A method for suppressing springback in curvature skin rubber stretch composite molding

Abstract

This invention discloses a method for suppressing springback in the composite forming of curved skin using rubber stretching. The process involves manufacturing a rubber forming and cutting mold, which includes: constructing a curved skin transition forming body according to the rubber forming and cutting mold; constructing an unfolded blank model according to the transition forming body; cutting the blank according to the unfolded dimensions of the unfolded blank model to obtain the unfolded blank; performing rubber forming on a rubber bladder / pad hydraulic press; and filing the cut edges of the curved skin to ensure smooth and streamlined edges. This method allows for reverse material storage in advance when designing the curved blank for parts with large curvature, preventing material thinning from exceeding tolerances. It indirectly controls the material stretching amount through a formula method, thereby eliminating springback through material stretching deformation and material thinning. This method has a complete design concept and can guide the design of similar curved skin forming, exhibiting strong versatility.

Description

Technical Field

[0001] This invention relates to a sheet metal parts forming technology in the field of aircraft manufacturing, specifically a method and forming mold for suppressing springback in rubber stretching composite forming of thin-walled aluminum alloy multi-curvature skin structural parts. Background Technology

[0002] Rubber forming is a precision sheet metal forming technology that utilizes the flow characteristics of high-pressure oil and rubber to form sheet metal. Rubber forming is used for a large number and variety of parts, widely distributed throughout the entire machine. However, the inherent springback problem of rubber forming severely restricts the depth and breadth of its application in production. Due to the elastic deformation of parts after rubber forming, a large amount of manual straightening is required to meet the part's shape accuracy requirements, resulting in low efficiency, high cost, and obvious hammer marks on the part surface. This contradicts the modern aerospace manufacturing enterprise's sustainable development philosophy of high quality, high efficiency, and low cost.

[0003] During rubber forming, the limited flow capacity of the rubber and the difficulty in pressing the blank edges lead to elastic deformation components in the plastic deformation of the material. After the forming force is unloaded, springback inevitably occurs due to the influence of elastic deformation and residual stress. Traditional methods rely on manual trimming after forming or designing compensation molds using a trial-and-error approach. These outdated methods have long manufacturing cycles and cannot guarantee the surface and internal quality of the parts. In recent years, a more common method is to use the springback compensation prediction function of finite element simulation in rubber forming to achieve geometric compensation of the mold. The simulation calculation results are used as the basis for manufacturing the springback compensation mold. This method is mostly applied to curved parts based on planes, calculating only the springback amount of the curved edge. The calculation amount is less than 50% of the overall part, and the compensation results are relatively accurate with small errors. However, for multi-curvature or variable curvature skin parts, since every point in rubber forming participates in springback deformation, the deformation mechanism is very complex, resulting in long simulation cycles, large errors in the springback calculation results, and extremely unsatisfactory compensation effects. Meanwhile, the above-mentioned method of calculating springback through simulation has a drawback: first, mold forming parts are manufactured according to the springback compensation profile, and then mold testing parts are manufactured according to the theoretical numerical model of the parts. This adds a set of tooling manufacturing costs and the process is relatively complicated. In addition, the number of sheet metal parts of aircraft is large, so the tooling manufacturing cost doubles, which cannot meet the overall development progress and development cost of the new aircraft.

[0004] Aircraft components, including cover skins, side skins, and fairing skins, are used to achieve functions such as shielding, support, and rectification. Due to their different installation locations, their curvature varies. The skin material is aluminum alloy, with a thickness ranging from 0.3mm to 2.0mm, and a maximum length ranging from 400mm to 2500mm. The maximum drop height H of the curvature skin is ≤200mm. The external structure includes uniform curvature, gradually changing curvature, and combinations of multiple curvatures. The design standards for these curvature skins all require strict shape specifications and a smooth surface quality. Previously, due to springback after forming, extensive finishing work was unavoidable for curvature skins. The more irregular the curvature, the greater the finishing work. Hammer marks severely affected the surface quality of the parts, leading to out-of-tolerance inspections and customer dissatisfaction. To reduce the workload of workers and improve the forming and surface quality of curvature skins, it is urgent to explore a springback-resistant forming method for curvature skins. This method should move away from relying solely on the skill level of sheet metal workers for finishing and achieve mechanized forming and application to forming molds. Summary of the Invention

[0005] To address the issues of high springback and poor surface quality after manual finishing of aluminum alloy curved skin forming, the present invention aims to provide a method for suppressing springback in curved skin rubber stretching composite forming and a forming mold.

[0006] A method for suppressing springback in curved skin rubber stretch composite forming, the specific process of which is as follows:

[0007] (a) Manufacturing a rubber forming and cutting die, the rubber forming and cutting die comprising:

[0008] A forming die body, on which there are 1 forming surface, 2 cutting surfaces and 2 blank-holding surfaces. The forming surface is located in the middle, with 1 cutting surface and 1 blank-holding surface connected in sequence on both sides. The forming surface is consistent with the outer contour surface of the curvature skin, and there is a curvature skin length boundary line set on it. The outer edge lines at the left and right ends of the forming surface are skin cutting lines, and the length L1 of the skin cutting line is greater than the length L0 of the curvature skin width boundary line; the cutting surface is perpendicular to the lower bottom surface of the forming die body, the length of the cutting surface is L1, and the width W of the cutting surface, W = 10 + 5×t, where t is the thickness of the curvature skin; the blank-holding surface includes a stretching surface, a groove surface and a compensation surface. The stretching surface is connected to and perpendicular to the cutting surface. The groove surface is arranged between the stretching surface and the compensation surface. The groove surface is composed of an inner side wall surface 21, an outer side wall surface 22 and a groove bottom surface 23. The depth B of the groove surface is B = 7 + 2×t, and the inner and outer side wall surfaces are connected to the groove bottom surface through a transition radius R0, and R0 satisfies 3×t ≤ R0 ≤ 4×t. The width N1 of the stretching surface is N1 ≥ 40mm, the width N2 of the compensation surface is N2 > 30mm, and there is a curvature blank width contour line set on the compensation surface. The stretching surface, the groove surface and the compensation surface are transitioned through a connection radius R1, and R1 ≥ 3×t. There are 2 positioning holes set on the compensation surface;

[0009] Multiple blank positioning blocks are arranged on the forming surface. The height D of the blank positioning block satisfies t < D ≤ 2×t;

[0010] Two blank-holding cover plates. The blank-holding cover plate has a convex block structure with a rectangular flat plate at the upper part and is matched with the groove surface at the lower part. The distance from the side of the convex block to the inner and outer side wall surfaces of the groove surface is 1.5×t. The value of the thickness F of the upper rectangular flat plate of the blank-holding cover plate needs to satisfy 10mm ≤ F < W. The length of the upper rectangular flat plate of the blank-holding cover plate is the same as the length of the groove surface. The distance J1 between the inner contour surface of the rectangular flat plate and the cutting surface is J1 ≥ 20mm. The distance J2 between the outer contour surface of the rectangular flat plate and the outer side wall surface of the groove surface is J2 ≥ 30mm. Each blank-holding cover plate is provided with a through hole corresponding to the positioning hole on the compensation surface and is fixedly connected to the forming die body through a connecting pin;

[0011] (b) Construct a curvature skin transitional forming body according to the rubber forming cutting die;

[0012] (c) Construct an unfolded blank model according to the transitional forming body;

[0013] (d) Cut the material according to the unfolded size of the unfolded blank model to obtain an unfolded blank;

[0014] (e) Perform rubber forming on a rubber bladder / pad hydraulic press;

[0015] (f) File and repair the cutting edge of the curvature skin to ensure the smooth streamline of the curvature skin edge.

[0016] Preferably, the surface of the transition forming body is consistent with the outer surface of the rubber forming cutting die forming die body. The distance between the two outer boundary lines of the transition forming body and the outer contour surface of the upper rectangular flat plate of the blank holder cover plate is 3-5 mm. The two outer boundary lines of the transition forming body are consistent with the curvature blank width contour line on the compensation surface of the forming die body. The overall unfolded length P0 of the transition forming body = P1 + 2×(W + N1 + J2 + 2×B + V + Δ), where P1 is the unfolded length of the curvature skin, V is the groove width of the groove surface, and Δ = 3-5 mm.

[0017] Preferably, the process of constructing a transition forming body unfolded blank is as follows:

[0018] Construct a curvature blank, the outer contour of which is consistent with the outer contour of the transition forming body, with straight sections at both ends and a curvature section in the middle. The straight sections and the curvature section are smoothly transitioned. The radius of curvature R of the curvature section m is determined according to the maximum drop height H of the curvature skin. When the drop height H ≤ 80 mm, the radius of curvature R m has a value range of R m > 1300 mm. When the drop height 80 mm < H ≤ 150 mm, the radius of curvature R m has a value range of 1000 mm ≤ R m ≤ 1300 mm. When the drop height 150 mm < H ≤ 200 mm, the radius of curvature R m has a value range of 800 mm ≤ R m ≤ 1000 mm;

[0019] Obtain an unfolded blank, the shape of which is consistent with the unfolded shape of the curvature blank, with a length of P2. After forming, the material thickness reduction rate The reduction rate k satisfies 5% ≤ k ≤ 15%.

[0020] Preferably, when calculating the reduction rate k, when the reduction rate k does not satisfy 5% ≤ k ≤ 15%, adjust the values of the radius of curvature R m and the width N1 of the stretching surface. When the reduction rate k < 5%, increase the radius of curvature R m , and when the reduction rate k > 15%, it is necessary to decrease the radius of curvature R m while increasing the width N1 of the stretching surface.

[0021] Preferably, the rubber forming process on a rubber bladder / pad hydraulic press is as follows:

[0022] Quench the unfolded blank according to the design requirements, and according to the radius of curvature R of the curvature blank mRolling out a certain curvature to obtain a curvature blank;

[0023] Install the rubber forming and cutting mold, place the forming mold body stably on the hydraulic press working platform, place the curvature blank on the forming mold body according to the width outline and length boundary line on the forming mold body, the multiple blank positioning blocks on the forming mold body restrict the offset of the curvature blank in the length direction, place the two pressure plate covers on the corresponding groove surfaces, insert the connecting pins into the positioning holes on the forming mold body through the through holes on the pressure plate, and lay a 15-20mm rubber pad on the rubber forming and cutting mold and the curvature blank before forming;

[0024] The forming pressure is set according to the thickness of the curved skin material. When the material thickness is 0.3mm≤t<0.6mm, the forming pressure is 120~150bar; when the material thickness is 0.6mm≤t<1.0mm, the forming pressure is 150~200bar; when the material thickness is 1.0mm≤t<1.5mm, the forming pressure is 200~250bar; and when the material thickness is 1.5mm≤t≤2.0mm, the forming pressure is 250~300bar. The principle for selecting the forming pressure is that within the forming pressure range corresponding to the selected material thickness, when the material thickness is small, the forming pressure is small, and vice versa.

[0025] Rubber forming is performed using the optimal plasticity period of aluminum alloy in its newly quenched state. The pressure plate presses the curvature blank into the groove surface, and the connecting pin enters the positioning hole. The curvature blank is gradually pressed towards the forming mold body and adheres to the forming mold body. When the curvature blank is formed into the shape of the cutting surface and the stretching surface, under the combined action of the forming pressure and the two skin cutting lines on the mold body, the two skin cutting lines on the forming mold body cut the curvature blank to obtain the curvature skin.

[0026] The beneficial effects of this invention are as follows: 1) This invention provides a design method for a curvature skin rubber stretching and cutting die, achieving cutting function while forming rubber, maximizing the potential of the rubber bladder / pad hydraulic press, improving work efficiency, and possessing significant practical value. 2) This invention provides a method for suppressing springback in curvature skin composite forming, transforming the compressive strain portion of rubber forming into tensile strain, ensuring that the curvature skin is always subjected to significant tensile stress under the compressive stress of rubber forming, thereby eliminating springback of the part. The principle is the same as that of skin stretching, improving the fitting accuracy between the skin and the die. 3) This method provides a design method for curvature skin curvature blanks and transition forming bodies. For parts with large curvature, the curvature blank is designed with reverse material storage in advance to prevent material thinning from exceeding tolerance. The amount of material stretching is indirectly controlled through a formula method, achieving the purpose of eliminating springback through material stretching deformation and material thinning. 4) This method describes in detail the curvature skin process design process and die design key points, with a complete design concept that can guide the forming design of similar curvature skins, exhibiting strong versatility.

[0027] The present application will be further described in detail below with reference to the accompanying drawings of the embodiments. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the curvature skin structure.

[0029] Figure 2 This is a schematic diagram of a rubber stretching and cutting die structure.

[0030] Figure 3 This is a schematic diagram of the pressure plate and forming mold body structure.

[0031] Figure 4 This is a schematic diagram of a transitional form body structure.

[0032] Figure 5 This is a schematic diagram of the corresponding structure between the curvature blank and the transition formed body.

[0033] Figure 6 This is a schematic diagram of the corresponding structure of the unfolded blank and the curvature blank.

[0034] Figure 7 This is a schematic diagram of the assembly relationship between the curvature blank and the forming mold.

[0035] Figure 8 This is a schematic diagram of the results of rubber stretching composite molding.

[0036] Figure 9 This is a schematic diagram of the corresponding structure of the curvature skin and the tension compensator.

[0037] Numbering in the diagram: 1. Curvature skin, 2. Outer surface, 3. Length boundary line, 4. Width boundary line, 5. Rubber forming cutting die, 6. Forming die body, 7. Pressure plate, 8. Forming surface, 9. Cutting surface, 10. Pressure surface, 11. Protrusion, 12. Inner contour surface, 13. Outer contour surface, 14. Through hole, 15. Connecting pin, 16. Skin cutting line, 17. Blank positioning block, 18. Stretched surface, 19. Groove surface, 20. Compensation surface, 21. Inner wall surface, 22. Outer wall surface, 23. Groove bottom surface, 24. Rectangular plate, 25. Curvature blank, 26. Width contour line, 27. Positioning hole, 28. Transition forming body, 29. Unfolded blank, 30. Stretched compensation body, 31. Curvature segment, 32. Straight segment Detailed Implementation

[0038] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0039] Referring to the accompanying drawings, the aircraft curvature skin design provided in the embodiments is as follows: Figure 1 As shown, the curvature skin 1 is an aluminum alloy sheet part with a certain curvature. It possesses different curvatures to achieve functions such as shielding, support, and aerodynamics on the aircraft. The material thickness t of the curvature skin 1 ranges from 0.3mm to 2.0mm, and the maximum length varies from 500mm to 2500mm. The outer contour of the curvature skin 1 is enclosed by the length boundary line 3 and the width boundary line 4. The maximum drop height H of the curvature skin 1 is ≤200mm. Depending on the installation environment, the curvature skin 1 can have several shapes, including constant curvature, gradually changing curvature, and combinations of multiple curvatures. The biggest drawback of forming the curvature skin 1 using existing processes is its large springback and failure to adhere to the mold after forming. Manual finishing cannot guarantee forming accuracy and surface quality; the thinner the material, the more obvious the hammer marks during finishing, and the thicker the material, the greater the finishing work, which cannot meet the requirements of aircraft development schedule and quality.

[0040] like Figure 2-9 As shown, a method for suppressing springback in curved skin rubber stretching composite forming includes the following steps:

[0041] (a) Manufacturing a rubber forming and cutting die 5, the rubber forming and cutting die 5 comprising:

[0042] A forming die body 6, on which there is 1 forming surface 8, 2 cutting surfaces 9 and 2 blank holding surfaces 10. The forming surface 8 is located in the middle, and one cutting surface 9 and one blank holding surface 10 are successively connected on both sides. The forming surface 8 is consistent with the outer surface 2 of the curvature skin 1, and there is a length boundary line 3 of the curvature skin 1 on it for positioning the curvature blank 20 before forming. The outer edge lines at the left and right ends of the forming surface 8 are skin cutting lines 16, which correspond to the width boundary lines 4 at both ends of the outer surface 2 of the curvature skin 1. The length L1 of the skin cutting line 16 is greater than the length L0 of the width boundary line 4 of the curvature skin 1. The cutting surface 9 is perpendicular to the lower bottom surface of the forming die body 6. The length of the cutting surface 9 is L1, and the width W of the cutting surface 9, W = 10 + 5×t. The blank holding surface 10 includes a stretching surface 18, a groove surface 19 and a compensation surface 20. The stretching surface 18 is connected to and perpendicular to the cutting surface 9. The groove surface 19 is arranged between the stretching surface 18 and the compensation surface 20. The groove surface is composed of an inner side wall surface 21, an outer side wall surface 22 and a groove bottom surface 23. The distance between the inner side wall surface 21 and the outer side wall surface 22, that is, the width V of the groove surface 19, V = 20 - 25mm. When the material thickness is small, the width V of the groove surface 19 takes a small value, otherwise it takes a large value. The depth B of the groove surface 19 = 7 + 2×t. The inner side wall surface 21, the outer side wall surface 22 and the groove bottom surface 23 are connected by a transition radius R0, and R0 satisfies 3×t ≤ R0 ≤ 4×t. The width N1 of the stretching surface 18 ≥ 40mm, the width N2 of the compensation surface 20 > 30mm. There is a width contour line 26 of the curvature blank 25 on the compensation surface 20. The stretching surface 18, the groove surface 19 and the compensation surface 20 are transitioned by a connection radius R1, and R1 ≥ 3×t. There are 2 positioning holes 27 on the compensation surface 20. The forming die body 6 needs to be made of die steel or carbon tool steel with a hardness greater than HRC55. Taking the illustrated curvature skin 1 as an example, the material thickness t of the curvature skin 1 = 1.2mm, the length L0 of the width boundary line 4 of the curvature skin 1 = 400mm, the length L1 of the skin cutting line 16 = 450mm, the width V of the groove surface 19 = 23mm, the width N1 of the stretching surface 18 = 42mm, the width N2 of the compensation surface 20 = 43mm. After calculation, the width W of the cutting surface 9 = 10 + 5×t = 16mm, the depth B of the groove surface 19 = 7 + 2×t = 9.4mm, the transition radius R0 = 4mm, and the connection radius R1 = 4mm;

[0043] Multiple blank positioning blocks 17 are arranged on the forming surface 8. The height D of the blank positioning blocks 17 satisfies t < D ≤ 2×t. When the calculated result D < 2mm, the height of the blank positioning blocks 17 is designed with D = 2mm because a too high blank positioning block 17 is not conducive to realizing the cutting function of the forming die body 4. Taking the illustrated curvature skin 1 as an example, the height D of the blank positioning blocks 17 = 2.4mm;

[0044] Two blank holding cover plates 7, the blank holding cover plate 7 has a structure with a rectangular flat plate 24 at the upper part and a convex block 11 that fits with the groove surface 19 at the lower part. The convex block 11 is obtained by offsetting 1.5×t inward from the groove surface 19 based on the groove surface 19 as the design reference. That is, the width P of the convex block 11 = V - 2×1.5×t. By increasing the working gap between the convex block 11 and the groove surface 19, the material flow during forming becomes smoother. The thickness F of the upper rectangular flat plate 24 of the blank holding cover plate 7 should not exceed the width W of the cutting surface 9, and the value of F needs to satisfy 10mm ≤ F < W. The length of the upper rectangular flat plate 24 of the blank holding cover plate 7 is the same as the length of the groove surface 19. Denote the inner side surface of the rectangular flat plate 24 corresponding to the cutting surface 9 as the inner profile surface 12 of the rectangular flat plate 24, and denote the outer side surface of the rectangular flat plate 24 corresponding to the inner profile surface 12 of the rectangular flat plate 24 as the outer profile surface 13 of the rectangular flat plate 24. The distance between the inner profile surface 12 and the outer profile surface 13 of the rectangular flat plate 24 is the width E of the blank holding cover plate 7. The width E of the blank holding cover plate 7 needs to meet two conditions. One is that the distance J1 between the inner profile surface 12 of the rectangular flat plate 24 and the cutting surface 9 is ≥ 20mm, and the other is that the distance J2 between the outer profile surface 13 of the rectangular flat plate 24 and the outer side wall surface 22 of the groove surface 19 is ≥ 30mm. There are 2 through holes 14 corresponding to the positioning holes 27 on the compensation surface 20 on each blank holding cover plate 7. The through holes 14 are arranged in the non-curved blank area within the range of J2 and are fixedly connected to the forming die body 6 through connecting pins 15. The blank holding cover plate 7 can be made of machinable plastic or die steel. The blank holding cover plate 7 presses the curved blank 25 onto the forming die body 6 to complete the forming and cutting of the curved blank 25. Taking the illustrated curved skin 1 as an example, the thickness F of the blank holding cover plate 7 = 15mm, the width E of the blank holding cover plate 7 = 75mm, the width P of the convex block 11 = 19.4mm, J1 = 22mm, and J2 = 33mm;

[0045] (b) Construct a transitional forming body 28 of the curved skin 1 according to the rubber forming cutting die 5;

[0046] (c) Construct an unfolded blank 29 model according to the transitional forming body 28;​​​​​​​​​​​Specifically, the surface of the transition forming body 28 is consistent with the outer surface of the forming die body 6 of the rubber forming cutting die 5. The length edge line of the transition forming body 28 corresponds to the length boundary line 3 of the curvature skin 1. The two outer boundary lines of the transition forming body 28 slightly exceed the outer contour surface 13 of the upper rectangular flat plate 24 of the blank holding cover plate 7 on the rubber forming cutting die 5, and the distance between the two outer boundary lines of the transition forming body 28 and the outer contour surface 13 of the rectangular flat plate 24 is 3 - 5 mm. The two outer boundary lines of the transition forming body 28 are consistent with the width contour line 26 of the curvature blank 25 on the compensation surface 20 of the forming die body 6. The overall unfolded length P0 of the transition forming body 28 = P1 + 2×(W + N1 + J2 + 2×B + V + Δ), where P1 is the unfolded length of the curvature skin 1, and Δ = 3 - 5 mm. Taking the curvature skin 1 shown in the figure as an example, the unfolded length P1 of the curvature skin 1 = 550 mm, and Δ = 5 mm. After calculation, the overall unfolded length P0 of the transition forming body 28 = 825.6 mm.

[0051] Specifically, the process of constructing the unfolded blank 29 of a transition forming body 28 is as follows:

[0052] Construct a curvature blank 25, whose outer contour is consistent with the outer contour of the transition forming body 28. The two ends are straight sections 32, and the middle part is a curvature section 31. The curvature section 31 corresponds to the curvature skin 1. The straight section 32 and the curvature section 31 are smoothly transitioned. The curvature radius R of the curvature section 31 m has a certain relationship with the maximum drop height H of the curvature skin 1 and is determined based on the maximum drop height H of the curvature skin 1. When the drop height H ≤ 80 mm, the value range of the curvature radius R m is R m > 1300 mm. When the drop height 80 mm < H ≤ 150 mm, the value range of the curvature radius R m is 1000 mm ≤ R m ≤ 1300 mm. When the drop height 150 mm < H ≤ 200 mm, the value range of the curvature radius R m is 800 mm ≤ R m ≤ 1000 mm. Due to the existence of curvature, the curvature blank 25 can store a part of the material in the reverse direction to prevent the material thickness from thinning out of tolerance due to excessive drop during the forming of the curvature blank 25. Taking the curvature skin 1 shown in the figure as an example, it is measured that the drop height H of the curvature skin 1 = 62 mm and H < 80 mm, then the value of the curvature radius R m is R m = 1400 mm;

[0053] Obtain an unfolded blank 29, whose shape is consistent with the unfolded shape of the curvature blank 25. The length of the unfolded blank 29 is P2, and the material thickness thinning rate after forming The thinning rate k satisfies 5% ≤ k ≤ 15%; taking the curvature skin 1 shown in the figure as an example, the curvature blank 25 is flattened, and the length P2 of the unfolded blank 29 is measured to be 745mm. After calculation, the material thickness reduction rate k of the curvature skin 1 is 9.8%, which meets the requirement of 5% ≤ k ≤ 15%.

[0054] Specifically, when calculating the thinning rate k, if the thinning rate k does not satisfy 5% ≤ k ≤ 15%, the radius of curvature R is adjusted. m Regarding the value of the width N1 of the stretched surface 18, when the thinning rate k < 5%, the radius of curvature R is increased. m To make the curvature of the blank as gentle as possible, or even use a flat blank, when the thinning rate k > 15%, the radius of curvature R needs to be reduced. m At the same time, increase the width N1 of the stretching surface 18 and reasonably adjust the relevant parameters to enable the curvature blank 25 material to obtain effective lateral stretching, thereby eliminating springback and avoiding insufficient material stretching, increased elastic deformation, which would lead to increased springback, or excessive material stretching and excessive material thickness reduction rate, which would affect product quality.

[0055] Specifically, the process of forming rubber on a rubber bladder / pad hydraulic press is as follows:

[0056] The unrolled blank 29 is quenched according to the design requirements, and the curvature radius R of the curvature blank 25 is determined accordingly. m Roll out a certain curvature to obtain a curvature blank of 25;

[0057] Install the rubber forming and cutting mold 5, and place the forming mold body 6 stably on the hydraulic press working platform. Place the curved blank 25 on the forming mold body 6 according to the width outline 26 and length boundary line 3. The multiple blank positioning blocks 17 on the forming mold body 6 restrict the offset of the curved blank 25 in the length direction. Place the two pressure plates 7 on their respective groove surfaces 19. Insert the connecting pins 15 through the through holes 14 on the pressure plates 7 into the positioning holes 27 on the forming mold body 6. Because the curved blank 25 has a certain curvature, the straight sections 32 at both ends of the curved blank 25 are not parallel to the hydraulic press working platform. The initial position of the pressure plates 7 has a certain tilt angle with the forming mold body 6. The tilt angle is determined by the radius of curvature R of the curved section 31 of the curved blank 25. m The effect of the radius of curvature R mThe greater the curvature, the gentler the slope, and the smaller the tilt angle. Conversely, the larger the tilt angle, the more likely it is to affect the positioning between the pressure plate 7 and the forming mold 6 when the tilt angle is greater than 30°. This can be achieved by manually correcting the straight sections 32 at both ends of the curvature blank 25 to ensure that the protrusion 11 of the pressure plate 7 enters the groove surface 19 of the forming mold 6 normally during forming. Before forming, a 15-20mm rubber pad with a hardness of 60A-65A is laid on the rubber forming and cutting mold 5 and the curvature blank 25. This serves to protect the equipment and increase the forming pressure.

[0058] The forming pressure is set according to the material thickness of the curvature skin 1. When the material thickness is 0.3mm≤t<0.6mm, the forming pressure is 120~150bar; when the material thickness is 0.6mm≤t<1.0mm, the forming pressure is 150~200bar; when the material thickness is 1.0mm≤t<1.5mm, the forming pressure is 200~250bar; and when the material thickness is 1.5mm≤t<2.0mm, the forming pressure is 250~300bar. The principle for selecting the forming pressure is that within the forming pressure range corresponding to the selected material thickness, when the material thickness is small, the forming pressure is small, and vice versa. Taking the curvature skin 1 shown in the figure as an example, the forming pressure of the rubber with a curvature blank of 25 is 220bar.

[0059] The curvature blank 25 is rubber-formed using the optimal plasticity period of the newly quenched aluminum alloy. At the start of forming, the pressure plate 7 presses the curvature blank 25 into the groove surface 19 of the forming mold 6. The connecting pin 15 is pressed into the positioning hole 27 of the forming mold 6. The curvature blank 25 is gradually pressed towards and adheres to the forming mold 6. When the curvature blank 25 forms the shape of the cutting surface 9 and the stretching surface 10, under the combined action of the forming pressure and the two skin cutting lines 16 on the forming mold 6, the two skin cutting lines 16 on the forming mold 6 cut the curvature blank 25. At the end of forming, one curvature skin 1 and two stretching compensators 30 are obtained. After stretching and pressing, the curvature skin 1 adheres to the forming mold 6, eliminating springback defects and meeting the assembly surface tolerance requirements.

[0060] Several points need to be noted: The curvature skin structure provided in the embodiment is relatively regular. This curvature skin rubber forming and cutting method is also applicable to variable curvature and irregular skin forming, with the same design concept. However, it is necessary to ensure that the width boundary line of the implemented curvature skin is straight. When forming this type of curvature skin rubber, the workbench of the equipment should not simultaneously place a mold with a height greater than that of this type of curvature skin rubber stretching and cutting mold, otherwise it will affect the curvature skin forming quality and cutting effect. All dimensions mentioned in this invention are in millimeters (mm). This invention involves both forming and cutting, so the forming mold rubber cutting line needs to have sufficient hardness and wear resistance. If the parts are produced in large batches, the forming mold rubber cutting line part can be made into an inlaid hard alloy to solve the problem of the mold being severely worn due to excessive use and unable to be repaired. According to the aircraft sheet metal technical manual, the rubber forming material is allowed to be... The material thickness reduction rate should not exceed 20% of the raw material thickness. Based on practical experience, a material thickness reduction rate within the range of 5% to 15% can effectively suppress springback. The calculation formula for the unfolded length P0 of the transition formed body described in this invention does not consider the size of the transition radius R0 and the connection radius R1, because the values ​​of the transition radius R0 and the connection radius R1 have too little impact on the overall unfolded length P0 and can be ignored. This invention utilizes the optimal plasticity period of aluminum alloy in the newly quenched state for rubber forming. After quenching, aluminum alloy can maintain high plasticity at room temperature for a period of time, but this time will not be too long. In order to make full use of the optimal plasticity period of aluminum alloy, rubber forming requires advance preparation, such as mold placement, etc. Otherwise, the quenched aluminum alloy sheet needs to be placed in a refrigerator for low-temperature storage to maintain the good plasticity of the aluminum alloy in the newly quenched state.

[0061] This specification uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for suppressing springback in curved skin rubber stretching composite forming, characterized in that... (a) Manufacturing a rubber forming and cutting die, the rubber forming and cutting die comprising: A forming mold body includes one forming surface, two cutting surfaces, and two pressing surfaces. The forming surface is located in the middle, with one cutting surface and one pressing surface connected sequentially on each side. The forming surface is consistent with the outer surface of the curvature skin and has a curvature skin length boundary line on it. The outer edges of the left and right ends of the forming surface are skin cutting lines, and the length of the skin cutting lines is... The length of the curvature skin width boundary line is greater than the length of the curve skin width boundary line. The cut surface is perpendicular to the bottom surface of the forming mold, and the length of the cut surface is... The width of the cut surface , , The thickness of the curvature skin; the pressing surface includes a stretching surface, a groove surface and a compensation surface, the stretching surface is connected to and perpendicular to the cutting surface, the groove surface is disposed between the stretching surface and the compensation surface, the groove surface is composed of an inner wall surface (21), an outer wall surface (22) and a groove bottom surface (23), and the depth of the groove surface is... The inner and outer wall surfaces meet the bottom surface of the trench via a transition radius. connect, satisfy The width of the stretching surface The width of the compensation surface The compensation surface is provided with a curvature blank width outline, and the stretching surface, the groove surface, and the compensation surface are connected by a connecting radius. transition, The compensation surface is provided with two positioning holes; Multiple blank positioning blocks are disposed on the forming surface, and the height of the blank positioning blocks is [missing information]. , satisfy ; Two pressure plate covers, each pressure plate having a rectangular flat top and a protrusion structure at the bottom that mates with the groove surface. The distance between the side of the protrusion and the inner and outer walls of the groove surface is [missing information]. The thickness of the upper rectangular plate of the pressure cover plate The value of must satisfy The length of the upper rectangular plate of the pressure cover is the same as the length of the groove surface, and the distance between the inner contour surface of the rectangular plate and the cutting surface is... The distance between the outer contour of the rectangular flat plate and the outer wall of the groove surface Each of the pressure plate is provided with a through hole corresponding to the positioning hole on the compensation surface, and is fixedly connected to the forming mold body by a connecting pin; (b) Construct a curvature skin transition body according to the rubber forming and cutting mold, wherein the distance between the two outer boundary lines of the transition body and the outer contour of the upper rectangular plate of the pressure plate is... The outer boundary lines of the transition forming body are consistent with the width contour line of the curvature blank on the compensation surface of the forming mold body, and the overall unfolded length of the transition forming body is... ,in The curvature skin unfolded length. The width of the groove surface is [the width of the groove]. ; (c) The blank model is developed according to the transitional forming body structure. The specific process is as follows: Construct a curvature blank whose outer contour matches the outer contour of the transition forming body, with straight sections at both ends and a curvature section in the middle. The straight sections and the curvature section transition smoothly, and the radius of curvature of the curvature section is... Based on the maximum drop height of the curvature skin Determined, when the drop height When, radius of curvature The range of values ​​is When the drop height When, radius of curvature The range of values ​​is When the drop height When, radius of curvature The range of values ​​is ; A unfolded blank is obtained, the shape of which is consistent with the unfolded shape of the curvature blank, and the length is... Material thickness reduction rate after forming Thinning rate satisfy ; (d) Cut the blank according to the unfolded dimensions of the unfolded blank model to obtain the unfolded blank; (e) Rubber forming on a rubber bladder / pad hydraulic press; (f) File and trim the edges of the curved skin to ensure that the edges of the curved skin are smooth and streamlined.

2. The method for suppressing springback in curved skin rubber stretching composite forming according to claim 1, characterized in that... In calculating the aforementioned thinning rate When the thinning rate Not satisfied When adjusting the radius of curvature and stretching surface width The value of , when the thinning rate When the radius of curvature is increased When the thinning rate At this time, it is necessary to reduce the radius of curvature. At the same time, increase the width of the stretching surface. .

3. The method for suppressing springback in curved skin rubber stretching composite forming according to claim 2, characterized in that... The specific process of rubber forming on a rubber bladder / pad hydraulic press is as follows: The unrolled blank is quenched according to the design requirements, and the curvature radius of the blank is determined according to the stated curvature. Rolling out a certain curvature to obtain a curvature blank; Install the rubber forming and cutting mold, place the forming mold body stably on the hydraulic press working platform, and place the curvature blank on the mold body according to the width outline and length boundary line on the forming mold body. The multiple blank positioning blocks on the forming mold body restrict the offset of the curvature blank in the width direction. Place the two pressure plates on the corresponding groove surfaces, and insert the connecting pins into the positioning holes on the forming mold body through the through holes on the pressure plates. Before forming, cover the rubber forming and cutting mold and the curvature blank with a layer of... Rubber pad; The forming pressure is set according to the curvature and thickness of the skin material. At that time, the forming pressure is When the material thickness At that time, the forming pressure is When the material thickness At that time, the forming pressure is When the material thickness At that time, the forming pressure is The principle for determining the forming pressure is that within the range of forming pressure corresponding to the selected material thickness, when the material thickness is small, the forming pressure should be small, and vice versa. Rubber forming is performed using the optimal plasticity period of aluminum alloy in its newly quenched state. The pressure plate presses the curvature blank into the groove surface, and the connecting pin enters the positioning hole. The curvature blank is gradually pressed towards the forming mold body and adheres to the forming mold body. When the curvature blank is formed into the shape of the cutting surface and the stretching surface, under the combined action of the forming pressure and the two skin cutting lines on the mold body, the two skin cutting lines on the forming mold body cut the curvature blank to obtain the curvature skin.

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