JP7276307B2 - Press molding method and press molding die - Google Patents

Description

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

Among press-formed products, for example, there is a product that includes a top plate portion that has a bifurcated shape in a plan view and a vertical wall portion that is continuous with the top plate portion, such as a lower arm that is an underbody part of an automobile. . An example of such a press-formed product will be described with reference to FIG.
A press-formed product 5 shown in FIG. 8 has a top plate portion 1 having a bifurcated shape in plan view, and a vertical wall portion 3 continuous with the top plate portion 1 . Hereinafter, such a bifurcated portion of the press-formed 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. Due to flange deformation, stretch flange cracks are likely to occur at the tip of the vertical wall portion 3 (portion o surrounded by a dashed circle in the figure).

In order to avoid stretch flange cracking as described above, such a press-formed product 5 is generally manufactured in a plurality of steps as described below.
First, a top plate portion 1 and a vertical wall portion 3 continuous from the top plate portion 1 via a first bent portion 2 are formed by form molding or the like by pressing a blank (metal plate) with a pad, 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 a second bent portion 11 is overmolded (first molding step).

Next, as shown in FIG. 10, the panel is trimmed along a predetermined trim line, unnecessary portions (hatched portions in the drawing) 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 (restrike), the vertical wall portion 3 composed of the portion corresponding to the intermediate vertical wall portion 9 and the flange portion 25 is formed (second forming step ) to produce the press-formed product 5 shown in FIG. The portion shown in gray in FIG. 8 is the portion corresponding to the second bent portion 11 bent back in the second forming step.

In the above-described method, by interposing the intermediate molded product 7 molded in the first molding step (stretch molding), the amount of stretch flanging deformation during the subsequent second molding step (restrike) is reduced. Furthermore, since the intermediate molded product 7 is provided with a surplus portion (a portion to be removed in the trimming process), the portion corresponding to the portion o shown in FIG. Since the material flow is suppressed in the second forming step, stretch flange cracking occurring at the o portion can be suppressed.
As such a press forming method, Patent Document 1 discloses an example in which stretch forming and trimming are performed in the same step.

JP 2017-217698 A

For press-formed products such as lower arms having various shapes, depending on the shape of the branch portion 23, not only the tip (o portion) of the vertical wall portion 3 formed at the center portion of the branch portion but also the vicinity of the center portion of the branch portion Parts bent back in the second forming step (parts on both sides of the central part of the branch in the bending ridgeline direction, which are parts a and b surrounded by dashed circles in FIG. 8, hereinafter simply referred to as "both sides of the branch") Also, cracks occur during molding. The inventors conducted molding analysis and press molding experiments using the finite element method, and clarified the reason why cracks occur in the parts a and b.

11(a) is an A'-A' sectional view of the intermediate molded product 7 shown in FIG. 10, and FIG. 11(b) is an AA sectional view of the press-formed product 5 shown in FIG. be. The A'-A' cross-sectional view and the AA cross-sectional view show cross sections of portions corresponding to the part a in the intermediate molded product 7 and the press-molded product 5, respectively.
The intermediate vertical wall portion 9, the second bent portion 11 and the flange portion 25 (see FIG. 11(a)) formed by the first forming step and the trimming step have the second bent portion 11 bent back by the second forming step. As a result, the vertical wall portion 3 is formed as shown in FIG. 11(b). At this time, since work hardening occurs in the portion corresponding to the bent back second bent portion 11, the thickness of the portion indicated by the arrow in the figure is reduced.
Furthermore, since the o-portion, which tends to cause material shortage due to stretch flanging deformation, is in the vicinity (see FIG. 8), a material flow from the a-portion to the o-portion occurs. Cracks occur in the part a due to both the reduction in plate thickness and the material flow. For the same reason, cracks also occur in the b portion.

In order to suppress the cracks that occur in the a part and the b part as described above, the bending radius of the second bent part 11 of the intermediate molded product 7 is increased to reduce the work hardening. should be reduced. However, if the amount of deformation in the first forming step is reduced for both parts a and b as well as part o, the amount of stretch flanging deformation in the subsequent second forming process increases, and cracks are likely to occur in part o. .
In this way, in the conventional technology, cracking of the tip (o part) of the vertical wall part 3 formed in the central part of the branch part and the bent back parts (a part, b part) on both sides of the branch part are prevented at the same time. The problem was that it was difficult to

The present invention has been made to solve such problems, and includes a top plate portion having a bifurcated shape in plan view, such as a lower arm, and a vertical wall portion continuing to the top plate portion. A press molding method and a press molding die capable of simultaneously preventing cracks in both the tip of the vertical wall formed in the center of the bifurcation and the bent back portions on both sides of the bifurcation when molding a molded product. intended to provide

(1) A press-molding method according to the present invention is 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 continuing to the top plate portion. In a state in which the metal plate is pressed against the punch with a pad, the top plate portion and an intermediate vertical wall portion that is continuous from the top plate portion via the first bent portion and becomes the base end side of the vertical wall portion. a first forming step in which the punch and the die work together to overhang the shelf portion continuous from the intermediate vertical wall portion through the second bent portion; and an unnecessary portion is removed from the shelf portion to form a flange and a second forming step of bending back the second bent portion to form the vertical wall portion composed of a portion corresponding to the intermediate vertical wall portion and the flange portion,
In the first forming step, the bending radius R _1C of the central portion of the branch portion in the first bent portion, the bending radius R _1S of the portions on both sides in the bending ridgeline direction of the central portion of the branch portion in the first bent portion, the second bending and the bending radius R _2S of the portions on both sides in the bending ridgeline direction of the central portion of the branch in the second bent portion are _{R 2C <} R _2S and R _2C <R _1C and R _1S ≦R _1C .

(2) A press molding die according to the present invention is for realizing the press molding method described in (1) above, and includes the top plate portion and a first bent portion from the top plate portion. A first mold for molding an intermediate molded product having an intermediate vertical wall portion that is continuous with the vertical wall portion on the base end side, and a shelf portion that is continuous from the intermediate vertical wall portion via the second bent portion; A trim mold that removes an unnecessary portion from the shelf portion to leave the flange portion, and bends back the second bent portion to form the vertical wall portion composed of the portion corresponding to the intermediate vertical wall portion and the flange portion. The first mold includes a punch having a punch shoulder for forming the first bent portion, a pad disposed opposite the punch and pressing a metal plate against the punch, and a die having a die shoulder for forming the second bent portion, wherein the radius of curvature R _PC of a portion of the punch shoulder forming the central portion of the bifurcation of the first bent portion, and the punch shoulder; Curvature radius R _PS of a portion forming both side portions in the bending ridge direction of the branch portion central portion of the first bent portion in the above, Curvature radius R of a portion forming the branch portion central portion of the second bent portion in the die shoulder portion _DC and the curvature radius RDS of the portion forming both side portions in the bending ridgeline direction of the central portion of the branch portion _of the second bent portion in the die shoulder portion are R _DC <R _DS and R _DC <R _PC , Further, it is characterized in that it is set so as to satisfy the relationship R _PS ≦R _PC .

In the present invention, in the first molding step for molding the intermediate molded product, the bending radius R _1C of the central portion of the branch portion in the first bent portion, the bending of the portions on both sides of the bending ridgeline direction of the central portion of the branch portion in the first bent portion The radius R _1S , the bending radius R _2C at the central portion of the branching portion of the second bending portion, and the bending radius R _2S of the portions on both sides of the central portion of the branching portion in the second bending portion in the bending ridgeline direction satisfy R _2C <R _2S , In addition, by molding so as to satisfy the relationships of R _2C < R _1C and R _1S ≤ R _1C , it is possible to promote material flow from the first bent portion toward the second bent portion at the central portion of the branch portion. In addition, it is possible to suppress the reduction in plate thickness of the bent back portions on both side portions of the branch portion while suppressing the amount of stretch flanging deformation in the second forming step of the central portion of the branch portion. As a result, it is possible to simultaneously prevent cracks at the tip of the vertical wall formed in the central portion of the bifurcation and at the bent back portions on both sides of the bifurcation.

BRIEF DESCRIPTION OF THE DRAWINGS 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 metal mold|die used for this. 3(a) is a cross section OO of FIG. 1(a), and FIG. 3(b) is a cross section PP of FIG. 1(a). is an explanatory diagram for explaining the relationship between bending radii. FIG. 1(a) is a view showing the OO cross section and the PP cross section at the second bent portion, explaining the difference between the bending radius of the central portion of the branching portion and the bending radius of both side portions of the branching portion of the second bending portion. It is an explanatory diagram for. It is explanatory drawing explaining the material flow which arises in a branch part center part and a branch part both sides. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of a trimming process and a trimming die used in the trimming process according to one embodiment of the present invention; It is explanatory drawing of the 2nd molding process which concerns on one embodiment of this invention, and the 2nd metal mold|die used for this. It is explanatory drawing explaining the subject which arises in the formation process of the target shape which concerns on one embodiment of this invention, and this target shape. It is explanatory drawing of the conventional press molding method (part 1). It is explanatory drawing of the conventional press molding method (the 2). FIG. 9 is an explanatory diagram for explaining the reason why cracks occur in parts a and b in the process of forming the target shape shown in FIG. 8 ;

In the press-molding method according to the present embodiment, a press-formed product 5 (see FIG. 8) having a top plate portion 1 having a bifurcated shape in plan view and a vertical wall portion 3 continuing to the top plate portion 1 is formed. As shown in FIG. 1, a metal plate is molded into an intermediate molded product 7 in a first molding step S1, and an unnecessary part is removed from the intermediate molded product 7 molded in the first molding step S1. It comprises a trimming step S3 and a second forming step S5 for forming the intermediate molded product 7 from which unnecessary portions are removed in the trimming step S3 into a target shape.
Each step will be described below. In FIG. 1, the same reference numerals are given to the same parts as those in FIGS.

<First molding step>
The first molding step S1 is a step of molding an intermediate molded product 7 as shown in FIG. It has an intermediate vertical wall portion 9 that is continuous through the vertical wall portion 3 and is on 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 through the second bent portion 11 .

In the first forming step S1 for forming such an intermediate molded product 7, as shown in FIG. This is performed by a first die 21 comprising a pad 17 for pressing the metal plate against the punch 15 and a die 19 having a die shoulder 19a for forming the second bent portion 11 .

FIG. 2(a) is an OO cross section (see the enlarged view of FIG. 1(a)) which is a cross section of the central part of the branch part of the intermediate molded product 7, and FIG. 1A) is a view showing the state of the molding bottom dead center of the PP cross section (see the enlarged view of FIG. 1(a)), which is the cross section of the part a side). The cross section of the other side of the branching portion (the side of the b portion) is the same as the cross section of the other side (the side of the a portion), so the illustration is omitted.
As can be seen by comparing FIG. 2(a) and FIG. 2(b), regarding the die shoulder portion 19a forming the second bent portion 11, the curvature radius R of the portion forming the central portion of the branch portion of the second bent portion 11 is _DC (hereinafter simply referred to as “die shoulder R _DC ”) is set smaller than the curvature radius R _DS (hereinafter simply referred to as “die shoulder R _DS ”) of the portion forming both side portions of the branch portion of the second bent portion 11 . (R _DC < R _DS ).
On the other hand, regarding the punch shoulder portion 15a that forms the first bent portion 2, the curvature radius R _PS (hereinafter simply referred to as the “punch shoulder R _PS ”) of the portion that forms both side portions of the branch portion of the first bent portion 2 is the highest. It is set to be less than the radius of curvature R _PC (hereinafter simply referred to as "punch shoulder R _PC ") of the portion forming the central portion of the branched portion of 1 bent portion 2 (R _PS ≤ R _PC ).
Furthermore, the die shoulder R _DC at the center of the branch is set smaller than the punch shoulder R _PC at the center of the branch (R _DC <R _PC ).
Between the center of the branching portion and both side portions of the branching portion of each of the die shoulder portion 19a and the punch shoulder portion 15a, a shape in which R gradually changes in the direction of the bending ridge line (gradually changing portion, enlarged view in FIG. 1(a)). It has become.

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

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 the OO cross section and the PP cross section, respectively, of the intermediate molded product 7 shown in the enlarged view of FIG. 1(a).
As shown in FIGS. 3(a) and 3(b), the intermediate molded product 7 has a bending radius R 1C at the central portion of the branching portion of the first bending portion 2 and a bending radius R _1C at both side portions of the branching portion of the first bending portion 2 . The radius R _1S , the bending radius R _2C of the central portion of the branch portion of the second bent portion 11 , and the bending radius R _2S of both sides of the branch portion of the second bent portion 11 satisfy R _2C <R _2S and R _2C < The relationship is R _1C and R _1S ≤ R _1C .
In the case of R _1S < R _1C , the first bent portion 2 with the bending radius R _1C at the center of the branch and the first bent portion 2 with the bending radius R _1S at both sides of the branch are bent in the bending ridge direction. It is a gradually changing portion in which the radius gradually decreases from the center toward both sides.
In addition, between the second bent portion 11 having a bending radius of R _2C at the central portion of the branch and the second bending portion 11 having a bending radius of R _2S at both sides of the branch, the bending radius is increased from the center toward both sides in the direction of the bending ridge line. It is a gradual change portion that gradually expands.
The reason why the intermediate molded product 7 is shaped as described above will be described below with reference to FIGS. 3 to 5. FIG.

FIG. 4 shows the OO cross section (solid line) and the PP cross section (broken line) of the second bent portion 11 in the enlarged view of FIG. be.
As shown in FIG. 4, by decreasing the bending radius (R _2C ) of the second bent portion 11 at the center of the branch and increasing the bending radius (R _2S ) of both sides of the branch, The line length (distance of solid line from point X to point Y) is long, and the line length (distance of broken line from point X to point Y) on the PP cross section is short. Therefore, in the first forming step S1, the amount of deformation at the central portion of the branch portion is larger than that at both side portions of the branch portion.
Note that the X point and the Y point are points common to both cross sections when the two 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 side portions of the branch portion (R _2C <R _2S ), and the first bending portion in the first forming step S1 The reason why the amount of deformation at the central portion of the bifurcation portion of the 2-bent portion 11 is greater than that at both side portions of the bifurcation portion is as follows.

In the press forming method of the present embodiment, the vertical wall portion 3 is formed in the center portion of the branch portion 23 by the first forming step S1 and the second forming step S5. Therefore, if the amount of deformation in the first forming step S1 is large, the amount of deformation in the second forming step S5 will be small.
Therefore, by forming the intermediate molded product 7 with a large deformation amount (larger area) at the central part of the branch part, the amount of stretch flanging deformation in the second forming step S5 is reduced, and o shown in FIG. Cracking of the part is suppressed.

On the other hand, on both sides of the branch portion, the bending radius _R2S is increased to suppress the amount of deformation of the intermediate molded product 7 during molding. Furthermore, as described above, the stretch flanging deformation that occurs in the o portion in the second forming step S5 is also reduced, so the material flow from both sides of the branch portion toward the o portion is also alleviated, and bending in the second forming step S5 Even if it returns, the crack of the a part and b part which were shown in FIG. 8 is suppressed.

In _{addition ,} in the intermediate molded product 7, as shown in FIG. Also, the bending radius of both side portions of the branch portion of the first bent portion 2 is equal to or greater than R _1S (R _2C <R _1C , R _1S ≤R _1C ). The reason why the first bent portion 2 is shaped as described above will be described below with reference to FIG.

FIG. 5 schematically shows the shapes of the first bent portion 2 and the second bent portion 11 of the portion shown in the enlarged view of FIG. 1(a).
FIG. 5(a) shows a comparative example in which the bending radius of the central part of the first bending part 2 and the bending radius of both side parts of the branching part are equal, and the bending radius R of the central part of the branching part of the second bending part 11 is the same. _2C (R _1S =R _1C <R _2C ).
FIG. 5B shows an example of the present embodiment, and as described above, the bending radius _R1C of the central portion of the branch portion of the first bent portion 2 is equal to the bending radius R1C of the central portion of the branch portion of the second bent portion 11. It is larger than R _2C and the bending radius R _1S of both sides of the branch portion in the first bent portion 2 (R _2C <R _1C , R _1S <R _1C ).
The arrows in the drawing indicate the material flow during the molding of the intermediate molded product 7 .
FIG. 5(c) shows another example of the present embodiment, and as described above, the bending radius _R1C of the central portion of the branch portion of the first bent portion 2 is equal to that of the central portion of the branch portion of the second bent portion 11. It is larger than the bending radius R _2C and equivalent to the bending radius R _1S of both sides of the bifurcation of the first bent portion 2 (R _2C <R _1C , R _1S =R _1C ). The bending radius R _1S of both sides of the branching portion of the first bent portion 2 may be smaller than the bending radius R _2S of both sides of the branching portion of the second bent portion 11 . In the figure, the longer the length of the arrow, the more material flows in that portion.

As can be seen by comparing FIG. 5(a) with FIGS. 5(b) and 5(c), in the present embodiment, the bending radius _R1C of the central portion of the branch portion of the first bending portion 2 is set to the second bending portion. By making the bending radius R 2C larger than the bending radius R _2C at the central portion of the branching portion of the portion 11 (R _2C <R _1C ), the material flow from the first bending portion 2 to the second bending portion 11 at the central portion of the branching portion increases.
This is because by increasing the bending radius, the material of the first bent portion 2 tends to flow out, and the material tends to be pulled toward the second bent portion 11 having a smaller bending radius.

In addition, compared with the case where the bending radius at the first bent portion 2 is the same at the center of the branch and on both sides of the branch (R _1S =R _1C ) (Fig. 5(c)), the bending radius at both sides of the branch is reduced to By making it smaller than the central part of the branch (R _1S <R _1C ) (FIG. 5(b)), the material flow on both sides of the branch is suppressed, and the material flow toward the second bent part 11 at the central part of the branch is further promoted.

As described above, the bending radius R _1C of the central portion of the branching portion of the first bending portion 2 is set to the bending radius R _2C of the central portion of the branching portion of the second bending portion 11 and the bending By making the radius R _1S or more (R _2C <R _1C , R _1S ≤ R _1C ), the flow of the material into the second bent portion 11 is promoted at the central portion of the branch portion, and the o portion at the time of the second forming step S5 cracking is further suppressed.

<Trim process>
The trim step S3 is a step of removing an unnecessary portion from the shelf portion 13 of the intermediate molded product 7 formed in the first forming step S1 to form the flange portion 25. As shown in FIG.

FIG. 6 is a diagram showing a state in the middle of trimming in the BB section of FIG. 1(b).
The trim step S3 is performed by a trim die 33 having an upper blade 27, a lower blade 29, and a plate retainer 31, as shown in FIG. The upper blade 27 and the lower blade 29 work together to remove unnecessary portions from the shelf 13 of the intermediate molded product 7, and each trim blade (trim blade) has 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 formed in the first forming step S1 is held between the lower blade 29 and the plate retainer 31, and for example, the upper blade 27 is initially held. A flange portion 25 is formed by relatively moving downward from a position (not shown) and cutting off an unnecessary portion (the hatched portion in FIG. 1B) from the shelf portion 13 .

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

FIG. 7 is a view showing the state of the restrike bottom dead center in the CC 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 unnecessary portions have been removed in the trimming step S3. Bend back.

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

As described above, in the first forming step S1, the amount of deformation of the central portion of the branch portion is increased, so in the second forming step S5, the amount of stretch-flange deformation of the central portion of the branch portion is reduced.
In addition, since the amount of deformation on both sides of the branch portion of the second bent portion 11 is reduced in the first forming step S1, the plate thickness reduction and work hardening when bending back are reduced, and the second forming step S5 When the second bent portion 11 is bent back, cracks are less likely to occur.

As described above, in the present embodiment, in the first forming step S1, the bending radius R _1C of the central portion of the branch portion of the first bent portion 2, the bending radius R _1S of both sides of the branch portion of the first bent portion 2, the The bending radius R _2C at the central portion of the bifurcated portion of the second bent portion 11 and the bending radius R _2S of both side portions of the bifurcated portion of the second bent portion 11 are R _2C <R _2S and R _2C <R _1C , and After forming so as to satisfy the relationship R _1S ≤ R _1C , removing unnecessary portions 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 stretch flanged. The part that becomes deformed is molded.

As a result, at the central portion of the bifurcation of the second bent portion 11, by increasing the amount of deformation during molding of the intermediate molded product 7, stretch flanging deformation during molding of the press-formed product 5 is suppressed. It is possible to prevent cracks from occurring at the tip of the wall portion 3 . Furthermore, during the molding of the intermediate molded product 7, the flow of material from the first bent portion 2 to the intermediate vertical wall portion 9 is promoted, so that the second bent portion 11 can be stretched strongly, and the pressing can be performed. A higher effect of preventing stretch-flange cracking can be obtained when molding the molded product 5 .

In addition, on both sides of the bifurcation of the second bent portion 11, by reducing the amount of deformation during molding of the intermediate molded product 7, reduction in plate thickness and work hardening of the bent back portion during molding of the press-formed product 5 are suppressed. In addition, since the stretch-flange deformation of the central portion of the branch portion is suppressed, the material flow toward the stretch-flange portion is also alleviated, so cracks occurring in the bend-back portion can be prevented.

In the above description, an example in which press molding is performed by dividing it into three steps has been described, but the present invention is not limited to this. may be performed in two steps. For example, if the punch 15 and the die 19 in the first forming step S1 are respectively provided with trim blades, the intermediate molded product 7 can be molded and at the same time the unnecessary parts can be removed.

Further, the vertical wall portions other than the branching portion 23 may be formed while the above-described three steps are being performed, or may be formed in a separate step without causing any problem in carrying out the present invention. Also, the molding of the top plate portion 1 is the same.

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

As a conventional example, two types of analysis were performed on the second bent portion 11 of the intermediate molded product 7 in which the bending radii of the central portion of the bifurcation portion and both side portions of the bifurcation portion were the same. The bending radius of the second bent portion 11 in the conventional example was set to 5 mm (conventional example 1) or 7 mm (conventional example 2) for both the central portion of the branch portion and both side portions of the branch portion. Further, the bending radius of the first bent portion 2 was set to 7 mm for both Conventional Example 1 and Conventional Example 2. FIG. Here, the bending radius is the radius of the circular arc at the plate thickness central portion (the same shall apply hereinafter).

Further, as Example 1 of the present invention, the bending radius of the central portion of the branching portion of the second bent portion 11 of the intermediate molded product 7 is smaller than the bending radius of both side portions of the branching portion, and the bending radius of the central portion of the branching portion of the first bent portion 2 is The radii smaller than the bending radii of both sides of the bifurcation were analyzed. The bending radius of the second bent portion 11 in Example 1 of the present invention was 5 mm at the central portion of the branch portion and 7 mm at both sides of the branch portion (parts a and b in FIG. 8). The central portion was 6 mm, and both sides of the bifurcation were 5 mm.

In addition, as an example 2 of the present invention, analysis was performed on the first bend portion 2 in which the bending radius of the central portion of the branch portion and the bending radius of the both side portions of the branch portion were the same as those of the example 1 of the present invention. In Invention Example 2, the bending radius of both sides of the branch portion of the first bent portion 2 was set to 6 mm, and the bending radius of the other portions was set to be the same as in Invention Example 1.
Table 1 shows the maximum plate thickness reduction rates of the parts a, b, and o (see FIG. 8) at the bottom dead center of the second forming step S5 obtained by CAE forming analysis.

According to the past knowledge of the inventors who made prototypes of various shapes of lower arms, in the case of a hot-rolled steel sheet with a thickness of 2.3 mm and a tensile strength of 780 MPa, if the thickness reduction rate exceeds 20% in CAE forming analysis, cracking will occur. Occur. Therefore, the forming limit at which cracks occur in this example was set at a plate thickness reduction rate of 20%.

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 forming limit, but the plate thickness reduction rate of parts a and b exceeds 20% of the forming limit. there is Therefore, it was determined that, in the press forming method of Conventional Example 1, cracks did not occur in the o portion, but cracks occurred in the a portion and the b portion.

Further, in the case of Conventional Example 2, the thickness reduction rate of parts a and b is less than 20% of the forming limit, but the thickness reduction rate of part o exceeds 20% of the forming limit. Therefore, in the press molding method of Conventional Example 2, it was judged that cracks did not occur in the parts a and b, but cracks occurred in the part o.

Next, in the case of Inventive Example 2, the plate thickness reduction rate was less than 20% of the forming limit in all of the parts a, b, and o, and it was determined that cracks did not occur in any of the parts.

On the other hand, in the case of Example 1 of the present invention, the plate thickness reduction rate was less than 20% of the forming limit in all of the parts a, b, and o, and it was determined that cracks did not occur in any of the parts. At the part o, the plate thickness reduction rate was improved as compared with Example 2 of the present invention, and better results were obtained for the prevention of stretch flange cracking.
As described above, from the results of the present example, it was found that cracking of the tip of the vertical wall portion at the center of the branching portion and both sides of the branching portion of the press-formed product having a bifurcated shape in plan view, such as the lower arm, can be prevented at the same time. rice field.

In Conventional Example 1 in Table 1 above, the bending radius of the central portion (o) of the second bent portion 11 and both sides of the branch (a and b) are the same, and the plate thickness of the central portion of the branch is This is an example in which the reduction rate is within the forming limit range, but the plate thickness reduction rate on both sides of the branch exceeds the forming limit range.
Further, in Conventional Example 2 in Table 1, the bending radius of the central portion of the branching portion of the second bent portion 11 and both side portions of the branching portion are the same, and the plate thickness reduction rate of the central portion of the branching portion exceeds the forming limit range. This is an example in which the plate thickness reduction rate of both sides is within the forming limit range.
Then, from Conventional Example 1, the bending radius at the central portion of the branch portion of the second bent portion 11 is preferably smaller, so the value set in Conventional Example 1 or less is set, and from Conventional Example 2, the second bent portion 11 It can be seen that the bending radii of both sides of the bifurcated portion should be larger than the value set in Conventional Example 2 because the larger the better.

From this, it can be understood that the bending radii of the central portion of the branching portion of the second bent portion 11 and both side portions of the branching portion should be set as follows.
That is, by setting the bending radius of the central portion of the branch portion of the second bending portion 11 and the bending radius of both side portions of the branch portion to be the same, and by variously changing the value and obtaining the plate thickness reduction rate at the restrike bottom dead center, Example where the bending radii are the same at the part and both sides of the branch, the thickness reduction rate at the central part of the branch is within the forming limit range, and the thickness reduction rate at both sides of the branch exceeds the forming limit (A value) and an example (B value) in which the plate thickness reduction rate at the center of the branch exceeds the forming limit range and the plate thickness reduction rate at both sides of the branch is within the forming limit. is less than or equal to the A value, which is within the forming limit range, and on both sides of the branch portion, it is equal to or more than the B value, which is within the forming limit range, and the bending radius of the central portion of the branch portion is set smaller than the bending radius of both side portions of the branch portion. .

1 top plate portion 2 first bent portion 3 vertical wall portion 5 press-molded product 7 intermediate molded product 9 intermediate vertical wall portion 11 second bent portion 13 shelf portion 15 punch 15a punch shoulder portion 17 pad 19 die 19a die shoulder portion 21 second 1 die 23 branching part 25 flange part 27 upper blade 29 lower blade 31 plate retainer 33 trim die 35 punch 37 pad 39 die 41 second die

Claims (2)

A press-molding method for press-molding a press-molded product having a top plate portion having a bifurcated shape in plan view and a vertical wall portion continuous to the top plate portion,
In a state in which the metal plate is pressed against the punch by a pad, the top plate portion, an intermediate vertical wall portion continuing from the top plate portion via the first bent portion and serving as the base end side of the vertical wall portion, and the intermediate a first forming step in which the shelf portion continuous from the vertical wall portion via the second bent portion is overhang-formed by cooperation of the punch and the die;
a trimming step of removing an unnecessary portion from the shelf portion to leave a flange portion;
A second forming step of bending back the second bent portion to form the vertical wall portion composed of a portion corresponding to the intermediate vertical wall portion and the flange portion,
In the first forming step, the bending radius R _1C of the central portion of the branch portion in the first bent portion, the bending radius R _1S of the portions on both sides in the bending ridgeline direction of the central portion of the branch portion in the first bent portion, the second bending and the bending radius R _2S of the portions on both sides in the bending ridgeline direction of the central portion of the branch in the second bent portion are _{R 2C <} R _2S and R _2C <R _1C and a press forming method characterized by forming so as to satisfy the relationship of R _1S ≦R _1C . 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 a first bent portion and that is on the base end side of the vertical wall portion; and is continuous from the intermediate vertical wall portion via a second bent portion. a first mold for molding an intermediate molded product having a shelf portion that
a trim mold that removes an unnecessary portion from the shelf portion to leave a flange portion;
a second mold that bends back the second bent portion to form the vertical wall portion composed of a portion corresponding to the intermediate vertical wall portion and the flange portion;
The first mold includes a punch having a punch shoulder for forming the first bent portion, a pad arranged opposite the punch for pressing a metal plate against the punch, and a die for forming the second bent portion. a die having a shoulder;
Curvature radius R _PC of a portion of the punch shoulder forming the central portion of the bifurcation of the first bent portion, and both side portions of the bending ridgeline direction of the central portion of the bifurcation of the first bent portion of the punch shoulder are formed. Curvature radius R _PS of the part that forms the branch part center part of the second bent part in the die shoulder R _DC , and the branch part center part of the second bent part in the die shoulder The curvature radius R _DS of the portion forming both side portions in the bending ridge direction is set so as to satisfy the relationships of R _DC < R _DS , R _DC < R _PC , and R _PS ≤ R _PC Characteristic press mold.

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