Sheet metal low thinning rate reverse deep drawing forming method

Abstract

The application discloses a sheet metal part low-thinning reverse deep drawing forming method, and the forming method comprises the following steps: S1, sheet metal part plate is deep drawn to form a first cylinder part, the first cylinder part is used as an outer ring of the sheet metal part, the first cylinder part has a fillet and a flange at an opening, and the drawing height of the first cylinder part guarantees a final process allowance; S2, the fillet and the flange in S1 are removed; S3, the bottom of the first cylinder part in S1 is reversely deep drawn to form a second cylinder part, and a first transition surface is formed between the second cylinder part and the bottom of the first cylinder part; and S4, the second cylinder part in S3 is reversely deep drawn as a whole to form a third cylinder part, and a second transition surface is formed between the third cylinder part and the bottom of the first cylinder part. The forming method can reduce the part thinning rate from 45% to 20%, and can better guarantee the final wall thickness, the forming qualified rate and the surface quality are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of deep drawing technology for parts, specifically to a method for reverse deep drawing of sheet metal parts with low thinning rate. Background Technology

[0002] Most components on aero engines operate in high-temperature, high-pressure environments, thus requiring high strength and rigidity. This necessitates stricter control over the thinning rate and appearance quality of sheet metal parts, with explicit technical requirements directly defined during the part design phase. For sheet metal parts on aero engines, which are already relatively thin and structurally complex, structural and space constraints, coupled with small corner radii and high forming difficulty, make it even more challenging to guarantee the required wall thickness.

[0003] Traditional sheet metal forming methods often use the flanging process for parts with high inner hole height. The flanging process is relatively simple, but cracks are very easy to form at the hole opening, resulting in a high scrap rate and a high thinning rate. According to some forming simulation results, the highest thinning rate can reach 50%, and the highest thinning rate measured in actual on-site processing can reach 45%, with obvious folding steps at the flanging point.

[0004] Instruction manual attached Figure 7 and attached Figure 8 The traditional sheet metal forming process is shown in the following diagram:

[0005] The first step is to draw and form the central circular bulge, while simultaneously bending and forming the outer ring structure;

[0006] The second step is reverse drawing to form the inner ring structure and part of the height;

[0007] The third step is to cut a center hole;

[0008] The fourth step is to form the inner hole by turning it.

[0009] In the above process, the outer corner radius is small in one step, making it difficult for material to flow in, while the center has a large concave corner radius, resulting in severe thinning. According to simulation analysis, as... Figure 5 As shown, the thinning rate at the center after the first step of forming has reached 23%. The inner hole height after the second step of forming is affected by the bending in the middle of the part and the small radius, which exacerbates the thinning of the inner ring structure of the part. The thinning of the cylindrical straight wall part is most severe at the radius. The radius of the second step is in the effective area of ​​the part after the fourth step of turning the hole. Moreover, according to the on-site processing observation, the radius will leave a deep step in the inner hole after turning, which is difficult to eliminate.

[0010] The inner holes of the aforementioned sheet metal parts need to be brazed to the corresponding fittings. The gap between the inner hole and the fittings needs to be controlled between 0.02 and 0.08 mm. The surface quality and perpendicularity of the inner hole are extremely important. The thinning rate after forming is also very strictly controlled. Traditional forming methods can no longer meet the requirements.

[0011] Patent CN114160700A discloses a method and mold for integral forming of annular lips for aero-engines. This application reduces the difficulty of deep drawing by decreasing the depth of the inner sidewall of the annular lip, and simultaneously, through the supplementary circular bottom surface, the material deformation approaches an equivalent double-stretch bulging state. It can increase the deformation of the inner sidewall and supplementary surface under greater forming force, resulting in uniform deformation, low thinning rate, and reduced material inflow into the flange edge. While the annular lip is also a thin-walled part, its forming process is similar to the aforementioned traditional sheet metal forming process: first, it is drawn downwards and in the reverse direction to form the annular sidewall and annular groove, and then drawn in the reverse direction to form the circular bottom. Clearly, the low thinning rate effect achievable by this technical solution is limited.

[0012] Patent CN112170648B discloses a double-layer cylindrical part forward and reverse deep drawing die and method. The die first uses a smaller diameter punch for forward deep drawing to form the inner circle, then uses a larger diameter ring for reverse deep drawing to form the outer circle. During the reverse deep drawing of the outer circle, the punch and back pressure punch move downwards with the ring. During the deep drawing process, under the combined pressure of the back pressure punch, the inward pressure of the ring's inner cavity, and the outward pressure of the punch, the thickness of the sheet metal covering the punch area remains essentially unchanged, effectively suppressing sheet metal thinning and preventing wrinkling. However, the rounded corners in this patent are formed by the ring pressing downwards; when the punch moves upwards to press the sheet metal, stress concentration and cracking can easily occur at the rounded corners. Summary of the Invention

[0013] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a reverse deep drawing forming method for sheet metal parts with low thinning rate. This forming method is particularly suitable for sheet metal parts with small rounded corners and deep drawing and bending composite forming.

[0014] The objective of this invention is achieved through the following technical solution:

[0015] A method for reverse deep drawing forming of sheet metal parts with low thinning rate, the forming method comprising the following steps:

[0016] S1. The sheet metal part is drawn into a first cylindrical part, which serves as the outer ring of the sheet metal part. The opening of the first cylindrical part has a first rounded corner and a flange edge. The stretching height of the first cylindrical part is drawn to ensure the final process allowance.

[0017] S2. Remove the first fillet and flange edge from S1;

[0018] S3. The bottom of the first cylindrical part in S1 is reverse-drawn to form the second cylindrical part, and a first transition surface is formed between the bottom of the second cylindrical part and the first cylindrical part.

[0019] S4. The second cylindrical section in S3 is reverse-drawn to form the third cylindrical section, and a second transition surface is formed between the bottom of the third cylindrical section and the first cylindrical section.

[0020] Furthermore, in S3, the first transition surface is a rounded corner surface, and the radius of the rounded corner surface is 8 to 10 times the thickness of the sheet metal part.

[0021] Furthermore, in S1, the radius of the first fillet is 5 to 8 times the thickness of the sheet metal part.

[0022] Furthermore, the mold used in the reverse drawing step S3 is also equipped with a limiting block and a positioning ring. The positioning ring is installed in the lower mold, and the limiting block is installed in the upper mold. The positioning ring has a bent inner wall that fits the bottom and outer surface of the first cylindrical part. The limiting block contacts the positioning ring when the upper and lower molds are closed to ensure the mold closing gap.

[0023] Furthermore, the mold closing gap is 1 to 1.1 times the material thickness gap.

[0024] Furthermore, the positioning ring is provided with guide posts.

[0025] Furthermore, the first transition surface is an inclined surface, and the angle between the first transition surface and the second transition surface is the same.

[0026] Furthermore, the length of the first transition surface is less than the length of the second transition surface, and the diameter of the second cylindrical section is greater than the diameter of the third cylindrical section.

[0027] Furthermore, the length of the reverse drawing section line in step S4 is greater than the length of the reverse drawing section line in step S3.

[0028] Furthermore, the bottom corner of the third cylindrical section is composed of a second rounded corner, a third rounded corner, and a sloped surface connecting the second rounded corner and the third rounded corner. The third rounded corner is connected to the bottom of the third cylindrical section, and the second rounded corner is connected to the side wall of the third cylindrical section. The radius of the third rounded corner is greater than the radius of the second rounded corner.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This forming method involves multiple reverse deep drawing operations on the sheet metal. After the first deep drawing, the rounded corner with the greatest thinning at the opening of the first cylinder is removed, allowing material to flow more easily into the straight wall section, resulting in no thinning of the first cylinder. During the second deep drawing, the first transition surface between the second and first cylinder sections is a large rounded corner or a large bevel. Its forming relies on the material thinning at the center of the second cylinder section and the material flow in from the straight wall section of the outer ring of the first cylinder section. By setting limit blocks and positioning rings for limiting, the flow of material into the straight wall section of the outer ring can be accelerated, effectively controlling the thinning rate of the second cylinder section. The third reverse deep drawing transforms the second cylinder section into the third cylinder section and the second transition surface. The main thinning occurs at the rounded corner of the bottom of the third cylinder section, which does not affect the effective surface thinning rate of the part. Furthermore, because the third reverse deep drawing involves length drawing, there is no material accumulation at the bends of the third cylinder section, ensuring the surface quality of the part.

[0031] Through practical processing, the thinning rate of parts can be reduced from 45% to 20%, while ensuring the final wall thickness of the molded parts. The molding qualification rate and surface quality are greatly improved. Attached Figure Description

[0032] Figure 1 This is a cross-sectional view of the structure of the rear sealing ring of the secondary guide described in Example 1;

[0033] Figure 2 This is a flowchart of the molding method described in Example 1;

[0034] Figure 3 This is a schematic diagram of the thinning rate of the molding method described in Example 1;

[0035] Figure 4 This is a schematic diagram of the mold structure for step S3 in the molding method described in Example 1;

[0036] Figure 5 This is a schematic diagram of the mold structure for step S4 in the molding method described in Example 1;

[0037] Figure 6 This is a schematic diagram of the stacked sealing rings of the secondary guide described in Example 1;

[0038] Figure 7 The background technology is the traditional sheet metal forming process;

[0039] Figure 8 This is a schematic diagram illustrating the thinning rate of traditional sheet metal forming processes in the background art. Detailed Implementation

[0040] To clearly illustrate the technical features of this solution, the following detailed description, in conjunction with the accompanying drawings, will explain the technical solution in detail.

[0041] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited to the specific embodiments disclosed below.

[0042] Furthermore, it should be understood in the description of this application that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0043] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0044] In this application, unless otherwise expressly specified and limited, the "above" or "below" of the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In the description of this specification, references to terms such as "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples.

[0045] Example 1

[0046] A low-thinning-rate reverse deep drawing method is provided for the rear sealing ring of the secondary guide vane on an aero-engine. The sheet metal for forming this part is high-temperature alloy GH3536 with a thickness of 0.8 mm. Figure 1 As shown, the final formed part has an inner hole 1, and the wall thickness design requirement is not less than 0.6. The traditional deep drawing process has a high thinning rate, which will produce a step at the inner hole, resulting in a poor appearance of the part.

[0047] like Figure 2 and Figure 3 As shown, the molding method of this embodiment includes the following steps:

[0048] S1. The sheet metal is deep-drawn to form the first cylindrical section 21, which serves as the outer ring of the part. The opening of the first cylindrical section has a first fillet 22 and a flange edge 23. The radius of the first fillet 22 is 5 to 8 times the thickness of the sheet metal part. The bottom corner of the first cylindrical section 21 is a second fillet 24. This step of deep drawing to form the second fillet 24 makes the material flow more easily during the deep drawing process. According to the simulation results, the thinning during deep drawing is at most at the second fillet 24, with a thinning of only 4%, and no thinning at other places. The stretching height of the first cylindrical section 21 should be appropriate to ensure that there is still a margin in the final process.

[0049] S2. Remove the first fillet 22 and flange edge 23 formed in S1, leaving the material in the straight wall section that is more likely to flow in during the subsequent deep drawing process;

[0050] S3. For example Figure 4 As shown, the bottom of the first cylindrical section 21 in S1 is reverse-drawn (reverse drawing is the opposite of the previous drawing direction) to form the second cylindrical section 31. This reverse drawing will form a first transition surface 32 between the bottom of the second cylindrical section 31 and the first cylindrical section 21. During the forming process of the second cylindrical section 31, the material mainly relies on the material thinning at the center and the material inflow at the outer straight wall to replenish it. According to the simulation results of this step, the thinning rate at the thinnest part of the material is 16%.

[0051] S4. For example Figure 5 As shown, the second cylindrical portion 31 in S3 is drawn again in the opposite direction (opposite to the drawing direction in S3) to form the third cylindrical portion 41, thus forming the inner hole profile of the part. A second transition surface 42 is formed between the bottom of the third cylindrical portion 41 and the first cylindrical portion 21. Then, the second fillet 24 is shaped. The shaping process does not increase the material thinning. The bottom of the third cylindrical portion 41, including the corner, is then machined away to form the inner hole 1 of the part.

[0052] When forming the inner hole profile in S4, a small-slope inclined surface 43 can be added to the bottom of the third cylinder 41 to reduce the drawing height. Specifically, the corner of the bottom of the third cylinder is composed of a second rounded corner 44, a third rounded corner 45, and the aforementioned small-slope inclined surface 43. The small-slope inclined surface connects the two rounded corners. The third rounded corner 45 is connected to the bottom of the third cylinder, and the second rounded corner 44 is connected to the side wall of the third cylinder. The radius of the third rounded corner 45 is larger than the radius of the second rounded corner 44. This can achieve the effect of reducing the drawing height by making the bottom of the third cylinder larger rounded corner. In this embodiment, the small-slope inclined surface is designed to be 10°.

[0053] In step S3 of the above forming method, to accelerate the inflow of the outer ring straight wall material and control the thinning as much as possible, a limiting device can be added to the forming mold in this step to give the forming mold a certain closing gap. The forming mold for this step is as follows: Figure 4 As shown, the punch 51 for forming the second cylindrical part 31 is set in the lower die of the mold. A positioning ring 52 is provided around the outside of the punch 51. The positioning ring 52 has a bent inner wall 521, which fits against the bottom and outer surface of the cylindrical part 21. The upper die of the mold is provided with a limiting block 53 that can contact the upper surface of the positioning ring 52 when the mold is closed. When the limiting block 53 and the positioning ring 52 are locked together, the mold closing gap is maintained at 1 to 1.1 times the material thickness gap.

[0054] Since the positioning ring 52 will be lifted up in the early stage of step S3 to allow the part to be placed, a guide must be provided for the positioning ring 52 to ensure that the inner and outer ring structures of the part are concentric. Specifically, a guide post 55 is fixedly installed on the lower mold base 54, and a through hole is opened on the positioning ring 52 for the guide post 55 to pass through, so as to ensure that the positioning ring 52 does not shift during the lifting and resetting process.

[0055] In this embodiment, the first transition surface 32 in S3 above is an inclined surface, and the first transition surface 32 and the second transition surface 42 have the same angle. That is, the forming angle of the first transition surface 32 is consistent with the final forming angle of the part at that point. However, the length of the first transition surface 32 must be less than the length of the second transition surface 42, and the diameter of the second cylindrical part 31 must be greater than the diameter of the third cylindrical part 41, leaving space for the reverse deep drawing forming of the third cylindrical part.

[0056] In step S4 above, the length of the reverse drawing profile section line must be greater than that in step S3. The main thinning in this step occurs at the bottom corner 43 of the third cylinder, which will eventually be removed by turning; therefore, it does not affect the effective profile thinning rate. The length drawing in step S4 avoids the formation of a thinning line between the second transition surface 42 and the wall of the third cylinder 41, as described above. Figure 6 The material stacking phenomenon shown is used to avoid the occurrence of part surface deviation problems.

[0057] It should be noted that the parts need to be coated with lubricating oil, such as castor oil, on both sides during the machining process to increase lubrication.

[0058] use Figure 4 The forming process of the mold shown in step S3 is as follows: After the mold is clamped, the mold is opened → the first ejector pin 56 lifts the positioning ring 52 until the part support surface is flush with the upper surface of the punch 51 → the part A is placed in the positioning ring 52 → the upper mold block 57 is pressed down → the limit block 53 and the positioning ring 52 collide and lock → the part is pressed and the gap is maintained → the upper mold continues to press down → the punch contacts the material at the center of the part → the profile is drawn upwards and deepened → the bottom of the positioning ring 52 is locked → the forming is completed.

[0059] use Figure 5 The forming process of the mold shown in step S4 is as follows: After the mold is clamped, the mold is opened → the second ejector pin 61 raises the second positioning ring 62 until the surface of the part does not interfere with the punch block 63 → the part is placed on the second positioning ring 62 → the upper die pressure block 1 64 and the upper die pressure block 2 65 are pressed down → the upper die pressure block 1 64 is pressed tightly with the second positioning ring 62 → the second rounded corner 24 is shaped → the upper die pressure block 2 65 is lower than the upper die pressure block 1 64 under the action of the spring → the upper die pressure block 1 64 and the upper die pressure block 2 65 continue to press down → the punch block 63 contacts the material at the center of the part → the third cylindrical part 41 is pulled up and deepened → the upper die pressure block 2 65 extends and keeps in contact with the material, so that the second transition surface 42 and the wall of the third cylindrical part 41 do not overlap and wrinkle → the bottom of the second positioning ring 62 is locked, and the forming is completed.

[0060] The molding method of this embodiment produces parts with a maximum thinning rate of 17% in molding simulation and a maximum thinning rate of 20% in actual on-site processing. The surface quality of the inner hole of the part is good, the thinning rate of the effective area of ​​the part is within 15%, the wall thickness is 0.68, the wall thickness meets the requirements of the design drawings, and the surface quality of the part is significantly improved.

[0061] Example 2

[0062] The difference between this embodiment and embodiment 1 is that the first transition surface in S3 is a rounded corner surface, and the radius of the rounded corner surface is designed to be 8 to 10 times the thickness of the sheet metal part.

[0063] Example 3

[0064] The difference between this embodiment and embodiment 1 is that when forming the inner hole profile in S4, the small slope of the bottom corner of the third cylinder is designed to be 20°.

[0065] Example 4

[0066] The difference between this embodiment and embodiment 1 is that when forming the inner hole profile in S4, the small slope slope at the bottom corner of the third cylinder is designed to be 30°.

[0067] Obviously, the above embodiments are merely examples to clearly illustrate the technical solutions of the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for reverse deep drawing forming of sheet metal parts with low thinning rate, characterized in that, The sheet metal part being formed is a rear sealing ring for a secondary guide vane on an aero-engine. The forming method includes the following steps: S1. The sheet metal part is drawn into a first cylindrical section, which serves as the outer ring of the sheet metal part. The opening of the first cylindrical section has a first rounded corner and a flange edge. The radius of the first rounded corner is 5 to 8 times the thickness of the sheet metal part. The bottom corner of the first cylindrical section is a second rounded corner. The stretching height of the first cylindrical section is drawn to ensure the final process allowance. S2. Remove the first fillet and flange edge from S1; S3. The bottom of the first cylindrical section in S1 is reverse-drawn to form the second cylindrical section. A first transition surface is formed between the bottom of the second cylindrical section and the first cylindrical section. The first transition surface is thickened. S4. The second cylindrical section in S3 is reverse-drawn to form the third cylindrical section. A second transition surface is formed between the bottom of the third cylindrical section and the first cylindrical section. The corner of the bottom of the third cylindrical section is composed of a second rounded corner, a third rounded corner, and a sloped surface connecting the second rounded corner and the third rounded corner. The third rounded corner is connected to the bottom of the third cylindrical section, and the second rounded corner is connected to the side wall of the third cylindrical section. The radius of the third rounded corner is greater than the radius of the second rounded corner. Then, the second rounded corner is shaped. The shaping process does not increase the material thinning. Then, the bottom of the third cylindrical section, including the corner, is machined away to form the inner hole of the part. The height of the inner hole of the part is higher than the height of the first cylindrical section.

2. The low-thinning-rate reverse deep drawing method for sheet metal parts according to claim 1, characterized in that, In S3, the first transition surface is a rounded corner surface, and the radius of the rounded corner surface is 8 to 10 times the thickness of the sheet metal part.

3. The low-thinning-rate reverse deep drawing method for sheet metal parts according to claim 1, characterized in that, The mold used in the reverse drawing step S3 is also equipped with a limiting block and a positioning ring. The positioning ring is installed in the lower mold, and the limiting block is installed in the upper mold. The positioning ring has a bent inner wall that fits the bottom and outer surface of the first cylindrical part. The limiting block contacts the positioning ring when the upper and lower molds are closed to ensure the mold closing gap.

4. The low-thinning-rate reverse deep drawing method for sheet metal parts according to claim 3, characterized in that, The mold closing gap is 1 to 1.1 times the material thickness gap.

5. The low-thinning-rate reverse deep drawing method for sheet metal parts according to claim 3, characterized in that, The positioning ring is equipped with guide posts.

6. The low-thinning-rate reverse deep drawing method for sheet metal parts according to claim 1, characterized in that, The first transition surface is an inclined surface, and the angle between the first transition surface and the second transition surface is the same.

7. The low-thinning-rate reverse deep drawing method for sheet metal parts according to claim 6, characterized in that, The length of the first transition surface is less than the length of the second transition surface, and the diameter of the second cylindrical section is greater than the diameter of the third cylindrical section.

8. The low-thinning-rate reverse deep drawing method for sheet metal parts according to claim 1, characterized in that, In step S4, the length of the reverse drawing section is greater than that in step S3.

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