die 1, the transition punch 10, and the limiting frame 6 are set according to the dimensions of the unfolded blank. The dimensional setting method of the forming mold includes: Check whether the edge distance between the blank edge and the annular process edge 3 of the die cavity or the annular process edge 16 of the punch is consistent at all positions in the circumferential direction and whether the edge distance is ≥30mm; if not, adjust the size of the forming die cavity 1 and the transition punch 10 to ensure that the flow of blank material during the forming process does not exceed the limit range of the annular process edge 3 of the die cavity and the annular process edge 16 of the punch. The outer surface of the limiting frame 6 is flush with the edge of the annular process edge 3 of the concave die or the annular process edge 16 of the convex die. The inner surface of the limiting frame 6 is controlled according to the edge size of the unfolded blank. The edge size of the unfolded blank is smaller than the inner surface size of the limiting frame 6, and the distance between the two at all circumferential positions is ≤3mm. If not, the size of the limiting frame 6 is adjusted to limit the maximum range of material flow of the unfolded blank during the hydroforming process. By setting the size of the limiting frame 6, the limiting frame 6 replaces the pin holes on the sheet metal parts in the prior art. On the one hand, it achieves strict restriction of the material flow of the unfolded blank; on the other hand, it avoids the process problems caused by the need to set pin holes on the sheet metal parts in the prior art.

[0007] Optionally, in the rubber bladder hydroforming mold for a sheet metal part with a large depth and multiple reinforcing ribs as described above, the root of each die forming groove 5 of the die forming surface 2 is provided with a die inlet fillet 17; and each reinforcing rib transition boss 15 of the punch forming surface 14 is provided with a reinforcing rib transition boss root fillet 18 and a reinforcing rib transition boss top fillet 19. The rounded corners 17 at the entrance of the die, 18 at the root of the reinforcing rib transition boss, and 19 at the top of the reinforcing rib transition boss are mirror-polished to facilitate material flow during the hydraulic forming process using the forming die 1 and the transition punch 10, and to prevent the material from tearing during forming due to excessive tooling roughness.

[0008] Optionally, in the above-described rubber bladder hydroforming mold for a sheet metal part with a large depth and multiple reinforcing ribs, the reinforcing rib transition boss 15 needs to be modified compared to the die forming groove 5. The depth of the reinforcing rib transition boss 15 and the radius of the fillet 18 at the root of the reinforcing rib transition boss must both be greater than the corresponding dimensions of the forming die 1. Specifically, the modification methods for each reinforcing rib transition boss 15 in the transition punch 10 include: The depth H of the reinforcing rib transition boss 15 is (1.05~1.15)×h, where h is the maximum depth of the reinforcing rib in the multi-rib sheet metal part 9; The radius R of the fillet 18 at the root of the reinforcing rib transition boss is (2~3)×r, where r is the radius of the fillet 12 at the root of the reinforcing rib of the multi-reinforcing rib sheet metal part 9; The fillet 19 at the top of the reinforcing rib transition boss is obtained by rounding the top surface of the reinforcing rib in the theoretical shape of the multi-reinforcing rib sheet metal part 9, so that the top surface 13 of the reinforcing rib of the pre-formed sheet metal part 9a obtained by the transition punch 10 is a smooth transition surface.

[0009] Optionally, in the rubber bladder hydroforming mold for a sheet metal part with great depth and multiple reinforcing ribs as described above, The forming die 1, transition punch 10, and limiting frame 6 are made of 45# steel and have a heat treatment state of HRC45-48.

[0010] Optionally, in the rubber bladder hydroforming mold for a sheet metal part with great depth and multiple reinforcing ribs as described above, The die forming groove 5 in the forming die 1 and the reinforcing rib transition boss 15 in the transition punch 10 are both set as multiple sets of "rice" shaped ring structures.

[0011] Secondly, the rubber bladder hydroforming method for a sheet metal part with large depth and multiple reinforcing ribs, as described above, involves performing the rubber bladder hydroforming method on the sheet metal part with large depth and multiple reinforcing ribs using the rubber bladder hydroforming mold described in any of the above claims, and includes the following steps: Step 1: Based on the theoretical shape of the multi-ribbed sheet metal part 9, fabricate a rubber bladder hydraulic forming mold, including: forming die 1, transition punch 10 and limiting frame 6; Step 2: Place the unfolded blank of the multi-ribbed sheet metal part 9 on the transition punch 10, and use the limiting frame 6 to fix the unfolded blank around the upper end face of the transition punch 10 to perform the first rubber bladder hydraulic forming to obtain the pre-formed sheet metal part 9a. Step 3: After completing the first rubber bladder hydroforming, remove the preformed sheet metal part 9a and the limiting frame 6, install the preformed sheet metal part 9a and the limiting frame 6 on the forming die 1 in sequence, and perform the second rubber bladder hydroforming to perform rubber bladder hydroforming on the preformed sheet metal part 9a to obtain the shaped sheet metal part 9b. Step 4: Place structurally matching rubber strips 11 at each reinforcing rib position of the shaped sheet metal part 9b located on the die forming surface 2 of the forming die 1, and perform the third rubber bladder hydraulic shaping to shape each reinforcing rib position through the rubber strips 11 and each die forming groove 5 in the die forming surface 2 of the forming die 1.

[0012] Optionally, in the above-described method for hydroforming a deep, multi-ribbed sheet metal part into a rubber bladder, the method for obtaining the unfolded blank of the multi-ribbed sheet metal part 9 used in step 2 is as follows: By importing the theoretical surface of the multi-ribbed sheet metal part 9 into the finite element analysis software, the unfolded shape of the hydraulic forming is calculated using the blank back calculation function, and the unfolded blank size is obtained.

[0013] Optionally, in the above-described method for hydroforming a deep, multi-ribbed sheet metal part with a rubber bladder, the pressure for hydroforming the rubber bladder in steps 2, 3, and 4 is set based on experience: In step 2, the process pressure for the first rubber bladder forming using the transition punch 10 is set to P1=70-90PA for hydraulic preforming. In step 3, the process pressure for the second rubber bladder forming using the forming die 1 is set to P2=P1, which is used to initially bring the excess material stored in the transition punch 10 during hydraulic pressure into the forming groove 5 of the die. In step 4, the process pressure for the third rubber bladder forming using the forming die 1 and the rubber strip 11 is set to P3=2P1, which is used to shape the sheet metal part 9b to obtain the multi-ribbed sheet metal part 9.

[0014] Optionally, in the above-described method for hydroforming a deep, multi-ribbed sheet metal part with a rubber bladder, the volume of the rubber strip 11 used in step 4 is determined using an equal volume conversion method. The method for determining the volume of the rubber strip 11 is as follows: The inner surface of the reinforcing rib in the theoretical shape of the multi-ribbed sheet metal part 9 is offset inward, and the offset gap is: g = (0.95~1.0)×δ; Wherein, δ is the material thickness of the multi-ribbed sheet metal part 9; The offset reinforcing rib surface is filled as a solid, and the volume of the rubber strip 11 is equal to the volume of this solid.

[0015] The beneficial effects of this invention are as follows: This invention provides a rubber bladder hydroforming mold and forming method for sheet metal parts with large depth and multiple reinforcing ribs. The technical solution of this invention first provides a rubber bladder hydroforming mold for sheet metal parts with large depth and multiple reinforcing ribs, including a forming die 1, a transition punch 10, and a limiting frame 6, and provides a corresponding forming method for the forming mold. In this forming method, the transition punch 10 and the limiting frame 6 are used to perform a first rubber bladder hydroforming on the unfolded blank. Secondly, the forming die 1 and the limiting frame 6 are used to perform a second rubber bladder hydroforming on the pre-formed sheet metal part 9a obtained by the first rubber bladder hydroforming, to obtain a corrected sheet metal part 9b. Finally, by placing structurally matching rubber strips 11 at the positions of each reinforcing rib of the corrected sheet metal part 9b on the forming surface 2 of the forming die 1, a third rubber bladder hydroforming is performed, so that each reinforcing rib position is corrected by the rubber strips 11 and each forming groove 5 in the forming surface 2 of the forming die 1, to obtain a sheet metal part 9 with multiple reinforcing ribs. The technical solution provided by this invention has the following beneficial effects: First, the use of six pairs of limiting frames to position the shape of the unfolded raw material not only eliminates the need for cutting ear pieces and deburring the cut areas after forming, but also partially overcomes the problems of twisting, warping, and cracking caused by pins restricting the material from being added inward, thus greatly reducing the skill requirements for operators. Second, when forming reinforcing ribs using transition punch 10, material can be pre-stored on both sides of the reinforcing ribs. The depth of the formed reinforcing ribs is greater than that of the die, and the surface of the triangular area is curved. A certain amount of material is stored in the triangular area, which facilitates the flow of the stored material to the reinforcing ribs when forming with the forming die later, which can greatly reduce the risk of sheet metal tearing during hydroforming. Third, the forming method of using rubber strip 11 in conjunction with die forming groove 5 during the forming of reinforcing ribs is adopted. The rubber strip 11 is used to bring the excess material stored in the transition punch during hydraulic pressure into the reinforcing ribs. The structure is simple, the operation is easy, the workload of workers is reduced, the processing cycle is shortened, and the skill requirements of operators are reduced. Fourth, the forming method provided by the present invention significantly reduces the amount of trimming required for multi-ribbed sheet metal parts, reduces the occurrence of hammer marks or slag damaging the material surface during the trimming process, and even damages the mechanical properties of the material, thereby improving the surface quality of the sheet metal parts. Attached Figure Description

[0016] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of the present invention and do not constitute a limitation on the technical solutions of the present invention.

[0017] Figure 1 This is a schematic diagram of the forming die in the rubber bladder hydroforming mold provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the transition punch in the rubber bladder hydroforming mold provided in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the assembly principle of the transition punch in the forming method provided in this embodiment of the invention. Figure 4 This is a schematic diagram illustrating the assembly principle of the forming die in the forming method provided in this embodiment of the invention. Figure 5 This is a schematic diagram illustrating the working principle of the limiting ring in the forming method provided in this embodiment of the invention; Figure 6 for Figure 2 A schematic cross-sectional view of the transition punch along AA provided in the illustrated embodiment; Figure 7 This is a schematic diagram illustrating the working principle of hydraulic straightening in the forming method provided in this embodiment of the invention.

[0018] Explanation of reference numerals in the attached figures: 1. Forming die, 2. Die forming surface, 3. Die ring process edge, 4. Positioning hole, 5. Die forming groove, 6. Limiting frame, 7. Connecting hole, 8. Positioning pin, 9. Multi-rib sheet metal part, 9a. Pre-formed sheet metal part, 9b. Correcting sheet metal part, 10. Transition punch, 11. Rubber strip, 12. Reinforcing rib root fillet, 13. Reinforcing rib top surface, 14. Punch forming surface, 15. Reinforcing rib transition boss, 16. Punch ring process edge, 17. Die entrance fillet, 18. Reinforcing rib transition boss root fillet, 19. Reinforcing rib transition boss top fillet. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

[0020] As explained in the background section, multi-ribbed sheet metal parts have been widely used in the aerospace industry due to their structural advantages. However, it has also been pointed out that multi-ribbed sheet metal parts are prone to tearing at the ribs during hydroforming due to insufficient local elongation.

[0021] In addition to the issues mentioned above, the forming of multi-ribbed panel parts also requires the use of pin holes and mold positioning. Currently, there are two main methods for making pin holes. One method is to make two or more pin holes in the diagonal area on the outer side of the unfolded blank. The main disadvantage of this method is that additional pin lugs need to be cut after forming. The other method is to make the pin holes directly on the diagonal part of the unfolded blank in order to reduce cutting. The main disadvantage of this method is that the diagonal pin holes restrict the material from being added inward during the forming process of the rubber bladder, causing uneven deformation and resulting in problems such as twisting, warping, and cracking of the sheet metal parts.

[0022] Currently, the main methods used to address the above two issues include: first, unloading the material midway through forming and using an aluminum hammer to level unevenly deformed areas; second, using rigid fixtures to fix the formed sheet metal parts for machining and milling to add pins and lugs. However, in the sheet metal field, the leveling level is mainly used to assess the operator's skill. Therefore, for sheet metal parts with excessive twisting or warping, the operator's skill requirements are high. Hammer marks or debris during the leveling process can easily damage the material surface and even impair the material's mechanical properties, seriously affecting the product's service life.

[0023] To address the above problems, the present invention provides a method and mold for forming rubber bladders for sheet metal parts with multiple reinforcing ribs.

[0024] The present invention provides the following specific embodiments, which can be combined with each other. For the same or similar concepts or processes, they may not be described again in some embodiments.

[0025] Traditional ribbed sheet metal parts are formed using a single die. Due to the large deformation and the numerous "X"-shaped reinforcing ribs further hindering material flow, insufficient local elongation leads to repeated tearing at the reinforcing rib areas during hydroforming. Furthermore, the need for pin holes during forming often results in diagonally spaced pin holes restricting material inwards, causing uneven deformation and leading to problems such as twisting, warping, and cracking of the sheet metal. Therefore, there is an urgent need for a rubber-blade forming method suitable for sheet metal parts with multiple reinforcing ribs.

[0026] like Figures 1 to 7 As shown, the present invention provides a method for hydroforming a rubber bladder for sheet metal parts with large depth and multiple reinforcing ribs, comprising the following steps: Step 1: Based on the theoretical shape of the multi-ribbed sheet metal part 9, fabricate a rubber bladder hydraulic forming mold, including: forming die 1, transition punch 10 and limiting frame 6; Step 2: Place the unfolded blank of the multi-ribbed sheet metal part 9 on the transition punch 10, and use the limiting frame 6 to fix the unfolded blank around the upper end face of the transition punch 10 to perform the first rubber bladder hydraulic forming to obtain the pre-formed sheet metal part 9a. Step 3: After completing the first rubber bladder hydroforming, remove the preformed sheet metal part 9a and the limiting frame 6, install the preformed sheet metal part 9a and the limiting frame 6 on the forming die 1 in sequence, and perform the second rubber bladder hydroforming to perform rubber bladder hydroforming on the preformed sheet metal part 9a to obtain the shaped sheet metal part 9b. Step 4: Place structurally matching rubber strips 11 at each reinforcing rib position of the sheet metal part 9b located on the die forming surface 2 of the forming die 1, and perform the third rubber bladder hydraulic correction, so as to correct each reinforcing rib position through the rubber strips 11 and each die forming groove 5 in the die forming surface 2 of the forming die 1, to obtain the multi-reinforcing rib sheet metal part 9.

[0027] The rubber bladder hydroforming method for sheet metal parts with large depth and multiple reinforcing ribs provided in this embodiment of the invention can form qualified sheet metal parts with multiple reinforcing ribs 9 through three rubber bladder hydroforming processes in steps 2 to 4.

[0028] Based on the process requirements for rubber bladder hydroforming of sheet metal parts with large depth and multiple reinforcing ribs in the embodiments of the invention, the first requirement in the embodiments of the invention is to prepare a set of rubber bladder hydroforming molds that can be used in the above-mentioned rubber bladder hydroforming method, such as... Figures 1 to 4 As shown, the rubber bladder hydraulic forming mold includes a forming die 1, a transition punch 10, and a limiting frame 6.

[0029] like Figure 1 As shown, the upper end face of the forming die 1 serves as the forming die surface 2. The forming die surface 2 is configured to match the theoretical shape of the multi-rib sheet metal part 9. Based on the multi-rib structure in the multi-rib sheet metal part 9, the forming die surface 2 is provided with a forming die groove 5 for forming each rib. The forming die surface 2 of the forming die 1 is provided with a die annular process edge 3 around its periphery. A positioning hole 4 is provided on the die annular process edge 3 so that a positioning pin 8 can be used to fix the limiting frame 6 on the die annular process edge 3.

[0030] like Figure 2 As shown, the upper end face of the transition punch 10 serves as the punch forming surface 14. The punch forming surface 14 is provided with reinforcing rib transition bosses 15 corresponding to the positions of each reinforcing rib in the theoretical surface of the multi-rib sheet metal part 9. Each reinforcing rib transition boss 15 is obtained by modifying the reinforcing rib surface at the corresponding position in the theoretical surface. The punch forming surface 14 of the transition punch 10 is provided with a punch annular process edge 16 around its periphery. A positioning hole 4 is provided on the punch annular process edge 16 to fix the limiting frame 6 on the punch annular process edge 16 using a positioning pin 8. The position of the positioning hole on the punch annular process edge 16 is consistent with the position of the positioning hole 4 on the die annular process edge 3.

[0031] like Figure 3 and Figure 4As shown, the limiting frame 6 is provided with an annular frame structure that matches both the annular process edge 3 of the concave die and the annular process edge 16 of the convex die. The limiting frame 6 is provided with a connecting hole 7 corresponding to the positioning hole 4. During the forming process, the positioning pin 8 is used to connect with the positioning hole 4 to fix the tooling.

[0032] The working principle of the limiting frame 6 in the forming mold provided in this embodiment of the invention is as follows: Figures 3 to 5 As shown, taking the connection between the limiting frame 6 and the forming die 1 as an example, the limiting frame 6 is placed on the annular process edge 3 of the forming die 1, and the connecting hole 7 of the limiting frame is connected and fixed to the positioning hole 4 of the forming die 1 by the positioning pin 8; the pre-formed sheet metal part 9a, which has been pre-formed by the transition punch 10, is placed on the forming surface 2 of the forming die 1, and the outer contour of the pre-formed sheet metal part 9a is limited by the limiting frame 6; the assembled forming die 1 and the pre-formed sheet metal part 9a are placed on the rubber bladder pressure worktable and pressure is applied to carry out the hydraulic forming process. During the hydraulic forming process, the material of the pre-formed sheet metal part 9a flows evenly into the forming groove from all directions around the reinforcing rib, so that the pre-formed sheet metal part 9a is basically kept flat, resulting in the shaped sheet metal part 9b; the shaped sheet metal part 9b can be further trimmed on the forming die 1 using the rubber strip 11; finally, the positioning pin 8 between the limiting frame 6 and the forming die 1 is removed, and the limiting frame 6 is separated from the forming die 1.

[0033] This invention provides a rubber-bladder hydroforming mold and forming method for sheet metal parts with large depth and multiple reinforcing ribs. The technical solution of this invention first provides a rubber-bladder hydroforming mold for sheet metal parts with large depth and multiple reinforcing ribs, including a forming die 1, a transition punch 10, and a limiting frame 6, and provides a corresponding forming method for the forming mold. In this forming method, the transition punch 10 and the limiting frame 6 are used to perform a first rubber-bladder hydroforming on the unfolded blank. Secondly, the forming die 1 and the limiting frame 6 are used to perform a second rubber-bladder hydroforming on the pre-formed sheet metal part 9a obtained from the first rubber-bladder hydroforming, resulting in a corrected sheet metal part 9b. Finally, by placing structurally matching rubber strips 11 at the positions of the reinforcing ribs of the corrected sheet metal part 9b on the forming surface 2 of the forming die 1, a third rubber-bladder hydroforming is performed. This corrects the reinforcing rib positions through the rubber strips 11 and the forming grooves 5 in the forming surface 2 of the forming die 1, resulting in a multi-reinforcing sheet metal part 9. The technical solution provided by this invention has the following specific beneficial effects: First, the use of six pairs of limiting frames to position the shape of the unfolded raw material not only eliminates the need for cutting ear pieces and deburring the cut areas after forming, but also partially overcomes the problems of twisting, warping, and cracking caused by pins restricting the material from being added inward, thus greatly reducing the skill requirements for operators. Second, when forming reinforcing ribs using transition punch 10, material can be pre-stored on both sides of the reinforcing ribs. The depth of the formed reinforcing ribs is greater than that of the die, and the surface of the triangular area is curved. A certain amount of material is stored in the triangular area, which facilitates the flow of the stored material to the reinforcing ribs when forming with the forming die later, which can greatly reduce the risk of sheet metal tearing during hydroforming. Third, the forming method of using rubber strip 11 in conjunction with die forming groove 5 during the forming of reinforcing ribs is adopted. The rubber strip 11 is used to bring the excess material stored in the transition punch during hydraulic pressure into the reinforcing ribs. The structure is simple, the operation is easy, the workload of workers is reduced, the processing cycle is shortened, and the skill requirements of operators are reduced. Fourth, the forming method provided by the present invention significantly reduces the amount of trimming required for multi-ribbed sheet metal parts, reduces the occurrence of hammer marks or slag damaging the material surface during the trimming process, and even damages the mechanical properties of the material, thereby improving the surface quality of the sheet metal parts.

[0034] In one implementation of the present invention, the dimensions of the forming die 1, the transition punch 10, and the limiting frame 6 in the rubber bladder hydroforming mold are set according to the dimensions of the unfolded blank. The dimension setting method of the forming mold includes: Check whether the edge distance between the blank edge and the annular process edge 3 of the die cavity or the annular process edge 16 of the punch is consistent at all positions in the circumferential direction and whether the edge distance is ≥30mm; if not, adjust the size of the forming die cavity 1 and the transition punch 10 to ensure that the flow of blank material during the forming process does not exceed the limit range of the annular process edge 3 of the die cavity and the annular process edge 16 of the punch. The outer surface of the limiting frame 6 is flush with the edge of the annular process edge 3 of the concave mold or the annular process edge 16 of the convex mold. The inner surface of the limiting frame 6 is controlled according to the edge size of the unfolded blank. The edge size of the unfolded blank is smaller than the inner surface size of the limiting frame 6, and the distance between the two at each position in the circumferential direction is ≤3mm. If not, the size of the limiting frame 6 is adjusted so that the limiting frame 6 can limit the maximum range of material flow of the unfolded blank during the hydroforming process.

[0035] It should be noted that by setting the size of the limiting frame 6, the limiting frame 6 is used to replace the function of the pin holes on the sheet metal parts in the prior art. On the one hand, it achieves strict restriction on the flow of the unfolded blank material; on the other hand, it avoids the process problems caused by setting pin holes on the sheet metal parts in the prior art.

[0036] In one embodiment of the present invention, the root of each die forming groove 5 of the die forming surface 2 is provided with a die inlet fillet 17; the reinforcing rib transition boss 15 of the punch forming surface 14 is provided with a reinforcing rib transition boss root fillet 18 and a reinforcing rib transition boss top fillet 19. The fillet 17 at the entrance of the die cavity, the fillet 18 at the root of the reinforcing rib transition boss, and the fillet 19 at the top of the reinforcing rib transition boss are mirror-polished to facilitate material flow during the hydroforming process using the forming die 1 and the transition punch 10, and to prevent the material from tearing during forming due to excessive tooling roughness.

[0037] It should be noted that, compared to the forming groove 5, the reinforcing rib transition bosses 15 in the transition punch 10 need to be modified, and the depth of the reinforcing rib transition bosses 15 and the radius of the fillet 18 at the root of the reinforcing rib transition bosses must both be larger than the corresponding dimensions of the forming die 1. Specifically, the modification methods for each reinforcing rib transition boss 15 in the transition punch 10 include: (1) The depth H of the reinforcing rib transition boss 15 is (1.05~1.15)×h, where h is the maximum depth of the reinforcing rib in the multi-rib sheet metal part 9; (2) The radius of the fillet 18 at the root of the reinforcing rib transition boss is R = (2~3) × r, where r is the radius of the fillet 12 at the root of the reinforcing rib of the multi-reinforcing rib sheet metal part 9; (3) The top fillet 19 of the reinforcing rib transition boss is obtained by rounding the top surface 13 of the reinforcing rib in the theoretical surface of the multi-reinforcing rib sheet metal 9, so that the top surface 13 of the reinforcing rib of the preformed sheet metal 9a obtained by the transition punch 10 is a smooth transition surface.

[0038] The working principle of the reinforcing rib transition boss 15 is as follows: Figure 6 As shown, when forming the reinforcing rib using the transition punch 10, material can be pre-stored on both sides of the reinforcing rib. The depth of the formed reinforcing rib is greater than the depth of the forming groove 5 in the forming die 1. The surface of the triangular area at the top of the reinforcing rib in the pre-formed sheet metal part 9a has an arc, and a certain amount of material is stored in the triangular area, which facilitates the flow of the stored material to the reinforcing rib when it is formed by the forming die 1 later.

[0039] In one embodiment of the present invention, the forming die 1, the transition punch 10, and the limiting frame 6 are made of 45# steel and the heat treatment state is HRC45-48.

[0040] In addition, the die forming groove 5 in the forming die 1 and the reinforcing rib transition boss 15 in the transition punch 10 are both set as multiple sets of "rice" shaped ring structures.

[0041] Based on the rubber bladder hydroforming mold designed in the above embodiments of the present invention, the specific implementation method of the rubber bladder hydroforming method for sheet metal parts with large depths and multiple reinforcing ribs provided by the present invention is described below: In one implementation of this invention, the method for obtaining the unfolded blank of the multi-reinforcing sheet metal part 9 used in step 2 is as follows: By importing the theoretical surface of the multi-reinforced sheet metal part 9 into finite element analysis software, the developed shape of the hydroforming is calculated using the blank back-calculation function to obtain the developed blank size.

[0042] In one implementation of the embodiment of the present invention, the pressures for rubber bladder hydroforming in steps 2, 3, and 4 are set according to experience: In step 2, the process pressure for the first rubber bladder forming using the transition punch 10 is set to P1 = 70 - 90 PA for hydro-preforming; In step 3, the process pressure for the second rubber bladder forming using the forming die 1 is set to P2 = P1, which is used to initially bring the excess material stored during the hydroforming of the transition punch 10 into the forming groove 5 of the die; In step 4, the process pressure for the third rubber bladder forming using the forming die 1 and the rubber strip 11 is set to P3 = 2P1, which is used to calibrate the calibrated sheet metal part 9b to obtain the multi-reinforced sheet metal part 9.

[0043] In one implementation of the embodiment of the present invention, the volume of the rubber strip 11 used in step 4 is determined by the equal-volume conversion method, and the determination method of the volume of the rubber strip 11 is as follows: The inner shape surface of the reinforcing rib in the theoretical surface of the multi-reinforced sheet metal part 9 is offset inward, and the offset gap is: g = (0.95 - 1.0) × δ; where δ is the material thickness of the multi-reinforced sheet metal part 9; The offset reinforcing rib surface is filled with a solid, and the volume of the rubber strip 11 is equal to the volume of this solid.

[0044] The function of the rubber strip 11 is as Figure 6 shown. During the forming process using the forming die 1, the rubber strip 11 is added in the area of the die forming groove 5 to bring the excess material stored during the hydroforming of the transition punch 10 into the reinforcing rib.

[0045] Each drawing in the embodiment of the present invention takes the "rice" character ring-shaped reinforced sheet metal part as an example to illustrate the structure of the rubber bladder hydroforming die for the plate-made large-depth multi-reinforced sheet metal part and the multi-reinforced sheet metal part. Similar methods for other sheet metal parts should fall within the protection scope of this application.

[0046] Although the disclosed embodiments of the present invention are as above, the content is only the embodiments adopted for the convenience of understanding the present invention and is not used to limit the present invention. Any person skilled in the art within the field of the present invention can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed by the present invention. However, the patent protection scope of the present invention shall still be subject to the scope defined by the appended claims.

Claims

1. A method for hydroforming a rubber bladder for sheet metal parts with large depth and multiple reinforcing ribs, characterized in that, A rubber bladder hydroforming method is used to perform rubber bladder hydroforming on sheet metal parts with large depth and multiple reinforcing ribs. The rubber bladder hydroforming mold includes: forming die (1), transition punch (10) and limiting frame (6). The upper end face of the forming die (1) is used as the die forming surface (2). The die forming surface (2) is set to match the theoretical shape of the multi-rib sheet metal part (9). Based on the multi-rib structure in the multi-rib sheet metal part (9), the die forming surface (2) is provided with a die forming groove (5) for forming each rib. The die forming surface (2) of the forming die (1) is provided with a die annular process edge (3) around its periphery. A positioning hole (4) is provided on the die annular process edge (3) so that a positioning pin (8) can be used to fix the limiting frame (6) on the die annular process edge (3). The upper end face of the transition punch (10) serves as the punch forming surface (14). The punch forming surface (14) is provided with reinforcing rib transition bosses (15) corresponding to the positions of each reinforcing rib in the theoretical surface of the multi-rib sheet metal part (9). Each reinforcing rib transition boss (15) is obtained by modifying the reinforcing rib surface at the corresponding position in the theoretical surface. When forming the reinforcing rib using the transition punch (10), material is pre-stored on both sides of the reinforcing rib. The depth of the formed reinforcing rib is greater than that of the forming die (1), and the surface of the triangular area has an arc. A certain amount of material is stored in the triangular area to facilitate subsequent forming with the forming die (1). At that time, the stored material flows to the reinforcing rib; the punch forming surface (14) of the transition punch (10) is provided with a punch annular process edge (16) around its periphery, and a positioning hole (4) is provided on the punch annular process edge (16) to fix the limiting frame (6) on the punch annular process edge (16) with a positioning pin (8); and the position of the positioning hole on the punch annular process edge (16) is consistent with the position of the positioning hole (4) on the die annular process edge (3); the die forming groove (5) in the forming die (1) and the reinforcing rib transition boss (15) in the transition punch (10) are all set with multiple sets of "rice" shaped annular structures; The limiting frame (6) is set as an annular frame structure that matches both the annular process edge (3) of the concave die and the annular process edge (16) of the convex die. The limiting frame (6) is provided with a connecting hole (7) corresponding to the positioning hole (4). During the forming process, the positioning pin (8) is used to connect with the positioning hole (4) to fix the tooling. The rubber bladder hydroforming method includes the following steps: Step 1: Based on the theoretical shape of the multi-ribbed sheet metal part (9), make a rubber bladder hydraulic forming mold, including: forming die (1), transition punch (10) and limiting frame (6). Step 2: Place the unfolded blank of the multi-ribbed sheet metal part (9) on the transition punch (10), and use the limiting frame (6) to fix the unfolded blank around the upper end face of the transition punch (10) to perform the first rubber bladder hydraulic forming to obtain the pre-formed sheet metal part (9a). Step 3: After completing the first rubber bladder hydroforming, take out the preformed sheet metal part (9a) and the limiting frame (6), install the preformed sheet metal part (9a) and the limiting frame (6) on the forming die (1) in sequence, and perform the second rubber bladder hydroforming to perform rubber bladder hydroforming on the preformed sheet metal part (9a) to obtain the shaped sheet metal part (9b). Step 4: Place structurally matching rubber strips (11) at each reinforcing rib position of the shaped sheet metal part (9b) located on the die forming surface (2) of the forming die (1), and perform a third rubber bladder hydraulic forming to correct each reinforcing rib position through the rubber strips (11) and each die forming groove (5) in the die forming surface (2) of the forming die (1) to obtain a multi-reinforcing sheet metal part (9).

2. The method for rubber bladder hydroforming of a sheet metal part with large depth and multiple reinforcing ribs according to claim 1, characterized in that, In the rubber bladder hydraulic forming mold, the dimensions of the forming die (1), the transition punch (10), and the limiting frame (6) are set according to the dimensions of the unfolded blank. The dimensions of the forming mold are set in the following ways: Check whether the edge distance between the blank edge and the annular process edge (3) of the die or the annular process edge (16) of the punch is consistent at each position in the circumferential direction and the edge distance is ≥30mm; if not, adjust the size of the forming die (1) and the transition punch (10) to ensure that the flow of blank material during the forming process does not exceed the limit range of the annular process edge (3) of the die and the annular process edge (16) of the punch; The outer surface of the limiting frame (6) is flush with the edge of the annular process edge (3) of the concave die or the annular process edge (16) of the convex die. The inner surface of the limiting frame (6) is controlled according to the edge size of the unfolded blank. The edge size of the unfolded blank is smaller than the inner surface size of the limiting frame (6), and the distance between the two at each position in the circumferential direction is ≤3mm. If not, the size of the limiting frame (6) is adjusted so that the limiting frame (6) can be used to limit the maximum range of material flow of the unfolded blank during the hydroforming process.

3. The method for rubber bladder hydroforming of a sheet metal part with large depth and multiple reinforcing ribs according to claim 1, characterized in that, The root of each die forming groove (5) of the die forming surface (2) is provided with a die inlet rounded corner (17); the root of each reinforcing rib transition boss (15) of the punch forming surface (14) is provided with a reinforcing rib transition boss root rounded corner (18) and a reinforcing rib transition boss top rounded corner (19). The positions of the die inlet fillet (17), the reinforcing rib transition boss root fillet (18), and the reinforcing rib transition boss top fillet (19) are mirror polished to facilitate material flow during the hydraulic forming process using the forming die (1) and the transition punch (10), and to prevent the material from tearing during forming due to excessive tooling roughness.

4. The method for rubber bladder hydroforming of a sheet metal part with large depth and multiple reinforcing ribs according to claim 3, characterized in that, The correction methods for each reinforcing rib transition boss (15) in the transition punch (10) include: The depth H of the reinforcing rib transition boss (15) is (1.05~1.15)×h, where h is the maximum depth of the reinforcing rib in the multi-rib sheet metal part (9); The radius of the fillet (18) at the root of the reinforcing rib transition boss is R = (2~3) × r, where r is the radius of the fillet (12) at the root of the reinforcing rib of the multi-reinforcing rib sheet metal part (9); The fillet (19) at the top of the reinforcing rib transition boss is obtained by rounding the top surface (13) of the reinforcing rib in the theoretical surface of the multi-reinforcing rib sheet metal part (9), so that the top surface (13) of the reinforcing rib of the preformed sheet metal part (9a) processed by the transition punch (10) is a smooth transition surface.

5. A method for hydroforming a rubber bladder for a sheet metal part with a large depth and multiple reinforcing ribs according to any one of claims 1 to 4, characterized in that, The forming die (1), transition punch (10), and limiting frame (6) are made of 45# steel and have a heat treatment state of HRC45-48.

6. The method for hydroforming a rubber bladder for a sheet metal part with a large depth and multiple reinforcing ribs according to claim 1, characterized in that, The method for obtaining the unfolded blank of the multi-ribbed sheet metal part (9) used in step 2 is as follows: By importing the theoretical shape of the multi-ribbed sheet metal part (9) into the finite element analysis software, the unfolded shape of the hydraulic forming is calculated using the blank back calculation function, and the unfolded blank size is obtained.

7. The method for hydroforming a rubber bladder for a sheet metal part with a large depth and multiple reinforcing ribs according to claim 1, characterized in that, The pressure for the rubber bladder hydraulic forming in steps 2, 3, and 4 is set based on experience. In step 2, the process pressure for the first rubber bladder forming using the transition punch (10) is set to P1=70-90PA for hydraulic preforming. In step 3, the process pressure for the second rubber bladder forming using the forming die (1) is set to P2=P1, which is used to initially bring the excess material stored in the forming groove (5) of the die when the transition punch (10) is hydraulically pumped. In step 4, the process pressure for the third rubber bladder forming using the forming die (1) and the rubber strip (11) is set to P3=2P1, which is used to shape the sheet metal part (9b) to obtain the multi-rib sheet metal part (9).

8. The method for hydroforming a rubber bladder for a sheet metal part with a large depth and multiple reinforcing ribs according to claim 1, characterized in that, The volume of the rubber strip (11) used in step 4 is determined using an equal volume conversion method. The method for determining the volume of the rubber strip (11) is as follows: The inner surface of the reinforcing rib in the theoretical shape of the multi-ribbed sheet metal part (9) is offset inward, and the offset gap is: g = (0.95 ~ 1.0) × δ; Wherein, δ is the material thickness of the multi-ribbed sheet metal part (9); The offset reinforcing rib surface is filled as a solid, and the volume of the rubber strip (11) is equal to the volume of the solid.

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