Multi-stage press forming method for sheet material and die mold device for sheet material forming

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 sheet materials, and more particularly to a method for multi-stage press forming sheet materials to manufacture a hat shape for fuel cells.

Background Art

[0002] In the recent 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 is steadily increasing, and the development of eco-cars such as hybrid, electric, and hydrogen fuel cell vehicles is 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 since press forming is performed using a smaller curvature than that of vehicle body parts, it is not easy to ensure a uniform thickness reduction rate compared to general steel sheets. Also, in order to improve the efficiency of fuel cells, 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, breakage occurs due to a concentrated load and an increase in the rapid thickness reduction rate, so manufacturing is not easy.

[0004] In the case of the conventional US Patent No. US9630229, a method of utilizing multi-stage forming (3-stage) was described to form a hat shape, but there is a limit in its applicability 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 provide a press forming method that uniformly forms a flat portion and has a uniform thickness reduction rate when manufacturing a hat shape of an extremely thin material (0.3 mm or less) in order to solve such conventional problems. However, such problems are exemplary and do not limit the scope of the present invention.

Means for Solving the Problems

[0006] According to one aspect of the present invention, there is provided a multi-stage press forming method for a plate material. The method is a method of forming a plate material so as to have a hat shape that protrudes from the bottom surface at a certain height and has a flat surface on the upper part, and includes: (S1) forming the plate material into a protruding portion shape having a curved surface on the upper part so that the thickness reduction rate of the plate material is uniform; (S2) moving the plate material in the central part left and right so that the protruding part has a flat surface, and forming corner parts at both ends; and (S3) flattening the protruding parts of the corner parts at both ends to form a flat surface.

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

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

[0009] According to one embodiment, in the step (S2), the corner parts at both ends protrude above the central part, and the protruding step difference can be 0.5 to 1% of the thickness of the plate material.

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

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

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

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

[0014] According to one embodiment, in the step (S3), a flat surface can be formed on the upper surface of the upper part of the plate material by the upper mold, and a region protruding downward can exist on the lower surface of the upper part of the plate material by the lower mold.

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

[0016] According to one embodiment, in the step (S3), the corner portions at both ends can have the same height as the central portion and a thickness 10 to 20% thicker than the thickness of the plate material at the central portion.

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

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

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

[0020] According to another aspect of the present invention, a mold device for forming a plate material is provided. The device has an upper mold and a lower mold on both sides of the plate material to be formed. The upper mold has a flat portion shape at the center, and the lower mold has a region corresponding to the flat portion protruding downward and can provide a space for accommodating the surplus of the material.

[0021] According to one embodiment, the upper die and the lower die may be provided with at least one passage through which a pressure medium can be charged.

Advantages of the Invention

[0022] According to the embodiment of the present invention configured as described above, when forming a plate material and manufacturing a hat shape for a fuel cell, it is possible to embody a uniform flat portion and minimize the thickness reduction rate.

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

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

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 showing step by step a multi-stage press forming method of a plate material according to an embodiment of the present invention.

[0027] The forming process in the present invention enables the formation of a Hat-type part. The Hat-type protrudes from an inflow part (10) located on the bottom surface at a certain height, and the upper part (20) is provided with a flat surface (22). Before press forming, the interval (P) of the Hat-type formed uniformly can be set first.

[0028] In the present invention, the plate material used for forming can be, for example, a metal material, but it is not particularly limited as long as it is a material that can be plastically formed.

[0029] Hereinafter, the multi-stage press forming process of the plate material according to the embodiment of the present invention will be described step by step.

[0030] (Step S1) As the first step of the forming process, it is a step of utilizing Sine Forming to minimize the influence on the ductility (elongation rate, %) of the plate material and form the initial shape. It is preferable to use a mold having a curved shape as a whole so that the thickness reduction rate of the plate material is uniform at the Hat-type inflow part (10) and the upper part (20). Since the mold does not have a flat surface, it can be different from the mold having the shape of the final part.

[0031] The height (H1) of the hat formed in step S1 can be 60 - 70% with respect to the previously set Hat-type interval (P). This is because when it is 70% or more, the risk of breakage increases due to extreme forming compared to the ductility of the material. If defects such as breakage occur, it may not be possible to form the final part.

[0032] (Step S2) As the second step, it is a preliminary forming step that utilizes Rippling Forming to secure a hat-shaped flat portion. The central plate material of the upper part (20) is moved left and right so that the protruding curved surface formed in Step S1 becomes flat, and the corner portions at both ends are formed. At this time, the corner portions at both ends can protrude upward by a predetermined height from the center and form a bent shape. By imparting a protrusion step (D1) of 0.5 to 1% of the thickness (t) of the plate material, it is possible to ensure in advance a margin for moving the material to both ends and flattening the protruding portions in Step S3 later. The protrusion step (D1) is uniformly applied by the upper mold and the lower mold and can be similarly formed at the upper and lower corner portions of the plate material.

[0033] Also, the height (H2) of the hat from the bottom surface to the topmost part is formed to be 1 to 2% higher than the height (H1) of the hat formed in Step (S1), so as to give an effect of moving the material to both ends.

[0034] On the other hand, it is preferable to impart the thickness (G1) of the plate material located at the corner portions at both ends to be 10 to 20% larger than the thickness (t) of the plate material in other regions. This can also be similarly applied to G2, which is the thickness of the corner portions in Step S3. Thereby, it is possible to minimize the portion where the thickness reduction rate increases.

[0035] (Step S3) As the third step, it is a process that utilizes Flattening Forming to flatten and correct the material that has moved to both ends in the second step. It is a manufacturing step in which pressure is applied to the plate material from the mold side having the shape of the final part, finally realizing a hat shape, correcting the flat portion once again, and perfectly realizing the hat shape.

[0036] Specifically, the upper mold serves to push down the protruding regions on the upper surfaces of the corner portions at both ends and stretch them in a straight line, and the lower mold serves to slightly lift up the lower surfaces of the corner portions at both ends. Thereby, the corner portions at both ends can be formed such that their height is the same as that of the central portion and they are 10 to 20% thicker than the thickness (t) of the plate material.

[0037] In the case of the hat height (H3), it can be formed to be 1 to 2% lower than the hat height (H2) formed in the step (S2), so that the flattening effect can be maximized. Also, in the case of G2, as described above, it is advisable to provide it to be 10 to 20% larger than the thickness (t) of the material to minimize the increasing part of the thickness reduction rate.

[0038] The form of the final part can be such that a flat surface is formed on the upper surface of the upper part of the plate material, and a region protruding downward can exist on the lower surface of the upper part of the plate material. Since the lengths of the flat surfaces provided on the upper and lower surfaces cannot be the same due to the hat-shaped structure in which the upper part of the plate material protrudes in a concave shape, in order to obtain a desired shape, a fine protruding step (D2) can be provided on the lower mold. For example, the protruding step (D2) can be 0.1 to 0.5% of the thickness (t) of the plate material. Thereby, the flattening effect on the upper part of the plate material can be strongly applied once again. Finally, the flat surface (22) can be formed with a length of 25 to 30% with respect to the hat-shaped interval (P).

[0039] The mold device for forming a plate material provided for manufacturing the parts as described above has an upper mold and a lower mold on both sides of the plate material to be formed. The upper mold has a flat part shape in the center, and the lower mold has a region corresponding to the flat part protruding downward, and can provide a space where the surplus of the material can be accommodated. The upper mold and the lower mold can be provided with at least one or more passages into which a pressure medium can be charged in order to press the plate material.

[0040] According to the embodiment of the present invention made as described above, due to the low ductility (30% or less) of the ultra-thin plate material for fuel cells, it is possible to manufacture a shape that is difficult to manufacture by conventional methods.

[0041] To verify this, a computer simulation before forming according to an embodiment of the present invention was carried out and is shown in FIG. 2. As shown in FIG. 2, in (S1) Sine Forming, a hat shape with a maximum thickness reduction rate of 21% can be manufactured, in (S2) Rippling Forming, a maximum of 29%, and in (S3) Flattening Forming, a maximum of 30%. Therefore, when the manufacturing method of the present invention is utilized, a hat shape can be manufactured in which a flat surface (22) can be secured at 25 to 30% with respect to the hat interval (P).

[0042] 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. As a result of forming an actual hat-shaped component, it can be confirmed that the thickness reduction rate is up to 30%, and a hat shape can be manufactured regardless of the ductility of the material.

[0043] The present invention has been described with reference to the embodiments shown in the drawings, but this is merely an example, and those having ordinary knowledge in the technical field will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention should be determined by the technical idea of the appended claims.

Industrial Applicability

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

Explanation of Signs

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

Claims

1. A method for forming a sheet material so as to have a hat-type shape that protrudes at a certain height from the bottom surface and has a flat surface on the upper part, comprising: (S1) forming the sheet material into a protruding portion having a curved surface on the upper part so that the thickness reduction rate of the sheet material is uniform; (S2) moving the sheet material in the central part 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. The method is a multi-stage press forming method for a sheet material.

2. Before the step (S1), further performing a step of setting a hat-shaped interval (P) that is uniformly formed. The multi-stage press forming method for a sheet material according to Claim 1.

3. In the step (S1), the height (H1) of the hat of the protruding portion protruding from the bottom surface is 60 to 70% with respect to the hat-shaped interval (P). The multi-stage press forming method for a sheet material according to Claim 2.

4. In the step (S2), the corner portions at both ends protrude above the central part, and the protruding step difference is 0.5 to 1% of the thickness of the sheet material. The multi-stage press forming method for a sheet material according to Claim 1.

5. The protruding step difference is formed identically on both sides of the sheet material by an upper mold and a lower mold. The multi-stage press forming method for a sheet material according to Claim 4.

6. In the step (S2), the thickness of the sheet material located at the corner portions at both ends is 10 to 20% thicker than the thickness of the sheet material in the central part. The multi-stage press forming method for a sheet material according to Claim 1.

7. The step (S2) is a step of forming the height (H2) of the hat 1 to 2% higher than the height (H1) of the hat formed in the step (S1). The multi-stage press forming method for a sheet material according to Claim 1.

8. The step (S3) is a step of forming the height (H3) of the hat 1 to 2% lower than the height (H2) of the hat formed in the step (S2). The multi-stage press forming method for a sheet material according to Claim 1.

9. The step (S3) is a step of forming a flat surface on the upper surface of the upper part of the sheet material by an upper mold, and there is a region protruding downward on the lower surface of the upper part of the sheet material by a lower mold. The multi-stage press forming method for a sheet material according to Claim 1.

10. The step difference of the protruding region is 0.1 to 0.5% of the thickness of the sheet material. The multi-stage press forming method for a sheet material according to Claim 9.

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

12. The step (S3) is performed by applying pressure to the sheet material from the die side having the shape of the final part. The multi-stage press forming method for a sheet material according to claim 1.

13. The material of the sheet material includes metal. The multi-stage press forming method for a sheet material according to claim 1.

14. The step (S3) is such that a flat surface is formed with a length of 25 to 30% with respect to the hat-shaped interval. The multi-stage press forming method for a sheet material according to claim 1.

15. A die device for forming a sheet material so as to have a hat-type that protrudes at a certain height from the bottom surface and is provided with a flat surface at the upper part, having an upper die and a lower die on both sides of the sheet material to be formed, the upper die having a flat part shape in the center, the lower die having at least one region corresponding to the flat part protruding downward and providing a space in which the surplus of the material can be accommodated. Die device for sheet material forming.

16. The upper die and the lower die are provided with at least one or more passages into which a pressure medium can be charged. The die device for sheet material forming according to claim 15.

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