Metal sheet forming method, intermediate shape design method, metal sheet forming die, computer program, and recording medium

Patent metadata

Field	Value
Publication number	US-11270047-B2
Application number	US-201716471442-A
Country	US
Kind code	B2
Filing date	Dec 25, 2017
Priority date	Dec 26, 2016
Publication date	Mar 8, 2022
Grant date	Mar 8, 2022

Abstract

A method of forming a metal sheet into a target shape by press-forming, such that the metal sheet is formed into an intermediate shape that is different from the target shape and then the target shape is formed from the intermediate shape, the method includes: when forming the intermediate shape from the metal sheet, forming the intermediate shape by forming a first region including at least a portion at which a ratio of sheet thickness reduction from the metal sheet is larger when the target shape is formed via the intermediate shape than when the target shape is formed directly from the metal sheet.

First claim

What is claimed is:

1. A method of forming a metal sheet into a target shape by press-forming, such that the metal sheet is formed into an intermediate shape that is different from the target shape and then the target shape is formed from the intermediate shape, the method comprising:
when forming the intermediate shape from the metal sheet, forming the intermediate shape by forming a first region including at least a portion at which a ratio of sheet thickness reduction from the metal sheet is larger when the target shape is formed via the intermediate shape than when the target shape is formed directly from the metal sheet; and
based on element data (B) for a post-forming shaped metal sheet and element data (D) for a hypothetical metal sheet prior to forming derived by finite element analysis in which a first step and a second step are sequentially performed:
imparting strain to at least one element, corresponding to the first region, in the element data (D), at a strain required for deformation into respective shapes of respective elements in the element data (B) that correspond to each of the at least one element in the element data (D);
for remaining elements in the element data (D), corresponding to a second region including at least a portion at which a ratio of sheet thickness reduction from the metal sheet is larger when the target shape is formed directly from the metal sheet than when the target shape is formed via the intermediate shape, imparting strain, having a smaller absolute value than strain required for deformation into respective shapes of respective elements in the element data (B) corresponding to each of the remaining elements, to the remaining elements or imparting no strain to the remaining elements; and
adopting a shape of element data (G) for a hypothetical metal sheet after deformation, in a case in which the hypothetical metal sheet prior to forming has been deformed, as the intermediate shape, wherein:
the first step comprises preparing element data (A) for a provisional metal sheet and the element data (B) for the post-forming shaped metal sheet; and
the second step comprises correcting the element data (A) so as to reduce a difference in shape between each corresponding element in the element data (A) and the element data (B), and deriving the element data (D).

2. The method of claim 1 , wherein, in the first step, the element data (B) is derived, by formation analysis using a finite element method, based on the element data (A).

3. The method of claim 1 , wherein, in the first step, the element data (A) is derived, by reverse analysis using a finite element method, based on the element data (B).

4. The method of claim 1 , wherein, in the second step, a step 2-1, a step 2-2, and a step 2-3 are sequentially performed such that the element data (A) is corrected so as to reduce the difference in shape between each corresponding element in the element data (A) and the element data (B), and the element data (D) is derived, wherein:
step 2-1 comprises deriving a stress (F 1 ) for each element in the element data (A), the stress (F 1 ) being a stress amount required to elastically deform each of the elements in the element data (A) into a shape of each corresponding element in the element data (B);
step 2-2 comprises building a finite element model (I) by applying a stress (F 2 ), having an absolute value that is not lower than the stress (F 1 ) derived in the step 2-1, to each of the elements in the element data (A) under application of a condition of restraining displacement in out-of-plane directions of nodes of each finite element; and
step 2-3 comprises deriving post-elastic-deformation element data (H) by performing elastic deformation analysis using a finite element method based on the finite element model (I) built in the step 2-2, correcting respective shapes of the finite elements in the element data (A) to respective shapes of the finite elements of the post-elastic-deformation finite element data (H), and adopting the corrected finite element data as the element data (D).

5. The method of claim 4 , wherein the stress (F 2 ) has an absolute value that is larger than the stress (F 1 ) but no more than 1.5 times larger than the stress (F 1 ).

6. The method of claim 1 , further comprising:
deriving a stress (F 3 ) for each element in the element data (D), the stress (F 3 ) being a stress amount required for elastic deformation into respective shapes of the respective elements in the element data (B) corresponding to the respective elements in the element data (D);
building a finite element model (J) by applying the stress (F 3 ) required for the elastic deformation to at least one of the elements in the element data (D), and by applying a stress having a smaller absolute value than the stress (F 3 ) required for the elastic deformation, or by applying no stress, to remaining elements in the element data (D); and
performing elastic deformation analysis based on the finite element model (J), using a finite element method, to derive the element data (G) for the hypothetical metal sheet after deformation, by:
imparting strain to at least one of the elements in the element data (D) at a strain required for deformation into respective shapes of the respective elements in the element data (B) corresponding to the at least one of the elements, and
imparting strain to remaining elements in the element data (D) at a strain having a smaller absolute value than the strain required for deformation into respective shapes of the respective elements in the element data (B) corresponding to the remaining elements, or imparting no strain to the remaining elements in the element data (D).

7. The method of claim 6 , further comprising applying stress to the remaining elements such that the stress applied to elements, among the remaining elements in the element data (D) that are in a vicinity of a boundary with the at least one of the elements, has a smaller absolute value than the stress (F 3 ), and the absolute value of the stress gradually decreases in a direction away from the elements in the vicinity of the boundary.

8. The method of claim 1 , further comprising recalculating the element data (D) by performing the first step and the second step, or by performing the second step, after substituting the element data (D) obtained in the second step in place of the element data (A) in the first step.

9. The method of claim 1 , further comprising:
setting an upper limit threshold value, or an upper limit threshold value and a lower limit threshold value, for a state change amount (ΔX) before and after forming for each corresponding element in the element data (D) and the element data (B); and
repeatedly recalculating the element data (D) by performing the first step and the second step, or by performing the second step, after substituting the element data (D) obtained in the second step in place of the element data (A) in the first step, either:
until the element data (D) has a maximum value of the state change amount (ΔX) that is not higher than the threshold value when the threshold value has only been set for the upper limit of the state change amount (ΔX), or
until the element data (D) has a maximum value and a minimum value of the state change amount (ΔX) lying in a range from the upper limit threshold value to the lower limit threshold value when the threshold values have been set for the upper limit and the lower limit of the state change amount (ΔX).

10. A method of forming a metal sheet into a target shape by press-forming such that the metal sheet is sequentially formed into a plurality of intermediate shapes that are different from the target shape and the target shape is formed from a

Assignees

• Nippon Steel Corp

Inventors

• Tanaka Yasuharu
• Miyagi Takashi
• Ogawa Misao

Classifications

• G06F2113/24

  Sheet material · CPC title

• B21D22/00

  Shaping without cutting, by stamping, spinning, or deep-drawing (otherwise than using rigid devices or tools or yieldable or resilient pads B21D26/00) · CPC title

• B21D22/26 Primary

  for making peculiarly, e.g. irregularly, shaped articles · CPC title

• G06F30/23 Primary

  using finite element methods [FEM] or finite difference methods [FDM] · CPC title

• B21D22/24

  involving two drawing operations having effects in opposite directions with respect to the blank · CPC title