A near-equal wall thickness compound stamping method for deep-cavity pots

Abstract

A kind of near-equal wall thickness composite stamping forming method of deep cavity pot, the theoretical model of the deep cavity pot contains circular flat top, cylindrical sidewall, flange edge, the fillet radius of the cylindrical sidewall at both ends is 1.6 times of wall thickness, the depth-diameter ratio of the cylindrical sidewall is greater than 0.5, and according to the theoretical model, the near-equal wall thickness composite stamping forming steps are as follows: according to the theoretical model, construct surface area equivalent drawing process model, the top surface of the process model is hyperbolic surface, and the fillet radius is greater than the corresponding fillet radius of the theoretical model;According to the process model, manufacture variable-clearance matching drawing die, carry out variable-pressure boundary load drawing forming on blank, form drawing semi-finished product matched with process model;According to the theoretical model, manufacture equal-clearance push deep die, carry out push deep shaping on drawing semi-finished product, so that the corresponding flat top and adjacent cylindrical sidewall area of the theoretical model are thickened, the corresponding flange edge and adjacent cylindrical sidewall area of the theoretical model are thinned, and the near-equal wall thickness deep cavity pot is formed.

Description

Technical Field

[0001] This application relates to a plastic processing technology in the field of aircraft manufacturing, specifically a method for forming deep cavity basin-shaped parts, which is particularly suitable for aluminum alloy small rounded corner deep cavity basin-shaped parts to achieve near-equal wall thickness forming by deep drawing and push-deep stamping. Background Technology

[0002] Stamping is a common plastic forming method to improve the forming efficiency of deep-cavity, thin-walled parts. The dies used for forming mainly have two structures, generally classified into drawing dies and push-die dies based on whether the die has a blank holder function or the way the blank is deformed. Both die structures have their own advantages and disadvantages. Drawing dies, due to the blank holder's wrinkle-suppressing effect, produce good surface quality, but require larger fillet radii and have significant thinning in the punch fillet area, making them unsuitable for forming small-radius, deep-cavity parts. Push-die dies, on the other hand, have a large forming depth limit and low thinning rate because the material edges are not constrained; however, they require repeated stops and hammering to prevent dead wrinkles, resulting in poor forming quality and low efficiency, and are generally suitable for parts with gentle curvature and small deformation. Therefore, existing conventional stamping methods cannot form deep cavities with large curvatures, especially small-radius, deep-cavity, basin-shaped parts. Currently, to address the problem of easy breakage during forming, multiple full annealing processes are usually used to restore plasticity and achieve greater material thinning, essentially sacrificing wall thickness and performance to meet forming requirements.

[0003] It is well known that deep drawing has specific requirements for the minimum ratio of die fillet radius to blank thickness, and various industries in China have formulated their own implementation standards. The domestic aviation manufacturing handbook (page 265) states that a reasonable die fillet radius is 4-8 times the blank thickness; the domestic aerospace standard QJ 20502-2016 (page 4) states that the die fillet radii are 5-8 times and 4-8 times the blank thickness, respectively; and the domestic aerospace standard AVI C PM 456-2022 (page 3) states that the die fillet radii are 5-10 times and 5-8 times the blank thickness, respectively. Therefore, the fillet radius is one of the important factors affecting the forming limit depth. For parts with high forming difficulty, the fillet radius can even reach tens of times the blank thickness. However, aerospace equipment has strict standards for product spatial assembly relationships and rivet distances. Increasing the forming radius would inevitably increase the width requirements of the pressure flange, which cannot meet the application requirements of high-end equipment that pursues ultimate space utilization. Summary of the Invention

[0004] To overcome the contradiction between excessive thinning and the required forming depth in existing technologies for forming deep-cavity basin-shaped parts with small rounded corners, this application aims to provide a near-equal wall thickness composite stamping forming method for deep-cavity basin-shaped parts. This method combines drawing and pushing techniques. First, the rounded corners are enlarged to meet the drawing requirements, preventing wrinkling while completing most of the deformation and material storage requirements. Then, pushing is used to reduce the material storage area, increasing the wall thickness and resulting in a deep-cavity basin-shaped part with uniform wall thickness. This solves the problems of excessive thinning and poor wall thickness uniformity in existing stamping methods for deep-cavity parts.

[0005] To achieve the aforementioned objectives, the technical solution adopted in this application is as follows:

[0006] A near-equal wall thickness composite stamping forming method for a deep-cavity basin-shaped part, wherein the theoretical model of the deep-cavity basin-shaped part includes a circular flat top surface, a cylindrical sidewall, and a flange edge, the radius of the fillet at both ends of the cylindrical sidewall is 1.6 times the wall thickness, and the depth-to-diameter ratio of the cylindrical sidewall is greater than 0.5. The theoretical model of the deep-cavity basin-shaped part is characterized by the following features:

[0007] Step 1) Construct a process model for deep drawing. The process model has the same surface area as the theoretical model. The radius of the fillet at both ends of the cylindrical sidewall is larger than that of the fillet at both ends of the cylindrical sidewall in the theoretical model. Its corresponding top surface is a hyperbolic arc surface that connects with the streamline of the cylindrical sidewall.

[0008] Step 2) Manufacture a drawing die according to the process model. The drawing die includes a die cavity, a punch, and a blank holder. The working surfaces of the die cavity, punch, and blank holder are in a variable clearance matching relationship.

[0009] Step 3) Manufacture a push-out die according to the theoretical model. The push-out die includes an upper die, a lower die, and an unloading plate. The matching gap between the working surfaces of the upper die, the lower die, and the unloading plate is consistent with the wall thickness of the theoretical model.

[0010] Step 4) The blank is drawn under variable pressure and edge load according to the drawing die to form a drawn semi-finished product that matches the process model;

[0011] Step 5) The deep-drawn semi-finished product is pushed and extruded into shape by the push-deep die, which reduces the area of ​​the hyperbolic arc top surface of the semi-finished product and thickens the flat top surface and adjacent cylindrical side wall area of ​​the theoretical model. This causes the flange edge and adjacent cylindrical side wall area of ​​the semi-finished product to be squeezed, while the flange edge and adjacent cylindrical side wall area of ​​the theoretical model are thinned, forming a deep cavity basin-shaped part with near-equal wall thickness that matches the theoretical model.

[0012] Furthermore, in step 1), the radius of the rounded corners at both ends of the cylindrical sidewall of the process model is not less than 5 times the wall thickness of the theoretical model, the diameter of its cylindrical sidewall is 0.5-1.0 mm smaller than the diameter of the cylindrical sidewall of the theoretical model, and its depth is 3-5 mm greater than the depth of the theoretical model.

[0013] Further, in step 2), the working surface of the drawing die is matched with the outer surface of the process model; the matching gap between the working surfaces of the punch and the die in the hyperbolic arc surface and adjacent cylindrical sidewall area of ​​the process model is 1.0-1.1 times the wall thickness of the theoretical model; the matching gap between the working surfaces of the punch and the die in the flange edge of the process model adjacent cylindrical sidewall area is 1.1-1.2 times the wall thickness of the theoretical model.

[0014] Furthermore, in step 3), when the upper and lower molds of the push-out mold are in the closed state, the lower surface of the unloading plate is in contact with the upper surface of the lower mold base.

[0015] Furthermore, in step 4), when the blank is drawn using a variable pressure edge load, the variable pressure edge load drawing method is as follows: before drawing, a plastic film is covered on both sides of the blank, and the sum of the thickness of the blank and the plastic film is 1.2-1.3 times the theoretical model wall thickness. A bearing ring is placed between the die and the pressure ring, and the thickness of the bearing ring is 1.1-1.2 times the theoretical model wall thickness. During drawing, a constant load is applied to the pressure ring. As the flange edge thickens, the plastic film is squeezed more, and the effective pressure edge load automatically increases.

[0016] Furthermore, in step 5), when the deep-drawn semi-finished product is pushed and extruded into shape by the push-deep die, the lower surface of the unloading plate is in contact with the upper surface of the lower die base and is in an unloaded state; when the shaping is completed and the part is unloaded, the unloading plate pushes the deep cavity basin-shaped part to separate from the lower die in an upward loading state.

[0017] The beneficial effects of this application are:

[0018] This application constructs a deep-drawing process model with large fillets and hyperboloidal surfaces, making the main deformation process more uniform. This not only improves the depth limit of the basin-shaped part but also increases the surface area of ​​the drawn top surface, storing sufficient material for shaping. This significantly reduces the thinning of the top surface during shaping and can even achieve thickening during shaping. This application employs a combination of variable-gap matching deep drawing and theoretically equal-gap deep drawing. It fully utilizes the flexible blank holder to increase the drawing depth and wrinkle suppression limit, while also utilizing beneficial frictional expansion to reduce thinning in the thickened area of ​​the cylindrical sidewall near the flange. Simultaneously, the equal-gap rigid mold forming can both compress to thicken the top surface and compress to thin the flange edge. Therefore, the deep-cavity basin-shaped part manufactured by this application has significant advantages such as uniform wall thickness and high precision.

[0019] The present application will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the theoretical model of the deep cavity basin-shaped component of this application.

[0021] Figure 2 This is a schematic diagram of the deep drawing process model for the deep cavity basin-shaped part of this application.

[0022] Figure 3 This is a schematic cross-sectional view showing the relationship between the theoretical model and the process model of the deep cavity basin-shaped part in this application.

[0023] Figure 4 This is a schematic diagram illustrating the deep drawing principle of the semi-finished deep-cavity basin-shaped part of this application.

[0024] Figure 5 This is a schematic diagram illustrating the principle of deep cavity basin-shaped component shaping in this application.

[0025] The numbering in the diagram is as follows: 1. Theoretical model, 2. Flat top surface, 3. Cylindrical side wall, 4. Flange edge, 5. Rounded corner, 6. Process model, 7. Hyperbolic arc surface, 8. Die, 9. Punch, 10. Pressure ring, 11. Upper die, 12. Lower die, 13. Unloading plate, 14. Pressure ring, 15. Blank, 16. Semi-finished product. Detailed Implementation

[0026] First, we will introduce the structure and forming process of the deep cavity basin-shaped part.

[0027] See attached document Figure 1 The aluminum alloy deep-cavity basin-shaped part has a depth of 65mm and a sidewall diameter of 126mm. Its theoretical model 1 includes a circular flat top surface 2, a cylindrical sidewall 3, and a flange edge 4. To meet the application requirements of high-end equipment that demand maximum space utilization, the radius of the fillet 5 at both ends of the cylindrical sidewall 3 in the theoretical model is only 1.6 times the wall thickness of the theoretical model 1. Due to the excessively small fillet radius, the actual deep drawing only reaches about 15% of the theoretical depth before cracking. According to production experience, the thinning of the crack zone in a single deep drawing of such parts generally exceeds 20%. Conventional methods require repeated annealing to restore plasticity in order to meet the forming depth requirements. In essence, this means meeting the forming depth requirements with an even higher thinning amount, which has long faced the problem of excessive thinning and the forming depth requirements being contradictory. Even if the basic shape of the product is formed, the maximum thinning rate exceeds 40%, while the maximum thickening rate exceeds 20%, and the maximum wall thickness difference reaches 60%. The excessive wall thickness difference seriously affects the shape accuracy and service life.

[0028] Next, we introduce the technical solution for near-equal wall thickness composite stamping forming of deep cavity basin-shaped parts.

[0029] To address the aforementioned issues arising from the excessively small radius of the fillet 5 at both ends of the cylindrical sidewall 3 in deep-cavity basin-shaped components, please refer to the attached document. Figure 1 To be continued Figure 5 The main steps of the technical solution in this application are as follows:

[0030] Step 1) Construct process model 6 for deep drawing, referring to Appendix Figure 1 and attached Figure 2The process model 6 has an equivalent surface area to the theoretical model 1. The radius of the fillet 5 at both ends of its cylindrical sidewall 3 is larger than that of the fillet 5 at both ends of the cylindrical sidewall 3 in the theoretical model 1. Its corresponding top surface is a hyperbolic arc surface 7 that connects with the streamline of the cylindrical sidewall 3. The following points need to be emphasized regarding the process model 6: First, to meet the requirements of deep drawing, the radius of the forming fillet 5 needs to be appropriately increased. Second, to improve the friction effect of the cylindrical sidewall 3 during deep drawing, the diameter of the cylindrical sidewall of the process model 6 should be appropriately smaller than the diameter of the cylindrical sidewall 3 in the theoretical model 1. Third, to avoid insufficient friction between the actual semi-finished product 16 and the lower die 12 during deep drawing, thus weakening the material storage effect, its top surface is designed as a hyperbolic arc surface 7 with a larger area. Fourth, to achieve the ideal effect, the overall principle of the above measures is surface equivalence, but it is necessary to avoid excessive and contradictory factors on one side. For example, an excessively large radius of the fillet 5 in the process model 6 may lead to an excessively small diameter of the cylindrical sidewall 3, resulting in excessive friction during deep drawing, causing defects such as sidewall scratches, excessive material feeding, and dead wrinkles on the flat top surface 2. Therefore, the radius of the rounded corners 5 at both ends of the cylindrical sidewall 3 of the process model 6 is not less than 5 times the thickness of the blank, and its top surface is a hyperboloid arc surface 7; the diameter of its cylindrical sidewall 3 is 0.5-1.0 mm smaller than the diameter of the cylindrical sidewall 3 of the theoretical model 1, and its depth is 3-5 mm greater than the depth of the theoretical model 1. By coordinating the ratio of the radius of the rounded corners 5 of the theoretical model 1 and the process model 6, the ratio of the cylindrical sidewall 3 to the forming depth, the purpose is to reduce the shape difference between the semi-finished product 16 and the theoretical model 1, so as to avoid excessive friction and surface scratches during the final shaping, and to avoid insufficient material storage and excessive wall thickness difference.

[0031] Step 2) Manufacture the drawing die according to process model 6, referring to the appendix. Figure 2 To be continued Figure 4 The deep drawing die includes a die 8, a punch 9, and a blank holder 10. The working surfaces of the die 8, punch 9, and blank holder 10 have a variable clearance matching relationship. The following points should be emphasized regarding the manufacturing of deep drawing dies: Wall thickness variation in deep drawing is a common characteristic of all deep-drawn parts. Especially to avoid excessive thickness in the sidewall area near the rounded corners of the die 8, resulting in interference fit and increased friction, the upper part of the cylindrical sidewall 3 is thinned. The die fit clearance considers not only the actual wall thickness variation during forming but also the influence of forming auxiliary materials (such as the thickness of the plastic film) on the fit clearance. Therefore, the working surface of the die 8 matches the outer surface of the process model 6; the matching clearance between the working surfaces of the punch 9 and the die 8 in the hyperboloid surface 7 of the process model 1 and the adjacent cylindrical sidewall 3 area is 1.0-1.1 times the wall thickness of the theoretical model 1; the matching clearance between the working surfaces of the punch 9 and the die 8 in the area adjacent to the cylindrical sidewall 3 of the process model flange edge 4 is 1.1-1.2 times the wall thickness of the theoretical model 1.

[0032] Step 3) Manufacture the push-out die according to the theoretical model, referring to the appendix. Figure 1 Appendix Figure 3 Appendix Figure 5The deep-drawing die includes an upper die 11, a lower die 12, and an unloading plate 13. The matching gap between the working surfaces of the upper die 11, the lower die 12, and the unloading plate 13 is consistent with the wall thickness of the theoretical model 1. The following points should be emphasized regarding the manufacturing of the deep-drawing die: During the deep-drawing and shaping die closing process, in order to subject the thickened flange edge 4 to strong compression and thinning, the required die-closing tonnage of the equipment must be several times, or even more than ten times, greater than the blank-pressing tonnage during deep drawing. The blank-pressing tonnage of ordinary equipment is generally insufficient to compress and thin the flange edge 4. Therefore, when the upper die 11 and the lower die 12 are in the closed state, the lower surface of the unloading plate 13 must be in contact with the upper surface of the lower die 12 die base to generate a sufficiently rigid compression effect.

[0033] Step 4) Refer to Appendix Figure 2 Appendix Figure 4 The blank 15 is drawn under variable pressure edge load according to the drawing die to form a drawn semi-finished product 16 that matches the process model 6. The following points need to be emphasized regarding variable pressure edge load deep drawing: First, the most commonly used deep drawing methods are fixed pressure edge gap and fixed pressure edge force. The fixed pressure edge gap method is the simplest and most applicable; a bearing ring 14 larger than the blank thickness is placed on the outside of the blank 15. Second, in fixed pressure edge gap deep drawing, only the load acting on the blank 15 is the effective pressure edge load; the load shared by the bearing ring 14 is an ineffective load. Third, under flexible pressure edge conditions, the friction between the blank 15 and the pressure ring 10 is significantly reduced, and the force is uniform, which can significantly improve the forming limit and surface quality. Therefore, the conditions for achieving variable pressure edge load deep drawing in this application are as follows: 1) Before deep drawing, a plastic film is covered on both sides of the blank 15, and the sum of the thickness of the blank and the plastic film is 1.2-1.3 times the wall thickness of the blank 15 or the theoretical model 1. 2) During the deep drawing process, a bearing ring 14 is placed at the edge of the blank holder 10 to maintain the bearing capacity matching gap between the die 8 and the blank holder 10 at 1.1-1.2 times the theoretical model wall thickness. 3) During deep drawing, a sufficient tonnage constant load is applied to the blank holder 10. As the thickness of the flange edge 4 increases and the plastic film is compressed, the effective blank holder load automatically increases. The advantages of the above measures are: in the flexible blank holder state, the actual blank holder load can be significantly increased, and a large tonnage constant load can be maintained continuously, while the effective blank holder load acting on the blank 15 is almost unaffected, which can significantly reduce the difficulty of controlling the blank holder load in the dynamic process.

[0034] Step 5) The deep-drawn semi-finished product 16 is pushed and extruded into shape using the push-die, reducing the area of ​​the hyperboloid top surface 7 of the semi-finished product 16 and thickening the flat top surface 2 and adjacent cylindrical side wall 3 area of ​​the theoretical model 1; the flange edge 4 and adjacent cylindrical side wall 3 area of ​​the semi-finished product 16 are compressed, thinning the flange edge 4 and adjacent cylindrical side wall 3 area of ​​the theoretical model 1, forming a near-equal wall thickness deep cavity basin-shaped part matching the theoretical model 1. The following points need to be emphasized regarding the use of the push-die: First, during the push-die process, the beneficial friction of the working surface of the lower die 12 on the cylindrical side wall 3 of the semi-finished product 16 should be utilized as much as possible to push more material in, making it easier for the flat top surface 2 and adjacent cylindrical side wall 3 area to thicken. Therefore, during the push-die shaping process of the semi-finished product 16, the lower surface of the unloading plate 13 is in contact with the upper surface of the die base of the lower die 12 and is in an unloaded state. Secondly, after the deep drawing and shaping are completed, because the diameter of the deep drawing semi-finished product 16 is too small, the cylindrical sidewall 3 of the deep cavity basin-shaped part will tightly wrap around the working surface of the lower die 12, making it difficult to unload the part. Therefore, when unloading the part after shaping, the unloading plate 13 needs to be loaded upward to push the deep cavity basin-shaped part to separate from the lower die 12. The purpose is to reduce the amount of manual unloading work.

[0035] Finally, the following additional explanations are needed regarding the technical aspects of this field:

[0036] This application addresses the challenge of forming deep-cavity basin-shaped parts with small rounded corners using existing stamping methods. Under conditions of equivalent area, the core principle is to maximize the radius of the rounded corners in the deformation transmission zone to meet the deep-drawing requirements. First, deep drawing is used to complete most of the deformation, and the material needed for shaping is stored in the easily thinned area. Then, beneficial friction is used to further push the material inward to compensate, further increasing the wall thickness in the thinned area. Finally, overall rigid extrusion is performed to achieve a uniform wall thickness. The inventive concepts, including the process model, mold structure, and operating techniques used in the embodiments of this application, can all be used to reduce the wall thickness difference of deep-cavity parts. This inventive concept is also applicable to deep cavities with small rounded corners, such as oblong and elliptical shapes. Therefore, the inventive concepts described in this specification are not significantly related to specific product shapes. Similar products, depending on the forming difficulty coefficient and product shape, can achieve similar effects even by referencing some of the inventive concepts in this specification, and thus fall within the scope of protection of this application.

Claims

1. A near-equal wall thickness composite stamping forming method for a deep-cavity basin-shaped part, wherein the theoretical model of the deep-cavity basin-shaped part includes a circular flat top surface, a cylindrical sidewall, and a flange edge, wherein the radius of the fillet at both ends of the cylindrical sidewall is 1.6 times the wall thickness, and the depth-to-diameter ratio of the cylindrical sidewall is greater than 0.5, characterized in that... Comprising the following contents: Step 1) Constructing a process model for deep drawing forming, the process model is equivalent to the surface area of the theoretical model, the corner radius of the cylindrical sidewall of the process model is greater than that of the theoretical model, and the corresponding top surface is a hyperbolic arc surface connected with the streamline of the cylindrical sidewall; the corner radius of the cylindrical sidewall of the process model is not less than 5 times the wall thickness of the theoretical model; Step 2) Manufacturing a deep drawing die according to the process model, the deep drawing die comprises a female die, a male die and a blank holder, and the working surfaces of the female die, the male die and the blank holder are in a variable gap matching relationship; the working surface of the female die of the deep drawing die matches the outer surface of the process model; the matching gap between the working surfaces of the male die and the female die in the hyperbolic arc surface and the adjacent cylindrical sidewall area of the process model is 1.0-1.1 times the wall thickness of the theoretical model; the matching gap between the working surfaces of the male die and the female die in the flange edge adjacent to the cylindrical sidewall area of the process model is 1.1-1.2 times the wall thickness of the theoretical model; Step 3) Manufacturing a push deep drawing die according to the theoretical model, the push deep drawing die comprises an upper die, a lower die and a stripper plate, and the matching gap between the working surfaces of the upper die, the lower die and the stripper plate is consistent with the wall thickness of the theoretical model; when the upper die and the lower die of the push deep drawing die are in a closed die state, the lower surface of the stripper plate is in contact with the upper surface of the lower die seat; Step 4) Variable pressure loading deep drawing forming of the blank according to the deep drawing die to form a deep drawing semi-finished product matched with the process model; when the variable pressure loading deep drawing forming of the blank according to the deep drawing die is performed, the variable pressure loading deep drawing forming is implemented as follows: before deep drawing forming, plastic film is covered on both sides of the blank, the sum of the thickness of the blank and the plastic film is 1.2-1.3 times the wall thickness of the theoretical model, and a pressure bearing ring is placed between the female die and the blank holder, the thickness of the pressure bearing ring is 1.1-1.2 times the wall thickness of the theoretical model; during deep drawing, a constant load is applied to the blank holder, and as the flange edge becomes thicker, the degree of plastic film extrusion increases, and the effective blank holder load automatically increases; Step 5) Push deep whole extrusion shaping of the deep drawing semi-finished product according to the push deep drawing die to reduce the area of the hyperbolic arc top surface of the semi-finished product, thicken the flat top surface and the adjacent cylindrical sidewall area corresponding to the theoretical model, extrude the flange edge and the adjacent cylindrical sidewall area of the semi-finished product, and thin the flange edge and the adjacent cylindrical sidewall area corresponding to the theoretical model of the model to form a deep cavity basin-shaped part matched with the theoretical model.

2. The method of nearly isowall thickness compound press forming of a deep-drawn pot-shaped part according to claim 1, characterized in that: When the push deep whole extrusion shaping of the deep drawing semi-finished product according to the push deep drawing die is performed, the lower surface of the stripper plate is in contact with the upper surface of the lower die seat, and is in an unloaded state; when the shaping is completed, the stripper plate is in an upward loaded state to separate the deep cavity basin-shaped part from the lower die.

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