Mold, Press Device, and Method for Manufacturing a Press-Molded Product

Abstract

To provide a mold which reduces spring back of a press molding and can improve dimensional accuracy, and has a simple structure.SOLUTION: A mold (10) includes dies (12L, 12R). The dies (12L, 12R) include die shoulders (121L, 121R), and die side faces (122L, 122R). The die side faces (122L, 122R) have a die upper side face (122a), and a die lower side face (122b). The die lower side face (122b) has a shape recessed outward in a width direction of the mold (10) with respect to the die upper side face (122a). When a length from the upper ends of the die shoulders (121L, 121R) to the lower end of the die upper side face (122a) is represented by H1, and a length from the lower end of the die upper side face (122a) to the lower end of the die lower side face (122b) is represented by H2, H1 is larger than a radius of curvature of the die shoulders (121L, 121R) by 5.0 mm or more, and H2 / H1 is 1.0 or more and 5.0 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a mold for pressing a plate-shaped material, a press device, and a method for manufacturing a press-formed product.

Background Art

[0002] Press-formed products are widely used as components constituting the body of an automobile or the like. The press-formed product has, for example, a top plate and vertical walls connected to both side edges of the top plate via bent portions. Such a press-formed product is manufactured by subjecting a plate-shaped material (metal plate) to press working. More specifically, a press-formed product is manufactured by using a mold including a punch and a die and subjecting the metal plate to drawing or bending.

[0003] When the metal plate is formed into a press-formed product by a mold and then the press-formed product is removed from the mold, springback occurs. More specifically, when the metal plate is bent by the mold during press working, tensile stress is generated on the outer side of the bend and compressive stress is generated on the inner side of the bend at the bent portion. However, when the forming is completed and the press-formed product is removed from the mold, due to the elastic recovery of the material, compressive stress is generated on the outer side of the bend and tensile stress is generated on the inner side of the bend. As a result, at the moment when the press-formed product is removed from the mold, a moment (wall-opening moment) that causes both vertical walls of the press-formed product to open outward occurs. Due to this moment, springback of the press-formed product occurs.

[0004] Molds for press working may be designed anticipating springback in order to obtain the target dimensional accuracy for press-formed products. That is, in the mold, the portions that form both vertical walls of the press-formed product are provided inside the positions of the target both vertical walls by the amount of wall opening expected due to springback. However, it is difficult to exactly match the expected amount of springback with the actual amount of springback. Also, since the amount of springback is proportional to the strength of the material, for example, when performing press working on high-strength materials such as high-tensile steel and ultra-high-tensile steel, the expected amount of springback becomes large. When designing the mold based on this expected amount, the portions of the mold that form both vertical walls of the press-formed product become negative angles, and there is a possibility that the mold structure may not be established. Therefore, it is difficult to obtain the target dimensional accuracy for press-formed products only by designing the mold anticipating springback.

[0005] Therefore, a technique has been proposed to obtain a press-formed product with the target dimensional accuracy without relying on the anticipation of springback. For example, Patent Document 1 discloses a method for manufacturing a press-formed product including a top plate and two vertical walls, and also including flanges extending outward from both vertical walls. The manufacturing method of Patent Document 1 includes, for example, a first press working step of manufacturing an intermediate formed product from a metal plate as a material, and a second press working step of manufacturing a final press-formed product from the intermediate formed product. In the first press working step, the metal plate is press-worked by a first punch and a first die, and the top plate and the bent portions of the press-formed product are formed, and a part of each vertical wall is formed. In the second press working step, the intermediate formed product obtained in the first press working step is press-worked by a second punch and a second die, and the remaining portions of each vertical wall and each flange are formed. According to Patent Document 1, by performing the forming of each flange last, the warping (opening) of each vertical wall due to springback can be reduced.

[0006] For example, Patent Document 2 discloses controlling the moving direction of a die using a cam mechanism during the manufacture of a press-formed product. The manufacturing method of Patent Document 2 includes a pressing and bending step of lowering the die toward the material on the punch to bend and form the material, and a drawing and bending step of moving the die in a direction approaching the punch using a cam to bend and form the material. In the drawing and bending step, since the dies provided on both sides of the punch contact the ends of the material and press the material toward the punch side, an upwardly convex deflection is formed in the material. According to Patent Document 2, by deflecting the material in this way, a spring go component acting in a direction to cancel out the springback component can be generated.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] In the manufacturing method of Patent Document 1, the top plate of the press-formed product and a part of each vertical wall are formed in advance, and the remaining parts of each vertical wall and each flange are formed last to reduce springback. Therefore, in the case of the manufacturing method of Patent Document 1, at least two press working steps are required to prevent deterioration of dimensional accuracy due to springback.

[0009] On the other hand, in the manufacturing method of Patent Document 2, a press-formed product can be manufactured in one press working step. However, in the case of the manufacturing method of Patent Document 2, since it is necessary to use a cam mechanism to control the moving direction of the die, there is a problem that the structure of the mold becomes complicated.

[0010] The present disclosure aims to provide a mold with a simple structure that can reduce springback of a press-formed product and improve dimensional accuracy.

Means for Solving the Problems

[0011] The mold according to the present disclosure is a mold for performing press working on a plate-shaped material. The mold includes a punch and a die. The punch includes a punch top surface, a punch side surface, and a punch shoulder. The punch shoulder constitutes a corner between the punch top surface and the punch side surface. The die includes a die shoulder, a die side surface, and a die flange surface. The die shoulder corresponds to the punch shoulder. The die side surface corresponds to the punch side surface. The die flange surface extends outward in the width direction of the mold from the die side surface. The die side surface has an upper die side surface and a lower die side surface. The upper die side surface is provided continuously with the die shoulder. The lower die side surface is disposed between the upper die side surface and the die flange surface. The lower die side surface has a concave shape facing outward in the width direction of the mold with respect to the upper die side surface. When the length in the vertical direction of the die from the upper end of the die shoulder to the lower end of the upper die side surface is H1, and the length in the vertical direction from the lower end of the upper die side surface to the lower end of the lower die side surface is H2, H1 is 5.0 mm or more larger than the radius of curvature of the die shoulder, and H2 / H1 is 1.0 or more and 5.0 or less.

Advantages of the Invention

[0012] The mold according to the present disclosure can reduce springback of a press-formed product and improve dimensional accuracy. Further, the mold according to the present disclosure has a simple structure.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

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Figure 3E

Figure 3F

Figure 3G

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Figure 10

Figure 11

Mode for Carrying Out the Invention

[0014] The mold according to the embodiment is a mold for performing press working on a plate-shaped material. The mold includes a punch and a die. The punch includes a punch top surface, a punch side surface, and a punch shoulder. The punch shoulder constitutes a corner between the punch top surface and the punch side surface. The die includes a die shoulder, a die side surface, and a die flange surface. The die shoulder corresponds to the punch shoulder. The die side surface corresponds to the punch side surface. The die flange surface extends outward in the width direction of the mold from the die side surface. The die side surface has a die upper side surface and a die lower side surface. The die upper side surface is provided continuously with the die shoulder. The die lower side surface is disposed between the die upper side surface and the die flange surface. The die lower side surface has a concave shape facing outward in the width direction of the mold with respect to the die upper side surface. When the length in the vertical direction of the die from the upper end of the die shoulder to the lower end of the die upper side surface is H1, and the length in the vertical direction from the lower end of the die upper side surface to the lower end of the die lower side surface is H2, H1 is 5.0 mm or more larger than the radius of curvature of the die shoulder, and H2 / H1 is 1.0 or more and 5.0 or less (first configuration).

[0015] When performing press working on a plate-shaped material using the mold according to the first configuration, with the material placed on the punch top surface, the die is relatively approached to the punch. As a result, first, the die lower side surface contacts the material on the punch top surface. The die lower side surface has a concave shape facing outward in the width direction of the mold with respect to the die upper side surface. Therefore, as the die approaches the punch, the material is guided by the die lower side surface and bends so as to have a convex shape on the side opposite to the approaching direction of the die with respect to the punch. When the die is further approached to the punch, the material contacts the die upper side surface, and the bent material is gradually bent back. As the approach of the die and the punch progresses, the bending of the material is reduced, and the material conforms to (wraps around) the punch shoulder and a bent portion is formed. When the punch and the die are finally closed, the bending of the material is completely bent back and disappears, and the material is clamped between the punch shoulder and the die shoulder, and between the punch side surface and the die upper side surface.

[0016] In this way, the mold with the first configuration is configured to bend the material into a convex shape on the side opposite to the approaching direction of the die with respect to the punch, and gradually bend back the bend of the material as the pressing process progresses. As a result, during the pressing process, tensile stress can be generated on the punch side and compressive stress can be generated on the die side, which is the side opposite to the punch, particularly in the portion of the material that becomes the vertical wall of the press-formed product. In the bent portion formed by the punch shoulder, compressive stress is generated on the punch side and tensile stress is generated on the die side. Therefore, the stress generated by the bending-back of the bend cancels out the stress in the bent portion, reducing the stress in the bent portion. When the forming of the press-formed product from the material is completed, the stress remaining in the bent portion and the stress remaining in the bent-back portion cause a wall-opening moment and a wall-closing moment in the press-formed product after demolding. These cancel each other out, reducing the wall-opening moment. Therefore, springback in the press-formed product after demolding can be reduced. As a result, the dimensional accuracy of the press-formed product can be improved. In addition, when performing a pressing process on the material using the mold according to the first configuration, only a normal mold closing operation needs to be performed, and a cam mechanism or the like for moving the die in a special direction is unnecessary. Therefore, the mold can have a simple structure.

[0017] In the first configuration, when the length in the vertical direction of the die from the upper end of the die shoulder to the lower end of the upper side surface of the die is H1, and the length in the vertical direction of the die from the lower end of the upper side surface of the die to the lower end of the lower side surface of the die is H2, H2 / H1 is set to be 1.0 or more and 5.0 or less. Thereby, since the length of the lower side surface of the die is sufficiently ensured, during the pressing process, the lower side surface of the die can greatly deflect the material over a wide range in the width direction. Therefore, the effect of canceling the stress and moment due to the springback of the deflection can be effectively exerted. Further, in the first configuration, since H1 is made 5.0 mm or more larger than the radius of curvature of the die shoulder and H2 / H1 is 1.0 or more and 5.0 or less, the length of the upper side surface of the die can also be ensured. Therefore, when the punch and the die are finally closed, the material can be firmly clamped between the side surface of the punch and the upper side surface of the die, and the material can be formed into the shape of the final pressed product. Therefore, it is not necessary to perform an additional pressing process, and the man-hours and costs in the manufacture of the pressed product can be reduced.

[0018] When H2 / H1 exceeds 5.0, the ratio occupied by the lower side surface of the die having a concave shape outward in the width direction of the mold on the die side surface becomes excessive, and the effect of deflecting the material by the lower side surface of the die saturates. Further, when H2 / H1 exceeds 5.0, the costs for manufacturing the mold and the like also increase. Therefore, as in the first configuration, it is preferable that H2 / H1 is 5.0 or less.

[0019] The lower side surface of the die may include a first connection portion, a second connection portion, and an intermediate portion. The first connection portion is continuously provided at the lower end of the upper side surface of the die and connects the lower side surface of the die to the upper side surface of the die. The second connection portion includes the lower end of the lower side surface of the die and connects the lower side surface of the die to the die flange surface. The intermediate portion is disposed between the first connection portion and the second connection portion and is positioned outside in the width direction than the first connection portion (second configuration).

[0020] The first connecting part is, for example, arc-shaped in a cross-sectional view of the die. In this case, the first connecting part preferably has a radius of curvature of 1.0 mm or more and 10.0 mm or less (the third configuration).

[0021] In the third configuration, among the lower side surfaces of the die, the radius of curvature of the first connecting part that connects the lower side surface of the die to the upper side surface of the die is set to 10.0 mm or less. In this case, on the die side surface having a predetermined size, the ratio occupied by the first connecting part and the lower side surface of the die including the first connecting part does not become too large, and it becomes easier to secure the length of the upper side surface of the die. Therefore, when the punch and the die are finally closed, the material can be more reliably clamped between the punch side surface and the upper side surface of the die.

[0022] When the first connecting part contacts the material during press working, indentation marks (bite-in marks) or bending bends of the first connecting part may remain on the material. On the other hand, in the third configuration, the radius of curvature of the first connecting part is set to 1.0 mm or more. Therefore, it is possible to avoid indentation marks and bending bends from remaining on the material.

[0023] The middle part may include a curved surface that is concave outward in the width direction of the mold with respect to the first connecting part (the fourth configuration). In this case, when the length in the width direction from the lower end of the upper side surface of the die to the lower end of the lower side surface of the die is W2, it is preferable that H2 / W2 is 1.0 or more and 5.0 or less (the fifth configuration).

[0024] When H2 / W2 is less than 1.0, that is, when W2 is large with respect to H2, the effect of bending the material by the lower side surface of the die saturates. Also, when H2 / W2 is less than 1.0, the cost for manufacturing the mold and the like also increases. On the other hand, when H2 / W2 exceeds 5.0, since W2 becomes small with respect to H2, the effect of bending the material by the lower side surface of the die becomes small. Therefore, when the middle part of the lower side surface of the die is mainly composed of a curved surface, it is preferable that H2 / W2 is 1.0 or more and 5.0 or less as in the fifth configuration.

[0025] The middle part may include an inclined surface that is inclined with respect to the horizontal plane (the sixth configuration). When the angle formed by the inclined surface with the horizontal plane is θ° for the angle formed by the punch side surface with the vertical plane, it is preferably (50 - θ)° or more and (78 - θ)° or less (the seventh configuration).

[0026] When the middle part of the lower die side surface is mainly composed of an inclined surface, if the angle of the inclined surface with respect to the horizontal plane is too large, the degree of the recess on the lower die side surface becomes small. Therefore, the effect of bending the material by the lower die side surface becomes small. On the other hand, if the angle of the inclined surface with respect to the horizontal plane is too small, the effect saturates. Also, as the angle of the inclined surface with respect to the horizontal plane becomes smaller, the degree of the recess on the lower die side surface becomes larger, so the mold becomes larger in size and the cost related to the manufacture of the mold and the like increases. Therefore, the angle formed by the inclined surface included in the middle part with respect to the horizontal plane is preferably (50 - θ)° or more and (78 - θ)° or less as in the seventh configuration, where the angle formed by the punch side surface with respect to the vertical plane is θ°.

[0027] The clearance between the punch side surface and the upper die side surface when the punch and the die are in the closed state may be smaller than the thickness of the material (the eighth configuration). The clearance is preferably 0.85 times or more and 0.95 times or less of the plate thickness (the ninth configuration).

[0028] In the eighth and ninth configurations, the clearance between the punch side surface and the upper die side surface is smaller than the thickness of the material. Therefore, when the punch and the die are finally closed, the material is strongly clamped between the punch side surface and the upper die side surface, and the deflection of the material is more firmly bent back. In this case, in the portion of the material that becomes the vertical wall of the press-formed product, a large tensile stress can be generated on the punch side, and a large compressive stress can be generated on the die side, which is the opposite side of the punch. Therefore, the effect of these stresses canceling the stress at the bent portion can be enhanced. As a result, the springback in the press-formed product after demolding can be further reduced, and the dimensional accuracy of the press-formed product can be further improved.

[0029] In the die according to the embodiment, when the punch and the die finally close in the press working of the plate-shaped material, while the material is clamped between the punch side surface and the upper die side surface, the concave lower die side surface does not substantially contact the material. Therefore, a load can be intensively applied to the portion of the material that becomes the vertical wall of the press-formed product. In particular, when the clearance between the punch side surface and the upper die side surface is smaller than the plate thickness of the material as in the eighth and ninth configurations, the portion of the material that becomes the vertical wall of the press-formed product can be pressed more strongly.

[0030] In a cam mechanism that moves the die obliquely downward as in Patent Document 2, it is difficult to strongly press the material in the plate thickness direction due to the die rigidity. On the other hand, in the eighth and ninth configurations, the cam mechanism is not used, and the clearance between the punch side surface and the upper die side surface is set to be smaller than the plate thickness of the material. Thereby, it becomes possible to strongly press the material in the plate thickness direction. Therefore, a larger stress can be generated in the portion of the material that becomes the vertical wall of the press-formed product, and the effect of canceling the stress in the bent portion by the stress can be enhanced. As a result, the springback in the press-formed product after demolding can be further reduced, and the dimensional accuracy of the press-formed product can be further improved.

[0031] The die may further include a pad corresponding to the punch top surface (tenth configuration).

[0032] The die according to the tenth configuration includes a pad in addition to the punch and the die. In this case, with the material held between the punch top surface and the pad, the die can be brought relatively close to the punch. Therefore, displacement of the material during press working can be prevented. Further, by forming the material while holding the material with the pad, the shape of the top plate of the press-formed product can be accurately formed.

[0033] The press device according to the embodiment manufactures a press-formed product from a plate-shaped material. The press device includes the above-described mold. The press device is configured such that, with the material disposed on the punch top surface held between the punch top surface and the pad, the forming of the material by the punch and the die is started (11th configuration).

[0034] The above press device further includes a die holder. The die holder supports the die and the pad so as to be integrally movable. The pad is connected to the die holder by an elastic member that can expand and contract (12th configuration).

[0035] The manufacturing method according to the embodiment is a method for manufacturing a press-formed product. The manufacturing method includes a first preparation step of preparing the above-described mold, a second preparation step of preparing a plate-shaped material, and a forming step of forming the material into a press-formed product using the mold. The forming step includes a step of disposing the material on the punch top surface, then bringing the die relatively close to the punch and contacting the lower side surface of the die with the material to deflect the material; a step of further bringing the die closer to the punch with the material deflected and contacting the upper side surface of the die with the material; a step of bending back the deflection of the material by the upper side surface of the die by further bringing the die closer to the punch while the upper side surface of the die is in contact with the material; and a step of closing the punch and the die and clamping the material between the punch shoulder and the die shoulder and between the punch side surface and the upper side surface of the die. When the punch and the die are completely closed, the material assumes a shape along the punch top surface, the punch shoulder, and the punch side surface (13th configuration).

[0036] In the above manufacturing method, in the first preparation step, a mold including a pad in addition to the punch and the die may be prepared. In this case, in the forming step, it is preferable to deflect the material by the lower side surface of the die with the material disposed on the punch top surface held between the punch top surface and the pad (14th configuration).

[0037] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The same or corresponding components in each figure are denoted by the same reference numerals, and the same description will not be repeated.

[0038] <First Embodiment> [Configuration of Press Device] FIG. 1 is a cross-sectional view showing a schematic configuration of a mold 10 according to the present embodiment. The cross-section is a cross-section obtained by cutting the mold 10 with a plane substantially perpendicular to the longitudinal direction of the mold 10. In the following description, the vertical direction on the plane of FIG. 1 is referred to as the vertical direction of the mold 10, and the horizontal direction on the plane of FIG. 1, that is, the direction substantially perpendicular to the plane composed of the longitudinal direction and the vertical direction of the mold 10 is referred to as the width direction of the mold 10. Also, the left side and the right side on the plane of FIG. 1 may be simply referred to as the left side and the right side.

[0039] The mold 10 is used to perform press working on a plate-shaped material (metal plate). By performing press working on the material with the mold 10, for example, a press-formed product that is a component of an automobile's underbody can be manufactured. Examples of components of an automobile's underbody include, in addition to arm components such as upper arms, lower arms, or trailing links, suspension members, torsion beams, and the like.

[0040] Referring to FIG. 1, when performing press working on the material, the mold 10 is attached to a press device 20. The mold 10 includes a punch 11, dies 12L, 12R, and a pad 13. In the present embodiment, the dies 12L, 12R, which are the upper mold of the mold 10, and the pad 13 are moved in the vertical direction by the press device 20. When a straight line pulled in the vertical direction is projected onto the cross-section of the mold 10, the direction of the straight line coincides with the vertical direction in the cross-sectional view of the mold 10. When the mold 10 is for forming a press-formed product having a linear shape in a side view, the vertical direction and the vertical direction in the cross-sectional view of the mold 10 always coincide over the entire length of the mold 10.

[0041] The punch 11 includes a punch top surface 111, punch shoulders 112L, 112R, and punch side surfaces 113L, 113R.

[0042] In the example shown in FIG. 1, the punch top surface 111 is a substantially flat surface. However, a groove or a stepped portion (step) extending in the longitudinal direction of the punch 11 may be formed on the punch top surface 111. The groove or the stepped portion may extend over the entire punch top surface 111 in the longitudinal direction of the punch 11, or may be provided on a part of the punch top surface 111.

[0043] In the width direction of the mold 10, punch shoulders 112L and 112R and punch side surfaces 113L and 113R are provided on both sides adjacent to the punch top surface 111. The punch shoulder 112L and the punch side surface 113L are disposed on the left side of the punch top surface 111. The punch shoulder 112R and the punch side surface 113R are disposed on the right side of the punch top surface 111.

[0044] The punch shoulders 112L and 112R are continuously provided on the punch top surface 111. More specifically, the punch shoulder 112L is continuous with the left edge of the punch top surface 111, and the punch shoulder 112R is continuous with the right edge of the punch top surface 111. The punch shoulders 112L and 112R each constitute a corner portion (ridge line portion) between the punch top surface 111 and the punch side surfaces 113L and 113R. Each of the punch shoulders 112L and 112R is, for example, substantially arc-shaped in a cross-sectional view of the punch 11.

[0045] Here, in the present embodiment, "substantially arc-shaped" is a concept that includes not only a curve that constitutes a part of a perfect circle but also smooth curves such as an elliptical curve and a spline curve. In the present embodiment, for smooth curves other than curves that constitute a part of a perfect circle, such as an elliptical curve and a spline curve, the radius of curvature is defined as the radius of a circle passing through three points: both ends of the curve and the midpoint of the curve.

[0046] In a cross-sectional view of the punch 11, the punch side surface 113L extends downward from the left punch shoulder 112L. In a cross-sectional view of the punch 11, the punch side surface 113R extends downward from the right punch shoulder 112R. In the example of the present embodiment, when viewed in the cross-section of the punch 11, the punch side surfaces 113L and 113R are inclined with respect to the vertical direction so as to be separated from each other as they go downward. However, the punch side surfaces 113L and 113R may extend substantially in the vertical direction when viewed in the cross-section of the punch 11.

[0047] The angle θ formed by the punch side surfaces 113L and 113R with the vertical plane L , θ R (°) may be the same or different. The angle θ L , θ R is each 0° or more. The angle θ L , θ R is preferably each 20° or less. The angle θ formed by the punch side surfaces 113L and 113R with the vertical plane L , θ R is the angle (acute angle side) formed by the punch side surfaces 113L and 113R with the vertical direction in the cross-section obtained by cutting the punch 11 with a plane composed of the vertical direction and the width direction. The vertical plane is the cross-section when the mold 10 is cut with a plane composed of the vertical direction and the longitudinal direction, or a plane composed of the vertical direction and the longitudinal direction. When the vertical plane is projected onto the cross-section of the mold 10, it becomes a straight line extending in the vertical direction.

[0048] When the mold 10 is attached to the press device 20, the dies 12L and 12R are positioned above the punch 11. Also, when the mold 10 is attached to the press device 20, the dies 12L and 12R are positioned on both sides of the pad 13 in the width direction of the mold 10. The die 12L is disposed on the left side of the pad 13. The die 12R is disposed on the right side of the pad 13.

[0049] The left die 12L includes a die shoulder 121L, a die side surface 122L, and a die flange surface 123L. The right die 12R includes a die shoulder 121R, a die side surface 122R, and a die flange surface 123R.

[0050] The left die shoulder 121L is provided corresponding to the left punch shoulder 112L. That is, the die shoulder 121L has a shape capable of sandwiching a material between it and the punch shoulder 112L when the punch 11 and the dies 12L, 12R are closed. Similarly, the right die shoulder 121R is provided corresponding to the right punch shoulder 112R. That is, the die shoulder 121R has a shape capable of sandwiching a material between it and the punch shoulder 112R when the punch 11 and the dies 12L, 12R are closed.

[0051] The die shoulders 121L, 121R are each substantially arc-shaped in a cross-sectional view of the dies 12L, 12R. The radius of curvature of the die shoulders 121L, 121R can be determined in relation to the radius of curvature of the corresponding punch shoulders 112L, 112R. For example, when the radius of curvature of the die shoulder 121L is Rd1, the radius of curvature of the punch shoulder 112L is Rp, and the thickness of the material is t, it is preferable that Rd1 ≤ Rp + t. Similarly, when the radius of curvature of the die shoulder 121R is Rd1, the radius of curvature of the punch shoulder 112R is Rp, and the thickness of the material subjected to press working is t, it is preferable that Rd1 ≤ Rp + t. However, the radius of curvature Rd1 of the left die shoulder 121L and the radius of curvature Rp of the punch shoulder 112L do not necessarily have to be the same as the radius of curvature Rd1 of the right die shoulder 121R and the radius of curvature Rp of the punch shoulder 112R.

[0052] The left die side surface 122L is provided corresponding to the left punch side surface 113L. That is, the die side surface 122L has a shape capable of sandwiching a material between a part of the die side surface 122L and the punch side surface 113L when the punch 11 and the dies 12L, 12R are closed. The right die side surface 122R is provided corresponding to the right punch side surface 113R. That is, the die side surface 122R has a shape capable of sandwiching a material between a part of the die side surface 122R and the punch side surface 113R when the punch 11 and the dies 12L, 12R are closed. Each of the die side surfaces 122L, 122R has a die upper side surface 122a and a die lower side surface 122b.

[0053] The die flange surfaces 123L and 123R extend outward in the width direction of the mold from the die side surfaces 122L and 122R. The die flange surface 123L is continuously provided on the left lower die side surface 122b. The die flange surface 123R is continuously provided on the right lower die side surface 122b.

[0054] Hereinafter, with reference to FIG. 2, the configurations of the upper die side surface 122a and the lower die side surface 122b will be described. FIG. 2 is a cross-sectional view showing an enlarged right die 12R of the mold 10.

[0055] The upper die side surface 122a is continuously provided on the die shoulder 121R. The upper die side surface 122a extends downward from the die shoulder 121R in a cross-sectional view of the die 12R. The upper die side surface 122a has a substantially linear shape in a cross-sectional view of the die 12R.

[0056] In a cross-section obtained by cutting the die 12R with a plane composed of the vertical direction and the width direction, the angle formed by the upper die side surface 122a and the vertical direction is substantially equal to the angle θ of the punch side surface 113R. R In the example of the present embodiment, the upper die side surface 122a is inclined with respect to the vertical direction in a cross-sectional view of the die 12R corresponding to the punch side surface 113R. More specifically, the upper die side surface 122a is inclined with respect to the vertical direction so as to widen outward in the width direction of the mold 10 as it goes downward.

[0057] The lower die side surface 122b is disposed between the upper die side surface 122a and the die flange surface 123R. The lower die side surface 122b has a concave shape facing outward in the width direction of the mold 10 with respect to the upper die side surface 122a. That is, the lower die side surface 122b is a region that is recessed outward in the width direction of the mold 10 compared to the upper die side surface 122a among the die side surfaces 122R. The lower die side surface 122b is disposed outward in the width direction of the mold 10 from the extension line of the upper die side surface 122a shown by the two-dot chain line in FIG. 2.

[0058] The lower die side surface 122b includes connection portions 122c, 122d and an intermediate portion 122e. On the lower die side surface 122b, the connection portions 122c, 122d are provided with the intermediate portion 122e therebetween. The connection portion 122c is disposed above the intermediate portion 122e. The connection portion 122d is disposed below the intermediate portion 122e.

[0059] The upper connection portion 122c is continuously provided at the lower end of the upper die side surface 122a. The connection portion 122c connects the lower die side surface 122b to the upper die side surface 122a. The connection portion 122c constitutes a corner between the upper die side surface 122a and the intermediate portion 122e of the lower die side surface 122b. In the present embodiment, the connection portion 122c is substantially arc-shaped in a cross-sectional view of the die 12R. The connection portion 122c smoothly connects the upper die side surface 122a and the lower die side surface 122b. The connection portion 122c preferably has a curvature radius Rd2 of 1.0 mm or more and 10.0 mm or less. The curvature radius Rd2 of the connection portion 122c is more preferably 1.0 mm or more and 4.0 mm or less.

[0060] The lower connection portion 122d includes the lower end of the lower die side surface 122b. The connection portion 122d connects the lower die side surface 122b to the die flange surface 123R. The connection portion 122d constitutes a corner between the intermediate portion 122e of the lower die side surface 122b and the die flange surface 123R. In the present embodiment, the connection portion 122d is substantially arc-shaped in a cross-sectional view of the die 12R. The connection portion 122d smoothly connects the lower die side surface 122b and the die flange surface 123R. From the viewpoint of preventing the material from leaving indentation marks, the connection portion 122d preferably has a curvature radius Rd3 of 1.0 mm or more. Also, from the viewpoint of preventing the enlargement of the mold 10 and reducing the cost, the connection portion 122d preferably has a curvature radius Rd3 of 16.0 mm or less. The curvature radius Rd3 of the connection portion 122d is more preferably 1.0 mm or more and 4.0 mm or less.

[0061] The intermediate portion 122e is disposed between the connection portion 122c and the connection portion 122d. The intermediate portion 122e is positioned outside in the width direction of the mold 10 than the upper connection portion 122c. That is, the intermediate portion 122e is recessed outward in the width direction of the mold 10 as compared with the die upper side surface 122a and the connection portion 122c connecting with the die upper side surface 122a.

[0062] In the present embodiment, the intermediate portion 122e is mainly composed of a curved surface. This curved surface has, for example, a concave shape facing outward in the width direction of the mold 10 with respect to the upper connection portion 122c. The shape of the curved surface constituting the intermediate portion 122e is, for example, an arc shape, an elliptical arc shape, or a parabolic shape, etc. in a cross-sectional view of the die 12R.

[0063] Continuing to refer to FIG. 2, the length in the vertical direction of the die 12R from the upper end of the die shoulder 121R to the lower end of the die upper side surface 122a is defined as the upper height H1 of the die side surface 122R. Also, the length in the vertical direction of the die 12R from the lower end of the die upper side surface 122a to the lower end of the die lower side surface 122b is defined as the lower height H2. The upper end of the die shoulder 121R is the R stop of the die shoulder 121R on the side opposite to the die side surface 122R. In the example of the present embodiment, the lower end of the die upper side surface 122a coincides with the upper R stop of the connection portion 122c of the die lower side surface 122b. Also, the lower end of the die lower side surface 122b is the R stop on the die flange surface 123R side of the connection portion 122d.

[0064] The upper height H1 of the die side surface 122R is 5.0 mm or more larger than the radius of curvature Rd1 of the die shoulder 121R. The ratio of the lower height H2 to the upper height H1: H2 / H1 is 1.0 or more and 5.0 or less.

[0065] The length in the width direction of the mold 10 from the lower end of the die upper side surface 122a to the lower end of the die lower side surface 122b is defined as the concave width W2. The concave width W2 is the depth of the concave die lower side surface 122b with respect to the die upper side surface 122a. The ratio of the lower height H2 to the concave width W2: H2 / W2 is preferably 1.0 or more and 5.0 or less.

[0066] When viewing the die 12R in cross-section, if the line length of the middle part 122e of the lower side surface 122b of the die is L, the line length L is preferably 1.03×A or more, and more preferably 1.08×A or more. The parameter A is represented by the following formula. A = ((H2 - Rd2 - Rd3) 2 + (W2 - Rd2 - Rd3) 2 ) 0.5

[0067] Returning to FIG. 1, the left die 12L substantially has a configuration in which the right die 12R is reversed left and right. That is, in the left and right dies 12L and 12R, the basic configurations of the upper die side surface 122a and the lower die side surface 122b are common. Therefore, for the left die 12L, detailed descriptions of the upper die side surface 122a and the lower die side surface 122b are omitted. Note that the dies 12L and 12R do not necessarily have a completely symmetric shape. The dimensions of each part of the left die 12L may be set within a preferable range in the same manner as the right die 12R, and do not necessarily coincide with the dimensions of each part of the right die 12R.

[0068] When the mold 10 is attached to the press device 20, the pad 13 is positioned above the punch 11 and between the left and right dies 12L and 12R. At this time, the pad 13 faces the punch top surface 111. More specifically, the lower surface of the pad 13 faces the punch top surface 111. The lower surface of the pad 13 has a shape corresponding to the punch top surface 111. In the present embodiment, the lower surface of the pad 13 is a flat surface corresponding to the punch top surface 111. For example, when a groove is formed in the punch top surface 111, a convex portion corresponding to the groove is formed on the lower surface of the pad 13. For example, when a stepped portion is formed in the punch top surface 111, a stepped portion corresponding to the stepped portion is formed on the lower surface of the pad 13.

[0069] The press device 20 is a device that uses the mold 10 to form a press-formed product from a plate-like material. The press device 20 includes, in addition to the mold 10, for example, a punch holder 21, a bolster 22, a die holder 23, and a slide 24.

[0070] The bolster 22 supports the punch 11 via the punch holder 21. More specifically, the punch holder 21 is fixed to the upper surface of the bolster 22, and the punch 11 is disposed on the punch holder 21. A plate-shaped spacer may be inserted between the punch holder 21 and the bolster 22 to adjust the position of the punch 11 in the vertical direction.

[0071] The left and right dies 12L, 12R and the pad 13 are supported by the slide 24 via the die holder 23. More specifically, the die holder 23 is fixed to the lower surface of the slide 24, and the dies 12L, 12R are fixed to the lower surface of the die holder 23. A plate-shaped spacer may be inserted between the slide 24 and the die holder 23 to adjust the position of the dies 12L, 12R in the vertical direction. The pad 13 is connected to the die holder 23 by an elastic member 25 that can expand and contract. The elastic member 25 is composed of, for example, a spring or a fluid pressure cylinder such as a gas cylinder. The pad 13 may be attached to an actuator (not shown) provided in the press device 20. However, the method using the elastic member 25 can make the structure of the press device 20 simpler than the actuator type.

[0072] The slide 24 is configured to be movable up and down with respect to the punch 11 by, for example, a mechanical or hydraulic mechanism (not shown) provided in the press device 20. As the slide 24 moves up and down, the die holder 23 also moves up and down. As the die holder 23 moves up and down, the dies 12L, 12R and the pad 13 move up and down with respect to the punch 11. That is, the dies 12L, 12R and the pad 13 are integrally supported by the die holder 23 so as to be movable.

[0073] [Method for manufacturing a press-formed product] Hereinafter, a method for manufacturing a press-formed product using the mold 10 will be described with reference to FIGS. 3A to 3G. FIGS. 3A to 3G are schematic diagrams for explaining the method for manufacturing a press-formed product. The method for manufacturing a press-formed product according to the present embodiment includes a step of preparing the mold 10, a step of preparing a plate-shaped material, and a forming step of forming the material into a press-formed product using the mold 10.

[0074] (First preparation step) When manufacturing a press-formed product, the mold 10 (FIGS. 1 and 2) configured as described above is prepared in advance. The mold 10 is attached to the press device 20 before starting the press working of the material.

[0075] (Second preparation step) Also, when manufacturing a press-formed product, a plate-shaped material M is prepared as shown in FIG. 3A. The material M is a metal plate, typically a steel plate. The plate thickness t of the material M is, for example, 0.8 mm or more and 4.0 mm or less. The material M has a tensile strength of, for example, 270 MPa or more and 1470 MPa or less. When the press-formed product to be manufactured is an arm part among the underbody parts of an automobile, the tensile strength of the material M is usually 590 MPa or more. When the press-formed product to be manufactured is a frame part such as a ladder frame of an automobile, the tensile strength of the material M is usually 590 MPa or more. When the press-formed product to be manufactured is a substantially U-shaped reinforcing part of the front floor tunnel part among the body skeleton parts of an automobile, the tensile strength of the material M is usually 590 MPa or more.

[0076] (Forming step) Next, the material M is press-worked using the mold 10 to form a press-formed product. The forming step includes steps (a) to (d). Hereinafter, steps (a) to (d) will be specifically described.

[0077] (Step (a)) As shown in FIG. 3B, when starting the pressing process of the material M, the dies 12L, 12R and the pad 13 attached to the pressing device 20 are located at the top dead center. In this state, the material M is placed on the punch top surface 111. In step (a), after placing the material M on the punch top surface 111, the dies 12L, 12R are relatively approached with respect to the punch 11, and the lower die side surfaces 122b are brought into contact with the material M to bend the material M.

[0078] More specifically, as shown in FIG. 3C, after placing the material M on the punch top surface 111, the slide 24 is lowered, so that the dies 12L, 12R supported by the slide 24 are lowered toward the material M and the punch 11. At this time, the pad 13 also descends toward the material M and the punch 11 together with the dies 12L, 12R. The pad 13 contacts the material M on the punch top surface 111 and holds down the material M. More specifically, the pad 13 presses from above the portion of the material M that is located at the center in the width direction of the mold 10.

[0079] As shown in FIG. 3D, with the material M clamped between the pad 13 and the punch top surface 111, the slide 24 is further lowered. At this time, the elastic member 25 connecting the pad 13 to the slide 24 contracts, so that the dies 12L, 12R descend relative to the pad 13. As a result, the lower die side surfaces 122b of the die side surfaces 122L, 122R come into contact with the material M. Each lower die side surface 122b contacts the material M at the connection portion 122d with the die flange surfaces 123L, 123R and then contacts the material M at the concave intermediate portion 122e. As the dies 12L, 12R descend, the material M is guided by the concave intermediate portion 122e and bends greatly so as to have a shape convex upward, i.e., in the direction opposite to the approaching direction of the dies 12L, 12R with respect to the punch 11. The portion of the material M clamped between the pad 13 and the punch top surface 111 does not lift, and the forming of the material M proceeds. The state in which the material M is clamped between the pad 13 and the punch top surface 111 is maintained until the forming is completed.

[0080] (Step (b)) In step (b), with the material M being deflected, the dies 12L and 12R are further moved closer to the punch 11, and the upper side surfaces 122a of each die are brought into contact with the material M. More specifically, as shown in FIG. 3E, the dies 12L and 12R are further lowered, and among the lower side surfaces 122b of each die, the connection portion 122c with the upper side surface 122a is brought into contact with the material M. Thereafter, when the dies 12L and 12R are further lowered, the upper side surfaces 122a of each die come into contact with the material M.

[0081] (Step (c)) In step (c), with the upper side surfaces 122a of each die remaining in contact with the material M, the dies 12L and 12R are further moved closer to the punch 11, whereby the deflection of the material M is bent back by the upper side surfaces 122a of each die. As shown in FIG. 3F, as the dies 12L and 12R are lowered, the deflection of the material M is bent back between the upper side surfaces 122a of each die and the punch side surfaces 113L and 113R. The deflection of the material M gradually decreases as the dies 12L and 12R are lowered further and the dies 12L and 12R approach the punch 11. Also, the material M winds around the punch shoulders 112L and 112R.

[0082] (Step (d)) In step (d), as shown in FIG. 3G, the punch 11 and the dies 12L and 12R are closed, and the material M is clamped between the punch shoulders 112L and 112R and the die shoulders 121L and 121R, and between the punch side surfaces 113L and 113R and the upper side surfaces 122a and 122a of the left and right dies. Thereby, the material M becomes the press-formed product 30. More specifically, by causing the dies 12L and 12R to reach the bottom dead center, the material M is pressed between the punch shoulders 112L and 112R and the die shoulders 121L and 121R, and the bent portion of the press-formed product is formed. Also, the material M is pressed between the punch side surface 113L and the upper side surface 122a of the left die 12L, and between the punch side surface 113R and the upper side surface 122a of the right die 12R, and both vertical walls of the press-formed product 30 are formed. At this time, the end portions of the material M, that is, the lower end portions of both vertical walls of the press-formed product 30, are not in contact with the die side surfaces 122L and 122R. When the dies 12L and 12R reach the bottom dead center, the deflection of the material M is completely bent back to become both vertical walls of the press-formed product 30.

[0083] When the die 12L reaches the bottom dead center and the punch 11 and the die 12L are in a completely closed state, the clearance between the punch side surface 113L and the upper die side surface 122a of the die 12L is preferably smaller than the plate thickness t of the material M. Similarly, when the die 12R reaches the bottom dead center and the punch 11 and the die 12R are in a closed state, the clearance between the punch side surface 113R and the upper die side surface 122a of the die 12R is preferably smaller than the plate thickness t of the material M. More preferably, the clearances between the punch side surfaces 113L, 113R and the left and right upper die side surfaces 122a, 122a are 0.85 times or more and 0.95 times the plate thickness t of the material M. The clearances between the punch shoulders 112L, 112R and the die shoulders 121L, 121R are typically equal to the clearances between the punch side surfaces 113L, 113R and the left and right upper die side surfaces 122a, 122a.

[0084] When the dies 12L, 12R reach the bottom dead center and the punch 11 and the dies 12L, 12R are completely closed, the entire material M comes into contact with the punch 11. When the punch 11 and the dies 12L, 12R are completely closed, the material M takes a shape along the punch top surface 111, the punch shoulders 112L, 112R, and the punch side surfaces 113L, 113R. Therefore, in a cross-section obtained by cutting the punch 11 and the formed material M in a plane composed of the vertical and width directions, the portions of the material M that are in contact with the punch side surfaces 113L, 113R, that is, the angles (acute angle sides) formed by both vertical walls of the press-formed product 30 with the vertical direction, are the angles θ L , θ R and are substantially the same.

[0085] [Press-formed product] FIG. 4 is a diagram illustrating a press-formed product 30 manufactured by the manufacturing method according to the present embodiment. The press-formed product 30 has a substantially U-shaped cross-section. The press-formed product 30 includes a top plate 31, left and right vertical walls 32L and 32R, and left and right bending portions 33L and 33R. The upper end of the left vertical wall 32L is connected to the left edge of the top plate 31 via the left bending portion 33L. The upper end of the right vertical wall 32R is connected to the right edge of the top plate 31 via the right bending portion 33R. The lower ends of the vertical walls 32L and 32R are free ends, respectively.

[0086] In the press-formed product 30 shown in FIG. 4, the top plate 31 has a flat shape. However, when a groove or a step is provided on the punch top surface 111, a groove or a step corresponding to the punch top surface 111 is formed on the top plate 31 of the press-formed product 30. One or more through-holes may be provided in the top plate 31. This through-hole may be a simple round hole, or may be a hole (a burring hole) formed by burring and having a shape in which the hole edge end protrudes. The through-hole in the top plate 31 can be formed after the press-formed product 30 is formed by the mold 10.

[0087] The press-formed product 30 shown in FIG. 4 has a linear shape when viewed from the top plate 31 side (in plan view). Also, the press-formed product 30 shown in FIG. 4 has a linear shape when viewed from the vertical wall 32L or vertical wall 32R side (in side view). However, as shown in FIG. 5, the press-formed product 30 may have a curved or bent shape in plan view. Alternatively, as shown in FIG. 6, the press-formed product 30 may have a curved or bent shape in side view.

[0088] The shape of the press-formed product 30 may be a combination of two or more of a straight portion, a curved portion, and a bent portion in a plan view. Further, the shape of the press-formed product 30 may be a combination of two or more of a straight portion, a curved portion, and a bent portion in a side view. Furthermore, the press-formed product 30 may have a shape in which portions having a substantially U-shaped cross section, such as a three-pronged shape or a four-pronged shape in a plan view, are branched into a plurality of branches. The press-formed product 30 may have a uniform cross-sectional shape throughout, or the cross-sectional shape may change in the middle.

[0089] [Effect] When performing press working using the mold 10 according to the present embodiment, the plate-shaped material M is greatly deflected by the lower die side surfaces 122b during the process of being formed into the press-formed product 30. Each lower die side surface 122b has a concave shape on the outer side in the width direction with respect to the upper die side surface 122a, and guides and deflects the material M so as to have a convex shape upward. As the dies 12L and 12R approach the punch 11, the material M comes into contact with the upper die side surfaces 122a, and the deflection of the material M is gradually bent back. The deflection of the material M decreases as the dies 12L and 12R approach the punch 11, and remains in the gaps between the punch side surfaces 113L and 113R and the upper die side surfaces 122a. Finally, when the punch 11 and the dies 12L and 12R are closed, the deflection of the material M is completely bent back and disappears, and the material M is sandwiched between the punch shoulders 112L and 112R and the die shoulders 121L and 121R, and between the punch side surfaces 113L and 113R and the upper die side surfaces 122a.

[0090] Thus, in this embodiment, the material M is bent upward and then bent back so as to have a convex shape during the pressing process. As a result, during the pressing process, tensile stress is generated on the punch 11 side, particularly in the portions of the material M that will become the vertical walls 32L and 32R of the press-formed product 30, and compressive stress is generated on the die 12L and 12R sides, which are opposite to the punch 11 side. On the other hand, in the bent portions 33L and 33R formed by the punch shoulders 112L and 112R, compressive stress is generated on the punch 11 side and tensile stress is generated on the die 12L and 12R sides during the pressing process. Therefore, the stress generated by bending back the deflection of the material M cancels out the stress in the bent portions 33L and 33R, reducing the stress in the bent portions 33L and 33R. Due to the stress remaining in the bent portions 33L and 33R and the stress remaining in the bent-back portion at the bottom dead center of forming, in the press-formed product 30 removed from the mold 10, a moment for wall opening and a moment for wall closing are generated and cancel each other out. Thus, the moment for wall opening generated during mold release in the press-formed product 30 can be reduced. As a result, springback in the press-formed product 30 can be reduced, and the dimensional accuracy of the press-formed product 30 can be improved. Further, when performing pressing on the material M using the mold 10, it is only necessary to lower the dies 12L and 12R directly downward. Therefore, a cam mechanism or the like for moving the dies 12L and 12R in a special direction is unnecessary, and the mold 10 can have a simple structure.

[0091] In the mold 10 according to this embodiment, when the upper height H1 of the die side surfaces 122L and 122R and the lower height H2 of the die side surfaces 122L and 122R are set, H2 / H1 is set to be 1.0 or more and 5.0 or less. Thereby, since the length of the concave die lower side surfaces 122b is sufficiently ensured on each of the die side surfaces 122L and 122R, during the pressing process, the material M can be greatly bent over a wide range in the width direction by each of the die lower side surfaces 122b. Therefore, the effect of stress cancellation due to bending back of the deflection can be effectively exerted.

[0092] In the mold 10 according to the present embodiment, the upper height H1 of the die side surface 122L is made 5.0 mm or more larger than the radius of curvature Rd1 of the die shoulder 121L, and the upper height H1 of the die side surface 122R is made 5.0 mm or more larger than the radius of curvature Rd1 of the die shoulder 121R. Then, for each of the die side surfaces 122L and 122R, the ratio of the lower height H2 to the upper height H1: H2 / H1 is set to be 1.0 or more and 5.0 or less. Therefore, the length of each die upper side surface 122a can also be ensured. Thus, when the punch 11 and the dies 12L and 12R are finally closed, the material M can be firmly clamped between the punch side surfaces 113L and 113R and each die upper side surface 122a. As a result, the bent portions of the material M during press working can be bent back, and the material M can be formed into the shape of the final press-formed product 30. Therefore, it is not necessary to perform an additional press working process, and the man-hours and costs in the manufacture of the press-formed product 30 can be reduced.

[0093] In order to cancel out the stress of the bent portions 33L and 33R generated during press working and the moment generated during mold release by bending back, it is important to firmly clamp the material M between each die upper side surface 122a near the punch shoulders 112L and 112R and the punch side surfaces 113L and 113R. In the mold 10 according to the present embodiment, as described above, by appropriately ensuring the length of each die upper side surface 122a, the material M can be firmly clamped between the punch side surfaces 113L and 113R and each die upper side surface 122a. Therefore, the stress of the bent portions 33L and 33R generated during press working and the moment generated during mold release can be effectively canceled out by bending back.

[0094] When H2 / H1 exceeds 5.0, in each of the die side surfaces 122L and 122R, the ratio occupied by the concave die lower side surface 122b increases, and the effect of bending the material M by each die lower side surface 122b saturates. Also, when H2 / H1 exceeds 5.0, the costs related to the manufacture of the mold 10 also increase. Therefore, it is preferable that H2 / H1 is 5.0 or less.

[0095] In the mold 10 according to the present embodiment, the radius of curvature of the connection portion 122c of each die lower side surface 122b with the die upper side surface 122a is preferably set to 10.0 mm or less. In this case, in each of the die side surfaces 122L and 122R having a predetermined size, the connection portion 122c and the ratio of the die lower side surface 122b occupying the connection portion 122c do not become too large, and it becomes easy to secure the length of the die upper side surface 122a. Therefore, when the punch 11 and the dies 12L and 12R are finally closed, the material M can be more reliably clamped between the punch side surfaces 113L and 113R and the respective die upper side surfaces 122a.

[0096] Further, in the present embodiment, the radius of curvature of the connection portion 122c is preferably set to 1.0 mm or more. Thereby, when the connection portion 122c contacts the material M during press working, it is possible to avoid leaving indentation marks and bending habits on the material M.

[0097] In the present embodiment, the intermediate portion 122e of each die lower side surface 122b includes a curved surface. The intermediate portion 122e has a concave shape toward the outside in the width direction of the mold 10 with respect to the connection portion 122c on the die upper side surface 122a side of the die lower side surface 122b. In this case, in each of the die side surfaces 122L and 122R, the ratio of the lower height H2 to the concave width W2: H2 / W2 is preferably 1.0 or more and 5.0 or less. The effect of bending the material M by each concave die lower side surface 122b improves as H2 / W2 becomes smaller, but when H2 / W2 is less than 1.0, the effect of bending the material M saturates. Also, when H2 / W2 is less than 1.0, the cost for manufacturing the mold 10 and the like also increases. On the other hand, when H2 / W2 exceeds 5.0, the concave width W2 becomes smaller with respect to the lower height H2, so the effect of bending the material M decreases.

[0098] In this embodiment, the longer the line length L of the middle portion 122e of the lower die side surface 122b is, the larger the indentation of the lower die side surface 122b becomes. The larger the indentation of the lower die side surface 122b is, the larger the deflection of the material M during the pressing process becomes. In this case, when the material M is firmly clamped between each upper die side surface 122a and the punch side surfaces 113L and 113R, the stress of the bent portions 33L and 33R generated during the pressing process and the moment generated during the mold release can be more effectively canceled by springback. That is, the larger the line length L is, the better the dimensional accuracy of the press-formed product 30 becomes. Therefore, the line length L is preferably 1.03 times or more, and more preferably 1.08 times or more of the above-described parameter A.

[0099] In the mold 10 according to this embodiment, the clearance between the punch side surfaces 113L and 113R and each upper die side surface 122a is preferably smaller than the plate thickness t of the material M in a state where the punch 11 and the dies 12L and 12R are closed. The clearance between the punch side surfaces 113L and 113R and each upper die side surface 122a is particularly preferably 0.85 times or more and 0.95 times or less of the plate thickness t. Thereby, when the punch 11 and the dies 12L and 12R are finally closed in the forming process, the material M is strongly clamped between the punch side surfaces 113L and 113R and each upper die side surface 122a, and the deflection of the material M is more surely springback. In this case, in the portion of the material M that becomes the vertical walls 32L and 32R of the press-formed product 30, a larger tensile stress can be generated on the punch 11 side and a larger compressive stress can be generated on the dies 12L and 12R side. Therefore, the effect of canceling the stress of the bent portions 33L and 33R by these stresses can be enhanced. As a result, the springback in the press-formed product 30 can be further reduced, and the dimensional accuracy of the press-formed product 30 can be further improved.

[0100] When performing press working on the material M using the mold 10 according to the present embodiment, when the punch 11 and the dies 12L and 12R are finally closed, the material M is clamped between the punch side surfaces 113L and 113R and the upper die side surfaces 122a. On the other hand, the lower die side surfaces 122b do not substantially contact the material M. Thereby, a load can be intensively applied to the portions of the material M that will become the vertical walls 32L and 32R of the press-formed product 30. In particular, when the clearance between the punch side surfaces 113L and 113R and the upper die side surfaces 122a is smaller than the plate thickness t of the material M, the portions of the material M that will become the vertical walls 32L and 32R of the press-formed product 30 can be pressed more strongly.

[0101] When the punch 11 and the dies 12L and 12R are completely closed, the lower die side surfaces 122b do not substantially contact the material M. That is, the portions of the material M that will become the lower ends of the vertical walls 32L and 32R of the press-formed product 30 are not clamped by the punch side surfaces 113L and 113R and the die side surfaces 122L and 122R. However, only elastic deformation occurs during press working in this portion, and plastic deformation does not occur. Therefore, even if the portions of the material M that will become the lower ends of the vertical walls 32L and 32R of the press-formed product 30 are not clamped by the punch side surfaces 113L and 113R and the die side surfaces 122L and 122R, when the punch 11 and the dies 12L and 12R are closed, the material M is formed into a shape along the punch 11.

[0102] When the punch 11 and the dies 12L and 12R are completely closed and the material M is formed into the press-formed product 30, it is desirable that the lower ends of the vertical walls 32L and 32R of the press-formed product 30 contact the punch side surfaces 113L and 113R as shown in FIG. 3G. That is, it is desirable that the punch side surfaces 113L and 113R have a shape that contacts the entire vertical walls 32L and 32R of the press-formed product 30 when the punch 11 and the dies 12L and 12R are completely closed. However, the punch side surfaces 113L and 113R may have a shape that does not contact the vertical walls 32L and 32R of the press-formed product 30 only at their lower portions. For example, as shown in FIG. 7, the punch side surfaces 113L and 113R may be configured such that only their lower portions have an angle smaller than the opening angle of the vertical walls 32L and 32R. The opening angle of the vertical walls 32L and 32R corresponds to the angles θ L , θ R . In this case, when the punch 11 and the dies 12L and 12R are completely closed, the lower ends of the vertical walls 32L and 32R do not contact the punch side surfaces 113L and 113R.

[0103] The mold 10 according to the present embodiment includes a pad 13 in addition to the punch 11 and the dies 12L and 12R. The press device 20 is configured such that the forming of the material M by the punch 11 and the dies 12L and 12R is started while the material M disposed on the punch top surface 111 is sandwiched between the punch top surface 111 and the pad 13. Therefore, when performing press working on the material M using the mold 10 and the press device 20, the dies 12L and 12R can be brought closer to the punch 11 while the material M is sandwiched between the punch top surface 111 and the pad 13. More specifically, the material M can be bent by the lower side surfaces 122b of the respective dies while the material M disposed on the punch top surface 111 is sandwiched between the punch top surface 111 and the pad 13. Thus, displacement of the material M during press working can be prevented. Further, by forming the material M while holding the material M with the pad 13, the shape of the top plate 31 of the press-formed product 30 can be accurately formed.

[0104] For example, as shown in FIG. 8, in order to suppress the wall opening of the press-formed product, pre-forming may be performed so that the material M bulges in a convex shape, and the pre-formed material M may be subjected to press working with a general punch 41 and dies 42L and 42R. However, in this case, since a pre-forming step for previously bulging the material M in a step separate from the press working step is required, the number of man-hours and costs related to the production of the pre-forming die and the press-formed product increase. Further, in the pre-forming step, since the target shape is a relatively gentle convex shape, particularly when the strength of the material M is large, the amount of deformation of the material M in pre-forming is within the range of elastic deformation. Therefore, the material M does not become a gentle convex shape after release from the pre-forming, but becomes a flat shape. That is, it is difficult to form the material M into a convex shape in the pre-forming step itself.

[0105] On the other hand, in the present embodiment, the material M is formed into the press-formed product 30 in one step without performing pre-forming of the material M. Therefore, the number of man-hours and costs related to the production of the press-formed product 30 can be suppressed. Further, since pre-forming of the material M is not performed, the problem of difficulty in forming the material M does not occur.

[0106] <Second Embodiment> FIG. 9 is a cross-sectional view of the die 10A according to the second embodiment. The die 10A has substantially the same configuration as the die 10 (FIGS. 1 and 2) according to the first embodiment. The die 10A is different from the die 10 according to the first embodiment only in the configuration of the die side surfaces 122L and 122R.

[0107] FIG. 10 is an enlarged cross-sectional view showing the right die 12R of the die 10A. In the die 10A, the basic configurations of the die side surfaces 122L and 122R of the left and right dies 12L and 12R are common. Therefore, the configuration of the die side surface 122R will be described with reference to FIG. 10 only for the right die 12R, and the detailed description of the die side surface 122L for the left die 12L will be omitted.

[0108] As shown in FIG. 10, in the present embodiment, an intermediate portion 122e of a lower side surface 122b of the die includes an inclined surface 122f that is inclined with respect to a horizontal plane. The horizontal plane is a cross-section obtained by cutting the mold 10 in a plane perpendicular to the vertical direction. When the horizontal plane is projected onto the cross-section of the mold 10, it becomes a straight line in the left-right direction. In the example of the present embodiment, the entire intermediate portion 122e is the inclined surface 122f. The inclined surface 122f descends as it extends outward in the width direction of the mold 10A from a connection portion 122c with the upper side surface 122a of the die. In the die side surface 122R, the ratio of the lower height H2 to the upper height H1: H2 / H1 is 1.0 or more and 5.0 or less, similar to the first embodiment. Also, similar to the first embodiment, the upper height H1 of the die side surface 122R is 5.0 mm or more greater than the radius of curvature Rd1 of the die shoulder 121R. Even with such a configuration, similar to the first embodiment, springback in the press-formed product 30 (FIGS. 4 to 6) can be reduced, and the dimensional accuracy of the press-formed product 30 can be improved.

[0109] In the die side surface 122R, the inclined surface 122f forms an angle ψ (°) with the horizontal plane. The angle ψ is the angle (acute angle side) formed by the inclined surface 122f with the width direction in a cross-section obtained by cutting the die 12R in a plane composed of the vertical direction and the width direction.

[0110] In the die side surface 122R, if the angle ψ of the inclined surface 122f is too large, the degree of concavity of the lower side surface 122b of the die with respect to the upper side surface 122a of the die becomes small. Therefore, during press working, the effect of bending the material by the lower side surface 122b of the die becomes small. In order to sufficiently exhibit the effect, the angle ψ is preferably (78 - θ R )° or less. On the other hand, if the angle ψ of the inclined surface 122f becomes small, the effect of bending the material during press working becomes large, but if the angle ψ is too small, the effect saturates. Also, as the angle ψ of the inclined surface 122f becomes smaller, the degree of concavity of the lower side surface 122b of the die becomes larger, so the mold 10A becomes larger in size, and the cost for manufacturing the mold 10A and the like increases. Therefore, the angle ψ formed by the inclined surface 122f with respect to the horizontal plane is (50 - θ R)° or more is preferable. Also in the left die side surface 122L (FIG. 9), similar to the right die side surface 122R, the angle of the inclined surface 122f is (50 - θ L )° or more and (78 - θ L )° or less is preferable. θ L , θ R is, as described in the first embodiment, the angle formed by the punch side surfaces 113L and 113R with the vertical plane respectively. The angle ψ of the inclined surface 122f may be the same or different between the left and right die side surfaces 122L and 122R.

[0111] In the die side surface 122R, the respective radii of curvature Rd2 and Rd3 of the connection portion 122c of the die lower side surface 122b with respect to the die upper side surface 122a and the connection portion 122d of the die lower side surface 122b with respect to the die flange surface 123R can be set in the same manner as in the first embodiment. Similarly, in the die side surface 122L (FIG. 9), the respective radii of curvature Rd2 and Rd3 of the connection portion 122c of the die lower side surface 122b with respect to the die upper side surface 122a and the connection portion 122d of the die lower side surface 122b with respect to the die flange surface 123L can be set in the same manner as in the first embodiment. The clearance between the punch side surfaces 113L and 113R and each die upper side surface 122a can also be set in the same manner as in the first embodiment.

[0112] In the example shown in FIGS. 9 and 10, in each die lower side surface 122b, the entire intermediate portion 122e is constituted by the inclined surface 122f. However, a part of the intermediate portion 122e may be the inclined surface 122f. For example, as shown in FIG. 11, in the die side surfaces 122L and 122R, a linear surface 122g extending in the width direction in a cross-sectional view of the mold 10A may be provided between the connection portion 122c between the die upper side surface 122a and the die lower side surface 122b and the inclined surface 122f. Alternatively, the connection portion 122c and the inclined surface 122f may be connected via a curved surface (not shown).

[0113] Although the embodiments according to the present disclosure have been described above, the present disclosure is not limited to the above embodiments, and various modifications are possible without departing from the spirit thereof.

[0114] For example, in each of the above embodiments, with the mold 10 attached to the press device 20, the dies 12L and 12R are disposed above the punch 11. Also, when performing press working on the material M, the dies 12L and 12R are moved toward the punch 11. However, contrary to each of the above embodiments, when performing press working on the material M, the dies 12L and 12R may be disposed below the punch 11. Also, by moving the punch 11 toward the dies 12L and 12R, the dies 12L and 12R may be relatively approximated to the punch 11.

[0115] The molds 10 and 10A according to each of the above embodiments include the left and right symmetric dies 12L and 12R. However, it is not necessary for the left die 12L and the right die 12R to have exactly symmetric shapes and dimensions.

[0116] In the first embodiment, the middle portion 122e of each die lower side surface 122b is mainly constituted by a curved surface. On the other hand, in the second embodiment, the middle portion 122e of each die lower side surface 122b is mainly constituted by a linear inclined surface 122f. The mold according to the present disclosure can also be configured by combining these embodiments. That is, in one of the dies 12L and 12R, like in the first embodiment, the middle portion 122e of the die lower side surface 122b may be mainly constituted by a curved surface (FIG. 2), and in the other of the dies 12L and 12R, like in the second embodiment, the middle portion 122e of the die lower side surface 122b may be mainly constituted by the inclined surface 122f (FIG. 10 or FIG. 11). Alternatively, a concave die lower side surface 122b may be provided only in one of the dies 12L and 12R, and it may not be necessary to provide a concave die lower side surface 122b in the other of the dies 12L and 12R.

[0117] The molds 10, 10A according to the above embodiments include pads 13. However, the molds 10, 10A may not include the pads 13. For example, when the width of the punch top surface 111 (the top plate 31 of the press-formed product 30) is relatively short when the molds 10, 10A are viewed in cross-section, or when the punch top surface 111 has a flat shape without grooves, steps, etc., even if the upper mold is composed only of the dies 12L, 12R, a press-formed product 30 with high dimensional accuracy can be obtained in one step.

[0118] However, when the width of the punch top surface 111 is relatively long when the molds 10, 10A are viewed in cross-section, or when grooves, steps, etc. are provided on the punch top surface 111, it is preferable that a pad 13 is present between the dies 12L and 12R. Alternatively, in the die 12L, a die top surface extending from the die shoulder 121L toward the die 12R side may be provided, and in the die 12R, a die top surface extending from the die shoulder 121R toward the die 12L side may be provided. Alternatively, by integrally forming the dies 12L, 12R, the connection portion with the dies 12L, 12R can be made the die top surface. Also, another mold may be provided between the dies 12L, 12R. By sandwiching the material M between the pad 13, the die top surface, or another mold between the dies 12L, 12R and the punch top surface 111, a predetermined shape can be given to the top plate 31 of the press-formed product 30, and a press-formed product 30 with high dimensional accuracy can be obtained in one step.

[0119] Among the molds 10, 10A provided with a die top surface and the molds 10, 10A provided with pads 13, the latter is preferable. In the case of the molds 10, 10A provided with a die top surface, when the dies 12L, 12R reach the bottom dead center, the material M is clamped by the die top surface and the punch top surface 111. However, during the press working, the material M on the punch top surface 111 cannot be pressed by the die top surface. On the other hand, in the case of the molds 10, 10A provided with pads 13, the material M on the punch top surface 111 can be pressed by the pads 13 from the initial stage of the press working. By forming the material M while pressing the material M with the pads 13, it is possible to prevent the displacement of the material M during the press working, and to suppress the unexpected deformation behavior (bending behavior) of the material M on the punch top surface 111. Also, the shape of the top plate 31 of the press-formed product 30 can be accurately formed. Therefore, as in each of the above embodiments, it is preferable that the molds 10, 10A include pads 13.

[0120] In the first embodiment, the middle portion 122e of each lower die side surface 122b is formed of a curved surface that smoothly continues from the upper connecting portion 122c to the lower connecting portion 122d. In the second embodiment, the middle portion 122e of each lower die side surface 122b is substantially composed of a single inclined surface 122f that continues from the upper connecting portion 122c to the lower connecting portion 122d. However, the shape of the middle portion 122e is not limited to these. For example, a step may be provided in the middle portion 122e.

Example

[0121] Hereinafter, the present disclosure will be described in more detail by way of examples. However, the present disclosure is not limited to the following examples.

[0122] [First Example] To confirm the effects according to the present disclosure, press working was performed using the mold 10 (Figs. 1 and 2) according to the first embodiment or the mold 10A (Figs. 9 and 10) according to the second embodiment to form a material (steel sheet) with a tensile strength TS = 1180 MPa and a plate thickness t = 1.6 mm into a press-formed product 30 having a substantially U-shaped cross section. In the press-formed product 30, the bending radius R (radius of curvature on the inner side of the bend) of the bent portions 33L and 33R was 8.0 mm, and the opening angle θ of the vertical walls 32L and 32R was 5°. The bending radius R of the bent portions 33L and 33R corresponds to the radius of curvature Rp of the punch shoulders 112L and 112R. The opening angle θ of the vertical walls 32L and 32R corresponds to the angles θ of the punch side surfaces 113L and 113R described in the above embodiment. L , θ R corresponds to.

[0123] For the CAE analysis, commercially available software (LS-DYNA ver971 rev7.12, manufactured by ANSYS) was used to perform a forming analysis and a springback analysis to evaluate the change amount Δθ (°) of the opening angle of the vertical walls 32L and 32R after springback. Δθ is the difference between the opening angle θ: 5° of the vertical walls 32L and 32R in the press-formed product 30 before removal from the mold 10 (before release) and the opening angle θ (°) of the vertical walls 32L and 32R after removal from the molds 10 and 10A (after release). The smaller Δθ is, the more the springback is reduced, which means that the dimensional accuracy of the press-formed product 30 is improved.

[0124] Table 1 shows the analysis results (No. 1 to 18) when using the mold 10 (Figs. 1 and 2) according to the first embodiment. In the mold 10, the middle portion 122e of the die lower side surface 122b is mainly composed of a curved surface. In this analysis, the line length L of the middle portion 122e of the die lower side surface 122b on the left and right die side surfaces 122L and 122R was set to 1.08 × A. The parameter A is expressed by the following equation. A = ((H2 - Rd2 - Rd3) 2 + (W2 - Rd2 - Rd3) 2 ) 0.5

[0125] The radius of curvature Rd1 of the die shoulders 121L and 121R was 9.6 mm, and the radius of curvature Rd3 of the connecting portion 122d of the lower die side surface 122b with respect to the die flange surfaces 123L and 123R was 4.0 mm. For comparison, Table 1 also shows the analysis results (comparative examples) when using a general mold, that is, a mold in which the concave lower die side surfaces 122b are not provided on the die side surfaces 122L and 122R.

[0126]

Table 1

[0127] As shown in Table 1, the change amount Δθ of the opening angle of the vertical walls 32L and 32R after springback became smaller than that of the comparative example in all of No.1 to No.18. However, in No.1 where the upper height H1 of the die side surfaces 122L and 122R was 3.0 mm larger than the radius of curvature Rd1 of the die shoulders 121L and 121R (H1 - Rd1 = 3.0), the change amount Δθ of the opening angle exceeded 7.0°, and the reduction effect of Δθ was small. This is presumably because the length of each upper die side surface 122a was short, and the upper die side surfaces 122a could not sufficiently hold the material in the state where the punch 11 and the dies 12L and 12R were closed (bottom dead center).

[0128] On the other hand, in No.3 where the upper height H1 of the die side surfaces 122L and 122R was 5.0 mm larger than the radius of curvature Rd1 of the die shoulders 121L and 121R (H1 - Rd1 = 5.0), the change amount Δθ of the opening angle became 5.0° or less. The Δθ in No.3 was 4.6°, which was less than half of the comparative example. In No.2 where the upper height H1 of the die side surfaces 122L and 122R was 12.0 mm larger than the radius of curvature Rd1 of the die shoulders 121L and 121R (H1 - Rd1 = 12.0), the change amount Δθ of the opening angle was 2.1°, which became even smaller. From this result, in order to effectively reduce springback and significantly improve the dimensional accuracy of the press-formed product 30, it is necessary to make the upper height H1 of the die side surfaces 122L and 122R 5.0 mm or more larger than the radius of curvature Rd1 of the die shoulders 121L and 121R (H1 - Rd1 ≥ 5.0).

[0129] In No. 4 where the radius of curvature Rd2 of the connecting portion 122c between the upper side surface 122a of the die and the concave lower side surface 122b of the die is 1.0 mm, the change amount Δθ of the opening angle is 1.8°, which is significantly smaller than that of the comparative example. Also, in No. 5 where the radius of curvature Rd2 of the connecting portion 122c is 10.0 mm, the change amount Δθ of the opening angle is 3.6°, which is significantly smaller than that of the comparative example. On the other hand, in No. 11 where the radius of curvature Rd2 of the connecting portion 122c is 12.0 mm, the change amount Δθ of the opening angle is 7.0° or less but exceeds 5.0°. In No. 11, although the effect of reducing Δθ was obtained, the degree of the effect was smaller compared to No. 5. Therefore, it can be understood that when the radius of curvature Rd2 of the connecting portion 122c is 10.0 mm or less, springback is more effectively reduced and the dimensional accuracy of the press-formed product 30 is further improved.

[0130] In No. 10 where the radius of curvature Rd2 of the connecting portion 122c is 0.5 mm, the change amount Δθ of the opening angle is 1.7°, which is almost equivalent to that of No. 4 where the radius of curvature Rd2 is 1.0 mm. However, in No. 10, bending distortion remained in the material. Therefore, the radius of curvature Rd2 of the connecting portion 122c is preferably 1.0 mm or more.

[0131] In No. 6 where the ratio of the lower height H2 to the upper height H1: H2 / H1 on the die side surfaces 122L and 122R is 1.0, the change amount Δθ of the opening angle is 2.8°, which is significantly smaller than that of the comparative example. Also, in No. 2 where H2 / H1 is 3.0, the change amount Δθ of the opening angle is 2.1°, which is significantly smaller than that of the comparative example. On the other hand, in No. 12 where H2 / H1 is 0.5, the change amount Δθ of the opening angle exceeds 7.0°, and the effect of reducing Δθ is small. Therefore, it can be said that by setting H2 / H1 to 1.0 or more, springback is effectively reduced and the dimensional accuracy of the press-formed product 30 is significantly improved.

[0132] For No. 7 where the ratio of the lower height H2 to the upper height H1, H2 / H1, is 5.0 on the die side surfaces 122L and 122R, the amount of change in the opening angle Δθ is 0.8°, which is significantly smaller than that of the comparative example. For No. 14 where H2 / H1 is 6.0, the amount of change in the opening angle Δθ is 0.8°, which is equivalent to that of No. 7. That is, when H2 / H1 exceeds 5.0, the effect of reducing springback and the accompanying effect of improving the dimensional accuracy of the press-formed product 30 are saturated. Also, when H2 / H1 exceeds 5.0, the lower die side surface 122b becomes longer, increasing the size of the die 10 and thus increasing the cost related to the die 10. Therefore, it can be said that by setting H2 / H1 to 5.0 or less, the dimensional accuracy of the press-formed product 30 can be efficiently improved.

[0133] For No. 8 where the ratio of the lower height H2 to the recess width W2, H2 / W2, is 1.0 on the die side surfaces 122L and 122R, the amount of change in the opening angle Δθ is 1.3°, which is significantly smaller than that of the comparative example. For No. 2 where H2 / W2 is 2.0 and No. 9 where H2 / W2 is 5.0, the amounts of change in the opening angle Δθ are 2.1° and 3.2° respectively, which are significantly smaller than that of the comparative example. On the other hand, for No. 13 where H2 / W2 is 6.0, the amount of change in the opening angle Δθ was 7.0° or less but exceeded 5.0°. In No. 13, although the effect of reducing Δθ was obtained, the degree of the effect was smaller compared to No. 9. Therefore, in order to more effectively reduce springback and further improve the dimensional accuracy of the press-formed product 30, it is preferable that H2 / W2 is 5.0 or less.

[0134] In No. 15 where H2 / W2 was 0.5, the change amount Δθ of the opening angle was 1.3°, which was equivalent to that of No. 8. That is, when H2 / W2 was less than 1.0, the effect of reducing springback and the accompanying effect of improving the dimensional accuracy of the press-formed product 30 were saturated. Also, when H2 / W2 was less than 1.0, since the concave width W2 became larger with respect to the lower height H2, the size of the mold 10 became larger, so the cost related to the mold 10 increased. Therefore, in order to more efficiently improve the dimensional accuracy of the press-formed product 30, it is preferable that H2 / W2 is 1.0 or more.

[0135] In No. 16 to No. 18, when the punch 11 and the dies 12L, 12R were in the closed state, the clearance CL between the punch side surfaces 113L, 113R and the upper die side surfaces 122a was smaller than the plate thickness t of the material. The clearances CL in No. 16 to No. 18 were 0.97 times the plate thickness t (CL / t = 0.97), 0.95 times the plate thickness t (CL / t = 0.95), and 0.85 times the plate thickness t (CL / t = 0.85), respectively. In No. 16 where CL / t was 0.97, the change amount Δθ of the opening angle was 2.0°, which was slightly reduced compared to No. 2 where CL / t was 1.00. On the other hand, in No. 17 where CL / t was 0.95, the change amount Δθ of the opening angle was 1.2°, which was significantly smaller compared to No. 2. In No. 18 where CL / t was 0.85, the change amount Δθ of the opening angle was further reduced to 0.6°. Therefore, in order to further improve the dimensional accuracy of the press-formed product 30, it is preferable that the clearance CL is smaller than the plate thickness t of the material, and it is particularly preferable that it is 0.85 times or more and 0.95 times or less the plate thickness t.

[0136] Table 2 shows the analysis results (No. 19 to No. 36) when using the mold 10A (Figs. 9 and 10) according to the second embodiment. In the mold 10A, the middle part 122e of the lower die side surface 122b is mainly composed of a linear inclined surface 122f. Hereinafter, for convenience of explanation, the mold 10A is referred to as a linear type, and the mold 10 in which the middle part 122e of the lower die side surface 122b is mainly composed of a curved surface is referred to as a curved type.

[0137] In this analysis, since the middle part 122e of the die lower side surface 122b on the left and right die side surfaces 122L and 122R is linear, the line length L of the middle part 122e is 1.00 × A. The parameter A is expressed by the following formula. The radius of curvature Rd1 of the die shoulders 121L and 121R is 9.6 mm, and the radius of curvature Rd3 of the connection part 122d of the die lower side surface 122b with respect to the die flange surfaces 123L and 123R is 4.0 mm. A = ((H2 - Rd2 - Rd3) 2 + (W2 - Rd2 - Rd3) 2 ) 0.5

[0138]

Table 2

[0139] The comparative examples in Table 2 are the same as those in Table 1. As shown in Table 2, the change amount Δθ of the opening angle of the vertical walls 32L and 32R after springback became smaller than that of the comparative example in all of No. 19 to 36. However, in No. 19 (H1 - Rd1 = 3.0) where the upper height H1 of the die side surfaces 122L and 122R is 3.0 mm larger than the radius of curvature Rd1 of the die shoulders 121L and 121R, similar to the curve type No. 1 (Table 1), the change amount Δθ of the opening angle exceeded 7.0°, and the reduction effect of Δθ was small.

[0140] On the other hand, in No. 21 where the upper height H1 of the die side surfaces 122L and 122R is 5.0 mm greater than the radius of curvature Rd1 of the die shoulders 121L and 121R (H1 - Rd1 = 5.0), the change amount Δθ of the opening angle became 5.0° or less. The Δθ in No. 21 is 4.8°, which is less than half of that in the comparative example. In No. 20 where the upper height H1 of the die side surfaces 122L and 122R is 12.0 mm greater than the radius of curvature Rd1 of the die shoulders 121L and 121R (H1 - Rd1 = 12.0), the change amount Δθ of the opening angle is 2.9°, which is even smaller. From these results, in the case of the straight-type die 10A as well as the curved-type die 10, in order to effectively reduce springback and improve the dimensional accuracy of the press-formed product 30, it is necessary to make the upper height H1 of the die side surfaces 122L and 122R 5.0 mm or more greater than the radius of curvature Rd1 of the die shoulders 121L and 121R (H1 - Rd1 ≧ 5.0).

[0141] In No. 22 where the radius of curvature Rd2 of the connection portion 122c between the upper die side surface 122a and the concave lower die side surface 122b is 1.0 mm, the change amount Δθ of the opening angle is 2.1°, which is significantly smaller than that in the comparative example. Also, in No. 23 where the radius of curvature Rd2 of the connection portion 122c is 10.0 mm, the change amount Δθ of the opening angle is 4.1°, which is significantly smaller than that in the comparative example. On the other hand, in No. 29 where the radius of curvature Rd2 of the connection portion 122c is 12.0 mm, the change amount Δθ of the opening angle became 7.0° or less but exceeded 5.0°. In No. 29, although the effect of reducing Δθ was obtained, the degree of the effect was smaller compared to No. 23. Therefore, in the case of the straight-type die 10A as well as the curved-type die 10, it can be understood that when the radius of curvature Rd2 of the connection portion 122c is 10.0 mm or less, springback is effectively reduced and the dimensional accuracy of the press-formed product 30 is further improved.

[0142] In No. 28 where the radius of curvature Rd2 of the connection part 122c is 0.5 mm, the change amount Δθ of the opening angle is 1.9°, which is slightly reduced compared to No. 22 where the radius of curvature Rd2 is 1.0 mm. However, in No. 28, bending distortion remained in the material. Therefore, also in the case of the straight type die 10A, the radius of curvature Rd2 of the connection part 122c is preferably 1.0 mm or more.

[0143] In No. 24 where the ratio of the lower height H2 to the upper height H1: H2 / H1 is 1.0 on the die side surfaces 122L and 122R, the change amount Δθ of the opening angle is 4.6°, which is significantly smaller compared to the comparative example. Also, in No. 20 where H2 / H1 is 3.0, the change amount Δθ of the opening angle is 2.9°, which is significantly smaller compared to the comparative example. On the other hand, in No. 30 where H2 / H1 is 0.5, the change amount Δθ of the opening angle exceeds 7.0°, and the reduction effect of Δθ was small. Therefore, also in the case of the straight type die 10A, similar to the curved type die 10, it can be said that by setting H2 / H1 to 1.0 or more, springback is effectively reduced and the dimensional accuracy of the press-formed product 30 is significantly improved.

[0144] In No. 25 where the ratio of the lower height H2 to the upper height H1: H2 / H1 is 5.0 on the die side surfaces 122L and 122R, the change amount Δθ of the opening angle is 1.8°, which is significantly smaller compared to the comparative example. In No. 32 where H2 / H1 is 6.0, the change amount Δθ of the opening angle is 1.8°, which is equivalent to No. 25. That is, when H2 / H1 exceeds 5.0, the reduction effect of springback and the accompanying improvement effect of the dimensional accuracy of the press-formed product 30 saturated. Also, in the straight type die 10A, when H2 / H1 exceeds 5.0, the lower die side surface 122b becomes longer, increasing the size of the die 10A and thus increasing the cost related to the die 10A. Therefore, it can be said that by setting H2 / H1 to 5.0 or less, the dimensional accuracy of the press-formed product 30 can be efficiently improved.

[0145] For No. 26 where the sum ψ(°) of the inclination angle ψ of the inclined surface 122f of the lower die side surface 122b on the die side surfaces 122L and 122R and the opening angle θ(°) of the vertical walls 32L and 32R of the press-formed product 30 is 50°, the change amount Δθ of the opening angle is 1.4°, which is significantly smaller than that of the comparative example. Even for No. 27 where ψ + θ is 78°, the change amount Δθ of the opening angle is 4.4°, which is significantly smaller than that of the comparative example. On the other hand, for No. 31 where ψ + θ is 80°, the change amount Δθ of the opening angle is 7.0° or less but exceeds 5.0°. In No. 31, although the effect of reducing Δθ was obtained, the degree of the effect was smaller compared to No. 27. Therefore, in the straight-type die 10A, in order to effectively reduce springback and further improve the dimensional accuracy of the press-formed product 30, it is preferable that the angle ψ of the inclined surface 122f is (78 - θ)° or less.

[0146] For No. 33 where the sum ψ + θ of the angle ψ of the inclined surface 122f and the opening angle θ of the vertical walls 32L and 32R is 48°, the change amount Δθ of the opening angle is 1.4°, which is equivalent to that of No. 26. That is, when ψ + θ is less than 50°, the effect of reducing springback and the accompanying effect of improving the dimensional accuracy of the press-formed product 30 are saturated. Also, when ψ + θ is less than 50°, the size of the die 10A becomes larger, so the cost related to the die 10A increases. Therefore, in order to more efficiently improve the dimensional accuracy of the press-formed product 30, it is preferable that the angle ψ of the inclined surface 122f is (50 - θ)° or more.

[0147] In Nos. 34 to 36, the clearance CL between the punch side surfaces 113L and 113R and the upper die side surfaces 122a is smaller than the plate thickness t of the material. The clearances CL in Nos. 34 to 36 are 0.97 times the plate thickness t (CL / t = 0.97), 0.95 times the plate thickness t (CL / t = 0.95), and 0.85 times the plate thickness t (CL / t = 0.85), respectively. In No. 34 where CL / t is 0.97, the change amount Δθ of the opening angle is 2.8°, which is slightly reduced compared to No. 20 where CL / t is 1.00. On the other hand, in No. 35 where CL / t is 0.95, the change amount Δθ of the opening angle is 1.9°, which is significantly smaller compared to No. 20. In No. 36 where CL / t is 0.85, the change amount Δθ of the opening angle is further reduced to 1.2°. Therefore, also in the case of the straight type die 10A, in order to further improve the dimensional accuracy of the press-formed product 30, similar to the curved type die 10, it is preferable that the clearance CL is smaller than the plate thickness t of the material, and it is particularly preferable that it is 0.85 times or more and 0.95 times or less the plate thickness t.

[0148] [Second Embodiment] Regarding the dies 10 and 10A, CAE analysis was performed under the same basic conditions as in the first embodiment, and the difference in effects due to the presence or absence of the pad 13 and the presence or absence of the die top surface was verified. The analysis results are shown in Table 3.

[0149] [Table 3]

[0150] The comparative example, No. 2, and No. 20 in Table 3 are the same as the comparative example, No. 2, and No. 20 in the first embodiment, respectively. The conditions of No. P2 are the same as those of No. 2 except that the pad 13 is not provided on the mold 10. The conditions of No. P20 are the same as those of No. 20 except that the pad 13 is not provided on the mold 10A. The conditions of No. D2 are the same as those of No. 2 except that the die top surfaces are provided on the dies 12L and 12R instead of the pad 13. The conditions of No. D20 are the same as those of No. 20 except that the die top surfaces are provided on the dies 12L and 12R instead of the pad 13. In No. 2, No. P2, and No. D2, the line length L of the intermediate portion 122e of the lower die side surface 122b of the left and right die side surfaces 122L and 122R was set to 1.08 × A.

[0151] As shown in Table 3, the change amount Δθ of the opening angle of the vertical walls 32L and 32R after springback became smaller than that of the comparative example in all of No. P2, No. D2, No. D20, and No. P20.

[0152] However, in No. P2 without the pad 13, Δθ became larger than that in No. 2 with the pad 13. In addition, in No. P20 without the pad 13, Δθ became larger than that in No. 20 with the pad 13. Therefore, in order to further reduce springback and more efficiently improve the dimensional accuracy of the press-formed product 30, it is preferable to provide a pad 13 for holding the material between the left and right dies 12L and 12R.

[0153] Also, in No. D2 where the die top surfaces are provided on dies 12L and 12R instead of pad 13, Δθ was larger than that in No. 2 having pad 13, but was smaller than that in No. P2 having neither pad 13 nor the die top surface. In addition, in No. D20 where the die top surfaces are provided on dies 12L and 12R instead of pad 13, Δθ was larger than that in No. 20 having pad 13, but was smaller than that in No. P20 having neither pad 13 nor the die top surface. Therefore, in order to further reduce springback and more efficiently improve the dimensional accuracy of the press-formed product 30, it is preferable to have a die top surface for holding the material, and it is more preferable to have pad 13.

[0154] [Third Embodiment] Regarding the mold 10, CAE analysis was performed under the same basic conditions as in the first embodiment, and the difference in effects due to the length L of the intermediate portion 122e of the lower side surface 122b of the die was verified. The analysis results are shown in Table 4. Table 4 shows the values obtained by dividing the line length L by a parameter A represented by the following equation. A = ((H2 - Rd2 - Rd3) 2 + (W2 - Rd2 - Rd3) 2 ) 0.5

[0155] [Table 4]

[0156] The comparative example and No. 2 in Table 4 are the same as the comparative example and No. 2 in the first embodiment, respectively. The condition of No. 200 is the same as that of No. 2, where the wire length L is 1.08 times that of parameter A, but H2 / W2 is different from that of No. 2. The condition of No. 201 is that the wire length L is 1.01 times that of parameter A, and the recess in the middle part 122e (the lower side surface of the die) is smaller than that of No. 200 and is almost linear. The condition of No. 202 is that the wire length L is 1.03 times that of parameter A, and the recess in the middle part 122e (the lower side surface of the die) is smaller than that of No. 200. The condition of No. 203 is that the wire length L is 1.06 times that of parameter A, and the recess in the middle part 122e (the lower side surface of the die) is larger than that of No. 202 but smaller than that of No. 2. The condition of No. 204 is that the wire length L is 1.10 times that of parameter A, and the recess in the middle part 122e (the lower side surface of the die) is the largest among those in Table 4.

[0157] As shown in Table 4, the change amount Δθ of the opening angle of the vertical walls 32L and 32R after springback became smaller than that of the comparative example in all of No. 200, No. 201, No. 202, No. 203, and No. 204.

[0158] Since Δθ is smaller in the order of the larger wire length L, that is, in the order of No. 204, No. 200, No. 203, No. 202, and No. 201, it can be said that the larger the wire length L, the more preferable. That is, the larger the wire length L, the larger the recess in the middle part 122e (the lower side surface of the die), and the larger the deflection of the material M during the pressing process. The larger the deflection of the material M during the pressing process, the more effectively the stress of the bending parts 33L and 33R generated during the pressing process and the moment generated during the mold release can be canceled out by bending back when the material M is firmly clamped between each upper side surface 122a of the die and the punch side surfaces 113L and 113R.

[0159] As shown in Table 4, in No. 200 where the wire length L is 1.03 times or more of parameter A, and in No. 202 to No. 204, the change amount Δθ of the opening angle became significantly smaller compared to the comparative example. In No. 200 and No. 204 where the wire length L is 1.08 times or more of parameter A, Δθ became even smaller. Therefore, the wire length L is preferably 1.03 times or more of parameter A, and more preferably 1.08 times or more of parameter A.

[0160] In No. 2, the wire length L is 1.08 times of parameter A, similar to No. 200, but H2 / W2 of No. 2 is smaller than that of No. 200. In No. 2, the change amount Δθ of the opening angle became smaller than that of No. 200.

Explanation of Signs

[0161] 10, 10A: Mold 11: Punch 111: Punch top surface 112L, 112R: Punch shoulders 113L, 113R: Punch side surfaces 12L, 12R: Die 121L, 121R: Die shoulders 122L, 122R: Die side surfaces 122a: Upper die side surface 122b: Lower die side surface 122c, 122d: Connection parts 122e: Intermediate part 122f: Inclined surface 123L, 123R: Die flange surfaces 13: Pad 20: Press device 30: Press-formed product

Claims

1. A mold for pressing a plate-shaped material, comprising: a punch including a punch top surface, a punch side surface, and a punch shoulder that forms a corner between the punch top surface and the punch side surface; a die including a die shoulder corresponding to the punch shoulder, a die side surface corresponding to the punch side surface, and a die flange surface extending outward in the width direction of the mold from the die side surface; and the mold is provided with: the die side surface has: a die upper side surface that is continuously provided on the die shoulder and is configured to sandwich the material together with the punch side surface when the punch and the die are closed; a die lower side surface that is disposed between the die upper side surface and the die flange surface and has a concave shape facing outward in the width direction with respect to the die upper side surface so as not to sandwich the material together with the punch side surface when the punch and the die are closed; and the mold has: when the length in the vertical direction of the die from the upper end of the die shoulder to the lower end of the die upper side surface is H1, and the length in the vertical direction from the lower end of the die upper side surface to the lower end of the die lower side surface is H2, H1 is more than 5.0 mm larger than the radius of curvature of the die shoulder, and H2 / H1 is 1.0 or more and 5.0 or less.

2. The mold according to claim 1, wherein: the die lower side surface has: a first connecting portion that is continuously provided at the lower end of the die upper side surface and connects the die lower side surface to the die upper side surface; a second connecting portion that includes the lower end of the die lower side surface and connects the die lower side surface to the die flange surface; and an intermediate portion that is disposed between the first connecting portion and the second connecting portion and is positioned outward in the width direction with respect to the first connecting portion. The mold includes the above.

3. The mold according to claim 2, wherein: the first connecting portion has an arc shape with a radius of curvature of 1.0 mm or more and 10.0 mm or less in a cross-sectional view of the die.

4. The mold according to claim 2 or 3, wherein: the intermediate portion includes a curved surface having a concave shape facing outward in the width direction with respect to the first connecting portion.

5. The mold according to claim 4, wherein: when the length in the width direction from the lower end of the die upper side surface to the lower end of the die lower side surface is W2, H2 / W2 is 1.0 or more and 5.0 or less.

6. The mold according to claim 2 or 3, wherein: the intermediate portion includes an inclined surface that is inclined with respect to a horizontal plane.

7. The mold according to claim 6, wherein when the angle formed by the inclined surface and the horizontal plane is set as (50 - θ)° or more and (78 - θ)° or less, where the angle formed by the punch side surface and the vertical plane is θ°, the mold.

8. The mold according to any one of claims 1 to 7, wherein when the punch and the die are in a closed state, the clearance between the punch side surface and the upper die side surface is smaller than the thickness of the material, the mold.

9. The mold according to claim 8, wherein the clearance is 0.85 times or more and 0.95 times or less of the thickness of the material, the mold.

10. The mold according to any one of claims 1 to 9, further comprising a pad corresponding to the top surface of the punch, the mold.

11. A press device for forming a press-formed product from a plate-shaped material, comprising the mold according to claim 10, and the press device is configured such that, with the material disposed on the top surface of the punch held between the top surface of the punch and the pad, the forming of the material by the punch and the die is started, the press device.

12. The press device according to claim 11, further comprising a die holder that supports the die and the pad so as to be integrally movable, and the pad is connected to the die holder by an elastic member that can expand and contract, the press device.

13. A method for manufacturing a press-formed product, comprising a first preparation step of preparing the mold according to any one of claims 1 to 10, a second preparation step of preparing a plate-shaped material, a forming step of forming the material into the press-formed product using the mold, wherein the forming step includes a step of disposing the material on the top surface of the punch, then bringing the die relatively close to the punch and contacting the lower die side surface with the material to bend the material, a step of further bringing the die closer to the punch with the material bent and contacting the upper die side surface with the material, a step of further bringing the die closer to the punch while the upper die side surface is in contact with the material, thereby bending back the bend of the material by the upper die side surface, a step of closing the punch and the die and clamping the material between the punch shoulder and the die shoulder and between the punch side surface and the upper die side surface, and A manufacturing method in which, when the punch and the die are completely closed, the material has a shape along the top surface of the punch, the shoulder of the punch, and the side surface of the punch.

14. The manufacturing method according to claim 13, wherein in the first preparation step, the mold according to claim 10 is prepared, and in the molding step, the material disposed on the top surface of the punch is bent by the lower side surface of the die while being sandwiched between the top surface of the punch and the pad.

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