Method for bending sheet metal and product of sheet metal

1. A method for bending a sheet metal, the method comprising:

a hardness adjusting process for changing hardness of at least a part of the sheet metal so as to form a blank including a high-hardness region and a low-hardness region having a hardness lower than a hardness of the high-hardness region; and

a bending process for bending an objective region to be processed, which includes the low-hardness region and the high-hardness region of the blank, so as to form a product,

wherein the hardness adjusting process comprises forming the objective region to be processed in at least a part of the sheet metal, wherein one side of the sheet metal is formed as the low-hardness region and the other side of the sheet metal is formed as the high-hardness region.

2. The method for bending a sheet metal according to claim 1 , wherein the hardness adjusting process includes a heating process for heating an entirety of the sheet metal and a hardening process for quenching only a region to be the high-hardness region.

3. The method for bending a sheet metal according to claim 2 , wherein the hardening process is a process for cooling only the region to be the high-hardness region by using a mold.

4. The method for bending a sheet metal according to claim 2 , wherein the hardening process is a process for water-cooling only the region to be the high-hardness region.

5. The method for bending a sheet metal according to claim 1 , wherein the hardness adjusting process comprises a welding process for positioning another sheet metal, having hardness different from the hardness of the sheet metal, in a region to be the high-hardness region or the low-hardness region, and welding the sheet metals to each other.

6. The method for bending a sheet metal according to claim 1 , wherein the hardness adjusting process is a process for heating a region to be the low-hardness region of the sheet metal, by using a laser.

7. The method for bending a sheet metal according to claim 1 , wherein the hardness of the low-hardness region is within a range from 30% to 70% of the hardness of the high-hardness region.

8. The method for bending a sheet metal according to claim 1 , wherein the low-hardness region of the blank is deformed by using a press brake in the bending process.

9. The method for bending a sheet metal according to claim 1 , wherein the low-hardness region of the blank is deformed by roll forming in the bending process.

10. A product manufactured by the method for bending a sheet metal according to claim 1 .

11. The product according to claim 10 , wherein the sheet metal is a high-strength steel sheet having tensile strength of 980 MPa or more.

12. The product according to claim 11 , wherein Vickers hardness of a region other than the deformed portion which is deformed by the bending process is 310 or more, and the hardness of the deformed portion is within a range from 40% to 80% of the hardness of the region other than the deformed portion.

13. The method for bending a sheet metal according to claim 1 , wherein the sheet metal is a high-strength steel sheet having tensile strength of 980 MPa or more.

14. The method for bending a sheet metal according to claim 1 , wherein the hardness adjusting process comprises a heating process for heating at least the objective region over a thickness direction of the sheet metal, and a hardening process for cooling a surface which corresponds to the side of the objective region having higher hardness.

15. The method for bending a sheet metal according to claim 14 , wherein the hardening process is a process for cooling the surface which corresponds to the side of the objective region having higher hardness.

16. The method for bending a sheet metal according to claim 14 , wherein the hardening process is a process for water-cooling the surface which corresponds to the side of the objective region having higher hardness.

17. The method for bending a sheet metal according to claim 1 , wherein the hardness adjusting process is a shot-peening process applied to one side of the sheet metal to be at least the objective region.

18. The method for bending a sheet metal according to claim 1 , wherein the hardness of the side of the objective region having lower hardness is within a range from 30% to 80% of the hardness of the side of the objective region having higher hardness.

19. The method for bending a sheet metal according to claim 1 , wherein the blank is deformed by roll forming in the bending process.

20. The method for bending a sheet metal according to claim 1 , wherein the sheet metal is a high-strength steel sheet having tensile strength of 980 MPa or more.

21. A method for manufacturing a blank as a product by carrying out a bending process, the method comprising:

a process for changing hardness of at least a part of a sheet metal so as to form a blank having an objective region to be processed, which includes a high-hardness region and a low-hardness region having a hardness lower than a hardness of the high-hardness region,

wherein the objective region to be processed is formed in a region of the blank including a region which is deformed by the bending process, and

wherein one side of the sheet metal is formed as the low-hardness region, and the other side of the sheet metal is formed as the high-hardness region.

22. The method for manufacturing a blank according to claim 21 , wherein the sheet metal is a high-strength steel sheet having tensile strength of 980 MPa or more.

23. A product manufactured by the method for bending a sheet metal according to claim 21 .

24. A blank according to claim 23 , wherein the sheet metal is a high-strength steel sheet having tensile strength of 980 MPa or more.

25. A method for manufacturing a blank by carrying out bending process, the method comprising:

a process for changing hardness of a sheet metal in a thickness direction thereof so as to form a blank having an objective region to be processed, the objective region being formed in at least a part of the sheet metal so that the objective region includes front and back sides having different hardness,

wherein the side of the objective region having lower hardness is formed in an inside region of a deformed portion which is deformed by the bending process.

26. The method for manufacturing a blank according to claim 25 , wherein the sheet metal is a high-strength steel sheet having tensile strength of 980 MPa or more.

27. The method for manufacturing a blank according to claim 25 , wherein Vickers hardness of a region other than the deformed portion which is deformed by the bending process is 310 or more, and the hardness of inside of the deformed portion is within a range from 40% to 85% of the hardness of the region other than the deformed portion.