A liquid-filled deep drawing die and deep drawing method for sheet metal parts with conformal cavities.

Abstract

A liquid-filled deep drawing die and deep drawing method for sheet metal parts with conformal cavities are disclosed. The part is deep-drawn in a semi-finished state, containing a pre-formed cavity and a flange edge. During the final deep drawing of the part, the cavity needs to be conformed. The deep drawing die includes a punch, a blank holder, a die, and a conforming module built into the die that can be raised and lowered. During the final deep drawing, the semi-finished part is first placed between the punch and the conforming module to press the pre-formed cavity. Then, the blank holder is lowered to press the flange edge area of ​​the semi-finished part. While the conforming module continues to support the pre-formed cavity, the punch pushes the conforming ejector to descend synchronously, passively filling the flange edge of the semi-finished part with liquid and deep drawing it into the required shape of the part. Finally, pulse pressure is applied to the lifting mechanism to make the liquid flow to the die to increase the buoyancy of the deep-drawn part, achieving automatic and flexible unloading.

Description

Technical Field

[0001] This application relates to a sheet metal plastic forming technology in the field of aircraft manufacturing, specifically a liquid-filled deep drawing die and deep drawing method for sheet metal parts with conformal cavities. It is particularly applicable to the final liquid-filled deep drawing of semi-finished annular deep cavity shell parts in a conformal state when the formed cavity is in the form-preserving state. Background Technology

[0002] For annular deep-cavity parts, due to the large amount of plastic deformation, the inner wall is typically drawn first to form a near-basin-shaped semi-finished product. Then, the outer wall is drawn again while maintaining the shape of the already formed cavity. The purpose of cavity shaping is to prevent distortion or even damage to the already formed surface under external forces during re-forming. This is a necessary technical means in the multi-pass forming process of parts with large amounts of plastic deformation or complex shapes, and it is widely used in aircraft sheet metal production. For example, in aircraft reinforced structural parts such as anti-directional curved frames and bulkheads containing reinforcing ribs and recesses, the common approach is to first form a rubber-bladed bend with the same reinforcement characteristics, and then protect the already formed area to form a bend in the opposite direction. The bend height that can be formed using the above common method is generally no more than 50mm, and the mold used for shaping is fixed vertically relative to the equipment, which cannot meet the forming requirements of annular deep-cavity shell parts.

[0003] It is well known that passive liquid filling has significant advantages in reducing drawing thickness and improving fatigue life, and is a flexible deep-drawing forming method with extremely high sealing requirements in high-pressure liquid environments. The applicant's prior patent, publication number CN114160700A, discloses a method for integral forming of annular lips for aero-engines. This method involves first deep-drawing the inner wall to form an approximately basin-shaped semi-finished product, and then deep-drawing the outer wall again while maintaining the shape of the inner wall. The shape-maintaining measure adopted is that an ejector rod passes through the die and acts on a shape-maintaining ejector, providing the shape-maintaining force required for the formed cavity during deep drawing. However, there are still some drawbacks: First, after forming, the inner wall is easily wrapped around the shape-maintaining ejector, or the outer wall springs back and gets stuck in the die, making unloading difficult. Second, a considerable number of domestic equipment, limited by their structural principles, only have single-action or double-action functions, unable to provide shape-maintaining functions or providing insufficient shape-maintaining force. Third, the conformal drawing power transmission requires multiple ejector pins to pass through the die cavity to avoid the through hole. Sufficient clearance is required between the ejector pins and the through hole to ensure that multiple ejector pins move in coordination at the same time. The lifting process of the conformal ejector pins faces the contradiction between sliding interference and high-pressure sealing, which further limits the engineering application of passive liquid filling deep drawing technology.

[0004] Purpose of the invention

[0005] To address the problem that existing deep drawing dies suffer from a contradiction between conformal force transmission and high-pressure sealing, preventing operation in high-pressure sealed environments and hindering the application of passive fluid-filled deep drawing, this application aims to provide a fluid-filled deep drawing die for sheet metal parts with conformal cavities. Another objective is to provide a fluid-filled deep drawing method for sheet metal parts with conformal cavities. Summary of the Invention

[0006] A liquid-filled deep drawing die for a sheet metal part with a conformal cavity is disclosed. The part is deep-drawn in a semi-finished state, and the semi-finished state contains a pre-formed cavity and a flange edge. The flange edge contains the material required for the final deep drawing of the part. The cavity is located in the middle of the part and contains an annular sidewall and a closed top. During the final deep drawing of the part, the cavity needs to maintain its conformity. The liquid-filled deep drawing die contains a punch, a blank holder, and a die. The working surface of the punch has a recessed cavity in the middle that matches the outer surface of the cavity. The working surface of the die has a central cavity in the middle. A liftable conformal module is provided in the central cavity. The working surface of the conformal module matches the inner surface of the cavity. The conformal module is positioned on a lifting mechanism through a positioning hole on its lower surface.

[0007] Furthermore, the lifting mechanism is a hydraulic actuator. The hydraulic chamber of the actuator is connected to the hydraulic source through the inlet and outlet. The telescopic end of the actuator is embedded in the positioning hole of the conformal module. The actuator body is fixed to the bottom of the central cavity of the die by bolts.

[0008] Furthermore, the lifting mechanism, through the filling and releasing of fluid in the hydraulic chamber, can meet the requirements of conformal clamping of sheet metal parts in the cavity during the fluid filling and deep drawing process, as well as flexible automatic unloading after deep drawing.

[0009] Furthermore, the depth of the cavity at the center of the die is greater than the sum of the heights of the lifting mechanism actuator cylinder body and the conforming module, the stroke of the lifting mechanism actuator cylinder is greater than the height of the die working surface, and the conforming module working surface is also provided with an exhaust hole that connects to the positioning hole.

[0010] A liquid-filled deep drawing method for sheet metal parts with conformal cavities, characterized by mainly including the following:

[0011] 1) Use the above-mentioned liquid-filled deep drawing die for conformal cavity sheet metal parts to perform liquid-filled deep drawing;

[0012] 2) Pre-drawing a blank into a semi-finished part, the semi-finished part containing a formed cavity and a flange edge, the flange edge containing the material required for the final deep drawing of the part;

[0013] 3) For conformal clamping preparation, first fill the hydraulic chamber of the lifting mechanism with liquid, so that the actuator pushes the conformal module to the predetermined height, place the cavity of the semi-finished product on the working surface of the conformal module, place the flange edge of the semi-finished product on the working surface of the die, and then lower the punch so that the avoidance cavity in the middle of the punch closes with the working surface of the conformal module to conformally clamp the cavity of the semi-finished product. Then lower the pressure ring to press the flange edge around the cavity between the pressure ring and the die.

[0014] 4) Deep drawing loading: Fill the die cavity with liquid and continue to lower the punch. During the lowering process, the conforming module maintains the conforming pressure between the punch and the avoidance cavity and lowers synchronously with the punch until the working surfaces of the punch and die are closed. The flange edge of the semi-finished product is passively filled with liquid and deep drawn into the shape required by the part.

[0015] 5) Part unloading: Sequentially remove the blank holder force, lower the lifting mechanism, raise the punch, and raise the blank holder ring. The part will automatically demold under the action of liquid buoyancy.

[0016] Furthermore, during the conformal clamping preparation process, the drain port of the lifting mechanism is closed; during the deep drawing loading process, the drain port of the lifting mechanism is opened and the pressure control valve is connected; during the parts unloading process, the drain port of the lifting mechanism is closed and pulse pressure is applied to the hydraulic chamber of the lifting mechanism.

[0017] Beneficial effects

[0018] This application utilizes a hydraulic lifting mechanism to provide the forming force for the deep drawing die, overcoming the challenge of conflicting force transmission and sealing in high-pressure, sealed environments. This further expands the application scope of passive liquid-filled deep drawing engineering, enabling the application of the high forming quality advantages of passive liquid-filled deep drawing in critical thin-walled aircraft parts. Integrating the hydraulic forming lifting mechanism into the deep drawing die not only achieves flexible forming but also allows for flexible automatic unloading, offering significant advantages such as superior forming quality, minimal unloading deformation, and simplified operation. Attached Figure Description

[0019] The present application will be further described in detail below with reference to the accompanying drawings of the embodiments:

[0020] Figure 1 This is a schematic diagram of the deep-drawn finished shape of a typical part to which this application applies.

[0021] Figure 2 This is a schematic diagram of the shape of a semi-finished product for deep drawing of typical parts applicable to this application.

[0022] Figure 3 This is a schematic diagram of the working state of the deep drawing die for shape preservation and clamping in this application.

[0023] Figure 4 This is a schematic diagram of the assembly structure of the drawing die lifting mechanism and the conformal module.

[0024] Figure 5 This is a schematic diagram of the deep drawing die cavity structure of this application.

[0025] Figure 6 This is a schematic diagram illustrating the working principle of the deep drawing die in the closed state.

[0026] The numbers in the diagram are explained as follows: 1. Part, 2. Semi-finished product, 3. Flange edge, 4. Cavity, 5. Annular sidewall, 6. Closed top, 7. Punch, 8. Pressure ring, 9. Die, 10. Avoidance cavity, 11. Central cavity, 12. Conformal module, 13. Hole positioning, 14. Lifting mechanism, 15. Hydraulic cavity, 16. Liquid inlet, 17. Liquid outlet, 18. Telescopic end, 19. Bolt, 20. Vent hole. Detailed Implementation

[0027] First, we will introduce the structural and forming process requirements of typical parts to which this application applies.

[0028] See attached document Figure 1 To be continued Figure 2 The aero-engine lip is one of the typical parts to which this application applies. Part 1 is an annular deep-cavity thin-shell structure containing inner and outer sidewalls, with a diameter greater than 1.7 meters and a depth of inner and outer sidewalls greater than 0.2 meters. For annular deep-cavity shell parts, in order to reduce the thinning rate of the inner sidewall, the inner sidewall is generally formed into an approximately basin-shaped cavity semi-finished product 2 by deep drawing. Then, when deep drawing is performed in the state of semi-finished product 2, semi-finished product 2 contains a formed cavity 4 and a flange edge 3. The flange edge contains the material required for the final forming of part 1. The cavity 4 is located in the middle of the part and contains an annular sidewall 5 and a closed top 6. During the final deep drawing of the part, the cavity 4 needs to maintain its shape. The applicant's prior patent publication number CN114160700A provides an integral forming method for an aero-engine annular lip, but there are still contradictions between the movement interference of the lifting components and the high-pressure sealing, which cannot give full play to the significant advantages of passive liquid filling flexibility and high forming limit, further limiting the engineering application of passive liquid filling deep drawing technology.

[0029] Next, the structural principle of the liquid-filled deep drawing die for typical parts applicable to this application will be introduced.

[0030] See attached document Figure 2 To be continued Figure 6To address the limitation of existing deep-drawing dies in operating under high-pressure, sealed liquid conditions, hindering the application of passive liquid-filled deep-drawing engineering, this application describes a deep-drawing die that shares similarities with existing deep-drawing dies in that it includes a punch 7, a blank holder 8, and a die 9. The difference lies in the addition of a liftable conforming module 12 within the die 9. The punch 7 has a recessed cavity 10 in its working surface that matches the outer surface of the cavity 4. The die 9 has a central cavity 11 in its working surface, within which the liftable conforming module 12 is located. The working surface of the conforming module 12 matches the inner surface of the cavity 4, and the conforming module 12 is positioned on a lifting mechanism 14 via a positioning hole 13 on its lower surface. It is important to note that the conforming module 12 is fixed to the lifting mechanism 14 solely by its own weight, without the need for a threaded connection. Unlike patent publication number CN114160700A, the lifting mechanism 14 can operate under high-pressure, sealed liquid conditions within the die, leveraging the advantages of liquid-filled flexible forming technology.

[0031] Furthermore, to address the requirements of providing sufficient support force for the conformal module 12, enabling free lifting and lowering, and ensuring complete isolation from the outside environment, the lifting mechanism 14 is a hydraulic actuator or jack mechanism. The hydraulic chamber 15 of the actuator is connected to the hydraulic source through the inlet 16 and outlet 17. The telescopic end 18 of the actuator is embedded in the positioning hole 13 of the conformal module 12, and the actuator body is fixed to the bottom of the central cavity 11 of the die by bolts 19. It should be emphasized that: firstly, compared with existing technologies, the main advancement of this application lies in integrating existing mature and reliable hydraulic transmission technology into the deep drawing die; secondly, it overcomes the problem that some existing deep drawing equipment, limited by their structural principles, cannot provide additional conformal force for hydraulic filling during deep drawing.

[0032] Furthermore, the lifting mechanism 14, through the filling and draining of the hydraulic chamber 15, can meet the requirements of maintaining the shape and clamping of the cavity during the liquid-filled deep drawing process of sheet metal parts, and flexibly unloading the parts after final forming. The following points should be noted: First, when filling the hydraulic chamber 15 with liquid, the shape-maintaining module 12 rises to a suitable position to prevent deformation of the cavity 4 of the semi-finished product 2. Second, when the hydraulic chamber 15 is under pressure and draining liquid, connecting the pressure control valve or adjusting the draining flow rate can provide sufficient and continuous shape-maintaining force. Third, during unloading, filling the hydraulic chamber 15 with liquid allows the liquid on the top surface of the hydraulic chamber to flow into the central cavity 11 of the die 9, increasing the buoyancy of the deep-drawn part 1 in the liquid, facilitating automatic unloading.

[0033] Furthermore, the depth of the central cavity 11 of the die is greater than the sum of the heights of the lifting mechanism 14's actuating cylinder body and the conforming module 12. It should be emphasized that the central cavity of the die includes the working surface of the die 9, and its depth refers to the sum of the heights of the working surface and the straight wall section. The stroke of the lifting mechanism 14's actuating cylinder is greater than the height of the working surface of the die 9, and the working surface of the conforming module 12 is also provided with an exhaust hole 20 connecting to the positioning hole 13. This serves two purposes: first, during part removal, the hydraulic cavity 15 is depressurized, and the conforming module 12 automatically disengages from the punch 7 under gravity; second, by refilling the hydraulic cavity 15, the conforming module 12 remains stationary, and the liquid flowing out from the top surface of the hydraulic cavity 15 allows the liquid level in the central cavity 11 of the die to rise rapidly, further increasing the buoyancy of the drawn part 1 in the liquid, facilitating automatic part removal.

[0034] Then, the method of using the liquid-filling deep drawing die according to this application for liquid-filling deep drawing of parts is introduced.

[0035] See attached document Figure 1 To be continued Figure 6 The implementation of liquid-filled deep drawing mainly includes the following:

[0036] 1) Use the above-mentioned liquid-filled deep drawing die for conformal cavity sheet metal parts to perform final liquid-filled deep drawing.

[0037] 2) The blank is pre-drawn into a semi-finished product 2, which contains a formed cavity 4 and a flange edge 3; the cavity 4 contains an annular sidewall 5 and a closed top 6, and the cavity 4 needs to maintain its shape when the part is finally drawn; the flange edge 3 contains the material required for the final forming of part 1, and the area of ​​the flange edge 3 is greater than or equal to the sum of the areas of the outer sidewall and the flange edge of the drawn part 1.

[0038] 3) Form-fitting and clamping preparation: First, fill the hydraulic chamber 15 of the lifting mechanism 14 with liquid, causing the actuator to push the form-fitting module 12 upward to the predetermined height. Place the cavity 4 of the semi-finished product 2 on the working surface of the form-fitting module 12, and place the flange edge 3 of the semi-finished product 2 on the working surface of the die 9. Then, lower the punch 7 so that the recessed cavity 10 in the middle of the punch closes with the working surface of the form-fitting module 12, forming and clamping the cavity 4 of the semi-finished product 2. Then, lower the pressure ring 8 to press the flange edge 3 around the cavity 4 between the pressure ring 8 and the die 9. Note that the minimum preset pressure of the hydraulic chamber 15 should be greater than or equal to the weight of the form-fitting module 10 divided by the bottom area of ​​the hydraulic chamber 15; excessive pressure is unnecessary.

[0039] 4) Deep drawing loading: Fill the die 9 with liquid and continue lowering the punch 7. During the descent of the punch 7, the conforming module 12 maintains the conforming pressure between itself and the avoidance cavity 10, and descends synchronously with the punch 7 until the working surfaces of the punch 7 and the die 9 close, passively drawing the flange edge 3 of the semi-finished product into the shape required for the deep-drawn finished part 1. It should be noted that: To reduce the difficulty of operation, the punch 7 can be used to forcibly push the conforming module downwards. The minimum preset pressure of the hydraulic cavity 15 of the lifting mechanism should be greater than or equal to the weight of the conforming module 12 divided by the sum of the bottom area of ​​the hydraulic cavity 15 and the maximum pressure required for the central cavity 11 of the die. Connecting the pressure control valve or adjusting the drainage flow rate can provide the required continuous conforming force.

[0040] 5) Part Unloading: First, release the blank holder force, lowering and lifting mechanism 14, raising punch 7, and raising blank holder ring 8 in sequence. The drawn part 1 will automatically demold under the action of liquid buoyancy. To reduce deformation during demolding, the following points need to be emphasized: First, the self-weight of the blank holder ring causes the liquid pressure retained in the die 9 to be significant, which may cause deformation during demolding. Second, at this time, the lowering and lifting mechanism 14 can quickly release pressure and utilize the gravity of the conforming module 12 to automatically separate it from the drawn part. Third, when opening the mold, the punch 7 should be raised to a suitable height first, and then the punch 7 and blank holder ring 8 should be raised synchronously. The purpose is to use the gravity of the blank holder ring 8 to automatically separate the drawn part from the punch 7. Fourth, before opening the mold, an appropriate amount of liquid needs to be retained in the die, but the liquid level should not be too high. The purpose is to use liquid buoyancy to unload the part and avoid excessive pressure deformation. Refer to the appendix. Figure 5 The drain outlet of the concave mold can be set to an appropriate height.

[0041] Furthermore, during the conformal clamping preparation process, the drain port 17 of the lifting mechanism 14 is closed to accelerate the rising speed of the conformal module 12. During the deep drawing loading process, the drain port 17 of the lifting mechanism 14 is opened, and the pressure control valve is connected to prevent a mismatch between the descending speed of the punch 7 and the conformal module 12. During the part unloading process, the drain port 17 of the lifting mechanism 14 is closed, and pulse pressure is applied to the hydraulic chamber 15. This is to direct the liquid on the top surface of the hydraulic chamber 15 towards the die to increase the buoyancy of the deep-drawn product, thus avoiding the problem of insufficient buoyancy due to the low height of the die drain port. It is important to emphasize that the conformal module 12 must not rise during the pulse pressure application to the hydraulic chamber 15. If the conformal module 12 rises, the buoyancy of the deep-drawn part 1 in the liquid will be significantly reduced, failing to achieve the effect of flexible unloading. The stroke of the actuator cylinder of the lifting mechanism 14 is artificially increased to achieve the purpose of flexible unloading. This is also a significant difference between this application and traditional unloading methods, utilizing large-area flexible and uniform buoyancy for easy operation.

[0042] Finally, the following additional explanations are needed regarding the technical aspects of this field:

[0043] The core of this application is the integration of a hydraulic lifting mechanism into a deep drawing die. This overcomes the limitations of existing deep drawing dies in providing shape-keeping force under high-pressure, closed liquid environments, and also overcomes the problem that some existing deep drawing equipment, due to structural limitations, cannot provide additional power for shape-keeping, thus restricting the application of passive liquid-filled deep drawing for complex parts. The method described in this specification is not only applicable to the typical parts listed herein, nor is it limited to passive liquid-filled deep drawing; other products requiring multi-pass forming can also achieve multi-pass deep drawing shape-keeping through traditional deep drawing methods, based on the specific product shape differences and drawing upon the inventive concept of this application. Therefore, other shaped products using similar dies to provide shape-keeping force or additional shape-keeping auxiliary actions for the equipment also fall within the scope of protection of this application.

Claims

1. A method for deep drawing sheet metal parts with conformal cavities using a liquid-filled deep drawing die, characterized in that... Includes the following: 1) The liquid-filled deep drawing die includes a punch, a blank holder, and a die. The working surface of the punch has a recessed cavity that matches the outer surface of the cavity. The working surface of the die has a central cavity. A liftable conforming module is installed in the central cavity. The working surface of the conforming module matches the inner surface of the cavity. The conforming module is positioned on the lifting mechanism through a positioning hole on its lower surface. The lifting mechanism is a hydraulic actuator. The hydraulic chamber of the actuator is connected to a hydraulic source through an inlet and an outlet. The telescopic end of the actuator is embedded in the positioning hole of the conforming module. The actuator body is fixed to the bottom of the central cavity of the die with bolts. The lifting mechanism can satisfy the conforming clamping of the cavity and the flexible automatic unloading of sheet metal parts after liquid-filled deep drawing by filling and releasing liquid through the hydraulic chamber. The depth of the central cavity of the die is greater than the sum of the heights of the actuator body and the conforming module of the lifting mechanism. The stroke of the actuator of the lifting mechanism is greater than the height of the working surface of the die. The working surface of the conforming module is also provided with an exhaust hole that connects to the positioning hole. 2) The sheet metal part with the conformal cavity is deep-drawn in a semi-finished state. The semi-finished product contains a formed cavity and a flange edge. The flange edge contains the material required for the final deep drawing of the part. The cavity is located in the middle of the part and contains an annular sidewall and a closed top. The cavity needs to maintain its conformal shape during the final deep drawing of the part. 3) For conformal clamping preparation, first fill the hydraulic chamber of the lifting mechanism with liquid, so that the actuator pushes the conformal module to the predetermined height, place the cavity of the semi-finished product on the working surface of the conformal module, place the flange edge of the semi-finished product on the working surface of the die, and then lower the punch so that the avoidance cavity in the middle of the punch closes with the working surface of the conformal module to conformally clamp the cavity of the semi-finished product. Then lower the pressure ring to press the flange edge around the cavity between the pressure ring and the die. 4) Deep drawing loading: Fill the die cavity with liquid and continue to lower the punch. During the lowering process, the conforming module maintains the conforming pressure between the punch and the avoidance cavity and lowers synchronously with the punch until the punch and die working surfaces close, passively filling the flange edge of the semi-finished product with liquid and drawing it into the shape required for the part. 5) Part unloading: Sequentially remove the blank holder force, lower the lifting mechanism, raise the punch, and raise the blank holder ring. The part will automatically demold under the action of liquid buoyancy.

2. The liquid-filled deep drawing method for sheet metal parts with conformal cavities as described in claim 1, characterized in that, During the conformal clamping preparation process, the drain port of the lifting mechanism is closed. During the deep drawing and loading process, the drain port of the lifting mechanism is opened and the pressure control valve is connected. During the parts unloading process, the drain port of the lifting mechanism is closed and pulse pressure is applied to the hydraulic chamber of the lifting mechanism.

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