Step-by-step hydraulic forming method for rubber bag of deep-cavity sheet metal part

Abstract

The invention discloses a rubber bag step-by-step hydraulic forming method for a deep-cavity sheet metal part. The rubber bag step-by-step hydraulic forming method comprises the steps that 1, an unfolded blank, a deep-cavity mold and a rubber block are constructed; 2, a deep cavity mold is placed on a rubber bag hydraulic machine, a rubber block is placed in a deep cavity of the deep cavity mold, an unfolded blank to be formed is placed on the inner surface of the deep cavity mold, a rubber bag is placed on the upper end face of the unfolded blank in an attached mode, the rubber bag is pressurized and filled with oil, and rubber bag hydraulic preforming is conducted; pre-forming the unfolded blank into a transition state part through hydraulic pressure; 3, a transition state part obtained through primary rubber bag hydraulic forming is placed in a deep cavity of the deep cavity mold, and a shape correcting rubber block is placed in a cavity of the transition state part; and 4, the rubber bag is placed on the upper end face of the transition state part in an attached mode, the shape correcting rubber block is located between the transition state part and the rubber bag, the rubber bag is pressurized and filled with oil, hydraulic shape correcting is conducted on the rubber bag, and the formed deep cavity sheet metal part is obtained.

Description

Technical Field

[0001] The present invention relates to, but is not limited to, a sheet metal parts hydraulic forming technology in the field of aircraft manufacturing technology, and in particular to a rubber bag step-by-step hydraulic forming method for a deep cavity sheet metal part. Background Art

[0002] Due to the special requirements of high strength and light weight of aircraft, sheet metal parts have always occupied a large proportion of the entire aircraft. Deep cavity sheet metal parts, as typical sheet metal parts, are widely used on aircraft as protective covers for various lighting systems and circuit systems. To ensure fit with the aircraft skin, aircraft deep cavity sheet metal parts are usually deep and complex in shape, so they have high requirements for the forming process.

[0003] Currently, deep-cavity sheet metal parts are often formed by deep drawing. By combining this with other stamping processes such as flanging, bulging, flaring, and shrinking, cylindrical, spherical, stepped, conical, box-shaped, and other irregularly shaped parts can be manufactured. However, due to the small drawing coefficient and large depth of deep-cavity sheet metal parts, severe plastic deformation occurs during the drawing process, resulting in excessive thinning at the corner radius of the box bottom of the deep-cavity sheet metal parts, causing cracks, poor product quality, and high scrap rates. Therefore, a multi-pass deep drawing process is required, and correspondingly, multiple sets of drawing dies need to be designed, resulting in complex die structures, difficult designs, high manufacturing costs, long processing preparation times, and low production efficiency. Summary of the Invention

[0004] The purpose of the present invention is to provide a step-by-step hydraulic forming method for a rubber bag of a deep-cavity sheet metal part, so as to solve the problem that in the existing forming method of deep-cavity sheet metal parts, the sheet metal parts may break due to plastic deformation during the drawing process, resulting in poor product quality, and the existing multi-pass drawing forming process requires multiple sets of drawing dies, resulting in high manufacturing costs, long processing preparation time and low production efficiency.

[0005] The technical solution of the present invention is as follows: The present invention provides a step-by-step hydraulic forming method of a rubber bladder for a deep cavity sheet metal part, comprising the following steps: Step 1: constructing a developed blank 3, a deep cavity mold 5, and a rubber block 4; wherein the inner surface 8 of the constructed deep cavity mold is the same as the theoretical outer surface 7 of the deep cavity sheet metal part; Step 2: Place the deep cavity mold 5 on the rubber bladder hydraulic press, place the rubber block 4 in the deep cavity of the deep cavity mold 5, place the expanded blank 3 to be formed on the inner surface 8 of the deep cavity mold, and place the rubber bladder 1 on the upper end surface of the expanded blank 3. Pressurize and fill the rubber bladder 1 with oil 2 to perform hydraulic preforming of the rubber bladder, and then hydraulically preform the expanded blank 3 into a transitional part 6; Step 3: After the rubber bladder is hydraulically preformed, the transitional part 6 and the rubber block 4 are removed, and the transitional part 6 obtained by the first rubber bladder hydraulic forming is placed in the deep cavity of the deep cavity mold 5, and the correction rubber block 14 is placed in the cavity of the transitional part 6; Step 4: The rubber bladder 1 is placed on the upper end surface of the transition state part 6, and the shaping rubber block 14 is located between the transition state part 6 and the rubber bladder 1. The rubber bladder 1 is pressurized and filled with oil 4. The rubber bladder 1 and the shaping rubber block 14 are used to hydraulically shape the transition state part 6 to obtain a formed deep cavity sheet metal part 13, and the shaping rubber block 14 and the deep cavity sheet metal part 13 are removed.

[0006] Optionally, in the above-mentioned step-by-step hydroforming method for a rubber bag of a deep cavity sheet metal part, the specific construction process of the unfolded blank 3, the deep cavity mold 5 and the rubber block 4 in step 1 includes: Step 1-1: construct unfolded blank 3; The theoretical outer surface 7 of the deep cavity sheet metal part is imported into the finite element analysis software, and the blank inverse calculation function is used to calculate the unfolded shape of the hydroformed blank to obtain the outer edge line of the unfolded blank 3; Determine the size of the unfolded blank according to the outer edge line of the unfolded blank 3; Step 1-2: constructing a deep cavity mold 5; The deep-cavity mold 5 adopts a concave mold structure. The inner surface 8 of the deep-cavity mold is the theoretical outer surface 7 of the deep-cavity sheet metal part. The outer edge line of the unfolded blank 3 is projected onto the corresponding position of the deep-cavity mold working surface 9 to obtain the unfolded blank outer contour line 10 on the deep-cavity mold 5. The deep-cavity mold working surface 9 is adjusted according to the unfolded blank outer contour line 10 so that the overall outer edge size of the adjusted deep-cavity mold working surface 9 is larger than the unfolded blank outer contour line 10. Steps 1-3: Construct the rubber block; The rubber block 4 adopts a rectangular parallelepiped structure, and the outer edge of the lower end surface of the rubber block is tangent to the inner surface 8 of the deep cavity mold.

[0007] Optionally, in the above-mentioned step-by-step hydroforming method for a rubber bag of a deep-cavity sheet metal part, the method of adjusting the deep-cavity mold working surface 9 according to the unfolded blank outer contour line 10 in step 1-2 includes: Determine whether the distance between the outer edge line of the unfolded blank 3 and the outer contour of the deep cavity mold working surface 9 at each circumferential position is the same, and the distance between the two is ≥80mm; if not, adjust the deep cavity mold working surface 9 to meet the above conditions.

[0008] Optionally, in the above-mentioned method for hydraulically forming a rubber bladder of a deep-cavity sheet metal part, the deep-cavity mold 5 is constructed in steps 1-2, further comprising: The deep cavity mold working surface 9, the deep cavity entrance fillet 11 and the deep cavity mold inner surface 8 are mirror polished; A vent hole 12 is provided at the lowest point of the inner surface 8 of the deep cavity mold, the diameter of the vent hole is φ10, and the vent hole passes through the deep cavity mold 5; The deep cavity mold 5 is made of 45# steel with a heat treatment temperature of HRC45-48.

[0009] Optionally, in the above-mentioned step-by-step hydraulic forming method of a rubber bag for a deep cavity sheet metal part, The number of hydraulic preforming of the rubber bladder in step 2 is at least 1, and the number of hydraulic preforming is set according to the theoretical outer surface 7 of the actual deep-cavity sheet metal part. By selecting the forming height H and reducing the volume of the rubber block 4 in sequence, multi-pass controllable hydraulic preforming is achieved; wherein, the volume of the rubber block 4 used for the first hydraulic preforming of the rubber bladder is the largest, and the volume of the rubber block 4 used for each subsequent hydraulic preforming of the rubber bladder decreases in sequence.

[0010] Optionally, in the above-mentioned method for hydraulically forming a rubber bladder of a deep cavity sheet metal part, in step 2, the forming height H of each hydraulic preforming is an adjustable parameter, and the calculation method of the forming height H includes: Step S-1: constructing a process mold; Import the theoretical outer surface 7 of the deep cavity sheet metal part into the 3D modeling software, select the lowest point Q of the deep cavity sheet metal part during hydroforming, and select a plane at a preset height h upward from point Q to establish the theoretical outer surface 7 of the deep cavity sheet metal part. This plane is used to cut the theoretical outer surface 7 of the deep cavity sheet metal part to establish the process mold α and process mold β of the deep cavity sheet metal part. Step S-2: constructing a process die; The process die is constructed with the process mold shape α as the inner surface. The unfolded blank 4 and the process die are imported into the finite element analysis software. The pressure P is set, the forming height H with the lowest thinning amount is selected, and the height h is adjusted based on the forming height H so that the total height of the deep cavity sheet metal part = H + h.

[0011] Optionally, in the above-mentioned step-by-step hydraulic forming method for a rubber bag of a deep cavity sheet metal part, in step 2, during each hydraulic preforming process, the calculated forming height H is controlled by adjusting the height of the rubber block 4, and the process is as follows: The height A of the rubber block is calculated using the equal volume conversion method, and the process mold β is offset into the theoretical outer surface 7 of the deep cavity sheet metal part. The offset gap is g = (0.95 ~ 1.0) × δ; Where δ is the material thickness of the deep cavity sheet metal part; Fill the offset surface into a solid. The volume of the rubber block 4 is equal to the volume of the solid. The height of the rubber block is A=V / S. Wherein, V is the volume of the rubber block 4, and S is the lower surface area of the rubber block 4.

[0012] Optionally, in the above-mentioned step-by-step hydroforming method for a rubber bladder of a deep cavity sheet metal part, the method of removing the transitional part 6 in step 3 is: By selecting a rubber block 4 with high elasticity, after the rubber bag 1 is separated from the deep cavity mold 5, the rubber block 4 rebounds upward to realize automatic unloading of the transition state part 6.

[0013] Optionally, in the above-mentioned step-by-step hydraulic forming method for a rubber bag of a deep cavity sheet metal part, the method of removing the deep cavity sheet metal part 13 in step 4 is: By selecting the shaping rubber block 14 with a larger surface roughness, after the rubber bag 1 is separated from the deep cavity mold 5, the shaping rubber block 14 expands and generates upward friction with the deep cavity sheet metal part 13, thereby realizing automatic unloading.

[0014] The beneficial effects of the present invention are as follows: the present invention provides a rubber bag step-by-step hydraulic forming method for deep cavity sheet metal parts, comprising: step 1, constructing an expanded blank 3, a deep cavity mold 5 and a rubber block 4, wherein the inner surface 8 of the constructed deep cavity mold is the same as the theoretical outer surface 7 of the deep cavity sheet metal part; step 2, placing the deep cavity mold 5 on the rubber bag hydraulic press, placing the rubber block 4 in the deep cavity of the deep cavity mold 5, placing the expanded blank 3 to be formed on the inner surface 8 of the deep cavity mold, placing the rubber bag 1 on the upper end surface of the expanded blank 3, pressurizing and filling the rubber bag 1 with oil 2, performing rubber bag hydraulic preforming, and hydraulically preforming the expanded blank 3. Forming into a transitional part 6; Step 3, removing the transitional part 6 and the rubber block 4, placing the transitional part 6 obtained by the first rubber bladder hydroforming into the deep cavity of the deep cavity mold 5, and placing the shape-correcting rubber block 14 into the cavity of the transitional part 6; Step 4, placing the rubber bladder 1 in close contact with the upper end surface of the transitional part 6, with the shape-correcting rubber block 14 located between the transitional part 6 and the rubber bladder 1, pressurizing and filling the rubber bladder 1 with oil 4, and hydraulically correcting the transitional part 6 through the rubber bladder 1 and the shape-correcting rubber block 14 to obtain a formed deep-cavity sheet metal part 13, and removing the shape-correcting rubber block 14 and the deep-cavity sheet metal part 13. The rubber bladder step-by-step hydroforming method provided by the present invention, which adopts the above-mentioned step-by-step hydroforming process, has the following beneficial effects: First, it effectively avoids the problem of complex mold structure, difficult design, and high manufacturing cost caused by the small drawing coefficient and large depth of deep-cavity parts, which requires multi-pass drawing and the design of multiple sets of drawing dies. The forming process provided by the present invention uses a simple rubber bladder hydraulic mold for step-by-step hydraulic forming, reducing mold costs. Second, by designing a combined tool for the stepwise hydroforming of the rubber bladder, a simple, low-cost rubber block 4 is incorporated into the tool to control the hydroforming height, thereby resolving the problem of exceeding the forming limit of the rubber bladder during the forming of sheet metal parts with deep cavities, which can lead to rupture of the rubber bladder. The forming process provided by the present invention has significant practical value. Furthermore, the volume of the rubber block 4 used for each hydroforming step decreases with each successive hydroforming step. Third, the technical solution provided by the present invention adopts an equal volume conversion method to calculate the required volume of the rubber block 4 in each hydraulic preforming process, accurately controlling the hydraulic height at each stage of the distributed hydraulic process, thereby reducing a large amount of trial and error costs; Fourth, the technical solution provided by the present invention also provides an automatic unloading method after hydraulic forming. By selecting appropriate rubber block 4 materials, the formed deep cavity sheet metal part 13 can be automatically popped out after hydraulic forming, which solves the problem of traditional manual unloading, which requires manual operation and a large workload, reduces the working hours in the production process, and improves production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0016] Figure 1 A schematic diagram of the rupture of direct rubber bladder hydroforming of deep cavity sheet metal parts in the prior art; Figure 2 A schematic diagram of preparation for the first hydraulic preforming in the step-by-step hydraulic forming method of the rubber bladder provided by an embodiment of the present invention; Figure 3 A schematic diagram of the first hydraulic preforming step in the step-by-step hydraulic forming method for a rubber bladder according to an embodiment of the present invention; Figure 4 A schematic diagram of preparation for the second hydraulic preforming in the step-by-step hydraulic forming method for a rubber bladder provided by an embodiment of the present invention; Figure 5 A schematic diagram of the second hydraulic preforming in the step-by-step hydraulic forming method for a rubber bladder provided by an embodiment of the present invention; Figure 6 Schematic diagram of the construction principle of the process surface of a deep cavity sheet metal part in an embodiment of the present invention; Figure 7 Schematic diagram of the structure of a deep cavity mold in an embodiment of the present invention; FIG8 is a schematic diagram showing the principle of performing multiple hydraulic preforming of a rubber bladder in the step-by-step hydraulic preforming method of the rubber bladder provided by an embodiment of the present invention; FIG8 a and FIG8 b are schematic diagrams comparing the forming height H in the first and second hydraulic preforming of the rubber bladder, respectively.

[0017] Description of reference numerals: 1. Rubber bladder, 2. Oil, 3. Expanded blank, 4. Rubber block, 5. Deep cavity mold, 6. Transition part, 7. Theoretical outer surface of deep cavity sheet metal part, 8. Inner surface of deep cavity mold, 9. Working surface of deep cavity mold, 10. Outer contour of expanded blank, 11. Inlet fillet, 12. Exhaust hole, 13. Deep cavity sheet metal part, 14. Correction rubber block. DETAILED DESCRIPTION

[0018] To make the purpose, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless there is a conflict, the embodiments and features in the embodiments of the present application can be combined with each other in any manner.

[0019] As explained in the background technology above, deep cavity sheet metal parts are widely used in aircraft. They are characterized by great depth and complex shapes, and therefore place high demands on the forming process. The following also describes the various problems that exist in the existing forming process of deep cavity sheet metal parts: On the one hand, due to the small drawing coefficient and large depth of deep-cavity sheet metal parts, severe plastic deformation occurs during the drawing process, resulting in excessive thinning at the corner radius of the deep-cavity sheet metal box bottom, causing cracks, resulting in poor product quality and high scrap rate; On the other hand, the current multi-pass deep drawing process requires the design of multiple sets of drawing dies, which results in complex die structure, difficult design, high manufacturing costs, long processing preparation time, and low production efficiency.

[0020] To address the problems of existing deep-cavity sheet metal drawing processes, the designers of this invention considered using rubber bladder hydroforming, replacing the male drawing die and blank holder with a self-deforming rubber bladder. The main advantages of this technology are: low mold cost, short processing preparation time, and high production efficiency. However, existing rubber bladder hydroforming technology is mainly suitable for sheet metal parts with shallow depths. For sheet metal parts with deep cavities, the forming limit of the rubber bladder will be exceeded during forming, resulting in bladder rupture. Figure 1 The circle.

[0021] To solve the above problems, the present invention provides a step-by-step hydraulic forming method for a rubber bladder of a deep-cavity sheet metal part. The step-by-step hydraulic forming method is suitable for forming deep-cavity sheet metal parts with large depth and complex structure.

[0022] The present invention provides the following specific embodiments that can be combined with each other. The same or similar concepts or processes may not be described in detail in some embodiments.

[0023] See attached Figure 1 The rubber bag hydroforming technology is mainly suitable for sheet metal parts with shallow depth. For sheet metal parts with deep cavities, the forming limit of the rubber bag will be exceeded during forming, resulting in the rupture of the rubber bag. Figure 1 Circle.

[0024] like Figures 2 to 7 As shown, the present invention provides a step-by-step hydroforming method for a deep cavity sheet metal rubber bladder, comprising the following steps: Step 1: constructing a developed blank 3, a deep cavity mold 5, and a rubber block 4; wherein the inner surface 8 of the constructed deep cavity mold is the same as the theoretical outer surface 7 of the deep cavity sheet metal part; Step 2: Place the deep cavity mold 5 on the rubber bladder hydraulic press, place the rubber block 4 in the deep cavity of the deep cavity mold 5, place the expanded blank 3 to be formed on the inner surface 8 of the deep cavity mold, and place the rubber bladder 1 on the upper end surface of the expanded blank 3. Pressurize the rubber bladder 1 with oil 2 to perform hydraulic pre-forming of the rubber bladder, and then hydraulically pre-form the expanded blank 3 into a transitional part 6. Step 3: After the rubber bladder is hydraulically preformed, the transitional part 6 and the rubber block 4 are removed, and the transitional part 6 obtained by the first rubber bladder hydraulic forming is placed in the deep cavity of the deep cavity mold 5, and the correction rubber block 14 is placed in the cavity of the transitional part 6; Step 4: The rubber bladder 1 is placed on the upper end surface of the transition state part 6, and the shaping rubber block 14 is located between the transition state part 6 and the rubber bladder 1. The rubber bladder 1 is pressurized and filled with oil 4. The rubber bladder 1 and the shaping rubber block 14 are used to hydraulically shape the transition state part 6 to obtain a formed deep cavity sheet metal part 13, and the shaping rubber block 14 and the deep cavity sheet metal part 13 are removed.

[0025] In one implementation of the embodiment of the present invention, the specific construction process of the unfolded blank 3, the deep cavity mold 5 and the rubber block 4 in the above step 1 is as follows: Step 1-1: construct unfolded blank 3; The theoretical outer surface 7 of the deep cavity sheet metal part is imported into the finite element analysis software, and the blank inverse calculation function is used to calculate the unfolded shape of the hydroformed blank to obtain the outer edge line of the unfolded blank 3; Determine the size of the unfolded blank according to the outer edge line of the unfolded blank 3; Step 1-2: constructing a deep cavity mold 5; The deep-cavity mold 5 adopts a concave mold structure. The inner surface 8 of the deep-cavity mold is the theoretical outer surface 7 of the deep-cavity sheet metal part. The outer edge line of the unfolded blank 3 is projected onto the corresponding position of the deep-cavity mold working surface 9 to obtain the unfolded blank outer contour line 10 on the deep-cavity mold 5. The deep-cavity mold working surface 9 is adjusted according to the unfolded blank outer contour line 10 so that the overall outer edge size of the adjusted deep-cavity mold working surface 9 is larger than the unfolded blank outer contour line 10. Steps 1-3: Construct the rubber block; The rubber block 4 adopts a rectangular parallelepiped structure, and the outer edge of the lower end surface of the rubber block is tangent to the inner surface 8 of the deep cavity mold.

[0026] In this implementation, the specific implementation of adjusting the deep cavity mold working surface 9 according to the unfolded blank outer contour line 10 in the above steps 1-2 includes: Determine whether the distance between the outer edge line of the unfolded blank 3 and the outer contour of the deep cavity mold working surface 9 at each circumferential position remains relatively uniform, and the distance between the two is ≥80mm; if not, adjust the deep cavity mold working surface 9 to meet the above conditions.

[0027] In this implementation, the deep cavity mold 5 is constructed in the above steps 1-2, further comprising: The deep cavity mold working surface 9, the deep cavity entrance fillet 11 and the deep cavity mold inner surface 8 are mirror polished; A vent hole 12 is provided at the lowest point of the inner surface 8 of the deep cavity mold, the diameter of the vent hole is φ10, and the vent hole passes through the deep cavity mold 5; The deep cavity mold 5 is made of 45# steel with a heat treatment temperature of HRC45-48.

[0028] In one implementation of an embodiment of the present invention, the rubber bag in step 2 is hydraulically preformed at least once, and the number of hydraulic preforming is set according to the theoretical outer surface 7 of the actual deep cavity sheet metal part. By selecting the forming height H and sequentially reducing the volume of the rubber block 4, multi-pass controllable hydraulic preforming is achieved.

[0029] In this implementation, the forming height H of each hydraulic preforming in step 2 is an adjustable parameter. The calculation method of the forming height H includes: Step S-1: constructing a process mold; Import the theoretical outer surface 7 of the deep cavity sheet metal part into the 3D modeling software, select the lowest point Q of the deep cavity sheet metal part during hydroforming, and select a plane at a preset height h upward from point Q to establish the theoretical outer surface 7 of the deep cavity sheet metal part. This plane is used to cut the theoretical outer surface 7 of the deep cavity sheet metal part to establish the process mold α and process mold β of the deep cavity sheet metal part. Step S-2: constructing a process die; The process die is constructed with the process mold shape α as the inner surface. The unfolded blank 4 and the process die are imported into the finite element analysis software. The pressure P is set, the forming height H with the lowest thinning amount is selected, and the height h is adjusted based on the forming height H so that the total height of the deep cavity sheet metal part = H + h.

[0030] In this implementation, during each hydraulic preforming process in step 2, the calculated forming height H is controlled by adjusting the height of the rubber block 4. The process is as follows: The height A of the rubber block is calculated using the equal volume conversion method, and the process mold β is offset into the theoretical outer surface 7 of the deep cavity sheet metal part. The offset gap is g = (0.95 ~ 1.0) × δ; Where δ is the material thickness of the deep cavity sheet metal part; Fill the offset surface into a solid. The volume of the rubber block 4 is equal to the volume of the solid. The height of the rubber block is A=V / S. Wherein, V is the volume of the rubber block 4, and S is the lower surface area of the rubber block 4.

[0031] In one implementation of the embodiment of the present invention, the method of removing the transitional state component 6 in step 3 is: By selecting a rubber block 4 with high elasticity, after the rubber bag 1 is separated from the deep cavity mold 5, the rubber block 4 rebounds upward to realize automatic unloading of the transition state part 6.

[0032] In one implementation of the embodiment of the present invention, the method of removing the deep cavity sheet metal part 13 in step 4 is: By selecting the shaping rubber block 14 with a larger surface roughness, after the rubber bag 1 is separated from the deep cavity mold 5, the shaping rubber block 14 expands and generates upward friction with the deep cavity sheet metal part 13, thereby realizing automatic unloading.

[0033] The present invention provides a rubber bladder step-by-step hydraulic forming method for deep-cavity sheet metal parts, comprising: step 1, constructing an expanded blank 3, a deep-cavity mold 5, and a rubber block 4, wherein the inner surface 8 of the constructed deep-cavity mold is the same as the theoretical outer surface 7 of the deep-cavity sheet metal part; step 2, placing the deep-cavity mold 5 on a rubber bladder hydraulic press, placing the rubber block 4 in the deep cavity of the deep-cavity mold 5, placing the expanded blank 3 to be formed on the inner surface 8 of the deep-cavity mold, placing the rubber bladder 1 in contact with the upper end surface of the expanded blank 3, pressurizing and filling the rubber bladder 1 with oil 2, and performing hydraulic preforming of the rubber bladder, and then forming the expanded blank 3 into a transitional part through the hydraulic preforming. The transitional part 6 is formed into a molded part 6; in step 3, the transitional part 6 and the rubber block 4 are removed, and the transitional part 6 obtained by the first rubber bladder hydroforming is placed in the deep cavity of the deep cavity mold 5, and the shape correction rubber block 14 is placed in the cavity of the transitional part 6; in step 4, the rubber bladder 1 is placed in a close fit on the upper end surface of the transitional part 6, with the shape correction rubber block 14 located between the transitional part 6 and the rubber bladder 1, and the rubber bladder 1 is pressurized and filled with oil 4. The transitional part 6 is subjected to rubber bladder hydraulic correction by the rubber bladder 1 and the shape correction rubber block 14 to obtain a formed deep cavity sheet metal part 13, and the shape correction rubber block 14 and the deep cavity sheet metal part 13 are removed. The rubber bladder step-by-step hydroforming method provided by the present invention adopts the above-mentioned step-by-step hydroforming process and has the following beneficial effects: First, it effectively avoids the problem of complex mold structure, difficult design, and high manufacturing cost caused by the small drawing coefficient and large depth of deep-cavity parts, which requires multi-pass drawing and the design of multiple sets of drawing dies. The forming process provided by the present invention uses a simple rubber bladder hydraulic mold for step-by-step hydraulic forming, reducing mold costs. Second, by designing a combined tool for the stepwise hydroforming of the rubber bladder, a simple, low-cost rubber block 4 is incorporated into the tool to control the hydroforming height, thereby resolving the problem of exceeding the forming limit of the rubber bladder during the forming of sheet metal parts with deep cavities, which can lead to rupture of the rubber bladder. The forming process provided by the present invention has significant practical value. Furthermore, the volume of the rubber block 4 used for each hydroforming step decreases with each successive hydroforming step. Third, the technical solution provided by the present invention adopts an equal volume conversion method to calculate the required volume of the rubber block 4 in each hydraulic preforming process, accurately controlling the hydraulic height at each stage of the distributed hydraulic process, thereby reducing a large amount of trial and error costs; Fourth, the technical solution provided by the present invention also provides an automatic unloading method after hydraulic forming. By selecting appropriate rubber block 4 materials, the formed deep cavity sheet metal part 13 can be automatically popped out after hydraulic forming, which solves the problem of traditional manual unloading, which requires manual operation and a large workload, reduces the working hours in the production process, and improves production efficiency.

[0034] Implementation example: As shown in FIG8 below, the specific manner of performing the rubber bladder hydraulic preforming multiple times in step 2 of the step-by-step hydraulic forming method of the rubber bladder of the deep cavity sheet metal part provided by the above embodiment of the present invention is schematically illustrated: Step K-1: First hydraulic preforming of the rubber bladder; According to steps S1-S3, the theoretical outer surface 7 of the deep cavity sheet metal part is imported into the 3D modeling software, α1, β1, H1, and h1 are constructed, the rubber block 4 is constructed, and the first rubber bladder hydraulic preforming is performed to obtain the transitional state part 6; At this time, it is noticed that the forming height H1 is too small. If the rubber bag is hydraulically shaped directly with the shaping rubber block 14, the risk of part tearing will be too high due to the hydraulic shaping height h1 being too high, and a second rubber bag hydraulic pre-forming is required.

[0035] Step K-2: Second rubber bladder hydraulic preforming; Steps S1-S3 are still executed. In this case, the expanded blank 3 in step S2 needs to be replaced with the transitional part 6 obtained in K-1. The forming height H2 with the lowest thinning amount is selected to obtain α2 and β2. The height h2 is adjusted based on the height H2 so that the total height of the deep cavity sheet metal part = H2 + h2. At this time, H2>H1 and h2 The process mold β2 is offset into the theoretical outer surface 7 of the deep cavity sheet metal part, and the offset surface is filled into a solid. Another rubber block 4 is selected, and the volume of the rubber block 4 is equal to the volume of the solid, and the second rubber bag hydraulic preforming is performed.

[0036] Then, steps 3 and 4 are performed to obtain the deep cavity sheet metal part 13 .

[0037] Although the embodiments disclosed herein are as described above, the contents are merely provided to facilitate understanding of the present invention and are not intended to limit the present invention. Any person skilled in the art may make any modifications and variations in the form and details of the embodiments without departing from the spirit and scope of the present invention. However, the scope of patent protection of the present invention shall remain subject to the scope defined by the appended claims.​

Claims

1. A step-by-step hydraulic forming method for a rubber bladder of a deep cavity sheet metal part, characterized in that , including the following steps: Step 1: constructing a developed blank 3, a deep cavity mold 5, and a rubber block 4; wherein the inner surface 8 of the constructed deep cavity mold is the same as the theoretical outer surface 7 of the deep cavity sheet metal part; Step 2: Place the deep cavity mold 5 on the rubber bladder hydraulic press, place the rubber block 4 in the deep cavity of the deep cavity mold 5, place the expanded blank 3 to be formed on the inner surface 8 of the deep cavity mold, and place the rubber bladder 1 on the upper end surface of the expanded blank 3. Pressurize and fill the rubber bladder 1 with oil 2 to perform hydraulic preforming of the rubber bladder, and then hydraulically preform the expanded blank 3 into a transitional part 6; Step 3: After the rubber bladder is hydraulically preformed, the transitional part 6 and the rubber block 4 are removed, and the transitional part 6 obtained by the first rubber bladder hydraulic forming is placed in the deep cavity of the deep cavity mold 5, and the correction rubber block 14 is placed in the cavity of the transitional part 6; Step 4: The rubber bladder 1 is placed on the upper end surface of the transition state part 6, and the shaping rubber block 14 is located between the transition state part 6 and the rubber bladder 1. The rubber bladder 1 is pressurized and filled with oil 4. The rubber bladder 1 and the shaping rubber block 14 are used to hydraulically shape the transition state part 6 to obtain a formed deep cavity sheet metal part 13, and the shaping rubber block 14 and the deep cavity sheet metal part 13 are removed.

2. The method for hydraulically forming a rubber bladder for a deep cavity sheet metal part according to claim 1, characterized in that: The specific construction process of the unfolded blank 3, deep cavity mold 5 and rubber block 4 in step 1 includes: Step 1-1: construct unfolded blank 3; The theoretical outer surface 7 of the deep cavity sheet metal part is imported into the finite element analysis software, and the blank inverse calculation function is used to calculate the unfolded shape of the hydroformed blank to obtain the outer edge line of the unfolded blank 3; Determine the size of the unfolded blank according to the outer edge line of the unfolded blank 3; Step 1-2: constructing a deep cavity mold 5; The deep-cavity mold 5 adopts a concave mold structure. The inner surface 8 of the deep-cavity mold is the theoretical outer surface 7 of the deep-cavity sheet metal part. The outer edge line of the unfolded blank 3 is projected onto the corresponding position of the deep-cavity mold working surface 9 to obtain the unfolded blank outer contour line 10 on the deep-cavity mold 5. The deep-cavity mold working surface 9 is adjusted according to the unfolded blank outer contour line 10 so that the overall outer edge size of the adjusted deep-cavity mold working surface 9 is larger than the unfolded blank outer contour line 10. Steps 1-3: Construct the rubber block; The rubber block 4 adopts a rectangular parallelepiped structure, and the outer edge of the lower end surface of the rubber block is tangent to the inner surface 8 of the deep cavity mold.

3. The method for hydraulically forming a rubber bladder for a deep cavity sheet metal part according to claim 2, characterized in that: The method of adjusting the deep cavity mold working surface 9 according to the unfolded blank outer contour line 10 in step 1-2 includes: Determine whether the distance between the outer edge line of the unfolded blank 3 and the outer contour of the deep cavity mold working surface 9 at each circumferential position is the same, and the distance between the two is ≥80mm; if not, adjust the deep cavity mold working surface 9 to meet the above conditions.

4. The method for hydraulically forming a rubber bladder of a deep cavity sheet metal part according to claim 2, wherein: The deep cavity mold 5 constructed in steps 1-2 further includes: The deep cavity mold working surface 9, the deep cavity entrance fillet 11 and the deep cavity mold inner surface 8 are mirror polished; A vent hole 12 is provided at the lowest point of the inner surface 8 of the deep cavity mold, the diameter of the vent hole is φ10, and the vent hole passes through the deep cavity mold 5; The deep cavity mold 5 is made of 45# steel with a heat treatment temperature of HRC45-48.

5. The method for hydraulically forming a rubber bladder of a deep cavity sheet metal part according to claim 1, characterized in that: The number of hydraulic preforming of the rubber bladder in step 2 is at least 1, and the number of hydraulic preforming is set according to the theoretical outer surface 7 of the actual deep-cavity sheet metal part. By selecting the forming height H and reducing the volume of the rubber block 4 in sequence, multi-pass controllable hydraulic preforming is achieved; wherein, the volume of the rubber block 4 used for the first hydraulic preforming of the rubber bladder is the largest, and the volume of the rubber block 4 used for each subsequent hydraulic preforming of the rubber bladder decreases in sequence.

6. The method for hydraulically forming a rubber bladder of a deep cavity sheet metal part according to claim 5, characterized in that: In step 2, the forming height H of each hydraulic preforming is an adjustable parameter. The calculation method of the forming height H includes: Step S-1: constructing a process mold; Import the theoretical outer surface 7 of the deep cavity sheet metal part into the 3D modeling software, select the lowest point Q of the deep cavity sheet metal part during hydroforming, and select a plane at a preset height h upward from point Q to establish the theoretical outer surface 7 of the deep cavity sheet metal part. This plane is used to cut the theoretical outer surface 7 of the deep cavity sheet metal part to establish the process mold α and process mold β of the deep cavity sheet metal part. Step S-2: constructing a process die; The process die is constructed with the process mold shape α as the inner surface. The unfolded blank 4 and the process die are imported into the finite element analysis software. The pressure P is set, the forming height H with the lowest thinning amount is selected, and the height h is adjusted based on the forming height H so that the total height of the deep cavity sheet metal part = H + h.

7. The method for hydraulically forming a rubber bladder of a deep cavity sheet metal part according to claim 6, characterized in that: In step 2, during each hydraulic preforming process, the calculated forming height H is controlled by adjusting the height of the rubber block 4. The process is as follows: The height A of the rubber block is calculated using the equal volume conversion method, and the process mold β is offset into the theoretical outer surface 7 of the deep cavity sheet metal part. The offset gap is g = (0.95 ~ 1.0) × δ; Where δ is the material thickness of the deep cavity sheet metal part; Fill the offset surface into a solid. The volume of the rubber block 4 is equal to the volume of the solid. The height of the rubber block is A=V / S. Wherein, V is the volume of the rubber block 4, and S is the lower surface area of the rubber block 4.

8. The method for hydraulically forming a rubber bladder of a deep cavity sheet metal part according to claim 1, characterized in that: The method of removing the transitional state component 6 in step 3 is: By selecting a rubber block 4 with high elasticity, after the rubber bag 1 is separated from the deep cavity mold 5, the rubber block 4 rebounds upward to realize automatic unloading of the transition state part 6.

9. The method for hydraulically forming a rubber bladder of a deep cavity sheet metal part according to claim 1, characterized in that: The method for removing the deep cavity sheet metal part 13 in step 4 is: By selecting the shaping rubber block 14 with a larger surface roughness, after the rubber bag 1 is separated from the deep cavity mold 5, the shaping rubber block 14 expands and generates upward friction with the deep cavity sheet metal part 13, thereby realizing automatic unloading.

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