Stainless steel deep U ship-shaped thick skin tailor-welding drawing shape control method and forming die

Abstract

The invention belongs to the technical field of aircraft manufacturing, and discloses a stainless steel deep U ship-shaped thick skin tailor-welding drawing shape control method and a forming die, which are used for reversely calculating various key sizes of a drawing process piece by constructing different drawing coefficients and controlling the deformation degree of each part of the drawing process piece. The technical problems that a stainless steel deep U-shaped ship-shaped thick skin blank is insufficient in size, prone to instability and wrinkling in the forming process and large in resilience after being formed are solved. According to different bearing strengths of all parts of a tailor-welded blank, structural design key points of the drawing die are specified in detail, including a gap between a convex die and a concave die, a blank pressing gap, a gap between a drawing rib and a drawing groove and the like, the design thought is complete, the structural design of similar dies can be guided, and the universality is high.

Description

Technical Field

[0001] The invention belongs to the technical field of sheet metal parts forming in aircraft manufacturing, and specifically relates to a method for suppressing instability of combined welding and deep drawing forming of stainless steel deep U-shaped thick skin and a forming die. Background Art

[0002] The skin products on the aircraft are mostly made of aluminum alloy to meet the overall lightweight design requirements of the aircraft. However, during the flight, some skin parts need to withstand large aerodynamic forces and transmit these forces to the connected fuselage and wing frames. For this reason, stainless steel skins are designed and adopted because of their high strength and good plasticity. Usually, the thickness of aircraft stainless steel skin parts is ≤1.0mm. Using thinner stainless steel skins to replace thicker aluminum alloy skins can make up for the large difference in weight of products made of different materials.

[0003] During aircraft design or aircraft maintenance, some parts need to bear greater loads and have special application functions such as temperature resistance, corrosion resistance, and resistance to longer-term fatigue stress. Stainless steel skins with a thickness of more than 1.0 mm are the preferred replacement materials for design because of their better strength and toughness, and can maintain the integrity of the aircraft structure under high-speed flight or extreme climate conditions, and their relatively low manufacturing cost. Domestic aviation uses stainless steel cold-rolled plates with a thickness of ≤4.0 mm, with a sheet width of 1 m and a length of 2 m. This also shows that aircraft stainless steel sheet metal parts are not designed to be large, and the weight has a more critical impact on aircraft flight.

[0004] The stainless steel skin of the aircraft thumb cover has a material thickness t in the range of 1.5mm≤t≤3.5mm, the part cross-section is a deep U-shape, and the overall structure is a 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-shaped bottom is <1m, the percentage of the projection length of the outer contour of the boat-shaped bottom to its theoretical arc length is in the range of 90% to 97%, the maximum size of the U-shaped section is >1m, the ratio of the depth of the U-shaped skin to the width between the two side walls of its section is close to 1:1, and the maximum chord height of the outer contour of the boat-shaped bottom is in the range of 90mm to 150mm. The characteristic of this type of skin parts is that the boat-shaped outer contour has a certain curvature and the arc length is close to 1m. If traditional stamping is used, the blanks at both ends of the skin are not subjected to longitudinal tensile stress during forming, and uniform shrinkage deformation cannot be achieved. The abundant material at the largest cross-section in the middle is bound to become unstable and wrinkle. The greater the curvature of the outer contour of the boat-shaped bottom, the earlier the wrinkles will occur; if deep drawing is used, the required blank size width must be greater than 1m, otherwise the edge pressing cannot be achieved, and the maximum width of the stainless steel plate is only 1m; if skin drawing is used, on the one hand, this type of stainless steel skin material is thicker and has a large chord height, which is prone to fatigue failure under the action of alternating loads. On the other hand, the single-side process margin of the skin horizontal drawing needs to be at least about 400mm, and there is still the problem of limited blank size and inability to form.

[0005] Taking into account the advantages and disadvantages of existing processes, a method for deep drawing and shape control of stainless steel deep U-shaped thick skin was explored to overcome the technical bottleneck of thumb cover skin forming and realize wrinkle suppression and springback control in deep drawing of complex parts. Summary of the invention

[0006] The present invention is to solve the technical problems that the rough size of the stainless steel deep U-shaped thick skin is insufficient, it is easy to become unstable and wrinkled during forming, and it has a large springback after forming. A stainless steel curvature skin welding deep drawing composite forming control method and forming die are proposed.

[0007] In order to achieve the above invention objectives, the technical solutions adopted in this application are as follows:

[0008] A stainless steel deep U-shaped ship-shaped thick skin tailor-made welding drawing and shaping method, the specific steps are as follows:

[0009] Step 1: construct a U-shaped skin drawing process part, the drawing process part is designed according to the U-shaped skin theoretical shape, and the drawing process part includes:

[0010] The main forming surface is a boat-shaped extension surface that matches the U-shaped skin profile surface. The consistency between the main forming surface and the U-shaped skin profile surface is determined by the material thickness t of the U-shaped skin. The main forming surface and the U-shaped skin profile surface 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 outer shape surface of the U-shaped skin. The main forming surface of the U-shaped skin is actually a springback compensation surface that takes into account the springback amount after forming. The offset b is the springback amount. The offset b is not a fixed value and can be revised according to the outer shape structure of the U-shaped skin.

[0011] The anti-wrinkle surface is a door opening-shaped plane that matches the shapes of the two ends of the main forming surface.

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

[0013] The flange surface is an annular surface that is opposite to the curvature of the U-shaped skin and matches the opening size of the semi-enclosed cabin. It is obtained by bending-stretching-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 is extended 50 to 60 mm outward. The extended curvature sealing surface cuts the semi-enclosed cabin into a die cabin. The semi-enclosed cabin cuts the extended curvature sealing surface into an annular surface, namely the flange surface. The flange surface and the die cabin are connected to form a drawing process part through the die corner radius R1.

[0014] The criterion for determining whether the offset b needs to be revised 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 recorded as w, and the cross-sectional dimension in the middle of the U-shaped skin is recorded as l. j , whether to revise the criteria When m h ≥0.55, the main forming surface shall be To offset, when m h When <0.55, the main forming surface is consistent with the U-shaped skin outer surface, and there is no need to consider the offset.

[0015] The design of the outer contour size of the main forming surface needs to be subject to certain restrictions. The arc length of the boat-shaped outer contour of the U-shaped skin is denoted as l0, and the arc length of the boat-shaped outer contour of the main forming surface 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).

[0016] Based on the length of the semi-enclosed cabin opening l c The inclination of the anti-wrinkle surface is optimized to improve the processability of the deep drawing process parts. The anti-wrinkle surface is divided into the initial anti-wrinkle surface and the optimized anti-wrinkle surface according to the criterion for whether it is optimized. The height of the initial anti-wrinkle surface is recorded as H2. The formula for whether the anti-wrinkle surface needs to be optimized is When m z >0.6, there is no need to optimize the initial anti-wrinkle surface inclination angle, the initial anti-wrinkle surface is the anti-wrinkle surface, when m z ≤0.6, it is necessary to tilt the initial anti-wrinkle surface outward by a certain angle θ to obtain an optimized anti-wrinkle surface, so as to reduce the forming height of the end of the drawing process part, and the optimized anti-wrinkle surface is the anti-wrinkle surface.

[0017] The initial anti-wrinkle surface tilts outwards by a distance of l b , l b =H2×sinθ, the semi-enclosed cabin structure with straight arms at both ends is optimized as above, and the opening length of the optimized semi-enclosed cabin is 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 >0.6 formula, the minimum value of the tilt angle θ can be calculated min , the tilt angle θ range 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, and must satisfy 20×t≤R≤50×t. At the same time, the outer contour size of the U-shaped skin must be considered when designing the value of the corner radius R. 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 curvature sealing surface is relatively gentle, and its design principle must meet the initial sealing surface length l z The arc length l of the curvature sealing surface q The percentage n≤98%, the value of n decreases with the increase of the height H1 of the semi-enclosed cabin. When H1≤400mm, n=1, and the initial sealing surface does not need to be reversely bent.

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

[0021] The radius of the die corner R1 connects the flange surface and the die body smoothly. The size of R1 is related to the thickness t of the U-shaped skin material. The value of R1 must meet 6×t <R1≤10×t。

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

[0023] The U-shaped skin unfolded blank is calculated by using the blank back calculation function of the finite element simulation software to obtain the U-shaped skin long strip 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 unfolded blank of the drawing process part is calculated by using the blank inverse calculation function of the finite element simulation software to obtain the oblong or nearly circular unfolded blank of the U-shaped skin drawing process part. As mentioned above, the maximum length and maximum width of the unfolded blank of the drawing process part are both >1m, and it is impossible to use the conventional aviation width 1m stainless steel plate to cut out the complete unfolded blank shape of the drawing process part.

[0025] The welded blank is a blank obtained by laser welding three sheets of sheet metal, and its outer dimensions are consistent with the shape of the unfolded blank of the drawing process part. The welded blank is divided into three parts by two straight weld lines: two crown-shaped compensation blanks and a drum-shaped controlled blank. The distance between the two straight weld lines is 1m, which is consistent with the width of conventional aviation stainless steel plates. The outer shape of the unfolded blank of the U-shaped skin is included in the contour of the controlled blank. The welded blank is formed by deep drawing to obtain the drawing process part. The two flat straight weld lines are deformed into two three-dimensional arched weld lines. The compensation blank is formed into an anti-wrinkle compensation part of the drawing process part, and the controlled blank is formed into a main forming part of the drawing process part. The drawing process part is composed of two anti-wrinkle compensation parts and a 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 margin to avoid the welding heat affected zone around the weld from affecting the quality of the U-shaped skin product.

[0026] Process blank: The process blank is a blank that is pre-bent into a blank with a curvature similar to that of the flange surface of the drawing process part, so as to reduce the pressure bearing force of the welded blank during deep drawing and make up for the material performance degradation defect that the material strength at the laser welding weld is 90% of the parent material strength.

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

[0028] The die is designed according to the outer shape structure of the drawing process part. The die is a block structure with a deep cavity. The die pressing surface is obtained by extending the flange surface of the drawing process part outward. The size of the die pressing surface is designed based on the outer shape line of the drawing process part. Longitudinal drawing grooves and transverse drawing grooves are arranged on the die pressing surface.

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

[0030] The punch is obtained by offsetting the die cavity inward. Its specific structure corresponds to the die cavity of the drawing die. It is a convex block structure with a large height. The convex model surface is divided into an arch surface and two wrapping surfaces by two corner boundary lines. The punch arch 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 the transition fillet surface of the die cavity. The punch wrapping surface is the anti-wrinkle surface of the drawing process part and its transition fillet surface offset inward by 1.2×t~1.5×t. The arch surface and the wrapping surface are smoothly connected. During forming, the two straight weld lines of the welded blank of the drawing process part are stretched along with the movement of the punch, and finally two three-dimensional arched weld lines are formed, which are mainly distributed in the punch wrapping surface.

[0031] A gap control groove is arranged in the non-process blank area on the working surface of the blank holder. The gap control groove is arranged near both sides of the compensation blank. The depth of the gap control groove is 3mm. The gap control pad matching its shape is filled in the gap control groove. The thickness of the gap control pad is determined according to the material flow during the pressure test of the deep drawing process. If the material flows evenly, the gap control pad can be omitted. If the material is obviously thinned or even cracked during deep drawing, the gap control pad is filled in the gap control groove. The thickness of the gap control pad is h. x =3+t+Δ, the value range of Δ is within the range of 0 to 0.8 mm. The higher the H1 of the drawing process part and the thicker the material thickness t, the larger the value of Δ.

[0032] Longitudinal drawing ribs and transverse drawing ribs are arranged within the outer shape line of the process blank on the working surface of the pressure ring. The positions and lengths of the longitudinal drawing ribs and the transverse drawing ribs correspond to the longitudinal edge line and the transverse edge line of the flange edge line of the drawing process part respectively. The distance between the longitudinal drawing ribs and the transverse drawing ribs and the flange edge line of the drawing process part is 5mm to 10mm.

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

[0034] The longitudinal drawing groove and transverse drawing groove on the die pressing surface match the longitudinal drawing ribs and transverse drawing ribs respectively. The gap between the longitudinal drawing groove and the longitudinal drawing ribs is designed according to 1.5×t, and the gap between the transverse drawing groove and the transverse drawing ribs is designed according to 1.5×t~2.0×t.

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

[0036] The cutting fixture is made of multiple stainless steel plates that are slotted together or spot welded. The multiple stainless steel plates are divided into two categories according to their functions. One is a strip-shaped stainless steel plate used for cutting and positioning of deep drawing process parts. There are usually 3-5 pieces, which are consistent with the inner shape of the cross section of the deep drawing process parts. They are distributed at the end face of the transition fillet surface and the middle section. The corner surface positioning plate and the middle section positioning plate are designed and manufactured. The deep drawing process parts are stuck on the outside of 3-5 strip-shaped stainless steel plates to prevent movement during laser cutting. The other is a slotted support plate for auxiliary support connection. The two types of stainless steel plates are mutually positioned by slots or spot welded to form a simple cutting fixture. The thickness of the stainless steel plate used in the cutting fixture is in the range of 2 to 3 mm.

[0037] When the cutting fixture is made by the slot splicing method, only the strip-shaped stainless steel plate can be made, and the slotted support plate connected by the auxiliary support can be used as a universal bracket. By replacing different strip-shaped stainless steel plates, different U-shaped skin laser cutting can be achieved.

[0038] Step 5: Make the process blank for the drawing process part.

[0039] 5-1: According to the design size of the blank of the drawing process, three corresponding rectangular stainless steel plates are welded into a whole. The gap between the two stainless steel plates is controlled at ≤0.2mm. The welding method is laser welding. If spot welding is used for positioning or wire filling welding is performed when weld defects occur, it is necessary to pay attention to the consistency of the material thickness at the weld and the material thickness t of the welded stainless steel plate. Otherwise, the uneven material thickness at the weld needs to be processed by grinding.

[0040] 5-2: According to the shape data of the blank for the drawing process part, the welded stainless steel plate is laser cut to obtain a welded blank with two straight weld lines, and a plastic film is applied to the side of the welded blank opposite to the die pressing surface, and the coated welded blank is rolled to have a curvature consistent with the die pressing surface to obtain the process blank for the drawing process part.

[0041] Step 6: Deep drawing is performed on a drawing machine.

[0042] 6-1: After assembling the punch and the blank holder, connect them to the lower bed of the drawing machine, connect the die to the upper bed of the drawing machine, the die pressing surface corresponds to the working surface of the blank holder, the die chamber corresponds to the punch surface, there is a guide hole on both sides of the die and the blank holder, and the guide column on the punch die seat is used to position the drawing direction;

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

[0044] 6-3: Lubricate the drawing die and the process blank, apply lubricating oil to the mating surface between the process blank and the die, apply lubricating oil to the die pressing surface and its cavity, and apply lubricating oil to the mating area between the process blank and the working surface of the blank holder;

[0045] 6-4: Place a gap control pad of appropriate thickness in the gap control groove of the blank holder;

[0046] 6-5: First deep drawing;

[0047] Start the deep drawing machine, and the die moves downward. When the die pressing surface touches the working surface of the blank holder, the machine starts to apply the blank holder force to make the edge area of ​​the process blank close to the die pressing surface and the blank holder working surface. As the die and the blank holder simultaneously perform deep drawing downward, the process blank begins to deform under the combined action of the blank holder force and the drawing force. Since the edge of the process blank is subjected to a large blank holder force and the resistance of the draw ribs, the wrinkling is effectively controlled. The longitudinal draw ribs and transverse draw ribs of different heights control the feeding speed of the process blank into the cavity. The different gaps between the male and female dies cause different tensile stresses in different areas of the process blank. The controlled blank is subjected to large tensile stress, the main forming part has a good die-fitting effect and small springback, the compensation blank is subjected to relatively small tensile stress, the weld is subjected to small tensile deformation, and the compensation part has relatively large springback. Due to the existence of the longitudinal tensile stress of the compensation blank, the edge of the main forming part does not accumulate material or wrinkle. After the forming is completed, a semi-finished U-shaped skin deep drawing process part is obtained.

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

[0049] 6-6: Solution heat treatment

[0050] In order to eliminate the large springback defect of stainless steel thick 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 correction

[0052] The semi-finished products of the drawing process that have undergone solution heat treatment are subjected to secondary drawing and shaping. The 10mm drawing height reserved for the first drawing increases the tensile deformation of the material and weakens the rebound and take-off of the material.

[0053] Step 7: Laser cutting on laser cutting equipment.

[0054] Fix the simple cutting fixture on the working platform of the laser cutting equipment, place the drawing process parts on the corner surface positioning plate and the middle section positioning plate of the simple cutting fixture, and perform U-shaped skin shape cutting according to the prepared laser cutting program. After removing the edge burrs, a U-shaped skin part with streamlined shape and size that meets the requirements of the drawing is obtained.

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

[0056] 1. The present invention provides a design method for a stainless steel deep U-shaped thick skin drawing process part. By constructing different drawing coefficients to reversely calculate the key dimensions of the drawing process parts, the deformation degree of each part of the drawing process parts is controlled to solve the wrinkling and cracking problems of the stainless steel deep cavity thick plate skin.

[0057] 2. The present invention provides an unconventional method for designing and manufacturing unfolded blanks. It adopts laser welding of multiple blanks to solve the problem of limited width of aviation stainless steel plates, designs the deformation trajectory of the weld from plane to three-dimensional, and provides a basis for the design of mold structure gap.

[0058] 3. The present invention provides a method for suppressing springback during deep drawing of thick stainless steel plate skins. By adopting a series of measures such as shape surface offset, anti-wrinkle surface design, stress relief treatment, and 10mm secondary deep drawing and correction, the springback and jump of parts are controlled, thereby improving the accuracy of the skinning die.

[0059] 4. The present invention provides a four-stage drawbead design method for a ship-shaped deep drawing process part, which better controls the wrinkling of a deep stainless steel thick skin. Drawbeads of different heights are matched according to the structural characteristics of the deep drawing process part. On the one hand, it avoids the occurrence of rupture on the dangerous fracture surface, and on the other hand, it alleviates the fracture caused by the weld strength being lower than the parent material.

[0060] 5. The present invention specifies the key points of the drawing die structure design in detail according to the different bearing strengths of various parts of the welded blank, including the gap between the male and female dies, the gap between the edge clamps, the gap between the draw ribs and the draw grooves, etc. The design concept is complete, can guide the design of similar die structures, and has strong versatility.

[0061] The present application is further described below in conjunction with the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0063] In the attached picture:

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

[0065] Figure 2It is a schematic diagram of the design structure of the initial wrinkle-proof surface and the main forming surface;

[0066] Figure 3 Schematic diagram of the structure designed to optimize the anti-wrinkle surface and the main forming surface;

[0067] Figure 4 It is a schematic diagram of the design structure of the die cabin and the flange surface;

[0068] Figure 5 It is a schematic diagram of the corresponding structure of the drawing process part and the unfolded blank;

[0069] Figure 6 Design structural diagram for welded blanks of drawing process parts;

[0070] Figure 7 It is a schematic diagram of the corresponding structure of the compensation part, the main forming part and the welded blank;

[0071] Figure 8 It is a schematic diagram of the structure of the drawing die concave die;

[0072] Fig. 9 It is a schematic diagram of the structure of the deep drawing die pressing edge ring;

[0073] Fig.10 It is a schematic diagram of the assembly structure of the drawing die edge ring and the punch;

[0074] Fig.11 This is a schematic diagram of the structure of a simple laser cutting fixture;

[0075] Fig.12 Schematic diagram of the U-shaped skin and laser cutting fixture assembly structure.

[0076] Explanation of reference numerals in the figure: 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 cabin, 7 initial sealing surface, 8 curvature sealing surface, 9 flange surface, 10 die cabin, 11 drawing process part, 12 U-shaped skin unfolded blank, 13 drawing process part unfolded blank, 14 straight weld line, 15 controlled blank, 16 compensation blank, 17 arched weld line, 18 transition fillet surface, 19 main forming part, 20 compensation part, 21 die, 22 process blank outline, 23 die pressing 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 draw rib, 32 transverse draw rib, 33 gap control groove, 34 gap control pad, 35 punch, 36 corner boundary line, 37 arch surface, 38 wrapping surface, 39 corner surface positioning plate, 40 mid-section positioning plate, 41 cutting fixture, 42 grooved support plate. DETAILED DESCRIPTION

[0077] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0078] Figure 1-12 It is a schematic diagram for explaining one embodiment of the present invention.

[0079] The aircraft U-shaped skin design provided in the embodiment 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. In order to achieve functions such as aircraft protection, covering and aesthetics, it has different curvatures. 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 outer contour of the boat-shaped bottom to its theoretical arc length l1 is in the range of 90% to 97%, and the arc length of the outer contour of the boat-shaped bottom l1<1m, and the maximum size l of the U-shaped section is j >1m, the width ratio between the height H0 of the U-shaped skin 1 and its two side walls 2 is close to 1:1. The curvature skin 1 cannot be formed using the existing aviation stainless steel plate due to insufficient blank size, and the thicker stainless steel has high yield strength and requires large deformation resistance, while the material strength of the laser welding weld area can only reach 90% of the parent material strength, the forming force is large and easy to break, the forming 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 stainless steel deep U-shaped ship-shaped thick skin tailor-made welding drawing and shaping control method comprises the following steps:

[0081] Step 1: construct a U-shaped skin 1 drawing process part 11, the drawing process part 11 is designed according to the theoretical shape of the U-shaped skin 1, and the drawing process 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 as the material thickness increases. When the offset b=0, it means that the main forming surface 3 is consistent with the outer shape surface of the U-shaped skin 1.

[0083] The anti-wrinkle surface is a door opening-shaped plane that matches the shapes of the two ends of the main forming surface 3 .

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

[0085] The flange surface 9 is an annular curved surface which is opposite to the curvature of the U-shaped skin 1 and matches the opening size of the semi-enclosed cabin body 6. It is obtained by bending-stretching-shearing the initial sealing surface 7. The initial sealing surface 7 is gently bent in the opposite direction to the curvature of the U-shaped skin 1. The curved curvature sealing surface 8 extends 50 to 60 mm outward. The extended curvature sealing surface 8 cuts the semi-enclosed cabin body 6 into a die cabin body 10. The semi-enclosed cabin body 6 cuts the extended curvature sealing surface 8 into an annular curved surface, namely the flange surface 9. The flange surface 9 and the die cabin body 10 are connected to form a drawing process part 11 through the die corner radius R1.

[0086] The main forming surface 3 of the U-shaped skin 1 is actually a springback compensation surface that takes into account the springback amount after forming. It is a deepening of the outer surface of the U-shaped skin 1, thereby eliminating the springback of the stainless steel U-shaped skin 1 after forming. 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. The width of the opening between the two side walls in the middle of the U-shaped skin 1 is recorded as w, and the cross-sectional dimension of the middle of the U-shaped skin 1 is recorded as l j , whether to revise the criteria When m h ≥0.55, the main forming surface 3 is To shift outward, when m h <0.55, the main forming surface 3 is consistent with the outer surface of the U-shaped skin 1, and there is no need to consider the offset. Taking the U-shaped skin 1 as an example, the material thickness t = 2.5mm, the calculated offset b = 0.5mm, but considering the outer structure of the U-shaped skin 1, the width of the opening between the two side walls 2 is measured to be w = 600mm, and the cross-sectional size l j =1336mm, then m h =0.45 and m h <0.55, which means that the U-shaped skin 1 is deep, the elongation of the deep-drawn material is large, and the deformation is sufficient, which can compensate for the influence of springback on the deep-drawn forming of the part. Therefore, the main forming surface 3 is consistent with the outer shape surface of the U-shaped skin 1, and the offset b=0.

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

[0088] According to the opening length l of the semi-enclosed cabin 6 c The inclination of the anti-wrinkle surface is optimized to improve the processability of the drawing process 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 criterion for whether it is optimized. The height of the initial anti-wrinkle surface 4 is recorded as H2. The formula for whether the anti-wrinkle surface needs to be optimized is: When m z >0.6, there is no need to optimize the inclination angle of the initial anti-wrinkle surface 4, the initial anti-wrinkle surface 4 is the anti-wrinkle surface, when m z ≤0.6, the initial anti-wrinkle surface 4 needs to be tilted outward at a certain angle θ to obtain an optimized anti-wrinkle surface 5, so as to reduce the forming height of the end of the drawing process part 11, and the optimized anti-wrinkle surface 5 is the anti-wrinkle surface. Taking the U-shaped skin 1 as an example, the height H2 of the initial anti-wrinkle surface 4 of the U-shaped skin 1 is measured to be 450mm, and the opening length l of the semi-enclosed cabin 6 is c =972mm, calculated m z =0.51 and m z <0.6, the initial anti-wrinkle surface 4 needs to be optimized and tilted outward at a certain angle θ.

[0090] The initial anti-wrinkle surface 4 tilts outwards by a distance l b , l b =H2×sinθ, the semi-enclosed cabin 6 with straight arms at both ends is optimized as above, and the opening length of the optimized semi-enclosed cabin 6 is 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 >0.6 formula, the minimum value of the tilt angle θ can be calculated min , the tilt angle θ range satisfies θmin <θ≤θ min +2°. Taking the U-shaped skin 1 as an example, the initial wrinkle-proof surface 4 height H2 = 450mm, the opening length of the semi-enclosed cabin 6 l c =972mm, the arc length of the main forming surface 3 boat-shaped outer contour l1 = 1000mm Substitute into the formula And m θ >0.6, we get θ min =10.75°, so the initial anti-wrinkle surface 4 is tilted outward at an angle θ=12° to obtain the optimized anti-wrinkle surface 5. The purpose of such design is to achieve that the stretching amount of the optimized anti-wrinkle surface 5 in the semi-enclosed cabin 6 is less than the stretching amount of the main forming surface 3.

[0091] The value of 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, the outer contour size of the U-shaped skin 1 needs to be considered when designing the value of the corner radius R. The principle is that the boundary line of the transition fillet surface 18 cannot enter the outer contour line of the U-shaped skin 1, and the distance between the boundary line of the transition fillet surface 18 and the outer contour line of the U-shaped skin is ≥10mm. Taking the U-shaped skin 1 shown in the figure as an example, the corner radius R of the transition fillet surface 18 is 32×t=80mm.

[0092] The curvature of the curvature sealing surface 8 is relatively gentle, and its design principle must meet the initial sealing surface 7 length l z The arc length l with curvature sealing surface 8 q The percentage n≤98%, the value of n decreases with the increase of the height H1 of the semi-enclosed cabin 6, when H1≤400mm, n=1, the initial sealing surface does not need to be reversely bent. Taking the U-shaped skin 1 shown in the figure as an example, the length l of the initial sealing surface 7 is obtained as above z =1159mm, combined with the curvature of the sealing surface 8 arc length l q =1173mm, Meet the design requirement of n≤98%, the curvature sealing surface 8 arc length l q On a circle with a radius of 2202 mm, the curvature is very gentle. The curvature sealing surface 8 effectively reduces the forming height of the anti-wrinkle surface, reduces the longitudinal stretching of the material, and the gentle curvature also reduces the risk of rupture during forming.

[0093] When designing the curvature of the curvature sealing surface 8, the outer contour size of the U-shaped skin 1 must also be considered to ensure that the distance between the opening line of the die cabin 10 and the outer contour line of the U-shaped skin is ≥10 mm.

[0094] The radius R1 of the concave die fillet smoothly connects the flange surface 9 and the concave die housing 10. The size of R1 is related to the thickness t of the U-shaped skin 1. The value of R1 should satisfy 6×t < R1 ≤ 10×t. Taking the U-shaped skin 1 shown in the figure as an example, the radius R1 of the concave die fillet is R1 = 10×t = 25 mm.

[0095] Step 2: Construct a process blank for the drawn part 11 of the U-shaped skin 1, which includes:

[0096] The developed blank 12 of the U-shaped skin. Use the blank reverse calculation function of the finite element simulation software to calculate the developed blank 12 of the U-shaped skin, and obtain a long strip or nearly square developed blank of the U-shaped skin 1. As mentioned above, the maximum length of the developed blank 12 of the U-shaped skin > 1 m and the maximum width < 1 m.

[0097] The developed blank 13 of the drawn part. Use the blank reverse calculation function of the finite element simulation software to calculate the developed blank 13 of the drawn part of the U-shaped skin 1, and obtain an oblong or nearly circular developed blank of the drawn part of the U-shaped skin 1. As mentioned above, both the maximum length and the maximum width of the developed blank 13 of the drawn part > 1 m, and it is impossible to cut out the complete shape of the developed blank of the drawn part 11 using a 1 m wide conventional aviation stainless steel plate.

[0098] The welded blank is a blank obtained by laser welding three sheet materials, and its outer shape size is the same as that of the developed blank 13 of the drawn part. The welded blank is divided into two crown-shaped compensation blanks 16 and a drum-shaped controlled blank 15 by two straight weld lines 14. The distance between the two straight weld lines 14 is 1 m, which is consistent with the width of the conventional aviation stainless steel plate. The outer shape of the developed blank 12 of the U-shaped skin is included in the contour of the controlled blank 15. After the welded blank is drawn and formed, the drawn part 11 is obtained, and the two plane straight weld lines 14 are deformed into two three-dimensional arched weld lines 17. The compensation blank 16 forms the anti-wrinkle compensator 20 of the drawn part 11, and the controlled blank 15 forms the main formed part of the drawn part 11. The drawn part 11 is composed of two anti-wrinkle compensators 20 and a main formed part 19 as a whole. The outer shape of the main formed part 19 covers the outer contour of the U-shaped skin 1 and leaves a process margin to avoid the influence of the welding heat affected zone around the weld on the product quality of the U-shaped skin.

[0099] The process blank is a blank obtained by pre-bending the welded blank into a shape with a curvature similar to that of the flange surface 9 of the drawn part 11, so as to reduce the blank holding force during the drawing of the welded blank and make up for the defect of the material property degradation that the material strength at the laser welding seam is 90% of the base material strength.

[0100] Step 3: Design the structure of the drawing die according to the drawn part 11, which includes:

[0101] The die 21 is designed according to the outer structure of the drawing process part 11. The die 21 is a block structure with a deep cavity. The die pressing surface 23 is obtained by extending the flange surface 9 of the drawing process part 11 outward. The size of the die pressing surface 23 is designed based on the outer shape line 22 of the process blank of the drawing process part 11. The die pressing surface 23 is provided with a longitudinal drawing groove 24 and a transverse drawing groove 25.

[0102] The blank holder 29 is designed according to the working surface of the die 21 and is a block structure with a hollow interior and a certain curvature. The working surface 30 of the blank holder matches the die pressing surface 23 and the outer contour is consistent. The working surface 30 of the blank holder is provided with the outer shape line 22 of the drawing process part 11 and its flange edge line 26, which are used for positioning the process blank and detecting the forming effect.

[0103] The punch 35 is obtained by inwardly offsetting the die chamber 10. The specific structure corresponds to the die chamber 10 of the drawing die. It is a convex block structure with a large height. The die surface of the punch 35 is divided into an arch surface 37 and two wrapping surfaces 38 by two corner boundary lines 36. The arch surface 37 of the punch 35 corresponds to the main forming surface 3 of the die chamber 10, which is obtained by inwardly offsetting the main forming surface 3 by 1.1×t. The wrapping surface 38 of the punch 35 corresponds to the anti-wrinkle surface of the die chamber 10 and its transition fillet surface 18. The punch 35 is formed by the two corner boundary lines 36. The wrapping surface 38 is obtained by offsetting the anti-wrinkle surface of the cavity chamber 10 and its transition fillet surface 18 inward by 1.2×t to 1.5×t. The arch surface 37 and the wrapping surface 38 are smoothly connected. During the forming process, the two straight weld lines 14 of the welded blank of the drawing process part 11 are stretched along with the movement of the punch 35, and finally two three-dimensional arched weld lines 17 are formed, which are mainly distributed in the wrapping surface 38 of the punch 35. The larger gap between the punch and the die here is conducive to reducing the tensile stress borne by the material in the weld area and avoiding the cracking of the weld.

[0104] A control gap groove 33 is provided in the non-process blank area of ​​the blank holder working surface 30. The control gap groove 33 is provided near both sides of the compensation blank 16. The depth of the control gap groove 33 is 3 mm. A control gap pad 34 matching the shape is filled in the control gap groove 33. The thickness of the control gap pad 34 is determined according to the material flow during the pressure test of the deep drawing process part 11. If the material flows evenly, the control gap pad 34 can be omitted. If the material is obviously thinned or even cracked during the pressure test, the control gap pad 34 is filled in the control gap groove 33. The thickness of the control gap pad 34 is h. x =3+t+Δ, Δ has a value range of 0 to 0.8 mm. The higher the H1 of the drawing process part 11 and the thicker the material thickness t, the larger the value of Δ. Taking the drawing process part 11 and the blank holder 29 as an example, the thickness of the gap control pad 34 h x =2.6mm.

[0105] A longitudinal drawing rib 31 and a transverse drawing rib 32 are arranged in the process blank outline 22 of the blank holding ring working surface 30. The positions and lengths of the longitudinal drawing rib 31 and the transverse drawing rib 32 correspond to the longitudinal edge line 27 and the transverse edge line 28 of the flange edge line 26 of the drawing process part 11, respectively. The distance between the longitudinal drawing rib 31 and the transverse drawing rib 32 and the flange edge line 26 of the drawing process part 11 is 5mm to 10mm. After the drawing rib is implemented, the blank holding resistance will increase the flange edge line 26 of the actual drawing process part 11 outward, so that the process blank of the drawing process part 11 is subjected to the resistance of the drawing rib from beginning to end, and the feeding speed is uniform, and the instability and wrinkling of thick plate stainless steel is controlled.

[0106] In order to achieve that the drawing resistance of the controlled blank 15 is greater than that of the compensation blank 16 during the drawing process, the height values ​​of the longitudinal draw rib 31 and the transverse draw rib 32 are restricted to a certain extent. The height h of the longitudinal draw rib section 31 is zj Satisfy the formula 3.5+t≤h zj ≤10, transverse drawbead 32 section height h hj Satisfy the formula 1.5+t≤h hj ≤6, and h zj ≥h hj +2, the drawbead height value is related to the material thickness t and height H1 of the deep drawing process part 11. When the material thickness t is thicker, the drawbead height takes a larger value, otherwise it takes a smaller value. When the height H1 is larger, the drawbead height takes a smaller value, otherwise it takes a larger value. The drawbead height value can be verified by deep drawing forming finite element simulation and adjusted and optimized. Taking the deep drawing process part 11 and the blank holder 29 as an example, the height h of the longitudinal drawbead section 31 zj =6mm. Transverse drawbead 32 section height h hj =4mm.

[0107] The longitudinal drawing groove 24 and the transverse drawing groove 25 on the die pressing surface 23 are matched with the longitudinal drawing rib 27 and the transverse drawing rib 28 respectively. The gap between the longitudinal drawing groove 24 and the longitudinal drawing rib 27 is designed according to 1.5×t, and the gap between the transverse drawing groove 25 and the transverse drawing rib 28 is designed according to 1.5×t~2.0×t. Taking the drawing process 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 rib 27 is designed according to 3.75mm, and the gap between the transverse drawing groove 25 and the transverse drawing rib 28 is designed according to 4.5mm.

[0108] Step 4: Rapidly construct the cutting fixture 41 according to the drawing process part 11.

[0109] The cutting fixture 41 is made of multiple stainless steel plates that are slotted together or positioned by spot welding. The multiple stainless steel plates are divided into two categories according to their functions. One category is a strip-shaped stainless steel plate used for cutting and positioning the deep drawing process part 11, usually 3-5 pieces, which are consistent with the inner shape of the cross section of the deep drawing process part 11 and are distributed at the end face and the middle cross section of the transition fillet surface 18. The corner surface positioning plate 39 and the middle cross section positioning plate 40 are designed and manufactured. The deep drawing process part 11 is stuck outside the 3-5 strip-shaped stainless steel plates to prevent movement during laser cutting. The other category is a slotted support plate 42 for auxiliary support connection. The two types of stainless steel plates are positioned mutually by slots or spot welded to form a simple cutting fixture 41. The thickness of the stainless steel plate used in the cutting fixture 41 is in the range of 2 to 3 mm.

[0110] When the cutting fixture 41 is made by slot splicing, only a strip-shaped stainless steel plate can be made, and the slotted support plate 42 connected with the auxiliary support can be used as a universal bracket. By replacing different strip-shaped stainless steel plates, laser cutting of different U-shaped skins 1 can be achieved.

[0111] Step 5: Make the process blank of the drawing process part 11.

[0112] 5-1: According to the design size of the blank 13 for the drawing process, three corresponding rectangular stainless steel plates are welded into a whole by laser welding. The gap between the two stainless steel plates is controlled to be ≤0.2mm. If spot welding is used for positioning or wire filling welding is performed when weld defects occur, it is necessary to pay attention to the consistency of the material thickness at the weld and the material thickness t of the welded stainless steel plate. Otherwise, the uneven material thickness at the weld needs to be processed by grinding. The uneven thickness of the weld material will increase the edge pressure resistance during drawing, which will have an adverse effect on the uniform flow of the drawn material.

[0113] 5-2: According to the shape data of the blank 13 of the drawing process part, the welded stainless steel plate is laser cut to obtain a welded blank with two straight weld lines 14, and a plastic film is applied to the side of the welded blank opposite to the die pressing surface 23, and the coated welded blank is rolled to have a curvature consistent with the die pressing surface 23 to obtain the process blank of the drawing process part 11.

[0114] Step 6: Deep drawing is performed on a drawing machine.

[0115] 6-1: After the punch 35 and the blank holder 29 are assembled, they are connected to the lower bed of the drawing machine, and the die 21 is connected to the upper bed of the drawing machine. The die pressing surface 23 corresponds to the blank holder working surface 30, and the die chamber 10 corresponds to the die surface of the punch 35. There is a guide hole on both sides of the die 21 and the blank holder 29, and the guide column on the die base of the punch 35 is used for positioning in the drawing direction;

[0116] 6-2: placing the coated process blank on the blank holder working surface 30 according to the process blank outline 22 on the blank holder working surface 30;

[0117] 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 pressing surface 23 and its cavity, and apply lubricating oil to the contact area between the process blank and the blank holder working surface 30;

[0118] 6-4: Place a gap control pad 34 of appropriate thickness in the gap control groove 33 of the blank holder 29;

[0119] 6-5: First deep drawing;

[0120] Start the deep drawing machine, the die 21 moves downward, when the die pressing surface 23 touches the blank holder working surface 30, the machine starts to apply the blank holding force, so that the edge area of ​​the process blank is close to the die pressing surface 23 and the blank holder working surface 30, as the die 21 and the blank holder 29 are synchronously drawn downward, the process blank begins to deform under the combined action of the blank holding force and the drawing force. Since the blank blank is subjected to a large blank holding force and the resistance of the draw ribs, the wrinkling is effectively controlled, and the longitudinal draw ribs 31 and the transverse draw ribs 32 of different heights are controlled. The feeding speed of the process blank into the cavity is controlled. 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 large tensile stress, so that the main forming part 19 has a good die-fitting effect and small springback. The compensation blank 16 is subjected to relatively small tensile stress, and the weld undergoes small tensile deformation. The springback of the compensation part 20 is relatively large. Due to the longitudinal wrapping force of the compensation blank 16, the edge of the main forming part 19 does not accumulate material or wrinkle. After the forming is completed, the U-shaped skin deep drawing process part 11 semi-finished product is obtained.

[0121] First drawing height H S =H1-10, and reserve 10mm of drawing height for secondary drawing and shaping. This not only reduces the first drawing forming height and the risk of rupture, but also solves the big springback problem caused by insufficient deformation during the secondary drawing and shaping.

[0122] 6-6: Solution heat treatment;

[0123] In order to eliminate the large springback defect of stainless steel thick skin drawing, the semi-finished product of the drawing process part 11 is subjected to solution heat treatment to obtain a uniform single-phase structure, restore the plasticity of the material, eliminate the residual stress generated in the drawing process, and improve the dimensional stability of the process part.

[0124] 6-7: Secondary deep drawing and shaping;

[0125] The semi-finished product 11 of the drawing process that has undergone solution heat treatment is subjected to secondary drawing and shaping. The 10mm drawing height reserved for the first drawing increases the tensile deformation of the material, improves the shaping and mold adhesion, and weakens the rebound and jump of the material.

[0126] Step 7: Laser cutting on laser cutting equipment.

[0127] Fix the simple cutting fixture 41 on the working platform of the laser cutting equipment, place the drawn process part 11 on the corner surface positioning plate 39 and the middle section positioning plate 40 of the simple cutting fixture 41, and perform the outer shape cutting of the U-shaped skin 1 according to the prepared laser cutting program. After removing the edge burrs, a U-shaped skin 1 part with streamlined shape and dimensions that meet the requirements of the drawing is obtained.

[0128] A few points need to be explained: All dimensions described in this invention are in millimeters (mm) unless otherwise specified; according to the Aviation Manufacturing Engineering Manual - Aircraft Sheet Metal Process, the allowable limit drawing coefficient for the first deep drawing of stainless steel is m j =0.52~0.55, the invention stipulates the drawing coefficient of the blank structure corresponding to different longitudinal and transverse positions of the drawing process parts, thereby constructing the drawing process parts structure, which can make the drawing process parts more manufacturable; the invention is applicable to austenitic stainless steel with a material thickness in the range of 1.5~3.5mm, and its drawing process parts and drawing die structure design ideas can also refer to precipitation hardened stainless steel and similar structures with stainless steel material thickness <1.5mm; the support plate used for positioning parts in the cutting fixture can be made of graphite materials to achieve heat insulation in the cut area and reduce the thermal impact on the material during laser cutting; the deep U-shaped skin targeted by the invention has a large chord height. If the curvature of the boat shape is relatively gentle and the chord height is less than 40mm, it is not necessary to adopt a full wrapping structure when unfolding the blank.

[0129] So far, the purpose of the present invention has been achieved.

[0130] The above are only 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 in the protection scope of the present invention.

Claims

1. A stainless steel deep U-shaped thick skin welding drawing and shaping method, characterized in that: The steps include: Step 1: Construct a U-shaped skin drawing process part. The drawing process part is designed according to the U-shaped skin theoretical shape, which includes: The main forming surface is a boat-shaped extension surface that matches the U-shaped skin outer surface. The consistency between the main forming surface and the U-shaped skin outer surface is determined by the material thickness t of the U-shaped skin. The main forming surface and the U-shaped skin outer surface maintain a certain outward offset b, and the offset b is linearly related to the material thickness t. The anti-wrinkle surface is a door opening-shaped plane that matches the shapes of both ends of the main forming surface; The transition fillet surface is an arched curved surface formed by smoothly connecting the anti-wrinkle surface and the main forming surface through a large corner radius R. The transition fillet surface connects the two anti-wrinkle surfaces and the main forming surface into a semi-enclosed cabin. The initial sealing surface is the closed surface at the opening of the semi-enclosed cabin. The flange surface is an annular surface that is opposite to the curvature of the U-shaped skin and matches the size of the opening of the semi-enclosed cabin; Step 2: Construct a U-shaped skin drawing process blank, which includes: U-shaped skin unfolded blank, using the blank back calculation function of finite element simulation software to calculate the U-shaped skin unfolded blank, and obtain the U-shaped skin long strip or nearly square unfolded blank; The expanded blank of the drawing process part is calculated by using the blank back calculation function of the finite element simulation software to obtain the oblong or nearly circular expanded blank of the U-shaped skin drawing process part; The welded blank is obtained by laser welding three sheets of sheet metal to form a blank with the same shape as the unfolded blank of the drawing process part. The welded blank is divided into two crown-shaped compensation blanks and one drum-shaped controlled blank by two straight weld lines. The process blank is a blank that is pre-bent from the welded blank into a blank with a curvature close to that of the flange surface of the drawing process part; Step 3: Design a drawing die structure according to the drawing process parts, which includes a concave die, a blank holder and a punch. A gap control groove is provided in the non-process blank area of ​​the blank holder working surface, and a gap control pad matching its shape is filled in the gap control groove. A longitudinal draw rib and a transverse draw rib are provided in the process blank outline of the blank holder working surface; Step 4: Rapidly construct a cutting fixture according to the drawing process parts, which is manufactured by slotting and splicing multiple stainless steel plates or positioning them by spot welding; Step 5: Make the process blank of the drawing process part. According to the design size of the blank of the drawing process part, weld three corresponding rectangular stainless steel plates into a whole, perform laser cutting, apply plastic film, and roll the curvature; Step 6: placing the process blank on a drawing machine for deep drawing, and obtaining a U-shaped skin deep drawing process part after the forming is completed; Step 7: Fix the cutting fixture on the work platform, place the drawn part obtained in step 6 on the cutting fixture, and perform laser cutting using laser cutting equipment to obtain a U-shaped skin part.

2. A stainless steel deep U-shaped ship-shaped thick skin tailor-welded drawing and shaping method according to claim 1, characterized in that: In step 1, the offset b is not a fixed value. The criterion for whether it needs to be revised 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 recorded as w, and the cross-sectional dimension of the middle of the U-shaped skin is recorded as l. j , whether to revise the criteria When m h ≥0.55, the main forming surface shall be To offset, when m h When <0.55, the main forming surface is consistent with the U-shaped skin outer surface, and there is no need to consider the offset.

3. A stainless steel deep U-shaped ship-shaped thick skin tailor-welding drawing and shaping method according to claim 2, characterized in that: In step 1, the design principle of the outer contour size of the main forming surface is: the arc length of the boat-shaped outer contour of the U-shaped skin is denoted as l0, and the arc length of the boat-shaped outer contour of the main forming surface is denoted as l1, and 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, and H1 needs to satisfy (H0+20)≤H1≤(H0+50).

4. A stainless steel deep U-shaped ship-shaped thick skin tailor-welding drawing and shaping method according to claim 1, characterized in that: In step 1, the inclination of the anti-wrinkle surface can be based on the length l of the semi-enclosed cabin opening. c The wrinkle-proof surface is divided into the initial wrinkle-proof surface and the optimized wrinkle-proof surface according to the criteria for optimization. The height of the initial wrinkle-proof surface is recorded as H2. The formula for whether the wrinkle-proof surface needs to be optimized is: When m z >0.6, there is no need to optimize the initial anti-wrinkle surface inclination angle, the initial anti-wrinkle surface is the anti-wrinkle surface, when m z When ≤0.6, it is necessary to tilt the initial anti-wrinkle surface outward at a certain angle θ to obtain an optimized anti-wrinkle surface, so as to reduce the forming height of the end of the drawing process part, and the optimized anti-wrinkle surface is the anti-wrinkle surface; The initial anti-wrinkle surface tilts outwards by a distance of l b , l b =H2×sinθ, the semi-enclosed cabin structure with straight arms at both ends is optimized as above, and the opening length of the optimized semi-enclosed cabin is 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 >0.6 formula, the minimum value of the tilt angle θ can be calculated min , the tilt angle θ range satisfies θ min <θ≤θ min +2°.

5. A stainless steel deep U-shaped ship-shaped thick skin tailor-welded drawing and shaping method according to claim 1 or 3, characterized in that: In step 1, the value of 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, the outer contour size of the U-shaped skin must be considered when designing the value of the corner radius R. 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.

6. The method for shaping a stainless steel deep U-shaped ship with thick skin by tailor-welding and drawing according to claim 1, characterized in that: In step 1, the flange surface is obtained by bending-stretching-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 is extended 50 to 60 mm outward. The extended curvature sealing surface cuts the semi-enclosed cabin into a die cabin. The semi-enclosed cabin cuts the extended curvature sealing surface into an annular surface, namely the flange surface. The flange surface and the die cabin are connected to form a drawing process part through the die corner radius R1.

7. A stainless steel deep U-shaped ship-shaped thick skin tailor-welding drawing and shaping method according to claim 6, characterized in that: The curvature of the curvature sealing surface is relatively gentle, and its design principle must meet the initial sealing surface length l z The arc length l of the curvature sealing surface q The percentage n≤98%, the value of n decreases with the increase of the height H1 of the semi-enclosed cabin. When H1≤400mm, n=1, and the initial sealing surface does not need to be reversely bent; When designing the curvature of the curvature sealing surface, the outer contour size of the U-shaped skin must also be considered to ensure that the distance between the opening line of the die cabin and the outer contour line of the U-shaped skin is ≥10mm.

8. The method for shaping a stainless steel deep U-shaped ship with thick skin by tailor-welding and drawing according to claim 6, characterized in that: The fillet radius R1 of the die connects the flange surface and the die cabin body smoothly. The size of R1 is related to the thickness t of the U-shaped skin material. The value of R1 must satisfy 6×t <R1≤10×t。 9. The method for shaping a stainless steel deep U-shaped ship with thick skin by tailor-welding and drawing according to 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 aviation stainless steel plates. The shape of the U-shaped skin unfolded blank is contained in the controlled blank contour. The welded blank is deep drawn to obtain a drawn process part. The two flat straight weld lines are deformed into two three-dimensional arched weld lines. The compensation blank is formed into an anti-wrinkle compensation part of the drawing process part, and the controlled blank is formed into a main forming part of the drawing process part. The drawing process part is composed of two anti-wrinkle compensation parts and a 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 margin.

10. A stainless steel deep U-shaped thick skin welding drawing die, characterized in that: include: The concave die is designed according to the outer shape structure of the drawing process part. The concave die is a block structure with a deep cavity. The pressing surface of the concave die is obtained by extending outward from the flange surface of the drawing process part. The size of the pressing surface of the concave die is designed based on the outer shape line of the process blank of the drawing process part. The pressing surface of the concave die is provided with longitudinal drawing grooves and transverse drawing grooves; The blank holder is designed according to the working surface of the die. It is a block structure with a certain curvature and a hollow interior. The working surface of the blank holder matches the pressing surface of the die and the outer contour is consistent. The working surface of the blank holder is provided with the outline of the drawing process blank and its flange edge line, which is used for blank positioning and forming effect detection. The punch is obtained by inward offset according to the cavity chamber. The specific structure corresponds to the cavity chamber of the drawing die. It is a convex block structure with a large height. The convex model surface is divided into an arch surface and two wrapping surfaces by two corner boundary lines. The punch arch surface corresponds to the main forming surface of the cavity chamber, and is obtained by inward offset of the main forming surface by 1.1×t. The punch wrapping surface corresponds to the anti-wrinkle surface and transition fillet surface of the cavity chamber. The punch wrapping surface is obtained by inward offset of the anti-wrinkle surface and transition fillet surface of the drawing process part by 1.2×t~1.5×t. The arch surface and the wrapping surface are smoothly connected. During forming, two straight weld lines of the welded blank of the drawing process part are stretched along with the movement of the punch, and finally two three-dimensional arched weld lines are formed, which are mainly distributed in the punch wrapping surface. A gap control groove is arranged in the non-process blank area on the working surface of the blank holder. The gap control groove is arranged near both sides of the compensation blank. The depth of the gap control groove is 3mm. The gap control pad matching its shape is filled in the gap control groove. The thickness of the gap control pad is determined according to the material flow during the pressure test of the deep drawing process. If the material flows evenly, the gap control pad can be omitted. If the material is obviously thinned or even cracked during deep drawing, the gap control pad is filled in the gap control groove. The thickness of the gap control pad is h. x =3+t+Δ, the value range of Δ is within the range of 0-0.8mm. The higher the H1 of the drawing process part and the thicker the material thickness t, the larger the value of Δ. Longitudinal drawing ribs and transverse drawing ribs are arranged in the outer shape line of the process blank on the working surface of the blank holder ring. The positions and lengths of the longitudinal drawing ribs and transverse drawing ribs correspond to the longitudinal edge line and transverse edge line of the flange edge line of the drawing process part respectively. The distance between the longitudinal drawing ribs and the transverse drawing ribs and the flange edge line of the drawing process part is 5mm to 10mm. There are certain restrictions on the height of the longitudinal and transverse draw bars. The cross-sectional height of the longitudinal draw bar h zj Satisfy the formula 3.5+t≤h zj ≤10, transverse drawbead section height h hj Satisfy the formula 1.5+t≤h hj ≤6, and h zj ≥h hj +2. The height of the drawbead is related to the material thickness t and the height H1 of the drawing process part. When the material thickness t is thicker, the drawbead height takes a larger value, otherwise it takes a smaller value. When the height H1 is larger, the drawbead height takes a smaller value, otherwise it takes a larger value. The finite element simulation of deep drawing can be used to verify the height of the drawbead and adjust and optimize it. The longitudinal drawing groove and transverse drawing groove on the die pressing surface match the longitudinal drawing ribs and transverse drawing ribs respectively. The gap between the longitudinal drawing groove and the longitudinal drawing ribs is designed according to 1.5×t, and the gap between the transverse drawing groove and the transverse drawing ribs is designed according to 1.5×t~2.0×t.

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