Multi-stage press molding method for sheet metal, and mold and die apparatus for sheet metal molding.

Abstract

The present invention relates to a method and an apparatus for forming a plate material so as to have a hat-type that protrudes at a certain height from the bottom surface and has a flat surface at the top. The method may include: (S1) forming the plate material into a protruding portion shape having a curved surface at the top so that the thickness reduction rate of the plate material is uniform; (S2) moving the plate material at the central portion left and right so that the protruding portion has a flat surface, and forming corner portions at both ends; and (S3) flattening the protruding portions of the corner portions at both ends to form a flat surface.

Description

Technical Field

[0001] The present invention relates to a multi-stage press forming method for a sheet material, and more particularly, to a method for multi-stage press forming a sheet material to manufacture a hat shape for a fuel cell.

Background Art

[0002] In recent years' automotive industry, environmental and fuel consumption regulations and safety standards have been strengthened. As a result, the application rate of ultra-high strength steel and hot stamping steel has been steadily increasing, and the development of eco-cars such as hybrid, electric, and hydrogen fuel cell vehicles has been increasing.

[0003] In the case of metal sheet materials used in hydrogen fuel cell vehicles among eco-cars, compared with the materials used in existing vehicle body parts, sheet materials with a very thin thickness (0.3 t or less) are used. When forming a sheet material using such an extremely thin material, due to the thin thickness, the resistance to fracture is low, and press forming is performed using a smaller curvature compared to vehicle body parts, so it is not easy to ensure a uniform thickness reduction rate compared to general steel sheets. Also, in order to improve the efficiency of the fuel cell, it is extremely important to ensure a flat portion of the hat-shaped flow path shape. In order to ensure the flat portion, the curvature of the flow path must be made small (0.1 to 0.3), but when the curvature is small, during press forming, fracture occurs due to concentrated load and an increase in the rapid thickness reduction rate, so manufacturing is not easy.

[0004] In the case of the conventional U.S. registered patent US9630229, a method using multi-stage forming (3-stage) was described to form a hat shape, but there are limitations in its application when the ductility (elongation rate) of the material is low.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention aims to solve the aforementioned problems of the conventional method by providing a press molding method that uniformly forms a flat portion and has a uniform thickness reduction rate when manufacturing a hat shape from an ultra-thin material (0.3 mm or less). However, these problems are illustrative and do not limit the scope of the present invention. [Means for solving the problem]

[0006] According to one aspect of the present invention, a multi-stage press forming method for sheet metal is provided. The method is a method for forming sheet metal so that it has a hat-type shape, which protrudes from the bottom surface at a certain height and has a flat surface at the top, and may include: (S1) forming the sheet metal into a protruding portion with a curved surface at the top so that the thickness reduction rate of the sheet metal is uniform; (S2) moving the central part of the sheet metal from side to side so that the protruding portion has a flat surface, thereby forming the corners at both ends; and (S3) straightening the protruding portions of the corners at both ends to form a flat surface.

[0007] According to one embodiment, a step of setting a uniformly formed hat-shaped spacing (P) may be performed before step (S1).

[0008] According to one embodiment, in step (S1), the height (H1) of the hat protruding from the bottom surface of the protruding portion may be 60-70% of the hat-shaped spacing (P).

[0009] According to one embodiment, in step (S2), the corners at both ends protrude above the central portion, and the protruding step may be 0.5 to 1% of the thickness of the plate material.

[0010] According to one embodiment, the protruding step can be formed identically on both sides of the sheet material by an upper mold and a lower mold.

[0011] According to one embodiment, in step (S2), the thickness of the plate material located at the corners at both ends can be 10 to 20 percent thicker than the thickness of the plate material in the central part.

[0012] According to one embodiment, step (S2) may be a step in which the height (H2) of the hat is formed to be 1-2% higher than the height (H1) of the hat formed in step (S1).

[0013] According to one embodiment, step (S3) may be a step in which the height of the hat (H3) is formed to be 1-2% lower than the height of the hat (H2) formed in step (S2).

[0014] According to one embodiment, in step (S3), a flat surface is formed on the upper surface of the upper part of the sheet material by the upper mold, and a region protruding downwards is created on the lower surface of the upper part of the sheet material by the lower mold.

[0015] According to one embodiment, the step in the protruding region may be 0.1 to 0.5% of the thickness of the plate material.

[0016] According to one embodiment, in step (S3), the corners at both ends may have the same height as the central part and a thickness that is 10 to 20% thicker than the thickness of the plate material in the central part.

[0017] According to one embodiment, step (S3) can be performed by applying pressure to the sheet material from the mold side having the shape of the final part.

[0018] According to one embodiment, the material of the plate may include metal.

[0019] According to one embodiment, step (S3) can be performed to form a flat surface with a length of 25-30% of the hat-shaped spacing.

[0020] Another aspect of the present invention provides a die apparatus for forming sheet material. The apparatus has an upper die and a lower die on both sides of the sheet material to be formed, the upper die having a flat portion in the center, and the lower die having a region corresponding to the flat portion that protrudes downward, providing a space in which excess material can be accommodated.

[0021] According to one embodiment, at least one or more passages for charging a pressure medium can be provided in the upper mold and the lower mold.

Advantages of the Invention

[0022] According to the embodiment of the present invention made as described above, when forming a plate material and manufacturing a hat shape for a fuel cell, a uniform flat portion can be realized, and the effect of minimizing the thickness reduction rate can be achieved.

[0023] Of course, such an effect does not limit the scope of the present invention.

Brief Description of the Drawings

[0024] [Figure 1] FIG. 1 is a diagram stepwise showing a multi-stage press forming method of a plate material according to an embodiment of the present invention. [Figure 2] FIG. 2 is a computer simulation result for predicting the thickness reduction rate when using the forming method according to an embodiment of the present invention. [Figure 3] FIG. 3 is a photograph showing a cross section of a component manufactured by the forming method according to an embodiment of the present invention.

Modes for Carrying Out the Invention

[0025] Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments of the present invention are provided to more fully explain the present invention to those having ordinary knowledge in the technical field. The following embodiments can be modified into various different forms, and the scope of the present invention is not limited to the following embodiments. Rather, those embodiments are provided to make the present disclosure more substantial and complete and to fully convey the idea of the present invention to those skilled in the art. Also, in the drawings, the thickness and size of each layer are exaggerated for the sake of convenience of explanation and clarity.

[0026] FIG. 1 is a diagram stepwise showing a multi-stage press forming method of a plate material according to an embodiment of the present invention.

[0027] The molding process in the present invention enables the molding of hat-shaped parts, the hat-shaped parts protruding from an inlet (10) located at the bottom surface at a certain height, and having a flat surface (22) at the top (20). Before press molding, the uniform spacing (P) of the hat-shaped parts can be set in advance.

[0028] In the present invention, the sheet material used for molding may typically be a metal material, but is not particularly limited as long as it is a material that can be plastically molded.

[0029] The multi-stage press forming process for sheet metal according to an embodiment of the present invention will be described step by step below.

[0030] (S1 step) As the first step of the molding process, this step utilizes sine forming to minimize the impact on the ductility (stretch rate, %) of the sheet material and to form the initial shape. It is preferable to use a mold that has a hat-shaped inlet (10) and an overall curved shape so that the rate of thickness reduction of the sheet material is uniform at the top (20). Since the mold does not have a flat surface, it can be used as a mold that has the shape of the final part.

[0031] The height of the hat (H1) formed in step S1 may be 60-70% of the previously set hat-shaped spacing (P). If it is 70% or more, the risk of fracture increases due to the extreme molding relative to the ductility of the material. If defects such as fracture occur, it may not be possible to form the final part.

[0032] (Step S2) The second step is a pre-forming step that utilizes rippling forming to secure a hat-shaped flat section. The central plate material of the upper part (20) is moved left and right to form the corners at both ends so that the protruding curved surface formed in step S1 becomes flat. At this time, the corners at both ends can protrude above the center by a predetermined height, forming a bent shape. The protruding step (D1) is given by 0.5 to 1% of the thickness (t) of the plate material, so that in step S3, the material can be moved to both ends and the protruding part can be corrected to be flat in advance. The protruding step (D1) can be applied identically by the upper and lower molds and can be similarly formed at the upper and lower corners of the plate material.

[0033] Furthermore, by shaping the hat so that the height (H2) from the base to the top is 1-2% higher than the height (H1) of the hat formed in step (S1), it is possible to create an effect that shifts the material to both ends.

[0034] On the other hand, it is preferable that the thickness of the plate material located at both corners (G1) be 10-20% greater than the thickness of the plate material in other areas (t). This can also be applied to the corner thickness G2 in step S3. This minimizes the portion where the thickness reduction rate increases.

[0035] (Step S3) The third step is to utilize Flattening Forming to flatten the material that was moved to both ends in the second step. Pressure is applied to the sheet material from the mold side which has the shape of the final part, finally creating a hat shape, and the flat parts are straightened once more to perfectly realize the hat shape.

[0036] Specifically, the upper mold pushes the protruding areas on the upper surfaces of the corners at both ends downward, extending them into a straight line, while the lower mold slightly raises the lower surfaces of the corners at both ends upward. As a result, the corners at both ends can be formed to have the same height as the central part and to be 10-20% thicker than the thickness (t) of the sheet metal.

[0037] For the hat height (H3), the flattening effect can be maximized by forming it to be 1-2% lower than the hat height (H2) formed in step (S2). Also, for G2, as explained earlier, it is best to apply it to be 10-20% greater than the material thickness (t) to minimize the increase in the thickness reduction rate.

[0038] The final part may have a flat surface formed on the upper surface of the upper part of the sheet metal, and a downwardly projecting region on the lower surface of the upper part of the sheet metal. Due to the hat-shaped structure in which the upper part of the sheet metal protrudes in a concave shape, the lengths of the flat surfaces on the upper and lower surfaces cannot be the same. Therefore, a minute protruding step (D2) can be added to the lower mold to obtain the desired shape. For example, the protruding step (D2) may be 0.1 to 0.5% of the thickness (t) of the sheet metal. This allows the effect of flattening the upper part of the sheet metal to be applied more strongly once again. Finally, the flat surface (22) may be formed with a length of 25 to 30% of the hat-shaped spacing (P).

[0039] A sheet metal forming die apparatus provided for manufacturing the above-described parts has an upper die and a lower die on both sides of the sheet metal to be formed, the upper die having a flat section in the center, and the lower die having a region corresponding to the flat section that protrudes downward, providing a space in which excess material can be accommodated. The upper die and the lower die may be provided with at least one passage through which a pressure medium can be introduced to pressurize the sheet metal.

[0040] According to the embodiment of the present invention described above, the low ductility (30% or less) of the ultrathin sheet material for fuel cells makes it possible to manufacture shapes that are difficult to produce using conventional methods.

[0041] To verify this, a computer simulation of the pre-molding process according to an embodiment of the present invention was performed and is shown in Figure 2. As shown in Figure 2, a hat shape can be manufactured with a maximum thickness reduction rate of 21% in (S1) Sine Forming, 29% in (S2) Rippling Forming, and 30% in (S3) Flattening Forming. Therefore, when utilizing the manufacturing method of the present invention, a hat shape can be manufactured in which a flat surface (22) of 25-30% of the hat spacing (P) can be secured.

[0042] Figure 3 is a photograph showing a cross-section of a part manufactured by the molding method according to an embodiment of the present invention. As a result of molding an actual hat-shaped part, it can be confirmed that the thickness reduction rate is a maximum of 30%, and that a hat shape can be manufactured regardless of the ductility of the material.

[0043] Although the present invention has been described with reference to the embodiments shown in the drawings, these are merely illustrative, and a person with ordinary skill in the art will understand that various modifications and equivalent other embodiments are possible. Therefore, the true scope of technical protection of the present invention should be determined by the technical idea of ​​the appended claims. [Industrial applicability]

[0044] The present invention can be used in the field of press forming, particularly in the field of multi-stage press forming and in the field of die forming for sheet metal, and can improve the reliability and competitiveness of products. [Explanation of Symbols]

[0045] 10:Inflow part 20: Top 22:Flat surface

Claims

1. A method for shaping a plate material so that it has a hat-type shape, which protrudes from the bottom surface at a certain height and has a flat surface on top, (S1) A step of forming a plate material into a protruding part with a curved surface on the upper part so that the rate of thickness reduction of the plate material is uniform; (S2) A step of moving the central plate material from side to side so that the protruding portion has a flat surface, thereby forming the corners at both ends; and, (S3) The step of straightening the protruding portions of the corners at both ends to form a flat surface; The above step (S3) is, The upper mold creates a flat surface on the upper surface of the sheet material, and the lower mold creates a region that protrudes downward on the lower surface of the upper surface of the sheet material. The step difference in the aforementioned protruding region is 0.1 to 0.5% of the thickness of the plate material. A multi-stage press forming method for sheet metal.

2. Before step (S1), The step of setting a uniformly formed hat-shaped spacing (P); further, A multi-stage press forming method for a sheet material according to claim 1.

3. In step (S1) above, The aforementioned protruding portion has a hat-shaped height (H1) that protrudes from the bottom surface, which is 60-70% of the hat-shaped spacing (P). The multi-stage press forming method for a sheet material according to claim 2.

4. In step (S2) above, The corners at both ends protrude upward from the central part. The protruding step is 0.5 to 1% of the thickness of the board. A multi-stage press forming method for a sheet material according to claim 1.

5. The aforementioned protruding steps are formed identically on both sides of the sheet material by the upper mold and the lower mold. The multi-stage press forming method for a sheet material according to claim 4.

6. In step (S2) above, The thickness of the plate material located at the corners of both ends is 10 to 20 percent thicker than the thickness of the plate material in the central part. A multi-stage press forming method for a sheet material according to claim 1.

7. The aforementioned step (S2) is, This step involves forming the hat height (H2) to be 1-2% higher than the hat height (H1) formed in step (S1). A multi-stage press forming method for a sheet material according to claim 1.

8. The above step (S3) is, This step involves forming the hat so that the height (H3) is 1-2% lower than the height (H2) of the hat formed in step (S2). A multi-stage press forming method for a sheet material according to claim 1.

9. In step (S3) above, The corners at both ends are the same height as the central part and have a thickness that is 10 to 20 percent thicker than the thickness of the central part of the plate. A multi-stage press forming method for a sheet material according to claim 1.

10. The above step (S3) is, This process involves applying pressure to a sheet metal from the mold side, which has the shape of the final part. A multi-stage press forming method for a sheet material according to claim 1.

11. The material of the aforementioned plate material includes metal, A multi-stage press forming method for a sheet material according to claim 1.

12. The above step (S3) is, The flat surface is formed with a length of 25-30% of the hat-shaped spacing. A multi-stage press forming method for a sheet material according to claim 1.

13. A mold apparatus for forming a sheet material so that it has a hat-type shape, which protrudes from the bottom surface at a certain height and has a flat surface on top, The sheet material to be molded has an upper mold and a lower mold on both sides. The upper mold has a flat section in the center. The lower mold has at least one region corresponding to the flat portion that protrudes downward, providing a space in which excess material can be accommodated. The step in the aforementioned space is 0.1 to 0.5% of the thickness of the molded plate material. Mold equipment for forming plate materials.

14. The upper mold and the lower mold are provided with at least one passage through which a pressure medium can be inserted. The die apparatus for forming sheet material according to claim 13.

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