Method of forming thin-walled enclosures with inwardly turned flanges

Abstract

The application discloses a thin-wall cover forming method with an inward flange, which comprises a drawing process and an internal high-pressure bulging process. The drawing process is to draw sheet metal by using a liquid-filled flange drawing die. The liquid-filled flange drawing die comprises a female die and a flange punch. The flange punch stops moving when it is lowered to a distance of the height h of the sheet metal. After the liquid chamber formed by the female die and the sheet metal is filled with liquid and pressurized to form a partial inward flange height, the flange punch is lowered again, so that the sheet metal is drawn into a cylindrical part with an inward flange and a drawing flange fillet, and the radius of the drawing flange fillet is greater than the radius of the flange fillet. The internal high-pressure bulging process is used to expand the cylindrical part into a cover, so that the drawing flange fillet is formed into a flange fillet. The forming method controls the distance between the flange punch and the sheet metal to a certain height before liquid drawing, provides a certain anti-expansion space for sheet metal forming, reduces the height difference of the liquid-filled'soft drawing rib', facilitates the flow of the sheet metal to the inward flange structure, and reduces the excessive thinning of the blank caused by subsequent drawing.

Description

Technical Field

[0001] This invention relates to the field of thin-walled parts forming technology, specifically to a method for forming a thin-walled cover with an inwardly turned edge. Background Technology

[0002] The casing of an aircraft engine is a sheet metal part that controls the aerodynamic shape of the engine and bears aerodynamic loads. A cross-sectional view of the casing of a certain type of aircraft engine is shown in the attached instruction manual. Figure 1 As shown, in order to meet the requirements of lightweight aircraft engines, the wall thickness of the casing parts is usually designed to be very small, generally less than 2mm, and the material is stainless steel. Figure 1 The casing parts have inward and outward convex features, with a relatively large inward convex height. The bottom of the part convexes outward, and the convex part forms a certain angle with the center line. The flange radius at the flange edge is small, and the flatness accuracy of the flange edge is required to be high.

[0003] The traditional forming process for the aforementioned aero-engine casing is as follows: the sheet metal is first formed into a cylindrical rotating part with an inner flange structure, and then the final part structure is formed by segmented bulging using a steel mold. Because the inner flange height of the casing part is relatively high, deep drawing into a cylindrical rotating part with a high inner flange requires three steps: first, the steel mold is deep drawn into a cylindrical rotating part with a low flange height; then, a bottom hole is cut, and the inner hole is bulged to increase the inner flange height. However, due to the small radius of the flange, the wall thickness is greatly reduced during deep drawing, and the inner flange height is large. Using the aforementioned bulging process, cracks are easily generated at the hole opening, and the thinning rate is high. Furthermore, this traditional forming method involves many steps, resulting in low processing efficiency. In the subsequent bulging process using the steel mold, the mold is assembled in segments, leaving parting marks on the surface of the formed part, affecting the appearance quality. Moreover, the flatness of the flange edge is poor after deep drawing, and subsequent bulging cannot correct the flange edge flatness, requiring manual correction by a fitter, which is time-consuming and labor-intensive.

[0004] A large annular lip piece integral liquid forming method is disclosed in patent CN110434216A, which comprises the following steps in sequence: placing a blank in a transition die; setting key process parameters such as the blank holder gap, liquid chamber pressure, and punch stroke; using a passive liquid filling forming scheme for transition forming to form an integral lip internal barrel-shaped part first; taking out the transition-shaped part after forming is completed; checking the wall thickness reduction rate of the transition lip part without forming quality problems, and if the reduction rate is large, heat treatment can be performed to improve the material forming limit; placing the transition lip part without any problems into a final forming die; using a passive liquid filling forming scheme for the final forming die to perform flanging on the transition lip part formed; taking out the final forming lip part after forming is completed, and checking key parameters such as the wall thickness reduction rate, the degree of die fit, and the surface roughness; and cutting off the flange edge and the internal barrel-shaped top end of the formed lip part that are not needed using a cutting machine to obtain the final part.

[0005] The above patent is a new technology for multi-step liquid filling forming on the basis of ensuring the integral forming of the lip part. Through two-step liquid filling forming process and one-step shaping process, the integral forming of the lip part is realized. However, in the passive liquid forming process of the technical scheme, the punch continuously descends into the die to form the inner flange, and as the punch descends and the liquid filling is synchronized, the liquid filling will occur reverse expansion, as shown in Figure 7 , a liquid filling "soft drawbead" height difference is generated on the part between the punch and the flange edge of the part, which causes the sheet material to fail to flow smoothly to the inner flange structure, affecting the forming effect of the inner flange of the part, and even possibly causing adverse effects of excessive thinning of the part. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a thin-walled cover forming method with an inner flange, which can make the inner flange size of the part qualified and effectively avoid excessive thinning of the sheet material, in view of the defects of the prior art.

[0007] The object of the present application is achieved by the following technical solutions:

[0008] A thin-walled cover forming method with an inner flange, comprising a drawing process and an internal high-pressure bulging process, the cover having a flange edge and a flange fillet, the drawing process being to draw sheet material using a liquid filling flanging drawing die, the liquid filling flanging drawing die comprising a female die and a flanging punch, the flanging punch stopping moving when descending to a height h from the sheet material, and waiting for the liquid in the liquid chamber formed by the female die and the sheet material to be pressurized to form a partial inner flange, and then the flanging punch descending again to draw the sheet material into a cylindrical part with an inner flange and a drawn flange fillet, the drawn flange fillet radius being greater than the flange fillet radius; the internal high-pressure bulging process being to expand the cylindrical part into a cover to form the drawn flange fillet into a flange fillet.

[0009] Further, the round radius of the flange is 5-8 times of the thickness of the sheet.

[0010] Further, the height of the cylindrical part is greater than the height of the cover, and the height of the cylindrical part is determined according to the principle of equal surface area, i.e., the height of the cylindrical part in the deep drawing process is calculated based on the surface area of the cover.

[0011] Further, the internal high-pressure bulging process is realized by using an internal high-pressure forming die, the internal high-pressure forming die comprises a split female die and a bulging punch, the bulging punch comprises a pressing surface for pressing the flange and a stepped end for forming the round corner of the flange, the stepped end is arranged at the pressing surface, and the end surface of the stepped end and the cylindrical part form a liquid chamber for the internal high-pressure bulging process; a sealing ring is arranged at the joint of the pressing surface and the end surface of the split female die, and the sealing ring is in contact with the flange.

[0012] Compared with the prior art, the present application has the following beneficial effects:

[0013] 1) The traditional liquid filling deep drawing process is overturned, the height of the flanging punch is controlled to be a certain height from the sheet before the liquid filling deep drawing, a certain anti-bulging space is provided for the sheet forming, then the sheet is anti-bulged by filling liquid, a certain inner flange height is formed, then the flanging punch is controlled to be lowered to draw the sheet. The height of the punch is higher than the sheet before the liquid filling deep drawing, the height difference of the liquid filling "soft draw bead" generated by the anti-bulging is reduced, the sheet is beneficial to flow to the inner flange structure, the excessive thinning of the blank caused by the subsequent deep drawing can be effectively reduced, and the height of the inner flange can be increased.

[0014] 2) The height of the cylindrical part is greater than the height of the cover, which is equivalent to compensating the bulging amount to the deep drawing height of the cylindrical part after the liquid filling flanging deep drawing. During the external bulging process of the cylindrical part in the internal high-pressure process, the deformation amount of the material is small, the further thinning of the part can be reduced, and the liquid chamber pressure required for the internal high-pressure forming is also reduced, thereby reducing the load of the related equipment and die.

[0015] 3) The thin-walled cover part processed by the present forming method is not prone to breaking, the processed part has high dimensional accuracy, uniform wall thickness distribution, good flange flatness, good surface quality, and high processing qualification rate. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 FIG. 4 is a partial cross-sectional view of the cover processed by the present application;

[0017] Figure 2 FIG. 5 is a schematic view of the cylindrical part formed by the liquid filling flanging deep drawing die according to Example 1;

[0018] Figure 3Fig. 2 is a schematic view of the liquid-filled deep drawing of the sheet metal with the height h between the flanging punch and the sheet metal as described in Example 1;

[0019] Figure 4 Fig. 3 is a schematic view of the height H of the cylindrical part after the deep drawing process as described in Example 1;

[0020] Figure 5 Fig. 4 is a schematic view of the inner high pressure forming die forming the cover as described in Example 2;

[0021] Figure 6 Fig. 5 is a schematic view of the inner high pressure forming die forming the cover as described in Example 3; Figure 5 Fig. 6 is an enlarged view of the I portion in Fig. 5;

[0022] Figure 7 Fig. 7 is a schematic view of the conventional liquid-filled forming flanging. DETAILED DESCRIPTION

[0023] In order to clearly illustrate the technical features of the present application, the following will describe the present application in detail with specific embodiments and with reference to the accompanying drawings.

[0024] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details and other implementations can be employed. Therefore, the scope of the present application is defined by the appended claims, not by the following detailed description.

[0025] In addition, in the description of the present application, it should be understood that the terms "center", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined as "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0026] In this application, unless specifically defined otherwise, the terms "mounting", "connected", "connection", "fixed", and the like, should be construed broadly and can be either fixed connections or detachable connections, or integrally formed; can be mechanical connections, or electrical connections, or communication connections; can be direct connections, or indirect connections via intermediate medium, or the internal communication of two elements, or the interaction relationship between two elements. For those skilled in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0027] In this application, unless specifically defined otherwise, the first feature is "on" or "under" the second feature, which can be direct contact between the first and second features, or indirect contact between the first and second features through an intermediate medium. In the description of the specification, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples.

[0028] Embodiment 1

[0029] This embodiment is directed to a cover on an aero-engine, Figure 1 The cross-sectional structure of the cover is shown, which has an inner flange 13 and an outer convex structure 14, and also has a flange edge 11 and a flange fillet 12. The size examples of the cover are given as follows: the wall thickness is 1 mm, the height of the inner flange 13 is 16.2 mm, the outer convex of the part cylinder bottom, the outer convex structure 14 is at an angle of 6° with the center line, the flange fillet 12 is R2, and the flatness requirement of the flange edge 11 is 0.1 mm.

[0030] Compared with the traditional forming process, the present forming method is mainly used for one-time forming of large inner flange height, and at the same time solves the problems of multiple forming processes of the cover, poor surface quality and large wall thickness reduction. The present forming method includes a drawing process and an internal high-pressure bulging process. The drawing process uses a liquid-filled flange drawing die to draw the sheet metal into a cylindrical part with an inner flange and a flange edge. The internal high-pressure bulging process uses internal high pressure to expand the obtained cylindrical part to form an outer convex structure, and at the same time shapes the flange fillet and the flange edge.

[0031] This embodiment describes the drawing process: the cut circular sheet is placed in a drawing die as shown in FIG. 1, and the die is closed to form a cylindrical part with an inner flange and a flange edge. Figure 2The liquid-filled flanging and deep-drawing die shown includes a female die 21, a flanging punch 22, and a blank holder 23, which holds the sheet metal in place (in this embodiment, a blank holder force of approximately 20 tons is used). When the die is in operation, as... Figure 2 , Figure 3 As shown, the flanging punch 22 stops moving when it descends to a height h from the sheet metal. The pressure booster of the liquid filling device matched with the mold is turned on to replenish the liquid in the liquid chamber formed by the female mold 21 and the sheet metal. The height of the replenished liquid is level with the pressure surface (i.e. the sheet metal surface). Then, the liquid filling and pressurization continue to form part of the inner flanging height of the sheet metal. Then, the flanging punch 22 is controlled to descend and the liquid chamber pressure is gradually increased to about 30MPa, so that the sheet metal is drawn into a cylindrical part with an inner flanging 13 and a drawn flange radius. The drawn flange radius is the initial forming of the cover flange radius 12. The radius of the drawn flange radius needs to be larger than the flange radius.

[0032] The above-mentioned deep drawing process differs from conventional liquid-filled deep drawing. In the liquid-filled flanging deep drawing process, a certain height h is reserved between the flanging punch and the sheet metal. This height provides sufficient space for liquid-filled back expansion, reduces the height difference of the liquid-filled "soft draw bead" caused by back expansion, facilitates the flow of the sheet metal to the inner flanging structure, reduces the possibility of excessive thinning of the billet during subsequent deep drawing, and also allows for the formation of a large inner flanging height in one step. In this embodiment, the reserved height h is 5mm.

[0033] Because the final flange fillet radius of the casing is relatively small, to avoid cracking during deep drawing and excessive wall thinning, the fillet radius of the deep-drawn flange is taken as 5 to 8 times the sheet thickness. That is, the fillet radius of the female die 21 at the flange edge is designed to be 5 to 8 times the sheet thickness. In this embodiment, the fillet radius of the female die is taken as 8mm. In the subsequent internal high-pressure forming process, the deep-drawn flange fillet is processed into the final flange fillet size by the action of internal high pressure.

[0034] To avoid further thinning of the wall thickness of drawn parts caused by conventional pure bulging, in the liquid-filled deep drawing and flanging process, such as Figure 4 The height H of the deep-drawn cylindrical part shown must be greater than the height of the final cover. The principle for determining the height of the cylindrical part is as follows: based on the principle of equal surface area, calculate the surface area of ​​the cover after high-pressure forming, and use this surface area as a benchmark to convert it into the height H of the liquid-filled, flanged, deep-drawn cylindrical part.

[0035] The design of the cylindrical part height H takes into account the pre-compensation of the bulging amount to the deep drawing height of the cylindrical part after liquid filling and flanging. During the internal high pressure forming and external bulging process, the material deformation is very small, which can reduce the further thinning of the part. At the same time, it can also reduce the liquid chamber pressure required for internal high pressure forming, and reduce the corresponding equipment and mold load.

[0036] The specific process of the deep drawing operation is as follows:

[0037] S1. The sheet is placed on the cavity 21, and the blank holder 23 presses the sheet;

[0038] S2. The flanging punch 22 goes down and stops at a certain height h from the sheet;

[0039] S3. The liquid supplement device booster is opened to supplement liquid, and the liquid supplement level is leveled with the sheet. Thereafter, the liquid chamber pressure P1 (30 MPa in the foregoing) is further increased, and the specific value of the liquid chamber pressure P1 is obtained through simulation calculation.

[0040] S4. The flanging punch 22 goes down to draw the sheet to the bottom, and the die closing gap is 1-1.2 times the thickness of the sheet.

[0041] Example 2

[0042] This embodiment describes the internal high-pressure bulging process: The internal high-pressure bulging process is realized by using the internal high-pressure forming die as shown in Figure 5 which can well form the outer convex structure of the cover shell. The die includes a split cavity 31 and a bulging punch 32. The bulging punch 32 includes a pressing surface that cooperates with the end surface of the split cavity 31 to press the flange edge of the cylindrical part, and a stepped end 321 that cooperates with the inner ring of the split cavity 31 to form the flange fillet 12, and the stepped end 321 is arranged at the pressing surface. The end surface of the stepped end 321 and the cylindrical part enclose a liquid chamber for the internal high-pressure bulging process. A sealing ring 33 is embedded at the cooperation position of the pressing surface and the end surface of the split cavity 31, and the sealing ring 33 contacts the flange edge 11, and the sealing ring 33 can effectively seal the entire liquid chamber.

[0043] The die closing gap of the internal high-pressure forming die is 1-1.2 times the thickness of the sheet. After the die is closed, there is still a gap G1 between the outer cylindrical surface of the stepped end 321 and the inner ring of the split cavity 31, and there is still a gap G2 between the pressing surface and the end surface of the split cavity 31. The two gaps mainly function as follows: through the liquid chamber pressure, the flange fillet 12 and the flange flat surface at the gap can be continuously shaped, the smaller flange fillet 12 can be shaped in place, and the flange flatness and surface quality can be improved. The radius of the split cavity 31 is adapted to the size of the flange fillet 12 of the cover shell. In this embodiment, the size of the gap G1 is 0.2-0.5 mm, and the size of the gap G2 is 0.5-3 mm.

[0044] To reduce the liquid volume of the liquid chamber and the liquid chamber pressure of the internal high-pressure forming, the internal high-pressure forming die of this embodiment further has a bulging support block 34 between the end surface of the stepped end 321 and the bottom of the cylindrical part. The bulging support block 34 is generally made of polyurethane, and the bulging support block 34 presses the bottom of the cylindrical part with a certain pressure, which can also effectively improve the forming quality of the inward flanging structure.

[0045] The specific process of the internal high-pressure bulging process is as follows:

[0046] S1. Control the closing of the female die cavity of the split female die 31, and place the deep drawn cylindrical part in the female die cavity;

[0047] S2. Place the bulging support block 34 at the bottom of the cylindrical part;

[0048] S3. The bulging punch 32 goes down to press the flange edge of the cylindrical part with a pressure of about 100 tons through the sealing ring 33;

[0049] S4. The booster starts the liquid supplementing operation, and pressurizes to the liquid chamber pressure P2, the specific value of which is obtained by simulation calculation, and in the embodiment, P2 is 60 MPa, and the high-pressure forming of the cylindrical part is completed.

[0050] After the high-pressure forming, according to the design size requirement of the cover shell, the excess size of the bottom hole and the flange edge of the part is cut off, and the final cover shell part is obtained.

[0051] Embodiment 3

[0052] In order to improve the material forming limit and prevent cracking during forming, a solid solution heat treatment process is added between the deep drawing process of Embodiment 1 and the high-pressure forming process of Embodiment 2.

[0053] The cover shell processed by the forming method has high size precision, uniform wall thickness distribution, good flange flatness, good surface quality, and the part is not prone to cracking during forming, and the part processing qualified rate is high.

[0054] Obviously, the above embodiments are only examples for clearly illustrating the technical solutions of the present application, and are not intended to limit the embodiments of the present application. For those skilled in the art, on the basis of the above description, other different forms of changes or modifications can also be made. Here, it is not necessary and impossible to exhaust all the embodiments. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A method of forming a thin-walled closure with an inwardly turned flange, characterized by, The cover shell has a flange edge and a flange round corner, the drawing process is to draw the plate by using a liquid-filled flanging drawing die, the liquid-filled flanging drawing die comprises a female die and a flanging punch, the flanging punch stops moving when it goes down to a distance of h from the plate, and then the liquid-filled flanging drawing die is filled with liquid to pressurize the liquid chamber formed by the female die and the plate to form a part of the inner flange, and then the flanging punch goes down again to draw the plate into a cylindrical part with an inner flange and a drawing flange round corner, the drawing flange round corner has a radius larger than that of the flange round corner; the inner high-pressure bulging process is used to expand the cylindrical part into a cover shell, so that the drawing flange round corner is formed into a flange round corner, and the height of the cylindrical part is greater than that of the cover shell.

2. The method of forming a thin-walled shell with an inwardly flanged rim according to claim 1, wherein, The drawing flange round corner has a radius of 5-8 times the thickness of the plate.

3. The method of forming a thin-walled shell with an inwardly flanged rim according to claim 1, wherein, The principle of determining the height of the cylindrical part is that the height of the cylindrical part in the drawing process is calculated according to the principle of equal surface area and based on the surface area of the cover shell.

4. The method of forming a thin-walled shell with flanged edges of claim 1, wherein, The closing gap of the liquid-filled flanging drawing die is 1-1.2 times the thickness of the plate.

5. The method of forming a thin-walled shell with flanged edges of claim 1, wherein, The inner high-pressure bulging process is realized by using an inner high-pressure forming die, the inner high-pressure forming die comprises a split female die and a bulging punch, the bulging punch comprises a pressing surface for pressing the flange edge in cooperation with the end surface of the split female die, and a stepped end for forming the flange round corner in cooperation with the inner ring of the split female die, the stepped end is arranged at the pressing surface, and the end surface of the stepped end and the cylindrical part form a liquid chamber for the inner high-pressure bulging process; a sealing ring is arranged at the cooperation position of the pressing surface and the end surface of the split female die, and the sealing ring is in contact with the flange edge.

6. The method of forming a thin-walled shell with flanged edges of claim 5, wherein, The closing gap of the inner high-pressure forming die is 1-1.2 times the thickness of the plate.

7. The method of forming a thin-walled shell with flanged edges of claim 5, wherein, The pressing surface and the end surface of the split female die have a gap therebetween.

8. The method of forming a thin-walled shell with flanged edges of claim 5, wherein, The outer circular surface of the stepped end and the inner ring of the split female die have a gap therebetween.

9. The method of forming a thin-walled shell with flanged edges of claim 5, wherein, The end surface of the stepped end and the bottom of the cylindrical part are provided with a bulging support block.

10. The method of forming a thin-walled shell with flanged edges of claim 1, wherein, The drawing process and the inner high-pressure bulging process are further provided with a solid solution heat treatment process.

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