Pressing device and method for manufacturing press-molded products

Abstract

To provide a new press device which reduces tensile residual stress generated in the inside of bending in a bent part of a press molded article in a pressing step.SOLUTION: A press device (100) includes a punch (10), a pad (30), dies (20L and 20R), and holders (40L and 40R). The dies (20L and 20R) have die lower surfaces (24L and 24R). The holders (40L and 40R) have holder upper surfaces (41L and 41R) facing the die lower surfaces (24L and 24R). The holder upper surfaces (41L and 41R) are below a top surface (11) of the punch (10) at a start point of pressing, and are arranged above the positions of the die lower surfaces (24L and 24R) when the dies (20L and 20R) reach a bottom dead point. The die lower surfaces (24L and 24R) include inclined surfaces (241L and 241R). The holder upper surfaces (41L and 41R) include inclined surfaces (411L and 411R).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a press apparatus and a method for manufacturing a press-molded product using the same. [Background technology]

[0002] Conventionally, press-formed products have been used as components for constructing automobile bodies and the like. Press-formed products are manufactured by pressing metal sheets. More specifically, press-formed products are manufactured by drawing or bending a metal sheet as a material using a mold consisting of a die and a punch.

[0003] In press working of metal plates, springback occurs when the press-formed product formed by the die is released from the die. That is, when the metal plate is bent by the die during press working, tensile stress occurs on the outside of the bend and compressive stress occurs on the inside of the bend in the bent part, but when the forming is completed and the press-formed product is removed from the die, elastic recovery of the material occurs. As a result, in the bent part of the press-formed product, stress occurs in the opposite direction to the direction of the stress during press working. As the reverse stress due to this springback is added to the stress at the end of forming, compressive stress remains on the outside of the bend and tensile stress remains on the inside of the bend in the bent part of the press-formed product.

[0004] In 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 undercarriage parts such as suspension members, relatively large stresses are repeatedly generated in the bent parts when the automobile starts, runs, or brakes, so that the greater the tensile stress remaining on the inner side of the bend, the lower the fatigue strength of the bent parts.

[0005] In order to resist fatigue failure caused by repeated loads, appropriate materials and plate thicknesses are used when manufacturing press-formed products for automobile parts. Also, to meet the need for lighter vehicles, metal plates, which are the raw materials, are becoming stronger and thinner. However, thinner materials result in higher repeated loads on press-formed products manufactured from the materials. Therefore, in order to achieve both weight reduction (thinner materials) and fatigue strength, it is necessary to reduce the tensile stress remaining on the inside of the bend in the bent part of the press-formed product.

[0006] Known methods for removing tensile residual stress from a press-formed product include heat treatment, shot peening, and impact treatment using an ultrasonic vibrator. However, these treatments must be performed in a separate process from the press working process, which increases the number of steps and costs required for manufacturing the press-formed product. In addition, shot peening has the problem that it is difficult to treat only the bent portion of the press-formed product, and also causes surface roughness of the press-formed product. Therefore, it is preferable that the tensile residual stress of the press-formed product is reduced in the press working process.

[0007] For example, Patent Document 1 discloses a technique for performing a so-called ironing process on a metal sheet 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 larger than the thickness of the metal sheet and equal to or smaller than 1.02 times the thickness. According to Patent Document 1, by setting the clearance in this manner, the residual stress in the portion of the metal sheet that is in contact with the shoulder of the die before bending begins is smaller than the residual stress in the portion that will finally come into contact with the shoulder, thereby improving the fatigue properties of the press-formed product.

[0008] Patent Document 2 discloses a press device that includes a die, a punch, and a pad facing the top surface of the punch. In this press device, the die descends, and the die and punch shoulder press the metal sheet to form a bent portion in the metal sheet, and then the pad descends 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 sheet, so that when the descended pad presses the metal sheet, the material of the metal sheet flows into the recess side of the top surface of the punch. According to Patent Document 2, such an inflow of material applies a tensile force to the inside of the bend of the bent portion, reducing the compressive stress and reducing the amount of springback after demolding. Therefore, the tensile residual stress on the inside of the bend can be reduced.

[0009] Patent Documents 3 to 5 disclose techniques for modifying the shape of a press-formed product itself in order to reduce the amount of springback after demolding. In Patent Documents 3 to 5, in a press-formed product having a generally hat-shaped cross section, unevenness or steps are provided on the vertical wall portion. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2002-316215 A [Patent Document 2] International Publication No. 2017 / 131042 [Patent Document 3] JP 2004-314123 A [Patent Document 4] JP 2006-272378 A [Patent Document 5] JP 2017-196646 A Summary of the Invention [Problem to be solved by the invention]

[0011] As described above, when a press-formed product is manufactured by pressing a metal plate, compressive stress remains on the outside of the bend and tensile stress remains on the inside of the bend in the bent portion of the press-formed product. In order to obtain a press-formed product having better fatigue properties, it is necessary to reduce the tensile residual stress on the inside of the bend. In addition, from the viewpoint of preventing an increase in the manufacturing steps and manufacturing costs of the press-formed product, it is preferable that the tensile residual stress on the inside of the bend is reduced in the press working process.

[0012] An object of the present disclosure is to provide a new press device that can reduce tensile residual stress that occurs on the inner side of a bent portion of a press-molded product during a press working process. [Means for solving the problem]

[0013] The press apparatus according to the present disclosure is a press apparatus for performing press working on a material that is a metal plate. The press apparatus includes a punch, a pad, a die, and a holder. The punch has a punch top surface, a punch shoulder, and a punch side surface. The punch shoulder is continuous with the punch top surface. The punch side surface extends downward from the punch shoulder. The pad is disposed above the punch so as to face the punch top surface. The pad is configured to be liftable and lowerable. The die is disposed above the punch and to the side of the pad. The die is configured to be liftable and lowerable. The die has a first die shoulder, a die side surface, and a die lower surface. The first die shoulder corresponds to the punch shoulder. The die side surface extends downward from the first die shoulder in correspondence with the punch side surface. The die lower surface is connected to a lower end of the die side surface via a second die shoulder. The holder is disposed to the side of the punch and below the die. The holder is configured to be liftable and lowerable. The holder has a holder upper surface. The holder upper surface faces the die lower surface. The die lower surface includes an inclined surface. The inclined surface of the die lower surface descends as it moves away from the second die shoulder. The holder upper surface is disposed below the punch top surface at the start of press working by the press device and above the position of the die lower surface when the die reaches the bottom dead center. The holder upper surface includes an inclined surface. The inclined surface of the holder upper surface descends as it moves away from the punch in correspondence with the inclined surface of the die lower surface. Effect of the Invention

[0014] According to the press device of the present disclosure, the tensile residual stress generated on the inner side of the bend in the bent portion of a press-formed product can be reduced during the press working process. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a press device according to a first embodiment. [Figure 2A] FIG. 2A is a schematic diagram for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 2B] FIG. 2B is a schematic view for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 2C] FIG. 2C is a schematic view for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 2D] FIG. 2D is a schematic diagram for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 2E] FIG. 2E is a schematic diagram for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 2F] FIG. 2F is a schematic view for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 2G] FIG. 2G is a schematic view for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 2H] FIG. 2H is a schematic view for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 2I] FIG. 2I is a schematic view for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 2J] FIG. 2J is a schematic view for explaining the method for manufacturing a press-formed product according to the first embodiment. [Diagram 3]FIG. 3 is a graph showing the relationship between the distance the holder descends while clamping the end of the material and the tensile residual stress on the inside of the bend in the bent portion of the press-formed product for the press apparatus and the manufacturing method of the press-formed product according to the first embodiment. [Figure 4] FIG. 4 is a graph showing the relationship between the vertical distance from the R end of the second die shoulder to the end of the material at the completion of forming and the tensile residual stress on the inside of the bend in the bent portion of the press-molded product for the press apparatus and the manufacturing method of the press-molded product according to the first embodiment. [Diagram 5] FIG. 5 is a graph showing the relationship between the dimensionless number Z of the holder load and the residual stress on the inner side of the bend in the bent portion of the press-formed product, for the press apparatus and the method for manufacturing a press-formed product according to the first embodiment. [Figure 6] FIG. 6 is a schematic diagram for explaining the method for manufacturing a press-formed product according to the second embodiment. [Figure 7] FIG. 7 is a perspective view showing a schematic configuration of the press-formed product according to the first embodiment. [Figure 8] FIG. 8 is a graph showing the analysis results of the second embodiment. [Figure 9] FIG. 9 is a graph showing the analysis results of the third embodiment. [Figure 10] FIG. 10 is a graph showing 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 in the bent portion of a conventional press-formed product. [Figure 11] FIG. 11 is a graph showing 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, based on the findings of the present inventors, with respect to the stress generated in the bending circumferential direction in the bent portion of a press-formed product. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In order to confirm the distribution of stress occurring in the bent portion of the press-formed product, the inventors carried out a CAE analysis of the press working using commercially available software (LS-DYNA ver971 rev7.12, manufactured by ANSYS, Inc.). The analysis conditions were as follows: Tensile strength of material: 980MPa Material thickness: 3.0mm Bend R (inner radius of curvature): 4.0 mm Shape of press-molded product (after processing): Two vertical walls and a top plate connecting the vertical walls (no flanges)

[0017] Regarding the stress generated in the circumferential direction in the bent part of a press-formed product, Fig. 10 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. Fig. 10 shows the stress (stress in the circumferential direction of bending) generated on a line from the R apex (center of R) on the inside of the bend to the R apex on the outside of the bend in the bent part of the press-formed product. As can be seen from Fig. 10, at the end of forming, in the bent part of the press-formed product, tensile stress occurs on the outside of the bend, and compressive stress occurs on the inside of the bend. On the other hand, after springback, in the bent part of the press-formed product, compressive residual stress occurs on the outside of the bend, and tensile residual stress occurs on the inside of the bend.

[0018] The inventors noticed that compressive residual stress occurs in the bent part of a press-formed product after springback not only in the region on the outer side of the bend but also in the vicinity of the neutral axis (center of plate thickness) in the region on the inner side of the bend, and came up with the idea of ​​applying tension to the bent part throughout the plate thickness during press working. The inventors thought that by applying tension to the bent part, it would be possible to reduce the compressive stress in the region on the inner side of the bend at the end of forming, and therefore the tensile residual stress after springback would also be reduced.

[0019] A CAE analysis was performed under the same conditions as above, except that the material was bent while tension was applied, and the stress distribution shown in Fig. 11 was obtained. As can be seen from Fig. 11, when the bent portion of the press-formed product was formed while tension was applied, the compressive stress on the inner side of the bend at the end of forming was reduced, and the tensile residual stress on the inner side of the bend after springback was reduced and further became a compressive residual stress. Therefore, the present inventors have studied the configuration of a new press device that can bend a material while tension is applied, and have completed a press device according to an embodiment.

[0020] The press apparatus according to the embodiment is a press apparatus for performing press working on a material that is a metal plate. The press apparatus includes a punch, a pad, a die, and a holder. The punch has a punch top surface, a punch shoulder, and a punch side surface. The punch shoulder is continuous with the punch top surface. The punch side surface extends downward from the punch shoulder. The pad is disposed above the punch so as to face the punch top surface. The pad is configured to be able to rise and fall. The die is disposed above the punch and to the side of the pad. The die is configured to be able to rise and fall. The die has a first die shoulder, a die side surface, and a die lower surface. The first die shoulder corresponds to the punch shoulder. The die side surface extends downward from the first die shoulder in correspondence with the punch side surface. The die lower surface is connected to a lower end of the die side surface via a second die shoulder. The holder is disposed to the side of the punch and below the die. The holder is configured to be able to rise and fall. The holder has a holder upper surface. The holder upper surface faces the die lower surface. The die lower surface includes an inclined surface. The inclined surface of the die lower surface descends as it moves away from the second die shoulder. The holder upper surface is disposed below the punch top surface at the start of press working by the press device and above the position of the die lower surface when the die reaches the bottom dead center. The holder upper surface includes an inclined surface. The inclined surface of the holder upper surface descends as it moves away from the punch in correspondence with the inclined surface of the die lower surface (first configuration).

[0021] When performing press working using the press device of the first configuration, a material, which is a metal plate, is placed on the top surface of the punch, and the pad and die are lowered to contact the material on the top surface of the punch in that order. That is, first, the pad presses down the material on the top surface of the punch from above, and then the die is caused to reach the bottom dead center. When the die reaches the bottom dead center, the material is pressed between the first die shoulder and die side surface and the punch shoulder and punch side surface.

[0022] Here, the die lower surface is connected to the lower end of the die side surface via the second die shoulder. That is, the die lower surface is provided below the first die shoulder and die side surface corresponding to the punch shoulder and punch side surface. On the other hand, the upper surface of the holder provided below the die is disposed above the position of the die lower surface when the die reaches the bottom dead center and below the punch top surface. Therefore, when the die descends, the die lower surface contacts the material before the first die shoulder and die side surface, and clamps the end of the material together with the holder upper surface. Since the material is held down by the pad in advance, the die lower surface and the holder upper surface clamp the end of the material, thereby applying tension to the material. After that, when the die further descends, the first die shoulder and die side surface come into contact with the material in a tensioned state, and a bent portion is formed by the first die shoulder and die side surface and the punch shoulder and punch side surface.

[0023] In this way, the press device according to the first configuration can be used to bend the material under tension to produce a press-formed product, thereby reducing the tensile residual stress that occurs on the inner side of the bend in the bent portion of the press-formed product.

[0024] When a press-formed product is produced by the press apparatus of the first configuration, the end of the material clamped between the lower surface of the die and the upper surface of the holder is pulled out along the inclined surfaces provided on the lower surface of the die and the upper surface of the holder as the die and the holder descend. In other words, as the molding of the material by the punch and die progresses, the surface area of ​​the material clamped between the lower surface of the die and the upper surface of the holder decreases. As a result, the load per unit area acting on the material from the lower surface of the die and the upper surface of the holder gradually increases, so that the tension applied to the material can be increased in the later stage of molding.

[0025] It is preferable that the angle that the inclined surface of the holder upper surface makes with the horizontal plane is not less than 10° and not more than 55° (second configuration).

[0026] When the die descends and the lower surface of the die clamps the end of the material together with the upper surface of the holder, a load perpendicular to the inclined surface of the holder is applied to the upper surface of the holder. If the inclined surface of the holder is steep, the horizontal component of the load on the upper surface of the holder increases. Also, the steeper the inclined surface of the holder is, the smaller the width (horizontal dimension) of the holder becomes, and the strength of the holder decreases. Therefore, in the second configuration, the angle that the inclined surface of the holder makes with the horizontal plane is limited to 55° or less. This makes it possible to suppress the horizontal component of the load on the upper surface of the holder and ensure the width of the holder. This makes it possible to make the holder less susceptible to damage, etc.

[0027] During press working, the end of the material is clamped between the lower surface of the die and the upper surface of the holder, and the end of the material is bent along the inclined surfaces of the lower surface of the die and the upper surface of the holder, and the second die shoulder adjacent to the lower surface of the die. If the inclined surface of the lower surface of the die and the inclined surface of the upper surface of the holder corresponding to the inclined surface are too gentle, the material will have a large bending tendency, which will affect the dimensional accuracy of the press-formed product manufactured from the material. In contrast, in the second configuration, the angle between the inclined surface of the upper surface of the holder and the horizontal plane is ensured to be 10° or more. Therefore, the bending tendency of the material caused by clamping between the lower surface of the die and the upper surface of the holder can be reduced, and the press-formed product can be manufactured with high accuracy.

[0028] The lifting stroke of the holder is preferably 5.0 mm or more and 25.0 mm or less (third configuration).

[0029] In the above press device, the holder is lowered together with the die in a state where the end of the material is sandwiched between the lower surface of the die and the upper surface of the holder. The longer the time that the end of the material is sandwiched between the lower surface of the die and the upper surface of the holder, the greater the tension on the material. However, if the tension on the material is excessive, cracks may occur in the material being pressed or in the press-formed product to be manufactured, for example, at the position of the punch shoulder or the punch side. On the other hand, if the tension on the material is too small, the tensile residual stress generated on the inner side of the bend in the bent part of the press-formed product to be manufactured may not be effectively reduced. Therefore, in the third configuration, the holder's lifting stroke is set to 5.0 mm and 25.0 mm or less, and the time that the end of the material is sandwiched between the lower surface of the die and the upper surface of the holder is appropriately secured. This makes it possible to suppress the occurrence of cracks due to the application of tension in the material or the press-formed product, and also to effectively exert the effect of reducing the tensile residual stress.

[0030] It is preferable that the vertical load applied to the upper surface of the holder is set so as to satisfy the following conditional formula, where F [kN] is the tensile strength of the material, TS [MPa] is the sheet thickness of the material, t [mm] is the longitudinal length of the portion of the material that is clamped between the lower surface of the die and the upper surface of the holder, and L [mm] is (fourth configuration). 0.04≦Z≦0.45 where Z = F / (TS × t × L)

[0031] According to the fourth configuration, the vertical load applied to the upper surface of the holder, i.e., the load in the same direction as the lifting stroke of the holder, is set to satisfy a predetermined conditional formula. This allows the load from the lower surface of the die to be applied to the upper surface of the holder appropriately, without being excessive or insufficient. This prevents the die from succumbing to the reaction force of the material, making it difficult to clamp the end of the material between the lower surface of the die and the upper surface of the holder, or increasing the tension applied, which can prevent cracks from occurring in the material or the press-formed product, for example, at the punch shoulder or side of the punch.

[0032] The second die shoulder preferably has an arc shape having a radius of curvature equal to or greater than the plate thickness of the material and equal to or less than four times the plate thickness in a cross-sectional view of the die (fifth configuration).

[0033] During press working, the material is sandwiched between the die lower surface and the holder upper surface, whereas the material is not sandwiched between the second die shoulder adjacent to the die lower surface and the holder upper surface. That is, the part of the holder upper surface facing the die lower surface contacts the material, whereas the part facing the second die shoulder does not contact the material. In the fifth configuration, the radius of curvature of the second die shoulder is limited to four times the thickness of the material or less, so that the contact area of ​​the holder upper surface with the material can be secured. Therefore, sufficient tension can be applied to the material during press working, and the tensile stress remaining on the inside of the bend in the bent part of the press-formed product can be effectively reduced.

[0034] In the fifth configuration, the radius of curvature at the second die shoulder is greater than or equal to the thickness of the material. Therefore, when the end of the material is clamped between the lower surface of the die and the upper surface of the holder, the material does not deform unnecessarily significantly at the position of the second die shoulder. This makes it possible to prevent the material from cracking at the position of the second die shoulder during press working, and to prevent the bending tendency at the second die shoulder from remaining in the press-formed product.

[0035] The press device may further include a distance block that is provided on the upper surface of the holder. The distance block can adjust the distance between the lower surface of the die that holds the material and the upper surface of the holder (sixth configuration).

[0036] According to the sixth configuration, a distance block is provided on the upper surface of the holder, which prevents the upper surface of the holder from colliding with the lower surface of the die when the die and the holder are lowered and the end of the material is pulled out from between the lower surface of the die and the upper surface of the holder.

[0037] The manufacturing method according to the embodiment is a method for manufacturing a press-formed product using the above-mentioned press machine. This manufacturing method includes the steps of preparing a material, which is a metal plate, placing the material on the punch top surface and lowering the pad and die, clamping an end of the material between the die bottom surface and the holder top surface after the pad presses the material on the punch top surface and before the die reaches the bottom dead center, and pressing the material with the first die shoulder and die side surface and the punch shoulder and punch side surface by allowing the die to reach the bottom dead center. The end of the material is pulled out along the inclined surface from between the die bottom surface and the holder top surface as the die descends, and is positioned between the die side surface and the punch side surface when the die reaches the bottom dead center (seventh configuration).

[0038] In the above manufacturing method, it is preferable that when the die reaches the bottom dead center, the upper surface of the holder is positioned outside the pressed material in the width direction of the press device (eighth configuration).

[0039] According to the eighth configuration, when the die reaches the bottom dead point, the upper surface of the holder is positioned outside the pressed material in the width direction of the press. In other words, when the die reaches the bottom dead point, the material falls out from between the lower surface of the die and the upper surface of the holder, and the material is naturally released from the clamping between the upper surface of the die and the upper surface of the holder. Therefore, there is no need to provide the press with a complex locking mechanism or the like for releasing the clamping of the material. This allows the press to have a simple configuration.

[0040] In the above manufacturing method, it is preferable that the prepared material is concavely bent at a position corresponding to the second die shoulder (ninth configuration).

[0041] According to the ninth configuration, the material before press processing is bent concavely in advance at a position corresponding to the second die shoulder. This makes it easier for the material to be clamped between the die lower surface connected to the second die shoulder and the holder upper surface during press processing. This allows tension to be applied to the material more effectively.

[0042] In the above manufacturing method, it is preferable that the prepared material is convexly bent at a position corresponding to the punch shoulder (tenth configuration).

[0043] In the above manufacturing method, the punch may have a groove or a step on the top surface of the punch. In this case, it is preferable that the prepared blank has a groove or a step formed therein that corresponds to the groove or the step on the top surface of the punch (eleventh configuration).

[0044] According to the tenth or eleventh configuration, the material is preformed to fit the punch. This allows the material on the punch to be more securely pressed by the pad during press working. Therefore, when the end of the material is clamped between the lower surface of the die and the upper surface of the holder, tension can be applied to the material more effectively.

[0045] In the above manufacturing method, the work hardening coefficient of the material is preferably 0.04 or less (twelfth configuration).

[0046] According to the twelfth configuration, since the work hardening index of the material is sufficiently small, 0.04 or less, the material is less likely to work harden during press working. In this case, the stress generated in the material during press working is small, and as a result, the stress due to springback is also small. Therefore, the residual stress of the press-formed product, which is the sum of the stress during press working and the stress due to springback, can be further reduced.

[0047] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and the same description will not be repeated.

[0048] First Embodiment [Press equipment configuration] 1 is a cross-sectional view showing a schematic configuration of a press machine 100 according to this embodiment. The press machine 100 is used to perform press working on a metal plate material to manufacture press-formed products such as automobile suspension parts. Examples of automobile suspension parts include arm parts such as upper arms, lower arms, and trail links, as well as suspension members and torsion beams.

[0049] Referring to FIG. 1, the press apparatus 100 includes a punch 10, dies 20L and 20R, a pad 30, and holders 40L and 40R. The press apparatus 100 further includes a punch holder 50, a bed 60, a die holder 70, a slide 80, and a cushion 90. The punch 10 and the dies 20L and 20R extend in a direction intersecting the plane of FIG. 1. Hereinafter, for the sake of convenience, with regard to the press apparatus 100 and its components, the direction in which the punch 10 and the dies 20L and 20R extend is referred to as the longitudinal direction, and the direction in which the punch 10 and the dies 20L and 20R approach and move away from each other (the vertical direction in the plane of FIG. 1) is referred to as the vertical direction (vertical direction). The direction perpendicular to the plane consisting of the longitudinal direction and the vertical direction, i.e., the direction crossing the punch 10 and the dies 20L and 20R, is referred to as the left-right direction or width direction. Moreover, with regard to the press device 100 and its components, a cross section cut along a plane perpendicular to the longitudinal direction is referred to as a transverse cross section.

[0050] The punch 10 is supported by a bed 60, which is a part of the main body of the press apparatus 100, via a punch holder 50. That is, the punch holder 50 is fixed to the upper surface of the bed 60, and the punch 10 is disposed on the punch holder 50. A plate-shaped spacer may be inserted between the bed 60 and the punch holder 50 to adjust the position of the punch 10 in the vertical direction.

[0051] The punch 10 has a punch top surface 11, left and right punch shoulders 12L, 12R, and left and right punch side surfaces 13L, 13R. In this embodiment, a groove 111 extending in the longitudinal direction is formed in the punch top surface 11. The groove 11 may extend over the entire punch top surface 11 in the longitudinal direction, or may be provided in a part of the punch top surface 11. The punch shoulder 12L and punch side surface 13L are provided on the left side of the punch top surface 11. The punch shoulder 12R and punch side surface 13R are provided on the right side of the punch top surface 11.

[0052] The punch shoulders 12L and 12R are provided so as to be continuous with the punch top surface 11. More specifically, the punch shoulder 12L is continuous with the left edge of the punch top surface 11, and the punch shoulder 12R is continuous with the right edge of the punch top surface 11. Each of the punch shoulders 12L and 12R is substantially arc-shaped in the cross-sectional view of the punch 10. The punch shoulders 12L and 12R are ridges (corners) between the punch top surface 11 and the punch side surfaces 13L and 13R, respectively. Hereinafter, the term "substantially arc-shaped" includes not only a curve that constitutes a 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 that passes through three points, namely, both ends of the curve and the midpoint of the curve, when cut in cross section.

[0053] The punch side surface 13L extends downward from the left punch shoulder 12L in a cross-sectional view of the punch 10. The punch side surface 13R extends downward from the right punch shoulder 12R in a cross-sectional view of the punch 10. Each of the punch side surfaces 13L, 13R is inclined with respect to a vertical plane parallel to the longitudinal direction so that the lower end is positioned outward in the width direction relative to the upper end. The angle (acute angle side) θ that the punch side surfaces 13L, 13R make with the vertical plane parallel to the longitudinal direction is L ,θ R The angle θ of the punch side surface 13L may be the same or different. L and the angle θ of the punch side surface 13R R is preferably 20° or less. The angle (acute angle) θ L ,θ Rmeans the angle (acute angle side) formed by punch side surfaces 13L, 13R and the vertical direction in a cross section cut by a plane consisting of the up-down direction and the width direction.

[0054] The dies 20L, 20R are disposed above the punch 10 and to the side of a pad 30, which will be described later. The die 20L is disposed above the punch 10, on the left side of the pad 30. The die 20R is disposed above the punch 10, on the right side of the pad 30. The dies 20L, 20R are configured to be movable up and down.

[0055] Each of the left and right dies 20L, 20R is attached to a slide 80 via a die holder 70. That is, the die holder 70 is fixed to the lower surface of the slide 80, and the dies 20L, 20R are fixed to the lower surface of the die holder 70. A plate-shaped spacer may be inserted between the slide 80 and the die holder 70 to adjust the positions of the dies 20L, 20R in the vertical direction. The slide 80 is configured to be able to rise and fall relative to the punch 10 by, for example, a mechanical or hydraulic mechanism (not shown) provided in the press device 100. As the slide 80 rises and falls, the dies 20L, 20R also rise and fall relative to the punch 10.

[0056] The left die 20L has a first die shoulder 21L, a die side surface 22L, a second die shoulder 23L, and a die lower surface 24L. The first die shoulder 21L is provided corresponding to the left punch shoulder 12L. That is, the first die shoulder 21L has a position and shape that allows the material to be pressed between the first die shoulder 21L and the punch shoulder 12L when the die 20L descends to the bottom dead center. The first die shoulder 21L, like the punch shoulder 12L, is substantially arc-shaped in the cross section of the die 20L. The radii of curvature of the first die shoulder 21L and the punch shoulder 12L can be appropriately determined according to the target press-molded product.

[0057] The die side 22L extends downward from the first die shoulder 21L in a cross-sectional view of the die 20L. The die side 22L is provided corresponding to the left punch side 13L. That is, the die side 22L has a position and shape that allows the material to be pressed between the die 20L and the punch side 13L when the die 20L descends to the bottom dead center. The die side 22L, like the punch side 13L, is inclined with respect to a vertical plane parallel to the longitudinal direction so that the lower end is positioned outward in the width direction relative to the upper end. The angle (acute angle side) that the die side 22L makes with the vertical plane parallel to the longitudinal direction is equal to the angle θ that the punch side 13L makes with the vertical plane parallel to the longitudinal direction. L is essentially equal to

[0058] The second die shoulder 23L is provided to be continuous with the lower end of the die side surface 22L. The second die shoulder 23L is substantially arc-shaped in a cross-sectional view of the die 20L. The second die shoulder 23L has a radius of curvature R equal to or larger than the thickness of the material to be press-formed. L It is preferable that the radius of curvature R of the second die shoulder 23L is L is preferably four times or less the plate thickness of the material.

[0059] The second die shoulder 23L is a ridge (corner) between the die side surface 22L and the die bottom surface 24L. The die bottom surface 24L is connected to the lower end of the die side surface 22L via the second die shoulder 23L. The die bottom surface 24L includes an inclined surface 241L that is inclined with respect to a horizontal plane. The inclined surface 241L is connected to the second die shoulder 23L and descends as it moves away from the second die shoulder 23L. That is, the inclined surface 241L descends from the second die shoulder 23L toward the outside in the width direction. The inclined surface 241L is an inclined surface whose end on the outside in the width direction is located lower than its end on the inside in the width direction. In this embodiment, the entire die bottom surface 24L is the inclined surface 241L.

[0060] The right die 20R has a first die shoulder 21R, a die side surface 22R, a second die shoulder 23R, and a die bottom surface 24R, similar to the left die 20L. However, the shapes of the die shoulders 21R, 23R, die side surface 22R, and die bottom surface 24R of the right die 20R may not be the same as the shapes of the die shoulders 21L, 23R, die side surface 22R, and die bottom surface 24L of the left die 20L. That is, in the press apparatus 100, the left and right dies 20L, 20R may have symmetrical shapes or asymmetrical shapes.

[0061] In the right die 20R, the first die shoulder 21R is provided corresponding to the right punch shoulder 12R. That is, the first die shoulder 21R has a position and shape that allows the material to be pressed between the first die shoulder 21R and the punch shoulder 12R when the die 20R descends to the bottom dead center. The first die shoulder 21R, like the punch shoulder 12R, is substantially arc-shaped in the cross-sectional view of the die 20R. The radii of curvature of the first die shoulder 21R and the punch shoulder 12R can be appropriately determined according to the target press-formed product.

[0062] The die side surface 22R extends downward from the first die shoulder 21R in a cross-sectional view of the die 20R. The die side surface 22R is provided corresponding to the right punch side surface 13R. That is, the die side surface 22R has a position and shape that allows the material to be pressed between the die side surface 22R and the punch side surface 13R when the die 20R descends to the bottom dead center. The die side surface 22R, like the punch side surface 13R, is inclined with respect to a vertical plane parallel to the longitudinal direction so that the lower end portion is positioned outward in the width direction relative to the upper end portion. The angle (acute angle side) that the die side surface 22R makes with the vertical plane parallel to the longitudinal direction is equal to the angle θ that the punch side surface 13R makes with the vertical plane parallel to the longitudinal direction. R is essentially equal to

[0063] The second die shoulder 23R is provided to be continuous with the lower end of the die side surface 22R. The second die shoulder 23R is substantially arc-shaped in a cross-sectional view of the die 20R. The second die shoulder 23R has a radius of curvature R equal to or larger than the thickness of the material to be press-formed. R It is preferable that the radius of curvature R of the second die shoulder 23R is Ris preferably four times or less the plate thickness of the material.

[0064] The second die shoulder 23R is a ridge (corner) between the die side surface 22R and the die bottom surface 24R. The die bottom surface 24R is connected to the lower end of the die side surface 22R via the second die shoulder 23R. The die bottom surface 24R includes an inclined surface 241R that is inclined with respect to a horizontal plane. The inclined surface 241R is connected to the second die shoulder 23R and descends as it moves away from the second die shoulder 23R. That is, the inclined surface 241R descends from the second die shoulder 23R toward the outside in the width direction. The inclined surface 241R is an inclined surface whose end on the outside in the width direction is located lower than its end on the inside in the width direction. In this embodiment, the entire die bottom surface 24R is the inclined surface 241R.

[0065] The pad 30 is disposed above the punch 10 and between the left and right dies 20L, 20R. The pad 30 is disposed so as to face the punch top surface 11. More specifically, the lower surface of the body 31 of the pad 30 faces the punch top surface 11. The lower surface of the pad body 31 has a shape corresponding to the punch top surface 11. In this embodiment, the lower surface of the pad body 31 is provided with a protrusion 311 extending in the longitudinal direction, which corresponds to the groove 111 of the punch top surface 11.

[0066] The pad 30 is configured to be movable up and down. The pad 30 is attached to a slide 80 via a die holder 70, and is therefore movable up and down relative to the punch 10. The pad body 31 is elastically supported on the die holder 70 by an expandable support member 32. The support member 32 is configured, for example, of a spring or a fluid pressure cylinder. When the support member 32 is in an expanded state, the lower surface of the pad body 31 is located lower than at least the first die shoulders 21L, 21R and the die side surfaces 22L, 22R.

[0067] The holders 40L, 40R are disposed on the sides of the punch 10 and below the dies 20L, 20R. More specifically, the holder 40L is disposed on the left side of the punch 10 and directly below the die lower surface 24L, and the holder 40R is disposed on the right side of the punch 10 and directly below the die lower surface 24R.

[0068] The holders 40L, 40R are configured to be movable up and down. The lifting stroke of the holders 40L, 40R is preferably set to 5.0 mm or more and 25.0 mm or less. The holders 40L, 40R are supported by a cushion 90.

[0069] The cushion 90 has left and right cushion pins 91L, 91R and a cushion body 92. The cushion pins 91L, 91R extend vertically through the bed 60 and are attached to the lower surfaces of the holders 40L, 40R. The cushion body 92 is disposed, for example, below the bed 60. The cushion body 92 has a mechanism (for example, a hydraulic mechanism) for raising and lowering the cushion pins 91L, 91R, similar to a die cushion of a general press device. As the cushion pins 91L, 91R rise and fall, the holders 40L, 40R rise and fall relative to the bed 60. The holders 40L, 40R generate pressure against the corresponding dies 20L, 20R by the cushion body 92 and the cushion pins 91L, 91R.

[0070] The left holder 40L has a holder upper surface 41L. The holder upper surface 41L faces the left die lower surface 24L. The holder upper surface 41L includes an inclined surface 411L inclined with respect to the horizontal plane in correspondence with the inclined surface 241L of the die lower surface 24L. The inclined surface 411L descends as it moves away from the punch 10. That is, the inclined surface 411L is an inclined surface whose outer end in the width direction is located lower than its inner end in the width direction. In this embodiment, the entire holder upper surface 41L is the inclined surface 411L.

[0071] In this embodiment, the holder upper surface 41L is disposed outside the second die shoulder 23L in the width direction. That is, the holder upper surface 41L faces the die lower surface 24L but does not face the second die shoulder 23L. However, a part of the holder upper surface 41L may be disposed at a position facing the second die shoulder 23L. More specifically, a part of the inclined surface 411L may be disposed at a position facing the second die shoulder 23L.

[0072] In the width direction, it is preferable that the position of the end portion of the holder upper surface 41L on the punch 10 side substantially coincides with the position of the end portion of the die lower surface 24L on the second die shoulder 23L side. However, because of possible processing errors and positional deviations in the width direction between the die 20L and the holder 40L during assembly, even if it is desired to coincide the position of the end portion of the holder upper surface 41L on the punch 10 side with the position of the end portion of the die lower surface 24L on the second die shoulder 23L side in the width direction, a part of the holder upper surface 41L can be disposed in a position facing the second die shoulder 23L.

[0073] The angle (acute angle side) ψ that the inclined surface 411L makes with the horizontal plane L It is preferable that the angle ψ of the inclined surface 411L is 10° or more. L It is preferable that the angle ψ of the inclined surface 411L is 55° or less. L is substantially the same as the angle that the inclined surface 241L of the die lower surface 24L makes with respect to the horizontal plane.

[0074] The right holder 40R has a holder upper surface 41R. The holder upper surface 41R faces the right die lower surface 24R. The holder upper surface 41R includes an inclined surface 411R inclined with respect to the horizontal plane in correspondence with the inclined surface 241R of the die lower surface 24R. The inclined surface 411R descends as it moves away from the punch 10. That is, the inclined surface 411R is an inclined surface whose outer end in the width direction is located lower than its inner end in the width direction. In this embodiment, the entire holder upper surface 41R is the inclined surface 411R.

[0075] In this embodiment, the holder upper surface 41R is disposed outside the second die shoulder 23R in the width direction. That is, the holder upper surface 41R faces the die lower surface 24R but does not face the second die shoulder 23R. However, a part of the holder upper surface 41R may be disposed at a position facing the second die shoulder 23R. More specifically, a part of the inclined surface 411R may be disposed at a position facing the second die shoulder 23R.

[0076] In the width direction, it is preferable that the position of the end of the holder upper surface 41R on the punch 10 side substantially coincides with the position of the end of the die lower surface 24R on the second die shoulder 23R side. However, because of possible processing errors and misalignment in the width direction between the die 20R and the holder 40R during assembly, even if it is desired to coincide in the width direction with the position of the end of the holder upper surface 41R on the punch 10 side with the position of the end of the die lower surface 24R on the second die shoulder 23R side, a part of the holder upper surface 41R can be disposed in a position facing the second die shoulder 23R.

[0077] Angle (acute angle) ψ between the inclined surface 411R and the horizontal plane R The angle ψ of the inclined surface 411R is preferably 10° or more. R It is preferable that the angle ψ of the inclined surface 411R is 55° or less. R is substantially the same as the angle ψ of the inclined surface 241R of the die lower surface 24R with respect to the horizontal plane. L , ψ R do not necessarily have to be the same.

[0078] In this embodiment, the press device 100 includes distance blocks 42L and 42R. The distance block 42L is provided on the left holder upper surface 41L and adjusts the distance between the die lower surface 24L and the holder upper surface 41L. The distance block 42L is disposed on the holder upper surface 41L toward the outer edge in the width direction. The distance block 42R is provided on the right holder upper surface 41R and adjusts the distance between the die lower surface 24R and the holder upper surface 41R. The distance block 42R is disposed on the holder upper surface 41R toward the outer edge in the width direction. Each thickness of the distance blocks 42L and 42R is preferably 0.9 times or more and 1.1 times or less of the plate thickness of the material to be subjected to the press working.

[0079] It is preferable that a plurality of distance blocks 42L are arranged in the longitudinal direction at a well-balanced pitch on the left holder upper surface 41L. Similarly, it is preferable that a plurality of distance blocks 42R are arranged in the longitudinal direction at a well-balanced pitch on the right holder upper surface 41R. In this case, the longitudinal length of each of the distance blocks 42L, 42R can be, for example, about 20.0 mm to 60.0 mm.

[0080] The material of the distance blocks 42L, 42R preferably has a lower strength than the material of the dies 20L, 20R and the holders 40L, 40R. Therefore, in this embodiment, the distance blocks 42L, 42R are separate members from the holders 40L, 40R. However, the distance blocks 42L, 42R may be integrally formed with the holders 40L, 40R.

[0081] [Method of manufacturing press-molded products] Hereinafter, a method for manufacturing a press-formed product using the press device 100 configured as described above will be described with reference to Fig. 2A to Fig. 2J. Fig. 2A to Fig. 2J are schematic diagrams for explaining the method for manufacturing a press-formed product. The method for manufacturing a press-formed product according to this embodiment includes a step of preparing a material and a step of performing press working on the material.

[0082] (preparation process) 2A, when producing a press-molded product, first, a material M is prepared. The material M is a metal plate, typically a steel plate. The material M has a plate thickness t of, for example, 2.0 mm or more and 8.0 mm or less. The material M has a tensile strength of, for example, 270 MPa or more and 1180 MPa or less. When the press-molded product to be produced is an arm part among the suspension parts of an automobile, the tensile strength of the material M is usually 590 MPa or more.

[0083] The work hardening index of the material M is preferably 0.04 or less. Furthermore, the ratio (yield ratio) YR=YS / TS of the yield stress YS to the tensile strength TS of the material M is preferably 0.95 or more. The work hardening index is an index showing how easily the material M is work-hardened, and the larger the value, the easier the material is to work-harden. The work hardening index (n value) is defined in JIS G 0202:2013, and is measured, for example, by the method specified in JIS Z 2253:2011. The yield ratio YR is a value that is inversely correlated with the n value, and therefore decreases as the n value increases.

[0084] (Press processing process) Next, the prepared material M is subjected to press working by the press device 100. The press working process includes a step (a) of lowering the dies 20L, 20R and the pad 30, a step (b) of clamping the material M between the dies 20L, 20R and the holders 40L, 40R, and a step (c) of pressing the material M between the dies 20L, 20R, the pad 30, and the punch 10. The press working process will be described in more detail below.

[0085] Process (a) 2B, when the press working by the press device 100 starts, the dies 20L, 20R and the pad 30 are located at the top dead center. At the start of the press working, the holder upper surfaces 41L, 41R are located below the punch top surface 11. Also, at the start of the press working, the holder upper surfaces 41L, 41R are located above the positions of the die lower surfaces 24L, 24R when the dies 20L, 20R reach the bottom dead center.

[0086] With the dies 20L, 20R and pad 30 positioned at the top dead center, the material M is placed on the punch top surface 11. At this point, the holder upper surfaces 41L, 41R are positioned below the punch top surface 11 and therefore do not come into contact with the material M on the punch top surface 11. After the material M is placed on the punch top surface 11, the slide 80 is lowered, thereby lowering the dies 20L, 20R and pad 30 attached to the slide 80 toward the material M. The pad 30 comes into contact with the material M on the punch top surface 11 prior to the dies 20L, 20R.

[0087] 2C, pad 30 presses down material M on punch top surface 11. More specifically, pad body 31 supported by slide 80 via support member 32 presses down a central portion in the width direction of material M on punch top surface 11 from above.

[0088] 2D, after the material M is pressed by the pad body 31, the slide 80 further descends. At this time, the support member 32 contracts, causing the dies 20L, 20R to descend relatively to the pad body 31 that is pressing down the material M. As a result, both ends (left and right ends) of the material M in the width direction are pressed down by the die lower surfaces 24L, 24R, and the material M begins to bend along the punch shoulders 12L, 12R.

[0089] Process (b) Referring to FIG. 2E, when the dies 20L and 20R are further lowered, the left and right ends of the material M come into contact with the holder upper surfaces 41L and 41R. The left end of the material M is sandwiched between the holder upper surface 41L and the die lower surface 24L after the pad 30 presses the material M on the punch top surface 11 and before the die 20L reaches the bottom dead point. The right end of the material M is sandwiched between the die lower surface 24R and the holder upper surface 41R after the pad 30 presses the material M on the punch top surface 11 and before the die 20R reaches the bottom dead point. The left and right ends of the material M are sandwiched between the inclined surfaces 241L and 241R of the die lower surfaces 24L and 24R and the inclined surfaces 411L and 411R of the holder upper surfaces 41L and 41R.

[0090] The holders 40L, 40R can generate pressure against the dies 20L, 20R and the material M by the cushion 90. The vertical load applied from the dies 20L, 20R and the material M to the holder upper surfaces 41L, 41R can be set by adjusting the pressure of the holders 40L, 40R by the cushion 90.

[0091] A load F in the vertical direction (the same direction as the lifting stroke of the holder 40L) applied to the holder upper surface 41L L It is preferable that the load F [kN] is set so as to satisfy the following conditional expression (1): R It is preferable that the load F [kN] is set so as to satisfy the following conditional expression (2). L ,F R may vary during the press working process within a range satisfying the conditional expressions (1) and (2). 0.04≦Z L ≦0.45 (1) However, Z L =F L / (TS×t×L L ) 0.04≦Z R ≦0.45 (2) However, Z R =F R / (TS×t×L R )

[0092] In conditional formulas (1) and (2), TS is the tensile strength of material M [MPa], t is the plate thickness of material M [mm], L L is the length [mm] in the longitudinal direction of the portion of the material M that is clamped between the die lower surface 24L and the holder upper surface 41L, and L R is the length [mm] of the portion of the material M that is sandwiched between the die lower surface 24R and the holder upper surface 41R in the longitudinal direction. L is the length of the left end of the material M in the longitudinal direction at the time when the die lower surface 24L and the holder upper surface 41L start to clamp the left end of the material M. R is the length of the right end of the material M in the longitudinal direction at the time when the die lower surface 24R and the holder upper surface 41R start to clamp the right end of the material M.

[0093] 2F, after the left and right ends of the material M are clamped between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R, the dies 20L, 20R are further lowered. This causes the holders 40L, 40R and the cushion pins 91L, 91R to also lower. As the die 20L and the holder 40L lower, the left end of the material M is drawn out from between the die lower surface 24L and the holder upper surface 41L along the inclined surfaces 241L, 411L toward the punch 10. Similarly, as the die 20R and the holder 40R lower, the right end of the material M is drawn out from between the die lower surface 24R and the holder upper surface 41R along the inclined surfaces 241R, 411R toward the punch 10.

[0094] Process (c) 2G, the dies 20L, 20R are finally caused to reach the bottom dead center, and the material M is pressed by the first die shoulders 21L, 21R and die sides 22L, 22R, and the punch shoulders 12L, 12R and punch sides 13L, 13R. The material M is also pressed by the pad body 31 and the punch top surface 11. When a part of the dies 20L, 20R corresponds to a part of the punch top surface 11, the material M is also pressed between the dies 20L, 20R and the punch top surface 11. In this way, a press-formed product is manufactured from the material M.

[0095] When the die 20L reaches the bottom dead point, the left end of the material M is completely pulled out from between the die lower surface 24L and the holder upper surface 41L, and is located between the die side surface 22L and the punch side surface 13L. When the die 20R reaches the bottom dead point, the right end of the material M is completely pulled out from between the die lower surface 24R and the holder upper surface 41R, and is located between the die side surface 22R and the punch side surface 13R. In the example of this embodiment, when the dies 20L and 20R reach the bottom dead point, the holder upper surfaces 41L and 41R are positioned outward in the width direction from the pressed material M.

[0096] 2H and 2I, the distance D1 by which the holder 40L descends while the die lower surface 24L and the holder upper surface 41L are clamping the left end of the material M is preferably 2.0 mm or more and 10.0 mm or less. After the left end of the material M is completely pulled out from between the die lower surface 24L and the holder upper surface 41L, it is preferable to quickly make the die 20L and the holder 40L reach the bottom dead center. When the die 20L and the holder 40L reach the bottom dead center, the distance D2 in the vertical direction between the bottom end of the material M between the die side surface 22L and the punch side surface 13L and the R end (upper side) of the second die shoulder 23L is, for example, 4.5 mm or less. Most preferably, the distance D2 is substantially 0 mm.

[0097] Although not shown in the figure, the distance by which the holder 40R descends when the die lower surface 24R and the holder upper surface 41R hold the right end of the material M is preferably 2.0 mm or more and 10.0 mm or less. After the right end of the material M is completely pulled out from between the die lower surface 24R and the holder upper surface 41R, it is preferable to quickly make the die 20R and the holder 40R reach the bottom dead center. When the die 20L and the holder 40L reach the bottom dead center, the vertical distance between the bottom end of the material M between the die side surface 22R and the punch side surface 13R and the R end (upper side) of the second die shoulder 23R is, for example, 4.5 mm or less. Most preferably, the distance is substantially 0 mm.

[0098] FIG. 2J is a perspective view partially showing the manufactured press-formed product 200. The press-formed product 200 has a top plate 201, left and right vertical walls 202L, 202R, and left and right bent portions 203L, 203R. The top plate 201 has a groove portion 204 extending in the longitudinal direction. The upper end of the left vertical wall 202L is connected to the left edge of the top plate 201 via the left bent portion 203L. The upper end of the right vertical wall 202R is connected to the right edge of the top plate 201 via the right bent portion 203R. The lower ends of the vertical walls 202L, 202R are each free ends. Each of the bent portions 203L, 203R is substantially arc-shaped in a cross-sectional view of the press-formed product 200.

[0099] [effect] In the press apparatus 100 according to this embodiment, at the start of press working, the holder upper surfaces 41L, 41R are disposed below the punch top surface 11 and above the position of the die lower surfaces 24L, 24R when the dies 20L, 20R reach the bottom dead point. Therefore, before the dies 20L, 20R reach the bottom dead point and the first die shoulders 21L, 21R press the material M, the die lower surfaces 24L, 24R come into contact with the material M and, together with the holder upper surfaces 41L, 41R, clamp the left and right ends of the material M pressed by the pads 30. This allows tension to be applied to the portions of the material M that will become the bent portions 203L, 203R of the press-formed product 200. In this way, by performing forming while tension is applied to the material M, it is possible to reduce the tensile residual stress that occurs on the inside of the bend in the bent portions 203L, 203R of the press-formed product 200 manufactured from the material M.

[0100] In this embodiment, the left and right ends of the material M sandwiched between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R are drawn along the inclined surfaces 241L, 241R, 411L, 411R as the dies 20L, 20R and the holders 40L, 40R descend. Therefore, as the dies 20L, 20R approach the bottom dead center, the surface area of ​​the material M sandwiched between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R decreases, and the load per unit area acting on the material M increases. Therefore, the tension applied to the material M can be gradually increased toward the end of molding. This effectively reduces the tensile residual stress generated on the inner side of the bend in the bent portions 203L, 203R of the press-formed product 200.

[0101] For example, when a press-formed product is manufactured from a metal plate material by drawing, the end of the material in the width direction is clamped between a die having a horizontal lower surface and a holder having a horizontal upper surface from the beginning of forming. In this case, tension is applied to the material from the beginning of forming. However, in drawing, the end of the material is clamped between the die and the holder even at the end of forming. Therefore, the press-formed product manufactured has a shape having a top plate, vertical walls connected to the left and right side edges of the top plate, and flanges protruding outward in the width direction from the lower ends of each vertical wall, that is, an approximately hat shape in cross section. In order to manufacture a press-formed product without a flange using drawing, it is necessary to once form the material into an approximately hat shape using a punch, a die, and a holder, and then trim the material after forming with the left and right vertical walls. However, since trimming of the material is generally performed parallel to the plate thickness direction, for example, when trimming left and right vertical walls that are inclined with respect to a vertical plane, a trimming blade of a pull-out type equipped with a complex cam mechanism or the like is required. In this case, problems occur such as an increase in the number of steps required to design the trim blade, an increase in the manufacturing cost of the trim blade, etc. Also, there is a problem that the yield of material decreases due to trimming the vertical wall.

[0102] On the other hand, in this embodiment, the left and right ends of the material M are clamped between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R not from the beginning of the forming process but from the middle of the forming process. However, when the dies 20L, 20R reach the bottom dead center, the left and right ends of the material M are completely pulled out from between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R and pressed between the die side surfaces 22L, 22R and the punch side surfaces 13L, 13R. Therefore, the material M can be bent while applying tension, and the press-formed product 200 without a flange can be directly formed. Therefore, there is no need for the design man-hours and manufacturing costs of the trim blades as in the case of using drawing, and a decrease in the yield of the material can be prevented.

[0103] In this embodiment, the holder upper surfaces 41L, 41R are positioned outside the material M after pressing when the dies 20L, 20R reach the bottom dead center. That is, the left and right ends of the material M are naturally pulled out from between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R when the dies 20L, 20R reach the bottom dead center. Therefore, it is not necessary to provide the press device 100 with a complicated locking mechanism or the like for releasing the material M from being clamped by the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R. Therefore, the press device 100 can be simply configured.

[0104] In general press working, the positional deviation of the material can be a problem. For example, when the heights of the left and right punch sides are different, the die with the larger height of the punch side of the left and right dies contacts the material first, which makes it easy for the positional deviation of the material to occur. When the material is positioned using a pilot pin or the like, if the positional deviation of the material occurs, the peripheral portion of the hole for the pilot pin in the material is deformed. On the other hand, the press device 100 according to this embodiment is configured so that the pad 30 first presses the center of the material M in the width direction. After the material M on the punch top surface 11 is pressed by the pad 30, the left and right ends of the material M are sandwiched between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R, thereby preventing the positional deviation of the material M during press working. Therefore, the press-molded product 200 can be manufactured with high precision.

[0105] In this embodiment, the angle ψ L , ψ R and are each preferably 10° or more. Here, the horizontal plane is a plane perpendicular to the direction in which the holders 40L and 40R move up and down (the up-down direction). L , ψ R By setting the angle ψ to 10° or more, the width of the holder upper surfaces 41L, 41R and the strength of the holders 40L, 40R can be ensured. Also, the bending tendency of the material M bent along the inclined surfaces 411L, 411R of the holder upper surfaces 41L, 41R, the inclined surfaces 241L, 241R of the die lower surfaces 24L, 24R, and the second die shoulders 23L, 23R can be reduced. Therefore, the press-formed product 200 can be manufactured with high accuracy. Note that the angle ψ L , ψ R This means the angle (acute angle side) formed by the inclined surfaces 411L, 411R of the holder upper surfaces 41L, 41R and the width direction in a cross section cut by a plane consisting of the up-down direction and the width direction.

[0106] In this embodiment, the angle ψ L , ψ R are preferably 55° or less, respectively. This prevents the inclined surfaces 411L, 411R from becoming too steep, and the horizontal component of the load applied vertically to the inclined surfaces 411L, 411R can be suppressed. This makes it possible to prevent damage to the holders 40L, 40R and the cushion pins 91L, 91R supporting the holders 40L, 40R, etc.

[0107] In this embodiment, in the later stage of forming the material M, the left and right ends of the material M are clamped between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R, and the holders 40L, 40R are lowered. The distance by which the holders 40L, 40R are lowered (lifting stroke) is preferably set to 5.0 mm or more. By setting the lifting stroke of each of the holders 40L, 40R to 5.0 mm or more, the clamping time of the left and right ends of the material M can be secured, and the tension applied to the material M can be increased. Therefore, the tensile residual stress generated on the inner side of the bend in the bent portions 203L, 203R of the press-formed product 200 can be effectively reduced.

[0108] In addition, the distance (lifting stroke) by which each of the holders 40L, 40R descends is preferably set to 25.0 mm or less. By setting each of the lifting strokes of the holders 40L, 40R to 25.0 mm or less, it is possible to prevent excessive tension from being applied to the material M. This makes it possible to suppress the occurrence of cracks in the material M or the press-molded product.

[0109] In order to apply an appropriate tension to the material M, strictly speaking, it is preferable to adjust the distance D1 by which the holders 40L and 40R are lowered while clamping the left and right ends of the material M. Fig. 3 is a graph showing the relationship between the distance D1 by which the holders 40L or 40R are lowered while clamping the end of the material M, and the tensile residual stress on the inner side of the bend in the bent part of the press-formed product. The graphs in Fig. 3 and Figs. 4 and 5 described later were created from the results obtained when a CAE analysis was performed using commercially available software (LS-DYNA ver971 rev7.12, manufactured by ANSYS) on press working in which a material M with a tensile strength of 980 MPa and a plate thickness of 3.0 mm is bent with a bend R (curvature radius on the inner side of the bend) of 4.0 mm to form a press-formed product without a flange.

[0110] As shown in FIG. 3, when the distance D1 is 2.0 mm or more, the tensile stress remaining on the inner side of the bend in the bent portion of the press-formed product is reduced. Therefore, the lowering distance D1 of the holders 40L, 40R in a state where the end of the material M is clamped is preferably 2.0 mm or more. The larger the distance D1, the longer the clamping time of the end of the material M, so that the tensile residual stress on the inner side of the bend is reduced. However, when the distance D1 exceeds 10.0 mm, the tension applied to the material M becomes excessive, and there is a possibility that cracks or the like may occur in the bent portion or the vertical wall. Therefore, the lowering distance D1 of the holders 40L, 40R in a state where the end of the material M is clamped is preferably 10.0 mm or less. By setting the distance D1 to 2.0 mm or more and 10.0 mm or less, an appropriate tension can be applied to the material M.

[0111] In this embodiment, when the dies 20L, 20R reach the bottom dead point, the vertical distance D2 between the lower end of the material M located between the die side surfaces 22L, 22R and the punch side surfaces 13L, 13R and the R end (upper side) of the second die shoulders 23L, 23R is set to, for example, 4.5 mm or less. This allows the left and right ends of the material M to be completely pulled out from between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R, and after the tension on the material M is reduced, the forming of the material M can be quickly completed.

[0112] FIG. 4 is a graph showing the relationship between the vertical distance D2 from the R end (upper side) of the second die shoulder 23L or 23R to the end of the material M at the completion of forming, and the tensile residual stress on the inner side of the bend in the bent part of the press-formed product. As shown in FIG. 4, the larger the distance D2 from the R end of the second die shoulder 23L, 23R to the material M, the larger the residual stress on the inner side of the bend in the bent part of the press-formed product. In order to effectively reduce the residual stress on the inner side of the bend, the distance D2 is preferably 4.5 mm or less. Most preferably, the distance D2 is 0 mm. By reducing the distance D2, the die including the punch 10 and the dies 20L, 20R can be made smaller, and the cost of manufacturing the die can be reduced.

[0113] In this embodiment, the vertical load F applied to the left holder upper surface 41L L is preferably set so as to satisfy the above conditional expression (1). In addition, the vertical load F applied to the right holder upper surface 41R is R is preferably set so as to satisfy the above conditional expression (2). L ,F R By setting the above, the left and right ends of the material M can be more reliably sandwiched between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R, and an appropriate tension can be applied to the material M.

[0114] 5 is a graph showing the relationship between the dimensionless number Z=F / (TS×t×L) of the holder load and the residual stress on the inner side of the bent portion of the press-formed product. In FIG. 5, the load F applied to the holder upper surface 41L is L and the load F applied to the right holder top surface 41R R The load F is expressed as the holder load F [kN] without distinguishing between the load F and the holder load F [kN]. The length L of the part of the material M that is clamped between the die lower surface 24L and the holder upper surface 41L in the longitudinal direction is expressed as the holder load F [kN]. L , and the longitudinal length L of the portion of the material M that is sandwiched between the die lower surface 24R and the holder upper surface 41R. R Without making a distinction, it is expressed as the length L [mm] of the clamped part of the material M. TS is the tensile strength [MPa] of the material M, and t is the plate thickness [mm] of the material M.

[0115] Referring to FIG. 5, when the dimensionless number Z of the holder load F is 0.04 or more, the die 20L, 20R does not succumb to the reaction force of the material M, and the die lower surface 24L, 24R securely holds the left and right ends of the material M together with the holder upper surface 41L, 41R, so that tension is effectively applied to the material M. Therefore, the tensile stress remaining on the inside of the bend in the bent part of the press-formed product is reduced. The larger the dimensionless number Z, the more the tension on the material M increases, and the more the tensile residual stress on the inside of the bend can be reduced. However, when the dimensionless number Z exceeds 0.45, the tension on the material M becomes excessive, and there is a possibility that cracks or the like may occur in the bent part or the vertical wall. Therefore, as shown in the above conditional expressions (1) and (2), it is preferable that the dimensionless number Z of the holder load F is 0.04 or more and 0.45 or less.

[0116] In this embodiment, the die lower surfaces 24L, 24R, together with the holder upper surfaces 41L, 41R, clamp the left and right ends of the material M, while the second die shoulders 23L, 23R adjacent to the die lower surfaces 24L, 24R do not substantially contribute to clamping the material M. The radius of curvature R of the second die shoulders 23L, 23R L ,R R If the radius of curvature R of the second die shoulders 23L and 23R is too large, the clamped portion of the material M will be reduced. L ,R R is preferably four times or less the sheet thickness t of the material M. This allows the material M to be sufficiently sandwiched between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R, so that the tensile residual stress on the inner side of the bend in the bent portions 203L, 203R of the press-formed product 200 can be effectively reduced.

[0117] In this embodiment, the radius of curvature R of the second die shoulders 23L and 23R L ,R R is preferably equal to or greater than the sheet thickness t of the material M. This makes it possible to prevent the material M from cracking at the positions of the second die shoulders 23L, 23R during press working. Also, it is possible to prevent bending tendencies from remaining at the second die shoulders 23L, 23R in the press-formed product 200 manufactured from the material M.

[0118] In this embodiment, distance blocks 42L, 42R are provided on the holder upper surfaces 41L, 41R. The distance blocks 42L, 42R can prevent the holder upper surfaces 41L, 41R from colliding with the die lower surfaces 24L, 24R when the left and right ends of the material M are pulled out from between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R. Even after the left and right ends of the material M are completely pulled out from between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R, the distance blocks 42L, 42R are pushed by the dies 20L, 20R, so that the holders 40L, 40R can be lowered together with the dies 20L, 20R.

[0119] In this embodiment, the thickness of each of the distance blocks 42L, 42R is preferably 1.1 times or less the thickness t of the material M. This allows the left and right ends of the material M to be more reliably clamped between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R, and tension can be effectively applied to the material M. In order to prevent the tension on the material M from becoming excessive, the thickness of each of the distance blocks 42L, 42R is preferably 0.9 times or more the thickness t of the material M.

[0120] The material of the distance blocks 42L, 42R preferably has a lower strength than the material of the dies 20L, 20R and the holders 40L, 40R. In this case, the distance blocks 42L, 42R function as a buffer between the dies 20L, 20R and the holders 40L, 40R, and therefore deformation of the dies 20L, 20R and the holders 40L, 40R can be prevented. Therefore, it is possible to prevent a decrease in dimensional accuracy of the press-molded product 200 to be manufactured due to deformation of the dies 20L, 20R or the holders 40L, 40R.

[0121] The residual stress of the press-formed product 200 is the sum of the stress when the material M is formed into the press-formed product 200 and the reversal stress due to springback when the press-formed product 200 is released from the mold. If the stress generated in the material M during forming is small, the stress due to springback is also small, and the residual stress of the press-formed product 200 is reduced. Therefore, in the manufacturing method of the press-formed product 200 according to this embodiment, preferably, a material M having a work hardening index of 0.04 or less is used. If the work hardening index of the material M is 0.04 or less, work hardening of the material M is unlikely to occur, and the stress generated in the material M during forming is also small. Therefore, the residual stress of the press-formed product 200 can be reduced.

[0122] <Second embodiment> In this embodiment, the same press apparatus 100 as in the first embodiment is used to manufacture a press-formed product 200 in a manner generally similar to that of the first embodiment. However, in this embodiment, the shape of the material M to be prepared is different from that of the first embodiment.

[0123] Fig. 6 is a cross-sectional view of the press apparatus 100 when the dies 20L, 20R are located at the top dead center, and shows a state in which the material M prepared in this embodiment is placed on the punch top surface 11. As shown in Fig. 6, in this embodiment, the material M is pre-formed into a shape that fits along the punch top surface 11 and the left and right punch shoulders 12L, 12R when placed on the punch top surface 11. More specifically, a groove M1 corresponding to the groove 111 of the punch top surface 11 is formed in the material M. In addition, the material M is bent convexly at positions M2 corresponding to each of the punch shoulders 12L, 12R so as to partially fit along the punch shoulders 12L, 12R.

[0124] Furthermore, the material M is bent concavely in advance at positions M3 corresponding to the left and right second die shoulders 23L, 23R. In other words, the material M is bent so that when the material M is placed on the punch top surface 11, the left and right ends to be sandwiched between the die lower surfaces 24L, 24R and the holder upper surfaces 41L, 41R will jump up slightly.

[0125] In the example shown in FIG. 6, when the material M is placed on the punch top surface 11, the left end of the material M is substantially parallel to the inclined surface 411L of the holder upper surface 41L. Also, when the material M is placed on the punch top surface 11, the right end of the material M is substantially parallel to the inclined surface 411R of the holder upper surface 41R. However, the left and right ends of the material M do not necessarily have to be parallel to the inclined surfaces 411L, 411R. For example, the angles that the left and right ends of the material M make with the horizontal plane are ψ L , ψ R It may deviate from this by about ±10°.

[0126] In this embodiment, the material M is preformed to a shape that conforms to the groove portion 111 of the punch top surface 11 and the punch shoulders 12L, 12R. Therefore, the material M is easily fitted to the punch 10, and the material M can be more reliably held between the punch 10 and the pad 30 during press working. In addition, since the material M is pre-bent at the portion corresponding to the second die shoulders 23L, 23R, the material M can be easily clamped between the die lower surfaces 24L, 24R adjacent to the second die shoulders 23L, 23R and the holder upper surfaces 41L, 41R. Therefore, tension can be applied to the material M more effectively. As a result, the effect of reducing the tensile residual stress generated on the inner side of the bend in the bent portions 203L, 203R of the press-formed product 200 (FIG. 2J) can be further improved.

[0127] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0128] For example, the press device 100 according to each of the above embodiments includes left and right holders 40L, 40R. However, the press device 100 may include only one of the holders 40L, 40R. That is, one of the left and right bent portions 203L, 203R of the press-formed product 200 can be formed while applying tension by the holder, and the other can be formed without applying tension by the holder. For example, when it is necessary to reduce the tensile residual stress on the inner side of the bend and obtain excellent fatigue characteristics in one of the left and right bent portions 203L, 203R of the press-formed product 200, while excellent fatigue characteristics are not required in the other, tension by the holder may be applied only to the side requiring excellent fatigue characteristics. When only one of the holders 40L, 40R is provided in the press device 100, the manufacturing cost of the press device 100 can be reduced.

[0129] In the press apparatus 100 according to each of the above embodiments, the entire holder upper surface 41L, 41R is the inclined surface 411L, 411R. However, a part of the holder upper surface 41L, 41R may be the inclined surface 411L, 411R. For example, the outer portion of the holder upper surface 41L, 41R in the width direction may be a horizontal surface, and a portion located inside the horizontal surface in the width direction (the portion on the punch 10 side) may be the inclined surface 411L, 411R. In this case, the distance blocks 42L, 42R may be disposed on a horizontal surface.

[0130] In the press apparatus 100 according to each of the above embodiments, the holders 40L, 40R can be raised and lowered by the cushion 90. However, the mechanism for raising and lowering the holders 40L, 40R is not limited to the cushion 90. For example, the holders 40L, 40R can be supported by an expandable support member such as a spring or a fluid pressure cylinder. In this case, when a load is applied from the dies 20L, 20R to the holder upper surfaces 41L, 41R, the support member contracts and the holders 40L, 40R descend. When the load is removed from the holder upper surfaces 41L, 41R, the support member expands and the holders 40L, 40R ascend.

[0131] In the press apparatus 100 according to each of the above embodiments, a groove 111 is formed in the punch top surface 11. However, a step (step) may be provided in the punch top surface 11 instead of the groove 111. This step may extend over the entire punch top surface 11 in the longitudinal direction, or may be provided in a part of the punch top surface 11. When a step is provided in the punch top surface 11, a corresponding step is also provided in the underside of the pad 30. When a step is provided in the punch top surface 11, a step corresponding to the step in the punch top surface 11 is formed in the top plate 201 of the press-formed product 200. A step corresponding to the step in the punch top surface 11 can also be formed in advance in the material M before press working.

[0132] However, the punch top surface 11 and the top plate 201 of the press-formed product 200 do not have to have a groove or a step. The punch top surface 11 and the top plate 201 of the press-formed product 200 may have a flat shape as a whole.

[0133] The overall shape of the press-molded product 200 can be appropriately selected depending on the purpose of use, etc. For example, the press-molded product 200 may be linear when viewed from the top plate 201 side (in a plan view), may be curved to the left or right, or may be curved up or down (curved when viewed in the width direction). The press-molded product 200 may have a shape that combines two or more types of straight portions and curved portions when viewed in a plan view. In addition, the press-molded product 200 may have a shape that combines two or more types of straight portions and curved portions when viewed in the width direction. Furthermore, the press-molded product 200 may have a shape in which a part having a roughly U-shaped cross section branches into multiple parts, such as a three-pronged or four-pronged shape when viewed in a plan view.

[0134] The press-molded product 200 does not need to have a uniform cross-sectional shape over the entirety. As long as the press-molded product has at least a part of a substantially U-shaped cross section, the press device and the manufacturing method according to each of the above embodiments can be applied.

[0135] One or more through holes may be formed in the top plate 201 of the press-molded product 200. The through holes may be simply round holes or may be holes (burring holes) formed by burring with protruding hole edges.

[0136] In the second embodiment, preforming is performed on the material M before pressing by the press device 100. In the second embodiment, the material M is subjected to formation of grooves M1 corresponding to the grooves 111 of the punch top surface 11, convex bending at positions M2 corresponding to the punch shoulders 12L and 12R, and concave bending at positions M3 corresponding to the second die shoulders 23L and 23R. However, in the second embodiment, any one or two of formation of grooves M1, convex bending at positions M2 corresponding to the punch shoulders 12L and 12R, and concave bending at positions M3 corresponding to the second die shoulders 23L and 23R may be performed on the material M. EXAMPLES

[0137] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples.

[0138] [First Example] In order to confirm the effect of the present disclosure, a CAE analysis was performed on the press processing in which a material (steel plate) having a tensile strength TS of 980 MPa and a plate thickness t of 3.0 mm is formed into a press-formed product 300 shown in FIG. 7 by the press device 100 shown in FIG. 1. The press-formed product 300 has a top plate 301, left and right vertical walls 302, and left and right bending portions 303. A groove portion 304 is formed in the top plate 301. The lower end of each vertical wall 302 is a free end. In other words, no flange is provided at the lower end of each vertical wall 302. The width of the top plate 301 is 80.0 mm, and the height of the vertical wall 302 is 25.0 mm. In addition, the bending radius (curvature radius on the inner side of the bending) of the bending portion 303 is 4.0 mm. The press-formed product 300 is curved in a plan view. The curvature radius on the inner side of the curve of the press-formed product 300 is 250.0 mm. The curvature R of the outer curve is 330.0 mm, obtained by adding the curvature R of the inner curve to the width of the top plate 301. Note that these dimensions are the dimensions on the inside of the press-formed product 300 (the surface on the inner side of the bend of the bent portion 303).

[0139] In the CAE analysis, commercially available software (LS-DYNA ver971 rev7.12, manufactured by ANSYS) was used to perform forming analysis and springback analysis to evaluate the maximum value of the residual stress (maximum principal stress) on the inner surface of the bent part 303 as the residual stress on the inner side of the bend. If the residual stress value is positive, it is tensile, and if it is negative, it is compressive. In the CAE analysis, of the elements divided in the plate thickness direction, the value of the element on the inner surface of the bend was used as the value of the inner surface of the bend. The analysis results are shown in Table 1.

[0140] [Table 1]

[0141] In Table 1, Comparative Example 1 is a result when a press-formed product 300 was formed by general pad bending. That is, in Comparative Example 1, the material was press-formed by the punch 10 and the dies 20L, 20R while being pressed by the pad 30, but the material was not clamped by the dies 20L, 20R and the holders 40L, 40R. In Comparative Example 1, after the press forming was completed and springback occurred, a residual stress of 580 MPa occurred on the inner surface of the bent portion 303 of the press-formed product 300.

[0142] Examples 1-1 to 1-18 are results when a press-formed product 300 was formed by the method according to the present disclosure. That is, in Examples 1-1 to 1-18, the dies 20L, 20R and the holders 40L, 40R clamped the widthwise end of the material from the middle of forming, and tension was applied to the material. In Examples 1-1 to 1-11, 1-13, 1-16 to 1-18, after the press forming was completed and springback occurred, the residual stress value on the inner surface of the bent portion 303 of the press-formed product 300 was smaller than that of Comparative Example 1. Therefore, it was confirmed that the effect of reducing the tensile residual stress on the inner surface of the bent portion 303 was obtained by applying tension to the material from the middle of forming.

[0143] In Examples 1-12, 1-14, and 1-15, the sheet thickness reduction rate of the material during press forming was 20% or more. When the sheet thickness reduction rate of the material is 20% or more in the CAE analysis, cracks often occur in the material or the press-formed product during actual press forming, so in Examples 1-12, 1-14, and 1-15, residual stress calculations were not performed.

[0144] (Holder lift stroke) In Example 1-12, the holder stroke (the lifting and lowering stroke of holders 40L, 40R) is 30.0 mm. In Example 1-12, it is believed that the large holder stroke caused the material thickness reduction rate to be 20% or more. On the other hand, in Example 1-2, in which the holder stroke was 25.0 mm, the material thickness reduction rate was less than 20%. From these results, in order to make it difficult for cracks to occur in the material or the press-molded product and to effectively exert the effect of reducing tensile residual stress in the present disclosure, it is preferable that the lifting and lowering stroke of holders 40L, 40R is 25.0 mm or less.

[0145] In Example 1-11, the holder stroke is 3.0 mm. In this Example 1-11, the residual stress on the inner side of the bend of the bent portion 303 is 547 MPa, and the effect of reducing the tensile residual stress is small. On the other hand, in Example 1-3, in which the holder stroke is 5.0 mm, the tensile residual stress is significantly reduced compared to Example 1-11. In Examples 1-1, 1-2, 1-4 to 1-10, etc., in which the holder stroke is larger than 5.0 mm, the effect of reducing the tensile residual stress is larger compared to Example 1-11. From this result, in order to effectively exert the effect of reducing the tensile residual stress in the present disclosure, it is preferable that the lifting stroke of the holders 40L and 40R is 5.0 mm or more.

[0146] (Holder load) In Example 1-14, the non-dimensional number Z of the holder load F is 0.50, and the holder load F is large. In Example 1-14, it is believed that the large holder load F caused the sheet thickness reduction rate of the material to be 20% or more. On the other hand, in Example 1-4, in which the non-dimensional number Z of the holder load F is 0.45, the sheet thickness reduction rate of the material was less than 20%. From this result, in order to make it difficult for cracks to occur in the material or the press-molded product and to effectively exert the effect of reducing tensile residual stress in the present disclosure, it is preferable that the non-dimensional number Z of the holder load F is 0.45 or less.

[0147] In Example 1-13, the non-dimensional number Z of the holder load F is 0.01, and the holder load F is insufficient. Therefore, in Example 1-13, the residual stress on the inner side of the bend of the bent portion 303 is 538 MPa, and the effect of reducing the tensile residual stress is small. On the other hand, in Example 1-5, in which the non-dimensional number Z of the holder load F is 0.04, the tensile residual stress is significantly reduced compared to Example 1-13. In Examples 1-1 to 1-4, 1-6 to 1-10, etc., in which the non-dimensional number Z is larger than 0.04, the effect of reducing the tensile residual stress is larger compared to Example 1-13. From this result, in order to effectively exert the effect of reducing the tensile residual stress in the present disclosure, it is preferable that the non-dimensional number Z of the holder load F is 0.04 or more.

[0148] (2nd die shoulder curvature radius) In Example 1-15, the bend R (radius of curvature R L ,R R ) is 2.0 mm, which is 0.67 times the sheet thickness t of the material. In Example 1-15, the radius of curvature R of the second die shoulders 23L and 23R L ,R R It is considered that the reduction in thickness of the blank was 20% or more due to the small radius of curvature R of the second die shoulders 23L, 23R. On the other hand, in Example 1-8 in which the bending R of the second die shoulders 23L, 23R was equal to the blank thickness t, the reduction in thickness of the blank was less than 20%. Therefore, in order to make it difficult for cracks to occur in the blank or the press-formed product and to effectively exert the effect of reducing the tensile residual stress in the present disclosure, it is necessary to reduce the radius of curvature R of the second die shoulders 23L, 23R. L ,R R is preferably equal to or greater than the plate thickness t of the material.

[0149] In Example 1-16, the bending radius R of the second die shoulders 23L, 23R is 15.0 mm, which is five times the plate thickness t of the material. In Example 1-16, the residual stress on the inner side of the bending of the bending portion 303 is 563 MPa, and the effect of reducing the tensile residual stress is small. On the other hand, in Example 1-9, in which the bending radius R of the second die shoulders 23L, 23R is four times the plate thickness t of the material, the tensile residual stress is significantly reduced compared to Example 1-16. Even in Examples 1-1 to 1-8, 1-10, etc., in which the bending radius R is less than four times the plate thickness t, the effect of reducing the tensile residual stress is greater compared to Example 1-16. From this result, in order to effectively exert the effect of reducing the tensile residual stress in the present disclosure, it is necessary to set the radius of curvature R of the second die shoulders 23L, 23R to 15.0 mm. L ,R R It is preferable that the radius of curvature R of the second die shoulders 23L, 23R is less than 5 times the plate thickness t of the material. L ,R R is less than four times the plate thickness t of the material.

[0150] (Holder face angle) In Example 1-17, the residual stress on the inner side of the bent portion 303 is 103 MPa, and the tensile residual stress is significantly reduced compared to Comparative Example 1. However, in Example 1-17, the angle ψ L , ψ R Since the holder face angle ψ was small at 7°, the bending tendency was large when the material passed through the second die shoulders 23L, 23R. On the other hand, in Example 1-6, in which the holder face angle ψ was 10°, the bending tendency was smaller than in Example 1-17. Therefore, in order to suppress the occurrence of bending tendency during press forming, the angle ψ of the inclined faces 241L, 241R, 411L, 411R is set to 10°. L , ψ R is preferably greater than 7°. More preferably, the angle ψ L , ψ R is greater than 10°.

[0151] In Example 1-18, the residual stress on the inner side of the bend of the bent portion 303 is 414 MPa, and the tensile residual stress is significantly reduced compared to Comparative Example 1. However, in Example 1-18, the face angle ψ of the holder is large at 60°, so the horizontal component of the load on the holder upper surfaces 41L, 41R is large. Therefore, there is concern that the holders 40L, 40R and the cushion pins 91L, 91R may be deformed or damaged. On the other hand, if the face angle ψ of the holder is 55° as in Example 1-7, the horizontal component of the load on the holder upper surfaces 41L, 41R is reduced to some extent, and it is considered that the holders 40L, 40R and the cushion pins 91L, 91R are less likely to be deformed or damaged. Therefore, the angle ψ of the inclined surfaces 241L, 241R, 411L, 411R is large. L , ψ R is preferably less than 60°. More preferably, the angle ψ L , ψ R is less than 55°.

[0152] [Second Example] In order to confirm the effect of preforming the material, a CAE analysis was performed using the same software as in Example 1. In this example, an analysis was performed on the press working of forming a material (steel plate) with a tensile strength TS of 980 MPa and a plate thickness t of 3.0 mm into a press-formed product without a flange. The results of the analysis are shown in Figure 8.

[0153] In Comparative Example 2 in FIG. 8, a press-formed product is formed by general pad bending, similarly to Comparative Example 1 in the first embodiment. Meanwhile, in Examples 2-1 to 2-3, press-formed products are formed by the press device 100 shown in FIG. 1 while applying tension to the material using the holders 40L and 40R. In Example 2-1, the material, which is a metal plate, is not preformed, but is used as is for press forming. In Example 2-2, a groove corresponding to the groove 111 of the punch top surface 11 is formed in advance in the material. In Example 2-3, in addition to the preforming in Example 2-2, the material is preformed by bending convexly at positions corresponding to the punch shoulders 12L and 12R and bending concavely at positions corresponding to the second die shoulders 23L and 23R. The preforming in Example 2-3 is the same as the preforming performed on the material in Example 1-10 (Table 1) of the first embodiment.

[0154] As shown in Fig. 8, even in Example 2-1, in which press forming was performed without preforming the material, the residual stress on the inner side of the bend of the bent portion was reduced to about half that of Comparative Example 2. In Examples 2-2 and 2-3, in which press forming was performed after preforming the material, the residual stress on the inner side of the bend of the bent portion was further reduced than in Example 2-1. Therefore, by preforming the material, it is possible to further improve the effect of reducing tensile residual stress.

[0155] [Third Example] In order to confirm the effect based on the work hardening exponent (n value) of the material, a CAE analysis was performed using the same software as in Example 1. In this example, as in Example 2, an analysis was performed on the press working of forming a material (steel plate) with a tensile strength TS = 980 MPa and a plate thickness t = 3.0 mm into a press-formed product without a flange. The results of the analysis are shown in Figure 9.

[0156] In Comparative Example 3 in FIG. 9, a press-formed product is formed by general pad bending, similar to Comparative Example 1 in the first embodiment. The n value of the material used in Comparative Example 3 is 0.08. On the other hand, in Examples 3-1 and 3-2, a material is formed into a press-formed product by the press device 100 shown in FIG. 1. The n value of the material used in Example 3-1 is 0.08, similar to Comparative Example 3, and the n value of the material used in Example 3-2 is 0.04. The yield ratio YR=yield stress YS / tensile strength TS of the material used in Comparative Example 3 and Example 3-1 is 0.88, and the yield ratio YR of the material used in Example 3-2 is 0.95.

[0157] As shown in FIG. 9, in both Example 3-1 and Example 3-2, the tensile residual stress on the inner side of the bend is reduced compared to Comparative Example 3. However, in Example 3-2, in which the n-value of the material is small, the effect of reducing the tensile residual stress is better than that of Example 3-1. From this result, it can be said that in order to improve the effect of reducing the tensile residual stress, it is preferable that the n-value of the material is small. The n-value of the material is preferably 0.04 or less. In addition, the yield ratio YR of the material is preferably 0.95 or more. [Explanation of symbols]

[0158] 100: Press equipment 10: Punch 11: Punch top surface 12L, 12R: Punch shoulder 13L, 13R: Punch side 20L, 20R: Die 21L, 21R: First die shoulder 22L, 22R: Die side 23L, 23R: 2nd die shoulder 24L, 24R: Die bottom surface 241L, 241R: Inclined surface 30: Pad 40L, 40R: Holder 41L, 41R: Holder top surface 411L, 411R: Inclined surface 42L, 42R: Distance block

Claims

1. A press device for performing press working on a metal plate material, a punch having a punch top surface, a punch shoulder continuous with the punch top surface, and a punch side surface extending downward from the punch shoulder; a pad disposed above the punch so as to face the top surface of the punch and configured to be liftable and lowerable; a die arranged above the punch and to the side of the pad, configured to be liftable, and having a first die shoulder corresponding to the punch shoulder, a die side surface extending downward from the first die shoulder corresponding to the punch side surface, and a die lower surface connected to a lower end of the die side surface via a second die shoulder; a holder arranged to the side of the punch and below the die, configured to be movable up and down, and having a holder upper surface facing a lower surface of the die; Equipped with the lower surface of the pad has a shape corresponding to the top surface of the punch; the die lower surface includes an inclined surface that descends away from the second die shoulder; a press device, wherein the holder upper surface is positioned below the punch top surface and above the position of the die lower surface when the die reaches bottom dead center at the start of press processing by the press device, and includes an inclined surface that descends as it moves away from the punch in correspondence with the inclined surface of the die lower surface.

2. The press device according to claim 1, A press apparatus, wherein the angle between the inclined surface of the holder upper surface and a horizontal plane is equal to or greater than 10° and equal to or less than 55°.

3. The press device according to claim 1 or 2, A press device, wherein the lifting and lowering stroke of the holder is 5.0 mm or more and 25.0 mm or less.

4. The press device according to any one of claims 1 to 3, A press apparatus in which a vertical load applied to the upper surface of the holder is set to satisfy the following conditional formula, where F [kN] is the load, TS [MPa] is the tensile strength of the material, t [mm] is the plate thickness of the material, and L [mm] is the longitudinal length of the portion of the material that is clamped between the lower surface of the die and the upper surface of the holder. 0.04≦Z≦0.45 where Z = F / (TS x t x L)

5. The press device according to any one of claims 1 to 4, The second die shoulder has an arc shape having a radius of curvature greater than or equal to a thickness of the material and less than or equal to four times the thickness when viewed in cross section of the die.

6. The press apparatus according to any one of claims 1 to 5, further comprising: a distance block provided on an upper surface of the holder and configured to adjust a distance between a lower surface of the die that holds the material and the upper surface of the holder; A press device comprising:

7. A method for producing a press-molded product using the press apparatus according to any one of claims 1 to 6, Providing a material which is a metal plate; placing the material on the top surface of the punch and lowering the pad and the die; a step of clamping an end of the material between a lower surface of the die and an upper surface of the holder after the pad presses the material on the top surface of the punch and before the die reaches a bottom dead center; a step of pressing the material by the first die shoulder and the die side surface and the punch shoulder and the punch side surface by causing the die to reach the bottom dead center; Equipped with the end of the material is pulled out along the inclined surface from between the lower surface of the die and the upper surface of the holder as the die descends, and is positioned between the die side surface and the punch side surface when the die reaches the bottom dead center.

8. The method according to claim 7, further comprising the steps of: When the die reaches the bottom dead center, an upper surface of the holder is positioned outside the pressed material in the width direction of the press device.

9. The method according to claim 7 or 8, A manufacturing method in which the prepared blank is concavely bent at a position corresponding to the second die shoulder.

10. The method according to any one of claims 7 to 9, A manufacturing method in which the prepared blank is convexly bent at a position corresponding to the punch shoulder.

11. The method according to any one of claims 7 to 10, The punch has a groove or a step on the top surface of the punch, A manufacturing method in which a groove or a step corresponding to the groove or the step on the top surface of the punch is formed in the prepared material.

12. The method according to any one of claims 7 to 11, The manufacturing method, wherein the work hardening index of the material is 0.04 or less.

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