Drawing method for improving forming depth limit of elliptical flat ball rectification skin

Abstract

The invention provides a deep drawing method for improving the forming depth limit of an elliptical flat ball rectification skin, which comprises the following steps: pressing an unfolded blank between a combined female die and a blank holder, enabling a rubber ring to turn up and deform due to bearing along with the descending of the female die and the blank holder, enabling the unfolded blank to be tightly attached to a male die under the thickness loading effect, and performing deep drawing forming; after deep drawing forming, the combined female die is lifted firstly, the rubber ring is unloaded and restored to push the semi-finished product to be automatically separated from the combined female die, and then the blank holder is lifted to separate the semi-finished product from the male die; the combined female die is of a middle hollow annular structure and is composed of a lower part and an upper part, the sum of the thickness of the lower part and the thickness of the upper part is larger than the height of the process model, and a rubber ring is embedded between the lower part and the upper part. The inner diameter of the rubber ring is smaller than that of the middle hollow annular structure, and the rubber ring makes contact with an unfolded blank during deep drawing forming.

Description

Technical Field

[0001] The present application relates to a plastic processing technology in the field of aircraft manufacturing, specifically a deep drawing method for improving the forming depth limit of an ellipsoidal fairing skin. Background Art

[0002] Deep drawing is to press the edge of the blank with the die and the blank holder, forcing the blank to form a three-dimensional hollow part under the action of the punch. Usually, the flange edge area of ​​the drawn part is subjected to the thickness loading of the blank holder, and its deformation thickening and wrinkle resistance limit is significantly higher than that of the suspended side wall area. After a large number of numerical simulations and engineering applications, it has been proved that when the flange edge thickens by more than 30% in numerical simulation, only slight wrinkling will be produced in actual deep drawing; and once the thickness of the suspended side wall area in numerical simulation exceeds 10%, the actual deep drawing will produce obvious wrinkles in the side wall area, and even material superposition dead wrinkle defects. The main reason for the obvious difference in wrinkle resistance of the drawn part is the difference in stress state in different areas during the deformation process. When the tangential compressive stress of the side wall area is greater than the radial tensile stress, the wrinkle is aggravated; while the flange edge area is always subjected to the thickness loading of the blank holder, and the wrinkle resistance is significantly improved.

[0003] It is well known that in the field of deep drawing, the most direct measure to deal with wrinkling or rupture problems is usually to increase or reduce the flow resistance, which is mainly achieved by improving lubrication or adjusting the edge clamping force. However, improving lubrication or adjusting the edge clamping force is only applicable to deep drawing parts with simple shapes and small forming depths. For irregular thin-walled deep cavity parts, dead wrinkles and ruptures often coexist in extreme contradictions, which greatly limits the processability of overall forming. In order to solve the above-mentioned forming difficulties faced by similar thin-walled parts, domestic patent publication numbers CN113751569A and CN10125499A both disclose corresponding technical means, which essentially improve the distribution of flange resistance through variable height or multi-point adjustable height draw ribs to alleviate the mutual problems of uneven deformation, wrinkling and rupture. However, there are still the following defects: First, the draw ribs only improve the distribution of flow resistance and only partially alleviate wrinkling; second, the essence of the draw ribs is to significantly increase the flow resistance of the flange. Although wrinkling can be alleviated, it will also increase the risk of rupture. Therefore, the above-mentioned public technology is only suitable for aircraft cockpit covers with gently curvature spherical thin shells with a width-to-depth ratio greater than 5. It cannot solve the contradictory problem of wrinkling and cracking for irregular ellipsoidal fairing skins with a width-to-depth ratio less than 0.7, steeper curvature and thinner wall thickness. Summary of the invention

[0004] In order to overcome the existing deep drawing technology to form irregular ellipsoidal deep cavity thin-walled parts, the wrinkling and rupture are extremely contradictory, which restricts the difficulty of increasing the forming depth or limiting the realization of overall forming. The purpose of this application is to provide a deep drawing method that improves the forming depth limit of the ellipsoidal rectifier skin. The principle is to apply circumferential pressure to the sheet material during the drawing process through a compression rubber ring embedded in the die, so that the wrinkle-prone side wall area of ​​the sheet material produces a wrinkle suppression effect similar to the flange edge under the action of continuous thickness loading, and at the same time significantly improves the beneficial friction effect between the sheet material and the punch. The purpose of significantly increasing the drawing depth and suppressing wrinkling and alleviating rupture is achieved.

[0005] The present invention provides a drawing method for improving the forming depth limit of an ellipsoidal fairing skin, wherein the ellipsoidal fairing skin is an irregular 1 / 4 ellipsoidal shell structure, the ratio of its major axis to its minor axis radius is greater than 1.5, and the depth-to-width ratio of its open end is greater than 1.3; the method comprises:

[0006] The expanded blank is pressed between the combined die and the blank holder. As the die and the blank holder descend, the rubber ring is deformed upward due to the load, so that the expanded blank is tightly attached to the punch under the action of thickness loading, and deep drawing is performed.

[0007] After deep drawing, the combined die is raised first, the rubber ring is unloaded and restored to push the semi-finished product and the combined die to separate automatically, and then the blank holder is raised to separate the semi-finished product from the punch;

[0008] The working surface of the punch matches the inner surface of the ellipsoidal shell of the process model, and the lower part of the working surface is a straight wall section matching the bottom of the ellipsoidal shell; the upper part of the process model contains an irregular 1 / 2 ellipsoidal shell, and the lower streamline of the ellipsoidal shell is connected with a supplementary fillet and a supplementary flange edge;

[0009] The blank holder is an annular flat plate structure, the upper surface of which matches the lower surface of the flange edge of the process model, and the avoidance through hole in the middle matches the straight wall section of the punch;

[0010] The combined concave die is a hollow annular structure in the middle, and is composed of a lower part and an upper part. The sum of the thickness of the lower part and the upper part is greater than the height of the process model. A rubber ring is embedded between the lower part and the upper part. The circumference of the inner hole of the rubber ring is smaller than the circumference of the hollow annular structure in the middle, and is in contact with the unfolded blank during deep drawing.

[0011] The outer contour of the unfolded blank is larger than the outer contour of the flange edge of the process model.

[0012] Optionally, the process model includes the profiles of the fairing skin and the symmetrical parts, and the profiles of the fairing skin and the symmetrical parts are fitted by streamlines of an intermediate transition surface, wherein the top width of the intermediate transition surface is smaller than the widths on both sides.

[0013] Optionally, the angle between the symmetry plane of the process model and the open end surface of the fairing skin and the symmetric part is between 8 and 12 degrees.

[0014] Optionally, the length-to-width ratio of the unfolded blank is smaller than the length-to-width ratio of the flange edge of the process model, and the margin between the unfolded contour and the flange edge contour in the minor axis direction is greater than the margin in the major axis direction.

[0015] Optionally, the lower surface of the combined concave mold lower part matches the flange edge of the process model and the upper surface of the adjacent supplementary fillet area, and the matching gap between the inner surface of the combined concave mold upper part and the punch is smaller than the thickness of the rubber ring.

[0016] Optionally, the bottom surface of the upper part of the combined die is provided with an annular concave step, which is consistent with the shape of the flange edge of the process model, and a plurality of positioning holes are provided in the annular concave step; the upper surface of the lower part of the combined die is provided with a plurality of positioning pins matching the positioning holes of the upper part, and the positioning pins penetrate the rubber ring and are inserted into the positioning holes to fix the rubber ring in the combined die.

[0017] Optionally, the thickness and width of the rubber ring are respectively greater than the depth and width of the annular concave step of the upper part of the combined concave die, and the ratio of the circumference of the inner hole of the rubber ring to the circumference of the bottom of the ellipsoidal shell of the process model is between 0.7 and 0.9.

[0018] Optionally, during deep drawing, lubricating oil is applied to the lower surface of the rubber ring to reduce the friction between the rubber ring and the upper surface of the unfolded blank, and the roughness is increased on the surface of the punch to increase the beneficial friction between the punch and the lower surface of the unfolded blank.

[0019] Optionally, when the combined concave die rises for unloading the drawing part, the blank holder is in an unloading static state.

[0020] The beneficial effects of this application are:

[0021] The present application constructs a process model by rotating the rectified skin and symmetrical parts, which can not only construct a streamline connection process model for the rectified skin and the symmetrical parts to achieve one-mold two-piece drawing, but also make the deformation method similar to the expansion of a balloon, alleviating the contradictory problem of wrinkling and rupture caused by the depth difference. The drawing die and forming method adopted in the present application use a rubber ring to cause the sheet to produce a thickness loading effect between the rubber ring and the punch, which can significantly suppress the wrinkling of the side wall area, and achieve the effect of reducing the clamping force without causing the wrinkling to increase, which is conducive to significantly improving the required drawing depth. The drawing die adopted in the present application only requires the punch and the concave model surface to match partially, which can significantly reduce the manufacturing cost of high-precision matching molds. Therefore, the drawing die and forming method adopted in the present application have significant advantages such as high forming depth limit, high mold surface utilization and forming efficiency, simple and easy to implement operation method, and strong technical versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1It is a schematic diagram of the shape of a typical fairing skin applicable to this application.

[0023] Figure 2 It is a schematic diagram of the shape of the unfolded blank of the fairing skin of the present application.

[0024] Figure 3 It is a structural schematic diagram of the deep drawing process model of the rectified skin of the present application.

[0025] Figure 4 It is a schematic diagram of the assembly of the drawing die of this application.

[0026] Figure 5 It is a structural schematic diagram of the punch of the drawing die of this application.

[0027] Figure 6 It is a schematic diagram of the assembly principle of the rubber ring of the drawing die and the lower part of the combined concave die of the present application.

[0028] Figure 7 It is a schematic diagram of the structure of the upper part of the combined concave die of the drawing die of the present application when viewed from above.

[0029] Figure 8 This is a schematic diagram of the forming principle of the initial stage of the rectified skin drawing of this application

[0030] Fig. 9 This is a schematic diagram of the forming principle of the final stage of the straightening skin drawing of this application

[0031] Explanation of the numbers in the figure: 1. Fairing skin, 2. Open end, 3. Process model, 4. Ellipsoidal shell, 5. Supplementary fillet, 6. Supplementary flange edge, 7. Expanded blank, 8. Punch, 9. Blank holder, 10. Combined die, 11. Straight wall section, 12. Avoid through hole, 13. Lower part, 14. Upper part, 15. Rubber ring, 16. Symmetrical part, 17. Transition surface, 18. Concave step, 19. Positioning hole, 20. Positioning pin, 21. Outer contour of flange edge, 22. Symmetrical surface. DETAILED DESCRIPTION

[0032] First, the typical fairing skin structure and forming processability are introduced.

[0033] See attached Figure 1The overall shape of the typical fairing skin 1 is an irregular 1 / 4 ellipsoid shell structure. Due to the high arch height at the open end 2 of the part, the part curvature is large, and the end of the part is a constricted shape, which increases the difficulty of forming the part. In addition, the internal and external stress distribution of the large-size, deep-cavity ellipsoid fairing skin is uneven. According to the traditional structural mold drawing forming, the problem of part cracking and wrinkling coexists, resulting in low mold adhesion after forming, poor shape accuracy, and low part batch qualification rate. For irregular ellipsoid fairing skins, deep drawing is the most ideal plastic processing method to improve quality and accuracy. However, only on the basis of deep drawing, overcoming the contradictory problem of wrinkling and cracking of irregular ellipsoid deep-cavity thin-walled parts formed by existing deep drawing technology can the depth of drawing be increased to achieve the purpose of suppressing wrinkling and alleviating cracking.

[0034] Secondly, the overall technical scheme of the deep drawing method for improving the forming depth limit of the ellipsoidal fairing skin is introduced.

[0035] like Figure 1-9 As shown, the present invention provides a drawing method for improving the forming depth limit of a fairing skin, wherein the fairing skin 1 is an irregular 1 / 4 ellipsoidal shell structure, wherein the ratio of its major axis to its minor axis radius is greater than 1.5, and the aspect ratio of its open end 2 is greater than 1.3. According to the theoretical model of the fairing skin 1, the following contents are included: 1) designing a drawing process model 3, wherein the upper part of the process model 3 contains an irregular 1 / 2 ellipsoidal shell 4, and the lower streamline of the ellipsoidal shell 4 is connected with a supplementary fillet 5 and a supplementary flange edge 6; 2) designing an unfolded blank 7, wherein the outer contour of the unfolded blank 7 is greater than the outer contour 21 of the flange edge of the process model 3; 3) manufacturing a drawing die, wherein the drawing die comprises a punch 8, a blank holder 9, and a combined die 10, wherein the working surface of the punch 8 matches the inner surface of the ellipsoidal shell 4 of the process model 3, and the lower part of the working surface is a straight wall section 11 matching the bottom of the ellipsoidal shell 4; the blank holder The ring 9 is an annular flat plate structure, and its upper surface matches the lower surface of the supplementary flange edge 6 of the process model 3, and the avoidance through hole 12 in the middle matches the straight wall section of the punch 8; the combined die 10 is a hollow annular structure in the middle, consisting of a lower part 13 and an upper part 14, and the sum of the thickness of the lower part 13 and the upper part 14 is greater than the height of the process model 3, and a rubber ring 15 is embedded between the lower part 14 and the upper part 13; 4) During deep drawing, the unfolded blank 7 is pressed between the combined die 10 and the pressure ring 9. As the combined die 10 and the pressure ring 9 descend, the rubber ring 15 is deformed upward due to the load, so that the sheet is tightly attached to the punch 8 under the action of thickness loading and generates beneficial friction, thereby realizing wrinkle suppression and crack slowing deep drawing; 5) After deep drawing, the parts are unloaded: first, the combined die 10 is raised, and the rubber ring 15 is unloaded and restored to push the semi-finished product and the combined die 10 to automatically separate, and then the pressure ring 9 is raised to separate the semi-finished product from the punch 8.

[0036] Furthermore, in step 1), the process model 3 includes the profiles of the fairing skin 1 and the symmetrical part 16, and the profiles of the fairing skin 1 and the symmetrical part 16 are streamlined by the intermediate transition surface 17, wherein the top width of the intermediate transition surface 17 is significantly smaller than the widths on both sides.

[0037] Furthermore, in step 1), the angle between the symmetry plane 22 of the process model 3 and the open end 2 of the fairing skin 1 and the symmetric part 16 is between 8 and 12 degrees.

[0038] Furthermore, in step 2), the aspect ratio of the unfolded blank 7 is smaller than the aspect ratio of the flange outer contour 21 of the process model 3, and the margin between the outer contour of the unfolded blank 7 and the flange outer contour 21 in the short axis direction is significantly larger than the margin in the long axis direction.

[0039] Furthermore, in step 3), the lower surface of the lower part 13 of the combined die 10 matches the upper surface of the supplementary flange edge 6 and the adjacent supplementary fillet 5 of the process model 3, and the matching gap between the inner surface of the upper part 14 of the combined die 10 and the punch 8 is smaller than the thickness of the rubber ring 15.

[0040] Furthermore, in step 3), the bottom surface of the upper component 14 of the combined die 10 is provided with an annular concave step 18, and the concave step 18 has the same shape as the supplementary flange edge 6 of the process model 3, and a plurality of evenly distributed positioning holes 19 are provided in the annular concave step 18; the upper surface of the lower component 13 of the combined die 10 is provided with a positioning pin 20 matching the positioning hole 19 of the upper component 14, and the positioning pin 20 penetrates the rubber ring 15 and is inserted into the positioning hole 19 to fix the rubber ring 15 in the combined die 10.

[0041] Furthermore, in step 3), the thickness and width of the rubber ring 15 are respectively greater than the depth and width of the annular concave step 18 of the upper part 14 of the combined die 10, and the ratio of the inner hole circumference of the rubber ring 15 to the bottom circumference of the ellipsoidal shell 4 of the process model 3 is between 0.7 and 0.9. Only when this ratio is met can the area of ​​the rubber ring 15 wrapped around the surface of the part during deep drawing reach the optimal value, so that the unfolded blank is tightly attached to the punch under the action of thickness loading, thereby suppressing wrinkling.

[0042] Furthermore, in step 4), during deep drawing, lubricating oil is applied to the lower surface of the rubber ring 15 to reduce the friction between the rubber ring 15 and the upper surface of the unfolded blank 7, and the roughness is increased on the surface of the punch 8 to increase the beneficial friction between the punch 8 and the lower surface of the unfolded blank 7.

[0043] Furthermore, in step 5), when the combined concave die 10 is raised for drawing and unloading, the blank holder 9 is in an unloading static state.

[0044] In summary, the essence of the deep drawing method for improving the forming depth limit of the ellipsoidal spheroidal fairing skin in this application is to apply circumferential pressure to the sheet material during the deep drawing process through the compression rubber ring embedded in the concave die, so that the wrinkle-prone side wall area of ​​the sheet material produces a wrinkle suppression effect similar to the flange edge under the action of continuous thickness loading, and at the same time significantly improves the beneficial friction effect between the sheet material and the punch. The purpose of significantly increasing the deep drawing depth, suppressing wrinkling, and alleviating cracking is achieved.

[0045] Finally, the following additional explanations are needed for the professional technology in this field:

[0046] The example described in this application specification is only one of the implementation plans for the ellipsoidal fairing skin, but it is not the only implementation plan. The invention concept is not only applicable to ellipsoidal deep cavity parts, but also to round, square, irregular curvature deep cavity parts, etc. The invention concept recorded in this specification has no obvious connection with the specific product shape. Similar products adopt similar technical means. According to the actual needs of the product, the corresponding purpose is achieved by adjusting the process model and the forming mold structure, which should also fall within the scope of protection of this application.

Claims

1. A deep drawing method for improving the forming depth limit of an ellipsoidal rectifier skin, characterized in that: The ellipsoidal fairing skin is an irregular 1 / 4 ellipsoidal shell structure, the ratio of its major axis to its minor axis radius is greater than 1.5, and the depth-to-width ratio of its open end is greater than 1.3; the drawing method comprises: The expanded blank is pressed between the combined die and the blank holder. As the die and the blank holder descend, the rubber ring is deformed upward due to the load, so that the expanded blank is tightly attached to the punch under the action of thickness loading, and deep drawing is performed. After deep drawing, the combined die is raised first, the rubber ring is unloaded and restored to push the semi-finished product and the combined die to separate automatically, and then the blank holder is raised to separate the semi-finished product from the punch; The working surface of the punch matches the inner surface of the ellipsoidal shell of the process model, and the lower part of the working surface is a straight wall section matching the bottom of the ellipsoidal shell; the upper part of the process model contains an irregular 1 / 2 ellipsoidal shell, and the lower streamline of the ellipsoidal shell is connected with a supplementary fillet and a supplementary flange edge; The blank holder is an annular flat plate structure, the upper surface of which matches the lower surface of the flange edge of the process model, and the avoidance through hole in the middle matches the straight wall section of the punch; The combined concave die is a hollow annular structure in the middle, and is composed of a lower part and an upper part. The sum of the thickness of the lower part and the upper part is greater than the height of the process model. A rubber ring is embedded between the lower part and the upper part. The circumference of the inner hole of the rubber ring is smaller than the circumference of the hollow annular structure in the middle, and is in contact with the unfolded blank during deep drawing. The outer contour of the unfolded blank is larger than the outer contour of the flange edge of the process model.

2. The deep drawing method for improving the forming depth limit of the ellipsoidal spheroidal skin according to claim 1, characterized in that The process model includes the profiles of the fairing skin and the symmetrical parts, and the profiles of the fairing skin and the symmetrical parts are fitted by the streamlines of the intermediate transition surface, wherein the top width of the intermediate transition surface is smaller than the widths on both sides.

3. The deep drawing method for improving the forming depth limit of the fairing skin as claimed in claim 2, characterized in that The angle between the symmetry plane of the process model and the open end surface of the symmetrical part is between 8 and 12 degrees.

4. The deep drawing method for improving the forming depth limit of the fairing skin according to claim 1, characterized in that The length-to-width ratio of the unfolded blank is smaller than the length-to-width ratio of the flange edge of the process model, and the margin between the unfolded contour and the flange edge contour in the short axis direction is larger than the margin in the long axis direction.

5. The deep drawing method for improving the forming depth limit of the fairing skin according to claim 1, characterized in that The lower surface of the lower part of the combined die matches the flange edge of the process model and the upper surface of the adjacent supplementary fillet area, and the matching gap between the inner surface of the upper part of the combined die and the punch is smaller than the thickness of the rubber ring.

6. The deep drawing method for improving the forming depth limit of the fairing skin as claimed in claim 5, characterized in that The bottom surface of the upper part of the combined die is provided with an annular concave step, which is consistent with the shape of the flange edge of the process model, and a number of positioning holes are provided in the annular concave step; the upper surface of the lower part of the combined die is provided with a number of positioning pins matching the positioning holes of the upper part, and the positioning pins penetrate the rubber ring and are inserted into the positioning holes to fix the rubber ring in the combined die.

7. The deep drawing method for improving the forming depth limit of the fairing skin according to claim 6, characterized in that The thickness and width of the rubber ring are respectively greater than the depth and width of the annular concave step of the upper part of the combined die, and the ratio of the circumference of the inner hole of the rubber ring to the circumference of the bottom of the ellipsoidal shell of the process model is between 0.7 and 0.

9.

8. The deep drawing method for improving the forming depth limit of the fairing skin as claimed in claim 1, characterized in that During deep drawing, lubricating oil is applied to the lower surface of the rubber ring to reduce the friction between the rubber ring and the upper surface of the unfolded blank, and the roughness is increased on the surface of the punch to increase the beneficial friction between the punch and the lower surface of the unfolded blank.

9. The deep drawing method for improving the forming depth limit of the fairing skin as claimed in claim 1, characterized in that When the combined die rises for deep drawing and unloading, the blank holder is in an unloading static state.

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