A deep drawing method to improve the forming depth limit of ellipsoidal flattened spherical straightening skin

Abstract

This invention provides a deep drawing method for improving the forming depth limit of an ellipsoidal spherical rectifying skin, comprising: pressing an unfolded blank between a combined die and a blank holder; as the die and blank holder descend, the rubber ring deforms upward due to bearing, causing the unfolded blank to be tightly adhered to the punch under thickness loading, thus forming the deep drawing; after deep drawing, the combined die is first raised, the rubber ring is unloaded and returns to push the semi-finished product to automatically separate from the combined die, and then the blank holder is raised to separate the semi-finished product from the punch; the combined die is a hollow annular structure in the middle, composed of a lower part and an upper part, the sum of the thicknesses of the lower part and the upper part being greater than the height of the process mold, and a rubber ring is embedded between the lower part and the upper part; the inner diameter of the rubber ring is smaller than the inner diameter of the hollow annular structure in the middle, and it contacts the unfolded blank during deep drawing.

Description

Technical Field

[0001] This 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 ellipsoidal flattened spherical fairing skin. Background Technology

[0002] Deep drawing involves pressing the edges of the blank with a die and a blank holder, forcing the blank to form a three-dimensional hollow part under the action of a punch. Typically, the flange edge area of ​​a deep-drawn part, due to the thickness loading of the blank holder, exhibits a significantly higher wrinkle resistance limit due to deformation thickening compared to the overhanging sidewall area. Extensive numerical simulations and engineering applications have demonstrated that numerical simulations show that flange edge thickening exceeding 30% results in only slight wrinkling during actual deep drawing; however, numerical simulations show that if the thickness of the overhanging sidewall area exceeds 10%, significant wrinkles, even material-accumulated dead wrinkles, will occur in the sidewall area during actual deep drawing. The main reason for the significant difference in wrinkle resistance in deep-drawn parts lies in the different stress states in different areas during deformation. The sidewall area exhibits intensified wrinkling when the tangential compressive stress is greater than the radial tensile stress; while the flange edge area, consistently subjected to the thickness loading of the blank holder, shows significantly improved wrinkle resistance.

[0003] In the field of deep drawing, the most direct measure to address wrinkling or cracking is usually to increase or decrease the flow resistance, primarily through improved lubrication or adjustment of the blank holder force. However, improving lubrication or adjusting the blank holder force is only suitable for deep-drawn parts with simple shapes and shallow forming depths. For irregular, thin-walled, deep-cavity parts, wrinkles and cracking often coexist in extreme contradictions, greatly limiting the feasibility of integral forming. To solve the aforementioned forming challenges faced by thin-walled parts, domestic patent publication numbers CN113751569A and CN10125499A have disclosed corresponding technical means. These essentially improve the flange edge resistance distribution through variable-height or multi-point adjustable-height draw beads, alleviating the mutual problem of uneven deformation, wrinkling, and cracking. However, the following drawbacks remain: first, draw beads only improve the flow resistance distribution, only partially alleviating wrinkling; second, draw beads significantly increase the flow resistance at the flange edge, which, while alleviating wrinkling, also increases the risk of cracking. Therefore, the above-disclosed technology is only suitable for thin-walled spherical shells with a diameter-to-depth ratio greater than 5, such as aircraft cockpit canopies. It cannot solve the contradictory problem of wrinkling and cracking for irregular ellipsoidal straightening skins with a width-to-depth ratio less than 0.7, steeper curvature, and thinner wall thickness. Summary of the Invention

[0004] To overcome the challenges posed by the extreme contradiction between wrinkling and cracking in existing deep-drawing techniques for forming irregular ellipsoidal deep-cavity thin-walled parts, which restricts the improvement of forming depth or limits the achievement of integral forming, this application aims to provide a deep-drawing method that increases the forming depth limit of ellipsoidal flattened spherical smoothing skins. The principle involves applying circumferential pressure to the sheet metal during the deep-drawing process using a compression rubber ring embedded in the die. This causes the wrinkle-prone sidewalls of the sheet metal to produce an approximate flange-like wrinkle-suppressing effect under continuous thickness loading, while simultaneously significantly improving the beneficial friction effect between the sheet metal and the punch. This achieves the goal of significantly increasing the deep-drawing depth while suppressing wrinkling and mitigating cracking.

[0005] This invention provides a deep drawing method for improving the forming depth limit of an ellipsoidal smoothing skin. The ellipsoidal smoothing skin is an irregular 1 / 4 ellipsoidal shell structure with a major axis to minor axis radius ratio greater than 1.5 and a depth-to-width ratio greater than 1.3 at its open end; comprising:

[0006] The unfolded blank is pressed between the combined die and the blank holder. As the die and the blank holder descend, the rubber ring deforms upward due to the load, causing the unfolded blank to be tightly attached to the punch under the action of thickness loading, thus forming a deep drawing.

[0007] After deep drawing, the combined die rises first, the rubber ring unloads and returns, pushing the semi-finished product to automatically separate from the combined die, and then the pressure ring rises 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 its working surface is a straight wall section that matches 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 supplementary fillets and supplementary flange edges.

[0009] The pressure ring is an annular flat plate structure, with its upper surface matching the lower surface of the flange edge of the process model, and its central through hole matching the straight wall section of the punch.

[0010] The combined die is a hollow annular structure in the middle, consisting of a lower part and an upper part. The sum of the thicknesses of the lower part and the upper part is greater than the height of the process mold. 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 it contacts 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 rectifier skin and symmetrical components, and the profiles of the rectifier skin and symmetrical components are fitted by the streamlines of the intermediate transition surface, wherein the top width of the intermediate transition surface is smaller than the width of the two sides.

[0013] Optionally, the angle between the symmetry plane of the process model and the open end face of the rectifier skin and symmetry component is between 8 and 12 degrees.

[0014] Optionally, the aspect ratio of the unfolded blank is smaller than the aspect ratio of the flange edge of the process model, and the distance between its unfolded profile and the flange edge profile in the minor axis direction is greater than the distance in the major axis direction.

[0015] Optionally, the lower surface of the combined die lower component matches the upper surface of the process model flange edge and the adjacent supplementary rounded corner area, and the matching gap between the inner surface of the combined die upper component and the punch is less than the thickness of the rubber ring.

[0016] Optionally, the bottom surface of the upper component of the combined die is provided with an annular recessed 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 recessed step; the upper surface of the lower component of the combined die is provided with a plurality of positioning pins that match the positioning holes of the upper component, and the positioning pins penetrate the rubber ring and insert into the positioning hole to fix the rubber ring in the combined die.

[0017] Optionally, the thickness and width of the rubber ring are greater than the depth and width of the annular concave step of the component on 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.

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

[0019] Optionally, when the drawing unloading die rises, the blank holder is in an unloading stationary state.

[0020] The beneficial effects of this application are:

[0021] This application constructs a process model using a rotating rectifier skin and symmetrical components. This model enables the streamlined connection between the rectifier skin and symmetrical components, achieving two-piece deep drawing in a single mold. Furthermore, the deformation method resembles the inflation of a balloon, mitigating the conflicting problems of wrinkling and cracking caused by depth differences. The deep drawing mold and forming method employed in this application utilize a rubber ring to create a thickness-wise loading effect between the rubber ring and the punch, significantly suppressing wrinkling in the sidewall area. This reduces the blank holder force without exacerbating wrinkling, thus facilitating a significant increase in the required deep drawing depth. The deep drawing mold used in this application only requires partial matching between the punch and die surfaces, significantly reducing the manufacturing cost of high-precision matching molds. Therefore, the deep drawing mold and forming method adopted in this application have significant advantages such as high forming depth limit, high mold surface utilization and forming efficiency, simple and easy-to-implement operation, and strong technical versatility. Attached Figure Description

[0022] Figure 1This is a schematic diagram of the shape of a typical rectifier skin to which this application applies.

[0023] Figure 2 This is a schematic diagram of the shape of the unfolded blank of the rectifying skin of this application.

[0024] Figure 3 This is a schematic diagram of the deep drawing process model of the rectifier skin of this application.

[0025] Figure 4 This is an assembly diagram of the deep drawing die for this application.

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

[0027] Figure 6 This is a schematic diagram illustrating the assembly principle of the rubber ring of the deep drawing die and the lower component of the combined die in this application.

[0028] Figure 7 This is a bottom view structural diagram of the upper component of the deep drawing die assembly in this application.

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

[0030] Figure 9 This is a schematic diagram of the forming principle of the final stage of the deep drawing of the rectifier skin in this application.

[0031] The numbers in the diagram are explained as follows: 1. Rectifier skin, 2. Open end, 3. Process model, 4. Ellipsoidal shell, 5. Supplementary fillet, 6. Supplementary flange edge, 7. Unfolded blank, 8. Punch, 9. Blank holder, 10. Combined die, 11. Straight wall section, 12. Avoidance through hole, 13. Lower part, 14. Upper part, 15. Rubber ring, 16. Symmetrical part, 17. Transition surface, 18. Recessed step, 19. Locating hole, 20. Locating pin, 21. Flange edge outer contour, 22. Symmetrical plane. Detailed Implementation

[0032] First, we will introduce the typical rectifier skin structure and its forming process.

[0033] See attached document Figure 1The typical rectifier skin 1 has an irregular 1 / 4 ellipsoidal shell structure. Due to the high arch height at the open end 2, the curvature of the part is large, and the end of the part is constricted, which increases the forming difficulty of the part. In addition, the large-size, deep-cavity ellipsoidal rectifier skin has uneven internal and external stress distribution. When deep drawing is performed using traditional molds, the part suffers from both cracking and wrinkling problems, resulting in low mold fit, poor shape accuracy, and low batch pass rate. For irregular ellipsoidal rectifier skins, deep drawing is the most ideal plastic processing method to improve quality and accuracy. However, only by overcoming the contradictory problems of wrinkling and cracking in the current deep drawing technology for forming irregular ellipsoidal deep-cavity thin-walled parts can the deep drawing depth be increased to suppress wrinkling and alleviate cracking.

[0034] Next, we introduce the overall technical solution for the deep drawing method to improve the forming depth limit of the ellipsoidal flattened spherical straightening skin.

[0035] like Figure 1-9 As shown, this invention provides a deep drawing method to improve the forming depth limit of a rectifier skin. The rectifier skin 1 is an irregular 1 / 4 ellipsoidal shell structure with a ratio of its major axis to minor axis radius greater than 1.5 and a depth-to-width ratio of its open end 2 greater than 1.3. Based on the theoretical model of the rectifier skin 1, the method includes the following: 1) Designing a deep drawing process model 3, the upper part of which contains an irregular 1 / 2 ellipsoidal shell 4, and the lower streamline of the ellipsoidal shell 4 is connected by supplementary fillets 5 and supplementary flange edges 6; 2) Designing an unfolded blank 7, the outer contour of which is larger than the outer contour 21 of the flange edge of the process model 3; 3) Manufacturing a deep drawing die, which includes a punch 8, a blank holder 9, and a combined die 10. 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 its working surface is a straight wall section 11 that matches the bottom of the ellipsoidal shell 4; the blank holder... Ring 9 is an annular flat plate structure, the upper surface of which matches the lower surface of the supplementary flange edge 6 of the process model 3, and the central through hole 12 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, the sum of the thicknesses 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 deforms upward due to the load, so that the sheet metal is tightly attached to the punch 8 under the action of thickness loading and generates beneficial friction, realizing wrinkle suppression and crack slowing deep drawing; 5) After deep drawing, the combined die 10 is raised first, the rubber ring 15 is unloaded and returns to push the semi-finished product to automatically separate from the combined die 10, and then the pressure ring 9 is raised to separate the semi-finished product from the punch 8.

[0036] Further, in step 1), the process model 3 includes the profiles of the rectifier skin 1 and the symmetrical component 16, and the profiles of the rectifier skin 1 and the symmetrical component 16 are fitted by the streamline of the intermediate transition surface 17, wherein the top width of the intermediate transition surface 17 is significantly smaller than the width of the two 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 rectifier skin 1 and the symmetry component 16 is between 8 and 12 degrees.

[0038] Furthermore, in step 2), the aspect ratio of the unfolded blank 7 is less than the aspect ratio of the flange outer contour 21 of the process model 3, and the distance between the outer contour of the unfolded blank 7 and the outer contour of the flange outer contour 21 in the minor axis direction is significantly greater than the distance in the major axis direction.

[0039] Further, 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 less than the thickness of the rubber ring 15.

[0040] Furthermore, in step 3), the bottom surface of the upper component 14 of the combined mold 10 is provided with an annular recessed step 18, which has the same shape as the supplementary flange edge 6 of the process model 3. Several evenly distributed positioning holes 19 are provided in the annular recessed step 18. The upper surface of the lower component 13 of the combined mold 10 is provided with a positioning pin 20 that matches the positioning hole 19 of the upper component 14. 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 mold 10.

[0041] Furthermore, in step 3), the thickness and width of the rubber ring 15 are greater than the depth and width of the annular concave step 18 of the upper component 14 of the combined die 10. The ratio of the inner 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 be guaranteed to reach the optimal value, so that the unfolded blank is tightly attached to the punch under the action of thickness loading, and wrinkling is suppressed.

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

[0043] Furthermore, in step 5), when the drawing unloading assembly die 10 rises, the pressure ring 9 is in an unloading stationary state.

[0044] In summary, the essence of the deep drawing method for improving the forming depth limit of the ellipsoidal flattened spherical straightening skin in this application lies in applying circumferential pressure to the sheet metal during the deep drawing process through a compression rubber ring embedded in the die. This causes the wrinkle-prone sidewalls of the sheet metal to produce an approximate flange-like wrinkle-suppressing effect under continuous thickness loading, while significantly improving the beneficial friction effect between the sheet metal and the punch. This achieves the goal of both significantly increasing the deep drawing depth and suppressing wrinkling and mitigating cracking.

[0045] Finally, the following additional explanations are needed regarding the technical aspects of this field:

[0046] The embodiments described in this application are merely one implementation scheme for the ellipsoidal spherical rectifying skin, and are not the only possible implementations. This inventive concept is not only applicable to ellipsoidal deep-cavity components, but also to circular, square, and irregularly curved deep-cavity components. The inventive concept described in this specification is not significantly related to the shape of a specific product. Similar products employing similar technical means, and achieving the corresponding purpose through adjustments to the process model and forming mold structure according to the actual needs of the product, 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 flattened spherical straightening skin, characterized in that, The ellipsoidal smoothing skin is an irregular 1 / 4 ellipsoidal shell structure with a major axis to minor axis radius ratio greater than 1.5 and a depth-to-width ratio at its open end greater than 1.3; the deep drawing method includes: The unfolded blank is pressed between the combined die and the blank holder. As the die and the blank holder descend, the rubber ring deforms upward due to the load, causing the unfolded blank to be tightly attached to the punch under the action of thickness loading, thus forming a deep drawing. After deep drawing, the combined die rises first, the rubber ring unloads and returns, pushing the semi-finished product to automatically separate from the combined die, and then the pressure ring rises 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 its working surface is a straight wall section that matches 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 supplementary fillets and supplementary flange edges. The pressure ring is an annular flat plate structure, with its upper surface matching the lower surface of the flange edge of the process model, and its central through hole matching the straight wall section of the punch. The combined die is a hollow annular structure in the middle, consisting of a lower part and an upper part. The sum of the thicknesses of the lower part and the upper part is greater than the height of the process mold. 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 it contacts 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 an ellipsoidal flattened spherical straightening skin as described in claim 1, characterized in that... The process model includes the profiles of the rectifier skin and symmetrical components. The profiles of the rectifier skin and symmetrical components are fitted by the streamlines of the intermediate transition surface, where the top width of the intermediate transition surface is smaller than the width of the two sides.

3. The deep drawing method for improving the forming depth limit of an ellipsoidal flattened spherical straightening skin as described in claim 2, characterized in that... The angle between the symmetry plane of the process model and the open end face of the rectifier skin and symmetry component is between 8 and 12 degrees.

4. The deep drawing method for improving the forming depth limit of an ellipsoidal flattened spherical straightening skin as described in claim 1, characterized in that... The aspect ratio of the unfolded blank is smaller than that of the flange edge of the process model, and the distance between its unfolded profile and the flange edge profile in the minor axis direction is greater than the distance in the major axis direction.

5. The deep drawing method for improving the forming depth limit of an ellipsoidal flattened spherical straightening skin as described in claim 1, characterized in that... The lower surface of the combined die lower component matches the upper surface of the process model flange edge and the adjacent supplementary rounded corner area, and the matching gap between the inner surface of the combined die upper component and the punch is less than the thickness of the rubber ring.

6. The deep drawing method for improving the forming depth limit of an ellipsoidal flattened spherical straightening skin as described in claim 5, characterized in that... The bottom surface of the upper component of the combined mold is provided with an annular recessed step, which is consistent with the shape of the flange edge of the process model. Several positioning holes are provided in the annular recessed step. The upper surface of the lower component of the combined mold is provided with several positioning pins that match the positioning holes of the upper component. The positioning pins penetrate the rubber ring and are inserted into the positioning holes to fix the rubber ring in the combined mold.

7. The deep drawing method for improving the forming depth limit of an ellipsoidal flattened spherical straightening skin as described in claim 6, characterized in that... The thickness and width of the rubber ring are greater than the depth and width of the annular concave step on 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 an ellipsoidal flattened spherical straightening skin as described in claim 1, characterized in that... During deep drawing, lubricating oil is applied to the lower surface of the rubber ring to reduce friction between the rubber ring and the upper surface of the unfolded blank, and the roughness of the punch surface is increased to increase 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 an ellipsoidal flattened spherical straightening skin as described in claim 1, characterized in that... When the drawing and unloading die rises, the blank holder is in an unloading and stationary state.

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