JP2022139485A - Method and facility for manufacturing press molded article - Google Patents

Abstract

To reduce tensile residual stress generated in the inside of bending in a bent part of a press molded article in a pressing step.SOLUTION: A method for manufacturing a press molded article (50) includes a first step and a second step. The first step presses a metal plate (30), and thereby obtains an intermediate article (40). The second step presses the intermediate article (40) using a mold (21) including a punch (26), a pad (28) and dies (27L and 27R), and obtains a press molded article (50). The second step includes the steps of: mounting the intermediate article (40) on the punch (26) so that a top plate (41) is arranged on a punch top surface (261) and projections (42L and 42R) are arranged at positions corresponding to punch shoulders (262L and 262R); pressing the top late (41) with the pad (28); bringing the dies (27L and 27R) into contact with flanges (44L and 44R); and crushing the projections (42L and 42R) with the dies (27L and 27R).SELECTED DRAWING: Figure 5A

Description

TECHNICAL FIELD The present disclosure relates to a method and equipment for manufacturing press-formed products.

2. Description of the Related Art Conventionally, press-formed products have been used as parts constituting automobile bodies and the like. A press-formed product is manufactured by pressing a metal plate. More specifically, a press-formed product is manufactured by drawing or bending a metal plate as a raw material using a mold including a die and a punch.

In press working of a metal plate, springback occurs when a press-molded product molded by a mold is released from the mold. That is, when a metal plate is bent by a die during press working, a tensile stress is generated on the outside of the bend and a compressive stress is generated on the inside of the bend. , elastic recovery of the material occurs. As a result, stress in the direction opposite to the direction of the stress during press working is generated in the bent portion of the press-formed product. The reversal stress due to this springback is added to the stress at the end of molding, so that in the bent portion of the press-formed product, compressive stress remains on the outside of the bend and tensile stress remains on the inside of the bend.

For press-formed products used as automobile parts, it is preferable that the tensile residual stress on the inner side of the bend is small. For example, in automobile underbody parts such as suspension members, relatively large stress is repeatedly generated in the bent portion when the automobile starts, runs, or brakes. Fatigue strength decreases.

In order to resist fatigue failure caused by repeated loads, appropriate materials and plate thicknesses are adopted when manufacturing press-formed products for automobile parts. In addition, in order to meet the need for weight reduction of vehicles, the strength and thickness of metal plates, which are the raw materials, are being increased. However, when the thickness of the material is reduced, the repeated load on the press-molded product manufactured from the material increases. Therefore, in order to achieve both weight reduction (thinning of the material) and fatigue strength, it is necessary to reduce the tensile stress remaining inside the bent portion of the press-formed product.

Heat treatment, shot peening, impact treatment using an ultrasonic vibrator, and the like are known as means for removing tensile residual stress from press-molded products. However, since these treatments must be performed in a process separate from the pressing process, they reduce the efficiency of manufacturing the press-formed product and increase the man-hours and cost required for manufacturing the press-formed product. Moreover, in shot peening, it is difficult to treat only the bent portion of the press-formed product, and in addition, there is a problem that the surface of the press-formed product is roughened. Therefore, it is preferable that the tensile residual stress in the bent portion of the press-formed product is reduced in the press working process.

For example, Patent Literature 1 discloses a technique of applying a so-called ironing process to a metal plate as a raw material in order to reduce tensile residual stress. In Patent Document 1, the clearance between the die and the punch is set to be equal to or greater than the thickness of the metal plate and equal to or less than 1.02 times the thickness of the metal plate. According to Patent Document 1, by setting the clearance in this way, the residual stress in the portion of the metal plate that is in contact with the shoulder of the mold from before the start of bending finally contacts the shoulder. Since the residual stress is smaller than the residual stress of the portion where the stress is applied, the fatigue characteristics of the press-formed product can be improved.

Patent Literature 2 discloses a press device including a die and a punch, as well as a pad facing the top surface of the punch. In this press device, the die is lowered, the die and the punch shoulder press the metal plate to form a bent portion in the metal plate, and then the pad is lowered toward the top surface of the punch. A recess is formed in the top surface of the punch, and this recess forms a space below the metal plate, so when the lowered pad presses the metal plate, the material of the metal plate flows into the recess side of the top surface of the punch. do. According to Patent Document 2, due to the inflow of such material, a force in the tensile direction is applied to the inner side of the bent portion to reduce the compressive stress, thereby reducing the amount of springback after releasing the mold. Therefore, the tensile residual stress inside the bend can be reduced.

Patent Documents 3 to 5 disclose techniques for devising the shape of the press-molded product itself in order to reduce the amount of springback after mold release. In Patent Documents 3 to 5, in a press-molded product having a substantially hat-shaped cross section, unevenness or steps are provided on the vertical wall portion.

Japanese Patent Application Laid-Open No. 2002-316215 WO2017/131042 Japanese Patent Application Laid-Open No. 2004-314123 JP 2006-272378 A JP 2017-196646 A

As described above, when a metal plate is pressed to produce a press-formed product, compressive stress remains on the outside of the bend and tensile stress remains on the inside of the bend at the bent portion of the press-formed product. In order to obtain press-formed products with better fatigue properties, it is particularly necessary to reduce the tensile residual stress on the inner side of the bend. In addition, from the viewpoint of preventing an increase in manufacturing man-hours and manufacturing costs of the press-formed product, it is preferable that the tensile residual stress on the inner side of the bend is reduced in the press working process.

An object of the present disclosure is to reduce the tensile residual stress generated inside the bend in the bent portion of the press-formed product in the press working process.

A method for manufacturing a press-formed product according to the present disclosure includes a first step and a second step. In the first step, an intermediate molded product is obtained by pressing a metal plate. The intermediate molded product includes a top plate, protrusions, vertical walls, and flanges. The protrusion is connected to the top plate and protrudes upward from the top plate. A vertical wall extends downwardly from the protrusion. A flange extends from the lower end of the vertical wall to the opposite side of the top plate. In the second step, a die is used to press the intermediate molded product to obtain a press molded product. The mold includes a punch, a pad and a die. A pad is positioned above the punch to face the punch. A die is positioned above the punch and to the side of the pad. The punch includes a punch top, a punch shoulder, and a punch side. The punch shoulder is continuous with the punch top surface. A punch side extends downwardly from the punch shoulder. The die includes an upper die shoulder, a die side surface, and a die lower surface. The upper die shoulder corresponds to the punch shoulder. A die side extends downwardly from the upper die shoulder corresponding to the punch side. The die bottom surface is connected to the bottom edge of the die side surface via the bottom die shoulder. The second step includes placing the intermediate molded product on the punch so that the top plate is arranged on the top surface of the punch and the convex portion is arranged at a position corresponding to the punch shoulder, lowering the pad, The process of pressing the top plate on the top of the punch with a pad, the process of lowering the die and contacting the flange with the top plate pressed by the pad, and the process of lowering the die further after the die contacts the flange. and squeezing the protrusions with a die.

Advantageous Effects of Invention According to the present disclosure, it is possible to reduce the tensile residual stress generated inside the bend in the bent portion of the press-formed product in the press working process.

FIG. 1 is a diagram schematically showing manufacturing equipment according to an embodiment and a process of manufacturing a press-formed product by the manufacturing equipment. FIG. 2 is a cross-sectional view showing a schematic configuration of a press device for manufacturing an intermediate molded product included in the manufacturing equipment according to the embodiment. FIG. 3 is a cross-sectional view showing a schematic configuration of a press device for manufacturing a press-formed product included in the manufacturing equipment according to the embodiment. FIG. 4A is a schematic diagram for explaining the first step of the method for manufacturing a press-formed product according to the embodiment. FIG. 4B is a schematic diagram for explaining the first step of the method for manufacturing a press-formed product according to the embodiment. FIG. 4C is a schematic diagram for explaining the first step of the method for manufacturing a press-formed product according to the embodiment. FIG. 4D is a schematic diagram for explaining the first step of the method for manufacturing a press-formed product according to the embodiment. FIG. 4E is a schematic diagram for explaining the first step of the method for manufacturing a press-formed product according to the embodiment. FIG. 5A is a schematic diagram for explaining the second step of the method for manufacturing a press-formed product according to the embodiment. FIG. 5B is a schematic diagram for explaining the second step of the method for manufacturing a press-formed product according to the embodiment. FIG. 5C is a schematic diagram for explaining the second step of the method for manufacturing a press-formed product according to the embodiment. FIG. 5D is a schematic diagram for explaining the second step of the method for manufacturing a press-formed product according to the embodiment. FIG. 5E is a schematic diagram for explaining the second step of the method for manufacturing a press-formed product according to the embodiment. FIG. 5F is a schematic diagram for explaining the second step of the method for manufacturing a press-formed product according to the embodiment. FIG. 5G is a schematic diagram for explaining the second step of the method for manufacturing a press-formed product according to the embodiment. FIG. 5H is a schematic diagram for explaining the second step of the method for manufacturing a press-formed product according to the embodiment. FIG. 6 shows the relationship between the height/width of the convex portion of the intermediate molded product obtained in the first step and the tensile residual stress inside the bend at the bent portion of the press molded product in the method for manufacturing a press-formed product according to the embodiment. It is a graph showing the relationship. FIG. 7 is a graph showing the relationship between the radius of curvature of the apex of the convex portion of the intermediate molded product and the tensile residual stress inside the bend of the bent portion of the press-formed product. FIG. 8 is a graph showing the relationship between the height of the intermediate molded product and the tensile residual stress inside the bend at the bent portion of the press-formed product. FIG. 9 is a graph showing the relationship between the angle of the flange of the intermediate molded product and the tensile residual stress inside the bend in the bent portion of the press-formed product. FIG. 10 is a graph showing the relationship between the length of the flange of the intermediate molded product and the tensile residual stress inside the bend in the bent portion of the press-formed product. FIG. 11 shows the relationship between the radius of curvature of the lower die shoulder of the mold used in the second step and the tensile residual stress on the inner side of the bend in the bent portion of the press-formed product in the method for manufacturing a press-formed product according to the embodiment. It is a graph showing. FIG. 12 is a graph showing the relationship between the position of the convex portion of the intermediate molded product with respect to the pad profile of the mold and the tensile residual stress inside the bend in the bent portion of the press molded product in the second step. FIG. 13 is a graph showing the relationship between the work hardening index of a metal plate, which is the material of the press-formed product, and the tensile residual stress inside the bend in the bent portion of the press-formed product. FIG. 14 is a schematic diagram showing a method of manufacturing a press-formed product according to a modification of the above embodiment. FIG. 15 is a graph showing the effect of the method of manufacturing a press-formed product according to the modification. FIG. 16 is a perspective view showing a schematic configuration of a press-formed product according to an example. FIG. 17 is a graph showing the stress distribution in the plate thickness direction generated at the end of forming and the residual stress distribution in the plate thickness direction after springback, with respect to the stress generated in the bending circumferential direction at the bent portion of the conventional press-formed product. is. FIG. 18 shows the knowledge of the present inventors, regarding the stress generated in the bending circumferential direction at the bent portion of the press-formed product, the stress distribution in the plate thickness direction generated at the end of forming, and the plate thickness direction after springback. It is a graph which shows residual-stress distribution.

The present inventors conducted CAE analysis of press working using commercially available software (LS-DYNA ver971 rev. Analysis conditions are as follows.
・Tensile strength of material: 980MPa
・Thickness of material: 3.0mm
・ Bending R (curvature radius inside bending): 4.0 mm
・Shape of press-formed product (after processing): A shape consisting of two vertical walls and a top plate that connects the vertical walls (without flanges)

FIG. 17 shows the stress distribution in the plate thickness direction at the end of forming and the residual stress distribution in the plate thickness direction after springback with respect to the stress generated in the bending circumferential direction at the bent portion of the press-formed product. FIG. 17 shows the stress (stress in the bending circumferential direction) generated on the line from the R vertex (center of R) on the inner side of the bend to the R vertex on the outer side of the bend at the bent portion of the press-formed product. As can be seen from FIG. 17, at the bent portion of the press-formed product at the end of molding, tensile stress is generated on the outside of the bend, and compressive stress is generated on the inside of the bend. On the other hand, after springback, compressive residual stress occurs on the outside of the bend and tensile residual stress occurs on the inside of the bend at the bent portion of the press-formed product.

The present inventors have found that in the bent portion of the press-formed product after springback, compressive residual stress is generated not only in the area on the outside of the bend, but also in the area on the inside of the bend near the neutral axis (thickness center). We paid attention to , and came up with the idea of applying tension to the bending part during press working. The present inventors have found that by performing press working while applying tension to the portion of the material that will be the bent portion, it is possible to reduce the compressive stress at the end of the forming in the region inside the bend. It was thought that the tensile residual stress after springback would also be reduced.

When CAE analysis was performed under the same conditions as above except that the material was bent while tension was applied, the stress distribution shown in FIG. 18 was obtained. As can be seen from FIG. 18, when the bent portion of the press-formed product is formed while tension is applied, the compressive stress on the inner side of the bend at the end of forming decreases, and the tensile residual stress on the inner side of the bend after springback decreases. , resulting in more compressive stress. Therefore, the present inventors have studied a method of applying tension to the bent portion of the press-formed product during press working, and have completed a method of manufacturing a press-formed product according to an embodiment.

A method for manufacturing a press-formed product according to an embodiment includes a first step and a second step. In the first step, an intermediate molded product is obtained by pressing a metal plate. The intermediate molded product includes a top plate, protrusions, vertical walls, and flanges. The protrusion is connected to the top plate and protrudes upward from the top plate. A vertical wall extends downwardly from the protrusion. A flange extends from the lower end of the vertical wall to the opposite side of the top plate. In the second step, a die is used to press the intermediate molded product to obtain a press molded product. The mold includes a punch, a pad and a die. A pad is positioned above the punch to face the punch. A die is positioned above the punch and to the side of the pad. The punch includes a punch top, a punch shoulder, and a punch side. The punch shoulder is continuous with the punch top surface. A punch side extends downwardly from the punch shoulder. The die includes an upper die shoulder, a die side surface, and a die lower surface. The upper die shoulder corresponds to the punch shoulder. A die side extends downwardly from the upper die shoulder corresponding to the punch side. The die bottom surface is connected to the bottom edge of the die side surface via the bottom die shoulder. The second step includes placing the intermediate molded product on the punch so that the top plate is arranged on the top surface of the punch and the convex portion is arranged at a position corresponding to the punch shoulder, lowering the pad, The process of pressing the top plate on the top of the punch with a pad, the process of lowering the die and contacting the flange with the top plate pressed by the pad, and the process of lowering the die further after the die contacts the flange. , and a step of crushing the protrusion with a die (first configuration).

In the method for manufacturing a press-formed product according to the first configuration, after pressing a metal plate into an intermediate formed product in the first step, in the second step, intermediate forming is performed using a mold including a punch, a pad, and a die. The product is press-processed to obtain a press-molded product. In the second step, first, the intermediate molded product is placed on a punch, and the top plate of the intermediate molded product is pressed from above by a pad. In this state, the die is brought into contact with the flange of the intermediate product, and the die is lowered as it is. The flange of the intermediate product is not bent back immediately after contact with the die, but is gradually bent back as the die descends. As a result, the molding progresses while the flange is caught by the lower die shoulder, and tension acts on the convex portion and the vertical wall provided between the top plate and the flange in the intermediate molded product. That is, tension is applied to the part of the intermediate product that will be the bent portion in the final press-formed product. Therefore, in the bent portion of the press-formed product, the compressive stress on the inner side of the bend at the end of forming can be reduced. As a result, the tensile stress remaining inside the bend after springback can be reduced.

Furthermore, in the second step, as the die descends, the protrusions of the intermediate product arranged at positions corresponding to the punch shoulders are crushed by the die and subjected to bending deformation. In the process in which the convex portion is bent back by the die and pushed into the punch shoulder, compressive stress is generated in the die-side (bending outer side) region and tensile stress is generated in the punch-side (bending inner side) region. These stresses generate tensile stress on the outside of the bend and compressive stress on the inside of the bend when the intermediate product conforms to (wraps around) the punch shoulder and forms a bent portion, that is, when the second process is completed. can be reduced. As a result, in the bent portion of the press-formed product after springback, the tensile residual stress generated inside the bend can be reduced.

It is difficult to flatten the convex portion only by applying tension to the convex portion located at the position corresponding to the punch shoulder. However, in the method of manufacturing a press-formed product according to the first configuration, the protrusion is crushed by the die in the second step. As a result, the convex portion can be firmly flattened. More specifically, the descending die hits the protrusion and crushes the protrusion from the top, thereby generating a large stress from the base to the top of the protrusion. That is, a large tensile stress is generated in the region inside the bend. Therefore, it is possible to effectively reduce the compressive stress generated on the inner side of the bending at the end of the second step. As a result, in the bent portion of the press-formed product after springback, the tensile residual stress generated inside the bend can be reduced.

In this way, as the molding progresses while the flange is caught on the lower die shoulder, tension is applied to the convex portion and vertical wall provided between the top plate and the flange in the intermediate molded product, and this convex portion By crushing from the top, the compressive stress generated inside the bending at the end of the second step can be significantly reduced. As a result, it is possible to remarkably reduce the tensile residual stress generated inside the bent portion of the press-formed product after springback.

As described above, according to the method for manufacturing a press-formed product according to the first configuration, it is possible to reduce the residual tensile stress generated inside the bend in the bent portion of the press-formed product in the press working process.

In the above manufacturing method, when the intermediate molded product is placed on the punch, the upper end of the projection is located inside the lower end of the side surface of the die in the width direction of the mold, and the lower end of the vertical wall is the width of the mold. It is preferably located outside the upper end of the punch side surface in the direction (second configuration).

According to the second configuration, when the intermediate molded product is placed on the punch, that is, at the start of the second step, the upper end of the convex portion is located inside the lower end of the side surface of the die in the width direction of the die. ing. As a result, it is possible to prevent the protrusion from being crushed by the lower die shoulder or the die lower surface at the beginning of the second step. In other words, in the middle or later stage of the second step, the convex portion can be crushed by the die to generate tensile stress in the area inside the bend. Therefore, it is possible to more effectively reduce the compressive stress generated inside the bend at the end of the second step. Therefore, in the bent portion of the press-formed product, it is possible to more reliably reduce the tensile residual stress generated on the inner side of the bend.

In the intermediate molded product placed on the punch, when the lower end of the vertical wall is located inside the upper end of the side surface of the punch in the width direction of the mold, the top plate of the intermediate molded product is lifted from the top surface of the punch. . If press molding is performed in this state, the intermediate molded product cannot be stably pressed by the pad, and the intermediate molded product may shift in the width direction (horizontal direction) of the mold during molding. The dimensional accuracy of press-molded products cannot be obtained. On the other hand, in the second configuration, when the intermediate molded product is placed on the punch, the lower end of the vertical wall is located outside the upper end of the side surface of the punch in the width direction of the mold. ing. Therefore, the top plate of the intermediate molded product does not rise from the top surface of the punch, and the intermediate molded product can be stably placed on the punch. Moreover, it is possible to prevent the pad from floating when the top plate of the intermediate molded product is pressed by the pad. Therefore, the dimensional accuracy of the press-molded product obtained in the second step can be stabilized.

In the intermediate molded product, the distance in the vertical direction from the connection between the projection and the top plate to the upper end of the projection is H1 [mm], and the intermediate molded product from the connection between the projection and the top plate to the upper end of the projection Assuming that the distance in the width direction is W1 [mm], H1/W1 is preferably 0.5 or more and 2.0 or less (third configuration).

According to the third configuration, in the intermediate molded product, the vertical distance (the height of the protrusion) H1 from the connection portion between the protrusion and the top plate to the upper end of the protrusion, and the distance between the protrusion and the top plate The ratio of the distance (the width of the protrusion) W1 in the width direction from the connecting portion to the upper end of the protrusion: H1/W1 is 0.5 or more. As a result, since the convex portion rises relatively sharply from the top plate, the amount of bending deformation of the convex portion due to the die can be ensured. Therefore, when the convex portion is bent back in the second step, tensile stress can be generated more effectively in the region inside the bend. Therefore, the compressive stress generated on the inner side of the bend at the end of the second step can be more reliably reduced, and the effect of reducing the tensile stress remaining on the inner side of the bend in the bent portion of the press-formed product can be improved. .

In the third configuration, the ratio of height H1 to width W1: H1/W1 is 2.0 or less in the convex portion of the intermediate molded product. As a result, the convex portion does not form an excessively steep shape with respect to the top plate, so that it is possible to suppress buckling of the convex portion when the convex portion is crushed by the die in the second step.

In the manufacturing method described above, the convex portion may include an arc-shaped apex in a cross-sectional view of the intermediate molded product. The apex preferably has a radius of curvature of 4 mm or more and 16 mm or less (fourth configuration).

In the fourth configuration, when viewed in cross section of the intermediate molded product, the convex portion includes an arc-shaped apex. By setting the radius of curvature of the apex to 4 mm or more, it is possible to suppress the buckling of the protrusions when the protrusions are pressed with a die. Further, by setting the radius of curvature of the top portion to 16 mm or less, the convex portion does not have an excessively gentle shape, so that in the second step, the tensile stress on the inner side of the bend due to the bending back deformation of the convex portion is more effectively generated. be able to. Therefore, the compressive stress generated inside the bend at the end of the second step can be further reduced, and the tensile stress remaining inside the bend at the bent portion of the press-formed product can be more reliably reduced.

In the mold used in the second step of the manufacturing method, the punch shoulder has, for example, an arc shape when viewed in cross section of the punch. When the intermediate product is placed on the punch, the distance D2 [mm] in the width direction of the mold from the end of the punch shoulder on the punch top surface side to the upper end of the projection is the same as that of the punch shoulder. It is preferable to satisfy the following equation, where positive is positive when positioned outside the end of the top surface side in the width direction, and negative when positioned inside in the width direction (fifth configuration).
-1.0 × Rp × (π-θ) ≤ D2 ≤ 2.5 × Rp × (π-θ)
where Rp is the radius of curvature "mm" of the punch shoulder, and θ is the angle [rad] formed between the top surface of the punch and the side surface of the punch.

According to the fifth configuration, the distance D2 in the width direction of the die from the end of the punch shoulder on the punch top surface side to the upper end of the projection is determined by the radius of curvature Rp of the punch shoulder and the distance between the punch top surface and the punch side surface. It is set so as to satisfy the above formula in relation to the angle θ. By setting the distance D2 in this way, the convex portion is likely to overlap the punch shoulder in the width direction of the die. In contrast, tensile stress can be generated more widely. Therefore, it is possible to more effectively reduce the compressive stress generated inside the bend when the intermediate molded product conforms to the punch shoulder and the bent portion is formed. As a result, in the bent portion of the press-formed product, it is possible to more reliably reduce the tensile stress remaining inside the bend after springback.

In the intermediate molded product, the distance in the vertical direction from the end of the flange on the vertical wall side to the top plate is preferably 6 mm or more (sixth configuration).

If the height of the intermediate molded product, that is, the vertical distance from the edge of the vertical wall side of the flange to the top plate is insufficient, when the die in contact with the flange descends in the second step, the vertical wall There may be general deflection and reduced tension applied to the ridges and vertical walls. On the other hand, in the sixth configuration, the height of the intermediate molded product is ensured to be 6 mm or more. As a result, in the second step, bending of the vertical wall of the intermediate molded product can be suppressed, and tension can be applied more effectively to the convex portion and the vertical wall. Therefore, in the bent portion of the press-formed product, it is possible to further reduce the compressive stress on the inner side of the bend at the end of the forming, and improve the effect of reducing the tensile stress remaining on the inner side of the bend after springback.

In the above manufacturing method, when the intermediate molded product is placed on the punch, the angle formed by the flange with respect to the horizontal plane is positive when the flange rotates upward around the end of the vertical wall side, and rotates downward. It is preferable that the angle is -40° or more and 40° or less (seventh configuration).

According to the seventh configuration, the angle formed by the flange of the intermediate molded product with respect to the horizontal plane is -40° or more. As a result, in the second step, when the die comes into contact with the flange of the intermediate product and descends, the flange is likely to catch on the shoulder of the lower die. Therefore, in the intermediate molded product, tension can be more reliably applied to the convex portion and the vertical wall provided between the top plate and the flange. Therefore, in the bent portion of the press-formed product, it is possible to more effectively reduce the compressive stress on the inner side of the bend at the end of the forming, and improve the effect of reducing the tensile stress remaining on the inner side of the bend after springback.

In the seventh configuration, the angle formed by the flange of the intermediate molded product with respect to the horizontal plane is 40° or less. As a result, when the die contacts the flange, it is possible to prevent the flange from buckling and the die from being damaged by the tip of the flange.

In the manufacturing method described above, the lower die shoulder preferably has an arcuate shape with a curvature radius of 1 mm or more and 12 mm or less when viewed in cross section of the die (eighth configuration).

In the manufacturing method according to the embodiment, in the second step, the top plate of the intermediate molded product is pressed with the pad, and then the die is brought into contact with the flange of the intermediate molded product. When the die is lowered in this state, the flange catches on the lower die shoulder and tension is applied to the intermediate product between the pad and the lower die shoulder. In order to make it easier to hook the flange on the lower die shoulder, it is preferable to reduce the radius of curvature of the lower die shoulder to some extent. Also, the smaller the radius of curvature of the lower die shoulder, the more the flange can be continuously hooked to the lower die shoulder until near the bottom dead center of the die. If the radius of curvature of the lower die shoulder is too large, the contact area between the intermediate molded product and the lower die shoulder will also be too large. In this case, when the die descends, the vertical walls and flanges of the intermediate molded product are bent as a whole, and the flange is less likely to catch on the shoulder of the lower die. The applied tension is reduced. In view of this point, in the eighth configuration, the radius of curvature of the lower die shoulder is set to 12 mm or less. As a result, in the second step, the contact area between the intermediate molded product and the lower die shoulder can be limited, and the flange is easily caught on the lower die shoulder. Tension can be applied more effectively to the intermediate molded product. Therefore, in the bent portion of the press-formed product, it is possible to further reduce the compressive stress on the inner side of the bend at the end of the forming, and improve the effect of reducing the tensile stress remaining on the inner side of the bend after springback.

If the radius of curvature of the lower die shoulder is less than 1 mm, the lower die shoulder may leave a bite mark on the press-formed product or cause a large bending habit in the press-formed product. Therefore, as in the eighth configuration, the radius of curvature of the lower die shoulder is preferably 1 mm or more.

In the above manufacturing method, the work hardening index of the metal plate is preferably 0.04 or less (ninth configuration).

According to the ninth configuration, the metal plate has a sufficiently small work hardening index of 0.04 or less. Therefore, work hardening of the material is less likely to occur in the first step of obtaining the intermediate molded product from the metal plate and the second step of obtaining the press-molded product from the intermediate molded product. In this case, the stress generated in the material is reduced in each step, and as a result, the stress due to springback is also reduced. Therefore, in each step, the residual stress, which is the sum of the stress at the end of molding and the reversal stress due to springback, can be reduced.

Manufacturing equipment according to the embodiment is manufacturing equipment for manufacturing a press-formed product. The manufacturing facility includes a first mold and a second mold. The first mold molds the metal plate into an intermediate molded product. The intermediate molded product includes a top plate, protrusions, vertical walls, and flanges. The protrusion is connected to the top plate and protrudes upward from the top plate. A vertical wall extends downwardly from the protrusion. A flange extends from the lower end of the vertical wall to the opposite side of the top plate. The second mold molds the intermediate molded product into a press molded product. A second mold includes a punch, a pad, and a die. The punch includes a punch top surface, a punch shoulder continuous with the punch top surface, and a punch side surface extending downwardly from the punch shoulder. The punch is configured such that the top plate is arranged on the top surface of the punch and the convex portion is arranged at a position corresponding to the punch shoulder when forming the intermediate product into a press-formed product. The pad is arranged above the punch and configured to be movable up and down. The pad is configured to face the top plate arranged on the top surface of the punch when forming the intermediate product into a press-formed product. The die is arranged above the punch and on the side of the pad and configured to be movable up and down. The die has an upper die shoulder corresponding to the punch shoulder, a die side surface extending downward from the upper die shoulder corresponding to the punch side surface, and a die lower surface connected to the lower end of the die side surface via the lower die shoulder. include. The die is configured such that the lower surface of the die faces the flange when the intermediate molded product is formed into a press-molded product.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each figure, the same or corresponding configurations are denoted by the same reference numerals, and the same description will not be repeated.

[production equipment]
FIG. 1 is a diagram schematically showing a manufacturing facility 100 according to this embodiment and a process of manufacturing a press-formed product by the manufacturing facility 100. As shown in FIG. Press-molded products are, for example, underbody parts of automobiles and frame parts such as ladder frames. Automobile undercarriage parts include, for example, arm parts such as upper arms, lower arms, and trail links, as well as suspension members, torsion beams, and the like.

As shown in FIG. 1 , the manufacturing facility 100 includes press devices 10 and 20 . The press machine 10 forms an intermediate product 40 from a metal plate 30 as a raw material. The press machine 20 molds a press-molded product 50 as a final molded product from the intermediate molded product 40 . The configuration of each of the press devices 10 and 20 will be described below with reference to FIGS. 2 and 3. FIG.

[Press equipment for intermediate molded products]
FIG. 2 is a cross-sectional view showing a schematic configuration of the pressing device 10 for obtaining the intermediate molded product 40 shown in FIG. As shown in FIG. 2, the press device 10 includes a mold 11, a bed 12, a slide 13, and mold holders 14,15. Mold 11 includes a punch 16 and a die 17 . The punch 16 and the die 17 extend in a direction that intersects the paper surface of FIG. Hereinafter, for convenience of explanation, regarding the press apparatus 10 and its components, the direction in which the die 11, that is, the punch 16 and the die 17 extend is referred to as the longitudinal direction, and the direction in which the punch 16 and the die 17 approach and separate (Fig. 2 ) is referred to as the up-down direction (vertical direction). A direction perpendicular to the plane consisting of the longitudinal direction and the vertical direction, that is, a direction crossing the punch 16 and the die 17 is referred to as a lateral direction or a width direction. Regarding the press device 10 and its constituent parts, a cross section taken along a plane perpendicular to the longitudinal direction is called a cross section.

The punch 16 is supported by a bed 12 that is part of the body of the press device 10 via a mold holder 14 . That is, a mold holder 14 is fixed on the upper surface of the bed 12 and a punch 16 is arranged on this mold holder 14 . A plate-shaped spacer may be inserted between the bed 12 and the mold holder 14 in order to adjust the position of the punch 16 in the vertical direction.

The punch 16 includes a punch top surface 161, left and right convex surfaces 162L, 162R, left and right punch side surfaces 163L, 163R, and left and right punch flange surfaces 164L, 164R.

In this embodiment, the punch top surface 161 has a longitudinally extending groove 161a. The groove portion 161 a may extend over the entire lengthwise direction of the punch top surface 161 or may be provided in a part of the lengthwise direction of the punch top surface 161 . In the example of this embodiment, the punch top surface 161 has an asymmetric shape with respect to a vertical plane parallel to the longitudinal direction, that is, a left-right asymmetric shape. However, the punch top surface 161 may have a symmetrical shape.

Both sides of the punch top surface 161 are provided with convex surfaces 162L and 162R. The convex surfaces 162L and 162R are provided continuously with the punch top surface 161. As shown in FIG. The convex surfaces 162L, 162R are typically provided continuously over the punch top surface 161 over the entire punch top surface 161 .

The convex surface 162L is connected to the left edge of the punch top surface 161. As shown in FIG. The convex surface 162</b>L protrudes upward from the punch top surface 161 . More specifically, the convex surface 162L protrudes upward as compared with a portion of the punch top surface 161 that is laterally outside (to the left) of the groove portion 161a. The convex surface 162L has a convex shape that once rises outward from the punch top surface 161 in the width direction and then descends. The top of the convex surface 162L has, for example, a substantially arcuate shape when the punch 16 is viewed in cross section. Hereinafter, the term "substantially arcuate" includes not only curves forming part of a perfect circle, but also smooth curves such as elliptical curves and spline curves. In addition, the radius of curvature of a smooth curve other than a curve that constitutes a part of a perfect circle is defined as the radius of a circle passing through three points, the two ends of the curve and the midpoint of the curve, when cut by a cross section. do.

The convex surface 162R is provided continuously with the right edge of the punch top surface 161. As shown in FIG. The convex surface 162</b>R protrudes upward from the punch top surface 161 . More specifically, the convex surface 162R protrudes upward as compared with the portion of the punch top surface 161 that is located on the widthwise outer side (right side) of the groove portion 161a. The convex surface 162R has a convex shape that once rises outward from the punch top surface 161 in the width direction and then descends. The top of the convex surface 162R has, for example, a substantially arcuate shape when the punch 16 is viewed in cross section. The convex surface 162R may have a shape symmetrical with the convex surface 162L with respect to a vertical plane parallel to the longitudinal direction, or may have an asymmetrical shape.

The punch side surfaces 163L and 163R extend downward from the convex surfaces 162L and 162R, respectively, when the punch 16 is viewed in cross section. The punch side surface 163L is provided continuously with the left convex surface 162L. The punch side surface 163R is provided continuously with the right convex surface 162R. In the example of this embodiment, each of the punch side surfaces 163L, 163R is inclined with respect to a vertical plane parallel to the longitudinal direction so that the lower end thereof is located outside the upper end thereof in the width direction. The punch side surfaces 163L and 163R may have a symmetrical shape with respect to a vertical plane parallel to the longitudinal direction, or may have an asymmetrical shape. Also, the punch side surfaces 163L, 163R may be smooth curves continuously provided from the convex surfaces 162L, 162R. The punch side surfaces 163L, 163R or the convex surfaces 162L, 162R may curve (bend) inward or outward in the width direction on the way from the upper ends of the convex surfaces 162L, 162R to the punch flange surfaces 164L, 164R.

The punch flange surfaces 164L, 164R extend outward in the width direction from the punch side surfaces 163L, 163R, respectively, in a cross-sectional view of the punch 16 . The punch flange surfaces 164L, 164R may extend substantially horizontally from the punch side surfaces 163L, 163R, but at least one of them may extend obliquely with respect to the horizontal surface. For example, the angle formed by each of the punch flange surfaces 164L and 164R with respect to the horizontal plane is positive when the punch flange surfaces 164L and 164R rotate upward around the widthwise inner end, and rotates downward. can be set in the range of -40° or more and 40° or less. The angle between the punch flange surfaces 164L, 164R and the horizontal plane is preferably -10° or more and 10° or less. Here, the horizontal plane means a plane perpendicular to the direction (vertical direction) in which the punch 16 and the die 17 approach and separate from each other. The angle formed by the punch flange surfaces 164L and 164R with respect to the horizontal plane means the angle (acute angle side) formed between the punch flange surfaces 164L and 164R and the width direction in a cross section cut along a plane consisting of the vertical direction and the width direction. .

The punch flange surface 164L is provided continuously with the lower end of the left punch side surface 163L. The punch flange surface 164R is provided continuously with the lower end of the right punch side surface 163R. A boundary portion between the punch flange surface 164L and the punch side surface 163L is preferably subjected to R chamfering. Similarly, the boundary portion between the punch flange surface 164R and the punch side surface 163R is preferably R-chamfered. That is, it is preferable that the boundary between the punch flange surface 164L and the punch side surface 163L and the boundary between the punch flange surface 164R and the punch side surface 163R are substantially arcuate in cross-sectional view of the punch 16, respectively.

A die 17 is arranged above the punch 16 . Die 17 is attached to slide 13 via mold holder 15 . That is, a mold holder 15 is fixed to the bottom surface of the slide 13 and a die 17 is fixed to the bottom surface of the mold holder 15 . A plate-shaped spacer may be inserted between the slide 13 and the mold holder 15 to adjust the position of the die 17 in the vertical direction. The slide 13 is configured to be able to move up and down with respect to the punch 16 by, for example, a mechanical or hydraulic mechanism (not shown) provided in the press device 10 . As the slide 13 moves up and down, the die 17 also moves up and down with respect to the punch 16 .

Die 17 has a forming surface corresponding to the forming surface of punch 16 . The molding surface of the die 17 has a shape that is offset from the molding surface of the punch 16 by the thickness of the metal plate 30 processed by the mold 11 . The forming surface of the die 17 has a shape offset from the forming surface of the punch 16 by 0.9 to 1.2 times the thickness of the metal plate 30, for example. The die 17 includes a die bottom surface 171, left and right concave surfaces 172L and 172R, left and right die side surfaces 173L and 173R, and left and right die flange surfaces 174L and 174R.

Die bottom surface 171 faces punch top surface 161 . The die bottom surface 171 is formed in a shape corresponding to the shape of the punch top surface 161 . In this embodiment, the die bottom surface 171 has a ridge portion 171 a corresponding to the groove portion 161 a of the punch top surface 161 .

Concave surfaces 172L and 172R are provided on both sides of the die bottom surface 171 corresponding to the convex surfaces 162L and 162R of the punch 16, respectively. The concave surfaces 172</b>L and 172</b>R are provided continuously with the die bottom surface 171 . Concave surfaces 172L and 172R are typically provided continuously on die bottom surface 171 over the entire longitudinal direction of die bottom surface 171, similarly to convex surfaces 162L and 162R of punch 16. As shown in FIG.

The concave surface 172</b>L is connected to the left edge of the die bottom surface 171 . The concave surface 172</b>L is recessed upward with respect to the die bottom surface 171 . More specifically, the concave surface 172L is recessed upward compared to a portion of the die bottom surface 171 that is outside (to the left of) the widthwise direction of the protrusion 171a. The concave surface 172L has a concave shape that once rises outward from the die bottom surface 171 in the width direction and then descends. The concave shape of the concave surface 172</b>L corresponds to the convex shape of the convex surface 162</b>L of the punch 16 . The bottom of the concave surface 172L has, for example, a substantially arcuate shape when the die 17 is viewed in cross section.

The concave surface 172</b>R is provided continuously with the right edge of the die bottom surface 171 . The concave surface 172</b>R is recessed upward with respect to the die bottom surface 171 . More specifically, the concave surface 172</b>R is recessed upward compared to a portion of the die bottom surface 171 on the width direction outer side (right side) of the protruded streak portion 171 a. The concave surface 172R has a concave shape that once rises outward from the die bottom surface 171 in the width direction and then descends. The concave shape of the concave surface 172R corresponds to the convex shape of the convex surface 162R of the punch 16. As shown in FIG. The bottom of the concave surface 172R has, for example, a substantially arcuate shape when the punch 16 is viewed in cross section.

The die side surfaces 173L and 173R extend downward from the concave surfaces 172L and 172R, respectively, when the die 17 is viewed in cross section. The die side surfaces 173L and 173R are surfaces corresponding to the punch side surfaces 163L and 163R, respectively. The die side surface 173L is provided continuously with the left concave surface 172L. The die side surface 173R is provided continuously with the right concave surface 172R. In the example of this embodiment, each of the die side surfaces 173L, 173R corresponds to the punch side surfaces 163L, 163R and is inclined with respect to a vertical plane parallel to the longitudinal direction.

The die flange surfaces 174L and 174R extend outward in the width direction from the lower ends of the die side surfaces 173L and 173R, respectively, in a cross-sectional view of the die 17 . The die flange surfaces 174L, 174R are surfaces corresponding to the punch flange surfaces 164L, 164R, respectively. The angle formed by the die flange surfaces 174L, 174R with respect to the horizontal plane is substantially equal to the angle formed by the punch flange surfaces 164L, 164R with respect to the horizontal plane.

The die flange surface 174L is provided continuously with the left die side surface 173L. The die flange surface 174R is provided continuously with the right die side surface 173R. The corners of the die flange surface 174L and the die side surface 173L are preferably rounded. Similarly, corners between the die flange surface 174R and the die side surface 173R are preferably rounded. That is, it is preferable that the corners between the die flange surface 174L and the die side surface 173L and the corners between the die flange surface 174R and the die side surface 173R are substantially arcuate in cross-sectional view of the die 17, respectively.

[Press equipment for final molded product]
FIG. 3 is a cross-sectional view showing a schematic configuration of a press device 20 for obtaining a press-molded product 50 (FIG. 1) as a final molded product.

As shown in FIG. 3 , the press device 20 includes a mold 21 , a bed 22 , a slide 23 and mold holders 24 and 25 . The mold 21 includes a punch 26, left and right dies 27L and 27R, and a pad 28. As shown in FIG. The punch 26 and the dies 27L, 27R extend in a direction crossing the plane of FIG. Regarding the press device 20 and its components, the direction in which the die 21, particularly the punch 26 and the dies 27L, 27R extend is called the longitudinal direction, and the direction in which the punch 26 and the dies 27L, 27R approach and separate (the paper surface of FIG. 3). up-down direction) is referred to as up-down direction (vertical direction). A direction perpendicular to the plane consisting of the longitudinal direction and the vertical direction, that is, a direction crossing the punch 26 and the dies 27L and 27R is referred to as a lateral direction or a width direction. Regarding the press device 20 and its constituent parts, a cross section cut along a plane perpendicular to the longitudinal direction is called a cross section.

The punch 26 is supported by a bed 22 that is part of the main body of the press device 20 via a mold holder 24 . That is, a mold holder 24 is fixed on the upper surface of the bed 22 and a punch 26 is arranged on this mold holder 24 . A plate-shaped spacer may be inserted between the bed 22 and the mold holder 24 to adjust the vertical position of the punch 26 .

The punch 26 includes a punch top surface 261, left and right punch shoulders 262L, 262R, and left and right punch side surfaces 263L, 263R.

In this embodiment, the punch top surface 261 is formed with a groove 261a extending in the longitudinal direction. The groove portion 261a is formed, for example, in a shape and size corresponding to the groove portion 161a (FIG. 2) of the punch top surface 161 in the press apparatus 10 shown in FIG. In the example shown in FIG. 3, the punch top surface 261 has an asymmetric shape with respect to a vertical plane parallel to the longitudinal direction, that is, a left-right asymmetric shape, like the punch top surface 161 (FIG. 2). However, the punch top surface 261 may have a symmetrical shape.

The punch shoulders 262L, 262R are provided continuously on the punch top surface 261. As shown in FIG. More specifically, the punch shoulder 262L continues to the left edge of the punch top surface 261, and the punch shoulder 262R continues to the right edge of the punch top surface 261. Each of the punch shoulders 262L, 262R has a substantially arcuate shape when the punch 26 is viewed in cross section. The punch shoulders 262L, 262R are ridges (corners) between the punch top surface 261 and the punch side surfaces 263L, 263R, respectively.

A punch side surface 263L extends downward from the left punch shoulder 262L in a cross-sectional view of the punch 26 . The punch side surface 263R extends downward from the right punch shoulder 262R in a cross-sectional view of the punch 26 . Each of the punch side surfaces 263L, 263R is inclined with respect to a vertical plane parallel to the longitudinal direction so that the lower end is located outside the upper end in the width direction. The angles (acute angle side) formed by the punch side surfaces 263L and 263R with respect to the vertical plane may be the same or different. The angle between the punch side surfaces 263L, 263R and the vertical plane is preferably 20° or less. The angle (acute angle side) formed between the punch side surfaces 263L and 263R and the vertical plane parallel to the longitudinal direction is defined by the punch side surfaces 263L and 263R and the vertical direction in a cross section cut along a plane consisting of the vertical direction and the width direction. It means an angle (acute angle side).

The dies 27L and 27R are arranged above the punch 26 and beside the pad 28. As shown in FIG. The dies 27L, 27R are attached to the slide 23 via a mold holder 25. As shown in FIG. Specifically, a mold holder 25 is fixed to the lower surface of the slide 23, and dies 27L and 27R are fixed to the lower surface of the mold holder 25. As shown in FIG. A plate-like spacer may be inserted between the slide 23 and the mold holder 25 to adjust the vertical positions of the dies 27L and 27R. The slide 23 can be moved up and down with respect to the punch 26 by a mechanical or hydraulic mechanism (not shown) provided in the press device 20, for example. As the slide 23 moves up and down, the dies 27L and 27R also move up and down with respect to the punch 26. As shown in FIG.

Left die 27L includes upper die shoulder 271L, die side 272L, lower die shoulder 273L, die lower surface 274L, and die upper surface 275L. Right die 27R includes upper die shoulder 271R, die side 272R, lower die shoulder 273R, die lower surface 274R, and die upper surface 275R. The left and right dies 27L, 27R may have a symmetrical shape with respect to a vertical plane parallel to the longitudinal direction, or may have an asymmetrical shape.

The upper die shoulders 271L, 271R are provided corresponding to the left and right punch shoulders 262L, 262R, respectively. The upper die shoulders 271L, 271R correspond to the punch shoulders 262L, 262R, respectively, and are substantially arcuate in cross-sectional view of the dies 27L, 27R. The upper die shoulders 271L, 271R are ridges (corners) between the die side surfaces 272L, 272R and the die upper surfaces 275L, 275R.

Die upper surfaces 275L and 275R are arranged inside the upper die shoulders 271L and 271R in the width direction. The die upper surface 275L is provided continuously from the right end of the upper die shoulder 271L and faces the punch top surface 261. As shown in FIG. The die upper surface 275R is provided continuously from the left end of the upper die shoulder 271R and faces the punch top surface 261. As shown in FIG. Die side surfaces 272L and 272R are arranged outside the upper die shoulders 271L and 271R in the width direction. The die side surface 272L is provided continuously from the left end of the upper die shoulder 271L. The die side surface 272R is provided continuously to the right end of the upper die shoulder 271R.

The die side surface 272L extends downward from the upper die shoulder 271L in a cross-sectional view of the die 27L. The die side surface 272R extends downward from the upper die shoulder 271R in a cross-sectional view of the die 27R. Die side surfaces 272L and 272R are provided corresponding to left and right punch side surfaces 263L and 263R, respectively. The die side surfaces 272L and 272R are inclined with respect to a vertical plane parallel to the longitudinal direction so that the lower ends are located outside the upper ends in the width direction corresponding to the punch side surfaces 263L and 263R, respectively. The angle (acute angle side) formed by the die side surfaces 272L and 272R with respect to the vertical plane is substantially equal to the angle (acute angle side) formed with the vertical plane parallel to the longitudinal direction by the punch side surfaces 263L and 263R.

In the left die 27L, the lower die shoulder 273L is provided continuously with the lower end of the die side surface 272L. In the right die 27R, the lower die shoulder 273R is provided continuously with the lower end of the die side surface 272R. The lower die shoulders 273L, 273R are substantially arcuate in cross-sectional view of the dies 27L, 27R, respectively. The lower die shoulders 273L, 273R are ridges (corners) between the die side surfaces 272L, 272R and the die lower surfaces 274L, 274R. Curvature radii Rd _L and Rd _R of the lower die shoulders 273L and 273R are preferably 1 mm or more and 12 mm or less, respectively.

In the left die 27L, the die bottom surface 274L is connected to the bottom edge of the die side surface 272L via a lower die shoulder 273L. On the right die 27R, the die bottom surface 274R is connected to the bottom edge of the die side surface 272R via a lower die shoulder 273R. The die lower surfaces 274L, 274R respectively extend outward in the width direction from the lower die shoulders 273L, 273R in a cross-sectional view of the dies 27L, 27R. In this embodiment, die lower surfaces 274L, 274R extend horizontally from lower die shoulders 273L, 273R. However, at least one of the die lower surfaces 274L and 274R may be inclined with respect to the horizontal plane. The horizontal plane means a plane perpendicular to the direction (vertical direction) in which the dies 27L and 27R move up and down.

The pad 28 is arranged above the punch 26 so as to face the punch top surface 261 . Pads 28 are arranged between the left and right dies 27L and 27R. The pad 28 can move up and down with respect to the punch 26 by being attached to the slide 23 via the mold holder 25 .

The pad 28 has a pad body 281 and a support member 282 . The lower surface of the pad body 281 faces the punch top surface 261 . The lower surface of the pad body 281 is formed in a shape corresponding to the punch top surface 261 . In the example of the present embodiment, a ridge portion 281a extending in the longitudinal direction is provided on the lower surface of the pad main body 281 corresponding to the groove portion 261a of the punch top surface 261 . The support member 282 elastically supports the pad body 281 with respect to the mold holder 25 . The support member 282 is, for example, an extendable member composed of a spring, a fluid pressure cylinder, or the like.

[Manufacturing method of press-molded product]
A method of manufacturing a press-formed product using the manufacturing equipment 100 will be described below. The method for manufacturing a press-formed product according to the present embodiment includes a first step of obtaining an intermediate formed product 40 by pressing a metal plate 30, and a press-formed product 50 by pressing the intermediate formed product 40. and a second step of obtaining. The press device 10 is used in the first step, and the press device 20 is used in the second step.

(First step)
4A to 4E are schematic diagrams for explaining the first step. First, referring to FIG. 4A, a metal plate 30 as a raw material is prepared when performing the first step. Metal plate 30 is typically a steel plate. The plate thickness t of the metal plate 30 is, for example, 2.0 mm or more and 8.0 mm or less. The metal plate 30 has, for example, a tensile strength of 270 MPa or more and 1180 MPa or less. When the press-formed product 50 to be manufactured is an arm part among automobile underbody parts, the tensile strength of the metal plate 30 is usually 590 MPa or more. Moreover, when the press-formed product 50 to be manufactured is a frame component such as an automobile ladder frame, the tensile strength of the metal plate 30 is usually 590 MPa or more.

The work hardening index of the metal plate 30 is preferably 0.04 or less. Moreover, the metal plate 30 preferably has a ratio of yield stress YS to tensile strength TS (yield ratio) YR=YS/TS of 0.95 or more. The work hardening index is an index indicating how easily the metal plate 30 is work hardened, and the larger the value, the easier the work hardening of the material. The work hardening index (n value) is defined in JIS G 0202:2013 and is measured by the method specified in JIS Z 2253:2011, for example. Since the yield ratio YR is a value that is inversely correlated with the n value, it decreases as the n value increases.

Next, the prepared metal plate 30 is press-worked using the die 11 included in the press device 10 . When starting press working, as shown in FIG. 4B, the metal plate 30 is placed on the punch 16 with the die 17 positioned at the top dead center. The metal plate 30 is supported, for example, by at least one of the convex surfaces 162L and 162R. Subsequently, the die 17 is lowered toward the metal plate 30 on the punch 16 by lowering the slide 13 .

As shown in FIG. 4C , when die 17 contacts metal plate 30 , metal plate 30 begins to deform along the forming surfaces of punch 16 and die 17 . As shown in FIG. 4D , when the die 17 reaches the bottom dead center, the metal plate 30 is pressed between the punch 16 and the die 17 to complete the intermediate product 40 .

FIG. 4E is a cross-sectional view (horizontal cross-sectional view) when the intermediate molded product 40 obtained in the first step is cut along a plane perpendicular to its longitudinal direction. The longitudinal direction and width direction of the intermediate molded product 40 coincide with the longitudinal direction and width direction of the mold 11 (FIG. 2). As shown in FIG. 4E, the intermediate molded product 40 includes a top plate 41, left and right convex portions 42L and 42R, left and right vertical walls 43L and 43R, and left and right flanges 44L and 44R.

The top plate 41 is a portion of the intermediate molded product 40 formed by the punch top surface 161 and the die bottom surface 171 (FIG. 2). Grooves 41 a are formed in the top plate 41 so as to correspond to the grooves 161 a of the punch top surface 161 and the ridges 171 a of the die bottom surface 171 .

The left and right convex portions 42L and 42R are connected to the top plate 41. As shown in FIG. The convex portion 42L is a portion of the intermediate molded product 40 formed by the convex surface 162L of the punch 16 and the concave surface 172L of the die 17 (FIG. 2). The convex portion 42R is a portion of the intermediate molded product 40 formed by the convex surface 162R of the punch 16 and the concave surface 172R of the die 17 (FIG. 2). Each of the protrusions 42L and 42R protrudes upward from the top plate 41. As shown in FIG. More specifically, the convex portion 42L protrudes upward as compared with a portion of the top plate 41 that is laterally outside (to the left) of the groove portion 41a. The convex portion 42R protrudes upward compared to a portion of the top plate 41 that is located on the widthwise outer side (right side) of the groove portion 41a.

The convex portions 42L and 42R respectively include top portions 421L and 421R. Each of the tops 421L and 421R has a substantially circular arc shape when the intermediate molded product 40 is viewed in cross section. Each of the tops 421L and 421R preferably has a radius of curvature of 4 mm or more and 16 mm or less. The radius of curvature here is the radius of curvature on the inside of the bending of the tops 421L and 421R.

A portion of the left convex portion 42L on the top plate 41 side, that is, a base portion 422L of the convex portion 42L is, for example, substantially arcuate in the cross-sectional view of the intermediate molded product 40 . The end (R stop) of the base portion 422L on the top plate 41 side is a connecting portion between the convex portion 42L and the top plate 41 . In the example of the present embodiment, the distance in the width direction of the intermediate molded product 40 from this connecting portion to the upper end of the convex portion 42L is defined as the width W1 _L [mm] of the convex portion 42L. Also, the distance in the vertical direction from the connecting portion between the convex portion 42L and the top plate 41 to the upper end of the convex portion 42L is defined as the height H1 _L [mm] of the convex portion 42L. However, the height _H1L is the vertical distance between the plate thickness center of the connecting portion and the plate thickness center of the upper end of the projection 42L.

The height _H1L of the projection 42L is preferably 5 mm or more and 25 mm or less. In the convex portion 42L, the ratio of the height _H1L to the width _W1L : _H1L / _W1L is preferably 0.5 or more and 2.0 or less.

Similarly, the portion of the right convex portion 42R on the top plate 41 side, that is, the base portion 422R of the convex portion 42R is, for example, substantially arcuate in cross-sectional view of the intermediate molded product 40 . An end (R stop) of the base portion 422R on the top plate 41 side is a connecting portion between the convex portion 42R and the top plate 41 . In the example of the present embodiment, the distance in the width direction of the intermediate molded product 40 from this connecting portion to the upper end of the projection 42R is the width W1 _R [mm] of the projection 42R. Further, the distance in the vertical direction from the connecting portion between the convex portion 42R and the top plate 41 to the upper end of the convex portion 42R is defined as the height H1 _R [mm] of the convex portion 42R. However, the height _H1R is the vertical distance between the plate thickness center of the connecting portion and the plate thickness center of the upper end of the projection 42R.

The height H1R of the projection _42R is preferably 5 mm or more and 25 mm or less. In the convex portion 42R, the ratio of the height H1R to the width _W1R : _H1R / _W1R is _preferably 0.5 or more and 2.0 or less.

The left and right vertical walls 43L, 43R extend downward from the projections 42L, 42R, respectively, when the intermediate molded product 40 is viewed in cross section. The vertical wall 43L is arranged to the left of the projection 42L and connects the projection 42L and the flange 44L. The vertical wall 43R is arranged to the right of the projection 42R and connects the projection 42R and the flange 44R. A connecting portion between the vertical wall 43L and the convex portion 42L and a connecting portion between the vertical wall 43R and the convex portion 42R have a smooth shape continuously provided from the convex portions 42L, 42R to the vertical walls 43L, 43R. may have. The vertical walls 43L, 43R or the projections 42L, 42R may be curved (bent) inward or outward in the width direction on the way from the upper ends of the projections 42L, 42R to the left and right flanges 44L, 44R. .

The left and right flanges 44L, 44R extend from the lower ends of the vertical walls 43L, 43R to the opposite side of the top plate 41 when the intermediate molded product 40 is viewed in cross section. The left flange 44L extends widthwise outward (to the left) from the vertical wall 43L in the cross-sectional view of the intermediate molded product 40 . The right flange 44R extends widthwise outward (to the right) from the vertical wall 43R in a cross-sectional view of the intermediate molded product 40 . The flanges 44L, 44R are connected to the vertical walls 43L, 43R via arc-shaped corners 45L, 45R, respectively, in the cross-sectional view of the intermediate molded product 40 .

The height H2 of the intermediate molded product 40 is preferably 6 mm or more. The height H2 of the intermediate molded product 40 is the vertical height from the end of the flanges 44L, 44R on the vertical walls 43L, 43R side, that is, the R stop on the flanges 44L, 44R side of the corners 45L, 45R to the top plate 41. say distance. However, the height H2 is the vertical distance between the thickness center of the flanges 44L and 44R on the side of the vertical walls 43L and 43R and the thickness center of the top plate 41 at the connection portion with the projections 42L and 42R. be. Vertical distance from the thickness center of the edge of the flange 44L on the side of the vertical wall 43L to the thickness center of the top plate 41 at the connection portion with the convex portion 42L, and the thickness of the edge of the flange 44R on the side of the vertical wall 43R If the vertical distance from the center to the thickness center of the top plate 41 at the connecting portion with the convex portion 42R is different, the height H2 of the intermediate molded product 40 is the smaller one of the two distances.

(Second step)
After completing the first step, the second step is performed. 5A to 5H are schematic diagrams for explaining the second step. In the second step, the intermediate molded product 40 obtained in the first step is press-worked using a mold 21 included in the press device 20 . The second step includes steps (a) to (d) described below.

step (a)
Referring to FIG. 5A, first, in step (a), intermediate molded product 40 is placed on punch 26 of mold 21 . More specifically, the intermediate molded product 40 is placed on the punch 26 so that the top plate 41 is arranged on the punch top surface 261 . Also, the intermediate molded product 40 is placed on the punch 26 so that the projections 42L, 42R are arranged at positions corresponding to the punch shoulders 262L, 262R, respectively. The top plate 41 is arranged, for example, so that the position of the groove portion 41a coincides with the position of the groove portion 261a of the punch top surface 261. As shown in FIG. The convex portions 42L and 42R that are continuous with the top plate 41 are preferably positioned outside the pad profile P in the width direction of the mold 21 . The pad profile P is the boundary portion between the pad body 281 and the dies 27L and 27R.

The protruding portions 42L and 42R are arranged at positions corresponding to the punch shoulders 262L and 262R, respectively, so that at least a part of the protruding portions 42L and 42R are pressed by the punch shoulders 262L and 262R and the upper die shoulders 271L and 271R. , the protrusions 42L and 42R are arranged. For example, the protrusions 42L and 42R are arranged so that at least a part thereof overlaps the punch shoulders 262L and 262R in the width direction of the die 21 .

5B, when the intermediate molded product 40 is placed on the punch 26, the upper end of the projection 42L is the lower end of the die side surface 272L (the die side surface 272L of the lower die shoulder 273L) in the width direction of the mold 21. It is preferably located inside the R stop on the side). That is, when the distance in the width direction between the upper end of the convex portion 42L and the lower end of the die side surface 272L is D1 _L [mm], it is preferable that D1 _L >0. The distance D1 _L is positive when the upper end of the convex portion 42L is inside the lower end of the die side surface 272L in the width direction, and negative when the upper end of the convex portion 42L is outside the lower end of the die side surface 272L in the width direction. do.

Similarly, when the intermediate molded product 40 is placed on the punch 26, the upper end of the convex portion 42R is the lower end of the die side surface 272R (the R stop on the die side surface 272R side of the lower die shoulder 273R) in the width direction of the mold 21. ) is preferably located inside. That is, it is preferable that D1 _R >0, where D1 _R [mm] is the distance in the width direction between the upper end of the convex portion 42R and the lower end of the die side surface 272R. The distance _D1R is positive when the upper end of the convex portion 42R is inside the lower end of the die side surface 272R in the width direction, and negative when the upper end of the convex portion 42R is outside the lower end of the die side surface 272R in the width direction. do.

More preferably, when the intermediate molded product 40 is placed on the punch 26, the width of the mold 21 from the end (R stop) of the punch shoulders 262L, 262R on the side of the punch top surface 261 to the upper ends of the projections 42L, 42R Each distance D2 _L and D2 _R [mm] in the direction is set so as to satisfy the following formula (1). In Equation (1), the distances D2 _L and D2 _R are collectively written as D2. Further, in the formula (1), the curvature radii Rp _L and Rp _R (mm) of the punch shoulders 262L and 262R, and the angles θ _L and θ _R [rad] formed between the punch top surface 261 and the punch side surface 263L in cross-sectional view are are collectively written as Rp and θ. That is, in the following formula (1), when the distance D2 is the distance D2 _L , Rp and θ are Rp _L and θ _L , respectively, and when the distance D2 is the distance D2 _R , Rp and θ are respectively Rp _R , θ _R . Regarding the distance D2, it is positive when the upper ends of the projections 42L and 42R are located on the outer side in the width direction of the corresponding ends of the punch shoulders 262L and 262R on the punch top surface 261 side, and negative when they are located on the inner side in the width direction. do.
−1.0×Rp×(π−θ)≦D2≦2.5×Rp×(π−θ) (1)

When the intermediate molded product 40 is placed on the punch 26, the lower end of the vertical wall 43L is outside the upper end of the punch side surface 263L (R stop of the punch shoulder 262L on the punch side surface 263L side) in the width direction of the die 21. preferably located. That is, when the distance in the width direction between the lower end of the vertical wall 43L and the upper end of the punch side surface 263L is D3 _L [mm], it is preferable that D3 _L >0. The distance D3L is positive when the lower end of the vertical wall 43L is outside the upper end of the punch side surface _263L in the width direction, and negative when the lower end of the vertical wall 43L is inside the upper end of the punch side surface 263L in the width direction. do. Regarding the distance _D3L , the lower end of the vertical wall 43L is the R stop on the vertical wall 43L side of the two R stops on the outside of the corner 45L, that is, on the inner side of the intermediate molded product 40 (punch 26 side). Say.

Similarly, when the intermediate molded product 40 is placed on the punch 26, the lower end of the vertical wall 43R is positioned in the width direction of the mold 21 from the upper end of the punch side surface 263R (R stop of the punch shoulder 262R on the punch side surface 263R side). are preferably located outside. That is, when the distance in the width direction between the lower end of the vertical wall 43R and the upper end of the punch side surface 263R is D3 _R [mm], it is preferable that D3 _R >0. The distance D3R is positive when the lower end of the vertical wall 43R is outside the upper end of the punch side surface _263R in the width direction, and negative when the lower end of the vertical wall 43R is inside the upper end of the punch side surface 263R in the width direction. do. Regarding the distance D3R, the lower end of the vertical wall 43R is the _R stop on the vertical wall 43R side of the two R stops on the outside of the corner 45R, that is, on the inner side of the intermediate molded product 40 (punch 26 side). Say.

5C, when intermediate molded product 40 is placed on punch 26, angles φ _L and φ _R formed by flanges 44L and 44R with respect to the horizontal plane are -40° or more and 40° or more, respectively. ° or less. More preferably, the angles φ _L and φ _R are -10° or more and 10° or less. More preferably, the angles φ _L and φ _R are substantially 0°. The angles φ _L and φ _R formed by the flanges 44L and 44R with the horizontal plane mean the angles (acute angle side) formed between the flanges 44L and 44R and the width direction in a cross section cut along a plane consisting of the vertical direction and the width direction. The angles φ _L and φ _R are rotated upward around the ends of the flanges 44L and 44R on the side of the vertical walls 43L and 43R (R stops (inside bending) on the flanges 44L and 44R of the corner portions 45L and 45R). It is positive when it is up, and negative when it is rotating downward. The angles φ _L and φ _R of the flanges 44L and 44R may be equal or different.

The lengths L _L and L _R of the flanges 44L and 44R are preferably 10 mm or more, respectively. The lengths _LL and LR are, respectively, from the ends of the flanges 44L and 44R on the vertical walls 43L and 43R side ( _R stops (inside bending) on the flanges 44L and 44R sides of the corners 45L and 45R) to the flanges 44L and 44R. It is the length along the flanges 44L and 44R to the tip (free end).

step (b)
Referring to FIG. 5A again, in the step (a), when the intermediate molded product 40 is placed on the punch 26, the die lower surfaces 274L and 274R face the flanges 44L and 44R, and the pad 28 faces the punch top surface 261. It faces the upper top plate 41 . Referring to FIG. 5D , in step (b), pad 28 is lowered and top plate 41 of intermediate molded product 40 on punch top surface 261 is pressed by pad 28 . Specifically, by lowering the slide 23 , the dies 27 L and 27 R and the pad 28 attached to the slide 23 are lowered toward the intermediate molded product 40 . Pad 28 contacts intermediate product 40 on punch 26 prior to dies 27L, 27R. The pad body 281 of the pad 28 presses the top plate 41 of the intermediate molded product 40 from above.

step (c)
Referring to FIG. 5E, after top plate 41 of intermediate molded product 40 is pressed by pad main body 281, slide 23 is further lowered. At this time, the support member 282 that supports the pad main body 281 is contracted, so that the dies 27L and 27R are lowered relative to the pad main body 281 that is holding the top plate 41 . In step (c), the dies 27L and 27R are lowered in this way, and the dies 27L and 27R are brought into contact with the flanges 44L and 44R while the top plate 41 is pressed by the pad 28 .

step (d)
After contacting the flanges 44L, 44R of the intermediate molded product 40, the dies 27L, 27R descend further while the flanges 44L, 44R and their vicinity are hooked on the lower die shoulders 273L, 273R. That is, the dies 27L, 27R come into contact with the flanges 44L, 44R of the intermediate molded product 40 and then descend further while keeping contact with the flanges 44L, 44R. Referring to FIG. 5F, as the dies 27L and 27R descend, the upper die shoulders 271L and 271R or their vicinity come into contact with the protrusions 42L and 42R and start crushing the protrusions 42L and 42R. The protrusions 42L and 42R are gradually crushed by, for example, the upper die shoulders 271L and 271R as well as the die upper surfaces 275L and 275R. When crushed, the protrusions 42L and 42R do not locally buckle, and the protrusions 42L and 42R as a whole conform to the punch 26 side. Thus, in step (d), after the dies 27L and 27R come into contact with the flanges 44L and 44R of the intermediate molded product 40, the dies 27L and 27R are further lowered to crush the protrusions 42L and 42R by the dies 27L and 27R. . On the other hand, the flanges 44L, 44R are gradually drawn out toward the punch 26 as the dies 27L, 27R descend.

Referring to FIG. 5G, finally, the dies 27L, 27R reach the bottom dead center, and the upper die shoulders 271L, 271R and the punch shoulders 262L, 262R and the die side surfaces 272L, 272R and the punch side surface 263L , 263R. The intermediate molded product 40 is also pressed between the pad body 281 and the punch top surface 261 . Thereby, the press-molded product 50 is manufactured.

When the dies 27L, 27R reach the bottom dead center, the flanges 44L, 44R of the intermediate molded product 40 are completely pulled out toward the punch 26 and are positioned between the die side surfaces 272L, 272R and the punch side surfaces 263L, 263R. Positioned. However, the flanges 44L, 44R are preferably in contact with the dies 27L, 27R until just before the dies 27L, 27R reach the bottom dead center. On the other hand, the convex portions 42L, 42R of the intermediate molded product 40 are completely crushed by the dies 27L, 27R when the dies 27L, 27R reach the bottom dead center. At least part of the projections 42L, 42R are pressed between the upper die shoulders 271L, 271R and the punch shoulders 262L, 262R.

FIG. 5H is a perspective view partially showing the manufactured press-molded product 50. FIG. The press-formed product 50 has a top plate 51, left and right vertical walls 52L and 52R, and left and right bent portions 53L and 53R. The top plate 51 is formed with a groove portion 51a extending in the longitudinal direction. The upper end of the left vertical wall 52L is connected to the left edge of the top plate 51 via the left bent portion 53L. The upper end of the right vertical wall 52R is connected to the right edge of the top plate 51 via the right bent portion 53R. The lower ends of the vertical walls 52L and 52R are free ends. Each of the bent portions 53L and 53R has a substantially arc shape when the press-formed product 50 is viewed in cross section.

[effect]
In the manufacturing method according to this embodiment, after the metal plate 30 is pressed into the intermediate molded product 40 in the first step, the intermediate molded product 40 is pressed in the second step to obtain the press molded product 50 . In the second step, the dies 27L, 27R are brought into contact with the flanges 44L, 44R of the intermediate molded product 40 while the top plate 41 of the intermediate molded product 40 is pressed from above by the pad 28 . The dies 27L, 27R descend while the flanges 44L, 44R are hooked on the lower die shoulders 273L, 273R. As a result, the portion of the intermediate molded product 40 that is outside the area pressed by the pad 28 in the width direction and extends to the area that is in contact with the lower die shoulders 273L and 273R, that is, the press-molded product Tension can be applied to the portions of 50 that will be the bent portions 53L and 53R. Therefore, in the bent portions 53L and 53R of the press-formed product 50, the compressive stress inside the bend at the end of the forming can be reduced. As a result, the tensile stress caused by springback is reduced, and the tensile stress remaining inside the bent portions 53L and 53R of the press-formed product 50 can be reduced.

In the manufacturing method according to the present embodiment, the convex portions 42L and 42R of the intermediate molded product 40 are crushed by the dies 27L and 27R in the second step and subjected to bending deformation. In the process in which the convex portions 42L and 42R are bent back by the dies 27L and 27R and pushed into the punch shoulders 262L and 262R, compressive stress is applied to the regions of the convex portions 42L and 42R on the die 27L and 27R side (outside bending). A tensile stress is generated in the area on the punch 26 side (inside of the bend). Due to these stresses, when the intermediate molded product 40 conforms to the punch shoulders 262L, 262R and the bent portions 53L, 53R are formed, the tensile stress generated on the outer side of the bend and the compressive stress generated on the inner side of the bend can be reduced. can. Therefore, in the bent portions 53L and 53R of the press-formed product 50 after springback, the tensile stress remaining inside the bend can be reduced.

It is difficult to flatten the protrusions 42L, 42R only by applying tension from the periphery to the protrusions 42L, 42R arranged at positions corresponding to the punch shoulders 262L, 262R. However, in the manufacturing method according to the present embodiment, since the dies 27L and 27R press the protrusions 42L and 42R from above in the second step, the protrusions 42L and 42R can be firmly flattened. More specifically, the descending dies 27L, 27R hit the projections 42L, 42R and crush the projections 42L, 42R from the tops 421L, 421R. As a result, a large stress is generated from the bases 422L, 422R of the projections 42L, 42R toward the tops 421L, 421R. That is, a large tensile stress is generated in the regions on the punch 26 side (bending inner side) of the convex portions 42L and 42R. Therefore, the compressive stress generated inside the bend at the end of the second step can be effectively reduced, and the tensile residual stress generated inside the bend at the bent portions 53L and 53R of the press-formed product 50 after springback can be reduced. can do.

In this way, the dies 27L and 27R descend while the flanges 44L and 44R are hooked on the lower die shoulders 273L and 273R, and while applying tension to the bent portions 53L and 53R of the press-formed product 50, It hits the convex portions 42L and 42R and crushes the convex portions 42L and 42R from the top portions 421L and 421R. As a result, the compressive stress generated on the inner side of the bend at the end of the second step can be significantly reduced, and the residual tensile stress generated on the inner side of the bend at the bent portions 53L and 53R of the press-formed product 50 after springback can be reduced. can be significantly reduced.

As described above, according to the method for manufacturing the press-formed product 50 according to the present embodiment, the residual tensile stress generated inside the bends of the bent portions 53L and 53R of the press-formed product 50 can be reduced in the press working process.

The pressing process is preferably performed using a simple pressing mechanism and a simple forming motion. A press working process using a simple press mechanism and a simple molding motion, for example, can be realized by using a single-action press device, and in effect, only by moving the upper die downward toward the lower die. press working process. In the manufacturing method according to this embodiment, a single-acting press device 20 is used in the second step. The press device 20 substantially forms the press-formed product 50 from the intermediate formed product 40 only by simultaneously lowering the dies 27L, 27R and the pad 28 toward the punch 26. As shown in FIG. That is, in this embodiment, the tensile residual stress generated inside the bends of the bent portions 53L and 53R of the press-formed product 50 can be reduced by a press working process using a simple press mechanism and a simple forming motion.

In the manufacturing method according to this embodiment, when the intermediate molded product 40 is placed on the punch 26, that is, at the start of the second step, the upper ends of the projections 42L and 42R are higher than the lower ends of the die side surfaces 272L and 272R, respectively. It is preferably located inside the mold 21 in the width direction. This prevents the protrusions 42L and 42R from being crushed by the lower die shoulders 273L and 273R and the die lower surfaces 274L and 274R at the beginning of the second step. In other words, after the contact between the dies 27L, 27R and the flanges 44L, 44R applies tension to the projections 42L, 42R, the dies 27L, 27R can crush the projections 42L, 42R, and the inner region of the bend Tensile stress can be effectively generated. Therefore, in the bent portions 53L and 53R of the press-formed product 50, the compressive stress generated on the inner side of the bend at the end of the second step can be more reliably reduced, and the tensile stress remaining on the inner side of the bend after springback can be reduced. You can improve the effect.

In the manufacturing method according to the present embodiment, when the intermediate molded product 40 is placed on the punch 26, the lower ends of the vertical walls 43L and 43R are positioned outside the upper ends of the punch side surfaces 263L and 263R in the width direction of the mold 21. do. That is, the intermediate molded product 40 is fitted to the punch 26 without the top plate 41 rising from the punch 26 at the start of the second step. Therefore, in the second step, when the pad 28 presses the top plate 41 of the intermediate molded product 40, the pad 28 can be prevented from being lifted up, and the molding can be stably performed. Therefore, the dimensional accuracy of the press-formed product 50 obtained in the second step can be stabilized.

In the convex portion 42L of the intermediate molded product 40, the ratio of the height _H1L to the width _W1L : _H1L / _W1L is preferably 0.5 or more and 2.0 or less. Similarly, in the convex portion 42R of the intermediate molded product 40, the ratio of the height H1R to the width _W1R : _H1R / _W1R is _preferably 0.5 or more and 2.0 or less. FIG. 6 is a graph showing the relationship between the height H1/width W1 and the tensile residual stress inside the bends of the bent portions 53L and 53R of the press-formed product 50. As shown in FIG. In FIG. 6, the widths W1 _L and W1 _R and the heights H1 _L and H1 _R of the projections 42L and 42R are collectively indicated as width W1 and height H1. In FIG. 6 and FIGS. 7 to 13 described later, bending R (curvature radius inside bending) of bending portions 53L and 53R from a metal plate 30 having a tensile strength of 980 MPa and a plate thickness of 3.0 mm: 4.0 mm, Vertical wall height: Shows the results obtained when CAE analysis was performed using commercially available software (LS-DYNA ver971 rev7.12, manufactured by ANSYS) for press processing to form the press-formed product 50 with a vertical wall height of 25 mm. .

As shown in FIG. 6, when H1/W1 is 0.5 or more, the tensile residual stress on the inner side of the bend is reduced by 100 MPa or more compared to when conventional press working is performed without using the intermediate molded product 40. . Therefore, H1/W1 is preferably 0.5 or more. The tensile residual stress on the inner side of the bend decreases as H1/W1 increases. However, as H1/W1 increases, the convex portions 42L and 42R rise sharply from the top plate 41. Therefore, in the second step, when the convex portions 42L and 42R are crushed by the dies 27L and 27R, the convex portions 42L and 42R rise sharply. 42R may buckle. In order to prevent buckling of the protrusions 42L and 42R, H1/W1 is preferably 2.0 or less.

In this embodiment, the convex portions 42L and 42R of the intermediate molded product 40 respectively include substantially arcuate apexes 421L and 421R when viewed in cross section. Each radius of curvature of the top portions 421L and 421R is preferably 4 mm or more and 16 mm or less. Each curvature radius here is a value on the inner side (punch 16 side) of the convex portions 42L and 42R. FIG. 7 is a graph showing the relationship between the radius of curvature of the top portions 421L and 421R and the tensile residual stress inside the bends of the bent portions 53L and 53R of the press-formed product 50. As shown in FIG.

As can be seen from FIG. 7, when the radius of curvature of the tops 421L and 421R is 16 mm or less, the tensile residual stress on the inner side of the bend is 100 MPa compared to when conventional press working is performed without using the intermediate molded product 40. or more. Therefore, the radius of curvature of the top portions 421L and 421R is preferably 16 mm or less. The tensile residual stress on the inner side of the bend decreases as the radius of curvature of the top portions 421L and 421R decreases. However, the radius of curvature of the tops 421L and 421R is preferably 4 mm or more. This is to prevent the protrusions 42L and 42R from buckling when the protrusions 42L and 42R are crushed by the dies 27L and 27R in the second step.

In this embodiment, when the intermediate molded product 40 is placed on the punch 26, that is, at the start of the second step, from the end of the punch shoulders 262L, 262R on the side of the punch top surface 261 to the upper ends of the projections 42L, 42R Each distance D2 [mm] in the width direction of the mold 21 is preferably set so as to satisfy the following formula (1).
−1.0×Rp×(π−θ)≦D2≦2.5×Rp×(π−θ) (1)

By setting the distance D2 in this manner, the protrusions 42L and 42R are likely to overlap in the range of the punch shoulders 262L and 262R in the width direction of the die 21 . Therefore, the stress due to bending deformation of the projections 42L, 42R can be generated widely in the regions of the punch shoulders 262L, 262R. Therefore, it is possible to more effectively reduce the compressive stress generated inside the bend when the intermediate molded product 40 conforms to the punch shoulders 262L and 262R to form the bent portions 53L and 53R. As a result, in the bent portions 53L and 53R of the press-formed product 50, the tensile residual stress generated inside the bend can be reduced more reliably.

In this embodiment, the height H2 of the intermediate molded product 40 is preferably 6 mm or more. FIG. 8 is a graph showing the relationship between the height H2 of the intermediate molded product 40 and the tensile residual stress inside the bending at the bent portions 53L and 53R of the press molded product 50. As shown in FIG.

As shown in FIG. 8, the tensile residual stress on the inner side of the bend decreases as the height H2 of the intermediate molded product 40 increases, as compared with the case where the conventional press working without using the intermediate molded product 40 is performed. In particular, when the height H2 of the intermediate molded product 40 is 6 mm or more, the tensile residual stress on the inner side of the bend is reduced by 200 MPa or more, and a remarkable residual stress reduction effect is exhibited. This is because the height H2 of the intermediate molded product 40 is sufficiently secured, so that when the dies 27L, 27R in contact with the flanges 44L, 44R descend in the second step, the vertical walls 43L, 43R This is because bending is suppressed and the flanges 44L and 44R are firmly hooked on the lower die shoulders 273L and 273R during molding, so that tension can be applied to the intermediate molded product 40 more effectively.

In this embodiment, the height H2 of the intermediate molded product 40 is defined as the vertical distance from the end of the flanges 44L, 44R on the side of the vertical walls 43L, 43R to the top plate 41 . Vertical distance from the thickness center of the edge of the flange 44L on the side of the vertical wall 43L to the thickness center of the top plate 41 at the connection portion with the convex portion 42L, and the thickness of the edge of the flange 44R on the side of the vertical wall 43R If the vertical distances from the center to the thickness center of the top plate 41 at the connecting portion with the convex portion 42R are different, the height H2 is the smaller of the two distances. However, both distances are preferably substantially equal.

For example, when the flange 44L side of the intermediate molded product 40 has a long vertical distance, that is, when the left punch side surface 163L is higher than the right punch side surface 163R in the mold 11 of the first step, the metal plate 30 , the die flange surface 174L comes into contact with the metal plate 30 before the die flange surface 174R. Therefore, the metal plate 30 tends to move into the space between the punch flange surface 164L and the die flange surface 174L, and there is a possibility that the press working cannot be performed stably. On the other hand, when the height of the punch side surface 163L on the left side is substantially equal to the height of the punch side surface 163R on the right side, the metal plate 30 is less likely to move, and stable press working can be achieved in the first step.

In this embodiment, when the intermediate molded product 40 is placed on the punch 26, that is, at the start of the second step, the angles φ _L and φ _R formed by the flanges 44L and 44R with respect to the horizontal plane are -40. ° or more and 40° or less. FIG. 9 is a graph showing the relationship between the angle φ and the tensile residual stress inside the bends of the bent portions 53L and 53R of the press-formed product 50. As shown in FIG. In FIG. 9, the angles φ _L and φ _R of the flanges 44L and 44R are collectively indicated as an angle φ.

As shown in FIG. 9, when the angle φ of the flanges 44L and 44R is −40° or more, the tensile residual stress on the inner side of the bend is less than that when the conventional press working without using the intermediate molded product 40 is performed. Reduce by 100 MPa or more. Therefore, the angle φ is preferably -40° or more. The tensile residual stress inside the bend decreases as the angle φ increases. However, if the angle φ becomes excessive, in the second step, the tips of the flanges 44L and 44R, which are free ends, contact the dies 27L and 27R instead of the surfaces of the flanges 44L and 44R, causing the flanges 44L and 44R to buckle. there is a possibility. Further, when the flanges 44L, 44R come into contact with the dies 27L, 27R at their tips, the contact surface pressure of the flanges 44L, 44R against the dies 27L, 27R increases, and the dies 27L, 27R may be damaged. Therefore, the angle φ of the flanges 44L, 44R is preferably 40° or less. More preferably, the angle φ of the flanges 44L, 44R is -10° or more and 10° or less.

In the present embodiment, the lengths L _L and L _R of the flanges 44L and 44R of the intermediate molded product 40 are preferably 10 mm or more. FIG. 10 is a graph showing the relationship between the length L and the tensile residual stress inside the bends of the bent portions 53L and 53R of the press-formed product 50. As shown in FIG. In FIG. 10, the lengths LL and LR of the flanges _44L and 44R are collectively indicated as length _L. As shown in FIG.

As shown in FIG. 10, when the length L of the flanges 44L and 44R is 10 mm or more, the tensile residual stress on the inner side of the bend is less than that when the conventional press working without using the intermediate molded product 40 is performed. Reduce by 100 MPa or more. This is because the length L of the flanges 44L, 44R is sufficiently ensured, so that the flanges 44L, 44R are likely to be caught by the lower die shoulders 273L, 273R in the second step until the latter stage of molding. This is because tension is applied more effectively to the vertical walls 43L and 43R. The tensile residual stress on the inner side of the bend decreases as the length L of the flanges 44L and 44R increases. Therefore, it is preferable that the length L of the flanges 44L and 44R is 10 mm or more.

Regarding the mold 21 used in the second step of the manufacturing method according to the present embodiment, the lower die shoulders 273L and 273R have a curvature of substantially 1 mm or more and 12 mm or less when viewed in cross section of the dies 27L and 27R. It is preferably arcuate with radii _RdL and _RdR . FIG. 11 is a graph showing the relationship between the radius of curvature Rd and the tensile residual stress inside the bends of the bent portions 53L and 53R of the press-formed product 50. As shown in FIG. In FIG. 11, the curvature radii Rd _L and Rd _R of the lower die shoulders 273L and 273R are collectively written as a curvature radius Rd.

As shown in FIG. 11, when the radius of curvature Rd of the lower die shoulders 273L and 273R is 12 mm or less, the tensile residual stress on the inner side of the bend is compared with that when the conventional press working without using the intermediate molded product 40 is performed. and significantly reduced. Therefore, the curvature radius Rd is preferably 12 mm or less. The tensile residual stress on the inner side of the bend decreases as the radius of curvature Rd decreases. However, if the curvature radius Rd is less than 1 mm, the lower die shoulders 273L and 273R may leave bite marks on the press-formed product 50 or cause the press-formed product 50 to develop a large bending habit. Therefore, it is preferable that the radius of curvature Rd of the lower die shoulders 273L, 273R is 1 mm or more.

In the present embodiment, when the intermediate molded product 40 is placed on the punch 26, that is, at the start of the second step, each of the protrusions 42L and 42R is outside the pad profile P in the width direction of the mold 21. is preferably located in FIG. 12 is a graph showing the relationship between the positions of the convex portions 42L and 42R with respect to the pad profile P and the tensile residual stress inside the bends of the bent portions 53L and 53R of the press-formed product 50. As shown in FIG.

As shown in FIG. 12, when a part of the protrusions 42L and 42R is located on the inner side of the pad profile P in the width direction and interferes with the pad main body 281, the protrusions 42L and 42R are positioned on the outer side of the pad profile P in the width direction. , and the effect of reducing the tensile residual stress on the inner side of the bend is small compared to the case where it does not interfere with the pad body 281 . Furthermore, when a part of the protrusions 42L and 42R is located inside the pad profile P in the width direction and interferes with the pad main body 281, the outer peripheral portion of the pad main body 281 pierces the protrusions 42L and 42R, thereby preventing the pressing. The molded product 50 may be damaged. Therefore, it is preferable that the protrusions 42L and 42R as a whole are located outside the pad profile P in the width direction so that the protrusions 42L and 42R do not interfere with the pad main body 281 at the start of the second step. However, as can be seen from FIG. 12, when the intermediate molded product 40 is used to obtain the press molded product 50, the intermediate molded product 40 is not used even if the protrusions 42L and 42R interfere with part of the pad main body 281. Tensile residual stress on the inner side of the bend can be significantly reduced compared to conventional press working.

The residual stress of the press-formed product 50 is the sum of the stress at the end of molding of the press-formed product 50 and the reversal stress due to springback when the press-formed product 50 is released from the mold. If the stress generated in the material during molding is small, the stress due to springback is also small, and the residual stress in the press-formed product 50 is reduced. Therefore, in the manufacturing method according to the present embodiment, the metal plate 30 preferably having a work hardening index of 0.04 or less is used as the material for the press-formed product 50 . If the work hardening index of the material is 0.04 or less, work hardening is less likely to occur in the first step and the second step, and the stress generated in the press-formed product 50 at the end of forming is also small. Therefore, the residual stress of the press-formed product 50 can be reduced.

FIG. 13 is a graph showing the relationship between the work hardening index (n value) of the metal plate 30 and the tensile residual stress inside the bends 53L and 53R of the press-formed product 50. As shown in FIG. As shown in FIG. 13, when a press-formed product 50 is obtained using the intermediate formed product 40, the tensile residual stress on the inner side of the bend can be reduced compared to conventional press working without using the intermediate formed product 40. can. However, when the n value of the metal plate 30 is 0.04, the tensile residual stress on the inner side of the bend can be reduced more remarkably than when the n value of the metal plate 30 is 0.08. Therefore, the n value of the metal plate 30 is preferably 0.04 or less.

For example, when a press-formed product is produced from a metal plate material by drawing, from the initial stage of forming, the widthwise end of the material is held between a die having a horizontal lower surface and a holder having a horizontal upper surface. . In this case, tension is applied to the material from the initial stage of molding. However, in draw forming, the end of the material is held between the die and the holder even at the end of forming. Therefore, the manufactured press-formed product has a shape having a top plate, vertical walls connected to the left and right side edges of the top plate, and flanges projecting outward in the width direction from the lower end of each vertical wall, that is, a cross section Visually, it has an approximate hat shape. In order to manufacture press-formed products without flanges using draw forming, it is necessary to first form the material into a rough hat shape using a punch, die, and holder, and then trim the formed material on the left and right vertical walls. be. However, in general, the material is trimmed parallel to the plate thickness direction. Needs a blade. In this case, problems arise such as an increase in the number of man-hours for designing the trim blade and an increase in the manufacturing cost of the trim blade. Another problem is that trimming the vertical walls reduces the material yield.

On the other hand, in the present embodiment, although the flanges 44L, 44R of the intermediate product 40 are in contact with the dies 27L, 27R during the second step, when the dies 27L, 27R reach the bottom dead center, the punch 26 It is completely pulled out to the side and pressed between the die side surfaces 272L, 272R and the punch side surfaces 263L, 263R. Therefore, the flangeless press-formed product 50 can be directly formed without trimming. Therefore, there is no need for design man-hours and manufacturing costs for trim blades, which are required when draw forming is used, and a decrease in material yield can be prevented.

In general press working, misalignment of materials can be a problem. For example, if the heights of the left and right punch sides are different, the die with the higher punch side surface contacts the material first among the left and right dies, so the material is likely to be misaligned. When the material is positioned using a pilot pin or the like, if the material is misaligned, the periphery of the hole for the pilot pin is deformed in the material. On the other hand, in the second step, the dies 27L and 27R are brought into contact with the intermediate molded product 40 after the pad 28 (the lower surface of the pad body 281) presses the top plate 41 of the intermediate molded product 40 in the present embodiment. Therefore, it is possible to prevent misalignment of the intermediate molded product 40 during press working. Therefore, the press-formed product 50 can be manufactured with high accuracy.

Although the embodiments according to the present disclosure have been described above, the present disclosure is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present disclosure.

In the above-described embodiment, after the metal plate 30 is molded into the intermediate molded product 40 in the first step, the intermediate molded product 40 is used as it is to form the press molded product 50 in the second step. However, one or more intermediate steps can also be provided between the first and second steps. That is, the intermediate molded product 40 can be processed after the first step, and the processed intermediate molded product 40 can be subjected to the second step.

For example, one or more through-holes can be formed in the top plate 41 of the intermediate molded product 40 between the first step and the second step. The through-hole may be a simple round hole, or may be a hole formed by burring and having a protruding edge (burring hole).

Further, for example, as schematically shown in FIG. 14, the vertical walls 43L, 43R and vertical walls 43L, 43R and the vertical walls 43L, 43R and the vertical walls 43L, 43R and Processing for changing the shape of the flanges 44L and 44R can be added. The intermediate molded product 40 processed in the intermediate step between the first step and the second step is molded into the press-molded product 50 in the second step as in the above embodiment.

FIG. 15 is a graph showing the relationship between the presence or absence of an intermediate step and the tensile residual stress inside the bending of the bent portions 53L and 53R of the press-formed product 50. As shown in FIG. In FIG. 15, from the metal plate 30 having a tensile strength of 980 MPa and a plate thickness of 3.0 mm, bending R (curvature radius inside the bending) of the bent portions 53L and 53R: 4.0 mm, vertical wall height: 25 mm. The results obtained when CAE analysis was performed using the commercially available software described above for the press work for molding the product 50 are shown. In the intermediate step, the vertical walls 43L, 43R and the flanges 44L, 44R are processed as shown in FIG. and the press-molded product 50 obtained in the second step.

As can be seen from FIG. 15, regardless of whether or not there is an intermediate process between the first process and the second process, the intermediate molded product 40 including the projections 42L, 42R and the flanges 44L, 44R is processed in the second process. By subjecting it to this, it is possible to reduce the tensile residual stress on the inner side of the bend compared to conventional press working.

In the above embodiment, an example in which the intermediate molded product 40 is press-molded by the mold 11 composed of the punch 16 and the die 17 has been described. That is, in the above embodiment, the intermediate molded product 40 is formed from the metal plate 30 by so-called stamping molding in the first step. However, the method of obtaining the intermediate molded product 40 is not limited to this. The intermediate molded product 40 can be obtained, for example, by pad bending forming while holding the top plate 41 with a pad, or by drawing forming while holding the flanges 44L and 44R with a holder. The configuration of the mold 11 for molding the intermediate molded product 40 can be selected as appropriate.

In the above embodiment, an example has been described in which the press device 10 including the die 11 is used in the first step, and the press device 20 including the die 21 and separate from the press device 10 is used in the second step. However, the mold 11 for the first process and the mold 21 for the second process may be installed in one press machine. For example, the first step and the second step can be carried out by a transfer-type pressing device provided with both the dies 11 and 21 .

In the above embodiment, the intermediate molded product 40 includes left and right convex portions 42L and 42R. However, the intermediate molded product 40 may include only one of the left and right convex portions 42L and 42R. That is, one of the left and right bent portions 53L and 53R of the press-formed product 50 is formed while applying tension due to bending-back deformation of the convex portion, and the other is formed without applying tension due to bending-back deformation of the convex portion. can do. For example, of the left and right bent portions 53L and 53R of the press-formed product 50, one needs to reduce the tensile residual stress on the inner side of the bend to obtain excellent fatigue characteristics, while the other needs to have excellent fatigue characteristics. If it is not necessary, tension due to bending deformation of the projection may be applied only to the side requiring excellent fatigue characteristics.

Similarly, the intermediate molded product 40 may include only one of the left and right flanges 44L, 44R. That is, in the second step, one of the left and right bent portions 53L and 53R of the press-formed product 50 is formed while applying tension by hooking the flange on the lower die shoulder, and the other is formed under such tension. It can be formed without giving. For example, of the left and right bent portions 53L and 53R of the press-formed product 50, one needs to reduce the tensile residual stress on the inner side of the bend to obtain excellent fatigue characteristics, while the other needs to have excellent fatigue characteristics. If not, only the side where good fatigue properties are desired should be tensioned by the flange.

In the above-described embodiment, the convex portions 42L and 42R of the intermediate molded product 40 respectively have generally arc-shaped apexes 421L and 421R. However, the apexes 421L and 421R do not necessarily have to be arc-shaped as a whole. For example, the top portions 421L and 421R may be provided with flat portions extending outward in the width direction in a cross-sectional view of the intermediate molded product 40 so that the convex portions 42L and 42R have a wide shape.

In the above embodiment, grooves 161a, 261a are formed in the punch top surfaces 161, 261 of the punches 16, 26 used in each process. However, the punch top surfaces 161 and 261 may be provided with stepped portions (steps) instead of the groove portions 161a and 261a. The stepped portion may extend over the entire punch top surface 161, 261 or may be provided on a part of the punch top surface 161, 261 in the longitudinal direction. When the punch top surfaces 161 and 261 are provided with stepped portions, the bottom surface 171 of the die 17 used in the first step and the lower surface of the pad 28 used in the second step also have corresponding stepped portions. be provided. When the punch top surface 161 is provided with a stepped portion, the top plate 41 of the intermediate molded product 40 is formed with a stepped portion corresponding to the stepped portion on the punch top surface 161 . When the punch top surface 261 is provided with a stepped portion, the top plate 51 of the press-formed product 50 is formed with a stepped portion corresponding to the stepped portion on the punch top surface 261 .

However, the punch top surfaces 161 and 261, the top plate 41 of the intermediate molded product 40, and the top plate 51 of the press-molded product 50 may not have grooves or steps. That is, the punch top surfaces 161 and 261, the top plate 41 of the intermediate molded product 40, and the top plate 51 of the press-molded product 50 may have a flat shape as a whole.

The overall shape of the press-formed product 50 can be appropriately selected according to the purpose of use. For example, the press-formed product 50 may be linear when viewed from the top plate 51 side (in plan view), may be curved left or right, or may be curved upward or downward. (shape curved when viewed from the width direction). The press-formed product 50 may have a shape in which two or more types of linear portions and curved portions are combined in plan view. Further, the press-formed product 50 may have a shape in which two or more types of linear portions and curved portions are combined when viewed in the width direction. Furthermore, the press-formed product 50 may have a shape such as a three-pronged shape, a four-pronged shape, or the like, in which a portion having an approximately U-shaped cross section branches into a plurality of branches. The shape of the mold 11 for the first step and the shape of the mold 21 for the second step can be selected according to the final shape of the press-molded product 50 .

The press-formed product 50 need not have a uniform cross-sectional shape throughout. As long as it is a press-formed product having at least a portion of a substantially U-shaped cross section, the press apparatus and manufacturing method according to each of the above-described embodiments can be applied.

The present disclosure will be described in more detail below by way of examples. However, the present disclosure is not limited to the following examples.

In order to confirm the effects of the present disclosure, a metal plate (steel plate) having a tensile strength of TS = 980 MPa and a plate thickness of t = 3.0 mm was formed into a press-formed product 60 shown in FIG. 16 by the manufacturing method according to the above embodiment. A CAE analysis was performed on the press working. The press-formed product 60 has a top plate 61 , left and right vertical walls 62 , and left and right bent portions 63 . A groove portion 61 a is formed in the top plate 61 . A lower end of each vertical wall 62 is a free end. That is, no flange is provided at the lower end of each vertical wall 62 . The width of the top plate 61 is 80.0 mm, and the height of the vertical wall 62 is 25.0 mm. Moreover, the bending R (curvature radius of the bending inner side) of the bent portion 63 was set to 4.0 mm. The press-formed product 60 is curved in plan view. The curvature R of the inner side of the curvature of the press-formed product 60 was set to 250.0 mm. The curve R on the outside of the curve is 36.0 mm, which is the sum of the curve R on the inside of the curve and the width of the top plate 61 . These dimensions are dimensions on the inner side of the press-formed product 60 (the surface on the inner side of the bend of the bent portion 63).

In the CAE analysis, using commercially available software (LS-DYNA ver971 rev7.12, manufactured by ANSYS), forming analysis and springback analysis are performed as the residual stress inside the bend to determine the residual stress on the surface inside the bend of the bend 63. (maximum principal stress) was evaluated. Residual stress values are tensile if positive and compressive if negative. In the CAE analysis, among the elements divided in the plate thickness direction, the value of the element on the inner surface of the bend was adopted as the value of the inner surface of the bend. Table 1 shows the results of the analysis.

No. in Table 1. 1 is the result (comparative example) when the press-formed product 60 was formed by general pad bending. That is, No. In 1, a press-formed product 60 was formed from a metal plate as a raw material using a mold composed of a punch, a die, and a pad without forming the intermediate formed product 40 as described in the above embodiment. . No. In No. 1, a residual stress of 580 MPa was generated on the inner surface of the bent portion 63 of the press-formed product 60 after springback occurred after the press forming was completed.

No. in Table 1. 2 to No. 27 is the result when the press-formed product 60 is formed by the method according to the present disclosure. That is, No. 2 to No. 27, first, an intermediate molded product similar to the intermediate molded product 40 described in the above embodiment is molded (first step), and this intermediate molded product is pad-bent to form a press-molded product 60 ( second step). In the second step, at the start of molding, the upper end of each convex portion of the intermediate molded product is arranged inward in the width direction from the lower end of the side surface of the die, and the lower end of each vertical wall of the intermediate molded product is positioned more than the upper end of the side surface of the punch. Placed on the outside in the width direction.

As shown in Table 1, No. 2 to No. Most of No. 27, which is a comparative example. 1, the residual stress on the inner surface of the bent portion 63 of the press-formed product 60 was reduced. In particular, No. 2 to 15, No. 1, which is a comparative example. Compared to 1, the residual stress was reduced by 100 MPa or more. Therefore, according to the method according to the present disclosure, it is possible to reduce the tensile stress remaining inside the bend of the bent portion 63 of the press-formed product 60 .

[Work hardening index (n value)]
No. 1 has a low work hardening index (n value) of 0.04 for the metal plate. In No. 15, for example, the n value of the material is 0.09. 2, the residual stress on the inner surface of the bent portion 63 of the press-formed product 60 was significantly reduced. Therefore, it can be said that the effect of reducing the tensile residual stress is improved by using a metal plate having an n value of 0.04 or less.

[Dimensions of convex part]
(Height H1/Width W1)
No. In 16, the ratio of height H1 to width W1: H1/W1 is 0.4 in the convex portion of the intermediate molded product molded in the first step. This No. In No. 16, the residual stress on the inner surface of the bent portion 63 of the press-formed product 60 was 531 MPa. The effect of reducing the tensile residual stress with respect to 1 was relatively small. On the other hand, no. In No. 4, the residual stress was 463 MPa, and a high tensile residual stress reduction effect was obtained. Therefore, in order to further improve the effect of reducing the tensile residual stress, H1/W1 is preferably 0.5 or more. Also, No. 16 and no. 4, the height H1 of the convex portion is preferably 5 mm or more.

No. with H1/W1 set to 2.1. In No. 17, buckling of the convex portion occurred when the convex portion of the intermediate molded product was crushed by the die in the second step. On the other hand, no. 3, buckling of the convex portion did not occur. Therefore, in order to suppress buckling of the convex portion, H1/W1 is preferably 2.0 or less. Also, No. 17 and No. 3, the height H1 of the convex portion is preferably 25 mm or less.

(curvature radius of top)
No. In 18, the bend R (curvature radius on the inside of the bend) of the top of the convex portion of the intermediate molded product formed in the first step is 2 mm. This No. In No. 18, in the second step, buckling of the protrusions occurred when the protrusions were crushed with a die. On the other hand, no. No buckling of the convex portion occurred in No. 5, which is a comparative example. Residual stress was also significantly reduced compared to 1. Therefore, in order to obtain a high reduction effect of tensile residual stress without causing buckling of the projection, it is preferable that the bending R of the top of the projection is 4 mm or more.

No. 4, in which the bending R of the top of the convex portion is 20 mm. In No. 19, the residual stress on the inner surface of the bent portion 63 of the press-formed product 60 was 509 MPa. The effect of reducing the tensile residual stress with respect to 1 was relatively small. On the other hand, no. In No. 6, the residual stress was 396 MPa. Compared to 1, the residual stress was reduced by nearly 200 MPa. From this result, in order to further improve the effect of reducing the tensile residual stress, it is preferable that the bending R of the top of the projection is 16 mm or less.

(flange length)
No. 20, the length L of the flange of the intermediate molded product molded in the first step is 8 mm. This No. 20, the residual stress on the inner surface of the bent portion 63 of the press-formed product 60 was 537 MPa. The effect of reducing the tensile residual stress with respect to 1 was relatively small. On the other hand, No. 1 with a flange length L of 10 mm. In No. 7, the residual stress was 415 MPa. Compared to 1, it was reduced by 100 MPa or more. Therefore, in order to further improve the effect of reducing the tensile residual stress, it is preferable that the length L of the flange is 10 mm or more.

[Molding height of intermediate molded product]
No. 21, the height H2 of the intermediate molded product molded in the first step is 4 mm. This No. 21, the residual stress on the inner surface of the bent portion 63 of the press-formed product 60 was 529 MPa. The effect of reducing the tensile residual stress with respect to 1 was relatively small. On the other hand, no. In No. 8, the residual stress was 391 MPa. significantly reduced compared to 1. Therefore, in order to further improve the effect of reducing the tensile residual stress, it is preferable that the height H2 of the intermediate molded product is 6 mm or more.

[Relationship between the intermediate molded product and the mold for the second process]
(Relative position of convex part to mold)
At the start of the second step, when the intermediate molded product is placed in the mold, the distance D2 [mm] in the width direction of the mold from the R stop on the punch top surface side of the punch shoulder to the upper end of the protrusion is , the curvature radius Rp [mm] of the punch shoulder, and the angle θ [rad] of the punch side surface with respect to the punch top surface. No. D2/(Rp×(π−θ)) set to −1.2. In No. 22, which is a comparative example, the residual stress on the inner surface of the bent portion 63 of the press-formed product 60 was 503 MPa. The effect of reducing the tensile residual stress with respect to 1 was relatively small. In addition, No. 1 in which D2/(Rp×(π−θ)) was set to 2.7. Even with No. 23, the residual stress was 543 MPa, and the effect of reducing the tensile residual stress was relatively low. On the other hand, No. 1 with D2/(Rp×(π−θ)) set to −1.0. No. 9, and D2/(Rp×(π−θ)) set to 2.5. In No. 10, the residual stress was 341 MPa and 451 MPa, respectively. Compared to 1, it was reduced by 100 MPa or more. From this result, in order to further improve the effect of reducing the tensile residual stress, the distance D2 should be -1.0 × Rp × (π-θ) or more and 2.5 × Rp × (π-θ) or less. is preferably set.

(flange angle)
No. In 24, at the start of the second step, the angle φ formed by the flange of the intermediate product with respect to the horizontal plane is −45°. That is, the flange of the intermediate molded product is rotated downward by 45° around the edge of the vertical wall. This No. In No. 24, which is a comparative example, the residual stress on the inner surface of the bent portion 63 of the press-formed product 60 was 524 MPa. The effect of reducing the tensile residual stress with respect to 1 was relatively small. On the other hand, no. In No. 11, the residual stress was 463 MPa. Compared to 1, it was reduced by 100 MPa or more. Therefore, in order to further improve the effect of reducing the residual tensile stress, it is preferable that the angle φ of the flange of the intermediate molded product at the start of the second step is -40° or more.

No. In 25, at the start of the second step, the angle φ formed by the flange of the intermediate product with respect to the horizontal plane is 45°. That is, the flange of the intermediate molded product is rotated upward by 45° around the end of the vertical wall. This No. At 25, in the second step, the leading edge (free end) of the flange of the intermediate product contacted the die and buckled. Also, No. In the case of 25, the tip of the flange tends to rub against the die, possibly resulting in damage to the die. On the other hand, no. In No. 12, buckling of the flange did not occur, and in No. 12, which is a comparative example. Residual stress was also significantly reduced compared to 1. Therefore, in order to obtain a high effect of reducing tensile residual stress without buckling of the flange, it is preferable that the angle φ of the flange is 40° or less.

(curvature radius of lower die shoulder)
No. In 26, the radius of curvature of the lower die shoulder (die shoulder Rd) was set to 0.5 mm in the mold used in the second step. The lower die shoulder is a portion where the flange of the intermediate molded product is caught when the die is lowered in the second step. No. In No. 26, a large bending tendency was generated in the press-formed product 60 in the second step due to the lower die shoulder. On the other hand, No. 1 with a die shoulder Rd of 1 mm. In No. 13, the press-formed product 60 had substantially no bending tendency, and the residual stress on the inner surface of the bent portion 63 of the press-formed product 60 was also reduced to that of No. 13, which is a comparative example. significantly reduced compared to 1. Therefore, the die shoulder Rd is preferably 1 mm or more in order to obtain a high effect of reducing the tensile residual stress without causing bending tendency.

No. 1 with a die shoulder Rd of 15 mm. No. 27, which is a comparative example, has a residual stress of 513 MPa. The effect of reducing the tensile residual stress with respect to 1 was relatively small. On the other hand, No. 1 with a die shoulder Rd of 12 mm. In No. 14, the residual stress was 438 MPa. Compared to 1, it was reduced by 100 MPa or more. Therefore, in order to improve the effect of reducing the tensile residual stress, it is preferable that the die shoulder Rd in the second step is 12 mm or less.

100: Manufacturing equipment 11: Mold (first mold)
21: Mold (second mold)
26: Punch 261: Punch top surface 262L, 262R: Punch shoulder 263L, 263R: Punch side surface 27L, 27R: Die 271L, 271R: Upper die shoulder 272L, 272R: Die side surface 273L, 273R: Lower die shoulder 274L, 274R: Die lower surface 28: Pad 30: Metal plate 40: Intermediate molded product 41: Top plate 42L, 42R: Convex part 421L, 421R: Top part 43L, 43R: Vertical wall 44L, 44R: Flange 50: Press molded product

Claims (10)

A method for manufacturing a press-molded product,
By pressing a metal plate, a top plate, a convex portion connected to the top plate and protruding upward from the top plate, a vertical wall extending downward from the convex portion, and from the lower end of the vertical wall a first step of obtaining an intermediate molded product including a flange extending on the opposite side of the top plate;
Using a mold that includes a punch, a pad that is arranged above the punch so as to face the punch, and a die that is arranged above the punch and to the side of the pad, the intermediate molded product is formed using a mold. a second step of pressing to obtain the press-formed product;
with
the punch includes a punch top surface, a punch shoulder continuous with the punch top surface, and a punch side surface extending downward from the punch shoulder;
The die is connected to an upper die shoulder corresponding to the punch shoulder, a die side surface extending downward from the upper die shoulder corresponding to the punch side surface, and a lower end of the die side surface via a lower die shoulder. a die underside;
The second step is
placing the intermediate molded product on the punch such that the top plate is arranged on the top surface of the punch and the convex portion is arranged at a position corresponding to the punch shoulder;
a step of lowering the pad and pressing the top plate on the top surface of the punch with the pad;
a step of lowering the die and bringing the die into contact with the flange while the top plate is pressed by the pad;
a step of further lowering the die after the die contacts the flange and crushing the convex portion with the die;
A manufacturing method, including: The manufacturing method according to claim 1,
When the intermediate molded product is placed on the punch, the upper end of the protrusion is located inside the lower end of the side surface of the die in the width direction of the mold, and the lower end of the vertical wall positioned outside the upper end of the punch side surface in the width direction of the punch. The manufacturing method according to claim 1 or 2,
The distance in the vertical direction from the connecting portion between the convex portion and the top plate to the upper end of the convex portion is H1 [mm], and the distance in the width direction of the intermediate molded product from the connecting portion to the upper end is W1 [mm]. ], H1/W1 is 0.5 or more and 2.0 or less. The manufacturing method according to any one of claims 1 to 3,
The manufacturing method according to claim 1, wherein the convex portion has an arcuate shape in a cross-sectional view of the intermediate molded product, and includes a top portion having a radius of curvature of 4 mm or more and 16 mm or less. The manufacturing method according to any one of claims 1 to 4,
The punch shoulder has an arc shape in a cross-sectional view of the punch,
When the intermediate molded product is placed on the punch, the distance D2 [mm] in the width direction of the mold from the end of the punch shoulder on the punch top surface side to the upper end of the convex portion is The manufacturing method satisfies the following formula, where the position outside the end of the punch shoulder in the width direction is positive, and the position inside the punch shoulder in the width direction is negative.
−1.0×Rp×(π−θ)≦D2≦2.5×Rp×(π−θ)
where Rp is the radius of curvature "mm" of the punch shoulder, and θ is the angle [rad] formed between the punch top surface and the punch side surface. The manufacturing method according to any one of claims 1 to 5,
The manufacturing method of the intermediate molded product, wherein a distance in the vertical direction from the end of the flange on the side of the vertical wall to the top plate is 6 mm or more. The manufacturing method according to any one of claims 1 to 6,
When the intermediate product is placed on the punch, the angle formed by the flange with respect to the horizontal plane is positive when the flange rotates upward around the edge of the vertical wall, and rotates downward. A manufacturing method in which the angle is -40° or more and 40° or less, with the case where the angle is negative. The manufacturing method according to any one of claims 1 to 7,
The manufacturing method, wherein the lower die shoulder has an arcuate shape with a radius of curvature of 1 mm or more and 12 mm or less in a cross-sectional view of the die. The manufacturing method according to any one of claims 1 to 8,
The manufacturing method, wherein the work hardening index of the metal plate is 0.04 or less. Manufacturing equipment for manufacturing press-molded products,
a metal plate comprising: a top plate; a projection connected to the top plate and projecting upward from the top plate; a vertical wall extending downward from the projection; a first mold for molding an intermediate product comprising a laterally extending flange;
a second mold for molding the intermediate molded product into the press molded product;
with
The second mold is
A punch including a punch top surface, a punch shoulder continuous with the punch top surface, and a punch side surface extending downward from the punch shoulder, wherein when forming the intermediate product into the press-formed product, the top surface the punch having a plate disposed on the top surface of the punch and the convex portion disposed at a position corresponding to the punch shoulder;
a liftable pad arranged above the punch, the pad facing the top plate arranged on the top surface of the punch when forming the intermediate product into the press-formed product;
A liftable die arranged above the punch and on the side of the pad, comprising an upper die shoulder corresponding to the punch shoulder and a die side surface extending downward from the upper die shoulder corresponding to the punch side surface and a die lower surface connected to the lower end of the die side surface via a lower die shoulder, wherein the die lower surface faces the flange when forming the intermediate molded product into the press-formed product. When,
manufacturing equipment, including;

Images