METHOD OF DESIGNING PRESS-FORMED PRODUCT, PRESS-FORMING DIE, PRESS-FORMED PRODUCT, AND METHOD OF PRODUCING PRESS-FORMED PRODUCT

Abstract

There is a need to suppress falling or rising of an end of a press-formed product and twisting of the press-formed product due to springback to suppress a shape defect of the press-formed product due to the springback and, in designing a shape of a press-formed product produced by press-forming a sheet material, a curvature radius (R1) of a concave curved portion and a curvature radius (R2) of a convex curved portion of a concave and convex curved shape of an additional shape arranged on the press-formed product where the concave curved portion and the convex curved portion are continuous are set to be the same.

Claims

1-8. (canceled)

9. A method of designing a press-formed product, wherein in designing a shape of a press-formed product produced by press-forming a sheet material, an additional shape having a concave and convex curved shape where a concave curved portion and a convex curved portion are continuous is arranged on the press-formed product, and a curvature radius of the concave curved portion and a curvature radius of the convex curved portion of the concave and convex curved shape are set to be the same.

10. The method according to claim 9, wherein the additional shape is added to improve rigidity of the press-formed product.

11. A press-forming die for producing a press-formed product provided with an additional shape having a concave and convex curved shape where a concave curved portion and a convex curved portion are continuous from a sheet material, wherein the press-forming die is provided with a die member including shoulder portions that each form the concave curved portion and the convex curved portion of the concave and convex curved shape of the additional shape arranged on the press-formed product, and curvature radii of the shoulder portions of the die member are the same.

12. The press-forming die according to claim 11, wherein the additional shape is added to improve rigidity of the press-formed product.

13. A press-formed product produced by press-forming a sheet material and provided with an additional shape having a concave and convex curved shape where a concave curved portion and a convex curved portion are continuous, wherein a curvature radius of the concave curved portion and a curvature radius of the convex curved portion of the concave and convex curved shape are the same.

14. The press-formed product according to claim 13, wherein the additional shape is added to improve rigidity of the press-formed product.

15. A method for producing a press-formed product, wherein, in producing a press-formed product provided with an additional shape having a concave and convex curved shape where a concave curved portion and a convex curved portion are continuous by press-forming a sheet material, a curvature radius of the concave curved portion and a curvature radius of the convex curved portion of the concave and convex curved shape are set to be the same.

16. The method according to claim 15, wherein the additional shape is added to improve rigidity of the press-formed product.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 is a perspective view illustrating a press-formed product of a configuration designed by a method of designing a press-formed product of an example.

[0043] FIGS. 2(a) and 2(b) are cross-sectional views of a rigidity shape of the press-formed product of the aforementioned example along line A-A and line B-B of FIG. 1.

[0044] FIG. 3 is a plan view illustrating a height directional displacement distribution by a springback analysis of a press-formed product of a comparative example by displacement contour.

[0045] FIG. 4 is a plan view illustrating a height directional displacement distribution by a springback analysis of the press-formed product of the aforementioned example by displacement contour.

[0046] FIGS. 5(a) to 5(c) are explanatory views of a cross-section of planar portions on both sides of a concave and convex curved shape, illustrating a state at press bottom dead center by a dotted line and a state after springback by a solid line, where FIG. 5(a) illustrates when the curvature radius R1 of a concave curved portion is the same as the curvature radius R2 of a convex curved portion, FIG. 5(b) illustrates when the curvature radius R1 of the concave curved portion is larger than the curvature radius R2 of the convex curved portion, and FIG. 5(c) illustrates when the curvature radius R1 of the concave curved portion is smaller than the curvature radius R2 of the convex curved portion.

REFERENCE SIGNS LIST

[0047] 1 press-formed product [0048] 2,3 additional shape [0049] 4 concave and convex curved shape [0050] R1 radius of concave curved portion [0051] R2 radius of convex curved portion

DETAILED DESCRIPTION

[0052] Examples will be described in detail below on the basis of the drawings. FIG. 1 is a perspective view illustrating a press-formed product of a configuration designed by a method of designing a press-formed product of an. FIGS. 2(a) and 2(b) are cross-sectional views of a rigidity shape of the press-formed product of the aforementioned example along line A-A and line B-B of FIG. 1. FIG. 3 is a plan view illustrating a height directional displacement distribution by a springback analysis of a press-formed product having an original shape, which is a comparative example, by displacement contour. FIG. 4 is a plan view illustrating a height directional displacement distribution by a springback analysis of the press-formed product of the aforementioned example by displacement contour. Reference numeral 1 denotes a press-formed product in the drawings.

[0053] The method of designing a press-formed product according to the example is to design the press-formed product 1, which is a front pillar lower inner material as a type of a body part of an automobile, and the press-formed product 1 has a thin trapezoidal shape that is easy to bend and twist, i.e., a shape with low rigidity, when it is without additional shapes 2, 3 illustrated in FIG. 1. A press-formed product to be an automobile body part often has such low rigidity shape. Therefore, the press-formed product 1 is provided, on a planar surface of the thin trapezoidal shape, with two additional shapes 2, 3 having an elliptical shape in a plan view and a planar top surface, for improvement of the rigidity.

[0054] The additional shapes 2, 3 of the aforementioned press-formed product 1 each have, at a peripheral edge portion, a concave and convex curved shape 4 having a substantially S-shaped cross-section where a concave curved portion and a convex curved portion are continuous, as the cross-sectional shapes are illustrated in FIGS. 2(a) and (b). In designing the shape of the press-formed product 1, in the original shape, a radius R1 of the concave curved portion and a radius R2 of the convex curved portion of the concave and convex curved shape 4 are set to mutually different values, i.e., R1>R2, as illustrated in FIG. 5(b), for example. The press-formed product 1 having the original shape is subjected to a press formation analysis and a springback analysis with a computer using known software. As a result, as indicated by displacement contours based on a reference height point designated by reference symbol O in FIG. 3, it can be seen that falling occurs largely on the left side of the additional shape 3 because a negative Z-directional displacement is large, and that the press-formed product 1 is twisted in the upper left direction from the additional shape 2 because a negative Z-directional displacement is much larger.

[0055] Therefore, by the method of designing a press-formed product of the example, a radius R1 of a concave curved portion and a radius R2 of a convex curved portion of a concave and convex curved shape 4 having a substantially S-shaped cross-section where the concave curved portion and the convex curved portion are continuous at a peripheral edge portion of each of the additional shapes 2, 3 are set to the same value, i.e., R1=R2, as illustrated in FIG. 5(a), for example, thereby designing the press-formed product 1 of the aforementioned example.

[0056] As is the original shape, the press-formed product 1 of the example in which the radius R1 of the concave curved portion and the radius R2 of the convex curved portion have the same value is subjected to a press formation analysis and a springback analysis with a computer using known software. As a result, as indicated by displacement contours based on a reference height point designated by reference symbol O in FIG. 4, it can be seen that falling is smaller than the original shape on the left side of the additional shape 3 because a negative Z-directional displacement is decreased, and that the press-formed product 1 is less twisted than the original shape in the upper left direction from the additional shape 2. Thus, by the design method of the example and with the press-formed product 1 of the example, falling or rising of an end of the press-formed product and twisting of the press-formed product can be suppressed, and a shape defect of the press-formed product due to springback can be suppressed.

[0057] A sheet material forming the press-formed product 1 of the example can be, for example, a 980 MPa-class high-tensile steel sheet having a thickness t: 0.9 mm, a yield point YP: 620 MPa, a tensile strength TS: 1030 MPa, and an elongation El: 15%. The method of producing a press-formed product of an example uses a press-forming die of an example to press-form the steel sheet to form the press-formed product 1 of the aforementioned example.

[0058] Therefore, the press-forming die of the aforementioned example includes, as a die member, a normal punch, die, and blank holder. The die has a thin trapezoidal shape above outward flanges positioned, in FIG. 1, at upper and lower ends of the press-formed product 1 and a concave portion having a shape that corresponds to the additional shapes 2, 3 protruding from a planar surface of the trapezoidal shape. The blank holder holds a steel sheet between the blank holder and a plane surface extending outward from the concave portion of the die. The punch pushes the steel sheet, which is held between the die and the blank holder, into the concave portion of the die to form the steel sheet into a thin trapezoidal shape, and pushes a convex portion of the leading end of the punch into the concave portion of the die to form the additional shapes 2, 3 by extrusion on the planar surface of the trapezoidal shape.

[0059] Radii of cross-sectional shapes of shoulder portions of concave portions of the die of the press-forming die of the aforementioned example that form the concave curved portions of the additional shapes 2, 3 are made to be substantially equal to the radius R1 of the concave curved portion, and radii of cross-sectional shapes of shoulder portions of convex portions of a leading end of the punch that form the convex curved portions of the additional shapes 2, 3 are made to be substantially equal to the radius R2 of the convex curved portion such that the radii of the cross-sectional shapes of the shoulder portions are equal to each other.

[0060] The press-formed product 1 produced using the press-forming die of the aforementioned example by the method of producing the press-formed product of the aforementioned example becomes the press-formed product of the aforementioned example in which the radius R1 of the concave curved portion and the radius R2 of the convex curved portion of the additional shapes 2, 3 are the same, and with the press-formed product and the method of producing the press-formed product, falling or rising of an end of the press-formed product and twisting of the press-formed product due to springback of the press-formed product can be suppressed, resulting that a shape defect of the press-formed product due to the springback can be suppressed.

[0061] The examples have been described heretofore. However, the method of designing a press-formed product, the press-forming die, the press-formed product, and the method of producing the press-formed product of are not limited to the aforementioned examples, but can be appropriately changed within the scope of the claims. For example, the shape of the press-formed product or the additional shapes may be those other than those illustrated in FIG. 1, and the concave and convex curved shape having the substantially S-shaped cross-section where the concave curved portion and the convex curved portion are continuous is not limited to the additional shape for improvement of the rigidity, but may be an additional shape for reduction of a bending moment, control of the flow rate of a material and the like.

INDUSTRIAL APPLICABILITY

[0062] Thus, by the method of designing a press-formed product, the press-forming die, the press-formed product, and the method of producing the press-formed product, falling and rising of an end of the press-formed product and twisting of the press-formed product due to the springback can be suppressed, and a shape defect of the press-formed product due to the springback can be suppressed.