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

Abstract

The present invention relates to a method and an apparatus for forming a sheet material into a cap shape protruding a height from a bottom surface and having a flat surface on an upper portion, the method comprising the steps of: (S1) forming the sheet material into a protruding shape having a curved surface on an upper portion such that the sheet material has a uniform thickness reduction rate; (S2) forming corner portions at both ends by moving the central portion of the plate material left and right so that the protruding portion has a flat surface; and (S3) forming a flat surface so that the protruding portion is flat by correcting the protruding portion at the corner portions at both ends.

Description

Technical Field

[0001] The present invention relates to a multi-stage press-forming method of a plate for a fuel cell, and more particularly, to a method of manufacturing a cap shape by performing multi-stage press-forming on the plate. Background Art

[0002] Currently, environmental regulations and fuel efficiency regulations and safety standards in the automotive industry are being strengthened. Accordingly, the application rate of ultra-high strength steel and hot stamping steel is increasing, and the development of environmentally friendly vehicles such as hybrid vehicles, electric vehicles and hydrogen fuel cell vehicles is increasing.

[0003] Plates that are much thinner (0.3t or less) than those used in known body components are currently being used as metal plates in hydrogen fuel cell vehicles in environmentally friendly vehicles. When such ultra-thin materials are used to form plates, due to the thin thickness, the fracture resistance is low, and since press forming is performed using a smaller curvature than the body components, it is not easy to ensure a uniform thickness reduction rate compared to ordinary steel plates. In addition, ensuring a flat portion of the cap-shaped flow path shape is very important for improving fuel cell efficiency. In order to ensure a flat portion, the curvature of the flow path must be small (0.1 to 0.3), but in the case of a small curvature, when press forming is performed, fracture occurs due to load concentration and a sharp increase in thickness reduction rate, so manufacturing is not easy.

[0004] Conventional US registered patent US 9630229 describes a method of forming a cap shape using multi-stage molding (3 stages), but there is a limitation that it is difficult to apply when the ductility (elongation) of the material is low. Summary of the invention

[0005] Technical issues

[0006] The present invention aims to solve the conventional problems, and an object of the present invention is to provide a press forming method that uniformly forms a flat portion and has a uniform thickness reduction rate when manufacturing a cap shape of an ultra-thin material (0.3 mm or less). However, this task is only an example, and the scope of the present invention is not limited thereto.

[0007] Technical Solution

[0008] According to one aspect of the present invention, a multi-stage press forming method of a sheet is provided. The method is a method of forming a plate into a hat shape, the hat shape protruding from the bottom surface to a certain height and having a flat surface at the upper part, and the method may include: (S1) forming the plate into a protruding shape having a curved surface at the upper part so that the thickness reduction rate of the plate is uniform; (S2) forming corner parts at both ends by moving the center part of the plate left and right so that the protruding part has a flat surface; and (S3) forming a flat surface by correcting the protruding part at the corner parts at both ends so that the protruding part is flat.

[0009] According to one embodiment, a step of providing a uniformly formed cap-shaped gap (P) may be further performed before step (S1).

[0010] According to one embodiment, in step (S1), a cap height (H1) of the protruding portion protruding from the bottom surface may be 60% to 70% of a gap (P) of the cap shape.

[0011] According to one embodiment, in step (S2), the corner portions at both ends may protrude upward more than the center portion, and the protrusion step difference may be 0.5% to 1% of the plate thickness.

[0012] According to one embodiment, the protruding step difference may be uniformly formed on both sides of the plate by the upper mold and the lower mold.

[0013] According to one embodiment, in step (S2), the plate thickness of the corner portions at both ends may be 10% to 20% greater than the plate thickness of the center portion.

[0014] According to one embodiment, the cap height (H2) formed in step (S2) may be 1% to 2% greater than the cap height (H1) formed in step (S1).

[0015] According to one embodiment, the cap height (H3) formed in step (S3) may be 1% to 2% smaller than the cap height (H2) formed in step (S2).

[0016] According to one embodiment, in step (S3), a flat surface may be formed on the upper surface of the plate by an upper mold, and a downwardly protruding area may be provided on the lower surface of the plate by a lower mold.

[0017] According to one embodiment, the step difference of the protruding area may be 0.1% to 0.5% of the plate thickness.

[0018] According to one embodiment, in step (S3), the corner portions at both ends may have the same height as the center portion, and the plate thickness of the corner portions is 10% to 20% greater than the plate thickness of the center portion.

[0019] According to one embodiment, in step (S3), pressure may be applied to the plate from the side of the mold having the final component shape.

[0020] According to one embodiment, the material of the plate may include metal.

[0021] According to one embodiment, in step (S3), the flat surface may be formed to have a length of 25% to 30% of the gap of the cap shape.

[0022] According to another aspect of the present invention, a plate forming die apparatus is provided. The apparatus may have an upper die and a lower die on both sides of a plate to be formed, the upper die may have a flat portion shape at the center, and the lower die may provide a space in which at least one area corresponding to the flat portion protrudes downward to accommodate the remaining portion of the plate.

[0023] According to one embodiment, the upper mold and the lower mold may be provided with at least one channel into which a pressure medium may be inserted.

[0024] Beneficial Effects

[0025] As described above, according to the embodiment of the present invention, when the cap shape for a fuel cell is manufactured by plate molding, there is an effect of achieving a uniform flat portion and minimizing the thickness reduction rate.

[0026] Of course, the scope of the present invention is not limited to this effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A step-by-step view of a multi-stage press forming method of a panel according to an embodiment of the present invention is shown.

[0028] Figure 2 is a computer simulation result for predicting the thickness reduction rate when the molding method according to the embodiment of the present invention is used.

[0029] Figure 3 is a photograph showing a cross section of a component manufactured by using a molding method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] 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 in order to more completely describe the present invention to those skilled in the art, and the following embodiments may be modified in various other forms, and the scope of the present invention is not limited to the following embodiments. On the contrary, the embodiments are provided in order to more truthfully and completely convey the ideas of the present invention to those skilled in the art. In addition, for the convenience and clarity of description, the thickness and size of each layer in the accompanying drawings are exaggerated.

[0031] Figure 1 A step-by-step view of a multi-stage press forming method of a panel according to an embodiment of the present invention is shown.

[0032] The molding process of the present invention can form a cap-shaped component that protrudes a certain height from an inlet (10) located at the bottom surface and has a flat surface (22) at the upper part (20). Before press molding, a uniformly formed cap-shaped gap (P) can be first set.

[0033] In the present invention, the plate that can be used for forming may be a representative metal material, but is not particularly limited as long as the metal material can be plastically formed.

[0034] Hereinafter, a multi-stage press-forming process of a plate according to an embodiment of the present invention will be described step by step.

[0035] (Step S1) The first step of the forming process is a step of forming an initial shape by utilizing sinusoidal forming while minimizing the effect on the ductility (elongation, %) of the plate. It is preferred to use a mold having an overall curved shape so that the thickness reduction rate of the plate is uniform in the inlet (10) and the upper part (20) of the cap shape. This mold is different from a mold having a final component shape in that the mold does not have a flat surface.

[0036] The cap height (H1) formed in step S1 may be 60% to 70% of the gap (P) of the pre-set cap shape. When the height exceeds 70%, the risk of fracture due to extreme forming increases compared to the ductility of the material. When defects such as fracture occur, the final component may not be formed.

[0037] (Step S2) The second step is a preliminary forming step of ensuring a flat portion of the cap shape by utilizing corrugation forming. The corner portions at both ends are formed by moving the center of the upper portion (20) of the plate left and right, so that the protruding curved surface formed in step S1 is flattened. In this case, the corner portions at both ends may protrude upward by a predetermined height than the center to form a curved shape. By setting the protruding step difference (D1) to 0.5% to 1% of the plate thickness (t), a margin can be ensured in advance so that the protruding portion formed by moving the plate toward both ends is flattened in the subsequent S3 step. The protruding step difference (D1) can be equally applied by the upper mold and the lower mold, thereby being equally formed at the upper corner portion and the lower corner portion of the plate.

[0038] In addition, the cap height (H2) from the bottom surface to the top may be formed to be 1% to 2% higher than the cap height (H1) formed in step (S1), thus having an effect of moving materials to both ends.

[0039] Meanwhile, preferably, the plate thickness (G1) at the corner portions at both ends is 10% to 20% greater than the plate thickness (t) in other regions. This also applies to the thickness G2 of the corner portions in step S3. Thus, the portion where the thickness reduction rate increases can be minimized.

[0040] (Step S3) is the third step, i.e., a process of correcting the material moved to both ends in the second step to be flattened by utilizing flattening molding. The third step is a manufacturing step of finally realizing the cap shape by applying pressure to the plate from the mold side having the final component shape and perfectly realizing the cap shape by correcting the flat portion again.

[0041] Specifically, the upper mold presses the upper protruding area of ​​the corner parts at both ends downward to make the upper protruding area straight, and the lower mold slightly lifts the lower surface of the corner parts at both ends upward. Thus, the corner parts at both ends can be set at the same height as the center, but can be 10% to 20% thicker than the plate thickness (t).

[0042] The cap height (H3) may be formed to be 1% to 2% lower than the cap height (H2) formed in step (S2), and thus, the flattening effect may be maximized. In addition, as described above, it is preferred to minimize the increase in the thickness reduction rate by increasing the thickness (t) of the material by 10% to 20%.

[0043] In the shape of the final component, a flat surface can be formed on the upper surface of the plate, but there may be downwardly protruding areas on the upper and lower surfaces of the plate. Due to the cap-shaped structure in which the upper portion of the plate is concavely protruding, the lengths of the flat surfaces of the upper and lower surfaces may not be equal to each other, so a smaller protruding step (D2) can be set on the lower mold to obtain the desired shape. For example, the protruding step (D2) can be 0.1% to 0.5% of the plate thickness (t). Thereby, the flattening effect of the upper portion of the plate can be more strongly applied. Finally, the flat surface (22) can be formed to have a length of 25% to 30% of the gap (P) of the cap shape.

[0044] The plate forming die apparatus provided for manufacturing the above-mentioned components has an upper die and a lower die located on both sides of the plate to be formed, the upper die having the shape of a central flat portion, and the lower die providing a space in which an area corresponding to the flat portion protrudes downward to accommodate the remaining portion of the plate. The upper die and the lower die may each be provided with at least one channel into which a pressure medium may be inserted to pressurize the plate.

[0045] According to the embodiment of the present invention implemented as described above, since the ultra-thin plate for a fuel cell has low ductility (30% or less), a shape that is difficult to manufacture by using a conventional method can be manufactured.

[0046] To verify this, a computer simulation was performed before molding according to an embodiment of the present invention. Figure 2 As shown. Figure 2 As shown, a hat shape having a maximum thickness reduction rate of 21% in (S1) sinusoidal forming, a maximum thickness reduction rate of 29% in (S2) corrugated forming, and a maximum thickness reduction rate of 30% in (S3) flattening forming can be manufactured. Therefore, when the manufacturing method of the present invention is used, a hat shape that can ensure a flat surface (22) of 25% to 30% compared to the hat gap (P) can be manufactured.

[0047] Figure 3 : is a photograph showing a cross section of a component manufactured by using a molding method according to an embodiment of the present invention. As a result of forming an actual hat-shaped component, it can be seen that the thickness reduction rate is 30% at most, and the hat shape can be manufactured regardless of the ductility of the material.

[0048] The present invention has been described with reference to the embodiments shown in the accompanying drawings, which are exemplary only, and those skilled in the art will appreciate that various modifications and other equivalent embodiments may be made from these embodiments. Therefore, the true technical protection scope of the present invention should be determined by the technical ideas of the attached patent claims.

[0049] Reference numerals list

[0050] 10: Entrance

[0051] 20: upper part

[0052] 22: Flat surface

[0053] Industrial Applicability

[0054] The present invention can be applied to the field of press forming, especially the field of multi-stage press forming and the field of plate forming dies, and the reliability and competitiveness of products can be improved.

Claims

1. A multi-stage press-forming method for forming a plate into a cap shape having a certain height protruding from a bottom surface and having a flat surface at an upper portion, the multi-stage press-forming method comprising: (S1) a step of molding the plate into a protruding shape having a curved surface at the upper portion so that the thickness reduction rate of the plate is uniform; (S2) a step of forming corner portions at both ends by moving the center portion of the plate left and right so that the protruding portion has a flat surface; and (S3) A step of forming a flat surface by trimming the protruding portion at both end corner portions so as to make the protruding portion flat.

2. The multi-stage press forming method of a plate according to claim 1, wherein: Prior to step (S1), a step of setting a gap (P) of the uniformly formed cap shape is further performed.

3. The multi-stage press forming method of a plate according to claim 2, wherein: In the step (S1), a cap height (H1) of a protruding portion protruding from a bottom surface is 60% to 70% of a gap (P) of a cap shape.

4. The multi-stage press forming method of a plate according to claim 1, wherein: In step (S2), the corner portions at both ends protrude upward relative to the central portion, and the protrusion step difference is 0.5% to 1% of the plate thickness.

5. The multi-stage press forming method of a plate according to claim 4, wherein: The protruding step difference is equally formed on both sides of the plate by the upper mold and the lower mold.

6. The multi-stage press forming method of a plate according to claim 1, wherein: In step (S2), the thickness of the plate at the corner portions at both ends is 10% to 20% greater than the thickness of the plate at the center portion.

7. The multi-stage press forming method of a plate according to claim 1, wherein: The cap height (H2) formed in step (S2) is 1% to 2% greater than the cap height (H1) formed in step (S1).

8. The multi-stage press forming method of a plate according to claim 1, wherein: The cap height (H3) formed in step (S3) is 1% to 2% smaller than the cap height (H2) formed in step (S2).

9. The multi-stage press forming method of a plate according to claim 1, wherein: In step (S3), a flat surface is formed on the upper surface of the plate by an upper mold, and a region protruding downward is provided on the lower surface of the plate by a lower mold.

10. The multi-stage press forming method of a plate according to claim 9, wherein: The step difference of the protruding area is 0.1% to 0.5% of the plate thickness.

11. The multi-stage press forming method of a plate according to claim 1, wherein: In step (S3), the corner portions at both ends have the same height as the center portion, and the plate thickness of the corner portions is 10% to 20% greater than the plate thickness of the center portion.

12. The multi-stage press forming method of a plate according to claim 1, wherein: In step (S3), pressure is applied to the plate from the side of the mold having the final component shape.

13. The multi-stage press forming method of a plate according to claim 1, wherein: The material of the plate includes metal.

14. The multi-stage press forming method of a plate according to claim 1, wherein: In step (S3), the flat surface is formed to have a length of 25% to 30% of the gap of the cap shape.

15. A plate forming die apparatus that forms a plate into a cap shape having a certain height protruding from a bottom surface and having a flat surface at an upper portion, the plate forming die apparatus comprising: The upper and lower dies on both sides of the plate to be formed, wherein the upper mold has a flat portion shape at the center, and The lower mold provides a space in which at least one area corresponding to the flat portion protrudes downward to accommodate the remaining portion of the board.

16. The plate forming die apparatus according to claim 15, wherein: The upper mold and the lower mold are provided with at least one channel into which a pressure medium can be inserted.

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