JP2020199539A - Press molding method for vehicular member component and press die therefor - Google Patents

Abstract

To provide a press molding method for a vehicular member component, by which die durability can be ensured and spring back, warp, etc. of the entire vertical wall portion can effectively be prevented, and to provide a press die therefor.SOLUTION: A press molding method for forming a vehicular member component M including a central part M1 and a vertical wall part M2 formed by bending a steel plate W comprises: a lower die 1 having a lower die punch 11 and a lower die cushion 12; and an upper die 2 having an upper die bending blade 21 and an upper die pad 22. The lower die cushion has, at an inner peripheral edge of a flange pressing part 121, a projecting molding part 122 projecting toward outside of the plate beyond a vertical wall molding part 111 of the lower die punch. The upper die bending blade has a recess molding part 212 that cooperates with a projection molding part in an upper part of a die R part 21R. When the upper die is moved downward to a position very close to a bottom dead point, the projection molding part and the recess molding part bend a leading-end flange part W1 of the steel plate into a step shape, thereby forming a level difference formation part M3 on the leading-end side of the vertical wall part. The upper die is moved downward to the bottom dead point while the projection molding part and the recess molding part keep gripping the level difference formation part.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for press-molding a member part for a vehicle and a press die thereof. Specifically, the present invention is a method for press-molding a member part for a vehicle formed in a substantially hat cross-sectional shape (including a substantially U-shaped cross-sectional shape) and a press thereof. Regarding the press die used for the molding method.

In recent years, as one of the measures to achieve both weight reduction and high strength of pressed parts constituting an automobile body, high-tensile steel sheets (for example, tensile strength: 590 MPa or more) have been promoted. However, in a vehicle member part having a substantially hat cross-sectional shape formed by drawing or bending a steel plate, springback, warpage, etc. are likely to occur in the vertical wall portion forming the substantially hat cross-sectional shape. For springback and warpage in this vertical wall, the residual stress (stress difference between inside and outside of the plate thickness) due to bending and back bending at the die R part of the press die during molding (drawing, bending) is the vertical wall part. It is known that the higher the tenth of the steel sheet, the more remarkable the occurrence.

For example, Patent Document 1 discloses a press working method for efficiently removing residual stress that causes springback, warpage, and the like in the vertical wall portion, and a press die thereof. That is, as shown in FIGS. 13A and 13B, the steps of forming the steel plate W0 into a hat cross-sectional shape by bending and further applying tension to the vertical wall portion W01 of the hat cross-sectional shape are continuously performed. A bending molding method and a mold 100 thereof are disclosed. The mold 100 has a pair of mold structures having an upper mold 101 and a lower mold 102, and the upper mold 101 has a pad 103 and a spring 104 for generating a reaction force of the pad 103. A part of the punch 105 of the lower die 102 is formed as a cushion 106, and the cushion 106 forms a part 106b of the vertical wall forming surface of the lower die 102. Further, a part 106b of the vertical wall forming surface has a shape that takes into consideration the prospect of the mold before the completion of molding, and a shape that does not consider the prospect of the mold at the time of completing the molding, depending on the position of the cushion 106. .. Then, between the start of deformation of the steel plate W0 and the completion of mold clamping by the cushion 106 and the spring 107 that supports the cushion 106 at a height at which the cushion 106 abuts on the steel plate W0 when the bending molding has progressed to some extent. A binding force control means for applying the binding force to the product portion of the steel sheet W0 or the minimum range adjacent to the product portion while gradually increasing the binding force is configured. Further, a protrusion 106c having a saw-toothed cross section is provided on the surface of the cushion 106 facing the vertical wall forming surface of the upper die 101. The protrusion 106c constitutes a second binding force control means that prevents the inflow of the steel plate W0 by biting into the steel plate W0.

Japanese Patent No. 3772965

However, according to the press processing method described in Patent Document 1, a part 106b of the vertical wall forming surface in the cushion 106 has a shape in consideration of the prospect of the mold before the completion of the mold clamping, depending on the position of the cushion 106. Since the shape does not consider the prospect of the mold at the time of the completion of mold clamping, a part 106b of the vertical wall forming surface of the cushion 106 is a steel plate with the vertical wall forming surface of the upper mold 101 before the completion of mold clamping. It is possible to pinch W0 in the plate thickness direction, but when the mold clamping is completed, the residual stress of the vertical wall portion W01 (stress inside and outside the plate thickness) due to bending and unbending by the die R portion 101a of the upper die 101. It was difficult to apply the tension in the vertical direction orthogonal to the plate thickness direction required for removing the difference) to the vertical wall portion W01 with which a part 106b of the vertical wall forming surface of the cushion 106 abuts. Therefore, the residual stress (stress difference between the inside and outside of the plate thickness) of the entire vertical wall portion W01 could not be removed, and the springback and warpage of the entire vertical wall portion W01 could not be eliminated.

Further, even if an attempt is made to increase the tension in the vertical direction with respect to the entire vertical wall portion W01 by forming the radius of curvature of the die R portion 101a small, the smaller the radius of curvature of the die R portion 101a, the closer to the die R portion 101a. In, local elongation is likely to occur, and the tension in the vertical direction is absorbed by this local elongation, so that the effect of increasing the tension in the vertical direction with respect to the entire vertical wall portion W01 can hardly be obtained. Further, as the radius of curvature of the die R portion 101a is reduced, the difference between the inside and outside of the plate in the residual stress of the vertical wall portion W01 due to bending and unbending by the die R portion 101a increases, and springback and the like increase. There is a problem that the amount is increased and the durability of the die R portion 101a is lowered. Further, the surface of the cushion 106 facing the vertical wall forming surface of the upper die 101 is provided with a protrusion 106c having a sawtooth blade-like cross section, but such a protrusion 106c is easily worn and is not practical. ..

The present invention has been made to solve the above problems, and is a method for press-molding a member part for a vehicle, which can secure mold durability and effectively eliminate springback and warpage of the entire vertical wall portion. The purpose is to provide the press die.

In order to achieve the above object, the press molding method for vehicle member parts and the press die thereof according to the present invention have the following configurations.
(1) A lower die having a lower die punch formed in a substantially hat cross-sectional shape and a lower die cushion having a flange holding portion formed on the outer peripheral side of the vertical wall molded portion of the lower die punch and being pressure-supported so as to be vertically movable. It has a mold, an upper die bending blade formed so as to face the lower die punch, and an upper die pad arranged on the inner peripheral side of the upper die bending blade and formed so that a steel plate can be pressed against the lower die punch. Equipped with an upper mold,
When the upper die facing the lower die descends from the top dead center to the bottom dead center, the lower die punch and the upper die bending blade are brought close to each other to bend the steel sheet, thereby forming a central portion and the central portion thereof. It is a press forming method of a member part for a vehicle formed into a substantially hat cross-sectional shape having vertical wall portions standing on both sides.
The lower mold cushion is provided with a convex molding portion that stands on the inner peripheral edge of the flange holding portion and projects stepwise from the vertical wall molding portion of the lower mold punch to the outside of the plate, and the upper mold bending blade has a die. A concave forming portion for narrowing the steel plate in cooperation with the convex forming portion is provided on the upper part of the R portion.
When the upper die is lowered to just before the bottom dead center, the convex molded portion and the concave molded portion bend the tip flange portion of the steel sheet in a stepped manner to form a stepped portion on the tip side of the vertical wall portion. It is characterized in that the upper mold is lowered to the bottom dead center in a state where the convex molded portion and the concave molded portion grip the stepped portion.

In the present invention, the lower die cushion is provided with a convex molded portion that stands on the inner peripheral edge of the flange holding portion and projects stepwise from the vertical wall formed portion of the lower die punch to the outside of the plate, and the upper die bending blade is provided with a convex molded portion. The upper part of the die R portion is provided with a concave forming portion that narrows the pressure of the steel sheet in cooperation with the convex forming portion, and when the upper mold is lowered to just before the bottom dead point, the convex forming portion and the concave forming portion are the tip flanges of the steel plate. A step-shaped portion is formed on the tip side of the vertical wall portion by bending the portion in a step shape, and the upper mold descends to the bottom dead point while the convex molded portion and the concave molded portion grip the step-shaped portion. The difference in residual stress generated on the outside and inside of the vertical wall due to bending and unbending of the steel plate by the upper bending blade acts through the stepped shape formed on the tip side of the vertical wall. It can be effectively eliminated by the tension in the direction, and the vertical wall portion can be frozen in a regular cross-sectional shape. Therefore, springback, warpage, and the like that occur in the vertical wall portion of the vehicle member parts can be eliminated over the entire vertical wall portion.

Further, since the upper die bending blade is provided with a concave forming portion that narrowly presses the steel plate in cooperation with the convex forming portion at the upper part of the die R portion, the steel plate bent by the upper die bending blade is a concave forming portion. It will come into contact with the die R portion of the upper bending blade diagonally via. Therefore, the amount of bending and handling of the steel sheet by the upper die bending blade can be dispersed or reduced as compared with the case where the steel sheet directly abuts on the die R portion of the upper die bending blade. As a result, the load on the upper bending blade due to the bending of the steel sheet can be reduced, and the durability of the upper bending blade can be improved.

Therefore, according to the present invention, it is possible to provide a method for press-molding a member part for a vehicle, which can secure mold durability and effectively eliminate springback, warpage, etc. of the entire vertical wall portion.

(2) In the press molding method for vehicle member parts described in (1),
The stepped portion includes a first bent portion that bends from the vertical wall portion to the outside of the plate at an obtuse angle, and a second bent portion that bends from the first bent portion to the inside of the plate at an obtuse angle. Prepare,
The bending clearance between the convex molded portion and the concave molded portion is substantially the same as the plate thickness of the steel plate.

In the present invention, the stepped portion includes a first bent portion that bends from the vertical wall portion to the outside of the plate at an obtuse angle, and a second bent portion that bends from the first bent portion to the inside of the plate at an obtuse angle. Since the bending clearance between the convex molded portion and the concave molded portion is substantially the same as the plate thickness of the steel plate, local elongation due to bending at each bent portion inside and outside the plate of the steel plate can be obtained. The plate thickness is unlikely to decrease. Further, on the inner side and the outer side of the plate in each bent portion, the frictional force due to the bending acts substantially evenly between the convex molded portion and the concave molded portion. Therefore, the tension in the vertical direction can be stably and equally applied from the stepped portion to the inside and outside of the plate of the vertical wall portion. As a result, the difference between the inside and outside of the plate of the residual stress generated in the entire vertical wall due to bending and unbending of the steel plate can be eliminated more stably, and the springback and warpage of the entire vertical wall are more stable. Can be resolved.

(3) In the press molding method for vehicle member parts according to (1) or (2).
The shoulder R portion of the convex molding portion and the die R portion of the concave molding portion are each formed with the same radius of curvature, and the convex molding portion and the concave molding portion form the stepped portion in a substantially S shape. It is characterized in that it is curved and gripped.

In the present invention, the shoulder R portion of the convex molding portion and the die R portion of the concave molding portion are formed with the same radius of curvature, and the convex molding portion and the concave molding portion form a substantially S-shaped stepped portion. Since it is curved and gripped, it is possible to avoid a local decrease in the thickness of the steel sheet, and the surface pressure when the convex molded portion and the concave molded portion grip the stepped portion is the same as the shoulder radius portion of the convex molded portion. It can be dispersed substantially uniformly with the die R portion of the concave molding portion. Therefore, the wear resistance (durability) of the convex molded portion and the concave molded portion can be further improved.

(4) In the press molding method for vehicle member parts according to any one of (1) to (3).
When the upper mold descends from immediately before the bottom dead center to the bottom dead center, the vertical wall portion is extended to the plastic deformation region while the convex molded portion and the concave molded portion grip the stepped portion. It is characterized by.

In the present invention, when the upper die descends from immediately before the bottom dead center to the bottom dead center, the vertical wall portion is stretched to the plastic deformation region while the convex molded portion and the concave molded portion grip the stepped portion. , It is possible to pull to the plastic deformation area including the elastic deformation area remaining near the bending neutral line of the vertical wall part, and the difference in residual stress is more reliably eliminated in the entire area from the inside of the plate to the outside of the plate of the vertical wall part. Can be made to.

(5) In the press molding method for vehicle member parts according to any one of (1) to (4).
The tip of the stepped portion is characterized in that a flange portion extending to the outside of the plate is formed with respect to the vertical wall portion.

In the present invention, since the flange portion extending to the outside of the plate with respect to the vertical wall portion is formed at the tip portion of the stepped portion, the lower end portion of the upper bending blade and the flange retainer of the lower cushion A flange portion can be interposed between the portions, and the bending clearance between the convex molded portion provided on the lower mold cushion and the concave molded portion provided on the upper mold bending blade is set to the bottom dead center from the time of bending the stepped portion. It can be stably maintained up to, and the reduction in the thickness of the stepped portion can be further prevented. Further, the rigidity of the step-shaped portion can be increased by the flange portion formed at the tip of the step-shaped portion. Therefore, when the upper die descends to the bottom dead center, the vertical tension can be more stably applied from the stepped portion to the vertical wall portion. As a result, springback, warpage, and the like that occur in the entire vertical wall portion of the vehicle member parts can be eliminated more stably.

(6) A press die used in the press molding method for vehicle member parts according to any one of (1) to (5).
The lower mold cushion is provided with a cushion plate to which a lower mold bending blade in which the convex molded portion and the flange holding portion are connected is fixed, and the upper mold is fixed to a bending blade to which the upper mold bending blade is fixed. Equipped with blocks
In the lower mold, the lower mold main body, the outer end portion of the cushion plate fixed to the lower mold main body, and the outer end portion of the bending blade fixing block are formed at least from immediately before the bottom dead center to the bottom dead center. It is characterized by including a guide member that guides in the vertical direction.

In the present invention, the lower mold cushion is provided with a cushion plate for fixing the lower mold bending blade in which the convex molding portion and the flange holding portion are connected, and the upper mold is fixed to the bending blade with the upper mold bending blade fixed. The lower mold is provided with a block, and the lower mold body, the outer end portion of the cushion plate fixed to the lower mold main body, and the outer end portion of the bending blade fixing block are killed from at least immediately before the bottom dead center. Since it is provided with a guide member that guides the convex molded portion in the vertical direction up to the point, the convex molded portion and the concave molded portion form a stepped portion, and the bending clearance between the convex molded portion and the concave molded portion in the gripped state is further increased. It can be maintained stably. Therefore, when the upper mold descends from immediately before the bottom dead center to the bottom dead center, tension in the vertical direction can be more stably applied from the stepped shape portion to the vertical wall portion, and the mold durability is improved. be able to. As a result, springback, warpage, and the like that occur in the entire vertical wall portion of the vehicle member parts can be eliminated more stably.

Therefore, according to the present invention, it is provided a press die used for a press forming method of a member part for a vehicle, which can secure mold durability and effectively eliminate springback and warpage of the entire vertical wall portion. Can be done.

(7) The press die according to (6).
The lower punch has a lower punch head on which the vertical wall forming portion is formed and a lower punch fixed to the lower body and integrally formed with a narrow width with respect to the lower punch head. Equipped with legs
The lower punch leg is characterized in that a regulating surface is formed which comes into contact with the inner end surface of the convex molded portion and regulates the bending of the convex molded portion to the inside of the plate.

In the present invention, the lower punch has a lower punch head on which a vertical wall molding portion is formed and a lower mold fixed to the lower body and integrally formed with a narrow width with respect to the lower punch head. The lower punch leg is provided with a punch leg, and the lower punch leg is formed with a regulating surface that comes into contact with the inner end surface of the convex molded portion and regulates the bending of the convex molded portion to the inside of the plate. Convex molding formed thinly by standing upright on the flange holding portion, with the regulation surface of the lower punch leg regulating the bending of the convex molding portion to the inside of the plate when the concave molding portion forms a stepped portion. It is possible to prevent cracks and damages in the part and further improve the durability of the mold.

Further, the convex molding portion and the concave molding portion are formed by the regulation surface of the lower punch leg portion restricting the bending of the convex molding portion inward to the plate when the convex molding portion and the concave molding portion form the stepped shape portion. It is possible to more stably maintain the bending clearance between the convex molded portion and the concave molded portion in a state where the portions form a stepped portion and are gripped. Therefore, when the upper die descends from immediately before the bottom dead center to the bottom dead center, the tension in the vertical direction can be more stably applied from the stepped shape portion to the vertical wall portion.

(8) The press die according to (6).
The lower punch has a lower punch head on which the vertical wall forming portion is formed, and a plurality of lower punch heads fixed to the lower body and divided into narrow widths with respect to the lower punch head. Equipped with a lower punch leg,
The lower punch head and the lower punch leg are fastened to each other, and the lower bending blade and the cushion plate are formed with through holes penetrating each lower punch leg. It is characterized by.

In the present invention, the lower punch has a lower punch head on which a vertical wall molding portion is formed and a plurality of lower punch heads fixed to the lower body and divided into narrow widths with respect to the lower punch head. It is equipped with a lower punch leg, the lower punch head and the lower punch leg are fastened, and the lower bending blade and the cushion plate have through holes that penetrate each lower punch leg. Therefore, when the convex molding portion and the concave molding portion form a stepped portion, the bending of the convex molding portion in the lower mold bending blade and the through hole in the lower mold bending blade and the cushion plate are formed. It is possible to prevent cracks, damages, etc. of the convex molded portion by suppressing the connection portion, and further improve the mold durability. In addition, even when the vertical wall portion of the vehicle member part is formed by bending in the width direction and it is difficult to form a guide surface for restricting the bending of the convex molded portion to the inside of the plate on the lower punch leg portion. , Easy mold making and cost effective.

Further, by regulating the bending of the convex molded portion inward of the plate when the convex molded portion and the concave molded portion form the stepped portion by the connecting portion in which the through hole is not formed in the lower bending blade. The bending clearance between the convex molded portion and the concave molded portion can be more stably maintained in a state where the convex molded portion and the concave molded portion form a stepped portion and are gripped. Therefore, when the upper die descends from immediately before the bottom dead center to the bottom dead center, the tension in the vertical direction can be more stably applied from the stepped shape portion to the vertical wall portion.

(9) The press die according to (8).
The guide member is provided with a stopper pin that regulates the amount of vertical movement stroke of the cushion plate.
The cushion plate is characterized in that a regulation block with which the stopper pin abuts is formed at an elevated position of the cushion plate in which the convex molded portion and the concave molded portion form the stepped portion. To do.

In the present invention, the guide member is provided with a stopper pin that regulates the vertical movement stroke amount of the cushion plate, and the cushion plate is raised so that the convex molded portion and the concave molded portion form a stepped portion. Since the regulation block that the stopper pin comes into contact with is formed at the position, the lower end of the lower punch head and the convex portion are formed at the raised position of the cushion plate in which the convex molded portion and the concave molded portion form a stepped portion. Avoiding collision with the upper end of the molded part, preventing cracks and damage of the convex molded part, poor fastening between the lower punch head and the lower punch leg, etc., and improving mold durability. Can be done.

According to the present invention, it is possible to provide a press forming method and a press die thereof, which can ensure mold durability and effectively eliminate springback, warpage, etc. of the entire vertical wall portion of a vehicle member part.

It is a schematic perspective view of the member part for a vehicle formed by the press molding method which concerns on embodiment of this invention. FIG. 5 is a sectional view taken along the line AA of the vehicle member parts shown in FIG. It is a processing cross-sectional view which shows the processing procedure in the press molding method of the member part for a vehicle shown in FIG. FIG. 3 (a) shows a cross-sectional view when the upper die bending blade starts bending the vertical wall portion in the vicinity of the lower die punch, and FIG. 3 (b) shows the upper die immediately before the bottom dead center. A cross-sectional view is shown when a convex molded portion provided on the lower die cushion and a concave formed portion provided on the upper die bending blade form a stepped portion, and FIG. 3 (c) shows a bottom dead center of the upper die. A cross-sectional view is shown when the vertical wall portion is subjected to vertical tension by descending to. It is a detailed sectional view of part B of FIG. 3 (b). It is a detailed cross-sectional view of part C of FIG. 3C. It is a partial cross-sectional view at the bottom dead center of the press die (first embodiment) used in the press molding method of the member parts for vehicles shown in FIG. It is a partial cross-sectional view at the bottom dead center of the press die (second embodiment) used in the press molding method of the member parts for vehicles shown in FIG. FIG. 5 is a CAE analysis diagram showing a stress distribution obtained by subtracting the tensile stress inside the plate from the tensile stress on the outside of the plate of the member parts for vehicles (before unloading) formed by this press molding method. FIG. 5 is a CAE analysis diagram showing a cross-sectional shape after unloading with respect to a normal cross-sectional shape of a vehicle member part molded by this press molding method. It is a processing sectional view which shows the processing procedure in the comparative example with respect to the press molding method of the member part for a vehicle shown in FIG. FIG. 10 (a) shows a cross-sectional view when the upper die bending blade starts bending the vertical wall portion in the vicinity of the lower die punch, and FIG. 10 (b) shows the upper die immediately before the bottom dead point. FIG. 10 (c) shows a cross-sectional view when the convex forming portion provided on the lower die punch and the concave forming portion provided on the upper die bending blade start forming a stepped portion at the tip of the vertical wall portion. Shows a cross-sectional view when the upper die descends to the lower dead point and tension is applied to the vertical wall portion in the vertical direction. FIG. 3 is a CAE analysis diagram showing a stress distribution obtained by subtracting the tensile stress inside the plate from the tensile stress on the outside of the plate of the member parts for vehicles (before unloading) formed by the press molding method of the comparative example shown in FIG. FIG. 5 is a CAE analysis diagram showing a cross-sectional shape after unloading with respect to a normal cross-sectional shape of a vehicle member part molded by the press molding method of the comparative example shown in FIG. It is sectional drawing which shows the main part of the bending molding die described in Patent Document 1. FIG. 13 (a) shows a state in which mold clamping has started, and FIG. 13 (b) shows a state before mold clamping is completed.

Next, a press molding method for vehicle member parts and a press die thereof according to an embodiment of the present invention will be described in detail with reference to the drawings. First, the structure of the member parts for vehicles formed by the press molding method according to the present embodiment will be described, and then the processing procedure of the press molding method for molding the member parts for the vehicle, and the press die used for the press molding method. The structure of (the first embodiment and the second embodiment) will be described. Next, the CAE analysis results of the stress distribution, the amount of springback, and the amount of warpage in the member parts for vehicles after bending by this press forming method will be described. In addition, the machining procedure of the comparative example for this press forming method will be described, and the CAE analysis results of the stress distribution, the springback amount, and the warp amount in the member parts for vehicles after bending according to the comparative example will be described.

<Structure of member parts for vehicles>
First, the structure of the vehicle member parts formed by the press molding method according to the present embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 shows a schematic perspective view of a member part for a vehicle formed by the press molding method according to the embodiment of the present invention. FIG. 2 shows a sectional view taken along the line AA of the vehicle member parts shown in FIG.

As shown in FIGS. 1 and 2, the vehicle member parts M formed by the press forming method according to the present embodiment stand up on the central portion M1 and both sides thereof by bending a steel plate W having a uniform plate thickness. It is a member part for a vehicle having a substantially hat cross-sectional shape provided with a vertical wall portion M2. Here, the vertical wall portion M2 of the vehicle member component M is formed substantially linearly in the longitudinal direction, but may be formed by being bent in the width direction. The substantially hat cross-sectional shape of the vehicle member component M is formed symmetrically, but may be asymmetrical. Further, although the vertical wall portion M2 having a substantially hat cross-sectional shape is erected substantially perpendicular to the central portion M1, the vertical wall portion M2 may be erected so as to slightly open the tip side to the outside of the plate. The steel sheet W used in this press forming method is not particularly limited, but a steel sheet having a tensile strength of about 590 to 980 Mpa can be used.

Further, in the member component M for this vehicle, the tip flange portion W1 in the width direction of the steel plate W is bent in a step shape to form a step-shaped portion M3 on the tip side of the vertical wall portion M2. The stepped shape portion M3 is formed in substantially the same cross section along the longitudinal direction of the vertical wall portion M2, and is also formed so as to project outward from the plate of the vertical wall portion M2. The amount t of the stepped shape portion M3 with respect to the vertical wall portion M2 is preferably about 1 to 3 times the plate thickness (for example, 2.6 mm) of the steel plate W.

Further, the stepped shape portion M3 has a first bending portion M31 in which the opening angle θ1 bends outward from the vertical wall portion M2 at an obtuse angle, and a first bending portion M31 in which the opening angle θ2 bends inward from the first bending portion M31 at an obtuse angle. It is provided with two bent portions M32. The opening angles θ1 and θ2 are preferably about 120 to 150 degrees. By setting the opening angles θ1 and θ2 to obtuse angles, it is possible to reduce the local thickness reduction and elongation due to bending in the first bending portion M31 and the second bending portion M32 as much as possible, and the length with respect to the vertical wall portion M2. This is because the tension in the direction can be stably applied.

Further, it is preferable that the tip portion M33 of the stepped shape portion M3 is formed with a flange portion M4 extending to the outside of the plate with respect to the vertical wall portion M2. The flange portion M4 is formed horizontally with a predetermined width, and the vehicle member component M is joined to the floor component or the like of the vehicle body by spot welding or the like. By forming the flange portion M4 on the tip portion M33 of the step-shaped portion M3, the bending clearance when forming the step-shaped portion M3 can be stably maintained, and it is easier to avoid a decrease in the plate thickness of the step-shaped portion M3. It is also possible to exert the effect and the effect of increasing the rigidity of the vertical wall portion M2.

<Press molding method and press die for member parts for vehicles>
Next, the press molding method and the press die of the vehicle member parts according to the present embodiment will be described with reference to FIGS. 3 to 7. FIG. 3 shows a partial cross-sectional view of a press die showing a processing procedure in the press molding method for vehicle member parts shown in FIG. FIG. 3 (a) shows a cross-sectional view when the upper die bending blade starts bending the vertical wall portion in the vicinity of the lower die punch, and FIG. 3 (b) shows the upper die immediately before the bottom dead center. A cross-sectional view is shown when the convex molded portion provided on the lower die cushion and the concave formed portion provided on the upper die bending blade form a stepped portion, and FIG. 3 (c) shows the upper die at the bottom dead center. A cross-sectional view is shown when the vertical wall portion is subjected to vertical tension by descending to. FIG. 4 shows a detailed cross-sectional view of part B of FIG. 3 (b). FIG. 5 shows a detailed cross-sectional view of part C of FIG. 3 (c). FIG. 6 shows a partial cross-sectional view at the bottom dead center of the press die (first embodiment) used in the press molding method of the vehicle member parts shown in FIG. FIG. 7 shows a partial cross-sectional view at the bottom dead center of the press die (second embodiment) used in the press molding method of the vehicle member parts shown in FIG.

As shown in FIGS. 3 to 5, in the press forming method of the vehicle member parts according to the present embodiment, the lower punch 11 formed in a substantially hat cross-sectional shape and the vertical wall forming portion 111 of the lower punch 11 are formed. A lower die 1 having a lower die cushion 12 having a flange pressing portion 121 formed on the outer peripheral side and pressure-supported so as to be vertically movable, an upper die bending blade 21 formed so as to face the lower die punch 11, and the upper die. It is provided with an upper die 2 having an upper die pad 22 arranged on the inner peripheral side of the die bending blade 21 and formed so that the steel plate W can be pressed against the lower die punch 11, and the upper die 2 facing the lower die 1 is on the upper die. When descending from the dead center to the bottom dead center, the lower punch 11 and the upper bending blade 21 are close to each other to bend the steel plate W, so that the central portion M1 and the vertical wall portions M2 standing on both sides thereof are formed. This is a press forming method for a member part M for a vehicle, which is formed in a substantially hat cross-sectional shape.

Here, the lower punch 11 is fastened to the lower body 13 on which the lower cushion 12 is placed. A pressure pin 31 that pressurizes the lower cushion 12 upward is mounted on the lower body 13. The pressurizing pin 31 is connected to a pressurizing device 3 (not shown), and the pressurizing device 3 is equipped with a locking mechanism for suspending the rise of the pressurizing pin 31 at the bottom dead center of the upper die 2. Further, the upper die bending blade 21 is fastened to the bending blade fixing block 23 of the upper die 2. The upper mold 2 is equipped with a pressure member 221 that pressurizes the upper mold pad 22 downward. The pressurizing member 221 is not particularly limited, but a gas cylinder that can easily secure a predetermined pressing force and a required expansion / contraction amount is preferable. Here, since the member parts M for the present vehicle are formed symmetrically, the lower mold 1 and the upper mold 2 shown in FIG. 3 show only the cross section of the right half for convenience.

Further, the lower cushion 12 is provided with a convex forming portion 122 that stands up on the inner peripheral edge of the flange pressing portion 121 and projects stepwise from the vertical wall forming portion 111 of the lower punch 11 to the outside of the plate. At the lower end of the vertical wall forming portion 111, a stopper portion 111S with which the upper end portion 122J of the convex forming portion 122 abuts is formed. The lower cushion 12 rises in response to an upward pressure applied to the pressure pin 31, and the rising position 122J of the upper end portion 122J of the convex forming portion 122 comes into contact with the stopper portion 111S (FIGS. 3A and 3B). ), And when the upper die 2 descends to the bottom dead center, the flange retainer 121 is pushed by the lower end 21K of the upper die bending blade 21 and comes into contact with the lower die body 13 (FIG. 3 (c). ) And move up and down. The vertical movement stroke amount d1 of the lower cushion 12 is preferably, for example, about 2 to 3 mm.

Further, in the present press forming method, the upper die bending blade 21 is provided with a concave forming portion 212 for narrowing the steel plate W in cooperation with the convex forming portion 122 of the lower die cushion 12 at the upper part of the die R portion 21R. .. Further, when the upper die 2 is lowered to just before the bottom dead center (up position of the lower die cushion 12: 2 to 3 mm above the bottom dead center), the convex forming portion 122 and the concave forming portion 212 are at the tip flange of the steel plate W. The step-shaped portion M3 is formed on the tip end side of the vertical wall portion M2 by bending the portion W1 in a step shape, and the upper mold 2 is lowered while the convex molding portion 122 and the concave molding portion 212 grip the step-shaped portion M3. Descend to dead center. The convex molding portion 122 and the concave molding portion 212 grip the stepped shape portion M3 from the inside and outside of the plate, and the upper mold 2 descends to the bottom dead center to form the inside (M21) of the vertical wall portion M2. The tension F in the vertical direction can be applied substantially evenly to the outside of the plate (M22). Therefore, the difference in the residual stress generated on the inner side and the outer side of the vertical wall portion M2 due to the bending and unbending of the steel plate W by the upper die bending blade 21 is the stepped shape portion formed on the tip side of the vertical wall portion M2. The vertical tension F acting via the M3 can be eliminated, and the vertical wall portion M2 can be frozen in a regular cross-sectional shape. Then, the springback, warpage, etc. that occur in the vertical wall portion M2 of the vehicle member component M can be eliminated over the entire vertical wall portion M2.

Further, in the present press molding method, the stepped shape portion M3 has a first bent portion M31 in which the opening angle θ1 bends outward from the vertical wall portion M2 at an obtuse angle, and an opening angle θ2 from the first bent portion M31 to the inside of the plate. A second bent portion M32 that bends at an obtuse angle is provided (see FIG. 2), and the bending clearance d2 between the convex forming portion 122 and the concave forming portion 212 is substantially the same as the plate thickness of the steel plate W. preferable. In this case, local elongation and decrease in plate thickness due to bending at the bent portions M31 and M32 are unlikely to occur on the inside and outside of the steel plate W, and the upper die 2 is immediately before the bottom dead center (the lower die cushion 12 rises). Position: When descending from the bottom dead center (2 to 3 mm above the bottom dead center) to the bottom dead center, the binding force of the convex molding portion 122 and the concave molding portion 212 with respect to the step shape portion M3 increases, and the vertical wall portion from the step shape portion M3. The vertical tension F can be applied stably and to the same extent on the inner side (M21) and the outer side (M22) of the M2 plate.

Further, in this press forming method, the shoulder R portion 122R of the convex forming portion 122 and the die R portion 212R of the concave forming portion 212 are formed with the same radius of curvature r1 and r2, respectively, and the convex forming portion 122 and the concave forming portion 122 are formed. It is preferable that the step portion 212 and the step portion M3 are curved in a substantially S shape to be gripped. In this case, since the step-shaped portion M3 is curved in a substantially S-shape, it is possible to avoid a local decrease in the thickness of the steel plate W, and the convex forming portion 122 and the concave forming portion 212 grip the step-shaped portion M3. The surface pressures T1 and T2 can be dispersed substantially uniformly between the shoulder R portion 122R of the convex molding portion 122 and the die R portion 212R of the concave molding portion 212. The radius of curvature r1 of the shoulder R portion 122R of the convex molding portion 122 and the radius of curvature r2 of the die R portion 212R of the concave molding portion 212 are about the same as the radius of curvature r3 of the die R portion 21R of the upper die bending blade 21. It is preferable to form the size larger than that.

Further, in this press molding method, when the upper die 2 descends from immediately before the bottom dead center (up position of the lower die cushion 12: 2 to 3 mm above the bottom dead center) to the bottom dead center, the convex molding portion 122 and the concave It is preferable to stretch the vertical wall portion M2 to the plastic deformation region while the molding portion 212 and the stepped portion M3 are gripped. In this case, the vertical wall portion M2 can be deformed to the plastic deformation region including the elastic deformation region remaining near the bending neutral line, and the entire area from the plate inner side (M21) to the plate outer side (M22) of the vertical wall portion M2. In, the difference in residual stress can be reliably eliminated.

Further, in this press molding method, it is preferable that the tip portion M33 of the stepped shape portion M3 is formed with a flange portion M4 extending to the outside of the plate with respect to the vertical wall portion M2. In this case, by interposing the flange portion M4 between the lower end portion 21K of the upper die bending blade 21 and the flange holding portion 121 of the lower die cushion 12, the convex forming portion 122 and the upper die bending blade provided in the lower die cushion 12 are provided. The bending clearance d2 with the concave forming portion 212 provided in 21 can be stably maintained from the time of bending of the step-shaped portion M3 to the bottom dead center, and the plate thickness reduction of the step-shaped portion M3 can be further prevented. Further, the rigidity of the step-shaped portion M3 can be increased by the flange portion M4 formed on the tip portion M33 of the step-shaped portion M3. As a result, when the upper die 2 descends to the bottom dead center, the tension F in the vertical direction can be stably applied from the stepped shape portion M3 to the vertical wall portion M2.

Next, the bending procedure in this press molding method will be described. That is, as shown in FIG. 3A, when the upper die 2 facing the lower die 1 descends from the top dead center, the upper die pad 22 presses the steel plate W against the lower die punch 11 for a vehicle. After forming the central portion M1 of the member component M, the lower die punch 11 and the upper die bending blade 21 are in close proximity to bend the steel plate W. Here, the steel plate W bent by the upper die bending blade 21 obliquely contacts the die R portion 21R of the upper die bending blade 21 via the die R portion 212R of the concave forming portion 212. Therefore, the bending amount and the handling amount of the steel sheet W by the upper die bending blade 21 can be dispersed or reduced as compared with the case where the steel sheet W directly abuts on the die R portion 21R of the upper die bending blade 21. The tip of the steel plate W is pushed by the pressure pin 31 of the pressurizing device 3 and comes into contact with the flange holding portion 121 of the lower cushion 12 in the ascending position, and the steel plate W is curved as the upper die 2 descends. Will be done.

Next, as shown in FIG. 3B, when the upper die 2 descends to just before the bottom dead center (up position of the lower die cushion 12: 2 to 3 mm above the bottom dead center), the lower die punch 11 When the vertical wall portion M2 is formed along the vertical wall forming portion 111 and the upper mold 2 descends to just before the bottom dead center (up position of the lower mold cushion 12: 2 to 3 mm above the bottom dead center). The convex molding portion 122 and the concave molding portion 212 bend the tip flange portion W1 of the steel plate W in a step shape to form a stepped shape portion M3 on the tip side of the vertical wall portion M2. Then, the convex forming portion 122 and the concave forming portion 212 grip the stepped portion M3 from both inside and outside the plate. Further, the flange holding portion 121 of the lower cushion 12 pressed by the pressurizing pin 31 of the pressurizing device 3 and the lower end portion 21K of the upper bending blade 21 face each other in the vertical direction with the pressing forces T3 and T4 of the steel plate W. By acting on the tip flange portion W1 of the above, the flange portion M4 is formed on the tip portion M33 of the stepped shape portion M3.

Next, as shown in FIG. 3C, the upper die 2 descends to the bottom dead center in a state where the convex forming portion 122 and the concave forming portion 212 hold the stepped shape portion M3, and the upper die bending blade 21 The difference in the residual stress generated on the inside and outside of the vertical wall portion M2 due to the bending and unbending of the steel plate W is affected by the vertical wall portion M3 formed on the tip side of the vertical wall portion M2. It is eliminated by the tension F in the direction. At this time, the vertical movement stroke amount d1 of the lower cushion 12 is 2 to 3 mm, but the vertical wall portion M2 is in the plastic deformation region while the convex molding portion 122 and the concave molding portion 212 hold the stepped shape portion M3. Can be stretched to and frozen in shape. When the upper die 2 rises from the bottom dead center, the locking mechanism of the pressurizing device 3 operates to suspend the ascending of the pressurizing pin 31. As a result, deformation of the vertical wall portion M2, the flange portion M4, and the like of the member component M for the vehicle can be prevented.

Next, a specific example of the press die used in this press molding method will be described with reference to FIGS. 3 to 7. The press dies 10A of the first embodiment and the press dies 10B of the second embodiment shown in FIGS. 6 and 7 have the same reference numerals as the mold structures shown in FIGS. 3 to 5. I'm using it.

That is, as shown in FIGS. 3 to 7, the press dies 10A of the first embodiment and the press dies 10B of the second embodiment used in the present press molding method are convex on the lower cushions 12A and 12B. Cushion plates 14A and 14B to which the lower die bending blades 15A and 15B to which the molding portions 122a and 122b and the flange pressing portions 121a and 121b are connected are provided, and the upper die 2 is bent by fixing the upper die bending blade 21. A blade fixing block 23 is provided, and the lower dies 1A and 1B are fixed to the lower die main body 13 and the lower die main body 13, and the outer ends 141A and 141B of the cushion plates 14A and 14B and the bending blade fixing block 23. The guide members 16A and 16B are provided to guide the outer end portion 231 of the above portion in the vertical direction from at least immediately before the bottom dead center to the bottom dead center. The upper mold 2 is provided with an upper mold main body 24 for fixing the bending blade fixing block 23 and the pressurizing member 221.

Further, guide plates 161A and 161B are fastened to the guide members 16A and 16B. The outer ends 141A and 141B of the cushion plates 14A and 14B and the outer end 231 of the bending blade fixing block 23 are in sliding contact with the guide plates 161A and 161B of the guide members 16A and 16B. As a result, the bending clearance d2 between the convex forming portions 122a and 122b and the concave forming portion 212 in a state where the convex forming portions 122a and 122b and the concave forming portion 212 form the stepped portion M3 and are gripped is more stable. Can be maintained. Therefore, when the upper die 2 descends from immediately before the bottom dead center to the bottom dead center, the tension F in the vertical direction can be more stably applied from the stepped shape portion M3 to the vertical wall portion M2.

Further, in the press die 10A of the first embodiment shown in FIG. 6, the lower punch 11A has a lower punch head 112a on which a vertical wall forming portion 111 is formed and a lower die fixed to the lower body 13. A lower punch leg 113a having a narrow width with respect to the punch head 112a and integrally formed with the punch head 112a is provided, and the lower punch leg 113a abuts on the inner end surface 1221a of the convex molding 122a to abut the convex molding 122a. A regulating surface 1131a is formed to regulate the bending of the plate inward. The convex molding portion 122a when the convex molding portion 122a and the concave molding portion 212 form the stepped shape portion M3 due to the contact between the inner end surface 1221a of the convex molding portion 122a and the regulation surface 1131a of the lower punch leg portion 113a. The regulation surface 1131a of the lower punch leg portion 113a regulates the bending of the plate inward, and cracks, damage, etc. of the convex molding portion 122a formed by standing upright on the flange holding portion 121a can be prevented.

Further, in the press die 10A of the first embodiment, the bending of the convex forming portion 122a inward to the plate when the convex forming portion 122a and the concave forming portion 212 form the stepped shape portion M3 is controlled by the lower punch leg portion. By restricting the regulation surface 1131a of 113a, the convex forming portion 122a and the concave forming portion 212 form the stepped portion M3, and the bending clearance d2 between the convex forming portion 122a and the concave forming portion 212 in the gripped state. Can be maintained more stably. The press die 10A of the first embodiment is suitable when the vertical wall portion M2 of the vehicle member component M is formed substantially linearly in the longitudinal direction.

Further, in the press die 10B of the second embodiment shown in FIG. 7, the lower punch 11B has a lower punch head 112b on which a vertical wall forming portion 111 is formed and a lower die fixed to the lower die body 13. A plurality of lower punch legs 113b formed by being narrowly divided with respect to the punch head 112b are provided, and the lower punch head 112b and the lower punch leg 113b are fastened to each other. The plurality of lower punch legs 113b may be formed in a columnar shape or a prismatic shape, and are arranged at appropriate intervals along the shape of the lower punch head 112b. Further, through holes 152B and 142B penetrating each of the lower punch leg portions 113b are formed in the lower mold bending blade 15B and the cushion plate 14B in which the convex forming portion 122b and the flange pressing portion 121b are connected. Therefore, when the convex forming portion 122b and the concave forming portion 212 form the stepped shape portion M3, the bending of the convex forming portion 122b in the lower mold bending blade 15B and the through hole 152B in the lower mold bending blade 15B are not formed. By restricting by the connecting portion 151B, cracking, damage, etc. of the convex molded portion 122b can be prevented, and the mold durability can be further improved. The press die 10B of the second embodiment is suitable when the vertical wall portion M2 of the vehicle member component M is formed by bending in the width direction. In this case, it is not necessary to form a guide surface for restricting the inward bending of the convex molded portion 122b on the lower punch leg portion 113b.

Further, in the press die 10B of the second embodiment, the guide member 16B is provided with a stopper pin 162B that regulates the vertical movement stroke amount d1 of the cushion plate 14B, and the cushion plate 14B is formed with a convex molding portion 122b and concave molding. A regulation block 143B with which the stopper pin 162B abuts is formed at an elevated position of the cushion plate 14B forming the stepped portion M3 with the portion 212. The regulation block 143B is formed with a groove hole that is separated from the stopper pin 162B by the vertical movement stroke amount d1 of the cushion plate 14B. Therefore, at the raised position of the cushion plate 14B where the convex forming portion 122b and the concave forming portion 212 form the stepped shape portion M3, the lower end of the lower punch head 112b and the upper end of the convex forming portion 122b collide with each other. By avoiding this, it is possible to prevent the convex molded portion 122b from being cracked or damaged, or to prevent the lower punch head 112b and the lower punch leg 113b from being poorly fastened.

<Evaluation results of vehicle member parts by this press molding method>
Next, as the evaluation results of the member parts for vehicles after bending by this press molding method, the CAE analysis results of the stress distribution, the springback amount, and the warp amount will be described with reference to FIGS. 8 and 9. FIG. 8 shows a CAE analysis diagram showing a stress distribution obtained by subtracting the tensile stress inside the plate from the tensile stress on the outside of the plate of the member parts for vehicles (before unloading) formed by this press molding method. FIG. 9 shows a CAE analysis diagram showing the cross-sectional shape of the vehicle member parts molded by this press molding method after unloading with respect to the normal cross-sectional shape. The steel plate W used in the CAE analysis has a tensile strength of 590 Mpa and a plate thickness of 2.6 mm.

(Stress distribution after bending)
As shown in FIG. 8, the distribution state of the difference between the inside and outside of the plate with respect to the tensile stress before unloading in the central portion M1, the vertical wall portion M2, the stepped portion M3, and the flange portion M4 after bending is displayed by the shade of dots. ing. The shade display of dots is divided into a plurality of stages from -10 to +10. As the dot density increases from 0 to +10, the tensile stress on the outside of the plate becomes larger than that on the inside of the plate. On the contrary, as the dot density becomes lighter from 0 to -10, the tensile stress inside the plate becomes larger than that outside the plate.

Then, in the region where the dot shading is from +4 to +10, the tensile stress on the outside of the plate becomes excessive from the inside of the plate, and after unloading (when removed from the mold after bending), conversely, the inside of the plate is more than the outside of the plate. Since the tensile residual stress of the plate becomes excessive, it springs back to the outside of the plate. On the other hand, in the range of dot shading from -4 to -10, the tensile stress inside the plate becomes excessive from the outside of the plate, and after unloading (when removed from the mold after bending), conversely from the inside of the plate. Since the tensile residual stress on the outside of the plate becomes excessive, spring go to the inside of the plate. In addition, in the range of dot shading from -3 to +3, the difference in tensile stress between the inside and outside of the plate is small, and even after unloading (when removed from the mold after bending), the inside and outside of the plate are displayed. Since the difference in the tensile residual stress on the outside is small, springback and the like hardly occur.

Here, in substantially the entire area of the vertical wall portion M2, the shade display of dots corresponds to the region from -3 to +3, and the inside and outside of the plate after unloading (when removed from the mold after bending). It was found that the difference in tensile residual stress was small and almost no springback or the like occurred. This is a stepped shape in which the difference in residual stress generated on the inside and outside of the vertical wall portion M2 due to bending and unbending of the steel plate W by the upper die bending blade 21 is formed on the tip side of the vertical wall portion M2. It can be inferred that this could be eliminated by the vertical tension F acting via the portion M3.

In the upper end of the first bent portion M31 of the stepped shape portion M3 and the intermediate portion between the second bent portion M32, the shade display of the dots corresponds to the region from +4 to +10, and after unloading (after bending, gold). The tensile residual stress inside the plate when removed from the mold) is excessive. This occurs when the convex molded portion 122 and the concave molded portion 212 form the stepped portion M3, and it is presumed that it is difficult to eliminate this difference in residual stress. However, the step-shaped portion M3 is a narrower region than the vertical wall portion M2, and can be easily solved by prospective molding of the step-shaped portion M3.

(Spring back amount and warpage amount after bending)
Further, as shown in FIG. 9, according to the CAE analysis diagram showing the cross-sectional shape (solid line) after unloading with respect to the normal cross-sectional shape (dotted line) of the vehicle member part M formed by the present press molding method, for the present vehicle. The amount of springback and the amount of warpage in the vertical wall portion M2 of the member parts were almost zero. However, a slight springback occurred in the stepped shape portion M3 and the flange portion M4. This is associated with the distribution state of the difference between the inside and outside of the plate with respect to the tensile stress before unloading shown in FIG.

<Press molding method and press die according to comparative example>
Next, in order to compare with the above-mentioned press molding method of the member parts for vehicles according to the present embodiment, the processing procedure and the press die in the press molding method of the comparative example will be described with reference to FIG. FIG. 10 shows a partial cross-sectional view of a press die showing a machining procedure in a comparative example of the vehicle member parts shown in FIG. 3 with respect to the press molding method. FIG. 10 (a) shows a cross-sectional view when the upper die bending blade starts bending the vertical wall portion in the vicinity of the lower die punch, and FIG. 10 (b) shows the upper die immediately before the bottom dead point. FIG. 10 (c) shows a cross-sectional view when the convex forming portion provided on the lower die punch and the concave forming portion provided on the upper die bending blade start forming a stepped portion at the tip of the vertical wall portion. Shows a cross-sectional view when the upper die descends to the lower dead point and tension is applied to the vertical wall portion in the vertical direction.

As shown in FIG. 10, in the press molding method of the comparative example, the lower die punch 11C formed in a substantially hat cross-sectional shape and the flange pressing portion 121C are formed on the outer peripheral side of the vertical wall forming portion 111C of the lower punch 11C. A lower mold 1C having a lower mold cushion 12C supported so as to be vertically movable, an upper mold bending blade 21 formed facing the lower mold punch 11C, and a steel plate arranged on the inner peripheral side of the upper mold bending blade 21. It is provided with an upper die 2 having an upper die pad 22 formed so that W can be pressed against the lower die punch 11C, and when the upper die 2 facing the lower die 1C descends from the top dead center to the bottom dead center, it is lowered. A member for a vehicle that forms a substantially hat cross-sectional shape including a central portion M1 and vertical wall portions M2 standing on both sides thereof by bending a steel plate W in close proximity to the mold punch 11C and the upper mold bending blade 21. This is a press forming method for the part M.

Here, the lower die punch 11C is provided with a convex forming portion 122C at the lower end of the vertical wall forming portion 111C, which projects stepwise from the vertical wall forming portion 111C to the outside of the plate, and the lower die cushion 12C is provided with the convex forming portion 122C. It is different from the press molding method of the vehicle member part M according to the present embodiment in that it is not provided, and other configurations are common. The configuration common to the type structure shown in FIG. 3 is designated by a common reference numeral, and the description thereof is omitted in principle.

As shown in FIG. 10A, when the upper die 2 facing the lower die 1C descends from the top dead center, the upper die pad 22 presses the steel plate W against the lower die punch 11C, and the vehicle member parts. After forming the central portion M1 of M, the lower punch 11C and the upper bending blade 21 are in close proximity to bend the steel plate W. At this stage, it is common to the above-described press molding method for vehicle member parts according to the present embodiment.

Next, as shown in FIG. 10B, when the upper die 2 descends to just before the bottom dead center (up position of the lower die cushion 12: 2 to 3 mm above the bottom dead center), the lower die punch 11C The vertical wall portion M2 is formed along the vertical wall forming portion 111C, and the convex forming portion 122C and the concave forming portion 212 bend the tip flange portion W1 of the steel plate W in a stepped manner to the tip side of the vertical wall portion M2. Starts to form the stepped shape portion M3. Further, the flange holding portion 121C of the lower cushion 12C and the lower end portion 21K of the upper bending blade 21 narrow the tip flange portion W1 of the steel plate W to form the flange portion M4 at the tip portion M33 of the stepped shape portion M3. .. However, since the convex forming portion 122C is integrally formed with the lower punch 11C, the plate thickness or more is greater than or equal to the plate thickness between the shoulder R portion 122R of the convex forming portion 122C and the die R portion 212R of the concave forming portion 212. A gap is formed. Therefore, the convex molding portion 122C and the concave molding portion 212 cannot sufficiently grip the stepped shape portion M3.

Next, as shown in FIG. 10C, when the upper mold 2 is lowered to the bottom dead center, the convex molding portion 122C and the concave molding portion 212 complete the formation of the stepped shape portion M3. While the upper die 2 descends from immediately before the bottom dead center to the bottom dead center, the convex molding portion 122C and the concave molding portion 212 are not in a state of sufficiently gripping the stepped shape portion M3, so that the vertical wall portion M2 is not sufficiently gripped. The tension F in the vertical direction cannot be sufficiently applied through the stepped shape portion M3, and the inside and outside of the plate generated in the vertical wall portion M2 as the steel plate W is bent and returned by the upper die bending blade 21. The difference in residual stress cannot be eliminated. At this time, since the flange holding portion 121C of the lower die cushion 12C and the lower end portion 21K of the upper die bending blade 21 narrowly press the flange portion M4 and descend, the step shape is formed through the die R portion 21R of the upper die bending blade 21. Although vertical tension can be applied to the portion M3, the step-shaped portion M3 is deformed and sufficient vertical tension cannot be transmitted to the vertical wall portion M2. Therefore, the vertical wall portion M2 cannot be stretched to the plastic deformation region and the shape cannot be frozen.

<Evaluation results of vehicle member parts by comparative example>
Next, CAE analysis results of stress distribution, springback amount, and warpage amount will be described with reference to FIGS. 11 and 12 as evaluation results of vehicle member parts after bending according to a comparative example. FIG. 11 shows a CAE analysis diagram showing a stress distribution obtained by subtracting the tensile stress inside the plate from the tensile stress on the outside of the plate of the member parts for vehicles (before unloading) formed by the press molding method of the comparative example shown in FIG. .. FIG. 12 shows a CAE analysis diagram showing a cross-sectional shape after unloading with respect to a normal cross-sectional shape of a vehicle member part molded by the press molding method of the comparative example shown in FIG. The steel plate W used in the CAE analysis has a tensile strength of 590 Mpa and a plate thickness of 2.6 mm.

(Stress distribution after bending)
As shown in FIG. 11, the distribution state of the difference between the inside and outside of the plate with respect to the tensile stress before unloading in the central portion M1, the vertical wall portion M2, the stepped portion M3, and the flange portion M4 having a substantially hat cross-sectional shape is displayed by the shade of dots. doing. The shading display of dots is divided into a plurality of stages from -10 to +10, as in the case shown in FIG. As the dot density increases from 0 to +10, the tensile stress on the outside of the plate becomes larger than that on the inside of the plate. On the contrary, as the dot density becomes lighter from 0 to -10, the tensile stress inside the plate becomes larger than that outside the plate.

Then, in the region where the dot shading is from +4 to +10, the tensile stress on the outside of the plate becomes excessive from the inside of the plate, and after unloading (when removed from the mold after bending), conversely, the inside of the plate is more than the outside of the plate. Since the tensile residual stress of the plate becomes excessive, it springs back to the outside of the plate. On the other hand, in the range of dot shading from -4 to -10, the tensile stress inside the plate becomes excessive from the outside of the plate, and after unloading (when removed from the mold after bending), conversely from the inside of the plate. Since the tensile residual stress on the outside of the plate becomes excessive, spring go to the inside of the plate. In addition, in the range of dot shading from -3 to +3, the difference in tensile stress between the inside and outside of the plate is small, and even after unloading (when removed from the mold after bending), the inside and outside of the plate are displayed. Since the difference in the tensile residual stress on the outside is small, springback and the like hardly occur.

Here, in the area of about 80% below the vertical wall portion M2, the shade display of dots corresponds to the area from +4 to +10, and the inside of the plate after unloading (when removed from the mold after bending). It was found that the amount of springback and the amount of warpage are large because the tensile residual stress of the plate is larger than that on the outside of the plate. This is because the convex molding portion 122C and the concave molding portion 212 are not in a state of sufficiently gripping the stepped shape portion M3 while the upper mold 2 descends from immediately before the bottom dead center to the bottom dead center. It can be inferred that the difference in the residual stress between the inside and outside of the plate generated in the vertical wall portion M2 due to the bending and unbending of the steel plate W by 21 cannot be eliminated.

(Spring back amount and warpage amount after bending)
Further, as shown in FIG. 12, according to the CAE analysis diagram showing the cross-sectional shape (solid line) after unloading with respect to the normal cross-sectional shape (dotted line) of the vehicle member component M formed by the press molding method of the comparative example, the vehicle. The springback amount α in the vertical wall portion M2 of the member parts for use was about 1.7 degrees. Further, a warp amount β of about the plate thickness was generated in the intermediate portion of the vertical wall portion M2. This is associated with the distribution state of the difference between the inside and outside of the plate with respect to the tensile stress before unloading shown in FIG.

<Effect>
As described in detail above, according to the press molding method of the vehicle member parts according to the present embodiment, the lower die cushion 12 stands on the inner peripheral edge of the flange holding portion 121 and stands on the vertical wall of the lower die punch 11. A convex forming portion 122 that projects stepwise from the forming portion 111 to the outside of the plate is provided, and the upper die bending blade 21 is concavely formed to narrow the steel plate W in cooperation with the convex forming portion 122 at the upper part of the die R portion 21R. When the upper die 2 is lowered to just before the bottom dead point, the convex forming portion 122 and the concave forming portion 212 bend the tip flange portion W1 of the steel plate W in a stepped manner to form the tip of the vertical wall portion M2. Since the step-shaped portion M3 is formed on the side and the upper die 2 descends to the bottom dead point while the convex forming portion 122 and the concave forming portion 212 grip the step-shaped portion M3, the steel plate W by the upper die bending blade 21 The difference in residual stress generated inside and outside the plate of the vertical wall portion M2 due to bending and unbending of the vertical wall portion M2 is the vertical tension acting through the stepped shape portion M3 formed on the tip side of the vertical wall portion M2. The vertical wall portion M2 can be effectively frozen by F to have a regular cross-sectional shape. Therefore, springback, warpage, and the like that occur in the vertical wall portion M2 of the vehicle member component M can be eliminated over the entire vertical wall portion M2.

Further, since the upper die bending blade 21 is provided with a concave forming portion 212 that narrows the steel plate W in cooperation with the convex forming portion 122 at the upper part of the die R portion 21R, the upper die bending blade 21 bends the steel plate W. The steel plate W is obliquely in contact with the die R portion 21R of the upper die bending blade 21 via the concave forming portion 212. Therefore, the bending amount and the handling amount of the steel sheet W by the upper die bending blade 21 can be dispersed or reduced as compared with the case where the steel sheet W directly abuts on the die R portion 21R of the upper die bending blade 21. As a result, the load on the upper bending blade 21 due to the bending of the steel plate W can be reduced, and the durability of the upper bending blade 21 can be improved.

Therefore, according to the present embodiment, it is possible to provide a method of press-molding the member component M for a vehicle, which can secure the mold durability and effectively eliminate the springback and warpage of the entire vertical wall portion M2.

Further, according to the present embodiment, the stepped shape portion M3 includes a first bent portion M31 in which the opening angle θ1 bends outward from the vertical wall portion M2 at an obtuse angle, and an opening angle from the first bent portion M31 to the inside of the plate. A second bent portion M32 in which θ2 bends at an obtuse angle is provided, and the bending clearance d2 between the convex molded portion 122 and the concave molded portion 212 is substantially the same as the plate thickness of the steel plate W. On the outside of the plate, local elongation and reduction in plate thickness due to bending at the bent portions M31 and M32 are unlikely to occur. Further, on the inside and outside of the plate in each of the bent portions M31 and M32, the frictional force due to the bending acts substantially evenly between the convex molded portion 122 and the concave molded portion 212. Therefore, the tension F in the vertical direction can be stably and equally applied from the stepped shape portion M3 to the inside and outside of the plate of the vertical wall portion M2. As a result, the difference between the inside and outside of the plate of the residual stress generated in the entire vertical wall portion M2 due to the bending and unbending of the steel plate W can be eliminated more stably, and the springback and warpage of the entire vertical wall portion M2 can be eliminated. Can be resolved more stably.

Further, according to the present embodiment, the shoulder R portion 122R of the convex molding portion 122 and the die R portion 212R of the concave molding portion 212 are formed with the same radius of curvature r1 and r2, respectively, and the convex molding portion 122 and the concave are formed. Since the forming portion 212 grips the step-shaped portion M3 by bending it in a substantially S shape, it is possible to avoid a local decrease in the thickness of the steel plate W, and the convex forming portion 122 and the concave forming portion 212 form the step-shaped portion. The surface pressures T1 and T2 when gripping the M3 can be substantially uniformly dispersed in the shoulder R portion 122R of the convex molding portion 122 and the die R portion 212R of the concave molding portion 212. Therefore, the wear resistance (durability) of the convex molded portion 122 and the concave molded portion 212 can be further improved.

Further, according to the present embodiment, when the upper die 2 descends from immediately before the bottom dead center to the bottom dead center, the vertical wall portion is in a state where the convex molding portion 122 and the concave molding portion 212 grip the stepped shape portion M3. Since M2 is stretched to the plastic deformation region, the entire vertical wall portion M2 including the elastic deformation region remaining near the bending neutral line of the vertical wall portion M2 can be pulled to the plastic deformation region, and the inside of the plate of the vertical wall portion M2. The difference in residual stress can be surely eliminated in the entire area from the plate to the outside of the plate.

Further, according to the present embodiment, since the flange portion M4 extending to the outside of the plate with respect to the vertical wall portion M2 is formed at the tip portion M33 of the stepped shape portion M3, the upper die bending blade 21 A flange portion M4 is interposed between the lower end portion 21K and the flange holding portion 121 of the lower mold cushion 12, and the convex molding portion 122 provided on the lower mold cushion 12 and the concave molding portion 212 provided on the upper mold bending blade 21 are bent. The clearance d2 can be stably maintained from the time of bending the step-shaped portion M3 to the bottom dead center, and the reduction in the plate thickness of the step-shaped portion M3 can be further prevented. Further, the rigidity of the step-shaped portion M3 can be increased by the flange portion M4 formed on the tip portion M33 of the step-shaped portion M3. Therefore, when the upper die 2 descends to the bottom dead center, the tension in the vertical direction can be more stably applied from the stepped shape portion M3 to the vertical wall portion M2. As a result, springback, warpage, and the like that occur in the entire vertical wall portion M2 of the vehicle member component M can be eliminated more stably.

Further, according to the press dies 10A and 10B used in the press molding method of the member parts for vehicles according to another embodiment, the lower mold cushions 12A and 12B have the convex molding portions 122a and 122b and the flange pressing portions 121a. Cushion plates 14A and 14B to which the lower mold bending blades 15A and 15B connected to 121b are fixed are provided, and the upper mold 2 is provided with a bending blade fixing block 23 to which the upper mold bending blade 21 is fixed. In 1A and 1B, at least the lower die body 13 and the outer end portions 141A and 141B of the cushion plates 14A and 14B and the outer end portion 231 of the bending blade fixing block 23 fixed to the lower die body 13 are killed. Since the guide members 16A and 16B for guiding in the vertical direction from immediately before the point to the bottom dead point are provided, the convex forming portions 122a and 122b and the concave forming portion 212 form the stepped shape portion M3 and are in a gripped state. The bending clearance d2 between the convex forming portions 122a and 122b and the concave forming portion 212 can be maintained more stably. Therefore, when the upper die 2 descends from immediately before the bottom dead center to the bottom dead center, the vertical tension F can be more stably applied from the stepped shape portion M3 to the vertical wall portion M2, and the mold durability The sex can be improved. As a result, springback, warpage, and the like that occur in the entire vertical wall portion M2 of the vehicle member component M can be eliminated more stably.

Therefore, according to the present and other embodiments, the press die used in the press forming method of the member parts for vehicles, which can secure the mold durability and effectively eliminate the springback and warpage of the entire vertical wall portion M2. 10A and 10B can be provided.

Further, according to the present and other embodiments, the lower punch 11A has a lower punch head 112a on which the vertical wall forming portion 111 is formed and a lower punch head 112a fixed to the lower body 13. The lower punch leg 113a is provided with a narrow width and integrally formed, and the lower punch leg 113a abuts on the inner end surface 1221a of the convex molding portion 122a and the convex molding portion 122a is bent inward. Since the regulation surface 1131a is formed, the lower die punch leg portion can prevent the convex molding portion 122a from bending inward when the convex molding portion 122a and the concave molding portion 212 form the stepped shape portion M3. The regulation surface 1131a of 113a is regulated to prevent cracks, damages, etc. of the convex molded portion 122a formed thinly by standing on the flange holding portion 121a, and the mold durability can be further improved.

Further, the restricting surface 1131a of the lower punch leg portion 113a regulates the bending of the convex forming portion 122a inward to the plate when the convex forming portion 122a and the concave forming portion 212 form the stepped shape portion M3. The bending clearance d2 between the convex forming portion 122a and the concave forming portion 212 in a state where the convex forming portion 122a and the concave forming portion 212 form the stepped shape portion M3 and is gripped can be maintained more stably. Therefore, when the upper die 2 descends from immediately before the bottom dead center to the bottom dead center, the tension F in the vertical direction can be more stably applied from the stepped shape portion M3 to the vertical wall portion M2.

Further, according to the present and other embodiments, the lower punch 11B has a lower punch head 112b in which the vertical wall forming portion 111 is formed and a lower punch head 112b fixed to the lower body 13. It is provided with a plurality of lower punch legs 113b formed by dividing the width narrowly, the lower punch head 112b and the lower punch leg 113b are fastened, and the lower bending blade 15B and the cushion are provided. Since the plate 14B is formed with through holes 152B and 142B penetrating each lower punch leg portion 113b, the lower die is bent when the convex forming portion 122b and the concave forming portion 212 form the stepped shape portion M3. The bending of the convex molding portion 122b in the blade 15B is regulated by the connecting portion 151B in which the through hole is not formed in the lower mold bending blade 15B to prevent cracking, damage, etc. of the convex molding portion 122b and improve the mold durability. It can be further improved. Further, when the vertical wall portion M2 of the vehicle member component M is formed by bending in the width direction, and it is difficult to form a guide surface for restricting the bending of the convex molded portion inward to the plate side on the lower punch leg portion. In addition, the mold can be easily manufactured, which is cost effective.

Further, when the convex forming portion 122b and the concave forming portion 212 form the stepped shape portion M3, the bending of the convex forming portion 122b to the inside of the plate is prevented by the connecting portion in which the through hole 152B is not formed in the lower mold bending blade 15B. By restricting by 151B, the convex forming portion 122b and the concave forming portion 212 form the stepped portion M3, and the bending clearance d2 between the convex forming portion 122b and the concave forming portion 212 in the gripped state is made more stable. Can be maintained. Therefore, when the upper die 2 descends from immediately before the bottom dead center to the bottom dead center, the tension F in the vertical direction can be more stably applied from the stepped shape portion M3 to the vertical wall portion M2.

Further, according to this other embodiment, the guide member 16B is provided with a stopper pin 162B that regulates the vertical movement stroke amount d1 of the cushion plate 14B, and the cushion plate 14B has a convex molding portion 122b and a concave molding portion 212. Since the regulation block 143B with which the stopper pin 162B abuts is formed at the raised position of the cushion plate 14B forming the step-shaped portion M3, the convex molded portion 122b and the concave molded portion 212 form the step-shaped portion M3. At the raised position of the cushion plate 14B forming the shape, the lower end of the lower punch head 112b and the upper end of the convex molding portion 122b are prevented from colliding with each other, so that the convex molding portion 122b is cracked or damaged, or the lower punch It is possible to prevent defective fastening between the head 112b and the lower punch leg 113b and improve mold durability.

<Modification example>
The above-described embodiment can be appropriately modified without changing the gist of the present invention. For example, according to the present embodiment, the tip portion M33 of the stepped shape portion M3 is formed with a flange portion M4 extending outward from the vertical wall portion M2, but the flange portion M4 is not always formed. It does not have to be formed.

The present invention can be used as a press molding method for vehicle member parts formed in a substantially hat cross-sectional shape (including a substantially U-shaped cross-sectional shape) and a press die used in the press molding method.

1, 1A, 1B Lower mold 2 Upper mold 10A, 10B Press mold 11, 11A, 11B Lower mold punch 12, 12A, 12B Lower mold cushion 13 Lower mold body 14A, 14B Cushion plate 15A, 15B Lower mold bending blade 16A, 16B Guide member 21 Upper type bending blade 21R Die R part 22 Upper type pad 23 Bending blade fixing block 111 Vertical wall forming part 112a, 112b Lower type punch head 113a, 113b Lower type punch leg part 121, 121a, 121b Flange holding part 122, 122a, 122b Convex molding part 122R Shoulder R part 141A, 141B Outer end part 142B, 152B Through hole 143B Regulation block 162B Stopper pin 212 Concave molding part 212R Die R part 231 Outer end part 1131a Control surface 1221a Member parts M1 Central part M2 Vertical wall part M3 Step shape part M31 First bending part M32 Second bending part M33 Tip part M4 Flange part W Steel plate W1 Tip flange part d1 Vertical movement stroke amount d2 Bending clearance r1, r2 Radius of curvature θ1, θ2 Opening angle

Claims (9)

A lower die having a lower die punch formed in a substantially hat cross-sectional shape and a lower die cushion having a flange holding portion formed on the outer peripheral side of the vertical wall molded portion of the lower die punch and being pressure-supported so as to be vertically movable. An upper die having an upper die bending blade formed so as to face the lower die punch and an upper die pad arranged on the inner peripheral side of the upper die bending blade and formed so that a steel plate can be pressed against the lower die punch. With
When the upper die facing the lower die descends from the top dead center to the bottom dead center, the lower die punch and the upper die bending blade are brought close to each other to bend the steel sheet, thereby forming a central portion and the central portion thereof. It is a press forming method of a member part for a vehicle formed into a substantially hat cross-sectional shape having vertical wall portions standing on both sides.
The lower mold cushion is provided with a convex molding portion that stands on the inner peripheral edge of the flange holding portion and projects stepwise from the vertical wall molding portion of the lower mold punch to the outside of the plate, and the upper mold bending blade has a die. A concave forming portion for narrowing the steel plate in cooperation with the convex forming portion is provided on the upper part of the R portion.
When the upper die is lowered to just before the bottom dead center, the convex molded portion and the concave molded portion bend the tip flange portion of the steel sheet in a stepped manner to form a stepped portion on the tip side of the vertical wall portion. A method for press-molding a member part for a vehicle, which comprises forming and lowering the upper mold to a bottom dead center in a state where the convex-molded portion and the concave-molded portion grip the step-shaped portion. In the press molding method for vehicle member parts according to claim 1,
The stepped portion includes a first bent portion that bends from the vertical wall portion to the outside of the plate at an obtuse angle, and a second bent portion that bends from the first bent portion to the inside of the plate at an obtuse angle. Prepare,
A method for press-molding a member part for a vehicle, wherein the bending clearance between the convex-molded portion and the concave-molded portion is substantially the same as the plate thickness of the steel plate. In the press molding method for vehicle member parts according to claim 1 or 2.
The shoulder R portion of the convex molding portion and the die R portion of the concave molding portion are each formed with the same radius of curvature, and the convex molding portion and the concave molding portion form the stepped portion in a substantially S shape. A method of press-molding a member part for a vehicle, which is characterized by being curved and gripped. In the method for press molding a member part for a vehicle according to any one of claims 1 to 3.
When the upper mold descends from immediately before the bottom dead center to the bottom dead center, the vertical wall portion is extended to the plastic deformation region while the convex molded portion and the concave molded portion grip the stepped portion. A method of press molding a member part for a vehicle, which comprises. In the method for press molding a member part for a vehicle according to any one of claims 1 to 4.
A method for press-molding a member part for a vehicle, characterized in that a flange portion extending to the outside of the plate is formed at the tip end portion of the step-shaped portion. A press die used in the press molding method for a member part for a vehicle according to any one of claims 1 to 5.
The lower mold cushion is provided with a cushion plate to which a lower mold bending blade in which the convex molded portion and the flange holding portion are connected is fixed, and the upper mold is fixed to a bending blade to which the upper mold bending blade is fixed. Equipped with blocks
In the lower mold, the lower mold main body, the outer end portion of the cushion plate fixed to the lower mold main body, and the outer end portion of the bending blade fixing block are formed at least from immediately before the bottom dead center to the bottom dead center. A press die characterized by being provided with a guide member that guides in the vertical direction. The press die according to claim 6.
The lower punch has a lower punch head on which the vertical wall forming portion is formed and a lower punch fixed to the lower body and integrally formed with a narrow width with respect to the lower punch head. Equipped with legs
The press die is characterized in that the lower die punch leg is formed with a regulating surface that comes into contact with the inner end surface of the convex molded portion and regulates the bending of the convex molded portion inward of the plate. The press die according to claim 6.
The lower punch has a lower punch head on which the vertical wall forming portion is formed, and a plurality of lower punch heads fixed to the lower body and divided into narrow widths with respect to the lower punch head. Equipped with a lower punch leg,
The lower punch head and the lower punch leg are fastened to each other, and the lower bending blade and the cushion plate are formed with through holes penetrating each lower punch leg. Press mold featuring. The press die according to claim 8.
The guide member is provided with a stopper pin that regulates the amount of vertical movement stroke of the cushion plate.
The cushion plate is characterized in that a regulation block with which the stopper pin abuts is formed at an elevated position of the cushion plate in which the convex molded portion and the concave molded portion form the stepped portion. Press mold to do.

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