JP2020124717A - Press forming method - Google Patents

Abstract

To provide a press forming method in which variation in shape of a press-formed article resulting from difference between material strengths of metal plates is reduced when forming a press-formed article having a hat type cross section shape.SOLUTION: The press forming method according to the present invention is a method in which each of a plurality of metal plates 27 different from each other in material strength is formed into a press-formed article 1 having a hat type cross section shape. The method comprises: a first forming step of forming each of the plurality of metal plates 27 into an intermediate formed article 11 having a top plate portion 3 and flange portion 7 having the same shape as the target of the press-formed article 1, and a vertical wall portion 15 with a step portion in which a step portion 13 is formed protruding outside compared to a vertical wall portion 5 of the target shape; and a second forming step of forming the intermediate formed article 11 into the target press-formed article 1. The step portion 13 has a concave R portion 13a at the end of a top plate portion side and a convex R portion 13b at the end of a flange portion side, wherein the curvature radius R of the convex R portion 13b is larger as the material strength of the metal plate 27 is higher.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a press-molding method for a hat-shaped cross-section press-formed product.

When a press-molded product is manufactured by press-molding, elastic recovery (spring back) after the press-molding may cause a shape defect, and it may be difficult to obtain a press-molded product having a target shape. Therefore, development of a press molding method that suppresses springback is desired.

Up to now, there have been reported some press forming methods for suppressing wall warpage due to springback of a press formed product having a hat-shaped cross-sectional shape having a top plate portion, a vertical wall portion, and a flange portion.
For example, in Patent Document 1, the interval between the end portions on the horizontal wall portion side of the vertical wall portion in the forming target shape is shorter than the interval between the end portions on the horizontal wall portion side of the vertical wall portion of the forming target shape of the forming member. A technique is disclosed in which the formed temporary formed body is subjected to draw forming, and thereafter, the vertical wall portion is expanded with a forming target shape. Then, according to this technique, the vertical wall portion of the temporary molded body can be reversely bent and bent back, and the stress that causes the wall warp existing in the vertical wall portion of the temporary molded body is eliminated, and the molding die It is said that by reducing the wall warp after the mold is released, the wall opening after the mold release can be suppressed.

Further, in Patent Document 2, as in Patent Document 1, by forming an intermediate molded product in which the punch bottom is smaller than the molding target shape, and by molding in the target shape in the next step, springback after release There is disclosed a technique for leaving the deformation that cancels the wall warp caused by the above.

However, when the material strength of the metal plate used for press molding changes, the springback behavior of the press molded product after releasing also changes, so the above technique requires changing the mold shape according to the material strength of the metal plate. , A new die is manufactured, or the die is repaired, which causes an increase in die cost.

Therefore, as a method of press-molding so that the springback behavior is the same even when the material strength changes, Patent Document 3 discloses a method of press-molding a thin metal plate into a hat cross-sectional shape using a punch, a die and a pad. There is disclosed a technique for reducing the amount of wall opening due to springback by changing the pressing force of a pad for pressing the metal plate according to the material strength of the metal plate.

JP, 2008-307557, A Japanese Patent No. 4681420 Japanese Patent No. 5890654

However, in the technique disclosed in Patent Document 3, it is necessary to reduce the pressing force of the pad as the material strength of the metal thin plate increases, and the unstable element during press molding increases. Therefore, a press-formed product obtained by press-forming metal plates having different material strengths has a problem in that a desired shape may not always be obtained after the press-forming, because the shape varies after the mold is released.

The present invention has been made to solve the above problems, and can reduce variation in shape due to springback after releasing a press-formed product that is press-formed using metal plates having different material strengths. An object is to provide a press molding method.

(1) In the press molding method according to the present invention, each of a plurality of metal plates having different material strengths is provided with a top plate part, a vertical wall part continuous from the top plate part, and a flange part continuous from the vertical wall part. And a top plate having the same shape as the target shape of the press-formed product, using a first die to form each of the plurality of metal plates. A first molding step of molding into an intermediate molded product having a step portion and a flange portion, and a vertical wall portion with a step portion in which a step portion protruding outward as compared with the vertical wall portion of the target shape is formed; A second molding step of molding the intermediate molded product into a press-molded product having the target shape by using the mold described in (4) above, wherein the stepped portion has a concave shape bent in a concave shape at its end on the top plate side. It is preferable to set the radius of curvature of the convex R portion to be larger as the material strength of the metal plate is higher, which has the R portion and the convex R portion bent in a convex shape at the end on the flange side. It is a feature.

(2) In the one described in (1) above, the first die molds the convex R portion, and at the same time, the convex R portion molding portion is replaceable according to the radius of curvature of the convex R portion. In the first forming step, the convex R-portion forming portion that forms the convex R-portion having a radius of curvature set based on the material strength of the metal plate is selected, and the selected convex shape is formed. It is characterized in that the above-mentioned first die having an R-portion molding portion attached thereto is used.

According to the present invention, when press-molding a hat-shaped cross-section press-formed product, it is possible to reduce variations in the shape of the press-formed product due to the difference in material strength of the metal plate.
Further, according to the present invention, by exchanging only a part of the die used for press-forming the press-formed product, metal plates having different material strengths can be punched separately, and die cost can be suppressed. Becomes

In the press molding method according to the embodiment of the present invention, (a) an intermediate molded product molded in the first molding step, and (b) a press molded product of a target shape, cross-sectional view in the longitudinal direction. In the press molding method according to the embodiment of the present invention, (a) a first mold used for molding an intermediate molded product, and (b) a second mold used for molding a press molded product having a target shape, It is sectional drawing which shows an example. It is a figure explaining spring back (wall warp of a vertical wall part, splash of a flange part) after mold release of a press-molded article of hat type section shape. In the press molding method according to the present embodiment, it is a diagram showing a moment generated in the vertical wall portion with a step in the process of molding an intermediate molded product into a press molded product having a target shape. It is a figure which shows the concrete shape and dimension of the 1st metal mold and 2nd metal mold used for the press molding method which concerns on this Embodiment. In this Embodiment, it is a figure explaining the amount of splashes of the flange part of the press molded product after mold release. In the present embodiment, it is an analysis result of the shape after release of a press-formed product formed by using a steel plate having a tensile strength of 440 MPa class and the amount of splash of the flange portion ((a) conventional method, (b) present invention ). In the present embodiment, it is an analysis result of a shape of a press-formed product formed by using a steel sheet having a tensile strength of 980 MPa class after release and the amount of splash of a flange portion ((a) conventional method, (b) present invention (R=4 mm), (c) present invention (R=10 mm)). In the present embodiment, it is a diagram comparing the shapes of the press-formed products formed by using the steel sheets of tensile strength 440 MPa class and 980 MPa class after release. In the press molding method according to the present invention, it is a diagram for explaining the shape of the step portion of the vertical wall portion with a step portion in the intermediate molded product. FIG. 3 is a diagram showing the shape and dimensions of a mold used for molding an intermediate molded product and a press-formed product having a target shape in Examples (height of step portion h=H/2). FIG. 3 is a diagram showing the shape and dimensions of a mold used for molding an intermediate molded product and a press-formed product having a target shape in Examples (height of stepped portion h=2H/3).

In the press molding method according to the embodiment of the present invention, each of a plurality of metal plates having different material strengths is provided with a top plate portion 3 and a vertical plate continuous from the top plate portion 3 as illustrated in FIG. A press-formed product 1 having a hat-shaped cross-section, which has a wall portion 5 and a flange portion 7 continuous from the vertical wall portion 5, is formed into an intermediate formed product 11 as shown in FIG. And a second molding step of molding the intermediate molded product 11 into the press-formed product 1 having a target shape. Hereinafter, each of the above steps will be described.

<First molding step>
In the first molding step, as illustrated in FIG. 2A, a plurality of metal plates 27 having different material strengths are pressed using a first mold 21 having a die 23 and a punch 25. A step portion formed with a top plate portion 3 and a flange portion 7 having the same shape as the target shape of the molded product 1 (FIG. 1B), and a step portion 13 protruding outward as compared with the vertical wall portion 5 having the target shape. It is a step of molding an intermediate molded product 11 (FIG. 1A) having the attached vertical wall portion 15.

The stepped portion 13 has a concave R portion 13a that is bent outwardly at an end portion on the top plate side, and a convex R portion 13b that is bent outwardly at an end portion on the flange portion side. , And a connecting surface portion 13c provided between the concave R portion 13a and the convex R portion 13b and connected to each R stop.

The concave R portion 13a is connected to the top plate side vertical wall portion 15a continuous from the top plate portion 3 at the R stop. On the other hand, the convex R portion 13b is connected to the flange side vertical wall portion 15b continuous from the flange portion 7 at the R stop.
As a result, the vertical wall portion 15 with a step portion formed with the step portion 13 has a shape in which the flange side vertical wall portion 15b projects outward as compared with the top plate side vertical wall portion 15a.

Then, the higher the material strength of the plurality of metal plates 27, the larger the radius of curvature R of the convex R portion 13b is set.
In this way, since the radius of curvature R of the convex R portion 13b can be easily changed according to the material strength of the metal plate 27, in the present embodiment, as shown in FIG. The mold 21 forms a convex R portion 13b, and as a convex R portion molding portion that can be exchanged according to the radius of curvature R of the convex R portion 13b, a pair of die-side convex R portion molding portions 23a is formed. It has a punch side convex R portion forming portion 25a. The die-side convex R portion forming portion 23a and the punch-side convex R portion forming portion 25a correspond to different curvature radii of the convex R portion 13b, and the die side convex R portion forming portion 23a and the punch for each curvature radius. It is assumed that there are prepared a plurality of sets that form the side convex R-portion forming portions 25a as one set.

Then, the die side convex R part forming part 23a and the punch side convex R part forming part 25a in which the radius of curvature R is set based on the material strength of the metal plate 27 are selected, and the selected die side convex R part is selected. The intermediate molded product 11 is molded using the first mold 21 to which the molding portion 23a and the punch-side convex R portion molding portion 25a are attached.

<Second molding step>
In the second molding step, as illustrated in FIG. 2B, the second mold 31 including the die 33, the punch 35, and the pad 37 is used to convert the intermediate molded product 11 into a press-formed product 1 having a target shape. This is the step of molding into. Here, the pad 37 presses the top plate portion 3 of the intermediate molded product 11 in cooperation with the punch bottom portion 35 a of the punch 35.

Next, by changing the curvature radius R of the convex R portion 13b formed in the intermediate molded product 11 by the press forming method according to the present embodiment, a press generated due to the difference in material strength of the metal plate 27 is produced. The reason why it is possible to suppress the variation in springback after the molded product 1 is released will be described below.

When a metal plate is formed into a press-formed product 1 having a target shape in one step by using a second die 31 as shown in FIG. 2B, punching is performed after releasing the die as shown in FIG. The opening widths of the left and right vertical wall portions 5 are combined by the combined springback of the opening of the shoulder R portion 4 (increasing the opening angle of the top plate portion 3 and the vertical wall portion 5) and the wall warp of the vertical wall portion 5. Opens wider than the opening width of the target shape (molding bottom dead center shape).

In order to join the flange portion 7 of the press-formed product 1 to another component (for example, spot welding), the position of the flange portion 7 is aligned with the joining surface of the other component (for example, the flange portion of the other component). There is a need. However, as shown in FIG. 3, when the punch shoulder R portion opens and the wall warps due to the spring back, the position of the flange portion 7 changes, that is, the flange portion 7 springs, and it may not be possible to join with other parts. there were. In particular, such a splash of the flange portion 7 is remarkable when the material strength of the metal plate is high, and greatly deviates from the target shape.

As described above, the press-molding method according to the present invention, in the process of molding the intermediate-molded product 11 having the stepped vertical wall portion 15 into the target-shaped press-molded product 1 in the second molding step, as shown in FIG. As shown, the punch shoulder R portion 17, the concave R portion 13a of the stepped vertical wall portion 15 and the moment in the die shoulder R portion 19 are applied to the convex R portion 13b in the opposite direction.

The moments applied to the punch shoulder R portion 17, the concave R portion 13a and the die shoulder R portion 19 are the springback (increasing the splash) component of the opening of the punch shoulder R portion and the wall warp after the mold release. On the other hand, the moment imparted to the convex R portion 13b becomes a spring go (reduction of splash) component.

Therefore, after releasing the press-formed product 1 formed in the second forming step, the spring back component in the punch shoulder R portion 17, the concave R portion 13a, and the die shoulder R portion 19 and the spring go component in the convex R portion 13b. Cancel each other out, and the springback of the vertical wall portion 5 is suppressed. As a result, the change in the position of the flange portion 7 after releasing the press-formed product 1 can be reduced.

Furthermore, in the press molding method according to the present invention, when molding is performed using each of a plurality of metal plates, in the first molding step, the higher the material strength of the metal plate, the more the convex R portion formed in the intermediate molded product 11. The radius of curvature R of 13b is set large. If the material strength increases and the radius of curvature R of the convex R portion is kept small in the first molding step, the sprung back after the first molding step becomes large, which affects the shape after the second molding step. In order to suppress the springback, the radius of curvature R of the convex R portion is increased.

As described above, it is possible to reduce the variation in the shape of the press-formed product by reducing the spring-back of the press-formed product formed by molding the metal plates having different material strengths to the same degree after the release. The results of press forming analysis of forming a press formed product for each metal plate and spring back analysis of the press formed product obtained by the press forming analysis will be described.

First, metal plates having different material strengths are used as steel plates having tensile strengths of 440 MPa class and 980 MPa class. For each steel plate, an intermediate molded product 11 by the first mold 21 shown in FIG. The press-molding analysis of the press-molded product 1 by the second mold 31 shown was performed.

Next, a springback analysis was performed after the release of the press-formed product 1 obtained by the press-formed analysis. Then, as shown in FIG. 6, the amount of splash of the flange portion 7 was obtained from the shape of the press-formed product 1 after release, which was obtained by springback analysis. The amount of splash of the flange portion 7 was calculated from the height in the molding direction of the evaluation point (black circle in FIG. 6) at the center of the flange portion 7 after release, with the flange portion having the target shape as the reference surface.

The radius of curvature Rx of the die-side convex R-portion molding portion 23a and the punch-side convex R-portion molding portion 25a in the first die 21 is the radius of curvature of the convex R-portion 13b formed in the intermediate molded product 11. It is set to correspond to R.

FIG. 7 shows an analysis result of the shape of the press-formed product 1 formed by using a steel plate having a tensile strength of 440 MPa class after releasing, and the amount of splash of the flange portion 7 obtained from the analysis result. Here, FIG. 7A is a result of a conventional method of molding the press-formed product 1 in one step using the second mold 31 (FIG. 2B) as a comparison target. b) is the result when the radius of curvature of the convex R portion 13b (FIG. 4) is set to R=4 mm in the first molding step in the press molding method according to the present invention.

From FIG. 7, the amount of splash of the flange portion 7 was 2.0 mm in the conventional method of molding in one step, whereas the amount of splash of the flange portion 7 was 1.6 mm in the press molding method according to the present invention. As compared with the conventional method, the amount of splash of the flange portion 7 is reduced.

FIG. 8 shows an analysis result of the shape of the press-formed product 1 formed by using a steel sheet having a tensile strength of 980 MPa class after the mold release, and the amount of splash of the flange portion 7 obtained from the analysis result. Further, FIG. 8A shows a result of a conventional method of forming the press-formed product 1 in one step using the second mold 31 as a comparison target. Further, FIG. 8(b) and FIG. 8(c) are both the results of molding by the press molding method according to the present invention. In the first molding step, the radius of curvature of the convex R portion 13b is R=4 mm and R= This is when set to 10 mm.

When the radius of curvature of the convex R portion 13b is set to R=4 mm, which is the same as that of the 440 MPa class steel sheet (FIG. 8(b)), the amount of splash of the flange portion 7 is 4.2 mm, and the flange portion 7 of the conventional method Although it is smaller than the amount of splash (Fig. 8(c), 6.2 mm), the deviation from the amount of splash (Fig. 7(b), 1.6 mm) when using a 440 MPa class steel sheet is large.
On the other hand, when the radius of curvature of the convex R portion 13b is set to be R=10 mm by increasing the radius of curvature of the convex R portion 13b (Fig. 8(c)), the amount of splash of the flange portion 7 is 2.0. mm, and the difference from the case of using a 440 MPa class steel sheet was reduced.

FIG. 9 shows a diagram comparing the shapes of the press-formed product 1 after releasing from the case where a steel sheet having a tensile strength of 440 MPa and a steel sheet having a tensile strength of 980 MPa are used.
When a 980 MPa grade steel sheet was used, a 440 MPa grade steel sheet was used, although the shape of the step portion 13 formed in the first forming step was slightly left on the vertical wall portion 5 of the press-formed product 1 after release. In this case, the shape was almost the same as that of the press-formed product 1. The difference in the amount of splash of the flange portion 7 between the tensile strength 440 MPa grade steel sheet and the 980 MPa grade steel sheet was 0.4 mm, and almost the same results were obtained.

As described above, according to the press-molding method according to the present embodiment, when each of a plurality of metal plates having different material strengths is molded into a press-molded product having a hat-shaped cross-sectional shape, the vertical wall portion of the press-molded product having the target shape is formed. An intermediate molded product in which a step portion protruding outwardly is formed, the intermediate molded product is molded into the press-formed product, and the higher the material strength of the metal plate is, the higher the convex R portion in the step portion is. By setting the radius of curvature to be large, it is possible to reduce the variation in springback of the press-formed product after release from the mold due to the difference in material strength of the metal plate.

Furthermore, according to the press molding method according to the present embodiment, the first mold for molding the intermediate molded product has a convex R-portion molding portion that can be replaced according to the radius of curvature of the convex R-portion. Then, only by selecting and attaching the mold of the convex R part molding part for molding the convex R part in which the radius of curvature is set based on the material strength of the metal plate, that is, a part of the first mold. It is possible to reduce the variation in shape due to springback and easily perform punching even for metal plates having different material strengths, and to reduce the die cost, simply by exchanging appropriately.

In addition, in the above description, in addition to the radius of curvature R of the convex R portion 13b, the step portion as shown in FIG. There are 13 heights h and widths W.
The height h of the stepped portion 13 is, for example, as shown in FIG. 10B, the height from the flange portion 7 to the R stop of the convex R portion 13b (the boundary between the convex R portion 13b and the connection surface portion 13c). can do.
Further, the width W of the step portion 13 is, for example, as shown in FIG. 10B, the distance between the R stop of the concave R portion 13a and the R stop of the convex R portion 13b in the step portion 13, that is, the connection. It can be the width of the surface portion 13c.

Furthermore, the target molding height H of the intermediate molded product 11 may be determined by the following formula when the press-molded product 1 of the target shape has the molding height H ₀ .
H ₀ ≤ H+W+R _P ＋R _a ＋R _b ＋R _d
Here, W is the width of the step portion 13, R _p is the radius of curvature of the punch shoulder R portion, R _a is the radius of curvature of the concave R portion, R _b is the radius of curvature of the convex R portion, and R _d is the die shoulder R portion. Radius of curvature (see FIG. 5).

In addition, in the intermediate molded product 11 shown in FIG. 1A, the top plate side vertical wall portion 15a and the flange side vertical wall portion 15b are parallel to each other in the cross-section orthogonal to the longitudinal direction of the intermediate molded product 11. In the invention, the top plate side vertical wall portion 15a and the flange side vertical wall portion 15b may not be parallel to each other.

Further, in the intermediate molded product 11 shown in FIG. 1A, the connecting surface portion 13c has a planar shape and is parallel to the top plate portion 3. However, according to the present invention, the connecting surface portion 13c and the top plate portion 3 are connected to each other. May not be parallel.

In the above description, the first molding step (see FIG. 2A) and the second molding step (see FIG. 2B) are both foam molding to form the intermediate molded product 11 and the press molded product 1. However, in the present invention, neither the first molding step nor the second molding step limits the molding method to foam molding.

Further, in the above description, in the first forming step, as shown in FIG. 2A, the metal plate 27 is formed by the die 23 and the punch 25, but the metal plate 27 is formed by the pad (not shown). You may press and shape. Further, in the second molding step, the pad 37 may not be used for molding.

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

In this embodiment, a hat-shaped cross-section press-formed product 1 having a top plate portion 3, a vertical wall portion 5 and a flange portion 7 as shown in FIG. Then, a press molding analysis for molding in two steps of the second molding step was performed. Then, by the press molding analysis, a springback analysis was performed after the mold release of the press molded product 1 molded to the molding bottom dead center in the second molding step.

As the dimensions of the target shape of the press-formed product 1 to be analyzed, the length L of the top plate portion 3 was 30 mm, the forming height H ₀ was 41 mm, and the width of the flange portion 7 was 20 mm. The radius of curvature of the punch shoulder R portion 4 was 3 mm, and the radius of curvature of the die shoulder R portion 6 was 4 mm.

In the press forming analysis, first, in the first forming step, the metal plate 27 shown in FIG. 10 is press formed using the first die 21 having the shape and dimensions shown in FIG. 11(a) or 12(a). The intermediate portion having a top plate portion 3 and a flange portion 7 having the same shape as the target shape of No. 1 and a vertical wall portion 15 with a step portion formed with a step portion 13 protruding outward as compared with the vertical wall portion 5 having the target shape. A molded product 11 is molded.

The intermediate molded product 11 molded in the first molding process has a top plate part 3 and a flange part 7 so that the top plate part 3 and the flange part 7 have the same shape as the top plate part 3 and the flange part 7 of the press-formed product 1 having a target shape. The length L of 3 was 30 mm, the width of the flange portion 7 was 20 mm, the radius of curvature of the punch shoulder R portion 17 was 3 mm, and the radius of curvature of the die shoulder R portion 19 was 4 mm. The target molding height H of the intermediate molded product 11 was set to 35 mm.

The step portion 13 formed on the stepped vertical wall portion 15 of the intermediate molded product 11 has a concave R portion 13a at the end portion on the top plate portion side and a convex R portion 13b at the end portion on the flange portion side. The shape and the radius of curvature R of the convex R portion 13b are changed according to the material strength of the metal plate 27 used for forming, as described later.

Further, the height h of the step portion 13 is H/2 or 2H/3, and the width W of the step portion 13 is 6 mm. Here, the height h of the step portion 13 is the height from the flange portion 7 to the R stop of the convex R portion 13b (the boundary between the convex R portion 13b and the connecting surface portion 13c), and the width W of the step portion 13 is The distance between the R stop of the concave R portion 13a and the R stop of the convex R portion 13b in the step portion 13, that is, the width of the connecting surface portion 13c.

When the height h of the stepped portion 13 is set to H/2, the height h of the stepped portion 13 is set to 2H/3 using the first mold 21 having the shape and dimensions shown in FIG. 11(a). When set, the first mold 21 having the shape and dimensions shown in FIG. 12A was used. The radius of curvature Rx of the die-side convex R-portion molding portion 23a and the punch-side convex R-portion molding portion 25a of the first die 21 is the curvature radius R set in the convex R-portion 13b of the intermediate molded product 11. It was set appropriately according to.

In the subsequent second molding step, the intermediate molded product 11 molded in the first molding step is made into a target shape by using the second mold 31 having the shape and size shown in FIG. 11B or 12B. It was molded into a press-molded product 1 (Fig. 1(b)).

Further, after the mold release, the spring-back analysis of the press-molded product 1 molded to the bottom dead center in the second molding step was performed to obtain the shape of the press-molded product 1 after the mold release.

In the present embodiment, the material strength of the metal plate 27 and the radius of curvature R of the convex R portion 13b of the intermediate molded product 11 molded in the first molding process are changed, respectively, and variations in springback caused by the difference in material strength. Was evaluated. Here, as the metal plate 27, a steel plate having a tensile strength of 440 MPa class, 780 MPa class, 980 MPa class, 1180 MPa class and 1470 MPa class was used. The radius of curvature R of the convex R portion 13b is set by appropriately setting the radius of curvature Rx of each of the die-side convex R-portion molding portion 23a and the punch-side convex R-portion molding portion 25a in the first die 21. changed.

The variation in shape of the press-formed product 1 in which the tensile strength of the steel plate and the radius of curvature R of the convex R portion 13b were changed after the mold was released was evaluated as follows.
First, a press forming analysis in which the tensile strength of the steel plate and the radius of curvature R of the convex R portion 13b are changed, and a springback analysis of the press formed product 1 at the forming bottom dead center obtained by the press forming analysis are performed, and the press forming is performed. The shape of the product 1 after release is determined.

The tensile strength and the convex shape of the steel sheet are based on the flange portion 7 after release of the press-formed product 1 when the radius of curvature of the convex R portion 13b is R=3 mm using a steel sheet having a tensile strength of 440 MPa. The amount of deviation, which is the difference in the height in the molding direction of the flange portion 7 after releasing the press-formed product 1 obtained by changing the radius of curvature R of the R portion 13b, is measured. In measuring the amount of deviation, the position of the top plate portion 3 of the press-formed product 1 was aligned and the difference in height in the molding direction at the center of the flange portion 7 was determined.

Further, as a comparison object, with respect to a steel plate having a tensile strength of 440 MPa class, 780 MPa class, 980 MPa class, 1180 MPa class and 1470 MPa class, a press-molded product 1 is molded in one step by using a second mold 31, and after release from the mold. The amount of deviation between the flange portion 7 and the reference flange portion 7 described above was measured, and the variation in the amount of splash of the flange portion of the press-formed product 1 (see FIG. 6) due to the difference in tensile strength of the steel plates was evaluated. ..

Tables 1 and 2 show the results of evaluating the amount of deviation of the flange portion 7 of the press-formed product 1 after release when the tensile strength of the steel sheet and the radius of curvature R of the convex R portion 13b are changed. Here, Table 1 shows the result when the height h of the step portion 13 is set to H/2, and Table 2 shows the result when the height h of the step portion 13 is set to 2H/3.

In Tables 1 and 2, when the deviation amount of the flange portion 7 is evaluated as “◯”, the measured deviation amount is within ±0.5 mm, and when the deviation amount is evaluated as “△”, the deviation amount is ±. Although it was over 0.5 mm, it was smaller than the deviation amount of the flange portion 7 measured for the press-formed product 1 in which a steel plate having the same tensile strength was formed in one step.

From Table 1 and Table 2, the deviation amount of the flange portion 7 is smaller than that of the press-formed product 1 formed in one step, in any of the tensile strength TS of the metal plate 27 and the curvature radius R of the convex R portion 13b. The result is that the variation in the amount of splash of the flange portion 7 due to the spring back is reduced.
Further, when the tensile strength of the steel plate is 780 MPa class, the deviation amount of the flange portion 7 is ±0.5 mm or less when using the 440 MPa class steel plate at the radius of curvature R=5.3 mm and 6 mm of the convex R portion 13b. Therefore, it can be seen that the variation in the amount of splash of the flange portion 7 due to the springback is sufficiently small.

Similarly, when the tensile strength of the steel plate is 980 MPa class, the radius of curvature R of the convex R portion 13b is 6 mm, 6.6 mm and 7 mm, and when it is 1180 MPa class, it is 1470 MPa class at R = 7 mm, 8 mm and 9 mm. In this case, when R=9 mm, 10 mm and 11 mm, the deviation from the flange 7 when using a 440 MPa class steel plate is within ±0.5 mm, and the variation in the amount of splash of the flange 7 due to springback is sufficient. It turns out to be small.

From these results, it is understood that by setting the radius of curvature R of the convex R portion 13b to be larger as the tensile strength of the steel sheet is increased, it is possible to reduce the variation in the amount of splashing of the flange portion 7 due to the difference in tensile strength. ..
In the present embodiment, no difference was found in the height h of the stepped portion 13 in the range of the radius of curvature R of the convex R portion 13b which can reduce the variation in the amount of splash of the flange portion 7. ..

Further, at least within the range of the tensile strength of the steel sheet and the radius of curvature R of the convex R portion 13b set in the present embodiment, the press-formed product 1 is formed in two steps by the press-forming method according to the present invention, and the tensile strength of the steel sheet is increased. The higher the strength is, the larger the radius of curvature R of the convex R portion 13b is set, so that the variation in the amount of splash of the flange portion 7 can be reduced as compared with the case where the press-formed product 1 is formed in one step. It was

As described above, in the press molding method according to the present invention, the higher the material strength of the metal plate is, the larger the radius of curvature of the convex R portion of the step portion in the intermediate molded product is set, thereby making the difference in the material strength of the metal plate. It was shown that the variation in the shape of the press-formed product caused by it can be reduced.

1 Press-formed product (target shape)
3 Top Plate Part 4 Punch Shoulder R Part 5 Vertical Wall Part 6 Die Shoulder R Part 7 Flange Part 11 Intermediate Molded Product 13 Step Part 13a Recessed R Part 13b Convex R Part 13c Connection Surface Part 15 Vertical Wall Part with Step Part 15a Top Plate Side vertical wall portion 15b Flange side vertical wall portion 17 Punch shoulder R portion 19 Die shoulder R portion 21 First mold (first molding step)
23 Die 23a Die-side convex R part forming part 25 Punch 25a Punch-side convex R part forming part 25b Punch bottom 27 Metal plate 31 Second mold (second forming step, conventional technique)
33 die 35 punch 35a punch bottom 37 pad

Claims (2)

Each of a plurality of metal plates having different material strengths, into a hat-shaped cross-section press-formed product 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. A press molding method for molding,
Using the first mold, each of the plurality of metal plates is projected outward as compared to the top plate portion and the flange portion having the same shape as the target shape of the press-formed product and the vertical wall portion having the target shape. A first molding step of molding into an intermediate molded product having a vertical wall portion with a step formed with the step
A second molding step of molding the intermediate molded product into a press-molded product having the target shape using a second mold,
The step portion has a concave R portion bent in a concave shape at an end portion on the top plate portion side and a convex R portion bent in a convex shape at an end portion on the flange portion side. A press forming method characterized in that the higher the material strength is, the larger the radius of curvature of the convex R portion is set. The first mold has a convex R portion molding portion that molds the convex R portion and is replaceable according to a radius of curvature of the convex R portion,
In the first forming step, the convex R-portion forming portion that forms the convex R-portion whose radius of curvature is set based on the material strength of the metal plate is selected, and the selected convex R-portion forming portion is selected. The press-molding method according to claim 1, wherein the first mold to which is attached is used.