A method for deep drawing and forming control of stainless steel deep U-shaped thick skin for ship assembly and forming die

Abstract

This invention belongs to the field of aircraft manufacturing technology and discloses a method for controlling the deep drawing and forming of stainless steel deep U-shaped thick skin panels. It utilizes different drawing coefficients to reverse-calculate key dimensions of the deep-drawn parts, controlling the degree of deformation in each part. This solves the technical problems of insufficient blank size in stainless steel deep U-shaped thick skin panels, easy instability and wrinkling during forming, and large springback after forming. Addressing the different load-bearing strengths of various parts of the welded blank, it details the key design points of the deep drawing die structure, including the gap between the punch and die, the blank holder gap, and the gap between the draw bead and the draw groove. The design concept is complete and can guide the design of similar die structures, exhibiting strong versatility.

Description

Technical Field

[0001] This invention application belongs to the field of sheet metal parts forming technology in aircraft manufacturing, specifically relating to a method and forming mold for suppressing instability in composite forming of welded deep drawing of thick stainless steel deep U-shaped boat skin. Background Technology

[0002] Aircraft skin components are mostly made of aluminum alloy to meet the overall lightweight design requirements of the aircraft. However, during flight, some skin components need to withstand significant aerodynamic forces and transmit these forces to the connected fuselage and wing frames. For this reason, stainless steel skin is designed and used due to its high strength and good plasticity. Typically, the thickness of stainless steel skin components in aircraft is ≤1.0mm. Replacing thicker aluminum alloy skin with thinner stainless steel skin can compensate for the significant weight difference between the different materials.

[0003] In aircraft design and maintenance, some components require greater load-bearing capacity and special application functions such as temperature resistance, corrosion resistance, and resistance to long-term fatigue stress. Stainless steel skin with a thickness greater than 1.0mm is the preferred replacement material due to its superior strength and toughness, enabling it to maintain the integrity of the aircraft structure under high-speed flight or extreme weather conditions. Furthermore, its relatively low manufacturing cost makes it the preferred material for replacement. Domestically, the stainless steel cold-rolled sheet used in aviation is ≤4.0mm thick, with a sheet width of 1m and a length of 2m. This illustrates that the size of stainless steel sheet metal parts for aircraft is not the primary design goal; weight is more crucial to the aircraft's flight performance.

[0004] The stainless steel skin of the aircraft thumb guard has a material thickness t within the range of 1.5mm≤t≤3.5mm. The part has a deep U-shaped cross-section and presents an overall boat-shaped structure with a certain arch height. The depth of such parts is ≥350mm, the arc length of the outer contour of the boat bottom is <1m, the percentage of the projected length of the outer contour of the boat bottom to its theoretical arc length is in the range of 90% to 97%, the maximum dimension of the U-shaped cross-section is >1m, the ratio of the depth of the U-shaped skin to the width between its two side walls is close to 1:1, and the maximum chord height of the outer contour of the boat bottom is in the range of 90mm to 150mm. The characteristic of this type of skin part is that the boat-shaped outer contour has a certain curvature and an arc length of nearly 1m. If traditional stamping is used, since the blanks at both ends of the skin are not subjected to longitudinal tensile stress during forming, uniform shrinkage deformation cannot be achieved. The excess material at the largest cross section in the middle will inevitably become unstable and wrinkle. The greater the curvature of the outer contour at the bottom of the boat shape, the earlier the wrinkles occur. If deep drawing is used, the required blank size width must be >1m, otherwise edge pressing cannot be achieved, while the maximum width of stainless steel plate is only 1m. If skin drawing is used, on the one hand, this type of stainless steel skin material is relatively thick and has a large chord height, which can easily lead to fatigue failure under alternating loads. On the other hand, the process allowance on one side of the skin horizontal drawing is at least about 400mm, and there is still a problem of limited blank size that cannot be formed.

[0005] By combining the advantages and disadvantages of existing processes, we explore a deep drawing and shaping method for stainless steel deep U-shaped thick skin, which overcomes the technical bottleneck of thumb cover skin forming and achieves wrinkle suppression and springback control in the deep drawing of complex parts. Summary of the Invention

[0006] This invention application addresses the technical problems of insufficient size in stainless steel deep U-shaped thick skin blanks, easy instability and wrinkling during forming, and large springback after forming. It proposes a method for controlling the shape of stainless steel curvature skin through welding and deep drawing composite forming, as well as a forming mold.

[0007] To achieve the aforementioned objectives, the technical solution adopted in this application is as follows:

[0008] A method for controlling the deep drawing shape of stainless steel deep U-shaped thick skin panels, the specific steps of which are as follows:

[0009] Step 1: Construct a U-shaped skin deep drawing part. The deep drawing part is designed according to the U-shaped skin theory. The deep drawing part includes:

[0010] The main forming surface is a boat-shaped extension surface that matches the outer surface of the U-shaped skin. The consistency between the main forming surface and the outer surface of the U-shaped skin is determined by the material thickness t of the U-shaped skin. The main forming surface and the outer surface of the U-shaped skin maintain a certain outward offset b. The offset b increases with the increase of material thickness. When the offset b = 0, it means that the main forming surface is consistent with the U-shaped skin outer surface. The main forming surface of the U-shaped skin is actually a springback compensation surface that takes into account the springback after forming. The offset b is the springback amount. The offset b is not a fixed value and can be revised according to the shape and structure of the U-shaped skin.

[0011] The anti-wrinkle surface is a doorway-shaped plane that matches the shape of both ends of the main forming surface.

[0012] The transition rounded corner surface is an arched curved surface formed by the smooth connection of the anti-wrinkle surface and the main forming surface through a large corner radius R. The transition rounded corner surface connects the two anti-wrinkle surfaces and the main forming surface into a semi-closed compartment. The initial sealing surface is the sealing surface at the opening of the semi-closed compartment.

[0013] The flange face is an annular curved surface that runs in the opposite direction to the curvature of the U-shaped skin and matches the opening size of the semi-enclosed chamber. It is obtained by bending, extending and shearing the initial sealing surface. The initial sealing surface is gently bent in the opposite direction to the curvature of the U-shaped skin. The curved sealing surface extends outward by 50-60mm. The extended curved sealing surface cuts the semi-enclosed chamber into a die chamber. The semi-enclosed chamber cuts the extended curved sealing surface into an annular curved surface, i.e., the flange face. The flange face and the die chamber are connected by the die fillet radius R1 to form the deep drawing part.

[0014] The criterion for determining whether the offset b needs revision is related to the structural dimensions of the U-shaped skin. The width of the opening between the two side walls in the middle of the U-shaped skin is denoted as w, and the cross-sectional dimension in the middle of the U-shaped skin is denoted as l. j Criteria for determining whether to revise When m h When ≥0.55, the main forming surface is according to Perform offset when m h When the value is less than 0.55, the main forming surface and the U-shaped skin outer surface remain consistent, and offset does not need to be considered.

[0015] The design of the outer contour dimensions of the main forming surface needs to be subject to certain restrictions. Let the arc length of the U-shaped skin boat-shaped outer contour be l0, and the arc length of the main forming surface boat-shaped outer contour be l1. l1 needs to satisfy (l0+40)≤l1≤1000. Let the maximum height of the U-shaped skin be H0, and the maximum height of the main forming surface be H1. H1 needs to satisfy (H0+20)≤H1≤(H0+50).

[0016] Based on the opening length l of the semi-enclosed cabin c The tilt angle of the anti-wrinkle surface is optimized to improve the manufacturability of the deep-drawing parts. The anti-wrinkle surface is divided into initial anti-wrinkle surface and optimized anti-wrinkle surface according to the criteria for optimization. The height of the initial anti-wrinkle surface is denoted as H2. The formula for determining whether the anti-wrinkle surface needs optimization is as follows: When m z When m > 0.6, there is no need to optimize the initial anti-wrinkle surface tilt angle; the initial anti-wrinkle surface is the anti-wrinkle surface itself. z When the value is ≤0.6, the initial anti-wrinkle surface needs to be tilted outward at a certain angle θ to obtain the optimized anti-wrinkle surface, so as to reduce the forming height of the end of the deep drawing process. The optimized anti-wrinkle surface is the anti-wrinkle surface mentioned above.

[0017] The initial anti-wrinkle surface is tilted outwards by a distance denoted as l. b , l b =H2×sinθ, as described above, the initial semi-enclosed cabin structure with straight arms at both ends is optimized into a semi-enclosed cabin structure with inclined arms at both ends. The optimized semi-enclosed cabin opening length l z =l c +2×l b The tilt angle θ must satisfy the formula And m θ >0.6, substitute the tilt angle θ into m θ The minimum tilt angle θ can be calculated using the formula >0.6. min The range of values ​​for the tilt angle θ satisfies θ min <θ≤θ min +2°.

[0018] The value of the corner radius R of the transition fillet surface is related to the thickness t of the U-shaped skin material. It must satisfy 20×t≤R≤50×t. At the same time, when designing the value of the corner radius R, the outer contour dimension of the U-shaped skin must be taken into account. The principle is that the boundary line of the transition fillet surface cannot enter the outer contour line of the U-shaped skin, and the distance between the boundary line of the transition fillet surface and the outer contour line of the U-shaped skin must be ≥10mm.

[0019] The curvature of the sealing surface is relatively gentle, and its design principle requires that the initial sealing surface length l be satisfied. z With curvature sealing surface arc length l q The percentage n ≤ 98%, and the value of n decreases as the height H1 of the semi-enclosed cabin increases. When H1 ≤ 400mm, n = 1, and the initial sealing surface does not need to be bent in the reverse direction.

[0020] When designing the curvature of the sealing surface, the outer contour dimensions of the U-shaped skin must also be considered to ensure that the distance between the opening line of the concave mold chamber and the outer contour line of the U-shaped skin is ≥10mm.

[0021] The fillet radius R1 of the die cavity smoothly connects the flange face and the die cavity body. The value of R1 is related to the thickness t of the U-shaped skin material, and the value of R1 must satisfy 6×t. <R1≤10×t。

[0022] Step 2: Construct a U-shaped skin deep drawing process blank, including:

[0023] The U-shaped skin unfolded blank is calculated using the blank back calculation function of finite element simulation software to obtain a U-shaped skin elongated or nearly square unfolded blank. As mentioned above, the maximum length of the U-shaped skin unfolded blank is >1m and the maximum width is <1m.

[0024] The blank for the deep drawing process is developed using the blank back calculation function of finite element simulation software. The result is an oblong or near-circular blank for the U-shaped skin deep drawing process. As mentioned earlier, the maximum length and maximum width of the blank for the deep drawing process are both >1m, making it impossible to cut the complete blank shape of the deep drawing process from a standard 1m width stainless steel plate.

[0025] The welded blank is formed by laser welding three plates into a single blank with the same dimensions as the blank for the deep drawing process. The welded blank is divided into three parts by two straight weld lines: two crown-shaped compensation blanks and one drum-shaped controlled blank. The distance between the two straight weld lines is 1m, consistent with the width of conventional aerospace stainless steel plates. The shape of the U-shaped skin blank is contained within the outline of the controlled blank. After deep drawing, the welded blank becomes the deep drawing part. The two planar straight weld lines are then transformed into two three-dimensional arched weld lines. The compensation blank forms the anti-wrinkle compensation part for the deep drawing part, and the controlled blank forms the main forming part for the deep drawing part. The deep drawing part consists of two anti-wrinkle compensation parts and one main forming part. The shape of the main forming part covers the outer contour of the U-shaped skin and leaves a process allowance to avoid the welding heat-affected zone around the weld from affecting the quality of the U-shaped skin product.

[0026] Process blanks are pre-bent into blanks with curvature similar to that of the flange surface of the deep-drawing part. This reduces the pressure on the edge of the welded blank during deep drawing and compensates for the material performance degradation at the laser-welded weld seam, where the material strength is 90% of the base material strength.

[0027] Step 3: Design the drawing die structure according to the drawing process, including:

[0028] The die is designed based on the shape and structure of the part to be drawn. The die is a block structure with a deep cavity. The die blanking surface extends outward from the flange of the part to be drawn. The size of the die blanking surface is designed to include the outline of the blank of the part to be drawn. The die blanking surface is provided with longitudinal drawing grooves and transverse drawing grooves.

[0029] The blank holder, designed according to the working surface of the die, is a block structure with a certain curvature and a hollow interior. The working surface of the blank holder matches the blank holder surface of the die and the outer contour is consistent. The working surface of the blank holder is provided with the outline of the blank of the deep drawing process and its flange edge line, which are used for blank positioning and inspection of forming effect.

[0030] The punch, obtained by offsetting inward from the die cavity, has a structure corresponding to the die cavity of the deep drawing die. It is a punch structure with a relatively large height. The punch surface is divided into one arched surface and two wrapping surfaces by two corner boundary lines. The punch arched surface corresponds to the main forming surface of the die cavity and is obtained by offsetting the main forming surface inward by 1.1×t. The punch wrapping surface corresponds to the anti-wrinkle surface and its transition fillet surface of the die cavity. The punch wrapping surface is obtained by offsetting the anti-wrinkle surface and its transition fillet surface of the deep drawing part inward by 1.2×t to 1.5×t. The arched surface and the wrapping surface are smoothly connected. During forming, the two straight weld lines of the welded blank of the deep drawing part are stretched along with the punch as it moves, eventually forming two three-dimensional arched weld lines, mainly distributed in the punch wrapping surface.

[0031] A clearance control groove is set in the non-process blank area of ​​the working surface of the blank holder. The clearance control groove is located near both sides of the compensation blank, and the groove depth is 3mm. A clearance control pad matching its shape is filled in the clearance control groove. The thickness of the clearance control pad is determined based on the material flow during the test pressing of the deep drawing process. If the material flow is uniform, the clearance control pad is not needed. If the material thins significantly or even cracks during deep drawing, a clearance control pad is filled in the clearance control groove, and the thickness of the clearance control pad is h. x =3+t+Δ, where Δ ranges from 0 to 0.8 mm. The higher the H1 of the deep drawing part and the thicker the material t, the larger the value of Δ.

[0032] Longitudinal and transverse drawing ribs are provided within the outline of the blank working surface of the pressure ring. The position and length of the longitudinal and transverse drawing ribs correspond to the longitudinal and transverse edge lines of the flange edge line of the deep drawing process part, respectively. The distance between the longitudinal and transverse drawing ribs and the flange edge line of the deep drawing process part is 5mm to 10mm.

[0033] There are certain restrictions on the height of longitudinal and transverse drawbars, and the longitudinal drawbar section height h zj Satisfying formula 3.5 + t ≤ h zj ≤10, height h of transverse drawbar section hj Satisfying formula 1.5 + t ≤ h hj ≤6, and h zj ≥h hj +2. The value of the drawbead height is related to the material thickness t and the height H1 of the deep-drawing part. When the material thickness t is thicker, the drawbead height should be larger, otherwise smaller. When the height H1 is larger, the drawbead height should be smaller, otherwise larger. The value of the drawbead height can be verified by deep-drawing finite element simulation and adjusted and optimized.

[0034] The longitudinal drawing groove and the transverse drawing groove on the die blanking surface are matched with the longitudinal drawing bead and the transverse drawing bead, respectively. The gap between the longitudinal drawing groove and the longitudinal drawing bead is designed to be 1.5×t, and the gap between the transverse drawing groove and the transverse drawing bead is designed to be 1.5×t~2.0×t.

[0035] Step 4: Quickly construct a cutting fixture according to the deep drawing process.

[0036] The cutting fixture is manufactured by interlocking multiple stainless steel plates through slots or by spot welding for positioning. These stainless steel plates are functionally divided into two categories: one is a strip of stainless steel plates, typically 3-5 plates, used for positioning the workpiece during the deep-drawing process. These plates maintain the same internal shape as the cross-section of the workpiece and are distributed at the transition rounded corners and the middle section. Corner positioning plates and middle section positioning plates are designed and manufactured. The deep-drawn workpiece is held in place by these 3-5 strips of stainless steel plates to prevent movement during laser cutting. The other category is a grooved support plate used for auxiliary support and connection. These two types of stainless steel plates are interlocked through slots or spot welded together to form a simple cutting fixture. The thickness of the stainless steel plates used in the cutting fixture is in the range of 2-3 mm.

[0037] When using the slot splicing method to make cutting fixtures, only strip stainless steel plates need to be made. The slotted support plate for auxiliary support connection can be used as a universal bracket. By changing different strip stainless steel plates, different U-shaped skin laser cutting can be achieved.

[0038] Step 5: Prepare the blank for the deep drawing process.

[0039] 5-1: Weld three corresponding rectangular stainless steel plates into a whole according to the design dimensions of the blank in the deep drawing process. The gap between the two pairs of stainless steel plates should be controlled within ≤0.2mm. The welding method is laser welding. If spot welding is used for positioning or filler welding is used to repair weld defects, it is important to ensure that the thickness of the material at the weld is consistent with the thickness t of the stainless steel plate being welded. Otherwise, the uneven thickness of the material at the weld needs to be corrected by grinding.

[0040] 5-2: Based on the blank shape data of the deep drawing process, the welded stainless steel plate is laser-cut to obtain a welded blank with two straight weld lines. A plastic film is applied to the side of the welded blank opposite to the die blank. The film-coated welded blank is rolled to have a curvature consistent with the die blank to obtain the process blank of the deep drawing process.

[0041] Step 6: Perform deep drawing on a deep drawing machine.

[0042] 6-1: After assembling the punch and blank holder, connect them to the lower bed surface of the deep drawing machine. Connect the die to the upper bed surface of the deep drawing machine. The die blank holder surface corresponds to the working surface of the blank holder. The die cavity corresponds to the punch surface. There is a guide hole on each side of the die and blank holder. The deep drawing direction is positioned by the guide post on the punch base.

[0043] 6-2: Place the coated blank on the working surface of the pressure ring according to the outline of the blank on the working surface of the pressure ring;

[0044] 6-3: Lubricate the drawing die and the process blank. Apply lubricating oil to the mating surface of the process blank and the die, apply lubricating oil to the die blank pressure surface and its cavity, and apply lubricating oil to the mating area of ​​the process blank and the working surface of the blank holder.

[0045] 6-4: Place a gap control pad of appropriate thickness inside the gap control groove of the pressure ring;

[0046] 6-5: First deep drawing;

[0047] The deep drawing machine is started, and the die moves downward. When the die blanking surface touches the working surface of the blanking ring, the machine begins to apply blanking force, so that the edge area of ​​the process blank is in close contact with the die blanking surface and the working surface of the blanking ring. As the die and blanking ring move downward in sync, the process blank begins to deform under the combined action of blanking force and deep drawing force. Because the edge of the process blank bears a large blanking force and draw bead resistance, wrinkling is effectively controlled. The longitudinal and transverse draw beads of unequal height control the feed speed of the process blank into the cavity. The different gaps between the punch and die cause different tensile stresses in different areas of the process blank. The controlled blank bears a large tensile stress, the main forming part has a good die-fitting effect and small springback. The compensating blank bears a relatively small tensile stress, the weld seam bears a small amount of tensile deformation, and the compensating part has a relatively large springback. Because of the longitudinal tensile stress of the compensating blank, no material accumulation or wrinkling occurs at the edge of the main forming part. After forming, a U-shaped skin deep drawing semi-finished product is obtained.

[0048] First deep drawing height H S =H1-10, reserving a 10mm drawing height for secondary drawing and shaping, which reduces the first drawing forming height and the risk of breakage, and solves the problem of large springback due to insufficient deformation during secondary drawing and shaping.

[0049] 6-6: Solution heat treatment

[0050] In order to eliminate the large springback defect in thick stainless steel skin during deep drawing, the semi-finished products of the deep drawing process are subjected to solution heat treatment to obtain a uniform single-phase structure and eliminate the residual stress generated during the deep drawing process.

[0051] 6-7: Secondary drawing and shaping

[0052] The semi-finished product of the deep drawing process after solution heat treatment is subjected to secondary deep drawing and shaping. The 10mm deep drawing height reserved in the first deep drawing increases the amount of material tensile deformation and weakens the springback of the material.

[0053] Step 7: Perform laser cutting on a laser cutting device.

[0054] The simple cutting fixture is fixed on the working platform of the laser cutting equipment. The deep-drawing part is placed on the corner positioning plate and the middle section positioning plate of the simple cutting fixture. The U-shaped skin is cut according to the prepared laser cutting program. After removing the edge burrs, a U-shaped skin part with a streamlined shape and dimensions that meet the requirements of the drawing is obtained.

[0055] Compared with the prior art, the beneficial effects of this application are:

[0056] 1. This invention provides a design method for stainless steel deep U-shaped thick skin deep drawing parts. By constructing different drawing coefficients, the key dimensions of the deep drawing parts are calculated in reverse, the deformation degree of each part of the deep drawing parts is controlled, and the wrinkling and cracking problems of stainless steel deep cavity thick plate skin are solved.

[0057] 2. This invention provides an unconventional method for designing and manufacturing unrolled blanks. It uses laser welding of multiple blanks to solve the problem of limited width of aerospace stainless steel plates and designs the deformation trajectory of the weld from a plane to a three-dimensional shape, providing a basis for the design of mold structure gaps.

[0058] 3. This invention provides a method for suppressing springback during deep drawing of stainless steel thick plate skin. By adopting a series of measures such as external surface offset, anti-wrinkle surface design, stress relief treatment, and 10mm secondary deep drawing correction, the springback of the part is controlled and the skin molding accuracy is improved.

[0059] 4. This invention provides a four-segment drawbead design method for ship-shaped deep-drawing parts, which effectively controls wrinkling of thick stainless steel skin with large depth. Based on the structural characteristics of the deep-drawing parts, drawbeads of different heights are matched, which on the one hand avoids cracking of dangerous fracture surfaces, and on the other hand alleviates the fracture caused by the weld strength being lower than that of the base material.

[0060] 5. This invention specifies in detail the key design points of deep drawing die structure for different parts of the welded blank, including the gap between the punch and die, the blank holder gap, the gap between the draw bead and the drawing groove, etc. The design concept is complete and can guide the design of similar die structures, and has strong versatility.

[0061] The present application will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0062] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0063] In the attached diagram:

[0064] Figure 1 This is a schematic diagram of a U-shaped skin structure;

[0065] Figure 2A schematic diagram of the initial anti-wrinkle surface and the main forming surface;

[0066] Figure 3 A schematic diagram illustrating the optimized design of the anti-wrinkle surface and the main forming surface;

[0067] Figure 4 A schematic diagram of the design structure of the concave mold chamber and the flange surface;

[0068] Figure 5 This is a schematic diagram showing the corresponding structure of the deep-drawing part and the unfolded blank;

[0069] Figure 6 A schematic diagram of the structural design for the welding blank of parts used in the deep drawing process;

[0070] Figure 7 This is a schematic diagram showing the corresponding structure of the compensation component and the main forming component to the welded blank.

[0071] Figure 8 This is a schematic diagram of the deep drawing die structure;

[0072] Figure 9 Schematic diagram of the deep drawing die edge ring structure;

[0073] Figure 10 A schematic diagram of the assembly structure of the drawing die pressing ring and the punch;

[0074] Figure 11 This is a schematic diagram of a simplified laser cutting fixture.

[0075] Figure 12 This is a schematic diagram of the assembly structure of the U-shaped skin and the laser cutting fixture.

[0076] The following are the annotations in the diagram: 1. U-shaped skin; 2. Side wall surface; 3. Main forming surface; 4. Initial anti-wrinkle surface; 5. Optimized anti-wrinkle surface; 6. Semi-enclosed chamber; 7. Initial sealing surface; 8. Curvature sealing surface; 9. Flange surface; 10. Die chamber; 11. Deep drawing part; 12. U-shaped skin unfolded blank; 13. Deep drawing part unfolded blank; 14. Straight weld line; 15. Controlled blank; 16. Compensating blank; 17. Arched weld line; 18. Transition rounded corner surface; 19. Main forming part; 20. Compensating part; 21. Die. 22. Process blank outline, 23. Die blanking surface, 24. Longitudinal drawing groove, 25. Transverse drawing groove, 26. Flange edge line, 27. Longitudinal edge line, 28. Transverse edge line, 29. Blank holder, 30. Blank holder working surface, 31. Longitudinal drawing bead, 32. Transverse drawing bead, 33. Clearance control groove, 34. Clearance control pad, 35. Punch, 36. Corner boundary line, 37. Arched surface, 38. Wrapping surface, 39. Corner positioning plate, 40. Mid-section positioning plate, 41. Cutting fixture, 42. Groove support plate. Detailed Implementation

[0077] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0078] Figure 1-12 This is a schematic diagram illustrating one embodiment of the present invention.

[0079] The aircraft U-shaped skin design provided in the embodiments is as follows: Figure 1 As shown, the U-shaped skin 1 is a stainless steel boat-shaped sheet metal part with a U-shaped cross-section and a certain curvature. It has different curvatures to achieve functions such as aircraft protection, coverage, and aesthetics. The material thickness t of the U-shaped skin 1 is in the range of 1.5mm to 3.5mm, and the maximum height H0 of the part is ≥350mm. The most significant structural feature of this type of stainless steel skin is that the percentage of the projected length of the boat-shaped bottom outer contour to its theoretical arc length l1 is in the range of 90% to 97%, and the arc length l1 of the boat-shaped bottom outer contour is <1m, and the maximum dimension l of the U-shaped cross-section is... j The height H0 of the U-shaped skin 1 is greater than 1m, and the width ratio between its two side walls 2 is close to 1:1. The curvature skin 1 cannot be formed using existing aerospace stainless steel plates due to insufficient blank size. Furthermore, thicker stainless steel has high yield strength and requires greater deformation resistance. The material strength in the laser-welded weld area can only reach 90% of the strength of the base material, resulting in high forming force and easy breakage. The forming size is small and the processing accuracy is low. The development of the U-shaped skin 1 has become a bottleneck problem due to the lack of existing technology.

[0080] like Figure 2-12 As shown, a method for controlling the deep drawing shape of stainless steel deep U-shaped thick skin is disclosed, comprising the following steps:

[0081] Step 1: Construct a U-shaped skin 1 deep drawing part 11. The deep drawing part 11 is designed according to the theoretical shape of the U-shaped skin 1. The deep drawing part 11 includes:

[0082] The main forming surface 3 is a boat-shaped extension surface that matches the outer surface of the U-shaped skin 1. The consistency between the main forming surface 3 and the outer surface of the U-shaped skin 1 is determined by the material thickness t of the U-shaped skin 1. The main forming surface 3 and the outer surface of the U-shaped skin 1 maintain a certain outward offset b. The offset b increases with the increase of material thickness. When the offset b = 0, it means that the main forming surface 3 and the outer surface of the U-shaped skin 1 are consistent.

[0083] The anti-wrinkle surface is a doorway-shaped plane that matches the shape of both ends of the main forming surface 3.

[0084] The transition rounded corner surface 18 is an arched curved surface formed by the smooth connection between the anti-wrinkle surface and the main forming surface 3 through a large corner radius R. The transition rounded corner surface 18 connects the two anti-wrinkle surfaces and the main forming surface 3 into a semi-closed compartment 6. The initial sealing surface 7 is the sealing surface at the opening of the semi-closed compartment 6.

[0085] Flange surface 9 is an annular curved surface that is opposite in curvature to the U-shaped skin 1 and matches the opening size of the semi-enclosed chamber 6. It is obtained by bending, extending and shearing the initial sealing surface 7. The initial sealing surface 7 is bent gently in the opposite direction to the curvature of the U-shaped skin 1. The curved sealing surface 8 extends outward by 50-60mm. The extended curved sealing surface 8 cuts the semi-enclosed chamber 6 into a die chamber 10. The semi-enclosed chamber 6 cuts the extended curved sealing surface 8 into an annular curved surface, i.e., flange surface 9. Flange surface 9 and die chamber 10 are connected by the die fillet radius R1 to form the deep drawing part 11.

[0086] The main forming surface 3 of the U-shaped skin 1 is actually a springback compensation surface that takes into account the springback after forming. It deepens the outer surface of the U-shaped skin 1, thereby eliminating the springback after the stainless steel U-shaped skin 1 is formed. The offset b is the springback amount. The offset b is not a fixed value and can be revised according to the outer structure of the U-shaped skin 1. The criterion for whether the offset b needs to be revised is related to the structural dimensions of the U-shaped skin 1. Let w be the width of the opening between the two side walls 2 in the middle of the U-shaped skin 1, and l be the cross-sectional dimension in the middle of the U-shaped skin 1. j Criteria for determining whether to revise When m h When ≥0.55, the main forming surface 3 is in accordance with Perform an outward offset when m h When the value is less than 0.55, the main forming surface 3 remains consistent with the outer surface of the U-shaped skin 1, and offset need not be considered. Taking the U-shaped skin 1 shown in the figure as an example, the material thickness t = 2.5 mm, and the calculated offset b = 0.5 mm, but considering the outer structure of the U-shaped skin 1, the measured width w at the opening between the two side walls 2 is 600 mm, and the cross-sectional dimension l j =1336mm, then m h =0.45 and m h <0.55 indicates that the U-shaped skin 1 is deep, the deep drawing material has a large elongation and sufficient deformation, which can compensate for the impact of springback on the deep drawing of the part. Therefore, the main forming surface 3 is consistent with the outer surface of the U-shaped skin 1, and the offset b = 0.

[0087] The design of the outer contour dimensions of the main forming surface 3 needs to be subject to certain restrictions. Let the arc length of the boat-shaped outer contour of the U-shaped skin 1 be denoted as l0, and the arc length of the boat-shaped outer contour of the main forming surface 3 be denoted as l1. l1 needs to satisfy (l0+40)≤l1≤1000. Let the maximum height of the U-shaped skin 1 be denoted as H0, and the maximum height of the main forming surface be denoted as H1. H1 needs to satisfy (H0+20)≤H1≤(H0+50). That is to say, although the main forming surface 3 is an extension of the outer surface of the U-shaped skin 1, the drawing depth cannot be excessively increased to prevent cracking during the drawing process of the part 11. Taking the U-shaped skin 1 in the figure as an example, the measured arc length of the boat-shaped outer contour of the U-shaped skin 1 is l0=924mm, and the maximum height H0=530mm. Therefore, the arc length of the boat-shaped outer contour of the main forming surface 3 is l1=1000mm, and the maximum height of the main forming surface is H1=560mm.

[0088] Based on the semi-enclosed cabin opening length l c The tilt angle of the anti-wrinkle surface is optimized to improve the manufacturability of the deep-drawing part 11. The anti-wrinkle surface is divided into an initial anti-wrinkle surface 4 and an optimized anti-wrinkle surface 5 according to the criteria for optimization. The height of the initial anti-wrinkle surface 4 is denoted as H2. The formula for determining whether the anti-wrinkle surface needs optimization is as follows: When m z When m > 0.6, there is no need to optimize the tilt angle of the initial anti-wrinkle surface 4; the initial anti-wrinkle surface 4 is the anti-wrinkle surface mentioned above. z When the initial anti-wrinkle surface 4 is ≤0.6, it is necessary to tilt the initial anti-wrinkle surface 4 outward at a certain angle θ to obtain the optimized anti-wrinkle surface 5, so as to reduce the forming height of the end of the deep-drawing part 11. The optimized anti-wrinkle surface 5 is the anti-wrinkle surface. Taking the U-shaped skin 1 shown in the figure as an example, the initial anti-wrinkle surface 4 height H2 of the U-shaped skin 1 is measured to be 450mm, and the opening length l of the semi-enclosed chamber 6 is... c =972mm, calculated m z =0.51 and m z If the value is less than 0.6, the initial anti-wrinkle surface 4 needs to be optimized by tilting it outward at a certain angle θ.

[0089] The initial anti-wrinkle surface 4 is inclined outward by a distance denoted as l. b , l b =H2×sinθ, as described above, the initial semi-enclosed cabin 6 with straight arms at both ends is optimized into a semi-enclosed cabin 6 with inclined arms at both ends. The opening length l of the optimized semi-enclosed cabin 6 is... z =l c +2×l b The tilt angle θ must satisfy the formula And m θ >0.6, substitute the tilt angle θ into m θ The minimum tilt angle θ can be calculated using the formula >0.6. min The range of values ​​for the tilt angle θ satisfies θ min <θ≤θmin +2°. Taking the U-shaped skin 1 shown in the figure as an example, substitute the height H2 = 450 mm of the initial anti-wrinkle surface 4, the opening length l of the semi-closed cabin 6 c = 972 mm, and the arc length l1 = 1000 mm of the ship-shaped outer contour of the main forming surface 3 into the formula and m θ > 0.6, to obtain θ min = 10.75°. Therefore, the initial anti-wrinkle surface 4 is inclined outward at an angle θ = 12° to obtain the optimized anti-wrinkle surface 5. The purpose of such design is to ensure that the stretching amount of the optimized anti-wrinkle surface 5 in the semi-closed cabin 6 is less than that of the main forming surface 3.

[0090] The corner radius R of the transition fillet surface 18 is related to the material thickness t of the U-shaped skin 1 and needs to satisfy 20×t ≤ R ≤ 50×t. At the same time, when designing the value of the corner radius R, the outer contour dimensions of the U-shaped skin 1 also need to be considered. The principle of taking values is that the boundary line of the transition fillet surface 18 cannot enter within the outer contour line of the U-shaped skin 1, ensuring that the distance between the boundary line of the transition fillet surface 18 and the outer contour line of the U-shaped skin is ≥ 10 mm or more. Taking the U-shaped skin 1 shown in the figure as an example, the corner radius R of the transition fillet surface 18 = 32×t = 80 mm.

[0091] The bending curvature of the curvature sealing surface 8 is relatively gentle. Its design principle needs to satisfy that the percentage n of the length l of the initial sealing surface 7 z to the arc length l of the curvature sealing surface 8 q ≤ 98%. The value of n decreases with the increase of the height H1 of the semi-closed cabin 6. When H1 ≤ 400 mm, n = 1, and the initial sealing surface does not need to be bent backward. Taking the U-shaped skin 1 shown in the figure as an example, as obtained above, the length l of the initial sealing surface 7 z = 1159 mm. Combining with the drawing, the arc length l of the curvature sealing surface 8 q = 1173 mm, meeting the design requirement of n ≤ 98%. The arc length l of the curvature sealing surface 8 q is on a circle with a radius of 2202 mm, and the curvature is very gentle. The curvature sealing surface 8 effectively reduces the forming height of the anti-wrinkle surface, reduces the longitudinal stretching amount of the material, and at the same time, the gentle curvature also reduces the risk of cracking during forming.

[0092] When designing the bending curvature of the curvature sealing surface 8, the outer contour dimensions of the U-shaped skin 1 also need to be considered, ensuring that the distance between the opening line of the die cavity 10 and the outer contour line of the U-shaped skin is ≥ 10 mm or more.

[0093] The die fillet radius R1 smoothly connects the flange surface 9 and the die cavity 10. The size of R1 is related to the material thickness t of the U-shaped skin 1, and the value of R1 needs to satisfy 6×t < R1 ≤ 10×t. Taking the U-shaped skin 1 shown in the figure as an example, the die fillet radius R1 = 10×t = 25 mm.

[0094] Step 2: Construct a U-shaped skin 1 deep drawing process part 11 blank, which includes:

[0095] The U-shaped skin unfolded blank 12 is calculated using the blank back calculation function of finite element simulation software to obtain a long strip or near square unfolded blank of U-shaped skin 1. As mentioned above, the maximum length of the U-shaped skin unfolded blank 12 is >1m and the maximum width is <1m.

[0096] The blank 13 of the deep drawing process is developed. The blank back calculation function of the finite element simulation software is used to calculate the blank 13 of the U-shaped skin 1 deep drawing process, and the oblong or near-circular blank of the U-shaped skin 1 deep drawing process is obtained. As mentioned above, the maximum length and maximum width of the blank 13 of the deep drawing process are both >1m, and it is impossible to cut the complete shape of the blank of the deep drawing process 11 from the conventional 1m width stainless steel plate of aviation.

[0097] The welded blank is formed by laser welding three sheets of material into a single blank with the same external dimensions as the drawn part 13. The welded blank is divided into three parts by two straight weld lines 14: two crown-shaped compensation blanks 16 and a drum-shaped controlled blank 15. The distance between the two straight weld lines 14 is 1m, consistent with the width of conventional aerospace stainless steel plates. The U-shaped skin drawn blank 12 is contained within the outline of the controlled blank 15. After deep drawing, the welded blank yields the drawn part 11. The two straight planar weld lines 14 are then transformed into two three-dimensional arched weld lines 17. The compensation blank 16 is formed into the anti-wrinkle compensation part 20 of the deep drawing part 11. The controlled blank 15 is formed into the main forming part of the deep drawing part 11. The deep drawing part 11 is composed of two anti-wrinkle compensation parts 20 and one main forming part 19. The shape of the main forming part 19 covers the outer contour of the U-shaped skin 1 and leaves a process allowance to avoid the welding heat-affected zone around the weld from affecting the quality of the U-shaped skin product.

[0098] The process blank is a pre-bent blank made by welding the blank into a blank with a curvature similar to that of the flange surface 9 of the deep drawing part 11. This reduces the pressure on the edge of the welded blank during deep drawing and compensates for the material performance defect at the laser welding weld where the material strength is 90% of the strength of the base material.

[0099] Step 3: Design the drawing die structure according to the drawing process part 11, which includes:

[0100] The die 21 is designed based on the external structure of the deep drawing part 11. The die 21 is a block structure with a deep cavity. The die blanking surface 23 is extended outward from the flange surface 9 of the deep drawing part 11. The size of the die blanking surface 23 is designed to include the outline 22 of the process blank of the deep drawing part 11. The die blanking surface 23 is provided with a longitudinal drawing groove 24 and a transverse drawing groove 25.

[0101] The blank holder 29, designed according to the working surface of the die 21, is a block structure with a certain curvature and a hollow interior. The working surface 30 of the blank holder matches the blank holder surface 23 of the die and the outer contour is consistent. The working surface 30 of the blank holder is provided with the outline line 22 of the process blank of the deep drawing process 11 and its flange edge line 26, which are used for positioning the process blank and checking the forming effect.

[0102] The punch 35 is obtained by offsetting inward from the die cavity 10. Its specific structure corresponds to the drawing die cavity 10, and it is a punch structure with a relatively large height. The surface of the punch 35 is divided into one arched surface 37 and two wrapping surfaces 38 by two corner boundary lines 36. The arched surface 37 of the punch 35 corresponds to the main forming surface 3 of the die cavity 10 and is obtained by offsetting the main forming surface 3 inward by 1.1×t. The wrapping surface 38 of the punch 35 corresponds to the anti-wrinkle surface and its transition fillet surface 18 of the die cavity 10. 5. The wrapping surface 38 is obtained by offsetting the anti-wrinkle surface of the die cavity 10 and its transition rounded corner surface 18 inward by 1.2×t to 1.5×t. The arched surface 37 and the wrapping surface 38 are smoothly connected. During the forming process, the two straight weld lines 14 of the drawing part 11 are stretched along with the punch 35 as it moves, and finally form two three-dimensional arched weld lines 17, which are mainly distributed in the wrapping surface 38 of the punch 35. The large gap between the punch and the die here helps to reduce the tensile stress on the material in the weld area and avoid the weld from cracking.

[0103] A clearance control groove 33 is provided in the non-process blank area of ​​the working surface 30 of the blank holder. The clearance control groove 33 is located on both sides near the compensation blank 16. The clearance control groove 33 is 3mm deep. A clearance control pad 34 matching its shape is filled in the clearance control groove 33. The thickness of the clearance control pad 34 is determined according to the material flow during the test pressing of the deep drawing part 11. If the material flow is uniform, the clearance control pad 34 is not needed. If the material thins significantly or even cracks during the test pressing, the clearance control pad 34 is filled in the clearance control groove 33. The thickness of the clearance control pad 34 is h. x = 3 + t + Δ, where Δ ranges from 0 to 0.8 mm. The higher the part 11H1 in the deep drawing process and the thicker the material t, the larger the value of Δ. Taking the deep drawing part 11 and the blank holder 29 in the figure as an example, the thickness h of the clearance pad 34 is... x =2.6mm.

[0104] Longitudinal drawbeads 31 and transverse drawbeads 32 are provided within the outer contour line 22 of the blank working surface 30 of the blank. The positions and lengths of the longitudinal drawbeads 31 and transverse drawbeads 32 correspond to the longitudinal edge line 27 and transverse edge line 28 of the flange edge line 26 of the deep-drawing part 11, respectively. The distance between the longitudinal drawbeads 31 and transverse drawbeads 32 and the flange edge line 26 of the deep-drawing part 11 is 5mm to 10mm. After the drawbeads are implemented, the blank holding resistance will cause the flange edge line 26 of the actual deep-drawing part 11 to increase outward, so that the blank of the deep-drawing part 11 is subjected to the resistance of the drawbeads from beginning to end, uniform feeding speed, and control of instability and wrinkling of thick stainless steel plates.

[0105] To ensure that the drawing resistance experienced by the controlled blank 15 is greater than that of the compensating blank 16 during the deep drawing process of part 11, there are certain restrictions on the height values ​​of the longitudinal drawbead 31 and the transverse drawbead 32. The height h of the longitudinal drawbead section 31 is... zj Satisfying formula 3.5 + t ≤ h zj ≤10, transverse drawbar, 32 section height h hj Satisfying formula 1.5 + t ≤ h hj ≤6, and h zj ≥h hj +2. The drawbead height is related to the material thickness t and height H1 of the deep-drawing part 11. When the material thickness t is thicker, the drawbead height should be larger; otherwise, a smaller value should be used. When the height H1 is larger, the drawbead height should be smaller; otherwise, a larger value should be used. The drawbead height can be verified and adjusted using finite element simulation of deep drawing. Taking the deep-drawing part 11 and blank holder 29 as an example, the height h of the longitudinal drawbead section 31 is... zj =6mm. Height h of transverse drawbar section 32. hj =4mm.

[0106] The longitudinal drawing groove 24 and the transverse drawing groove 25 on the die blanking surface 23 are respectively matched with the longitudinal drawing bead 27 and the transverse drawing bead 28. The gap between the longitudinal drawing groove 24 and the longitudinal drawing bead 27 is designed to be 1.5×t, and the gap between the transverse drawing groove 25 and the transverse drawing bead 28 is designed to be 1.5×t to 2.0×t. Taking the deep drawing part 11 and the die 21 shown in the figure as an example, the gap between the longitudinal drawing groove 24 and the longitudinal drawing bead 27 is designed to be 3.75mm, and the gap between the transverse drawing groove 25 and the transverse drawing bead 28 is designed to be 4.5mm.

[0107] Step 4: Quickly construct the cutting fixture 41 according to the deep drawing process part 11.

[0108] The cutting fixture 41 is manufactured by interlocking multiple stainless steel plates through slots or by spot welding for positioning. These stainless steel plates are functionally divided into two categories: one category consists of strip-shaped stainless steel plates, typically 3-5 plates, used for positioning the deep-drawing workpiece 11 during cutting. These plates maintain the same internal shape as the cross-section of the deep-drawing workpiece 11 and are distributed at the end face of the transition rounded corner surface 18 and the middle section. Corner positioning plates 39 and middle section positioning plates 40 are designed and manufactured to secure the deep-drawing workpiece 11 to the outside of these 3-5 strip-shaped stainless steel plates, preventing movement during laser cutting. The other category consists of grooved support plates 42 used for auxiliary support and connection. The two types of stainless steel plates are positioned together through slots or spot welded to form the simple cutting fixture 41. The thickness of the stainless steel plates used in the cutting fixture 41 is in the range of 2-3 mm.

[0109] When the cutting fixture 41 is made using the slot splicing method, only the strip stainless steel plate needs to be made. The slotted support plate 42 for auxiliary support connection can be used as a universal bracket. By replacing different strip stainless steel plates, different U-shaped skin 1 laser cutting can be achieved.

[0110] Step 5: Prepare the blank for the deep drawing process 11.

[0111] 5-1: According to the design dimensions of blank 13 in the deep drawing process, three corresponding rectangular stainless steel plates are welded into a whole by laser welding. The gap between the two pairs of stainless steel plates is controlled to be ≤0.2mm. If spot welding is used for positioning or filler welding is used to repair weld defects, it is important to ensure that the thickness of the material at the weld is consistent with the thickness t of the stainless steel plate being welded. Otherwise, the uneven thickness of the material at the weld needs to be treated by grinding. Uneven thickness of the weld material will increase the edge pressure resistance during deep drawing and have an adverse effect on the uniform flow of the deep drawing material.

[0112] 5-2: Based on the shape data of the blank 13 for the deep drawing process, the welded stainless steel plate is laser-cut to obtain a welded blank with two straight weld lines 14. A plastic film is applied to the side opposite to the die pressing surface 23 of the welded blank. The film-coated welded blank is rolled to have a curvature consistent with the die pressing surface 23 to obtain the process blank of the deep drawing process 11.

[0113] Step 6: Perform deep drawing on a deep drawing machine.

[0114] 6-1: After assembling the punch 35 and the blank holder 29, connect them to the lower bed surface of the deep drawing machine. Connect the die 21 to the upper bed surface of the deep drawing machine. The die blank holder surface 23 corresponds to the blank holder working surface 30. The die cavity 10 corresponds to the punch 35 profile. There is a guide hole on each side of the die 21 and the blank holder 29. The deep drawing direction is positioned by the guide post on the punch 35 die holder.

[0115] 6-2: Place the coated process blank on the working surface 30 of the pressure ring according to the outline 22 of the process blank on the working surface 30 of the pressure ring;

[0116] 6-3: Lubricate the drawing die and the process blank. Apply lubricating oil to the contact surface between the process blank and the die 21, apply lubricating oil to the die blank pressure surface 23 and its cavity, and apply lubricating oil to the contact area between the process blank and the working surface 30 of the blank holder.

[0117] 6-4: Place a gap control pad 34 of appropriate thickness inside the gap control groove 33 of the pressure ring 29;

[0118] 6-5: First deep drawing;

[0119] The deep drawing machine is started, and the die 21 moves downward. When the die blanking surface 23 touches the blank holder working surface 30, the machine begins to apply blanking force, causing the edge area of ​​the blank to adhere firmly to the die blanking surface 23 and the blank holder working surface 30. As the die 21 and blank holder 29 move downward simultaneously, the blank begins to deform under the combined action of the blanking force and the deep drawing force. Because the blank blanking area bears a large blanking force and drawbead resistance, wrinkling is effectively controlled. The uneven longitudinal drawbeads 31 and transverse drawbeads 32 control wrinkling. The different gaps between the punch 35 and the die 21 cause different tensile stresses in different areas of the process blank. The controlled blank 15 is subjected to a large tensile stress, which makes the main forming part 19 have a good mold-fitting effect and small springback. The compensation blank 16 is subjected to a relatively small tensile stress, and the weld seam bears a small amount of tensile deformation. The compensation part 20 has a relatively large springback. Due to the longitudinal wrapping force of the compensation blank 16, no material accumulation or wrinkling occurs at the edge of the main forming part 19. After forming, the U-shaped skin deep drawing process part 11 semi-finished product is obtained.

[0120] First deep drawing height H S =H1-10, reserving a 10mm drawing height for secondary drawing and shaping, thus reducing the first drawing forming height and the risk of breakage, and solving the problem of large springback caused by insufficient deformation during secondary drawing and shaping.

[0121] 6-6: Solution heat treatment;

[0122] To eliminate the large springback defect in thick stainless steel skin during deep drawing, the semi-finished part 11 of the deep drawing process is subjected to solution heat treatment to obtain a uniform single-phase structure, restore the material's plasticity, eliminate residual stress generated during the deep drawing process, and improve the dimensional stability of the part.

[0123] 6-7: Secondary drawing and shaping;

[0124] The semi-finished product 11, which has undergone solution heat treatment, is subjected to secondary deep drawing and shaping. The 10mm deep drawing height reserved in the first deep drawing increases the amount of material stretching deformation, improves the shaping and mold fit, and weakens the springback of the material.

[0125] Step 7: Perform laser cutting on a laser cutting device.

[0126] The simple cutting fixture 41 is fixed on the working platform of the laser cutting equipment. The deep-drawing part 11 is placed on the corner positioning plate 39 and the middle section positioning plate 40 of the simple cutting fixture 41. The U-shaped skin 1 is cut according to the prepared laser cutting program. After removing the edge burrs, the U-shaped skin 1 part with streamlined shape and dimensions that meet the requirements of the drawing is obtained.

[0127] Several points need to be clarified: All dimensions described in this invention, unless otherwise specified, are in millimeters (mm); according to the "Aerospace Manufacturing Engineering Handbook—Aircraft Sheet Metal Process," the allowable limit for the first deep drawing of stainless steel is m. j =0.52~0.55, this invention specifies the drawing coefficient of the blank structure corresponding to different positions in the longitudinal and transverse directions of the deep-drawing process part, thereby constructing the structure of the deep-drawing process part, which makes the deep-drawing process part more manufacturable; the scope of this invention is applicable to austenitic stainless steel with a material thickness in the range of 1.5~3.5mm, and the design concept of its deep-drawing process part and deep-drawing die structure can also draw on precipitation hardening stainless steel and similar structures of stainless steel material thickness <1.5mm; the support plate used to position the part in the cutting fixture can be made of graphite-based material to achieve heat insulation of the cutting area and reduce the thermal impact on the material during laser cutting; this invention targets deep U-shaped boat skin with a large chord height. If the boat shape curvature is relatively gentle and the chord height is less than 40mm, the unfolded blank does not need to adopt a fully wrapped structure.

[0128] Thus, the objective of this invention has been achieved.

[0129] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling the deep drawing shape of stainless steel deep U-shaped thick skin panels, characterized in that, Includes the following steps: Step 1: Construct a U-shaped skin deep drawing part. The deep drawing part is designed according to the U-shaped skin theory, including: The main forming surface is a boat-shaped extension surface that matches the U-shaped skin outline. The consistency between the main forming surface and the U-shaped skin outline is determined by the material thickness t of the U-shaped skin. The main forming surface and the U-shaped skin outline maintain a certain outward offset b, and the offset b is linearly related to the material thickness t. The anti-wrinkle surface is a doorway-shaped plane that matches the shape of both ends of the main forming surface; The transition rounded corner surface is an arched curved surface formed by the smooth connection of the anti-wrinkle surface and the main forming surface through a large corner radius R. The transition rounded corner surface connects the two anti-wrinkle surfaces and the main forming surface into a semi-closed compartment. The initial sealing surface is the sealing surface at the opening of the semi-closed compartment. The flange face is an annular curved surface that is opposite to the curvature of the U-shaped skin and matches the opening size of the semi-enclosed cabin. Step 2: Construct a U-shaped skin deep drawing process blank, which includes: The U-shaped skin unfolded blank is calculated using the blank back calculation function of finite element simulation software to obtain a U-shaped strip or near square unfolded blank. The blank of the deep drawing process is developed. The blank is calculated by using the blank back calculation function of finite element simulation software to obtain the oval or near-circular blank of the U-shaped skin deep drawing process. The welded blank is a blank whose external dimensions are consistent with the shape of the drawn part after laser welding of three plates. The welded blank is divided into three parts: two crown-shaped compensation blanks and one drum-shaped controlled blank by two straight weld lines. Process blanks are blanks that are pre-bent into shapes with a curvature similar to that of the flange surface of the deep-drawing part. Step 3: Design the drawing die structure according to the drawing process, which includes a die, a blank holder and a punch. A clearance control groove is set in the non-process blank area of ​​the working surface of the blank holder. A clearance control pad matching its shape is placed in the clearance control groove. Longitudinal drawing ribs and transverse drawing ribs are set in the process blank outline of the working surface of the blank holder. Step 4: Construct a cutting fixture quickly according to the deep drawing process. It is made by interlocking multiple stainless steel plates or by spot welding for positioning. Step 5: Make the blank for the deep drawing process. Weld three corresponding rectangular stainless steel plates into a whole according to the design dimensions of the blank for the deep drawing process, perform laser cutting, apply plastic film, and roll the curvature. Step 6: Place the blank on a deep drawing machine for deep drawing. After the forming is completed, a U-shaped skin deep drawing part is obtained. Step 7: Fix the cutting fixture on the work platform, place the deep-drawn part obtained in Step 6 on the cutting fixture, and perform laser cutting using a laser cutting device to obtain a U-shaped skin part.

2. The method for controlling the deep drawing and welding of stainless steel deep U-shaped thick skin as described in claim 1, characterized in that, In step 1, the offset b is not a constant value. The criterion for whether it needs to be revised is related to the structural dimensions of the U-shaped skin. Let w be the width of the opening between the two side walls in the middle of the U-shaped skin, and l be the cross-sectional dimension in the middle of the U-shaped skin. j Criteria for determining whether to revise When m h When ≥0.55, the main forming surface is according to Perform offset when m h When the value is less than 0.55, the main forming surface and the U-shaped skin outer surface remain consistent, and offset does not need to be considered.

3. The method for controlling the deep drawing and welding of stainless steel deep U-shaped thick skin according to claim 2, characterized in that, In step 1, the design principle for the outer contour dimensions of the main forming surface is as follows: the arc length of the U-shaped skin boat-shaped outer contour is denoted as l0, and the arc length of the main forming surface boat-shaped outer contour is denoted as l1. l1 needs to satisfy (l0+40)≤l1≤1000; the maximum height of the U-shaped skin is denoted as H0, and the maximum height of the main forming surface is denoted as H1. H1 needs to satisfy (H0+20)≤H1≤(H0+50).

4. The method for controlling the deep drawing and welding of stainless steel deep U-shaped thick skin as described in claim 1, characterized in that, In step 1, the inclination of the anti-wrinkle surface can be determined based on the opening length l of the semi-enclosed chamber. c The anti-wrinkle surface is optimized and divided into initial anti-wrinkle surface and optimized anti-wrinkle surface according to the criteria for whether optimization is needed. The height of the initial anti-wrinkle surface is denoted as H2. The formula for determining whether the anti-wrinkle surface needs optimization is as follows: When m z When m > 0.6, there is no need to optimize the initial anti-wrinkle surface tilt angle; the initial anti-wrinkle surface is the anti-wrinkle surface itself. z When the value is ≤0.6, the initial anti-wrinkle surface needs to be tilted outward at a certain angle θ to obtain the optimized anti-wrinkle surface, so as to reduce the forming height at the end of the deep drawing process. The optimized anti-wrinkle surface is the anti-wrinkle surface mentioned above. The initial anti-wrinkle surface is tilted outwards by a distance denoted as l. b , l b =H2×sinθ, as described above, the initial semi-enclosed cabin structure with straight arms at both ends is optimized into a semi-enclosed cabin structure with inclined arms at both ends. The optimized semi-enclosed cabin opening length l z =l c +2×l b The tilt angle θ must satisfy the formula And m θ >0.6, substitute the tilt angle θ into m θ The minimum tilt angle θ can be calculated using the formula >0.

6. min The range of values ​​for the tilt angle θ satisfies θ min <θ≤θ min +2°.

5. A method for controlling the deep drawing and welding of stainless steel deep U-shaped thick skin according to claim 1 or 3, characterized in that, In step 1, the corner radius R of the transition fillet surface is related to the thickness t of the U-shaped skin material, and must satisfy 20×t≤R≤50×t. At the same time, when designing the corner radius R, the outer contour dimension of the U-shaped skin must be considered, and the principle of taking the value is that the boundary line of the transition fillet surface cannot enter the outer contour line of the U-shaped skin, so as to ensure that the distance between the boundary line of the transition fillet surface and the outer contour line of the U-shaped skin is ≥10mm.

6. The method for controlling the deep drawing and welding of stainless steel deep U-shaped thick skin as described in claim 1, characterized in that, In step 1, the flange face is obtained by bending, extending and shearing the initial sealing face. The initial sealing face is bent gently in the opposite direction to the curvature of the U-shaped skin. The curved sealing face extends outward by 50-60mm. The extended curved sealing face cuts the semi-enclosed chamber into a die chamber. The semi-enclosed chamber cuts the extended curved sealing face into an annular curved surface, i.e., the flange face. The flange face and the die chamber are connected by the die fillet radius R1 to form the deep drawing part.

7. The method for controlling the deep drawing and welding of stainless steel deep U-shaped thick skin as described in claim 6, characterized in that, The curvature of the sealing surface is relatively gentle, and its design principle requires that the initial sealing surface length l be satisfied. z With curvature sealing surface arc length l q The percentage n ≤ 98%, and the value of n decreases as the height H1 of the semi-enclosed cabin increases. When H1 ≤ 400mm, n = 1, and the initial sealing surface does not need to be bent in the reverse direction. When designing the curvature of the sealing surface, the outer contour dimensions of the U-shaped skin must also be considered to ensure that the distance between the opening line of the concave mold chamber and the outer contour line of the U-shaped skin is ≥10mm.

8. The method for controlling the deep drawing and welding of stainless steel deep U-shaped thick skin according to claim 6, characterized in that, The fillet radius R1 of the die cavity smoothly connects the flange face and the die cavity body. The value of R1 is related to the thickness t of the U-shaped skin material, and the value of R1 must satisfy 6×t. <R1≤10×t。 9. The method for controlling the deep drawing and welding of stainless steel deep U-shaped thick skin as described in claim 1, characterized in that, In step 1, the distance between the two straight weld lines is 1m, which is consistent with the width of conventional aerospace stainless steel plates. The U-shaped skin unfolded blank is contained within the controlled blank outline. After the welded blank is deep-drawn, the deep-drawn part is obtained. The two planar straight weld lines are then deformed into two three-dimensional arched weld lines. The anti-wrinkle compensation part of the deep-drawn part is formed by compensating the blank. The controlled blank is formed into the main forming part of the deep-drawn part. The deep-drawn part consists of two anti-wrinkle compensation parts and one main forming part as a whole. The shape of the main forming part covers the outer contour of the U-shaped skin and leaves a process allowance.

10. A stainless steel deep U-shaped thick skin welding and deep drawing forming die, characterized in that, include: The die is designed based on the shape and structure of the deep drawing part. The die is a block structure with a deep cavity. The die blanking surface extends outward from the flange of the deep drawing part. The size of the die blanking surface is designed to include the outline of the process blank of the deep drawing part. The die blanking surface is provided with longitudinal drawing grooves and transverse drawing grooves. The blank holder, designed according to the working surface of the die, is a block structure with a certain curvature and a hollow interior. The working surface of the blank holder matches the blank holder surface of the die and the outer contour is consistent. The working surface of the blank holder is provided with the outline of the blank of the deep drawing process and its flange edge line, which are used for blank positioning and inspection of forming effect. The punch, obtained by offsetting inward from the die cavity, has a structure corresponding to the die cavity of the deep drawing die. It is a punch structure with a relatively large height. The punch surface is divided into one arched surface and two wrapping surfaces by two corner boundary lines. The punch arched surface corresponds to the main forming surface of the die cavity and is obtained by offsetting the main forming surface inward by 1.1×t. The punch wrapping surface corresponds to the anti-wrinkle surface and its transition fillet surface of the die cavity. The punch wrapping surface is obtained by offsetting the anti-wrinkle surface and its transition fillet surface of the deep drawing part inward by 1.2×t to 1.5×t. The arched surface and the wrapping surface are smoothly connected. During forming, the two straight weld lines of the welded blank of the deep drawing part are stretched along with the punch as it moves, and finally form two three-dimensional arched weld lines, which are mainly distributed in the punch wrapping surface. A clearance control groove is set in the non-process blank area of ​​the working surface of the blank holder. The clearance control groove is located near both sides of the compensation blank, and the groove depth is 3mm. A clearance control pad matching its shape is filled in the clearance control groove. The thickness of the clearance control pad is determined based on the material flow during the test pressing of the deep drawing process. If the material flow is uniform, the clearance control pad is not needed. If the material thins significantly or even cracks during deep drawing, a clearance control pad is filled in the clearance control groove, and the thickness of the clearance control pad is h. x =3+t+Δ, where Δ ranges from 0 to 0.8 mm. The higher the H1 of the deep-drawing part and the thicker the material t, the larger the value of Δ. Longitudinal and transverse drawing ribs are provided within the outline of the blank working surface of the pressure ring. The position and length of the longitudinal and transverse drawing ribs correspond to the longitudinal and transverse edge lines of the flange edge line of the deep drawing process part, respectively. The distance between the longitudinal and transverse drawing ribs and the flange edge line of the deep drawing process part is 5mm to 10mm. There are certain restrictions on the height of longitudinal and transverse drawbars, and the longitudinal drawbar section height h zj Satisfying formula 3.5 + t ≤ h zj ≤10, height h of transverse drawbar section hj Satisfying formula 1.5 + t ≤ h hj ≤6, and h zj ≥h hj +2. The value of the drawbead height is related to the material thickness t and the height H1 of the deep drawing process. When the material thickness t is thicker, the drawbead height should be larger, otherwise it should be smaller. When the height H1 is larger, the drawbead height should be smaller, otherwise it should be larger. The value of the drawbead height can be verified by deep drawing finite element simulation and adjusted and optimized. The longitudinal drawing groove and the transverse drawing groove on the die blanking surface are matched with the longitudinal drawing bead and the transverse drawing bead, respectively. The gap between the longitudinal drawing groove and the longitudinal drawing bead is designed to be 1.5×t, and the gap between the transverse drawing groove and the transverse drawing bead is designed to be 1.5×t~2.0×t.

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