PRESS-FORMING METHOD

Abstract

Provided is a press-forming method including three steps for preventing spring-back in a hat-shaped cross section shape of a final formed article. In the first step, from a blank, a preformed article in a first form is obtained, the preformed article including a top surface, left and right vertical walls, and left and right tapered portions extending outward from lower ends of the left and right vertical walls, respectively, of a final formed article having a hat-shaped cross section. In the second step, the compression can be applied to the entirety of the top surface, the left and right vertical walls, and the left and right flanges of the final formed article having the hat-shaped cross section, whereby the spring-back can be sufficiently prevented. In the third step, obtain the final formed article having the hat-shaped cross section.

Description

This application is based on and claims the benefit of priority from Chinese Patent Application No. 202210305026.1, filed on 25 Mar. 2022, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a press-forming method.

Related Art

A technique has been proposed for obtaining, from a plate-like blank, a final formed article having a hat-shaped cross section by press-forming, the final formed article including a top surface, vertical walls continuing to both ends of the top surface, left and right flanges extending from lower ends of the vertical walls, and bent portions interposed between the vertical walls and the flanges (for example, see Japanese Unexamined Patent Application, Publication No. 2017-42791).

Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2017-42791

SUMMARY OF THE INVENTION

In the technique disclosed in Japanese Unexamined Patent Application, Publication No. 2017-42791, the following two forming steps are provided when the formed article including the flanges bent in a longitudinal direction at a pair of vertical walls in the hat-shaped cross section is obtained by press-forming. In the first forming step, the flange to be subjected to a shrinkage flange deformation is formed to be short in a line length in the longitudinal direction, and the flange to be subjected to a stretch flange deformation is formed to be long in a line length in the longitudinal direction. In the second forming step, a final formed article is formed using a mold with a product shape. Thus, it is considered that spring-back can be reduced. However, according to the technique disclosed in Japanese Unexamined Patent Application, Publication No. 2017-42791, even when compression is applied to the flanges and local portions in the vicinity thereof, it is difficult to apply compression to the entirety of the top surface, the vertical walls, and the flanges. Therefore, the effect of preventing the spring-back is limited.

The present invention has been made in view of the circumstances described above, and is to provide a press-forming method capable of sufficiently preventing spring-back by applying compression to the entirety of the top surface, the vertical walls, and the flanges in the hat-shaped cross section of the final formed article.

(1) The present invention provides a method of press-forming, from a blank (for example, a blank 2 to be described below), a final formed article (for example, a final formed article 1 to be described below) having a hat-shaped cross section and including a top surface (for example, a top surface 3 to be described below), left and right vertical walls (for example, a left vertical wall 4 and a right vertical wall 5 to be described below) continuing to left and right ends of the top surface, left and right flanges (for example, a left flange 6 and a right flange 7 to be described below) extending from lower ends of the left and right vertical walls, respectively, and left and right bent portions (for example, a left bent portion 8 and a right bent portion 9 to be described below) interposed respectively between the left vertical wall and the left flange and between the right vertical wall and the right flange, the press-forming method including: a first step (for example, a processing step corresponding to a phase P1 to be described below) of obtaining, from the blank, a preformed article in a first form (for example, a preformed article 30 in a first form to be described below) including the top surface, the left and right vertical walls, and left and right tapered portions (for example, a left tapered portion 31 and a right tapered portion 32 to be described below) extending outward from the lower ends of the left and right vertical walls, respectively; a second step (for example, a processing step corresponding to a phase P2 to be described below) of forming the left and right bent portions by, in a state where the top surface of the preformed article in the first form is held by an upper die (for example, a second upper die 14 to be described below) and a punch (for example, a floating punch 16 to be described below) of a lower die (for example, a second lower die 15 to be described below), pushing the left and right tapered portions into recesses for curling forming (for example, a left recess 17 and a right recess 18 to be described below) provided in the lower die, and forming the left and right flanges by lowering of the upper die to obtain a preformed article in a second form (for example, a preformed article 40 in a second form to be described below); and a third step (for example, a processing step corresponding to a phase P3 and a phase P4 to be described below) of obtaining the final formed article having the hat-shaped cross section by reforming the left and right bent portions and the left and right flanges of the preformed article in the second form.

In the press-forming method according to (1) described above, the preformed article in the first form is obtained from the blank in the first step, the preformed article including the top surface, the left and right vertical walls, and the left and right tapered portions extending respectively outward from the lower ends of the left and right vertical walls in the final formed article having the hat-shaped cross section. In the second step, the left and right tapered portions are pushed into the recesses for curling forming provided in the lower die in the state where the top surface of the preformed article in the first form is held by the upper die and the punch of the lower die, thereby forming the left and right bent portions, and the left and right flanges are formed by the lowering of the upper die to obtain the preformed article in the second form. In the third step, the left and right bent portions and the left and right flanges of the preformed article in the second form are reformed to obtain the final formed article having the hat-shaped cross section. In the course of obtaining the preformed article in the second form in the second step, the compression can be applied to the entirety of the top surface, the left and right vertical walls, and the left and right flanges of the final formed article having the hat-shaped cross section, whereby the spring-back can be sufficiently prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing steps of obtaining a final formed article from a blank by a press forming method as an embodiment of the present invention;

FIG. 2 is a view showing a first step in the press forming method shown in FIGS. 1; and

FIG. 3 is a view showing a second step in the press-forming method shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing steps of obtaining a final formed article from a blank by a press-forming method as an embodiment of the present invention. In FIG. 1, an upper stage shows a final formed article 1 in a transverse manner, and a lower stage shows a progress of a process phase from left to right in a transverse manner along with a cross-sectional view of the final formed article 1. A phase is denoted as PO in which a supplied blank 2 is unprocessed.

A phase is indicated by P1 in which a preformed article 30 in a first form is obtained by a first step. A phase is indicated by P2 in which a preformed article 40 in a second form is obtained by a second step. Phases are indicated by P3 and P4 in which the final formed article 1 is obtained by a third step.

The final formed article 1 has a hat-shaped cross section. A site of the final formed article 1 having the hat-shaped cross section includes a top surface 3 and a left vertical wall 4 and a right vertical wall 5 continuing to left and right ends of the top surface 3. Furthermore, the site of the final formed article 1 having the hat-shaped cross section includes a left flange 6 and a right flange 7 extending from a lower end of the left vertical wall 4 and a lower end of the right vertical wall 5, respectively. In addition, the site of the final formed article 1 having the hat-shaped cross section includes a left bent portion 8 interposed between the left vertical wall 4 and the left flange 6 and a right bent portion 9 interposed between the right vertical wall 5 and the right flange 7.

FIG. 2 is a view showing the first step. The first step is a processing step of the phase P1 in FIG. 1. In the first step, from the blank 2, the preformed article 30 in the first form is obtained which includes a top surface 33 in a first form, a left vertical wall 34 in a first form, a right vertical wall 35 in a first form, and a left tapered portion 31 and a right tapered portion 32 in a first form extending respectively outward (downward in FIG. 2) from lower ends of the left vertical wall 34 in the first form and the right vertical wall 35 in the first form.

The first step includes processing steps of a phase P11, a phase P12, and a phase P13. Hereinafter, the processing steps of the phase P11, the phase P12, and the phase P13 are simply referred to as a phase P11, a phase P12, and a phase P13. The preformed article 30 in the first form is shown in the phase P13.

In the phase P11, an edge of the blank 2 is clamped and fixed in a state of being pressed against a first upper die 11 by a blank holder 10. In this state, a projection 12a on an upper side of a first lower punch 12 contacts a lower surface of the blank 2, but a movable pad 13 on a side of the first upper die 11 does not contact an upper surface of the blank 2.

Next, in the phase P12, the first upper die 11 is lowered together with the movable pad 13 in a state where the blank 2 is held by the blank holder 10. At this time, the movable pad 13 is brought into contact with and pressed from above against a site of the blank 2 supported by an upper end surface of the first lower punch 12 including the projection 12a.

Next, in the phase P13, the first upper die 11 is lowered in the state where the contact site on the blank 2 side is held with the movable pad 13 brought into contact with and pressed from above. The preformed article 30 in the first form is obtained in such a processing step of phase P13. In the phase P13, the top surface 33 in the first form corresponding to the top surface 3 of the final formed article 1 is formed. Further, when ends of the blank 2 are pressed by the first upper die 11 and a left inclined portion 12b and a right inclined portion 12c having inclined surfaces which are outwardly inclined below the first lower punch 12, respectively, the left tapered portion 31 and the right tapered portion 32 are formed.

FIG. 3 is a view showing the second step. The second step is the processing step of the phase P2 in FIG. 1. In the second step, in a state where the top surface 33 in the first form of the preformed article 30 in the first form is held by an upper die and a punch of a lower die, the left tapered portion 31 and the right tapered portion 32 are pushed into recesses for curling forming provided in a lower die to form left and right bent portions, and left and right flanges are formed by lowering of the upper die, whereby a preformed article 40 in a second form is obtained.

Next, a more specific description will be given. The second step includes processing steps of a phase P21, a phase P22, and a phase P23. Hereinafter, the processing steps of the phase P21, the phase P22, and the phase P23 are simply referred to as a phase P21, a phase P22, and a phase P23, respectively. The preformed article 40 in the second form is shown in the phase P23.

In the phase P21, the top surface 33 in the first form of the preformed article 30 in the first form is held by a second upper die 14 as an upper die and a floating punch 16 of a second lower die 15 as a lower die. In other words, the top surface 33 in the first form is pressed against the second upper die 14 by the floating punch 16 and is adjusted in posture. At this time, the left tapered portion 31 of the preformed article 30 in the first form hangs down from a lower end of the second upper die 14 toward a left recess 17 for curling forming of the second lower die 15. Similarly, the right tapered portion 32 of the preformed article 30 in the first form hangs down from the lower end of the second upper die 14 toward a right recess 18 for curling forming of the second lower die 15.

Next, in the phase P22, the second upper die 14 is lowered, and the left tapered portion 31 of the preformed article 30 in the first form is pushed into the left recess 17 of the second lower die 15 from a hanging end thereof. Similarly, the right tapered portion 32 of the preformed article 30 in the first form is pushed into the right recess 18 of the second lower die 15 from a hanging end thereof. At this time, the left tapered portion 31 and the right tapered portion 32 are formed so as to extend outward, and move along R-shaped surfaces of the left recess 17 and the right recess 18 to be curled.

Next, in the phase P23, the second upper die 14 is lowered to a bottom dead center. In the course of the lowering, the left tapered portion 31 is pinched between the second upper die 14 and the second lower die 15, and is formed into a left vertical wall 44 in a second form, a left bent portion 48 in a second form, and a left flange 46 in a second form of the preformed article 40 in the second form. At the same time, the right tapered portion 32 is pinched between the second upper die 14 and the second lower die 15, and is formed into a right vertical wall 45 in a second form, a right bent portion 49 in a second form, and a right flange 47 in a second form of the preformed article 40 in the second form.

In the course of transition from the phase P22 to the phase P23, the left vertical wall 34 of the preformed article 30 in the first form is pushed into the left recess 17 of the second lower die 15 and is curled. At the same time, the right vertical wall 35 of the preformed article 30 in the first form is pushed into the right recess 18 of the second lower die 15 and is curled.

Therefore, a sufficient compressive force can be applied to a part in a wide range from the left vertical wall 44 in the second form to the left bent portion 48 in the second form and the left flange 46 in the second form. At the same time, a sufficient compressive force can be applied to an entire wide range from the right vertical wall 45 in the second form to the right bent portion 49 in the second form and the right flange 47 in the second form. Therefore, spring-back of the final formed article 1 is prevented.

As described above, in the processing step up to the phase P2 through the phase P1 in FIG. 1, a pressing force f1 is applied to the formed article having a shape and dimensions close to those of the final formed article 1 in the phase P3 such that the final shape and dimensions of the top surface 43 as the wavy surface are obtained, and thus the formed article is deformed. Further, in the phase P4, pressing forces f2 and f3 are applied to the left vertical wall 44 and the right vertical wall 45 to strictly adjust a separation dimension between the left vertical wall 44 and the right vertical wall 45, and further, the left flange 46 and the right flange 47 are reformed by trimming or the like, whereby the final formed article 1 having the hat-shaped cross section is obtained. The phase P3 and the phase P4 correspond to the third step of reforming the left bent portion 48, the right bent portion 49, the left flange 46, and the right flange 47 of the preformed article 40 in the second form and obtaining the final formed article 1 having the hat-shaped cross section. After the third step, the final formed article 1 is delivered.

According to the press-forming method of the present embodiment, the following effect is obtained.

In the press-forming method according to (1) described above, the preformed article 30 in the first form is obtained from the blank 2 in the processing step of the phase P1 which is the first step, the preformed article including the top surface 3, the left vertical wall 4, the right vertical wall 5, and the left tapered portion 31 and the right tapered portion 32 extending respectively outward from the lower ends of the left vertical wall 4 and the right vertical wall 5 in the final formed article 1 having the hat-shaped cross section. In the processing step of the phase P2 which is the second step, the left tapered portion 31 and the right tapered portion 32 are pushed into the left recess 17 and the right recess 18 for curling forming provided in the second lower die 15 in the state where the top surface 33 of the preformed article 30 in the first form is held by the second upper die 14 and the floating punch 16 of the second lower die 15, thereby forming the left bent portion 48 and the right bent portion 49, and the left and right flanges are formed by the lowering of the second upper die 14 to obtain the preformed article 40 in the second form. In the processing steps of the phase P3 and the phase P4 which are the third step, the left bent portion 48, the right bent portion 49, the left flange 46, and the right flange 47 of the preformed article 40 in the second form are reformed to obtain the final formed article 1 having the hat-shaped cross section. From the phase P22 to the phase P23, which are steps of obtaining the preformed article of the preformed article 40 in the second form in the processing step of the phase P2 which is the second step, the compression can be applied to the entirety of the top surface 3, the left vertical wall 4, the right vertical wall 5, the left flange 6, and the right flange 7 of the final formed article 1 having the hat-shaped cross section, whereby the spring-back can be sufficiently prevented.

Although the embodiment of the present invention has been described above, the present invention is not limited thereto. Detailed configurations may be changed as appropriate within the scope of the present invention. For example, the top surface 3 is a wavy surface with the projection only on the left vertical wall 4 in the above-described example, but may be a wavy surface with a projection on the right vertical wall 5.

EXPLANATION OF REFERENCE NUMERALS

1 . . . final formed article

2 . . . blank

30 . . . preformed article in first form

40 . . . preformed article in second form

3 . . . top surface

4 . . . left vertical wall

5 . . . right vertical wall

6 . . . left flange

7 . . . right flange

8 . . . left bent portion

9 . . . right bent portion

10 . . . blank holder

11 . . . first upper die

12 . . . first lower punch

12a . . . projection

12b . . . left inclined portion

12c . . . right inclined portion

13 . . . movable pad

14 . . . second upper die

15 . . . second lower die

16 . . . floating punch

17 . . . left recess

18 . . . right recess

30 . . . preformed article in first form

31 . . . left tapered portion

32 . . . right tapered portion

40 . . . preformed article in second form

Claims

1. A method of press-forming, from a blank, a final formed article having a hat-shaped cross section and including a top surface, left and right vertical walls continuing to left and right ends of the top surface, left and right flanges extending from lower ends of the left and right vertical walls, respectively, and left and right bent portions interposed respectively between the left vertical wall and the left flange and between the right vertical wall and the right flange, the press-forming method comprising:

a first step of obtaining, from the blank, a preformed article in a first form including the top surface, the left and right vertical walls, and left and right tapered portions extending outward from the lower ends of the left and right vertical walls, respectively;

a second step of forming the left and right bent portions by, in a state where the top surface of the preformed article in the first form is held by an upper die and a punch of a lower die, pushing the left and right tapered portions into recesses for curling forming provided in the lower die and forming the left and right flanges by lowering of the upper die to obtain a preformed article in a second form; and

a third step of obtaining the final formed article having the hat-shaped cross section by reforming the left and right bent portions and the left and right flanges of the preformed article in the second form.