Method for controlling deep drawing instability of small-corner narrow-taper variable-curvature skin

Abstract

The invention provides a drawing instability control method for a small-corner narrow-taper variable-curvature skin. The drawing instability control method mainly comprises the following steps that a variable-curvature skin drawing process molded surface is constructed; determining the size of an unfolded blank; a drawing die structure of the variable-curvature skin is designed; and drawing and forming. According to the method, an end hemispherical closed structure is designed on the basis of the variable-curvature skin, and a variable-curvature skin drawing process molded surface is further constructed, so that a drawing die structure is determined. According to the method, the flowing speed and the flowing amount of the material are effectively controlled, so that the defects of wrinkling, cracking, springback and the like are avoided, uniform deformation of the part is realized, and the dimensional precision and the surface quality of the formed variable-curvature skin are greatly improved.

Description

Technical Field

[0001] The invention relates to a sheet metal parts forming technology in the field of aircraft manufacturing, in particular to a method for controlling deep drawing instability of a small-angle, narrow-cone, variable-curvature skin. Background Art

[0002] Variable curvature skin is an important part of the aircraft. In the aircraft structure, it not only bears the role of maintaining the aerodynamic shape and reducing air resistance, but also needs to withstand various loads and stresses during flight. Therefore, its manufacturing precision and quality requirements are extremely high. The shape of the variable curvature skin is usually more complex and has certain special designs. One type of small-angle, narrow-cone variable curvature skin has an overall shape extending from the root to the tip, showing a gradually narrowing cone with a sharp tip and a relatively small transition angle, which leads to uneven and unpredictable flow of the material during the forming process. For a long time, traditional drop forming processing with a high degree of manual intervention has been used. During the forming process, defects such as cracking, wrinkling, thinning, and rebound are prone to occur. In addition, the production efficiency is low, the internal damage risk is large, and the scrap rate is high, which seriously affects the forming accuracy and surface quality of this type of skin, and cannot meet the high quality and high stability requirements of modern aviation manufacturing.

[0003] In order to solve the problems of uneven material flow, poor surface quality and low tire pasting accuracy in the forming of small-angle, narrow-cone variable curvature skins, it is urgent to improve the forming process methods and mold structures to improve the manufacturing accuracy and surface quality of variable curvature skins and meet the high quality and high stability requirements of modern aircraft parts production. Summary of the invention

[0004] In order to solve the problems of unstable quality and uncontrollable deformation of small-angle, narrow-cone variable curvature skins during long-term press forming, easy instability and wrinkling, fatigue cracking during the forming process, low precision of variable curvature skins attached to the tire, and difficulty in meeting assembly requirements, the purpose of the present invention is to provide a method for controlling instability in deep drawing of small-angle, narrow-cone variable curvature skins.

[0005] The present invention provides a method for controlling the instability of deep drawing of a skin with a small turning angle and a narrow tapered variable curvature, comprising the following steps:

[0006] Step 1, constructing a variable curvature skin drawing process profile;

[0007] Step 2: Determine the size of the unfolded blank;

[0008] Step 3, designing a drawing die structure of the variable curvature skin according to the variable curvature skin drawing process profile;

[0009] Step 4: Deep drawing;

[0010] Step 5: Cut the shape.

[0011] Optionally, the step 1 constructs a variable curvature skin drawing process profile, and the specific process is as follows:

[0012] In the CATIA environment, the drawing process surface is designed based on the variable curvature skin surface;

[0013] Step 1-1: Construct auxiliary horizontal plane α

[0014] An auxiliary horizontal plane α is established with the variable curvature skin endpoints A, B, C, and D; the drawing direction F of the variable curvature skin is perpendicular to the auxiliary horizontal plane α;

[0015] Step 1-2: Create the initial work surface

[0016] The gradual concave cavity and outer edge flange of the variable curvature skin are extracted respectively, excluding the transition corner area; the gradual concave cavity is extended outward along the curvature to obtain the transition extension surface, and the outer edge flange is extended inward and outward to obtain the transition flange surface; the transition extension surface and the transition flange surface intersect at the conical curve L1, and the conical curve L1 is used to cut the transition extension surface and the transition flange surface to obtain the initial working surface;

[0017] Step 1-3: Design the hemispherical closure at the end

[0018] Extract the contour line of the opening of the variable curvature skin end, and extend it 15mm to 20mm outward along the curvature of the variable curvature skin to obtain the transition margin area; create a spline L2 with points E and N as control points and AN and BE as tangent directions; take the midpoint F of the spline L2 and the contour arc of the variable curvature skin end The midpoint G, with the midpoints F and G as control points, establish the guide line L3; through The spline L2 and the guide line L3 create a multi-section surface, and finally a hemispherical closed body is obtained;

[0019] Step 1-4: Design the drawing process profile

[0020] The filling function is used to fill the gap between the outer edge flange and the hemispherical closed body to obtain the annular flange surface, the hemispherical closed body and the annular flange surface are spliced ​​into a whole, and a variable fillet transition is performed to obtain a closed extension body; the fillet radius of the initial working surface is transitioned according to the variable curvature skin corner radius R=3.8mm and then combined with the closed extension body to obtain the initial process surface; the flange outer contour line L4 of the initial process surface is extracted and extended outward by 90mm along the flange curvature direction to obtain the initial flange surface; the initial process surface and the initial flange surface are combined into a variable curvature skin drawing process surface.

[0021] Optionally, the step 2 is to determine the size of the unfolded blank, and the specific process is as follows:

[0022] Step 2-1: Import the variable curvature skin surface into the finite element analysis software, and use the blank inverse calculation function to calculate the unfolded blank size and the unfolded outline of the variable curvature skin.

[0023] Optionally, the step 3 is to design a drawing die structure of a variable curvature skin, and the specific process is as follows:

[0024] Step 3-1: Design the die structure

[0025] The initial flange surface of the drawing process profile is extended outward along the curvature, and the extended drawing process profile is used as the concave model surface; the shape of the outer contour surface of the concave die is adapted to the concave model surface, the outer contour surface of the concave die can include the drawing process profile as a whole, the outer contour line of the concave die and the initial flange surface are relatively uniform, and the distance between the two is ≧50mm, and a variable curvature skin contour line is drawn on the outer contour surface of the concave die;

[0026] Step 3-2: Design the blank holder structure

[0027] The outer contour surface of the die is extracted as the working profile of the blank holder. Three calendering ribs are arranged on the working profile of the blank holder, including one V-shaped calendering rib and two arc-shaped calendering ribs, to control the material flow and ensure uniform deformation of the raw material. The center line of the calendering rib matches the shape of the outer contour line of the initial process profile flange. The center line of the arc-shaped calendering rib is offset 15mm to 18mm outward from the outer contour line of the annular flange surface, and then evenly divided into three equal parts. The middle part is removed, and the arcs at both ends are retained.

[0028] A split horizontal plane β is established through the midpoint G, and the split horizontal plane β is perpendicular to the auxiliary horizontal plane α; the center line of the V-shaped rib is offset 15mm to 18mm outward from the outer edge flange contour line of the variable curvature skin, and the split horizontal plane β is used to remove the redundant line segments at both ends; the cross-sectional dimensions of the V-shaped rib and the arc-shaped rib are both semicircular cross-sectional dimensions, but the dimensions are different; the V-shaped rib is distributed around the gradually changing deep cavity of the variable curvature skin, where the curvature of the outer shape changes greatly, the fillet radius R1 of the V-shaped rib is 3.5mm, and the height H1 is 6mm to 7mm; two arc-shaped ribs are distributed around the closed extension body, with a fillet radius R2=4.5mm and a height H2=5mm;

[0029] Step 3-3: Design the calendering ribs of the die

[0030] The calendering ribs of the die are distributed on the initial flange surface of the outer contour of the die. The calendering rib structure of the die matches the calendering ribs of the blank holder, and the shapes and sizes of the two correspond to each other.

[0031] Step 3-4: Design the punch structure

[0032] The punch structure is designed based on the outer contour surface of the die, and the shape of the punch working surface is adapted to the inner shape of the drawing process surface.

[0033] Optionally, the gap between the working surface of the punch and the outer contour surface of the die is i=(1.0-1.1)δ;

[0034] δ is the material thickness of the variable curvature skin.

[0035] Optionally, the step 4 of deep drawing is as follows:

[0036] Step 4-1: Install the drawing die

[0037] Install the concave die on the work surface of the deep drawing machine, install the punch and blank holder on the work surface under the deep drawing machine, and ensure the matching accuracy between the blank holder and the punch; ensure the parallelism and verticality of the concave and punch to the work surface, and install them firmly; use the adjustment device of the press to adjust the closing height of the die; apply an appropriate amount of lubricant on the contact surface between the die and the blank;

[0038] Step 4-2: Expand the blank and position it

[0039] Use a clean cotton cloth to clean the unrolled blank to be formed, and lay a plastic film evenly on the surface of the unrolled blank; clean the effective molding surface and the effective pressing surface of the mold again, and apply a proper amount of lubricant; position the unrolled blank on the blank holder;

[0040] Step 4-3: Deep drawing

[0041] The die moves downward along the drawing direction F until it closes with the blank holder, and then continues to move downward with the blank holder clamped. The expanded blank is subjected to a certain blank holder force. Under the action of the punch, the expanded blank gradually deforms and enters the cavity of the die. During the drawing process, the presence of V-shaped calendering ribs and arc-shaped calendering ribs increases the resistance to material flow, avoiding wrinkles and cracks during forming. When the expanded blank completely enters the gap between the die and the punch, the drawing ends, and the initial process part is obtained after removing the plastic film.

[0042] Step 4-4: Heat treatment

[0043] According to the requirements of the digital model, the initial process parts are subjected to solution heat treatment to improve their strength and hardness;

[0044] Step 4-5: Reshaping after heat treatment

[0045] During the heat treatment process, the deformed initial process parts are corrected by deep drawing equipment or manual shaping to make them fit perfectly with the die.

[0046] Optionally, the specific process of cutting the shape in step 5 is as follows:

[0047] The initial process parts are cut and sanded according to the variable curvature skin outline on the outer contour surface of the die, and finally the variable curvature skin parts that meet the requirements of the design digital model are obtained.

[0048] Optionally, the variable fillet radius Rf gradually increases from both ends to the middle, and the gradient value range is Rf=3.8mm~25mm.

[0049] The beneficial effects of the present invention are as follows: the present invention provides a method for controlling the instability of deep drawing of a small-angle, narrow-cone variable curvature skin. A hemispherical closed structure at the end is designed based on the variable curvature skin, which increases the plastic deformation area of ​​the variable curvature skin during the deep drawing process, balances the material flow, and avoids transition accumulation or insufficiency in local areas. V-shaped calendering ribs and arc-shaped calendering ribs are designed according to the principle of being perpendicular to the flow stress of the raw material, which effectively controls the material flow speed and flow amount, thereby avoiding the occurrence of defects such as wrinkling, cracking and rebound, and achieving uniform deformation of parts. The present invention provides a narrow-cone variable curvature skin deep drawing forming process method with a relatively small transition angle, which replaces the traditional drop forming, can make the material better fit the mold shape, and greatly improves the dimensional accuracy and surface quality of the variable curvature skin after forming. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a schematic diagram of the variable curvature skin structure;

[0051] Figure 2 This is a schematic diagram of the initial working surface of the variable curvature skin;

[0052] Figure 3 This is a schematic diagram of the initial process profile of the variable curvature skin;

[0053] Figure 4 This is a schematic diagram of the variable curvature skin drawing process profile;

[0054] Figure 5 It is a schematic diagram of the variable curvature skin concave mold structure;

[0055] Figure 6 This is a schematic diagram of the variable curvature skin pressure ring structure;

[0056] Figure 7 This is a schematic diagram of the variable curvature skin drawing die structure;

[0057] Description of reference numerals:

[0058] 1 variable curvature skin, 2 variable curvature skin outer surface, 3 gradual concave cavity, 4, outer edge flange, 5 transition extension surface, 6 transition flange surface, 7 initial working surface, 8 transition allowance area, 9 end hemispherical closed body, 10 annular flange surface, 11 closed extension body, 12 initial process surface, 13 initial flange surface, 14 drawing process surface, 15 unfolded blank, 16 concave model surface, 17 concave die outer contour, 18 concave die, 19 V-shaped rolling rib, 20 circular arc rolling rib, 21 pressure ring, 22 rolling concave rib, 23 punch, 24 variable curvature skin outer line, L1 conical curve, L2 spline, L3 guide line, L4 initial process surface flange outer contour line, L5 rough material unfolded outer contour line, L6 initial flange surface outer contour line. DETAILED DESCRIPTION

[0059] The present application is further described in detail below in conjunction with the accompanying drawings of the embodiments.

[0060] The present invention provides a method for controlling the instability of deep drawing of a skin with a small turning angle and a narrow tapered variable curvature, wherein the deep drawing die is composed of a concave die, a convex die and a blank holder. The deep drawing die structure model is established based on the digital model of the variable curvature skin product by using CATIA three-dimensional design software. The forming method comprises the following steps:

[0061] Step 1: Construct variable curvature skin drawing process profile

[0062] In the CATIA environment, the drawing process surface is designed based on the variable curvature skin surface;

[0063] Step 1-1: Construct auxiliary horizontal plane α

[0064] An auxiliary horizontal plane α is established with the variable curvature skin endpoints A, B, C, and D; the drawing direction F of the variable curvature skin is perpendicular to the auxiliary horizontal plane α;

[0065] Step 1-2: Create the initial work surface

[0066] The gradual concave cavity and outer edge flange of the variable curvature skin are extracted separately, excluding the transition corner area. The gradual concave cavity is extended outward along the curvature to obtain the transition extension surface, and the outer edge flange is extended inward and outward to obtain the transition flange surface. The transition extension surface and the transition flange surface intersect at the conical curve L1, and the conical curve L1 is used to cut the transition extension surface and the transition flange surface to obtain the initial working surface;

[0067] Step 1-3: Design the hemispherical closure at the end

[0068] Extract the contour line of the variable curvature skin end opening, and extend 15mm to 20mm outward along the curvature of the variable curvature skin to obtain the transition margin area. Create a spline L2 with points E and N as control points and AN and BE as tangent directions; take the midpoint F of the spline L2 and the contour arc of the variable curvature skin end The midpoint G, with the midpoints F and G as control points, establish the guide line L3; through The spline L2 and the guide line L3 create a multi-section surface, and finally a hemispherical closed body is obtained.

[0069] Step 1-4: Design the drawing process profile

[0070] The filling function is used to fill the gap between the outer flange and the hemispherical closed body to obtain the annular flange surface, the hemispherical closed body and the annular flange surface are spliced ​​into a whole, and a variable fillet transition is performed to obtain a closed extension body. Variable fillet radius R f The gradient value range is R. f =3.8mm~25mm. The fillet radius of the initial working surface is transitioned according to the variable curvature skin corner radius R=3.8mm and combined with the closed extension body to obtain the initial process profile. The flange outer contour line L4 of the initial process profile is extracted and extended outward 90mm along the flange curvature direction to obtain the initial flange surface, and the initial process profile and the initial flange surface are combined into the variable curvature skin drawing process profile.

[0071] Step 2: Determine the size of the unfolded blank

[0072] Step 2-1: Import the variable curvature skin surface into the finite element analysis software, and use the blank inverse calculation function to calculate the unfolded blank size and the unfolded outline of the variable curvature skin.

[0073] Step 3: Design the drawing die structure of the variable curvature skin

[0074] The drawing die structure is designed based on the drawing process profile of the variable curvature skin and the unfolded blank, including the concave die, the convex die and the blank holder, a total of three parts

[0075] Step 3-1: Design the die structure

[0076] The initial flange surface of the drawing process profile is extended outward along the curvature, and the extended drawing process profile is used as the concave model surface. The shape of the outer contour surface of the die is adapted to the concave model surface, and the size of the outer contour surface of the die is designed by referring to the drawing process profile surface. The outer contour surface of the die can contain the drawing process profile as a whole, and the distance between the outer contour surface of the die and the outer contour line of the initial flange surface is relatively uniform, and the distance between the two is ≧50mm, ensuring that the mold has sufficient strength and rigidity to withstand various loads during the forming process. Draw the variable curvature skin outline on the outer contour surface of the die.

[0077] Step 3-2: Design the blank holder structure

[0078] The outer contour surface of the die is extracted as the working surface of the blank holder. There are three calendering ribs on the working surface of the blank holder, one V-shaped calendering rib and two arc-shaped calendering ribs, to control the material flow and ensure uniform deformation of the raw material. The center line of the calendering rib matches the shape of the outer contour line of the initial process profile flange. The center line of the arc-shaped calendering rib is offset 15mm to 18mm outward from the outer contour line of the annular flange surface, and then evenly divided into three equal parts, removing the middle part and retaining the arcs at both ends. The split horizontal plane β is established through the end point G, and the split horizontal plane β is perpendicular to the auxiliary horizontal plane α. The center line of the V-shaped calendering rib is offset 15mm to 18mm outward from the outer edge flange contour line of the variable curvature skin, and the split horizontal plane β is used to remove the redundant line segments at both ends. The cross-sectional dimensions of the V-shaped calendering rib and the arc-shaped calendering rib are both semicircular cross-sectional dimensions, but the dimensions are different. The V-shaped ribs are distributed around the gradually changing deep cavity of the variable curvature skin, where the curvature of the outer shape changes greatly. The fillet radius of the V-shaped ribs is R1 = 3.5mm, and the height is H1 = 6mm to 7mm. Two arc-shaped ribs are distributed around the closed extension body, with a fillet radius of R2 = 4.5mm and a height of H2 = 5mm.

[0079] Step 3-3: Design the calendering ribs of the die

[0080] The die's calendering ribs are distributed on the initial flange surface of the die's outer contour. The die's calendering rib structure matches the blank holder's calendering ribs. Their shapes and sizes correspond to each other, and an appropriate gap is maintained to achieve good material flow.

[0081] Step 3-4: Design the punch structure

[0082] The punch structure is designed based on the outer contour surface of the die, and the shape of the die working surface is adapted to the inner shape of the drawing process surface. The gap value between the punch working surface and the outer contour surface of the die is recorded as i. The variable curvature skin material is aluminum alloy, and the manufacturing accuracy requirement is high. The drawing gap i = (1.0 ~ 1.1) δ can make the wall thickness of the variable curvature skin uniform, thereby improving its surface quality and dimensional accuracy.

[0083] Step 4: deep drawing;

[0084] Step 4-1: Install the drawing die

[0085] Install the concave die on the work surface of the drawing machine, and install the punch and blank holder on the work surface under the drawing machine to ensure the matching accuracy between the blank holder and the punch. Ensure the parallelism and verticality of the concave and punch to the work surface, and install them firmly. Use the adjustment device of the press to adjust the closing height of the die. Apply an appropriate amount of lubricant on the contact surface between the die and the blank to reduce friction and improve production efficiency;

[0086] Step 4-2: Expand the blank and position it

[0087] Use a clean cotton cloth to clean the unrolled blank to be formed, and lay a plastic film evenly on the surface of the unrolled blank. Clean the effective mold surface and the effective pressing surface of the mold again, and apply an appropriate amount of lubricant. Position the unrolled blank on the blank holder.

[0088] Step 4-3: Deep drawing

[0089] The die moves downward along the drawing direction F until it closes with the blank holder, and then continues to move downward with the blank holder clamped. The expanded blank is subjected to a certain blank holder force. Under the action of the punch, the expanded blank gradually deforms and enters the cavity of the die. During the drawing process, the presence of V-shaped calendering ribs and arc-shaped calendering ribs increases the resistance to material flow and avoids wrinkling and rupture during forming. When the expanded blank enters the gap between the die and the punch, the drawing ends, and the initial process part is obtained after removing the plastic film.

[0090] Step 4-4: Heat treatment

[0091] According to the requirements of the digital model, the initial process parts are subjected to solution heat treatment to improve their strength and hardness. Taking advantage of the good plasticity of the material during the aging period, subsequent shape trimming and cutting are carried out.

[0092] Step 4-5: Reshaping after heat treatment

[0093] During the heat treatment process, the initial process parts may be deformed due to thermal stress and structural transformation. The deformed initial process parts are corrected by deep drawing equipment or manual shaping to make them fit the die perfectly.

[0094] Step 5: Cutting the Outline

[0095] The initial process parts are cut and sanded according to the variable curvature skin outline on the outer contour surface of the die, and finally the variable curvature skin parts that meet the requirements of the design digital model are obtained.

[0096] Referring to the accompanying drawings, the aircraft sheet metal parts provided in the embodiment are as follows Figure 1 As shown in the figure, the prominent features of the small-angle, narrow-cone variable curvature skin are: the overall shape is saddle-shaped and the surface is smooth and continuous; when viewed from the side, the distance between the highest point and the bottom of the skin is about 130mm, presenting an asymmetric shape; and the transition curve from the root to the tip is relatively gentle, the corner radius is relatively small, about 3.8mm; the end opening size is close to 270mm. Due to the complex structural characteristics of this type of variable curvature skin, there are obvious differences in the flow speed and flow amount of the material in different areas. In the narrow conical area, from the wide end to the narrow end, the flow speed of the material gradually increases and the flow amount gradually decreases; the existence of small angles makes the material flow relatively slow, which is prone to stress concentration.

[0097] The overall shape of the variable curvature skin 1 is saddle-shaped, and the transition angle is relatively small. The material flows unevenly and unpredictably during the forming process. The variable curvature skin 1 has long been processed by step-down forming. During the forming process, defects such as cracking, wrinkling, thinning, and rebound are prone to occur. In addition, the production efficiency is low, the internal damage risk is high, and the scrap rate is high, which seriously affects the forming accuracy and surface quality of this type of skin.

[0098] like Figures 1 to 7 As shown, a method for controlling the instability of deep drawing of a small-angle, narrow-cone variable-curvature skin comprises the following steps:

[0099] Step 1: Construct variable curvature skin drawing process profile 14

[0100] In CATIA environment, the drawing process surface is designed based on the variable curvature skin profile surface 2;

[0101] Step 1-1: Construct auxiliary horizontal plane α

[0102] An auxiliary horizontal plane α is established with the endpoints A, B, C, and D of the variable curvature skin 1; the drawing direction F of the variable curvature skin 1 is perpendicular to the auxiliary horizontal plane α;

[0103] Step 1-2: Create the initial work surface 7

[0104] The gradual concave cavity 3 and the outer edge flange 4 of the variable curvature skin 1 are extracted respectively, excluding the transition corner area. The gradual concave cavity 3 is extended outward along the curvature to obtain the transition extension surface 5, and the outer edge flange 4 is extended inward and outward to obtain the transition flange surface 6. The transition extension surface 5 and the transition flange surface 6 intersect at the conical curve L1, and the conical curve L1 is used to cut the transition extension surface 5 and the transition flange surface 6 to obtain the initial working surface 7;

[0105] Step 1-3: Design the end hemispherical closure 9

[0106] Extract the contour line of the opening of the variable curvature skin 1 end, and extend it 15mm to 20mm outward along the curvature of the variable curvature skin to obtain the transition margin area 8. Create a spline L2 with points E and N as control points and AN and BE as tangent directions; take the midpoint F of the spline L2 and the contour arc of the variable curvature skin 1 end The midpoint G, with the midpoints F and G as control points, establish the guide line L3. The spline L2 and the guide line L3 create a multi-section surface, and finally a hemispherical closed body 9 is obtained.

[0107] Step 1-4: Design the drawing process profile 14

[0108] The gap between the outer flange 4 and the hemispherical closed body 9 is filled with a filling function to obtain an annular flange surface 10, the hemispherical closed body 9 and the annular flange surface 10 are spliced ​​into a whole, and a variable fillet transition is performed to obtain a closed extension body 11. Variable fillet radius R f The gradient value range is R. f =3.8mm~25mm. The fillet radius of the initial working surface 7 is transitioned according to the corner radius R=3.8mm of the variable curvature skin 1 and combined with the closed extension body 11 to obtain the initial process profile 12. The flange outer contour line L4 of the initial process profile 12 is extracted and extended outward by 90mm along the flange curvature direction to obtain the initial flange surface 13, and the initial process profile 12 and the initial flange surface 13 are combined to form the variable curvature skin 1 drawing process profile 14.

[0109] Step 2: Determine the size of the unfolded blank 15

[0110] Step 2-1: Import the variable curvature skin 1 profile into the finite element analysis software, and use the blank inverse calculation function to calculate the size of the unfolded blank 15 of the variable curvature skin 1 and the unfolded outline L5 of the blank;

[0111] Step 3: Design the drawing die structure of the variable curvature skin 1

[0112] The drawing die structure is designed based on the drawing process profile 14 of the variable curvature skin 1 and the unfolded blank 15, including a concave die 18, a convex die 23 and a blank holder 21, which are three parts in total.

[0113] Step 3-1: Design the structure of the die 18

[0114] The initial flange surface 13 of the drawing process profile 14 is extended outward along the curvature, and the extended drawing process profile 14 is used as the concave model surface 16. The shape of the concave mold outer contour surface 17 is adapted to the concave model surface 16, and the concave mold outer contour surface 17 can include the drawing process profile 14 as a whole, and the distance between the concave mold outer contour surface 17 and the outer contour line L6 of the initial flange surface 13 is relatively uniform, and the distance between the two is ≧50mm, ensuring that the mold has sufficient strength and rigidity to withstand various loads during the forming process. The variable curvature skin outline 24 is drawn on the concave mold outer contour surface 17.

[0115] Step 3-2: Design the structure of the blank holder 21

[0116] The outer contour surface 17 of the die is extracted as the working profile of the blank holder 21. There are three ribs on the working profile of the blank holder 21, one V-shaped rib 19 and two arc-shaped ribs 20, to control the material flow and ensure uniform deformation of the raw material. The center line of the rib matches the shape of the outer contour line L4 of the flange of the initial process profile 12, where the center line of the arc-shaped rib 20 is offset 15mm to 18mm outward from the outer contour line of the annular flange surface 10, and then evenly divided into three equal parts, removing the middle part and retaining the arcs at both ends. The splitting horizontal plane β is established through the end point G, and the splitting horizontal plane β is perpendicular to the auxiliary horizontal plane α. The center line of the V-shaped rib 19 is offset 15mm to 18mm outward from the outer edge flange 4 contour line of the variable curvature skin 1, and the cutting horizontal plane β is used to remove the redundant line segments at both ends. The cross-sectional dimensions of the V-shaped rib 19 and the arc-shaped rib 20 are both semicircular cross-sectional dimensions, but the dimensions are different. The V-shaped ribs 19 are distributed around the gradually changing deep cavity 3 of the variable curvature skin 1, where the curvature of the outer shape changes greatly, and the fillet radius R1 of the V-shaped ribs 19 is 3.5 mm, and the height H1 is 6 mm to 7 mm. Two arc-shaped ribs 20 are distributed around the closed extension body 11, and the fillet radius R2 is 4.5 mm, and the height H2 is 5 mm.

[0117] Step 3-3: Design the calendering rib 22 of the die 18

[0118] The rolled ribs 22 of the die 18 are distributed on the initial flange surface 13 of the die outer contour surface 17. The rolled ribs 22 of the die 18 match the rolled ribs of the blank holder 21. The shapes and sizes of the two correspond to each other and an appropriate gap is maintained to achieve good material flow.

[0119] Step 3-4: Design the structure of the punch 23

[0120] The structure of the punch 23 is designed based on the outer contour surface 17 of the die, and the shape of the working surface of the die 18 is adapted to the inner shape of the drawing process surface 14. The clearance value between the working surface of the punch 23 and the outer contour surface 17 of the die is recorded as i. The variable curvature skin 1 is made of aluminum alloy and has high manufacturing accuracy requirements. The drawing clearance i=(1.0~1.1)δ can make the wall thickness of the variable curvature skin 1 uniform, thereby improving its surface quality and dimensional accuracy.

[0121] Step 4: deep drawing;

[0122] Step 4-1: Install the drawing die

[0123] Install the die 18 on the work surface of the drawing machine, and install the punch 23 and the blank holder 21 on the work surface under the drawing machine, ensuring the matching accuracy between the blank holder 21 and the die 23. Ensure the parallelism and verticality of the die 18 and the punch 23 to the work surface, and install them firmly. Use the adjustment device of the press to adjust the closing height of the die. Apply an appropriate amount of lubricant on the contact surface between the die and the unfolded blank to reduce friction and improve production efficiency;

[0124] Step 4-2: Expand the blank 15 and position it

[0125] Use a clean cotton cloth to clean the unrolled blank 15 to be formed, and lay a plastic film evenly on the surface of the unrolled blank 15. Clean the effective molding surface and the effective pressing surface of the mold again, and apply a proper amount of lubricant. Position the unrolled blank 15 on the blank holder 21.

[0126] Step 4-3: Deep drawing

[0127] The die 18 moves downward along the drawing direction F until it closes with the blank holder 21, and then continues to move downward with the blank holder 21 while clamping the expanded blank 15. The expanded blank 15 is subjected to a certain blank holder force. Under the action of the punch 23, the expanded blank 15 gradually deforms and enters the cavity of the die 18. During the drawing process, the presence of the V-shaped calendering ribs 19 and the arc-shaped calendering ribs 20 increases the resistance to material flow and avoids wrinkling and cracking during forming. When the expanded blank 15 completely enters the gap between the die 18 and the punch 23, the drawing is completed, and the initial process part is obtained after removing the plastic film.

[0128] Step 4-4: Heat treatment

[0129] According to the requirements of the digital model, the initial process parts are subjected to solution heat treatment to improve their strength and hardness. Taking advantage of the good plasticity of the material during the aging period, subsequent shape trimming and cutting are carried out.

[0130] Step 4-5: Reshaping after heat treatment

[0131] During the heat treatment process, the initial process part may be deformed due to thermal stress and structural transformation. The deformed initial process part is corrected by deep drawing equipment or manual shaping to make it fit the die 18 completely.

[0132] Step 5: Cutting the Outline

[0133] The initial process parts are cut and sanded according to the variable curvature skin outline 24 on the outer contour surface 17 of the concave mold, and finally the variable curvature skin 1 parts that meet the design digital model requirements are obtained.

Claims

1. A method for controlling the instability of deep drawing of a small-angle, narrow-cone variable-curvature skin, characterized in that: The following steps are involved: Step 1, constructing a variable curvature skin drawing process profile; Step 2: Determine the size of the unfolded blank; Step 3, designing a drawing die structure of the variable curvature skin according to the variable curvature skin drawing process profile; Step 4: Deep drawing; Step 5: Cut the shape.

2. A method for controlling instability of deep drawing of a small-angle, narrow-cone variable-curvature skin according to claim 1, characterized in that: The step 1 constructs a variable curvature skin drawing process profile, and the specific process is as follows: In the CATIA environment, the drawing process surface is designed based on the variable curvature skin surface; Step 1-1: Construct auxiliary horizontal plane α An auxiliary horizontal plane α is established with the variable curvature skin endpoints A, B, C, and D; the drawing direction F of the variable curvature skin is perpendicular to the auxiliary horizontal plane α; Step 1-2: Create the initial work surface The gradual concave cavity and outer edge flange of the variable curvature skin are extracted respectively, excluding the transition corner area; the gradual concave cavity is extended outward along the curvature to obtain the transition extension surface, and the outer edge flange is extended inward and outward to obtain the transition flange surface; the transition extension surface and the transition flange surface intersect at the conical curve L1, and the conical curve L1 is used to cut the transition extension surface and the transition flange surface to obtain the initial working surface; Step 1-3: Design the hemispherical closure at the end Extract the contour line of the opening of the variable curvature skin end, and extend it 15mm to 20mm outward along the curvature of the variable curvature skin to obtain the transition margin area; create a spline L2 with points E and N as control points and AN and BE as tangent directions; take the midpoint F of the spline L2 and the contour arc of the variable curvature skin end The midpoint G, with the midpoints F and G as control points, establish the guide line L3; through The spline L2 and the guide line L3 create a multi-section surface, and finally a hemispherical closed body is obtained; Step 1-4: Design the drawing process surface The filling function is used to fill the gap between the outer edge flange and the hemispherical closed body to obtain the annular flange surface, the hemispherical closed body and the annular flange surface are spliced ​​into a whole, and a variable fillet transition is performed to obtain a closed extension body; the fillet radius of the initial working surface is transitioned according to the variable curvature skin corner radius R=3.8mm and then combined with the closed extension body to obtain the initial process surface; the flange outer contour line L4 of the initial process surface is extracted and extended outward by 90mm along the flange curvature direction to obtain the initial flange surface; the initial process surface and the initial flange surface are combined into a variable curvature skin drawing process surface.

3. The method for controlling the instability of deep drawing of a small-angle, narrow-cone variable-curvature skin according to claim 2 is characterized in that: The step 2 described above determines the size of the unfolded blank, and the specific process is as follows: Step 2-1: Import the variable curvature skin surface into the finite element analysis software, and use the blank inverse calculation function to calculate the unfolded blank size and the unfolded outline of the variable curvature skin.

4. A method for controlling instability of deep drawing of a small-angle, narrow-cone variable-curvature skin according to claim 3, characterized in that: The step 3 designs the drawing die structure of the variable curvature skin, and the specific process is as follows: Step 3-1: Design the die structure The initial flange surface of the drawing process profile is extended outwardly along the curvature, and the extended drawing process profile is used as the concave model surface; The shape of the outer contour surface of the die is adapted to the concave model surface. The outer contour surface of the die can include the drawing process profile as a whole. The distance between the outer contour surface of the die and the outer contour line of the initial flange surface is relatively uniform, and the distance between the two is ≧50mm. A variable curvature skin contour line is drawn on the outer contour surface of the die. Step 3-2: Design the blank holder structure The outer contour surface of the die is extracted as the working profile of the blank holder. Three calendering ribs are arranged on the working profile of the blank holder, including one V-shaped calendering rib and two arc-shaped calendering ribs, to control the material flow and ensure uniform deformation of the raw material. The center line of the calendering rib matches the shape of the outer contour line of the initial process profile flange. The center line of the arc-shaped calendering rib is offset 15mm to 18mm outward from the outer contour line of the annular flange surface, and then evenly divided into three equal parts. The middle part is removed, and the arcs at both ends are retained. A split horizontal plane β is established through the midpoint G, and the split horizontal plane β is perpendicular to the auxiliary horizontal plane α; the center line of the V-shaped rib is offset 15mm to 18mm outward from the outer edge flange contour line of the variable curvature skin, and the split horizontal plane β is used to remove the redundant line segments at both ends; the cross-sectional dimensions of the V-shaped rib and the arc-shaped rib are both semicircular cross-sectional dimensions, but the dimensions are different; the V-shaped rib is distributed around the gradually changing deep cavity of the variable curvature skin, where the curvature of the outer shape changes greatly, the fillet radius R1 of the V-shaped rib is 3.5mm, and the height H1 is 6mm to 7mm; two arc-shaped ribs are distributed around the closed extension body, with a fillet radius R2=4.5mm and a height H2=5mm; Step 3-3: Design the calendering ribs of the die The calendering ribs of the die are distributed on the initial flange surface of the outer contour of the die. The calendering rib structure of the die matches the calendering ribs of the blank holder, and the shapes and sizes of the two correspond to each other. Step 3-4: Design the punch structure The punch structure is designed based on the outer contour surface of the die, and the shape of the punch working surface is adapted to the inner shape of the drawing process surface.

5. A method for controlling instability of deep drawing of a small-angle, narrow-cone variable-curvature skin according to claim 4, characterized in that: The gap between the punch working surface and the outer contour surface of the die is i = (1.0 ~ 1.1) δ; δ is the material thickness of the variable curvature skin.

6. The method for controlling instability of deep drawing of a small-angle, narrow-cone variable-curvature skin according to claim 1 is characterized in that: The step 4 of deep drawing is as follows: Step 4-1: Install the drawing die Install the concave die on the work surface of the deep drawing machine, and install the punch and blank holder on the work surface under the deep drawing machine to ensure the matching accuracy between the blank holder and the punch; ensure the parallelism and verticality of the concave and punch to the work surface, and install them firmly; use the adjustment device of the press to adjust the closing height of the die; Apply an appropriate amount of lubricant on the contact surface between the mold and the blank; Step 4-2: Expand the blank and position it Use a clean cotton cloth to clean the unrolled blank to be formed, and lay a plastic film evenly on the surface of the unrolled blank; clean the effective molding surface and the effective pressing surface of the mold again, and apply a proper amount of lubricant; position the unrolled blank on the blank holder; Step 4-3: Deep drawing The die moves downward along the drawing direction F until it closes with the blank holder, and then continues to move downward with the blank holder clamped. The expanded blank is subjected to a certain blank holder force. Under the action of the punch, the expanded blank gradually deforms and enters the cavity of the die. During the drawing process, the presence of V-shaped calendering ribs and arc-shaped calendering ribs increases the resistance to material flow, avoiding wrinkles and cracks during forming. When the expanded blank completely enters the gap between the die and the punch, the drawing ends, and the initial process part is obtained after removing the plastic film. Step 4-4: Heat treatment According to the requirements of the digital model, the initial process parts are subjected to solution heat treatment to improve their strength and hardness; Step 4-5: Reshaping after heat treatment During the heat treatment process, the deformed initial process parts are corrected by deep drawing equipment or manual shaping to make them fit perfectly with the die.

7. The method for controlling the instability of deep drawing of a small-angle, narrow-cone variable-curvature skin according to claim 1 is characterized in that: The specific process of cutting the shape in step 5 is as follows: The initial process parts are cut and sanded according to the variable curvature skin outline on the outer contour surface of the die, and finally the variable curvature skin parts that meet the requirements of the design digital model are obtained.

8. The method for controlling the instability of deep drawing of a small-angle, narrow-cone variable-curvature skin according to claim 2 is characterized in that: The variable fillet radius Rf increases gradually from both ends to the middle, and the gradient value range is Rf=3.8mm~25mm.

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