JP7103331B2 - Press molding method - Google Patents

Description

The present invention relates to a press forming method, and more particularly to a press forming method of a press-formed product having a hat-shaped cross section that curves along the longitudinal direction in a plan view.

Generally, as a measure against wrinkles that occur in the press forming process of a press-molded product, in order to suppress the inflow of materials in the press forming process, for example, in draw forming, the cushion pressure for holding the blank between the die and the blank holder is increased for forming. And, as disclosed in Non-Patent Document 1, a technique of providing a shape such as a bead at a portion where the plate thickness of the blank increases with the inflow of materials is applied.

Thin Steel Sheet Molding Technology Study Group, Press Molding Difficulty Handbook 4th Edition, "Chapter 5 Poor Surface Shape Accuracy and Molding Difficulty Evaluation", pp.244-247, Nikkan Kogyo Shimbun, Ltd., (2017)

As shown in FIG. 4A, the top plate portion 43, the vertical wall portion 45 and the vertical wall portion 47 continuous from the top plate portion 43, and the flange portion continuous from each of the vertical wall portion 45 and the vertical wall portion 47. The press-formed product 41, which has a cross-sectional hat shape including 49 and a flange portion 51 and is curved along the longitudinal direction in a plan view, is the center of the flange portion 49 inside the curvature in the press forming process. There is a problem that the material flows in toward the surface and wrinkles are likely to occur at the tip in the width direction.

In order to suppress the occurrence of wrinkles in the press-molded product 41, as described above, the die and the blank holder are drawn by increasing the cushion pressure for sandwiching the portion corresponding to the flange portion of the blank, thereby curving. There is an effect that the inflow of material in the inner flange portion 49 can be suppressed and the occurrence of wrinkles can be suppressed. However, on the other hand, there is a problem that the punch shoulder R portion 44 on the curved inner side of the press-molded product 41 is cracked. Therefore, it has been desired to press-mold a press-molded product while suppressing wrinkles by bending molding instead of draw molding.

Further, as disclosed in Non-Patent Document 1, the technique of forming a bead as a wrinkle-removing shape in a portion where wrinkles are likely to occur in the press-molding process involves changing the product shape of the press-molded product. Therefore, it may not be possible to apply it as a countermeasure against wrinkles.

The present invention has been made in order to solve the above-mentioned problems, and is obtained by bending molding while preventing cracks and suppressing wrinkles without requiring a change in the product shape in the longitudinal direction in a plan view. It is an object of the present invention to propose a press molding method for press molding a press-molded product having a cross-section hat shape curved along the above.

(1) The press molding method according to the present invention is
It has a cross-sectional hat shape having a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion, and is press-molded to be curved along the longitudinal direction in a plan view. The product is press-molded in two steps by bending and molding.
The first molding step of bending and molding the blank into an intermediate molded product having a hat shape in cross section and curving along the longitudinal direction in a plan view.
The second molding is performed by bending the intermediate molded product into the press-molded product in which the radius of curvature of the curvature along the longitudinal direction at the bottom dead point of molding is smaller than the radius of curvature of the curvature after springback of the intermediate molded product. With the process,
In the second molding step, the restrained shape portion having a shape that restrains the inflow of the material from both ends in the longitudinal direction to the center in the curved inner flange portion of the intermediate molded product is formed on the curved inner flange portion of the press molded product. It is characterized in that it is formed at both ends in the longitudinal direction.

(2) The press molding method according to the present invention is
It has a cross-sectional hat shape having a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion, and is press-molded to be curved along the longitudinal direction in a plan view. The product is press-molded in two steps by bending and molding.
The first molding step of bending and molding the blank into an intermediate molded product having a hat shape in cross section and curving along the longitudinal direction in a plan view.
The second molding is performed by bending the intermediate molded product into the press-molded product in which the radius of curvature of the curvature along the longitudinal direction at the bottom dead point of molding is smaller than the radius of curvature of the curvature after springback of the intermediate molded product. With the process,
In the second molding step, the restrained shape portion having a shape that restrains the inflow of the material from both ends in the longitudinal direction to the center in the flange portion on the curved inner side of the intermediate molded product is formed on the top plate portion and the curved inner side of the press molded product. It is characterized in that it is formed at both ends in the longitudinal direction of each of the flange portions of the above.

(3) In the above-mentioned (1) or (2),
The restraint-shaped portion formed in the second molding step is characterized in that it is a stepped portion recessed in a stepped shape in the press molding direction.

(4) In the above (1) or (2),
The restraint-shaped portion formed in the second molding step is characterized by being a convex or concave bead portion extending in a direction of a predetermined angle from the curvature of the press-molded product.

According to the present invention, when bending and molding a press-formed product having a cross-sectional hat shape and curving along the longitudinal direction in a plan view, a blank is bent along a longitudinal direction in a plan view and having a cross-section hat shape. The first molding step of bending and molding the intermediate molded product, and the radius of curvature of the curvature of the intermediate molded product along the longitudinal direction at the bottom dead point of molding are larger than the radius of curvature of the curvature of the intermediate molded product after springback. The second molding step includes a second molding step of bending and molding into the small press-molded product, and the second molding step restrains the inflow of material from both ends in the longitudinal direction to the center at the flange portion on the curved inner side of the intermediate molded product. By forming the restraint-shaped portions having a shape to be formed at both ends in the longitudinal direction of the flange portions on the curved inner side of the press-formed product, a force for pushing the flange portions on the curved inner side to the outer side of the curved product acts, and the above-mentioned By applying tension toward both ends in the longitudinal direction while restraining the inflow of material toward the center of the flange portion on the inner side of the curve, the compressive stress on the flange portion on the inner side of the curve is relaxed and the occurrence of wrinkles is suppressed. The press-molded product can be press-molded by bending.

It is a figure explaining the press molding method which concerns on embodiment of this invention ((a) perspective view of the press-molded article to be molded, (b) suppresses the wrinkle which occurs in the flange part on the curved inner side of the press-molded article. Explanatory drawing of the reason why it is possible, (c) (i) plan view of the intermediate molded product bent and molded in the first molding step, (c) (ii) the press molded product bent and molded in the second molding step. Plan view). It is a figure which shows (a) the first die used in the 1st molding step, (b) the 2nd die used in the 2nd molding step in the press molding method which concerns on embodiment of this invention. It is a figure which shows the concrete shape as an example of the die of the 2nd die used in the 2nd molding process in the press molding method which concerns on embodiment of this invention. It is a figure explaining the wrinkle which occurs in the press molding process of the press-molded product to be molded in this invention, and the means which suppresses the occurrence of the wrinkle ((a) wrinkle generation, (b) suppression of the wrinkle generation). It is a figure which shows the press-molded article which formed the bead portion as another example of the restraint shape portion in the press-molding method which concerns on embodiment of this invention ((a) plan view, (b) perspective view). It is a figure explaining another aspect of the press molding method which concerns on embodiment of this invention ((a) perspective view of a press-molded article, (b) BB sectional view of a press-molded article and a die and a punch, (1). c) (i) Plan view of the intermediate molded product bent and molded in the first molding step, (c) (ii) Plan view of the press molded product bent and molded in the second molding step). In the Example, it is a figure which shows the result of the plate thickness average stress distribution in the circumferential direction at the molding bottom dead center of the press-molded product which concerns on a comparative example ((a) the die used for molding, (b) the plate in the circumferential direction. Thickness average stress distribution). In the Example, it is a figure which shows the result of the plate thickness average stress distribution in the circumferential direction at the molding bottom dead center of the press-molded article which concerns on the invention example.

As shown as an example in FIG. 1A, the present invention includes a top plate portion 3, a vertical wall portion 5 and a vertical wall portion 7 continuous from the top plate portion 3, and a vertical wall portion 5 and a vertical wall portion 7. A press-molded product 1 having a cross-sectional hat shape having a flange portion 9 and a flange portion 11 continuous from each and curved along the longitudinal direction in a plan view is targeted for molding. In the press-formed product 1, the vertical wall portion 5 and the flange portion 9 are inside the curve, and the vertical wall portion 7 and the flange portion 11 are outside the curve.

The press molding method according to the embodiment of the present invention is to press-mold the press-molded product 1 illustrated in FIG. 1 (a) by bending molding, and the die 15 shown as an example in FIG. 2 (a). Using the first mold 13 provided with the punch 17, the blank 19 is bent and molded into an intermediate molded product 21 (FIG. 2B) which has a cross-sectional hat shape and is curved along the longitudinal direction in a plan view. The intermediate molded product 21 is bent and molded into the press-molded product 1 by using the first molding step to be performed and the second mold 33 including the die 35 and the punch 37 shown as an example in FIG. 2 (b). It is provided with two molding steps.

Hereinafter, each of the above steps will be described. In the following description, the radius of curvature of the curvature of the intermediate molded product 21 and the press molded product 1 is the top plate portion 3 and the top plate portion 23 that are curved along the longitudinal direction, as shown in FIG. 1 (c). The radius of curvature of the curve passing through the center in the width direction (the alternate long and short dash line in FIGS. 1 (c) (i) and (ii)) is used.

<First molding process>
In the first molding step, the blank 19 is formed by using the first mold 13 including the die 15 and the punch 17 shown in FIG. 2 (a), as shown in FIGS. 1 (c) and 1 (i). It has a top plate portion 23, a vertical wall portion 25 and a vertical wall portion 27 continuous from the top plate portion 23, and a flange portion 29 and a flange portion 31 continuous from each of the vertical wall portion 25 and the vertical wall portion 27. This is a step of bending and molding into an intermediate molded product 21 which has a cross-sectional hat shape and is curved along the longitudinal direction in a plan view.

Then, in the first molding step, the radius of curvature R ₁ of the curvature along the longitudinal direction after the intermediate molded product 21 is separated from the first mold 13 and springed back (FIGS. 1 (c) and 1 (i)). Is intermediately molded so as to be larger than the radius of curvature R ₂ (FIGS. 1 (c) and (ii)) of the curvature along the longitudinal direction of the press-molded product 1 that was bent and molded to the bottom dead point of molding in the second molding step. Product 21 is bent and molded.

The radius of curvature R ₁ of the curvature of the intermediate molded product 21 after springback is obtained in the first molding step by, for example, obtaining by CAE analysis (press molding analysis and springback analysis) by a press molding experiment, a finite element method, or the like. The radius of curvature of the curve at the bottom dead point of molding can be set as appropriate.

<Second molding process>
In the second molding step, the second mold 33 including the die 35 and the punch 37 shown in FIGS. 1 (b) and 2 (b) was used, and the second mold 33 was bent and molded in the first molding step and released. The radius of curvature R ₂ (FIGS. 1 (c) and (ii)) of the curvature of the intermediate molded product 21 along the longitudinal direction at the bottom dead point of molding is the curvature of the intermediate molded product 21 after springback after mold release. This is a step of bending and molding a press-molded product 1 having a radius of curvature R ₁ (FIGS. 1 (c) and (ii)) smaller than the radius of curvature R 1.

Further, in the second molding step, the stepped portion 9a of the intermediate molded product 1 is pressed as a restrained shape portion having a shape that restrains the inflow of the material from both ends in the longitudinal direction to the center in the flange portion 29 on the curved inner side of the intermediate molded product 21. It is formed at both ends in the longitudinal direction of the flange portion 9 on the inner side of the curve.

Note that FIG. 1B is a cross-sectional shape of AA along the central line (dashed line) of the flange portion 9 on the curved inner side shown in FIG. 1A.
Further, as shown in FIGS. 1B and 2B, the die 35 and the punch 37 include a flange forming portion 35a and a flange forming portion 37a for forming the flange portion 9 on the curved inner side of the press-molded product 1. It has a step forming portion 35b and a step forming portion 37b provided at both ends in the longitudinal direction of each of the flange forming portion 35a and the flange forming portion 37a and forming a step portion 9a at both ends in the longitudinal direction of the flange portion 9 on the curved inner side. It is a thing. In the present embodiment, the step portion 9a formed by the step forming portion 35b and the step forming portion 37b is assumed to be recessed in a step shape in the press forming direction.
FIG. 3 shows an example of a specific shape of the die 35.

Hereinafter, the reason why the press-molded product 1 can be press-molded by bending while suppressing the occurrence of wrinkles in the flange portion 9 on the curved inner side by the press-molding method according to the embodiment of the present invention will be described.

As shown in FIG. 4A, when a press-molded product 41 having a hat-shaped cross section curved along the longitudinal direction in a plan view is press-molded in one step by conventional bending molding, the flange portion 49 inside the curvature is formed. Since the material flows from both ends in the longitudinal direction toward the center at the portion corresponding to the tip in the width direction, compressive deformation occurs at the center in the longitudinal direction of the flange portion 49 and wrinkles occur.

On the other hand, in the press molding method according to the present embodiment, as described above (FIG. 1 (c)), when the press molded product 1 is bent and molded in the two steps of the first molding step and the second molding step. , The radius of curvature R1 of the curvature of the intermediate molded product 21 bent and molded in the first molding step after springback is the radius of curvature _R1 of the curvature of the press-molded product 1 bent and molded in the second molding step at the bottom dead point of molding. By bending and molding the intermediate molded product 21 in the first molding step so as to be larger than ₂ , the intermediate molded product 21 tries to return to the radius of curvature R ₁ during bending molding in the second molding step, and the inside of the curve is curved. A force acts to push the flange portion 9 out of the curve.

Further, when the flange portion 9 on the curved inner side of the press-molded product 1 is molded in the second molding step, the inflow of the material from both ends in the longitudinal direction to the center is restrained at the flange portion 29 on the curved inner side of the intermediate molded product 21. As the restraint shape portion having a shape, the step portion 9a is formed at both ends in the longitudinal direction of the flange portion 9 by the step forming portion 35b of the die 35 and the step forming portion 37b of the punch 37 (FIG. 2B).

In this way, by exerting a force that pushes the flange portion 9 on the inner side of the curve to the outside of the curve and forming step portions 9a at both ends in the longitudinal direction, the flange portion 9 on the inner side of the curve is centered in the longitudinal direction. Tension is applied toward both ends in the longitudinal direction while restraining the inflow of the material toward it. As a result, the compressive stress in the flange portion 9 on the inner side of the curve is relaxed, the occurrence of wrinkles is suppressed, and the press-formed product 1 can be press-formed by bending.

In particular, the intermediate molded product 21 that is bent and molded in the first molding step has a cross-sectional hat shape that is curved along the longitudinal direction in a plan view, and has a shape similar to that of the press molded product 1. Therefore, in the process of bending and molding the intermediate molded product 21 into the press-molded product 1 in the second molding step, the material inflow toward the center in the longitudinal direction is easily restrained by the stepped portion 9a formed on the flange portion 9 on the inner side of the curvature. , The effect of preventing the occurrence of wrinkles is enhanced.

It should be noted that the radius of curvature _R1 of the curvature after the intermediate molded product 21 bent and molded in the first molding step springs back and the curvature at the bottom dead point of the press molded product 1 bent and molded in the second molding step. The larger the difference from the radius of curvature R ₂ , the greater the force that pushes the flange portion 9 inside the curvature to the outside of the curvature in the second molding step, and the greater the effect of relaxing the compressive stress.

However, if the radius of curvature _R1 of the curvature of the intermediate molded product 21 after springback is too large, the intermediate molded product 21 does not fit into the second mold 33 in the second molding step, and it is difficult to perform bending molding. May be.

Therefore, the radius of curvature of the curve at the bottom dead point of the intermediate molded product 21 in the first molding step is about the same as the radius of curvature R ₂ of the curve at the bottom dead point of the press molded product 1 in the second molding step. Alternatively, it is desirable to make it smaller so that the radius of curvature R ₁ of the curvature of the intermediate molded product 21 after springback becomes larger than the radius of curvature R ₂ of the curvature at the bottom dead point of molding of the press molded product 1. ..

Further, as shown in FIG. 1A, the position where the step portion 9a is formed in the second molding step may be outside from both ends in the longitudinal direction of the press-molded product 1a having a product shape. Then, with respect to the press-molded product 1 in which the step portion 9a is formed, the portion 1b on the end portion side in the longitudinal direction including the step portion 9a is cut along the dotted line shown in FIG. 1 (a), and the remaining central side in the longitudinal direction is cut. By collecting the sample, it is possible to easily obtain a press-molded product 1a having a product shape in which wrinkles are suppressed in the flange portion 9 on the curved inner side.

Further, regarding the specific shape such as the step depth in the press molding direction of the step portion 9a, in the second molding step, the inflow of the material at both ends of the curved inner flange portion 29 of the intermediate molded product 21 in the longitudinal direction is restrained. At the same time, tension may be applied to both ends in the longitudinal direction, and the tension may be appropriately set so as to be able to effectively suppress the occurrence of wrinkles in the flange portion 9 in the second molding step.

The above description is for a case where a step portion 9a as shown in FIG. 1B is formed as a restraint shape portion formed on both ends in the longitudinal direction of the flange portion 9 on the curved inner side of the press-formed product 1. Met.

However, the press molding method according to the present invention does not limit the specific shape of the restraint shape portion to the step portion 9a, and the flange portion 29 on the curved inner side of the intermediate molded product 21 is centered from both ends in the longitudinal direction. Any shape may be used as long as it can restrain the inflow of the material toward the surface and apply tension toward both ends in the longitudinal direction.

For example, in the present invention, as shown in FIG. 5, the top plate portion 63, the vertical wall portion 65 and the vertical wall portion 67 continuous from the top plate portion 63, and the vertical wall portion 65 and the vertical wall portion 67 are continuous. It has a cross-sectional hat shape having a flange portion 69 and a flange portion 71, and is curved along the longitudinal direction in a plan view. Like a press-molded product 61, both ends of the curved inner flange portion 69 in the longitudinal direction. In addition, a bead portion 69a extending in a direction orthogonal to the curvature may be formed by a die and a punch (not shown). Further, the bead portion 69a shown in FIG. 5 may have a predetermined angle (an angle formed with the tangential direction of the curve) as long as it is not in the tangential direction of the curve, and the predetermined angle is more preferably 45 ° to 90 °. Further, although it is formed in a concave shape in the press molding direction, it may be formed in a convex shape in the press molding direction as the restraint shape portion.

In the above-mentioned press molding method according to the present embodiment, the stepped portion 9a is formed only at both ends in the longitudinal direction of the curved inner flange portion 9 as the restraint shape portion, but the press molding according to the present embodiment. As another aspect of the method, the first molding step of bending and molding the blank 19 into the intermediate molded product 21 as described above (FIG. 2A), and the die 95 and the punch 97 as shown in FIG. 6 are used. Using the provided second mold 93, the radius of curvature R ₂ (FIGS. 6 (c) and (ii)) of the curvature along the longitudinal direction at the bottom dead point of molding is the curvature of the intermediate molded product 21 after springback. It may be bent and molded by the second molding step of bending and molding into a press-molded product 81 smaller than the radius of curvature R ₁ (FIGS. 6 (c) and (i)) of.

FIG. 6 shows that in the second molding step, stepped portions 89a are formed as restraint-shaped portions at both ends in the longitudinal direction of the flange portion 89 inside the curvature, and stepped portions 83a are formed as restraint-shaped portions at both ends in the longitudinal direction of the top plate portion 83. Is illustrated by exemplifying the case where the die 95 and the punch 97 are formed. FIG. 6B has a cross-sectional shape along the central line (dashed line) of the top plate portion 83 of FIG. 6A, and the top plate forming portion 95a of the die 95 and the top plate forming portion 97a of the punch 97. As a result, the central side of the top plate portion 83 in the longitudinal direction is formed, and the step forming portions 95b of the die 95 and the step forming portions 97b of the punch 97 form the step portions 83a at both ends of the top plate portion 83 in the longitudinal direction. Shown.

As described above, also in another aspect of the present embodiment, the radius of curvature R ₁ of the curvature of the intermediate molded product 21 after springback is calculated from the radius of curvature R ₂ of the curvature at the bottom dead point of the press molded product 81. By increasing the value, a force acts to return to the radius of curvature R ₁ of the intermediate molded product 21 during bending molding in the second molding step, and to push the flange portion 89 inside the curvature to the outside of the curvature.

Further, by forming the stepped portion 89a and the stepped portion 83a in the second molding step, the inflow of the material from the longitudinal end portion of the flange portion 29 on the curved inner side of the intermediate molded product 21 toward the center is restrained and the molding is performed. Just before the dead center, tension is applied toward both ends in the longitudinal direction, and the compressive stress is relaxed.

As a result, the press-molded product 81 can be press-molded by suppressing the occurrence of wrinkles in the flange portion 89 inside the curve.

Even when the intermediate molded product 21 is bent and molded into the press molded product 81, the radius of curvature of the curvature at the bottom dead point of the intermediate molded product 21 in the first molding step is set as in the above-described embodiment. The radius of curvature _R1 of the curvature of the intermediate molded product 21 after springback is equal to or smaller than the radius of curvature of the curvature of the press-molded product 81 at the bottom dead point of molding in the second molding step. It is desirable that the radius of curvature of the curve at the bottom dead point of molding is larger than R ₂ .

Further, as shown in FIG. 6A, the positions where the stepped portion 89a and the stepped portion 83a are formed in the second molding step may be outside from both ends in the longitudinal direction of the press-molded product 8a having a product shape. Then, the portions 81b on both ends in the longitudinal direction of the press-molded product 81 are cut off along the dotted line shown in FIG. A press-molded product 81a having a product shape in which wrinkles are suppressed can be easily obtained.

The restraint-shaped portions formed on both ends of the top plate portion 83 and the flange portion 89 in the longitudinal direction extend in a direction orthogonal to the curvature of the press-molded product, as in the above-described press molding method according to the present embodiment. The bead portion may be convex or concave in the press forming direction. Further, the bead portion may have a predetermined angle (an angle formed with the tangential direction of the curve) if the bead portion is not in the tangential direction of the curve of the press-molded product, and the predetermined angle is more preferably 45 ° to 90 °.

The press forming method according to the present invention is a case where a steel plate having a material strength of 440 MPa class to 1470 MPa class is used as a blank and a press-formed product having a cross-section hat shape curved along the longitudinal direction in a plan view is press-formed by bending. It can be preferably applied.

Further, the press-molded product targeted for molding in the above description has a cross-sectional hat shape that curves in a plan view over the entire length in the longitudinal direction, but the present invention has a portion that curves in the longitudinal direction in a plan view. A press-molded product having a cross-section hat shape having a portion extending linearly from both ends or one end in the longitudinal direction of the curved portion may be targeted for molding.

Even when a press-molded product having such a linearly extending portion is bent-molded by the press-molding method according to the present invention, the intermediate molded product is bent-molded in the first molding step, followed by the second molding. In the process, the restraint shape portion may be formed in the flange portion and / or the top plate portion in the portion extending linearly and outside the product shape.

CAE analysis was performed to confirm the action and effect of the press molding method according to the present invention. The results will be described below.

In the example, a press-molded product 1 having a hat-shaped cross section curved in the longitudinal direction in the plan view shown in FIG. 1A was targeted for molding, and CAE analysis was performed in the process of press-molding the press-molded product 1. In the CAE analysis, the blank used for press forming was a steel plate having a thickness of 1.0 mm and a tensile strength of 980 MPa.

The dimensions of the target shape of the press-molded product 1 are as follows: at the bottom dead point of molding, the radius of curvature R ₂ of the curvature along the center in the width direction of the top plate portion 3 is 270 mm, the width of the top plate portion 3 is 30 mm, and the molding height ( The height of the vertical wall portion 5 and the vertical wall portion 7 in the press forming direction) was set to 40 mm, and the flange widths of the flange portion 9 and the flange portion 11 were set to 40 mm.

In the examples, the press-molded product 1 was press-molded by the press-molding method according to the present invention as an example of the invention.
In the example of the invention, first, as a first molding step, as shown in FIG. 2A, the intermediate molded product 21 is bent by using a first mold 13 including a die 15 and a punch 17 for the blank 19. Molded.
Subsequently, as the second molding step, the intermediate molded product 21 is bent and molded into the press molded product 1 using the second mold 33 provided with the die 35 and the punch 37 as shown in FIG. 2 (b). , Step portions 9a recessed in the press forming direction were formed at both ends of the flange portion 9 on the curved inner side in the longitudinal direction.

In the example of the invention, the radius of curvature of the curvature at the bottom dead center of molding of the intermediate molded product 21 which is bent and molded by the die 15 and the punch 17 in the first molding step is set to 265 mm. At this time, the radius of curvature R ₁ of the curvature of the intermediate molded product 21 became about 290 mm due to the springback after the first molding step.

Then, in the subsequent second molding step, the radius of curvature R ₂ of the curvature at the bottom dead center of molding of the press-molded product 1 obtained by bending and molding the intermediate molded product 21 was set to 270 mm. Further, the step depth in the press forming direction of the step portion 9a formed at both ends of the flange portion 9 on the curved inner side in the longitudinal direction is set to 20 mm, and the step portion 9a makes both ends of the flange portion 29 on the curved inner side of the intermediate molded product 21. The part was bent in the press forming direction by about 20 mm.

In the CAE analysis according to the invention example, as the first molding step, a press molding analysis of a process of bending and molding the blank 19 into the intermediate molded product 21 was performed. Then, the springback analysis of the intermediate molded product 21 was performed to obtain the intermediate molded product 21 after the springback.

Next, as a second molding step, a press molding analysis was performed in a process of bending and molding the intermediate molded product 21 after springback obtained by springback analysis into the press molded product 1.

Further, in the example, as a comparison target, as shown in FIG. 7A, as a conventional press molding method, a mold 53 provided with a die 55 and a punch 57 is used, and the blank 59 is formed at the bottom dead point of molding. A CAE analysis of the process of bending and molding a press-molded product 41 (see FIG. 4) having a radius of curvature of R ₂ in one step was performed as a conventional example.

Regarding the average stress distribution of the plate thickness in the circumferential direction at the bottom dead center of molding, the case of the press-molded product 41 according to the conventional example is shown in FIG. 7B, and the case of the press-molded product 1 according to the invention example is shown in FIG. Here, the stresses shown in FIGS. 7 (b) and 8 have a positive value indicating a tensile stress and a negative value indicating a compressive stress.

From FIGS. 7 (b) and 8, it can be seen that the compressive stress is relaxed in the flange portion 9 on the inside of the curve according to the invention example, as compared with the flange portion 49 on the inside of the curve according to the conventional example.

As described above, according to the press forming method according to the present invention, when a press-formed product having a cross-section hat shape curved along the longitudinal direction in a plan view is press-formed by bending forming, the compressive stress at the flange portion inside the curvature is applied. It was suggested that it could alleviate and suppress the occurrence of wrinkles.

1 Press-molded product 1a Press-molded product (product shape)
1b part (longitudinal end)
3 Top plate part 5 Vertical wall part 7 Vertical wall part 9 Flange part (curved inside)
9a Stepped part 11 Flange part 13 First mold 15 Die 17 Punch 19 Blank 21 Intermediate molded product 23 Top plate part 25 Vertical wall part 27 Vertical wall part 29 Flange part (curved inside)
31 Flange part 33 Second mold 35 Die 35a Flange forming part 35b Step forming part 37 Punch 37a Flange forming part 37b Step forming part 41 Press molded product 43 Top plate part 44 Punch shoulder R part 45 Vertical wall part 47 Vertical wall part 49 Flange (inside curved)
51 Flange part 53 Mold 55 Die 57 Punch 59 Blank 61 Press-molded product 63 Top plate part 65 Vertical wall part 67 Vertical wall part 69 Flange part (curved inside)
69a bead part (restraint shape part)
71 Flange 81 Press-molded product 81a Press-molded product (product shape)
81b part (longitudinal end)
83 Top plate part 83a Step part (restraint shape part)
85 Vertical wall part 87 Vertical wall part 89 Flange part (curved inside)
91 Flange part 93 Second mold 95 Die 95a Top plate molding part (center part in the longitudinal direction)
95b Step forming part 97 Punch 97a Top plate forming part (center part in the longitudinal direction)
97b Step forming part

Claims (4)

It has a cross-sectional hat shape having a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion, and is press-molded to be curved along the longitudinal direction in a plan view. This is a press molding method in which a product is press molded in two steps by bending molding.
The first molding step of bending and molding the blank into an intermediate molded product having a hat shape in cross section and curving along the longitudinal direction in a plan view.
The second molding is performed by bending the intermediate molded product into the press-molded product in which the radius of curvature of the curvature along the longitudinal direction at the bottom dead point of molding is smaller than the radius of curvature of the curvature after springback of the intermediate molded product. With the process,
In the second molding step, the restrained shape portion having a shape that restrains the inflow of the material from both ends in the longitudinal direction to the center in the curved inner flange portion of the intermediate molded product is formed on the curved inner flange portion of the press molded product. A press molding method characterized in that it is formed at both ends in the longitudinal direction. It has a cross-sectional hat shape having a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion, and is press-molded to be curved along the longitudinal direction in a plan view. This is a press molding method in which a product is press molded in two steps by bending molding.
The first molding step of bending and molding the blank into an intermediate molded product having a hat shape in cross section and curving along the longitudinal direction in a plan view.
The second molding is performed by bending the intermediate molded product into the press-molded product in which the radius of curvature of the curvature along the longitudinal direction at the bottom dead point of molding is smaller than the radius of curvature of the curvature after springback of the intermediate molded product. With the process,
In the second molding step, the restrained shape portion having a shape that restrains the inflow of the material from both ends in the longitudinal direction to the center in the flange portion on the curved inner side of the intermediate molded product is formed on the top plate portion and the curved inner side of the press molded product. A press molding method characterized in that the flange portions of the flange portion are formed at both ends in the longitudinal direction. The press molding method according to claim 1 or 2, wherein the restraint shape portion formed in the second molding step is a step portion recessed in a step shape in the press molding direction. The press according to claim 1 or 2, wherein the restraint-shaped portion formed in the second molding step is a convex or concave bead portion extending in a direction of a predetermined angle from the curvature of the press-molded product. Molding method.

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