JP2022070366A - Press molding method and press molding mold - Google Patents

Abstract

To provide a press molding method capable of simultaneously preventing cracking of a top plate having a shape branching into two in a plan view, the tip of a longitudinal wall formed on the center of the branching part when a press molding having the longitudinal wall connected to the top plate is formed, and bent-back parts on both sides of the branching part, and provide a press molding mold.SOLUTION: The press molding method according to the present invention includes: a first molding step S1 of molding, to protrude, a top plate 1, a first bent part 2, an intermediate longitudinal wall 9 which becomes a base end side of a longitudinal wall 3, a second bent part 11, and a shelf 13; a trim step S3 of removing an unnecessary part from the shelf 13 and leaving a flange 25; and a second molding step S5 of bending back the second bent part 11 and molding the longitudinal wall 3. Molding is performed so as to satisfy the relationship of R2C<R2S<R1, where R1 denotes a bending radius of the entire branching part of the first bent part 2, R2C denotes a bending radius of the center of the branching part of the second bent part 11, and R2S denotes a bending radius of parts on both sides of the center of the branching part of the second bent part 11 in a bending ridge direction.SELECTED DRAWING: Figure 1

Description

The present invention relates to a press forming method and a press forming die for press forming a member such as an automobile part from a metal base plate, and in particular, a top plate portion having a bifurcated shape in a plan view, such as a lower arm, and the same. The present invention relates to a press forming method and a press forming die of a press-molded product having a continuous vertical wall portion on a top plate portion.

Some press-molded products have a top plate portion having a bifurcated shape in a plan view and a vertical wall portion continuous with the top plate portion, such as a lower arm which is an automobile undercarriage component. .. An example of such a press-molded product will be described with reference to FIG. 7.
The press-molded product 5 shown in FIG. 7 has a top plate portion 1 having a bifurcated shape in a plan view, and a vertical wall portion 3 continuous with the top plate portion 1. Hereinafter, the bifurcated portion of the press-molded product 5 is referred to as a bifurcated portion 23.

When the vertical wall portion 3 is formed on the top plate portion 1 having a bifurcated shape as shown in FIG. 7, the vertical wall portion 3 formed on the bent portion (central portion of the branch portion) of the top plate portion 1 extends. Since the flange is deformed, the tip of the vertical wall portion 3 (the o portion surrounded by the broken line circle in the figure) is likely to be stretched and the flange is cracked.

In order to avoid the above-mentioned stretch flange cracking, such a press-molded product 5 is generally manufactured by a plurality of steps as described below.
First, by foam molding or the like in which a blank (metal plate) is pressed by a pad, the top plate portion 1 and the vertical wall portion 3 are continuously connected from the top plate portion 1 to the first bent portion 2 as shown in FIG. An intermediate molded product 7 having an intermediate vertical wall portion 9 on the base end side and a shelf portion 13 continuous from the intermediate vertical wall portion 9 via the second bent portion 11 is overhanged and molded (first molding step).

Next, as shown in FIG. 9, the panel is trimmed along a predetermined trim line, unnecessary portions (parts shown by diagonal lines in the figure) are removed from the shelf portion 13 of the intermediate molded product 7, and the flange portion 25 is removed. Leave (trim process). Then, by bending back the second bent portion 11 and erecting the flange portion 25 (restrict-like), the vertical wall portion 3 including the intermediate vertical wall portion 9 and the portion corresponding to the flange portion 25 is formed (second molding step). ), The press-molded product 5 shown in FIG. 7 is manufactured. The portion shown in gray in FIG. 7 is a portion corresponding to the second bent portion 11 that has been bent back in the second molding step.

In the method described above, the amount of elongation flange deformation during the subsequent second molding step (restoric) is reduced by interposing the intermediate molded product 7 molded by the first molding step (overhang molding). Further, since the intermediate molded product 7 is provided with a surplus portion (a portion to be removed in the trim step), a portion corresponding to the o portion shown in FIG. 7 during overhang molding (a portion indicated by a broken line circle in the state of FIG. 8). Since the material flow is suppressed, it is possible to suppress the stretched flange cracking that occurs in the o portion during the second molding step.
As such a press molding method, Patent Document 1 discloses an example in which overhang molding and trimming are carried out in the same process.

JP-A-2017-21766898

The inventors conducted molding analysis and press molding experiments by the finite element method for press-molded products such as lower arms having various shapes, and depending on the shape of the branch portion 23, the vertical wall formed in the central portion of the branch portion. Not only the tip (o part) of the part 3, but also the part bent back in the second molding step in the vicinity of the central part of the branch part (the part a and b surrounded by the broken line circle in FIG. 7 and the branch in the bending ridge line direction). It was clarified that cracks also occur during molding in the parts on both sides of the central part, hereinafter simply referred to as "both sides of the branch part"). The reason why the cracks occur in the a part and the b part will be described with reference to FIGS. 7, 9, and 10.

10 (a) is a cross-sectional view taken along the line A'-A'of the intermediate molded product 7 shown in FIG. 9, and FIG. 10 (b) is a cross-sectional view taken along the line AA of the press-molded product 5 shown in FIG. be. The cross-sectional view taken along the line A'-A'and the cross-sectional view taken along the line AA show a cross-sectional view of a portion corresponding to the portion a in the intermediate molded product 7 and the press-molded product 5.
The intermediate vertical wall portion 9, the second bent portion 11 and the flange portion 25 (see FIG. 10A) formed by the first forming step and the trim step are bent back by the second forming step. As a result, as shown in FIG. 10B, the vertical wall portion 3 is formed. At this time, work hardening occurs in the portion corresponding to the second bent portion 11 that has been bent back, so that the plate thickness of the portion indicated by the arrow in the figure decreases.
Further, since the o portion where the material shortage is likely to occur due to the deformation of the stretch flange is in the vicinity (see FIG. 7), the material flow from the a portion to the o portion is generated. Due to both the reduction of the plate thickness and the action of the material flow, cracks occur in the a part. Further, for the same reason, the b portion is also cracked.

In order to suppress cracks that occur in parts a and b as described above, work hardening is reduced by increasing the bending radius of the second bent portion 11 of the intermediate molded product 7, and in the first molding step. The amount of deformation of may be reduced. However, if the amount of deformation in the first molding step is small in addition to the parts a and b, the amount of deformation of the stretched flange in the subsequent second molding step is large, and the part o is liable to crack. ..
As described above, in the conventional technique, the tip (o portion) of the vertical wall portion 3 formed in the central portion of the branch portion and the bent back portions (a portion and b portion) on both side portions of the branch portion are prevented from cracking at the same time. There was a problem that it was difficult to do.

The present invention has been made to solve such a problem, and is a press provided with a top plate portion having a bifurcated shape in a plan view, such as a lower arm, and a vertical wall portion continuous with the top plate portion. When molding a molded product, a press molding method and a press molding die that can prevent cracking at the same time for both the tip of the vertical wall formed in the center of the branch and the bent back portion on both sides of the branch are used. The purpose is to provide.

(1) The press molding method according to the present invention is to press-mold a press-molded product having a top plate portion having a bifurcated shape in a plan view and a vertical wall portion continuous with the top plate portion. Then, with the metal plate pressed against the punch with a pad, the top plate portion and the intermediate vertical wall portion that is continuous from the top plate portion via the first bent portion and is the base end side of the vertical wall portion. The first molding step in which the punch and the die cooperate to overhang and mold the shelf portion continuous from the intermediate vertical wall portion via the second bent portion, and the flange portion by removing the unnecessary portion from the shelf portion. The first forming step comprises a trim step to be left, and a second forming step of bending back the second bent portion to form the vertical wall portion including the intermediate vertical wall portion and the portion corresponding to the flange portion. Is the bending radius R ₁ of the entire branch portion in the first bending portion, the bending radius R _2C of the central portion of the branch portion in the second bending portion, and both sides in the bending ridge direction of the central portion of the branch portion in the second bending portion. It is characterized in that the bending radius R _2S of the portion of is formed so as to satisfy the relationship of R _2C <R _2S <R ₁ .

(2) The press-molding die according to the present invention is for realizing the press-molding method according to (1) above, via the top plate portion and the top plate portion to the first bent portion. An intermediate vertical wall portion that is continuously on the base end side of the vertical wall portion, and a first mold for molding an intermediate molded product having a shelf portion that is continuous from the intermediate vertical wall portion via a second bent portion. A trim mold for removing an unnecessary portion from the shelf portion to form a flange portion, and the vertical wall portion composed of a portion corresponding to the intermediate vertical wall portion and the flange portion by bending back the second bent portion. A second die for forming is provided, and the first die includes a punch having a punch shoulder portion for forming the first bent portion, and a pad arranged facing the punch and pressing a metal plate against the punch. , A die having a die shoulder portion for forming the second bent portion, a radius of curvature R _P of the punch shoulder portion, and a portion of the die shoulder portion for forming the central portion of the branch portion of the second bent portion. The radius of curvature R _DC and the radius of curvature R _DS of the portion forming both sides in the bending ridge direction of the central portion of the branch portion of the second bending portion in the die shoulder have a relationship of R _DC <R _DS < _RP . It is characterized by being set to satisfy.

In the present invention, in the first molding step of molding the intermediate molded product, the bending radius R1 of the entire branch portion in the _first bent portion, the bending radius R _2C of the central portion of the branch portion in the second bent portion, and the second. By forming so that the bending radii R _2S of both sides in the bending ridge direction at the center of the bending portion satisfy the relationship of R _2C <R _2S <R ₁ , from the first bending portion to the second bending portion. While promoting the material flow toward the branch portion, it is possible to suppress the amount of extension flange deformation in the second forming step of the branch portion, and to suppress the decrease in the plate thickness of the bending back portion at both side portions of the branch portion. As a result, it is possible to prevent cracking of the tip of the vertical wall portion formed in the central portion of the branch portion and the bent back portion on both sides of the branch portion at the same time.

It is explanatory drawing of the press molding method which concerns on one Embodiment of this invention. It is explanatory drawing of the 1st molding process which concerns on one Embodiment of this invention, and the 1st mold used for this. 3A is a view showing an OO cross section of FIG. 1A, FIG. 3B is a view showing a PP cross section of FIG. 1A, and is a first bending portion and a second bending portion. It is explanatory drawing explaining the relationship of the bending radius of, and the material flow which occurs in the central part of a branch part and both sides of a branch part. FIG. 1A is a diagram showing an OO cross section and a PP cross section in the second bent portion of FIG. 1A, and explains the difference between the bending radius of the central portion of the branch portion and the bending radius of both sides of the branch portion in the second bent portion. It is explanatory drawing to do. It is explanatory drawing of the trim process which concerns on one Embodiment of this invention, and the trim mold used for this. It is explanatory drawing of the 2nd molding process which concerns on one Embodiment of this invention, and the 2nd mold used for this. It is explanatory drawing explaining the target shape which concerns on one Embodiment of this invention, and the problem which arises in the molding process of the target shape. It is explanatory drawing of the conventional press molding method (the 1). It is explanatory drawing of the conventional press molding method (the 2). It is explanatory drawing explaining the reason why the part a and part b are cracked in the process of forming the target shape shown in FIG. 7.

In the press molding method according to the present embodiment, a press-molded product 5 (see FIG. 7) having a top plate portion 1 having a bifurcated shape in a plan view and a vertical wall portion 3 continuous with the top plate portion 1 is provided. As shown in FIG. 1, unnecessary portions are removed from the first molding step S1 for molding the metal plate into the intermediate molded product 7 and the intermediate molded product 7 molded in the first molding step S1. It includes a trim step S3 and a second molding step S5 for molding the intermediate molded product 7 from which unnecessary portions have been removed in the trim step S3 into a target shape.
Hereinafter, each step will be described. In FIG. 1, the same parts as those in FIGS. 7 to 9 and the corresponding parts for explaining the target shape and the intermediate molded product 7 are designated by the same reference numerals.

<First molding process>
The first molding step S1 is a step of molding the intermediate molded product 7 as shown in FIG. 1A, and the intermediate molded product 7 includes the top plate portion 1 and the top plate portion 1 to the first bent portion 2. It has an intermediate vertical wall portion 9 that is continuously interposed via the base end side of the vertical wall portion 3, and a shelf portion 13 that is continuous from the intermediate vertical wall portion 9 via the second bent portion 11.

As shown in FIG. 2, the first forming step S1 for forming such an intermediate molded product 7 is arranged so as to face the punch 15 and the punch 15 having the punch shoulder portion 15a for forming the first bent portion 2. This is done by a first mold 21 composed of a pad 17 that presses a metal plate against a punch 15 and a die 19 having a die shoulder portion 19a that forms a second bent portion 11.

FIG. 2A is an OO cross section which is a cross section of the central portion of the branch portion of the intermediate molded product 7 (see the enlarged view of FIG. 1A), and FIG. 2B is one of both side portions of the branch portion (see FIG. 1A). It is a figure which shows the state of the molding bottom dead center of the PP cross section (see the enlarged view of FIG. 1A) which is the cross section of a part side). Since the cross section of the other side (b part side) of both side portions of the branch portion is the same as that of one side (a part side), the illustration is omitted.
As can be seen by comparing FIG. 2 (a) and FIG. 2 (b), with respect to the die shoulder portion 19a for forming the second bent portion 11, the radius of curvature R of the portion for forming the central portion of the branch portion of the second bent portion 11. _DC (hereinafter simply referred to as "die shoulder R _DC ") is set smaller than the radius of curvature R _DS (hereinafter simply referred to as "die shoulder R _DS ") of the portion forming both sides of the branch portion of the second bending portion 11. (R _DC <R _DS ).
In the die shoulder portion 19a, between the central portion of the branch portion and both side portions of the branch portion, R is gradually changed in the bending ridge line direction (gradual change portion).
Further, with respect to the punch shoulder portion 15a forming the first bent portion 2, the radius of curvature R _P of the punch shoulder portion 15a is set to be even larger than the die shoulder R _DC and the die shoulder R _DS (R _DC <R _DS ). < _RP ).

In the first molding step S1 using the first mold 21 as described above, the die 19 is moved from the initial position (not shown) with the metal plate held by the punch 15 and the pad 17 in FIG. 2 (a). ), By lowering to the position of the bottom dead center shown in FIG. An intermediate molded product 7 (see FIG. 1A) having an intermediate vertical wall portion 9 and a shelf portion 13 continuous from the intermediate vertical wall portion 9 via the second bent portion 11 is formed.

The shapes of the first bent portion 2 and the second bent portion 11 in the intermediate molded product 7 will be described with reference to FIG. 3 (a) and 3 (b) are an OO cross section and a PP cross section of the intermediate molded product 7 shown in the enlarged view of FIG. 1 (a).
As shown in FIGS. 3 (a) and 3 (b), in the intermediate molded product 7, the bending radius _R1 of the entire branch portion in the first bent portion 2 and the bending radius of the central portion of the branch portion in the second bent portion 11 The bending radii R _2S of both sides of the branch portion in the second bent portion 11 and R _2C have a relationship of R _2C <R _2S <R ₁ .
Further, between the second bending portion 11 having a bending radius R _2C at the center of the branch portion and the second bending portion 11 having a bending radius R _2S at both sides of the branch portion, the bending radius is from the center to both sides in the bending ridge line direction. It is a gradually expanding part (Fig. 1 (a) enlarged view).
The reason why the shape of the intermediate molded product 7 is made as described above will be described below with reference to FIGS. 3 and 4.

FIG. 4 shows the OO cross section (solid line) and the PP cross section (broken line) of the second bent portion 11 superimposed so that the difference in bending radius can be easily understood.
As shown in FIG. 4, by reducing the bending radius (R _2C ) of the second bending portion 11 at the center of the branch portion and increasing the bending radius (R 2S) at both sides of the branch portion, the bending radius (R _2S ) of both sides of the branch portion is increased in the OO cross section. The line length (distance of the solid line from point X to point Y) is long, and the line length in the PP cross section (distance of the broken line from point X to point Y) is short. Therefore, in the first molding step S1, the amount of deformation of the central portion of the branch portion is larger than that of both side portions of the branch portion.
It should be noted that points X and Y are points common to both cross sections when both cross sections are overlapped.

In this way, the bending radius of the central portion of the branch portion in the second bent portion 11 of the intermediate molded product 7 is made smaller than the bending radius of both sides of the branch portion (R _2C <R _2S ), and the first molding step S1 is performed. 2 The reason why the amount of deformation of the central portion of the branch portion of the bent portion 11 is larger than that of both sides of the branch portion is as follows.

In the press molding method of the present embodiment, since the vertical wall portion 3 is formed in the central portion of the branch portion of the branch portion 23 by the first molding step S1 and the second molding step S5, the first molding step is performed. If the amount of deformation in S1 is large, the amount of deformation of the stretched flange in the second forming step S5 is small.
Therefore, by forming the intermediate molded product 7 with a large deformation amount (large area) at the center of the branch portion during molding, the stretch flange deformation amount in the second molding step S5 becomes small, and o shown in FIG. Cracking of the part is suppressed.

On the other hand, at both sides of the branch portion, the bending radius R _2S is increased to suppress the amount of deformation of the intermediate molded product 7 during molding, so that the reduction in the plate thickness of the second bent portion 11 can be suppressed. Further, as described above, since the elongation flange deformation that occurs in the o portion in the second forming step S5 is also reduced, the material flow from both side portions of the branch portion to the o portion is also alleviated, and the bending is performed in the second forming step S5. Even if it is returned, the cracking of the a part and the b part shown in FIG. 7 is suppressed.

Further, in the intermediate molded product 7, as shown in FIG. 3, the bending radius R ₁ of the first bent portion 2 is larger than the bending radii R _2C and R _2S of the second bent portion 11. The larger the bending radius, the easier it is for the material to flow, and the smaller the bending radius, the easier it is for the material to stay. Therefore, the material is pulled from the first bent portion side to the second bent portion 11 side, and the material flows from the first bent portion 2 toward the second bent portion 11 (see the white arrow). As a result, the inflow of the material into the second bent portion 11 is promoted in both the central portion of the branch portion and both sides of the branch portion, and the crack in the o portion and the cracks in the a portion and the b portion at the time of the second molding step S5 are further cracked. It is suppressed.

<Trim process>
The trim step S3 is a step of removing unnecessary portions from the shelf portion 13 of the intermediate molded product 7 molded in the first molding step S1 to form the flange portion 25.

FIG. 5 is a diagram showing a state in the middle of trimming in the BB cross section of FIG. 1 (b).
As shown in FIG. 5, the trim step S3 is performed by a trim mold 33 having an upper blade 27, a lower blade 29, and a plate retainer 31. The upper blade 27 and the lower blade 29 are for collaborating to remove unnecessary portions from the shelf portion 13 of the intermediate molded product 7, and each of them has a trim blade having a shape corresponding to the cutting line (trim line). (Not shown).

In the trim step S3, a part of the top plate portion 1 and the shelf portion 13 of the intermediate molded product 7 molded in the first molding step S1 is sandwiched between the lower blade 29 and the plate retainer 31, for example, the upper blade 27 is initially used. The flange portion 25 is formed by moving relatively downward from the position (not shown) and cutting off the unnecessary portion (the portion shown by the diagonal line in FIG. 1B) from the shelf portion 13.

<Second molding process>
The second molding step S5 is a step of bending back the second bent portion 11 of the intermediate molded product 7 from which the unnecessary portion was removed in the trim step S3 to form the vertical wall portion 3 and molding the intermediate wall portion 3 into a target shape.

FIG. 6 is a diagram showing the state of the rest-like bottom dead center in the CC cross section of FIG. 1 (c).
The second molding step S5 is performed by a second mold 41 having a punch 35, a pad 37, and a die 39, as shown in FIG.
The punch 35 has a molding surface corresponding to the inner surface of the press-molded product 5, and grips the top plate portion 1 of the intermediate molded product 7 together with the pad 37. Further, the die 39 has a molding surface corresponding to the outer surface of the vertical wall portion 3 of the press-molded product 5, and the second bent portion 11 of the intermediate molded product 7 from which the unnecessary portion has been removed in the trim step S3. Bend back.

In the second molding step S5 using the second mold 41 as described above, the die 39 is placed in the initial position (not shown) with the top plate portion 1 of the intermediate molded product 7 being gripped by the punch 35 and the pad 37. ) To the position of the bottom dead center shown in FIG. 6, the second bent portion 11 is bent back and the flange portion 25 is erected to form the vertical wall portion 3, and the press molding shown in FIG. 1 (c) is performed. Mold the product 5.

As described above, since the amount of deformation of the central portion of the branch portion is increased in the first molding step S1, the amount of deformation of the central portion of the branch portion is small in the second molding step S5, and the deformation of the stretch flange is reduced. ..
Further, since the amount of deformation at both side portions of the branch portion is reduced in the first forming step S1, the work hardening of the second bent portion 11 is reduced, and the second bent portion 11 is bent in the second forming step S5. It is hard to crack when returning.

As described above, in the present embodiment, in the first forming step S1, the bending radius R1 of the entire branch portion in the _first bending portion 2, the bending radius R 2C of the central portion of the branch portion in the second bending portion 11, and the bending radius R _2C , After forming the bending radius R _2S on both sides of the branch portion in the second bent portion 11 so as to satisfy the relationship of R _2C <R _2S <R ₁ , the unnecessary portion is removed in the trim step S3 to form the flange portion 25. In the second forming step S5, the second bent portion 11 is bent back and the portion where the extension flange is deformed is formed.

As a result, in the central portion of the branch portion, the amount of deformation in the second molding step S5 is reduced and the elongation flange deformation is suppressed, so that cracking at the tip of the vertical wall portion 3 can be prevented.
Further, at both sides of the branch portion, the reduction in the plate thickness of the bend-back portion is suppressed, and the elongation flange deformation at the center portion of the branch portion is suppressed, so that the material flow is also alleviated, so that cracks that occur in the bend-back portion occur. Can be prevented.
Further, since the material inflow from the first bent portion 2 to the second bent portion 11 is promoted in both the central portion of the branch portion and both side portions of the branch portion, the crack prevention effect is further improved.

In the above description, an example in which the press molding is carried out by dividing it into three steps has been described, but the present invention is not limited to this, and the first molding step S1 and the trimming step S3 are carried out in one step as a whole. It may be performed in two steps. For example, if trim blades are provided on the punch 15 and the die 19 in the first molding step S1, the intermediate molded product 7 can be molded and unnecessary portions can be removed at the same time.

Further, the vertical wall portion other than the branch portion 23 may be molded during the above-mentioned three steps, or may be molded in another step without any problem in carrying out the present invention. The same applies to the molding of the top plate portion 1.

In order to confirm the effect of the present invention, CAE analysis was performed on press molding with the lower arm component as the target shape as shown in FIG.
The metal plate used as the material was a hot-rolled steel plate having a plate thickness of 2.3 mm and a tensile strength of 780 MPa class.
The press molding step was the three steps of the first molding step S1, the trim step S3, and the second molding step S5 described in the first embodiment.

As a conventional example, two types of second bent portions 11 of the intermediate molded product 7 having the same bending radius at the center portion of the branch portion and both sides of the branch portion were analyzed. The bending radius of the second bent portion 11 in the conventional example is 5 mm (conventional example 1) or 7 mm (conventional example 2) for both the central portion of the branched portion and both side portions of the branched portion. Further, the bending radius of the first bent portion 2 was set to 7 mm in both the conventional example 1 and the conventional example 2. Here, the bending radius is the radius of the central portion of the plate thickness with respect to the arc (the same applies hereinafter).

Further, as a comparative example, the bending radius of the central portion of the branch portion in the second bent portion 11 of the intermediate molded product 7 is smaller than the bending radius of both sides of the branch portion, and the bending radius of the first bent portion 2 is the second bent portion 11. The ones smaller than the bending radii of both sides of the bifurcation in the above were analyzed. The bending radius of the second bent portion 11 in the comparative example was 5 mm at the central portion of the branch portion, 7 mm at both side portions of the branch portion (parts a and b in FIG. 8), and the bending radius of the first bent portion 2 was 6 mm.

Further, as an example of the present invention, the bending radius of the central portion of the branch portion in the second bent portion 11 of the intermediate molded product 7 is smaller than the bending radius of both sides of the branch portion, and the bending radius of the first bent portion 2 is the second bent portion. The one larger than the bending radius of both sides of the branch portion in No. 11 was analyzed. In the example of the invention, the bending radius of the second bent portion 11 is 5 mm at the center of the branch portion, 7 mm at both sides of the branch portion, and the bending radius of the first bent portion 2 is 10 mm.
Table 1 shows the maximum plate thickness reduction rate of the a part, the b part, and the o part (see FIG. 7) at the bottom dead center of the second molding step S5 obtained by the CAE molding analysis.

According to the past findings of the inventors who prototyped lower arms of various shapes, in the case of a hot-rolled steel sheet with a plate thickness of 2.3 mm and a tensile strength of 780 MPa, cracks occur when the plate thickness reduction rate exceeds 20% in CAE forming analysis. Occur. Therefore, the molding limit at which cracks occur in this embodiment is set to a plate thickness reduction rate of 20%.

In the conventional example 1 of Table 1 above, the bending radii of the branch portion central portion (o portion) and the branch portion both side portions (a portion and b portion) of the second bent portion 11 are the same, and the plate thickness of the branch portion central portion is the same. This is an example in which the reduction rate is within the molding limit range, but the plate thickness reduction rate on both sides of the branch portion exceeds the molding limit range.
As shown in Table 1, in the case of Conventional Example 1, the plate thickness reduction rate of part o is less than 20% of the molding limit, but the plate thickness reduction rate of parts a and b exceeds 20% of the molding limit. There is. Therefore, in the press molding method of Conventional Example 1, it was determined that cracks did not occur in the o part, but cracks occurred in the a part and the b part.

Further, in the conventional example 2 of Table 1, the bending radius of the central portion of the branch portion of the second bent portion 11 and the bending radius of both side portions of the branch portion are the same, the plate thickness reduction rate of the central portion of the branch portion exceeds the molding limit range, and the branch portion is formed. This is an example in which the plate thickness reduction rate on both sides is within the molding limit range.
In the case of Conventional Example 2, the plate thickness reduction rate of the a part and the b part is less than 20% of the molding limit, but the plate thickness reduction rate of the o part exceeds the molding limit of 20%. Therefore, in the press molding method of Conventional Example 2, it was determined that cracks did not occur in the a part and the b part, but cracks occurred in the o part.

Next, in the case of the comparative example, the plate thickness reduction rate was less than 20% of the molding limit in all of the a part, the b part, and the o part, and it was determined that cracking did not occur in any place, but in the b part. The value was close to 20% of the molding limit.

On the other hand, in the case of the invention example, the plate thickness reduction rate was less than 20% of the molding limit in all of the a part, the b part, and the o part, and it was determined that no cracking occurred at any place. Furthermore, the plate thickness reduction rate was improved at each site as compared with the comparative example, and better results were obtained.
As described above, from the results of this embodiment, it was found that the tip of the vertical wall portion at the center of the branch portion of the press-molded product having a bifurcated shape such as the lower arm and the cracking at both sides of the branch portion can be prevented at the same time. rice field.

Further, from the above, it can be seen that the bending radius of the central portion of the branch portion and the both side portions of the branch portion of the second bent portion 11 may be set as follows.
That is, the bending radii of the branch portion center portion and the branch portion both side portions of the second bending portion 11 are made the same, and the values are variously changed to obtain the plate thickness reduction rate of the rest-like bottom dead point. An example (A value) in which the bending radii of both sides of the branch portion are the same, the plate thickness reduction rate of the central portion of the branch portion is within the molding limit range, and the plate thickness reduction rate of both sides of the branch portion exceeds the molding limit. , An example (B value) in which the plate thickness reduction rate at the central portion of the branch portion exceeds the molding limit range and the plate thickness reduction rate at both sides of the branch portion is within the molding limit is obtained in advance, and bending of the central portion of the branch portion is performed. The radius should be less than or equal to the A value within the molding limit range, the bending radius on both sides of the branch should be greater than or equal to the B value within the molding limit range, and the bending radius at the center of the branch should be smaller than the bending radius on both sides of the branch. It is good to set.

1 Top plate part 2 1st bent part 3 Vertical wall part 5 Press-molded product 7 Intermediate molded product 9 Intermediate vertical wall part 11 2nd bent part 13 Shelf part 15 Punch 15a Punch shoulder part 17 Pad 19 Die 19a Die shoulder part 21 No. 1 Mold 23 Branch part 25 Flange part 27 Upper blade 29 Lower blade 31 Plate holder 33 Trim mold 35 Punch 37 Pad 39 Die 41 Second mold

Claims (2)

A press-molding method for press-molding a press-molded product having a top plate portion having a bifurcated shape in a plan view and a vertical wall portion continuous with the top plate portion.
With the metal plate pressed against the punch with a pad, the top plate portion, the intermediate vertical wall portion that is continuous from the top plate portion via the first bent portion, and is the base end side of the vertical wall portion, and the intermediate portion. The first molding step in which the punch and the die cooperate to overhang and mold a shelf portion continuous from the vertical wall portion via the second bent portion.
The trim process of removing unnecessary parts from the shelf part and leaving the flange part,
A second molding step of bending back the second bent portion to form the vertical wall portion including the intermediate vertical wall portion and the portion corresponding to the flange portion is provided.
In the first forming step, the bending radius R ₁ of the entire branch portion in the first bending portion, the bending radius R _2C of the central portion of the branch portion in the second bending portion, and the central portion of the branch portion in the second bending portion. A press molding method characterized in that the bending radii R _2S of the portions on both sides in the bending ridge line direction satisfy the relationship of R _2C <R _2S <R ₁ . A press-molding die for realizing the press-molding method according to claim 1.
The top plate portion, an intermediate vertical wall portion that is continuous from the top plate portion via the first bent portion and is the base end side of the vertical wall portion, and continuous from the intermediate vertical wall portion via the second bent portion. The first mold for molding an intermediate molded product having a shelf portion to be molded,
A trim mold that removes unnecessary parts from the shelf and forms the flange part,
A second mold for forming the vertical wall portion including the intermediate vertical wall portion and the portion corresponding to the flange portion by bending back the second bent portion is provided.
The first mold includes a punch having a punch shoulder portion for forming the first bent portion, a pad arranged facing the punch and pressing a metal plate against the punch, and a die for forming the second bent portion. With a die with a shoulder,
The radius of curvature R _P of the punch shoulder, the radius of curvature R _DC of the portion of the die shoulder that forms the central portion of the branch of the second bend, and the branch of the second bend in the die shoulder. A press molding mold characterized in that the radius of curvature R _DS of the portion forming both sides in the bending ridge direction of the central portion is set so as to satisfy the relationship of R _DC <R _DS < _RP .

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