JP6870672B2 - Press molding method - Google Patents

Description

The present invention relates to a method for press molding a metal member.
Here, the metal member includes a hot-rolled steel sheet, a cold-rolled steel sheet, a surface-treated steel sheet obtained by subjecting the steel sheet to surface treatment (electrozinc plating, hot-dip galvanizing, organic film treatment, etc.), stainless steel, aluminum, magnesium, etc. , A plate composed of various metals may be used.

In recent years, high-strength thin steel sheets have been applied to automobile parts in order to reduce the weight of automobile bodies for the purpose of reducing _{CO 2 emissions.} In the manufacture of automobile parts, press molding, which is excellent in manufacturing cost, is often applied.
However, for example, when a hat-shaped cross-sectional part curved in the direction of the top plate is press-molded, the end portion of the material to be molded, which is the flange portion, shrinks during the molding process and wrinkles occur due to flange deformation. There is a problem that it is easy to use, and when a high-strength thin steel plate is used, it is difficult to crush the generated wrinkles, which is a particular problem.

As a technique for suppressing the occurrence of wrinkles due to such shrinkage flange deformation, Patent Document 1 states that when a part having a U-shaped or hat-shaped cross-sectional shape and curved in the longitudinal direction is formed, the flange of the part is formed. By simultaneously molding two parts so that they are symmetrical with respect to the part, the material is preferentially moved from the top plate side of the part to cause expansion flange deformation, and the contraction flange deformation of the flange part is caused. A technique for suppressing the occurrence of wrinkles is disclosed.

Further, in Patent Document 2, when a press-molded product having a hat-shaped cross section is formed by pressing a blank material using a wrinkle pressing die, the wrinkle pressing force for a region where shrinkage flange deformation occurs is increased at the end of press molding. The method of making it is disclosed.

Japanese Patent No. 5967386 Japanese Patent No. 57833339

The method disclosed in Patent Document 1 can be applied only to the case of press-molding a curved part in a horizontal plane orthogonal to the molding direction, and is convex in the direction of the top plate portion targeted by the present invention. There is a problem that it cannot be applied to press-molded products that are curved in the direction of.

Further, the method disclosed in Patent Document 2 can be applied only to draw forming using a blank holder, and in draw forming of a high-strength steel plate having low ductility, there is a risk that cracks will occur if the tension during forming is large. There is. Moreover, it cannot be applied to foam molding.

The present invention has been made to solve such a problem, and a high-strength steel plate can be applied as a material to be molded when forming a press-molded product that is convexly curved in the direction of the top plate in the longitudinal direction. It is an object of the present invention to provide a press molding method capable of reducing wrinkles caused by shrink molding of a flange portion by foam molding without using a blank holder.

(1) In the press molding method according to the present invention, a top plate portion having a convex shape in the direction of the top plate portion along the longitudinal direction, a pair of vertical wall portions continuing on both sides of the top plate portion, and the pair of vertical walls. It has a flange portion that is convex in the direction of the top plate along the longitudinal direction following the portion, and the radius of curvature of the longitudinal ridge that connects the top plate and the vertical wall is the longitudinal ridge that connects the vertical wall and the flange. This is a press molding method for a press-molded product having a cross-section hat shape larger than the radius of curvature of, which has a top plate portion, a vertical wall portion, and a flange portion, and is bent at both ends in the longitudinal direction of the top plate portion due to material surplus. A first molding step of forming an intermediate shape press-molded product having a shape of the above, and a second molding step of forming the intermediate shape press-molded product formed in the first molding step into a target shape. 1 The forming step is a punch and a die having a top plate forming portion, a vertical wall forming portion and a flange forming portion, and at the bottom dead point, at least both ends in the longitudinal direction between the punch and the top plate forming portion of the die. There is a gap of 2 mm or more over a range of 25% or more of the total length from each portion, and the vertical wall forming portion in the punch is more than the radius of curvature R1 of the longitudinal ridge line connecting the top plate forming portion and the vertical wall forming portion in the punch. It is characterized in that a first molding mold having a large radius of curvature R2 of a longitudinal ridge line connecting the flange molding portion and the flange molding portion is used.

(2) Further, in the one described in (1), the gap is 5 mm or less.

(3) Further, in the one according to (1) or (2), the radius of curvature R2 of the longitudinal ridge in the punch of the first molding die is four times or more the radius of curvature R1 of the longitudinal ridge. It is characterized by being.

In the press molding method according to the present invention, the first molding die is used to have a top plate portion, a vertical wall portion, and a flange portion, and bending caused by a material surplus is applied to both ends of the top plate portion in the longitudinal direction. By providing a first molding step of molding the intermediate shape press-molded product to have and a second molding step of molding the intermediate-shaped press-molded product molded in the first molding step into a target shape, the longitudinal direction is provided. When molding a press-molded product that curves convexly toward the top plate, a high-strength steel plate can be applied as the material to be molded, and the flange is shrunk by foam molding without using a blank holder. Wrinkles caused by molding can be reduced.

It is a figure explaining the press molding method which concerns on embodiment of this invention, (a) is a figure explaining the die used in the 1st molding process, (b) is a figure explaining the die used in the 2nd molding process. is there. It is a figure explaining the press-molded article molded by the press-molding method which concerns on embodiment of this invention, (a) is the explanatory view of the intermediate-shaped press-molded article molded by the 1st molding step, (b). Is an explanatory view of a press-molded product having a target shape formed by the second molding step. It is a figure which shows the shape of the 1st punch used in the 1st molding process which concerns on this invention. It is a figure explaining the cross-sectional shape of the mold and the press-molded article at the bottom dead point of the 1st molding process which concerns on Embodiment 1 of this invention, (A) is the cross-sectional view of AA, (B) is B- B sectional view. It is a figure which shows the shape of the 2nd punch used in the 2nd molding process which concerns on this invention. It is a figure explaining the cross-sectional shape of the mold and the press-molded article at the bottom dead point of the 2nd molding process which concerns on this invention, (A) is the cross-sectional view of AA, (B) is the cross-sectional view of BB. .. It is a figure explaining the cross-sectional shape of the mold and the press-molded article at the bottom dead point of the 1st molding process which concerns on Embodiment 2 of this invention, (A) is the cross-sectional view of AA, (B) is B- B sectional view. It is a figure which shows an example of the press-molded article which is the target shape in this invention. It is a figure explaining the problem in the conventional press molding method, (a) is a figure which shows the die used for the conventional press molding, and (b) is the figure which shows the press-molded article by the conventional press molding method.

The target shape of the present invention is a cross-sectional hat shape having a top plate portion having a convex shape in the top plate direction along the longitudinal direction and a flange portion having a convex shape in the top plate direction along the longitudinal direction by at least two steps. It is to be molded.
The principle is as shown below.

In the first molding step, by making the radius of curvature of the ridge line connecting the vertical wall portion and the flange portion larger than the radius of curvature of the ridge line connecting the top plate portion and the vertical wall portion, the vertical wall portion is formed from the central portion in the longitudinal direction. It will be started first, and a material flow will occur from the central portion in the longitudinal direction to both ends in the longitudinal direction.

In addition, since it has a convex shape in the direction of the top plate, as the molding of the vertical wall portion progresses, a material flow occurs toward the central portion in the longitudinal direction, but the radius of curvature of the ridge line connecting the vertical wall portion and the flange portion is increased. As a result, the height of the vertical walls at both ends in the longitudinal direction is lower than the target shape, so that the amount of deformation toward the central portion in the longitudinal direction is smaller than that of the target shape, and the shrinkage flange deformation is small.
By these actions, it is possible to suppress the occurrence of wrinkles due to the deformation of the shrinking flange that occurs in the vertical wall portion and the central portion in the longitudinal direction of the flange portion.

Further, at the bottom dead center, molding is performed so that a gap is formed between the punch and the top plate forming portion of the die, so that in the gap, both ends of the top plate portion in the longitudinal direction are bent due to the excess material. ..

After that, in the second molding step, the target shape is formed so that the radius of curvature of the ridge line connecting the vertical wall portion and the flange portion is smaller than the radius of curvature of the ridge line connecting the top plate portion and the vertical wall portion.
In the central portion of the material to be molded in the longitudinal direction, the shrinkage flange deformation is suppressed by the first molding step, and the radius of curvature of the ridge line connecting the top plate and the vertical wall is the same as in the first molding step, so further shrinkage occurs. Flange deformation is unlikely to occur.
At both ends of the material to be molded in the longitudinal direction, the excess material that is bent on the top plate easily flows from the vertical wall to the flange, so molding to the target shape can be achieved only by the material flow near both ends. Complete.

By suppressing the material flow from both ends in the longitudinal direction to the central portion by the method described above, it is possible to form the target shape while suppressing the wrinkles in the central portion in the longitudinal direction that have conventionally occurred.
Hereinafter, embodiments will be specifically described.

[Embodiment 1]
In the press molding method according to the embodiment of the present invention, a material to be molded made of a metal plate is form-molded into a press-molded product 6 having a hat-shaped cross section as shown in FIG.
Hereinafter, the press-molded product 6 to be molded in the present embodiment will be described, and then each step of the press-molding method according to the present embodiment will be described in detail.

<Press molded product>
The press-molded product 6 whose target shape is the target shape of the present embodiment is a top plate portion 1 having a convex shape in the top plate direction along the longitudinal direction and a vertical wall portion 3 following the top plate portion 1 as shown in FIG. And, it is formed into a cross-sectional hat shape having a flange portion 5 having a convex shape in the top plate direction along the longitudinal direction following the vertical wall portion 3.
Here, as shown in FIG. 8, the radius of curvature of the ridge line connecting the top plate portion 1 and the vertical wall portion 3 (hereinafter referred to as the top plate side ridge line 15) in the target shape is defined as the top plate side curvature radius r3, and the vertical wall. The radius of curvature of the ridge line connecting the portion 3 and the flange portion 5 (hereinafter referred to as the flange side ridge line 17) is defined as the flange side curvature radius r4.
The present invention is intended for a target shape in which the flange-side curvature radius r4 is smaller than the top plate-side curvature radius r3.
Hereinafter, the press-molded product formed by the press-molding method according to the present embodiment will also be described with reference to the same reference numerals for the same parts.

Conventionally, in the press-molded product 6 as described above, the metal plate is sandwiched by the relative movement of the die 37 and the punch 39 by using the mold 41 composed of the die 37 and the punch 39 as shown in FIG. 9A. It is molded by a molding method consisting of one step of bending molding.
In order to explain the shape of the mold 41 in an easy-to-understand manner, FIG. 9A is a surface that is the right half of the mold 41 and enables the material to be molded in the mold 41 to be molded (hereinafter, a molding surface portion). ) Is illustrated. The same applies to the subsequent illustrations relating to the mold.

In the press-molded product 43 formed by the conventional press-molding method, as shown in FIG. 9B, wrinkles 45 due to shrinkage flange deformation were generated in the vertical wall portion 3 and the flange portion 5 in the central portion in the longitudinal direction.
In particular, when the metal plate used is a high-strength steel plate with low ductility, it is difficult to crush the generated wrinkles 45 later, so a press forming method for reducing the occurrence of wrinkles 45 due to shrinkage flange deformation is required. Will be done.

Therefore, in the press molding method according to the embodiment of the present invention, the first molding die 7 as shown in FIG. 1 (a) is used, and the material to be molded is an intermediate shape press molded product 9 (FIG. 2 (a)). ) And the second molding die 11 as shown in FIG. 1 (b), the intermediate shape press-molded product 9 is made into the target shape press-molded product 13 (FIG. 2 (b)). By providing a second molding step for molding, the occurrence of wrinkles due to shrinkage flange deformation is reduced.
Each step will be specifically described below.

<First molding process>
In the first molding step, as shown in FIG. 1 (a), the material to be molded 23 is shown in FIG. 2 (a) by using the first molding die 7 having the first punch 19 and the first die 21. This is a step of forming into an intermediate shape press-molded product 9.

≪First molding mold≫
The first punch 19 and the first die 21 of the first molding die 7 have top plate forming portions 19a and 21a, vertical wall forming portions 19b and 21b, and flange forming portions 19c and 21c, respectively.

At the bottom dead center, the first punch 19 and the first die 21 have a gap of 2 mm or more over the entire length in the longitudinal direction between the top plate forming portion 19a of the first punch 19 and the top plate forming portion 21a of the first die 21. It is formed so that h can be formed.
At the bottom dead center in the first forming step, the material to be formed 23 is sandwiched between the flange forming portion 19c of the first punch 19 and the flange forming portion 21c of the first die 21.

FIG. 3 shows the shape of the molded surface portion of the first punch 19.
In the first punch 19, the radius of curvature of the ridge line connecting the top plate molding portion 19a and the vertical wall molding portion 19b (hereinafter referred to as the top plate side ridge line 25) is defined as the top plate side curvature radius R1, and the vertical wall molding portion 19b and the flange molding are performed. When the radius of curvature of the ridge line connecting the portions 19c (hereinafter referred to as the flange side ridge line 27) is the flange side curvature radius R2, the flange side curvature radius R2 is set to be larger than the top plate side curvature radius R1 (R1 < R2). In other words, in the first punch 19, the flange side ridge line 27 has a gentler bend than the top plate side ridge line 25.

Since the flange-side curvature radius R2 of the first punch 19 is larger than the top plate-side curvature radius R1, the line length in the direction orthogonal to the longitudinal direction of the first punch 19 (hereinafter, simply referred to as “longitudinal orthogonal direction”) is longitudinal. than the line length L _a in the direction central portion, towards the line length L _B in the vicinity of the longitudinal end portions are shorter (L _a> L _B).

Further, the top plate side curvature radius R1 of the first punch 19 is set to be substantially the same as the top plate side curvature radius r3 of the target shape, and further, the central portion in the longitudinal direction of the first punch 19 (the height of the vertical wall is high). The height of the vertical wall forming portion 19b in the highest portion) is set to be substantially the same as the height of the vertical wall portion 3 having the target shape.

The shape of the first die 21 is set as follows so that a gap h is formed over the entire length in the longitudinal direction between the first punch 19 and the top plate forming portion 19a of the first punch 19 in accordance with the shape of the first punch 19. ..
The top plate side ridge line and the flange side ridge line of the first die 21 have the same radius of curvature as the top plate side ridge line 25 and the flange side ridge line 27 of the corresponding first punch 19.
Further, the height of the vertical wall forming portion 21b of the first die is higher than the height of the vertical wall forming portion 19b of the first punch 19 by the gap h over the entire length in the longitudinal direction.
Therefore, at the bottom dead center of the first molding step, a gap h is formed between the top plate molding portions 19a and 21a over the entire length in the longitudinal direction.

≪Intermediate shape press molded product≫
The intermediate shape press-molded product 9 is formed when it is press-molded using the first molding die 7 described above (see FIG. 2A).
The intermediate shape press-molded product 9 will be described below with reference to FIGS. 2 (a) and 4.

FIG. 4 is a diagram showing a state of bottom dead center when the first molding step is performed using the first molding die 7.
FIG. 4 (A) shows a cross-sectional view along the line AA in the central portion in the longitudinal direction (the portion where the height of the vertical wall is the highest), and FIG. 4 (B) shows the vicinity of one end in the longitudinal direction. A cross-sectional view taken along the line BB is shown.

At the bottom dead center of the first molding step, the ridge line connecting the vertical wall portion 3 and the flange portion 5 of the material to be molded 23 is gentler than the target shape. Therefore, the height of the vertical wall forming portions 19b and 21b of the first punch 19 and the first die 21 is higher than that of both ends in the longitudinal direction, and the forming of the vertical wall portion 3 starts from the central portion in the longitudinal direction. Therefore, a material flow occurs from the central portion in the longitudinal direction of the material to be molded 23 toward both ends. As the molding of the vertical wall part progresses, a material flow occurs toward the central part in the longitudinal direction, but by increasing the radius of curvature of the ridgeline connecting the vertical wall part and the flange part, the height of the vertical wall at both ends in the longitudinal direction is targeted. Since it is lower than the shape, the amount of deformation toward the central portion in the longitudinal direction is smaller than that of the target shape. Due to these actions, the action of wrinkling due to shrinkage flange deformation is smaller than that of the target shape.

Further, as shown in FIG. 4, the vertical wall portion 3 and the flange portion 5 of the material to be molded 23 are sandwiched between the vertical wall forming portions 19b and 21b and the flange forming portions 19c and 21c of the first punch 19 and the first die 21. However, since the top plate portion 1 of the material to be molded 23 is not sandwiched by a gap h between the top plate forming portions 19a and 21a of the first punch 19 and the first die 21, it is in a state where bending is likely to occur. It has become.

Further, as described above, the line length in the longitudinal direction perpendicular to the first punch 19, also the line length L _A in the longitudinal direction central portion, since the direction of the line length L _B in the vicinity of the longitudinal end portions are shorter ( L _A > L _B ) (see FIG. 3), at the bottom dead point of the first molding step, a material surplus of the material to be molded 23 is generated in the vicinity of the longitudinal end portion of the material to be molded 23 (see FIG. 4 (B)). ).

As described above, in the first molding step, the influence of wrinkles due to shrinkage flange deformation is reduced in the central portion in the longitudinal direction as compared with the target shape, and material surplus is generated at both ends in the longitudinal direction and the top plate portion. By providing the gap h in the longitudinal direction, the central portion in the longitudinal direction is shrunk to suppress the occurrence of wrinkles due to the deformation of the flange, and the top plate portions at both ends in the longitudinal direction are bent due to the excess material. FIG. 2A. The intermediate shape press-molded product 9 as shown in the above can be molded.

It should be noted that the gap h needs to be 2 mm or more in order to sufficiently cause the top plate portion 1 to bend.

However, if the gap h is too large, the material surplus in the central portion in the longitudinal direction of the material to be molded 23 described above becomes too large in the top plate portion 1, and the material surplus in the top plate portion 1 is used as the vertical wall in the second molding step described later. It may not be fully applied to the molding of the portion 3, and wrinkles may occur in the flange portion 5 in the central portion in the longitudinal direction.
Therefore, the gap h is preferably 5 mm or less.

<Second molding process>
In the second molding step, as shown in FIG. 1B, the intermediate shape press-molded product 9 molded in the first molding step using the second molding die 11 having the second punch 29 and the second die 31. Is a step of forming into a product shape press-molded product 13 as shown in FIG. 2 (b).

≪Second molding mold≫
The second punch 29 and the second die 31 of the second molding die 11 have top plate forming portions 29a and 31a, vertical wall forming portions 29b and 31b, and flange forming portions 29c and 31c, respectively.
The top plate forming portions 29a and 31a, the vertical wall forming portions 29b and 31b, and the flange forming portions 29c and 31c are set to have the same shape as the target shape.

FIG. 5 shows the shape of the molded surface portion of the second punch 29.
In the second punch 29, the radius of curvature of the ridge line connecting the top plate forming portion 29a and the vertical wall forming portion 29b (hereinafter referred to as the top plate side ridge line 33) is defined as the top plate side curvature radius R3, and the vertical wall forming portion and the flange forming portion. When the radius of curvature of the ridge line connecting the two (hereinafter referred to as the flange side ridge line 35) is the flange side curvature radius R4, the flange side curvature radius R4 is smaller than the top plate side curvature radius R3 (R3> R4). In other words, in the second punch 29, the flange side ridge line 35 has a steeper bend than the top plate side ridge line 33.

Further, with respect to the line length in the longitudinal direction orthogonal to the person is short of the line length L _B of the longitudinal ends near the line length L _A of the longitudinal center portion in the first punch 19 (L _A> L _B) In the second punch 29, _{the line length L D} near the end in the longitudinal direction is longer _{than the line length L C in the center in the longitudinal direction (L C} <L _D ).
For longitudinal line length of the central portion L _A and the length of the line length L _C of the longitudinal center portion of the second punch 29 of the first punch 19 is the same (L _A = L _C), the second punch 29 The line length L _D is longer than _{the line length L B} of the first punch 19 _{(L B} <L _D ) (see FIGS. 3 and 5).

≪Product shape press molded product≫
The product shape press-molded product 13 is formed when press-molded using the above-mentioned second molding die 11.
The product shape press-molded product 13 will be described below with reference to FIG.

FIG. 6 is a diagram showing a state of bottom dead center when the second molding step is performed using the second molding die 11.
FIG. 6 (A) shows a cross-sectional view along the line AA in the central portion in the longitudinal direction (the portion where the height of the vertical wall is the highest), and FIG. 6 (B) is in the vicinity of one end in the longitudinal direction. A cross-sectional view taken along the line BB is shown.

As described above, the line length in the longitudinal orthogonal direction near the end in the longitudinal direction is _{longer than the line length L B} of the first punch 19 because _{the line length L D} of the second punch 29 is longer (L _B < L _D ) (see FIGS. 3 and 5), at the bottom dead center of the second molding step, in the vicinity of the longitudinal end portion of the material to be molded 23, the material causing the top plate portion 1 to bend is at a height. The bending of the top plate portion 1 is eliminated by flowing to the vertical wall portion 3 where the height is raised (see FIG. 6B).

As for the central portion in the longitudinal direction, as described above, since the top plate side curvature radii R1 and R3 of the first punch 19 and the second punch 29 are both set to be substantially the same as the target shape, shrinkage that causes wrinkles. Flange deformation hardly occurs.

As a result, in the second molding step, the product shape press-molded product 13 having the target shape as shown in FIG. 2B can be molded.
Comparing the product shape press-molded product 13 shown in FIG. 2 (b) molded by the press-molding method according to the present embodiment with the press-molded product 43 shown in FIG. 9 (b) molded by the conventional press-molding method. It can be seen that the wrinkles in the central part in the longitudinal direction are reduced.

[Embodiment 2]
In the first embodiment, at the bottom dead center of the first molding step, a gap h is formed between the first punch 19 and the top plate forming portions 19a and 21a of the first die 21 over the entire length in the longitudinal direction. ..
However, in the present invention, the top plate portion 1 of the intermediate shape press-molded product 9 is made to positively generate bending due to the excess material at both ends in the longitudinal direction, and almost no bending occurs in the central portion in the longitudinal direction ( 2 (a) and 4 (A)).
Therefore, it is not essential to generate a gap h in the central portion in the longitudinal direction between the top plate forming portions 19a and 21a of the first punch 19 and the first die 21, and the total length is 25 from at least both ends in the longitudinal direction. A gap h of 2 mm or more may be provided over a range of about%.

Therefore, in the present embodiment, at the bottom dead center of the first molding step, there is no gap in the central portion in the longitudinal direction between the top plate forming portions 19a and 21a of the first punch 19 and the first die 21, and the intermediate shape press is performed. A gap h is formed so as to gradually increase toward the vicinity of both ends in the longitudinal direction in which the molded product 9 is bent.

The press molding method according to this embodiment will be described below with reference to FIG. 7.
The same parts as those in the first embodiment will be described with reference to the same reference numerals.

The shape of the first punch 19 in the present embodiment is the same as that in the first embodiment, and the radius of curvature R2 on the flange side is set to be larger than the radius of curvature R1 on the top plate side (R1 <R2) (FIG. 3).

The shape of the first die 21 has a radius of curvature of the top plate side ridge line of the first die 21 so that a gap gradually increases from the central portion in the longitudinal direction to both ends between the top plate forming portions 19a and 21a. It is set to be larger than the radius of curvature of the top plate side ridge line 25 of one punch.
The flange-side ridgeline of the first die 21 has the same radius of curvature as the flange-side ridgeline 27 of the first punch 19.
Further, the height of the vertical wall forming portion 21b in the central portion in the longitudinal direction of the first die 21 (the portion where the height of the vertical wall is the highest) is equal to the height of the vertical wall forming portion 19b of the first punch 19.
As a result, at the bottom dead center of the first molding step, a gap h is provided in a range where the intermediate shape press-molded product 9 is to be bent.

FIG. 7 is a diagram showing a state of bottom dead center when the first molding step is performed using the first molding die 7 as described above.
FIG. 7 (A) shows a cross-sectional view along the line AA in the central portion in the longitudinal direction (the portion where the height of the vertical wall is the highest), and FIG. 7 (B) is in the vicinity of one end in the longitudinal direction. A cross-sectional view taken along the line BB is shown.

In the present embodiment, there is no gap between the top plate forming portions 19a and 21a in the central portion in the longitudinal direction (see FIG. 7A), but since there is a gap h in the range where the bending occurs, the first At the bottom dead center of the molding process, the same action as that described in the first embodiment occurs, and both ends of the top plate portion 1 of the material to be molded 23 in the longitudinal direction are bent due to the excess material (FIG. 7 (FIG. 7). B) See).
Therefore, as shown in FIG. 2A, it can be molded into a shape similar to the intermediate shape press-molded product 9 similar to that of the first embodiment.

Similar to the first embodiment, in order to sufficiently cause bending at both ends in the longitudinal direction of the top plate portion 1, the gap h needs to be 2 mm or more in a range of 25% or more of the total length from the ends of both ends in the longitudinal direction. Is.

The second molding step of the present embodiment is carried out using the second molding die 11 having the same shape as that of the first embodiment.
At the bottom dead center of the second molding step, as described in the first embodiment, the intermediate shape press-molded product 9 is molded into the product-shaped press-molded product 13 as shown in FIG. 2 (b).

A specific example in the case where the press molding is performed while satisfying the above-mentioned requirements in the first embodiment will be described below.

Nos. 1-1 to 1-9 in Table 1 are press-molded with a cross-section hat-shaped press-molded product having a top plate side curvature radius r3 = 400 mm and a flange side curvature radius r4 = 200 mm as a target shape.
Further, Nos. 2-1 to 2-6 are press-molded with a cross-section hat-shaped press-molded product having a top plate side curvature radius r3 = 600 mm and a flange side curvature radius r4 = 400 mm as a target shape.
The above two types of target shapes were press-molded by the conventional press-molding method and the press-molding method of the present invention, and the plate thickness increase rate of the flange portion in the obtained press-molded product was evaluated.

No. 1-1 and No. 2-1 are molded by a conventional press molding method consisting of one step. Further, Nos. 1-2 to 1-9 and Nos. 2-2 to 2-6 were molded by the press molding method of the present invention consisting of two steps.
R1 indicates the radius of curvature on the top plate side of the punch, and R2 indicates the radius of curvature on the flange side of the punch.
h indicates a gap (mm) between the top plate molding portions 19a and 21a at the bottom dead center of the first molding step.
The flange portion plate thickness increase rate indicates the plate thickness increase rate with respect to the molded material before molding at the thickest portion of the flange portion of the molded material after molding.
In the evaluation, "○" indicates that the plate thickness increase rate is smaller and wrinkles are reduced than in the conventional example, and "◎" indicates that the plate thickness increase rate is smaller than in the conventional example and the flange plate thickness increase rate is reduced. Is suppressed to 4% or less.

As shown in Table 1, in each of the two target shapes, the press-molded product obtained by the press-molding method of the present invention has a smaller increase rate of the flange plate thickness than the conventional press-molding method. Wrinkles are less likely to occur.

Comparing No.1-3 and No.2-4, the flange-side curvature radius R2 in the first molding process is twice the top plate-side curvature radius R1, but No.1-3 is No.2. The effect of reducing the plate thickness increase rate is smaller than that of -4. This is due to the property that the shrinkage flange deformation becomes more remarkable as the radius of curvature that becomes convex upward becomes smaller.

Therefore, in order to prevent wrinkles caused by the deformation of the shrinking flange that becomes convex upward, the smaller the radius of curvature, the larger the magnification of the radius of curvature R2 on the flange side in the first molding step with respect to the radius of curvature R1 on the top plate side. There is a need.
However, in the case where the flange-side curvature radius R2 in the first punch 19 is set to 4 times or more the top plate-side curvature radius R1 and the upwardly convex top plate-side curvature radius r3 is 400 mm or more as the target shape. The occurrence of wrinkles could be sufficiently reduced (see Nos. 1-5 to 1-8).

1 Top plate part 3 Vertical wall part 5 Flange part 6 Press-molded product (target shape)
7 1st molding die 9 Intermediate shape press molded product 11 2nd molding die 13 Product shape Press molded product 15 Top plate side ridge line (target shape)
17 Flange side ridge line (target shape)
19 1st punch 19a Top plate forming part 19b Vertical wall forming part 19c Flange forming part 21 1st die 21a Top plate forming part 21b Vertical wall forming part 21c Flange forming part 23 Material to be molded 25 Top plate side ridge line (1st punch)
27 Flange side ridge (1st punch)
29 2nd punch 29a Top plate forming part 29b Vertical wall forming part 29c Flange forming part 31 2nd die 31a Top plate forming part 31b Vertical wall forming part 31c Flange forming part 33 Top plate side ridge line (2nd punch)
35 Flange side ridge line (second punch)
37 die (conventional example)
39 punch (conventional example)
41 Mold (conventional example)
43 Press-molded product (conventional example)
45 Wrinkles r3 Top plate side radius of curvature (target shape)
r4 Flange side radius of curvature (target shape)
R1 Top plate side radius of curvature (1st punch)
R2 Flange side radius of curvature (first punch)
R3 Top plate side radius of curvature (second punch)
R4 Flange side radius of curvature (second punch)

Claims (3)

A top plate portion having a convex shape in the direction of the top plate portion along the longitudinal direction, a pair of vertical wall portions continuing on both sides of the top plate portion, and a top plate portion direction along the longitudinal direction following the pair of vertical wall portions. A press-molded product with a cross-section hat shape that has a convex flange and the radius of curvature of the longitudinal ridge that connects the top plate and the vertical wall is larger than the radius of curvature of the longitudinal ridge that connects the vertical wall and the flange. It is a press molding method of
A first molding step of forming an intermediate-shaped press-molded product having a top plate portion, a vertical wall portion, and a flange portion and having bending caused by a material surplus at both ends in the longitudinal direction of the top plate portion.
The intermediate shape press-molded product molded in the first molding step is provided with a second molding step of forming a foam into a target shape.
The first forming step is a punch and die having a top plate forming portion, a vertical wall forming portion, and a flange forming portion, and at a bottom dead point, at least in the longitudinal direction between the punch and the top plate forming portion of the die. There is a gap of 2 mm or more from both ends of the punch over a range of 25% or more of the total length, and the vertical wall of the punch is more than the radius of curvature R1 of the longitudinal ridge line connecting the top plate forming portion and the vertical wall forming portion of the punch. A press molding method characterized in that a first molding die having a large radius of curvature R2 of a longitudinal ridge line connecting a molding portion and a flange molding portion is used. The press molding method according to claim 1, wherein the gap is 5 mm or less. The press molding method according to claim 1 or 2, wherein the radius of curvature R2 of the longitudinal ridge in the punch of the first molding die is four times or more the radius of curvature R1 of the longitudinal ridge.

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