JP7709032B2 - Mold, press device, and method for manufacturing press-molded product - Google Patents

Description

This disclosure relates to a die for press working a plate-shaped material, a press device, and a method for manufacturing a press-molded product.

Press-formed products are widely used as components for automobile bodies and the like. A press-formed product has, for example, a top plate and vertical walls connected to both side edges of the top plate via bent sections. Such press-formed products are manufactured by subjecting a plate-shaped material (metal plate) to press processing. More specifically, press-formed products are manufactured by drawing and bending a metal plate using a mold including a punch and a die.

After a metal plate is formed into a press-formed product using a die, springback occurs when the press-formed product is released from the die. More specifically, when a metal plate is bent by the die during press working, tensile stress occurs on the outside of the bend and compressive stress occurs on the inside of the bend at the bent part, but when forming is completed and the press-formed product is removed from the die, compressive stress occurs on the outside of the bend and tensile stress occurs on the inside of the bend due to the elastic recovery of the material. As a result, the moment the press-formed product is removed from the die, a moment is generated that causes both vertical walls of the press-formed product to open outward (wall-opening moment). This moment causes springback in the press-formed product.

In order to obtain the target dimensional accuracy of the press-formed product, press dies are sometimes designed with springback in mind. That is, the part of the die that forms the vertical walls of the press-formed product is located inside the target position of the vertical walls by the amount that is expected to cause the walls to open due to springback. However, it is difficult to accurately match the expected amount of springback with the actual amount of springback. In addition, since the amount of springback is proportional to the strength of the material, the expected amount of springback is large when press-forming high-strength materials such as high-tensile steel and ultra-high-tensile steel. If the die is designed based on this expected amount, the part of the die that forms the vertical walls of the press-formed product will have a negative angle, and there is a possibility that the structure of the die will not be valid. Therefore, it is difficult to obtain the target dimensional accuracy of the press-formed product by simply designing the die with springback in mind.

Therefore, a technique has been proposed for obtaining a press-formed product with a target dimensional accuracy without relying on the expectation of springback. For example, Patent Document 1 discloses a method for manufacturing a press-formed product that includes a top plate, two vertical walls, and flanges extending outward from both vertical walls. The manufacturing method of Patent Document 1 includes, for example, a first press processing step for manufacturing an intermediate formed product from a metal plate as a material, and a second press processing step for manufacturing a final press-formed product from the intermediate formed product. In the first press processing step, a first punch and a first die press the metal plate to form the top plate and bent parts of the press-formed product, and form parts of each vertical wall. In the second press processing step, a second punch and a second die press the intermediate formed product obtained in the first press processing step, and form the remaining parts of each vertical wall and each flange. According to Patent Document 1, by forming each flange last, it is possible to reduce the warping (opening) of each vertical wall due to springback.

For example, Patent Document 2 discloses that a cam mechanism is used to control the direction of die movement when manufacturing press-formed products. The manufacturing method of Patent Document 2 includes a push-bending process in which the die is lowered toward the material on the punch to bend the material, and a close-bending process in which the die is moved toward the punch using a cam to bend the material. In the close-bending process, the dies on both sides of the punch come into contact with the ends of the material and press the material toward the punch, forming an upward convex deflection in the material. According to Patent Document 2, by bending the material in this way, a spring-go component that acts in a direction that cancels the spring-back component can be generated.

International Publication No. 2016/051765 Patent No. 5808297

In the manufacturing method of Patent Document 1, the top plate and part of each vertical wall of the press-formed product are formed first, and the remaining parts of each vertical wall and each flange are formed last, thereby reducing springback. Therefore, in the case of the manufacturing method of Patent Document 1, at least two press processing steps are required to prevent deterioration of dimensional accuracy due to springback.

On the other hand, the manufacturing method of Patent Document 2 makes it possible to manufacture a press-molded product in a single press processing step. However, the manufacturing method of Patent Document 2 requires the use of a cam mechanism to control the direction of die movement, which creates the problem of a complex die structure.

The objective of this disclosure is to provide a mold with a simple structure that can reduce springback in press-molded products and improve dimensional accuracy.

The die according to the present disclosure is a die for performing press working on a plate-shaped material. The die 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 from the die side surface in the width direction of the die. The die side surface has a die upper side surface and a die lower side surface. The die upper side surface is provided continuous 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 die relative to the die upper side surface. If the length of the die in the vertical direction from the top of the die shoulder to the bottom of the upper side of the die is H1, and the length of the die in the vertical direction from the bottom of the upper side of the die to the bottom of the lower side of the die 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.

The die according to the present disclosure can reduce springback in press-molded products and improve dimensional accuracy. In addition, the die according to the present disclosure has a simple structure.

FIG. 1 is a cross-sectional view showing a schematic configuration of a mold according to a first embodiment. FIG. 2 is an enlarged cross-sectional view of the right-hand die of the mold shown in FIG. FIG. 3A is a schematic diagram for explaining the method for manufacturing a press-formed product according to the first embodiment. FIG. 3B is a schematic diagram for explaining the method for manufacturing a press-formed product according to the first embodiment. FIG. 3C is a schematic diagram for explaining the method for manufacturing a press-formed product according to the first embodiment. FIG. 3D is a schematic diagram for explaining the method for manufacturing a press-formed product according to the first embodiment. FIG. 3E is a schematic diagram for explaining the manufacturing method of the press-formed product according to the first embodiment. FIG. 3F is a schematic diagram for explaining the manufacturing method of the press-formed product according to the first embodiment. FIG. 3G is a schematic diagram for explaining the manufacturing method of the press-formed product according to the first embodiment. FIG. 4 is a diagram illustrating a press-formed product manufactured by the manufacturing method according to the first embodiment. FIG. 5 is a diagram illustrating another press-formed product manufactured by the manufacturing method according to the first embodiment. FIG. 6 is a diagram illustrating still another press-molded product manufactured by the manufacturing method according to the first embodiment. FIG. 7 is a partial cross-sectional view of a mold according to a modified example of the first embodiment. FIG. 8 is a schematic diagram for explaining a method for manufacturing a die and a press-molded product different from the first embodiment. FIG. 9 is a cross-sectional view showing a schematic configuration of a mold according to the second embodiment. FIG. 10 is an enlarged cross-sectional view of the right-hand die of the mold shown in FIG. FIG. 11 is a cross-sectional view of a die according to a modification of the second embodiment.

The die according to the embodiment is a die for performing press working on a plate-shaped material. The die 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 from the die side surface in the width direction of the die. The die side surface has a die upper side surface and a die lower side surface. The die upper side surface is provided continuous 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 die relative to the die upper side surface. When the length of the die in the vertical direction from the top of the die shoulder to the bottom of the upper side of the die is H1, and the length of the die in the vertical direction from the bottom of the upper side of the die to the bottom of the lower side of the die 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).

When a plate-shaped material is pressed using a die according to the first configuration, the die is moved relatively close to the punch with the material placed on the top surface of the punch. This causes the lower side of the die to come into contact with the material on the top surface of the punch. The lower side of the die has a concave shape toward the outside in the width direction of the die relative to the upper side of the die. Therefore, as the die is brought closer to the punch, the material is guided by the lower side of the die and bends to a convex shape on the opposite side to the approach direction of the die to the punch. When the die is brought even closer to the punch, the material comes into contact with the upper side of the die, and the bent material is gradually bent back. As the die and punch approach each other, the bending of the material is reduced, and the material fits (wraps) around the punch shoulder to form a bent portion. When the punch and die are finally closed, the bending of the material is completely bent back and disappears, and the material is sandwiched between the punch shoulder and the die shoulder, and between the punch side and the upper side of the die.

In this way, the die according to the first configuration is configured to bend the material so that it has a convex shape on the side opposite to the approach direction of the die to the punch, and to gradually bend the material back as the press working progresses. As a result, during the press working, tensile stress can be generated on the punch side, and compressive stress can be generated on the die side, which is the opposite side of the punch, in the material, particularly in the part that will become the vertical wall of the press-formed product. In the bent part formed by the punch shoulder, compressive stress is generated on the punch side, and tensile stress is generated on the die side, so the stress generated by the bending back of the bending cancels out with the stress in the bent part, reducing the stress in the bent part. In the press-formed product after demolding, a wall opening moment and a wall closing moment occur due to the stress remaining in the bent part and the stress remaining in the bent back part at the time when the molding of the material into the press-formed product is completed, but these cancel out each other, and the wall opening moment decreases. Therefore, the 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. Furthermore, when pressing a material using the die according to the first configuration, it is only necessary to perform the normal die closing operation, and no cam mechanism or the like is required to move the die in a special direction. Therefore, the die can have a simple structure.

In the first configuration, when the length of the die in the vertical direction from the upper end of the die shoulder to the lower end of the upper side of the die is H1, and the length of the die in the vertical direction from the lower end of the upper side of the die to the lower end of the lower side of the die is H2, H2/H1 is set to 1.0 or more and 5.0 or less. As a result, the length of the lower side of the die is sufficiently secured, so that the material can be largely deflected over a wide range in the width direction by the lower side of the die during press processing. Therefore, the effect of canceling out the stress and moment due to the bending back of the deflection can be effectively exerted. In addition, in the first configuration, H1 is set to be 5.0 mm or more larger than the radius of curvature of the die shoulder, and H2/H1 is set to be 1.0 or more and 5.0 or less, so that the length of the upper side of the die can also be secured. Therefore, when the punch and die are finally closed, the material can be firmly clamped between the punch side and the upper side of the die, and the material can be formed into the shape of the final press-formed product. Therefore, there is no need to perform an additional press processing process, and the man-hours and costs in manufacturing the press-formed product can be reduced.

When H2/H1 exceeds 5.0, the proportion of the die side surface that is occupied by the lower side surface of the die, which has a concave shape facing outward in the width direction of the die, becomes too large, and the effect of bending the material by the lower side surface of the die becomes saturated. In addition, when H2/H1 exceeds 5.0, the cost of manufacturing the die also increases. Therefore, as in the first configuration, it is preferable that H2/H1 is 5.0 or less.

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 provided continuous with 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 outward in the width direction from the first connection portion (second configuration).

The first connection portion has, for example, an arc shape when viewed in cross section of the die. In this case, it is preferable that the first connection portion has a radius of curvature of 1.0 mm or more and 10.0 mm or less (third configuration).

In the third configuration, the radius of curvature of the first connection portion of the lower die side surface that connects the lower die side surface to the upper die side surface is set to 10.0 mm or less. In this case, the proportion of the first connection portion and the lower die side surface including the first connection portion in the die side surface having a predetermined size does not become too large, making it easier to ensure the length of the upper die side surface. Therefore, when the punch and die are finally closed, the material can be more reliably clamped between the punch side surface and the upper die side surface.

When the first connection portion comes into contact with the material during press processing, a bite mark or bend of the first connection portion may remain in the material. In contrast, in the third configuration, the radius of curvature of the first connection portion is set to 1.0 mm or more. This makes it possible to prevent bite marks or bends from remaining in the material.

The middle portion may include a curved surface having a concave shape toward the outside in the width direction of the die relative to the first connection portion (fourth configuration). In this case, when the length in the width direction from the bottom end of the upper side surface of the die to the bottom 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 (fifth configuration).

When H2/W2 is less than 1.0, i.e., when W2 is large relative to H2, the effect of bending the material by the lower side of the die saturates. Furthermore, when H2/W2 is less than 1.0, the cost of manufacturing the mold increases. On the other hand, when H2/W2 exceeds 5.0, W2 becomes small relative to H2, so the effect of bending the material by the lower side of the die becomes small. Therefore, when the middle part of the lower side 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.

The middle portion may include an inclined surface that is inclined with respect to the horizontal plane (sixth configuration). The angle that the inclined surface makes with the horizontal plane is preferably greater than or equal to (50-θ)° and less than or equal to (78-θ)°, where θ° is the angle that the punch side surface makes with the vertical plane (seventh configuration).

When the middle part of the lower die side is mainly composed of inclined surfaces, if the angle of the inclined surface with respect to the horizontal plane is too large, the degree of indentation of the lower die side will be small. Therefore, the effect of the lower die side bending the material will be small. On the other hand, if the angle of the inclined surface with respect to the horizontal plane is too small, the effect will be saturated. Furthermore, the smaller the angle of the inclined surface with respect to the horizontal plane, the greater the degree of indentation of the lower die side, which will increase the size of the die and the cost of manufacturing the die. Therefore, as in the seventh configuration, it is preferable that the angle that the inclined surface included in the middle part makes with respect to the horizontal plane is (50-θ)° or more and (78-θ)° or less, where θ° is the angle that the punch side makes with respect to the vertical plane.

The clearance between the side of the punch and the side of the upper part of the die when the punch and die are in a closed state may be smaller than the thickness of the material (eighth configuration). It is preferable that the clearance is 0.85 times or more and 0.95 times or less the thickness of the material (ninth configuration).

In the eighth and ninth configurations, the clearance between the punch side and the die upper side is smaller than the thickness of the material. Therefore, when the punch and die are finally closed, the material is tightly clamped between the punch side and the die upper side, and the material is more firmly bent back. In this case, in the part of the material that will become the vertical wall of the press-formed product, a larger tensile stress can be generated on the punch side, and a larger compressive stress can be generated on the die side, which is the opposite side of the punch. This enhances the effect of these stresses canceling out the stress in the bent part. 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.

In the die according to the embodiment, when the punch and die are finally closed during press working of a plate-shaped material, the material is clamped between the side of the punch and the upper side of the die, while the concave lower side of the die does not substantially come into contact with the material. This allows the load to be concentrated on the portion of the material that will become the vertical wall of the press-formed product. In particular, when the clearance between the side of the punch and the upper side of the die is smaller than the thickness of the material, as in the eighth and ninth configurations, the portion of the material that will become the vertical wall of the press-formed product can be pressed more strongly.

In the cam mechanism that moves the die diagonally downward as in Patent Document 2, it is difficult to strongly press the material in the thickness direction due to the die rigidity. In contrast, in the eighth and ninth configurations, a cam mechanism is not used, and the clearance between the punch side and the upper die side is set to be smaller than the material thickness. This makes it possible to strongly press the material in the thickness direction. Therefore, a larger stress can be generated in the part of the material that will become the vertical wall of the press-formed product, and this stress can increase the effect of canceling out the stress in the bent part. 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.

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

The die according to the tenth configuration includes a pad in addition to a punch and a die. In this case, the die can be moved relatively close to the punch while the material is being pressed between the top surface of the punch and the pad. This makes it possible to prevent the material from shifting position during press processing. In addition, by forming the material while the material is being pressed with the pad, the shape of the top plate of the press-formed product can be precisely formed.

The press device according to the embodiment manufactures press-formed products from plate-shaped material. The press device is equipped with the above-mentioned die. The press device is configured so that the forming of the material by the punch and die is started in a state in which the material placed on the punch top surface is clamped between the punch top surface and the pad (eleventh configuration).

The press device further includes a die holder. The die holder supports the die and the pad so that they can move together. The pad is connected to the die holder by an expandable elastic member (12th configuration).

The manufacturing method according to the embodiment is a method for manufacturing a press-molded product. The manufacturing method includes a first preparation step of preparing the above-mentioned die, a second preparation step of preparing a plate-shaped material, and a molding step of molding the material into a press-molded product using the die. The molding step includes a step of placing the material on the top surface of the punch, moving the die relatively close to the punch, and contacting the lower side surface of the die with the material to warp the material, a step of moving the die further close to the punch in a warped state and contacting the upper side surface of the die with the material, a step of bending back the warp of the material by the upper side surface of the die by moving the die further close to the punch while keeping the upper side surface of the die in contact with the material, and a step of closing the punch and die to sandwich 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 die are completely closed, the material takes a shape that conforms to the punch top surface, punch shoulder, and punch side surface (thirteenth configuration).

In the above manufacturing method, in the first preparation step, a die including a pad in addition to the punch and die may be prepared. In this case, in the molding step, it is preferable to bend the material placed on the top surface of the punch by the lower side of the die while the material is sandwiched between the top surface of the punch and the pad (14th configuration).

Embodiments of the present disclosure will be described below with reference to the drawings. In each drawing, the same or equivalent components are given the same reference numerals, and the same description will not be repeated.

First Embodiment
[Configuration of the Pressing Device]
Fig. 1 is a cross-sectional view showing a schematic configuration of a mold 10 according to this embodiment. The cross-section is a cross section cut along a plane substantially perpendicular to the longitudinal direction of the mold 10. In the following description, the vertical direction on the paper surface of Fig. 1 is referred to as the vertical direction of the mold 10, and the left-right direction on the paper surface of Fig. 1, i.e., the direction substantially perpendicular to the plane consisting of the longitudinal direction and the vertical direction of the mold 10, is referred to as the width direction of the mold 10. The left and right sides on the paper surface of Fig. 1 may also be simply referred to as the left and right sides.

The die 10 is used to perform press working on a plate-shaped material (metal plate). By pressing the material with the die 10, it is possible to manufacture press-formed products, such as automobile suspension parts. Examples of automobile suspension parts include arm parts such as upper arms, lower arms, and trail links, as well as suspension members and torsion beams.

Referring to FIG. 1, when press processing is performed on a material, the die 10 is attached to the press device 20. The die 10 includes a punch 11, dies 12L and 12R, and a pad 13. In this embodiment, the dies 12L and 12R, which are the upper dies of the die 10, and the pad 13 are moved vertically by the press device 20. When a straight line drawn in the vertical direction is projected onto a cross section of the die 10, the direction of the straight line coincides with the up-down direction in the cross section of the die 10. When the die 10 is used to mold a press-molded product having a linear shape in a side view, the vertical direction and the up-down direction in the cross section of the die 10 always coincide over the entire length of the die 10.

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

In the example shown in FIG. 1, the punch top surface 111 is a substantially flat surface. However, the punch top surface 111 may have a groove or step (step) formed therein that extends in the longitudinal direction of the punch 11. The groove or step may extend over the entire punch top surface 111 in the longitudinal direction of the punch 11, or may be provided in only a portion of the punch top surface 111.

In the width direction of the die 10, punch shoulders 112L, 112R and punch side surfaces 113L, 113R are provided on either side of the punch top surface 111. The punch shoulder 112L and punch side surface 113L are located on the left side of the punch top surface 111. The punch shoulder 112R and punch side surface 113R are located on the right side of the punch top surface 111.

The punch shoulders 112L, 112R are provided contiguous to 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, 112R form corners (ridges) between the punch top surface 111 and the punch side surfaces 113L, 113R, respectively. Each of the punch shoulders 112L, 112R is, for example, substantially arc-shaped when viewed in cross section of the punch 11.

In this embodiment, the concept of being substantially arc-shaped includes not only curves that form part of a perfect circle, but also smooth curves such as elliptical curves and spline curves. In this embodiment, for smooth curves other than curves that form part of a perfect circle, such as elliptical curves and spline curves, the radius of curvature is defined as the radius of a circle that passes through three points: both ends of the curve and the midpoint of the curve.

In a cross-sectional view of the punch 11, the punch side 113L extends downward from the left punch shoulder 112L. In a cross-sectional view of the punch 11, the punch side 113R extends downward from the right punch shoulder 112R. In the example of this embodiment, when viewed in the cross-section of the punch 11, the punch sides 113L, 113R are inclined in the vertical direction so as to move away from each other as they extend downward. However, the punch sides 113L, 113R may also extend substantially in the vertical direction when viewed in the cross-section of the punch 11.

The angles θ _L and θ _R (°) that the punch side surfaces 113L and 113R make with the vertical plane may be the same or different. The angles θ _L and θ _R are each 0° or more. It is preferable that the angles θ _L and θ _R are each 20° or less. The angles θ _L and θ _R that the punch side surfaces 113L and 113R make with the vertical plane are the angles (acute angle side) that the punch side surfaces 113L and 113R make with the vertical direction in a cross section of the punch 11 cut with a plane consisting of the vertical direction and the width direction. The vertical plane is a plane consisting of the vertical direction and the longitudinal direction, or a cross section of the die 10 cut with a plane consisting of the vertical direction and the longitudinal direction. When the vertical plane is projected onto a cross section of the die 10, it becomes a straight line extending in the vertical direction.

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 either side of the pad 13 in the width direction of the mold 10. The die 12L is positioned on the left side of the pad 13. The die 12R is positioned on the right side of the pad 13.

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.

The left die shoulder 121L is provided to correspond to the left punch shoulder 112L. That is, the die shoulder 121L has a shape that allows the material to be clamped between the punch shoulder 112L and the die shoulder 121L when the punch 11 and the dies 12L, 12R are closed. Similarly, the right die shoulder 121R is provided to correspond to the right punch shoulder 112R. That is, the die shoulder 121R has a shape that allows the material to be clamped between the punch shoulder 112R and the die shoulder 121R when the punch 11 and the dies 12L, 12R are closed.

The die shoulders 121L and 121R are substantially arc-shaped in the cross-sectional view of the dies 12L and 12R, respectively. The radius of curvature of the die shoulders 121L and 121R can be determined in relation to the radius of curvature of the corresponding punch shoulders 112L and 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 to be 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.

The left die side 122L is provided to correspond to the left punch side 113L. That is, the die side 122L has a shape that allows the material to be sandwiched between a portion of the die side 122L and the punch side 113L when the punch 11 and the dies 12L, 12R are closed. The right die side 122R is provided to correspond to the right punch side 113R. That is, the die side 122R has a shape that allows the material to be sandwiched between a portion of the die side 122R and the punch side 113R when the punch 11 and the dies 12L, 12R are closed. Each of the die sides 122L, 122R has a die upper side 122a and a die lower side 122b.

The die flange surfaces 123L, 123R extend outward in the width direction of the die from the die sides 122L, 122R. The die flange surface 123L is continuous with the left die lower side surface 122b. The die flange surface 123R is continuous with the right die lower side surface 122b.

The configuration of the upper die side surface 122a and the lower die side surface 122b will be described below with reference to Figure 2. Figure 2 is an enlarged cross-sectional view of the right die 12R of the mold 10.

The die upper side surface 122a is continuous with the die shoulder 121R. The die upper side surface 122a extends downward from the die shoulder 121R in a cross-sectional view of the die 12R. The die upper side surface 122a has a substantially straight shape in a cross-sectional view of the die 12R.

In a cross section of the die 12R cut along a plane consisting of the vertical and width directions, the angle between the die upper side surface 122a and the vertical direction is substantially equal to the angle _θR of the punch side surface 113R. In this embodiment, the die upper side surface 122a is inclined with respect to the vertical direction in the cross section of the die 12R in correspondence with the punch side surface 113R. More specifically, the die upper 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 extends downward.

The die lower side surface 122b is disposed between the die upper side surface 122a and the die flange surface 123R. The die lower side surface 122b has a shape that is concave toward the outside in the width direction of the mold 10 with respect to the die upper side surface 122a. In other words, the die lower side surface 122b is an area of the die side surface 122R that is concave toward the outside in the width direction of the mold 10 compared to the die upper side surface 122a. The die lower side surface 122b is disposed outward in the width direction of the mold 10 from the extension line of the die upper side surface 122a shown by the two-dot chain line in FIG. 2.

The die lower side surface 122b includes connection portions 122c and 122d and an intermediate portion 122e. On the die lower side surface 122b, the connection portions 122c and 122d are arranged on either side of the intermediate portion 122e. The connection portion 122c is disposed above the intermediate portion 122e. The connection portion 122d is disposed below the intermediate portion 122e.

The upper connection portion 122c is provided continuously with the lower end of the die upper side surface 122a. The connection portion 122c connects the die lower side surface 122b to the die upper side surface 122a. The connection portion 122c forms a corner portion between the die upper side surface 122a and the middle portion 122e of the die lower side surface 122b. In this 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 die upper side surface 122a and the die lower side surface 122b. The connection portion 122c preferably has a radius of curvature Rd2 of 1.0 mm or more and 10.0 mm or less. It is more preferable that the radius of curvature Rd2 of the connection portion 122c is 1.0 mm or more and 4.0 mm or less.

The lower connection portion 122d includes the lower end of the die lower side surface 122b. The connection portion 122d connects the die lower side surface 122b to the die flange surface 123R. The connection portion 122d forms a corner between the middle portion 122e of the die lower side surface 122b and the die flange surface 123R. In this 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 die lower side surface 122b and the die flange surface 123R. From the viewpoint of preventing a bite mark from being left on the material, the connection portion 122d preferably has a curvature radius Rd3 of 1.0 mm or more. In addition, from the viewpoint of preventing the mold 10 from becoming large and reducing costs, the connection portion 122d preferably has a curvature radius Rd3 of 16.0 mm or less. It is more preferable that the curvature radius Rd3 of the connection portion 122d is 1.0 mm or more and 4.0 mm or less.

The intermediate portion 122e is disposed between the connection portion 122c and the connection portion 122d. The intermediate portion 122e is positioned further outward in the width direction of the mold 10 than the upper connection portion 122c. In other words, the intermediate portion 122e is recessed outward in the width direction of the mold 10 compared to the die upper side surface 122a and the connection portion 122c with the die upper side surface 122a.

In this embodiment, the middle portion 122e is mainly composed of a curved surface. This curved surface has, for example, a concave shape that faces outward in the width direction of the mold 10 relative to the upper connecting portion 122c. The shape of the curved surface that constitutes the middle portion 122e is, for example, a circular arc shape, an elliptical arc shape, a parabolic shape, or the like, when viewed in a cross section of the die 12R.

Still referring to FIG. 2, the length of the die 12R in the vertical direction 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 of the die 12R in the vertical direction 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 end of the die shoulder 121R on the side opposite the die side surface 122R. In this embodiment example, the lower end of the die upper side surface 122a coincides with the R end on the upper side 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 end on the die flange surface 123R side of the connection portion 122d.

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.

The length in the width direction of the mold 10 from the bottom end of the upper die side surface 122a to the bottom end of the lower die side surface 122b is defined as the recessed width W2. The recessed width W2 is the depth of the lower die side surface 122b, which is recessed relative to the upper die side surface 122a. The ratio of the lower height H2 to the recessed width W2: H2/W2, is preferably 1.0 or more and 5.0 or less.

When the die 12R is viewed in cross section, the line length of the intermediate portion 122e of the die lower side surface 122b is L, and the line length L is preferably 1.03×A or more, and more preferably 1.08×A or more. The parameter A is expressed by the following formula.
A=((H2-Rd2-Rd3) ² +(W2-Rd2-Rd3) ² ) ^0.5

Returning to FIG. 1, the left die 12L has a configuration that is essentially a mirror image of the right die 12R. In other words, the basic configurations of the upper die side surface 122a and the lower die side surface 122b are the same for the left and right dies 12L and 12R. Therefore, detailed descriptions of the upper die side surface 122a and the lower die side surface 122b of the left die 12L are omitted. Note that the dies 12L and 12R do not need to have completely symmetrical shapes. The dimensions of each part of the left die 12L need only be set within the preferred range, similar to the right die 12R, and do not need to match the dimensions of each part of the right die 12R.

When the die 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, 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 this embodiment, the lower surface of the pad 13 is a flat surface corresponding to the punch top surface 111. For example, if 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, if a step is formed in the punch top surface 111, a step corresponding to the step is formed on the lower surface of the pad 13.

The press device 20 is a device that uses the die 10 to form a press-formed product from a plate-shaped material. In addition to the die 10, the press device 20 is equipped with, for example, a punch holder 21, a bolster 22, a die holder 23, and a slide 24.

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.

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 positions 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, 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 allows the press device 20 to have a simpler structure than the actuator type.

The slide 24 is configured to be able to rise and fall relative to the punch 11, for example, by a mechanical or hydraulic mechanism (not shown) provided in the press device 20. As the slide 24 rises and falls, the die holder 23 also rises and falls. As the die holder 23 rises and falls, the dies 12L, 12R and the pad 13 rise and fall relative to the punch 11. In other words, the dies 12L, 12R and the pad 13 are supported by the die holder 23 so that they can move as a unit.

[Method of manufacturing press-molded products]
Hereinafter, a method for manufacturing a press-molded product using the die 10 will be described with reference to Figures 3A to 3G. Figures 3A to 3G are schematic diagrams for explaining the method for manufacturing a press-molded product. The method for manufacturing a press-molded product according to this embodiment includes a step of preparing the die 10, a step of preparing a plate-shaped material, and a molding step of molding the material into a press-molded product using the die 10.

(First preparation step)
When manufacturing a press-molded product, the die 10 (FIGS. 1 and 2) configured as described above is prepared. The die 10 is attached to the press device 20 before starting press working of a material.

(Second preparation process)
In addition, when manufacturing a press-molded 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-molded product to be manufactured is an arm part among the suspension parts of an automobile, the tensile strength of the material M is usually 590 MPa or more. When the press-molded 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-molded product to be manufactured is a roughly U-shaped reinforcing part of a front floor tunnel part among the body frame parts of an automobile, the tensile strength of the material M is usually 590 MPa or more.

(molding process)
Next, the material M is pressed using the die 10 to form a press-formed product. The forming process includes steps (a) to (d). Steps (a) to (d) will be described in detail below.

(Step (a))
3B, when starting press working of material M, the dies 12L, 12R and pad 13 attached to the press device 20 are positioned at the top dead center. In this state, material M is placed on the punch top surface 111. In step (a), after material M is placed on the punch top surface 111, the dies 12L, 12R are moved relatively close to the punch 11, and the lower side surfaces 122b of each die are brought into contact with material M, thereby bending material M.

To explain more specifically, as shown in FIG. 3C, after placing material M on the punch top surface 111, the slide 24 is lowered, causing the dies 12L, 12R supported by the slide 24 to lower toward the material M and punch 11. At this time, the pad 13 also lowers toward the material M and punch 11 together with the dies 12L, 12R. The pad 13 comes into contact with the material M on the punch top surface 111 and presses down the material M. More specifically, the pad 13 presses down from above a portion of the material M that is located in the center in the width direction of the die 10.

As shown in FIG. 3D, the slide 24 is further lowered while the material M is sandwiched between the pad 13 and the punch top surface 111. At this time, the elastic member 25 connecting the pad 13 to the slide 24 is contracted, causing the dies 12L and 12R to descend relative to the pad 13. As a result, the lower die side surfaces 122b of the die sides 122L and 122R come into contact with the material M. Each lower die side surface 122b comes into contact with the material M at the connection portion 122d with the die flange surface 123L and 123R, and then comes into contact with the material M at the concave intermediate portion 122e. As the dies 12L and 12R descend, the material M is guided by the concave intermediate portion 122e and bends significantly to the side opposite to the approach direction of the dies 12L and 12R to the punch 11, that is, to a convex shape upward. The portion of the material M sandwiched between the pad 13 and the punch top surface 111 does not rise up, and the molding of the material M proceeds. The material M is held between the pad 13 and the punch top surface 111 until forming is complete.

(Step (b))
In step (b), while the material M is being deflected, the dies 12L and 12R are brought even closer to the punch 11, so that the upper side surface 122a of each die comes into contact with the material M. More specifically, as shown in Fig. 3E, the dies 12L and 12R are further lowered, so that the connection portion 122c of each lower side surface 122b with the die upper side surface 122a comes into contact with the material M. Thereafter, when the dies 12L and 12R are further lowered, each upper side surface 122a of the die comes into contact with the material M.

(Step (c))
In step (c), the dies 12L and 12R are brought closer to the punch 11 while keeping the upper side surfaces 122a of the dies in contact with the material M, so that the deflection of the material M is bent back by the upper side surfaces 122a of the dies. As shown in Fig. 3F, as the dies 12L and 12R descend, the deflection of the material M is bent back between the upper side surfaces 122a of the dies and the punch side surfaces 113L and 113R. The deflection of the material M is gradually reduced as the dies 12L and 12R continue to descend and approach the punch 11. The material M is also wrapped around the punch shoulders 112L and 112R.

(Step (d))
In step (d), as shown in FIG. 3G, the punch 11 and the dies 12L, 12R are closed, and the material M is sandwiched between the punch shoulders 112L, 112R and the die shoulders 121L, 121R, and between the punch side surfaces 113L, 113R and the left and right die upper side surfaces 122a, 122a. As a result, the material M becomes the press-formed product 30. More specifically, by making the dies 12L, 12R reach the bottom dead center, the material M is pressed between the punch shoulders 112L, 112R and the die shoulders 121L, 121R, and the bent parts of the press-formed product are formed. In addition, the material M is pressed between the punch side surface 113L and the die upper side surface 122a of the left die 12L, and between the punch side surface 113R and the die 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 ends of the material M, i.e., the lower ends of both vertical walls of the press-formed product 30, are not in contact with the die side surfaces 122L, 122R. When the dies 12L, 12R reach the bottom dead center, the material M is completely bent back to become both vertical walls of the press-formed product 30.

When the die 12L reaches the bottom dead center and the punch 11 and the die 12L are completely closed, the clearance between the punch side 113L and the die upper side 122a of the die 12L is preferably smaller than the sheet 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 closed, the clearance between the punch side 113R and the die upper side 122a of the die 12R is preferably smaller than the sheet thickness t of the material M. More preferably, the clearance between the punch side 113L, 113R and the left and right die upper side 122a, 122a is 0.85 times or more and 0.95 times the sheet thickness t of the material M. The clearance between the punch shoulder 112L, 112R and the die shoulder 121L, 121R is typically equal to the clearance between the punch side 113L, 113R and the left and right die upper side 122a, 122a.

When the dies 12L, 12R reach the bottom dead point 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 that conforms to the punch top surface 111, the punch shoulders 112L, 112R, and the punch side surfaces 113L, 113R. Therefore, in a cross section of the punch 11 and the material M after molding cut along a plane consisting of the vertical and width directions, the portions of the material M that contact the punch side surfaces 113L, 113R, i.e., the angles (acute angle sides) that both vertical walls of the press-formed product 30 make with the vertical direction, are substantially the same as the angles θ _L , θ _R of the punch side surfaces 113L, 113R.

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

In the press-formed product 30 shown in FIG. 4, the top plate 31 has a flat shape. However, if the punch top surface 111 has a groove or step, the top plate 31 of the press-formed product 30 has a groove or step corresponding to the punch top surface 111. The top plate 31 may have one or more through holes. The through holes may be simply round holes, or may be holes (burring holes) formed by burring processing with protruding hole edges. The through holes in the top plate 31 can be formed after the press-formed product 30 is formed by the die 10.

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

The shape of the press-molded product 30 may be a combination of two or more straight sections and curved or bent sections in a plan view. The shape of the press-molded product 30 may be a combination of two or more straight sections and curved or bent sections in a side view. Furthermore, the press-molded product 30 may have a shape in which a part having a roughly U-shaped cross section branches into multiple parts, such as a three-pronged or four-pronged shape in a plan view. The press-molded product 30 may have a uniform cross-sectional shape throughout, or the cross-sectional shape may change along the way.

[effect]
When press working is performed using the die 10 according to this embodiment, the plate-shaped material M is largely deflected by each die lower side surface 122b during the process of forming into the press-molded product 30. Each die lower side surface 122b has a concave shape on the outer side in the width direction relative to the die upper side surface 122a, and guides and deflects the material M so that it has a convex shape upward. As the dies 12L and 12R approach the punch 11, the material M comes into contact with each die upper side surface 122a, and the deflection of the material M is gradually bent back. The deflection of the material M is reduced as the dies 12L and 12R approach the punch 11, and remains in the gap between the punch side surfaces 113L and 113R and each die upper side surface 122a. When the punch 11 and the dies 12L, 12R are finally closed, the deflection of the material M is completely bent back and disappears, and the material M is clamped between the punch shoulders 112L, 112R and the die shoulders 121L, 121R, and between the punch side surfaces 113L, 113R and each die upper side surface 122a.

In this manner, in this embodiment, the material M is bent and bent back so as to have a convex shape upward during the press working process. As a result, during press working, tensile stress is generated on the punch 11 side, and compressive stress is generated on the die 12L, 12R side, which is the opposite side of the punch 11, in the material M, particularly in the portion that will become the vertical walls 32L, 32R of the press-formed product 30. On the other hand, in the bent portions 33L, 33R formed by the punch shoulders 112L, 112R, compressive stress is generated on the punch 11 side, and tensile stress is generated on the die 12L, 12R side during press working. Therefore, the stress generated by bending back the deflection of the material M cancels out the stress of the bent portions 33L, 33R, reducing the stress of the bent portions 33L, 33R. Due to the stress remaining in the bent portions 33L, 33R and the stress remaining in the bent back portion at the bottom dead center of the forming, a wall opening moment and a wall closing moment are generated in the press-formed product 30 removed from the die 10, which cancel each other out. Therefore, the wall opening moment that occurs in the press-formed product 30 when it is released from the mold 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. In addition, when performing press processing 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 not required, and the mold 10 can have a simple structure.

In the mold 10 according to this embodiment, when the upper height H1 of the die side surfaces 122L, 122R and the lower height H2 of the die side surfaces 122L, 122R are set, H2/H1 is set to 1.0 or more and 5.0 or less. This ensures that the length of the concave die lower side surface 122b is sufficient for each of the die side surfaces 122L, 122R, so that the material M can be largely deflected over a wide range in the width direction by each die lower side surface 122b during press working. This allows the effect of canceling out the stresses caused by bending back the deflection to be effectively exerted.

In the die 10 according to this embodiment, the upper height H1 of the die side 122L is set to be 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 122R is set to be 5.0 mm or more larger than the radius of curvature Rd1 of the die shoulder 121R, and 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 for each of the die sides 122L and 122R. Therefore, the length of each die upper side 122a can be secured. Therefore, when the punch 11 and the die 12L and 12R are finally closed, the material M can be firmly clamped between the punch side 113L and 113R and each die upper side 122a. As a result, the parts of the material M that are bent during the press process can be bent back, and the material M can be formed into the shape of the final press-molded product 30. Therefore, there is no need to perform an additional press process, and the man-hours and costs in manufacturing the press-molded product 30 can be reduced.

In order to cancel the stress of the bent portions 33L, 33R generated during press working and the moment generated during demolding by bending back, it is important to firmly hold the material M between the upper die side surfaces 122a near the punch shoulders 112L, 112R and the punch side surfaces 113L, 113R. In the die 10 according to this embodiment, as described above, the length of each upper die side surface 122a is appropriately secured, so that the material M can be firmly held between the punch side surfaces 113L, 113R and each upper die side surface 122a. Therefore, the stress of the bent portions 33L, 33R generated during press working and the moment generated during demolding can be effectively canceled by bending back.

When H2/H1 exceeds 5.0, the proportion of the concave die lower side surface 122b in each of the die sides 122L, 122R increases, and the effect of each die lower side surface 122b in bending the material M saturates. In addition, when H2/H1 exceeds 5.0, the cost of manufacturing the mold 10 also increases. Therefore, it is preferable that H2/H1 is 5.0 or less.

In the mold 10 according to this embodiment, it is preferable that the radius of curvature of the connection portion 122c of each die lower side surface 122b with the die upper side surface 122a is set to 10.0 mm or less. In this case, in each of the die sides 122L, 122R having a predetermined size, the connection portion 122c and the proportion of this connection portion 122c that is occupied by the die lower side surface 122b do not become too large, making it easier to ensure the length of the die upper side surface 122a. Therefore, when the punch 11 and the dies 12L, 12R are finally closed, the material M can be more reliably clamped between the punch sides 113L, 113R and each die upper side surface 122a.

In addition, in this embodiment, it is preferable that the radius of curvature of the connection portion 122c is set to 1.0 mm or more. This makes it possible to prevent bite marks or bending tendencies from remaining in the material M when the connection portion 122c comes into contact with the material M during press processing.

In this 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 of the die lower side surface 122b on the die upper side surface 122a side. In this case, it is preferable that the ratio of the lower height H2 to the concave width W2: H2/W2 is 1.0 or more and 5.0 or less in each of the die sides 122L and 122R. The smaller H2/W2 is, the more effective the concave lower side surface 122b is in bending the material M, but when H2/W2 is less than 1.0, the effect of bending the material M is saturated. In addition, when H2/W2 is less than 1.0, the cost of manufacturing the mold 10 also increases. On the other hand, when H2/W2 is more than 5.0, the concave width W2 is smaller than the lower height H2, so the effect of bending the material M is reduced.

In this embodiment, the greater the line length L of the middle portion 122e of the die lower side surface 122b, the greater the concave portion of the die lower side surface 122b. The greater the concave portion of the die lower side surface 122b, the greater the deflection of the material M during press processing. In this case, when the material M is firmly clamped between each die upper side surface 122a and the punch side surfaces 113L, 113R, the stress of the bent portions 33L, 33R generated during press processing and the moment generated during demolding can be more effectively canceled by bending back. In other words, the greater the line length L, the better the dimensional accuracy of the press-molded product 30. Therefore, the line length L is preferably 1.03 times or more, and more preferably 1.08 times or more, of the above-mentioned parameter A.

In the die 10 according to this embodiment, the clearance between the punch side 113L, 113R and each die upper side 122a is preferably smaller than the sheet thickness t of the material M when the punch 11 and the die 12L, 12R are closed. It is particularly preferable that the clearance between the punch side 113L, 113R and each die upper side 122a is 0.85 times or more and 0.95 times or less of the sheet thickness t. As a result, when the punch 11 and the die 12L, 12R are finally closed in the forming process, the material M is tightly sandwiched between the punch side 113L, 113R and each die upper side 122a, and the deflection of the material M is more reliably bent back. In this case, in the part of the material M that becomes the vertical walls 32L, 32R of the press-molded product 30, a larger tensile stress can be generated on the punch 11 side, and a larger compressive stress can be generated on the die 12L, 12R side. Therefore, the effect of these stresses canceling out the stress of the bending parts 33L, 33R can be enhanced. As a result, 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.

When press working is performed on the material M using the die 10 according to this embodiment, when the punch 11 and the dies 12L, 12R are finally closed, the material M is clamped between the punch side surfaces 113L, 113R and the upper die side surfaces 122a. Meanwhile, the lower die side surfaces 122b do not substantially come into contact with the material M. This allows the load to be concentrated on the portions of the material M that will become the vertical walls 32L, 32R of the press-formed product 30. In particular, when the clearance between the punch side surfaces 113L, 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, 32R of the press-formed product 30 can be pressed more strongly.

When the punch 11 and the dies 12L, 12R are completely closed, the lower side surfaces 122b of each die do not substantially come into contact with the material M. That is, the portion of the material M that will become the lower end portions of the vertical walls 32L, 32R of the press-formed product 30 is not clamped between the punch side surfaces 113L, 113R and the die side surfaces 122L, 122R. However, in this portion, only elastic deformation occurs during press working, and no plastic deformation occurs. Therefore, even if the portion of the material M that will become the lower end portions of the vertical walls 32L, 32R of the press-formed product 30 is not clamped between the punch side surfaces 113L, 113R and the die side surfaces 122L, 122R, when the punch 11 and the dies 12L, 12R are closed, the material M is formed into a shape that conforms to the punch 11.

When the punch 11 and the die 12L, 12R are completely closed and the material M is molded into the press-formed product 30, it is preferable that the lower end of the vertical wall 32L, 32R of the press-formed product 30 contacts the punch side surface 113L, 113R as shown in FIG. 3G. That is, it is preferable that the punch side surface 113L, 113R has a shape that contacts the entire vertical wall 32L, 32R of the press-formed product 30 when the punch 11 and the die 12L, 12R are completely closed. However, the punch side surface 113L, 113R may have a shape that does not contact the vertical wall 32L, 32R of the press-formed product 30 only at its lower portion. For example, as shown in FIG. 7, the punch side surface 113L, 113R may be configured such that only its lower portion has an angle smaller than the opening angle of the vertical wall 32L, 32R. The opening angles of the vertical walls 32L, 32R correspond to the angles θ _L , θ _R that the punch side surfaces 113L, 113R make with the vertical plane. In this case, when the punch 11 and the die 12L, 12R are completely closed, the lower ends of the vertical walls 32L, 32R do not come into contact with the punch side surfaces 113L, 113R.

The die 10 according to this embodiment includes a pad 13 in addition to the punch 11 and the dies 12L and 12R. The press device 20 is configured so that the forming of the material M by the punch 11 and the dies 12L and 12R is started in a state where the material M placed on the punch top surface 111 is sandwiched between the punch top surface 111 and the pad 13. Therefore, when the die 10 and the press device 20 are used to perform press processing of the material M, the dies 12L and 12R can be brought close to the punch 11 in a state where the material M is sandwiched between the punch top surface 111 and the pad 13. More specifically, the material M can be deflected by the lower side surface 122b of each die in a state where the material M placed on the punch top surface 111 is sandwiched between the punch top surface 111 and the pad 13. Therefore, it is possible to prevent the positional deviation of the material M during press processing. In addition, by forming the material M in a state where the material M is pressed by the pad 13, the shape of the top plate 31 of the press-formed product 30 can be precisely formed.

For example, as shown in FIG. 8, in order to prevent the wall of the press-formed product from opening, it is possible to preform the material M so that it expands in a convex shape, and then press the preformed material M using a general punch 41 and dies 42L, 42R. However, in this case, a preforming process is required to expand the material M in advance in a process separate from the press processing process, which increases the man-hours and costs involved in the manufacture of the preforming mold and the press-formed product. In addition, since the desired shape in the preforming process is a relatively gently convex shape, the amount of deformation of the material M in the preforming process falls within the range of elastic deformation, especially when the material M has a high strength. Therefore, the material M does not have a gently convex shape after the preforming is released, but rather has a flat shape. In other words, it is difficult to form the material M into a convex shape in the preforming process.

On the other hand, in this embodiment, the material M is not preformed, and the material M is formed into the press-formed product 30 in one process. This makes it possible to reduce the number of steps and costs involved in manufacturing the press-formed product 30. In addition, because the material M is not preformed, the problem of difficulty in forming the material M does not arise.

Second Embodiment
9 is a cross-sectional view of the mold 10A according to the second embodiment. The mold 10A has almost the same configuration as the mold 10 according to the first embodiment (FIGS. 1 and 2). The mold 10A differs from the mold 10 according to the first embodiment only in the configuration of the die sides 122L and 122R.

Figure 10 is an enlarged cross-sectional view of the right die 12R of the mold 10A. In the mold 10A, the basic configuration of the die side surfaces 122L, 122R of the left and right dies 12L, 12R is the same. Therefore, the configuration of the die side surface 122R only for the right die 12R will be described with reference to Figure 10, and a detailed description of the die side surface 122L for the left die 12L will be omitted.

As shown in FIG. 10, in this embodiment, the middle part 122e of the die lower side surface 122b includes an inclined surface 122f inclined with respect to the horizontal plane. The horizontal plane is a cross section of the die 10 cut along a plane perpendicular to the vertical direction. When the horizontal plane is projected onto a cross section of the die 10, it becomes a straight line in the left-right direction. In the example of this embodiment, the entire middle part 122e is the inclined surface 122f. The inclined surface 122f descends from the connection part 122c with the die upper side surface 122a toward the outside in the width direction of the die 10A. 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, as in the first embodiment. Also, as in 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 this configuration, as in the first embodiment, it is possible to reduce springback in the press-formed product 30 (FIGS. 4 to 6) and improve the dimensional accuracy of the press-formed product 30.

On the die side 122R, the inclined surface 122f forms an angle ψ (°) with the horizontal plane. The angle ψ is the angle (acute angle side) that the inclined surface 122f makes with the width direction in a cross section of the die 12R cut by a plane consisting of the up-down and width directions.

In the die side surface 122R, if the angle ψ of the inclined surface 122f is too large, the degree of recession of the die lower side surface 122b relative to the die upper side surface 122a becomes small. Therefore, the effect of bending the material by the die lower side surface 122b during press processing becomes small. In order to fully exert this effect, it is preferable that the angle ψ is (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 processing becomes large, but if the angle ψ is too small, this effect becomes saturated. In addition, the smaller the angle ψ of the inclined surface 122f, the greater the degree of recession of the die lower side surface 122b, so the die 10A becomes larger, and the cost of manufacturing the die 10A increases. Therefore, it is preferable that the angle ψ of the inclined surface 122f with respect to the horizontal plane is (50-θ _R )° or more. In the left die side surface 122L (FIG. 9), similarly to the right die side surface 122R, it is preferable that the angle of the inclined surface 122f is equal to or greater than (50-θ _L )° and equal to or less than (78-θ _L )°. As described in the first embodiment, θ _L and θ _R are angles that the punch side surfaces 113L, 113R make with the vertical plane, respectively. The angle ψ of the inclined surface 122f may be the same for the left and right die side surfaces 122L, 122R or may be different.

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

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

Although the embodiments of 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 of the present disclosure.

For example, in each of the above embodiments, with the die 10 attached to the press device 20, the dies 12L and 12R are positioned above the punch 11. Furthermore, when press working is performed on the material M, the dies 12L and 12R are moved toward the punch 11. However, contrary to each of the above embodiments, when press working is performed on the material M, the dies 12L and 12R may be positioned below the punch 11. Furthermore, by moving the punch 11 toward the dies 12L and 12R, the dies 12L and 12R may be brought relatively closer to the punch 11.

The molds 10, 10A according to each of the above embodiments include dies 12L, 12R that are symmetrical on the left and right. However, the left die 12L and the right die 12R do not need to have strictly symmetrical shapes and dimensions.

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

The dies 10, 10A according to the above embodiments are provided with a pad 13. However, the dies 10, 10A do not have to be provided with a pad 13. For example, if the width of the punch top surface 111 (top plate 31 of the press-molded product 30) is relatively short when the dies 10, 10A are viewed in cross section, or if the punch top surface 111 has a flat shape without grooves or steps, a press-molded product 30 with good dimensional accuracy can be obtained in one process even if the upper die is composed of only dies 12L, 12R.

However, when the punch top surface 111 is relatively long when the die 10, 10A is viewed in cross section, or when the punch top surface 111 has a groove or step, it is preferable that the pad 13 is present between the die 12L and the die 12R. Alternatively, the die 12L may have a die top surface extending from the die shoulder 121L to the die 12R side, and the die 12R may have a die top surface extending from the die shoulder 121R to the die 12L side. Alternatively, the dies 12L and 12R may be integrally formed, and the connection portion with the dies 12L and 12R may be the die top surface. Also, another die may be provided between the dies 12L and 12R. By sandwiching the material M between the pad 13, the die top surface, or another die between the dies 12L and 12R and the punch top surface 111, a predetermined shape can be given to the top plate 31 of the press-molded product 30, and a press-molded product 30 with good dimensional accuracy can be obtained in one process.

Between the die 10, 10A provided with a die top surface and the die 10, 10A provided with a pad 13, the latter is preferred. In the case of the die 10, 10A provided with a die top surface, when the die 12L, 12R reaches the bottom dead center, the material M is sandwiched between the die top surface and the punch top surface 111, but the material M on the punch top surface 111 cannot be pressed by the die top surface during press processing. On the other hand, in the case of the die 10, 10A provided with a pad 13, the material M on the punch top surface 111 can be pressed by the pad 13 from the beginning of press processing. By forming the material M while pressing the material M with the pad 13, it is possible to prevent the material M from shifting in position during press processing, and to suppress unexpected deformation behavior (deflection behavior) of the material M on the punch top surface 111. In addition, the shape of the top plate 31 of the press-formed product 30 can also be precisely formed. Therefore, as in each of the above embodiments, it is preferable that the die 10, 10A is provided with a pad 13.

In the first embodiment, the intermediate portion 122e of each die lower side surface 122b is formed of a curved surface that smoothly continues from the upper connection portion 122c to the lower connection portion 122d. In the second embodiment, the intermediate portion 122e of each die lower side surface 122b is essentially formed of a single inclined surface 122f that continues from the upper connection portion 122c to the lower connection portion 122d. However, the shape of the intermediate portion 122e is not limited to this. For example, the intermediate portion 122e may have a step.

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

[First embodiment]
In order to confirm the effect of the present disclosure, a CAE analysis was carried out on a press process in which a material (steel plate) having a tensile strength TS = 1180 MPa and a plate thickness t = 1.6 mm was formed into a press-formed product 30 having a generally U-shaped cross section using the die 10 according to the first embodiment (FIGS. 1 and 2) or the die 10A according to the second embodiment (FIGS. 9 and 10). In the press-formed product 30, the bending R (curvature radius on the inner side of the bending) of the bending parts 33L, 33R was 8.0 mm, and the opening angle θ of the vertical walls 32L, 32R was 5°. The bending R of the bending parts 33L, 33R corresponds to the curvature radius Rp of the punch shoulders 112L, 112R. The opening angle θ of the vertical walls 32L, 32R corresponds to the angles θ _L and θ _R of the punch side surfaces 113L, 113R described in the above embodiment.

For the CAE analysis, commercially available software (LS-DYNA ver. 971 rev. 7.12, manufactured by ANSYS) was used to perform molding analysis and springback analysis to evaluate the change in the opening angle of the vertical walls 32L, 32R after springback, Δθ (°). Δθ is the difference between the opening angle θ: 5° of the vertical walls 32L, 32R in the press-molded product 30 before removal from the mold 10 (before demolding) and the opening angle θ (°) of the vertical walls 32L, 32R after removal from the molds 10, 10A (after demolding). The smaller Δθ is, the more the springback is reduced, which means that the dimensional accuracy of the press-molded product 30 is improved.

Table 1 shows the analysis results (No. 1 to 18) when the die 10 (FIGS. 1 and 2) according to the first embodiment is used. In the die 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, 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

The radius of curvature Rd1 of the die shoulders 121L, 121R was 9.6 mm, and the radius of curvature Rd3 of the connection portion 122d of the die lower side surface 122b to the die flange surfaces 123L, 123R was 4.0 mm. For comparison, Table 1 also shows the analysis results (comparative example) when a general die was used, that is, a die in which the die sides 122L, 122R do not have a concave die lower side surface 122b.

As shown in Table 1, the change in the opening angle Δθ of the vertical walls 32L, 32R after springback was smaller in all of Nos. 1 to 18 than in the comparative example. However, in No. 1 (H1-Rd1=3.0), where the upper height H1 of the die side surfaces 122L, 122R was 3.0 mm larger than the radius of curvature Rd1 of the die shoulders 121L, 121R, the change in the opening angle Δθ exceeded 7.0°, and the effect of reducing Δθ was small. This is thought to be because the length of each upper die side surface 122a was short, and each upper die side surface 122a was unable to sufficiently press down on the material when the punch 11 and dies 12L, 12R were closed (bottom dead center).

On the other hand, in No. 3 (H1-Rd1=5.0), where the upper height H1 of the die side surfaces 122L, 122R is 5.0 mm larger than the radius of curvature Rd1 of the die shoulders 121L, 121R, the change in the opening angle Δθ was 5.0° or less. Δθ in No. 3 was 4.6°, less than half that of the comparative example. In No. 2 (H1-Rd1=12.0), where the upper height H1 of the die side surfaces 122L, 122R is 12.0 mm larger than the radius of curvature Rd1 of the die shoulders 121L, 121R, the change in the opening angle Δθ was 2.1°, which was smaller. From these results, in order to effectively reduce springback and significantly improve the dimensional accuracy of the press-formed product 30, the upper height H1 of the die side surfaces 122L, 122R must be 5.0 mm or more greater than the radius of curvature Rd1 of the die shoulders 121L, 121R (H1-Rd1≧5.0).

In No. 4, where the radius of curvature Rd2 of the connection 122c between the upper die side surface 122a and the concave lower die side surface 122b is 1.0 mm, the change in the opening angle Δθ is 1.8°, which is significantly smaller than that of the comparative example. In No. 5, where the radius of curvature Rd2 of the connection 122c is 10.0 mm, the change in the opening angle Δθ 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 connection 122c is 12.0 mm, the change in the opening angle Δθ 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 than that of No. 5. Therefore, it can be seen that when the radius of curvature Rd2 of the connection 122c is 10.0 mm or less, springback is more effectively reduced and the dimensional accuracy of the press-formed product 30 is more improved.

In No. 10, where the radius of curvature Rd2 of the connection portion 122c is 0.5 mm, the change in the opening angle Δθ was 1.7°, which was almost the same as that of No. 4, where the radius of curvature Rd2 was 1.0 mm. However, in No. 10, the material retained a bending tendency. Therefore, it is preferable that the radius of curvature Rd2 of the connection portion 122c is 1.0 mm or more.

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

In No. 7, where the ratio of the lower height H2 to the upper height H1 on the die side surfaces 122L and 122R: H2/H1 is 5.0, the change in the opening angle Δθ was 0.8°, which was significantly smaller than that of the comparative example. In No. 14, where H2/H1 is 6.0, the change in the opening angle Δθ was 0.8°, which was equivalent to that of No. 7. In other words, when H2/H1 exceeds 5.0, the effect of reducing springback and the associated effect of improving the dimensional accuracy of the press-formed product 30 are saturated. In addition, when H2/H1 exceeds 5.0, the die lower side surface 122b becomes longer, which increases the size of the die 10, and therefore increases the cost of the die 10. Therefore, it can be said that the dimensional accuracy of the press-formed product 30 can be efficiently improved by setting H2/H1 to 5.0 or less.

In No. 8, where the ratio of the lower height H2 to the recess width W2 on the die side 122L, 122R: H2/W2 is 1.0, the change in the opening angle Δθ was 1.3°, which was significantly smaller than that of the comparative example. In No. 2, where H2/W2 is 2.0, and No. 9, where H2/W2 is 5.0, the change in the opening angle Δθ was 2.1° and 3.2°, respectively, which was significantly smaller than that of the comparative example. On the other hand, in No. 13, where H2/W2 is 6.0, the 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 than that of 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.

In No. 15, where H2/W2 was 0.5, the change in the opening angle Δθ was 1.3°, which was equivalent to No. 8. In other words, when H2/W2 was below 1.0, the effect of reducing springback and the associated effect of improving the dimensional accuracy of the press-formed product 30 were saturated. Furthermore, when H2/W2 was less than 1.0, the recess width W2 became large relative to the lower height H2, which increased the size of the die 10, and therefore increased the cost of the die 10. Therefore, in order to more efficiently improve the dimensional accuracy of the press-formed product 30, it is preferable that H2/W2 be 1.0 or more.

In Nos. 16 to 18, the clearance CL between the punch side 113L, 113R and each die upper side 122a when the punch 11 and the dies 12L, 12R are in a closed state is smaller than the sheet thickness t of the material. The clearances CL in Nos. 16 to 18 are 0.97 times (CL/t = 0.97), 0.95 times (CL/t = 0.95), and 0.85 times (CL/t = 0.85) the sheet thickness t, respectively. In No. 16, where CL/t is 0.97, the change in the opening angle Δθ was 2.0°, which was slightly smaller than that in No. 2, where CL/t is 1.00. On the other hand, in No. 17, where CL/t is 0.95, the change in the opening angle Δθ was 1.2°, which was significantly smaller than that in No. 2. In No. 18, where CL/t is 0.85, the change in the opening angle Δθ is even smaller at 0.6°. Therefore, in order to further improve the dimensional accuracy of the press-molded 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 the clearance CL is 0.85 times or more and 0.95 times or less than the plate thickness t.

The analysis results (No. 19 to 36) when using the mold 10A according to the second embodiment (Figures 9 and 10) are shown in Table 2. In the mold 10A, the middle portion 122e of the lower die side surface 122b is mainly composed of a linear inclined surface 122f. For ease of explanation, the mold 10A will be referred to as the linear type below, and the mold 10 in which the middle portion 122e of the lower die side surface 122b is mainly composed of a curved surface will be referred to as the curved type below.

In this analysis, the line length L of the intermediate portion 122e of the die lower side surface 122b at the left and right die sides 122L, 122R is 1.00×A because the intermediate portion 122e is linear. The parameter A is expressed by the following equation. The radius of curvature Rd1 of the die shoulders 121L, 121R was 9.6 mm, and the radius of curvature Rd3 of the connection portion 122d of the die lower side surface 122b to the die flange surfaces 123L, 123R was 4.0 mm.
A=((H2-Rd2-Rd3) ² +(W2-Rd2-Rd3) ² ) ^0.5

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

On the other hand, in No. 21 (H1-Rd1=5.0), where the upper height H1 of the die side surfaces 122L, 122R is 5.0 mm larger than the radius of curvature Rd1 of the die shoulders 121L, 121R, the change in the opening angle Δθ was 5.0° or less. Δθ in No. 21 was 4.8°, less than half that of the comparative example. In No. 20 (H1-Rd1=12.0), where the upper height H1 of the die side surfaces 122L, 122R is 12.0 mm larger than the radius of curvature Rd1 of the die shoulders 121L, 121R, the change in the opening angle Δθ was 2.9°, which was smaller. From these results, in the case of the straight-line die 10A, as in the case of the curved-line 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, 122R 5.0 mm or more greater than the radius of curvature Rd1 of the die shoulders 121L, 121R (H1-Rd1≧5.0).

In No. 22, where the radius of curvature Rd2 of the connection 122c between the upper die side surface 122a and the concave lower die side surface 122b is 1.0 mm, the change in the opening angle Δθ was 2.1°, which was significantly smaller than that of the comparative example. In No. 23, where the radius of curvature Rd2 of the connection 122c is 10.0 mm, the change in the opening angle Δθ was 4.1°, which was significantly smaller than that of the comparative example. On the other hand, in No. 29, where the radius of curvature Rd2 of the connection 122c is 12.0 mm, the change in the opening angle Δθ was 7.0° or less, but exceeded 5.0°. In No. 29, the effect of reducing Δθ was obtained, but the degree of the effect was smaller than that of No. 23. Therefore, in the case of the straight-line type die 10A, as in the case of the curved-line type die 10, 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.

In No. 28, where the radius of curvature Rd2 of the connection portion 122c is 0.5 mm, the change in the opening angle Δθ 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, the material retained a bending tendency. Therefore, even in the case of the straight-line type mold 10A, it is preferable that the radius of curvature Rd2 of the connection portion 122c is 1.0 mm or more.

In No. 24, where the ratio of the lower height H2 to the upper height H1 on the die side 122L, 122R: H2/H1 is 1.0, the change in the opening angle Δθ was 4.6°, which was significantly smaller than the comparative example. In No. 20, where H2/H1 is 3.0, the change in the opening angle Δθ was 2.9°, which was significantly smaller than the comparative example. On the other hand, in No. 30, where H2/H1 is 0.5, the change in the opening angle Δθ exceeded 7.0°, and the effect of reducing Δθ was small. Therefore, in the case of the straight-line type die 10A, as in the curved-line 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.

In No. 25, where the ratio of the lower height H2 to the upper height H1 on the die side surfaces 122L and 122R: H2/H1 is 5.0, the change in the opening angle Δθ was 1.8°, which was significantly smaller than that of the comparative example. In No. 32, where H2/H1 is 6.0, the change in the opening angle Δθ was 1.8°, which was equivalent to that of No. 25. In other words, when H2/H1 exceeds 5.0, the effect of reducing springback and the associated effect of improving the dimensional accuracy of the press-formed product 30 are saturated. Also, even in the case of a straight-line type die 10A, if H2/H1 exceeds 5.0, the die lower side surface 122b becomes longer, which increases the size of the die 10A, and therefore increases the cost of the die 10A. Therefore, it can be said that the dimensional accuracy of the press-formed product 30 can be efficiently improved by setting H2/H1 to 5.0 or less.

In No. 26, where the sum of the angle ψ (°) of the inclined surface 122f of the die lower side surface 122b at 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: ψ + θ is 50°, the change in the opening angle Δθ was 1.4°, which was significantly smaller than the comparative example. In No. 27, where ψ + θ is 78°, the change in the opening angle Δθ was 4.4°, which was significantly smaller than the comparative example. On the other hand, in No. 31, where ψ + θ is 80°, the change in the opening angle Δθ was 7.0° or less, but exceeded 5.0°. In No. 31, the effect of reducing Δθ was obtained, but the degree of the effect was smaller than that of No. 27. Therefore, in order to effectively reduce springback in the linear type die 10A and further improve the dimensional accuracy of the press-formed product 30, it is preferable that the angle ψ of the inclined surface 122f be (78-θ)° or less.

In No. 33, in which the sum of the angle ψ of the inclined surface 122f and the opening angle θ of the vertical walls 32L and 32R: ψ + θ was 48°, the change in the opening angle Δθ was 1.4°, which was equivalent to No. 26. In other words, when ψ + θ was below 50°, the effect of reducing springback and the associated effect of improving the dimensional accuracy of the press-formed product 30 were saturated. In addition, when ψ + θ was less than 50°, the size of the die 10A became large, and the cost related to the die 10A increased. 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 be (50-θ)° or more.

In Nos. 34 to 36, the clearance CL between the punch side surfaces 113L, 113R and each die upper side surface 122a is smaller than the sheet thickness t of the material. The clearances CL in Nos. 34 to 36 are 0.97 times (CL/t = 0.97), 0.95 times (CL/t = 0.95), and 0.85 times (CL/t = 0.85) the sheet thickness t, respectively. In No. 34, where CL/t is 0.97, the change in the opening angle Δθ was 2.8°, which was slightly smaller than that in No. 20, where CL/t is 1.00. On the other hand, in No. 35, where CL/t is 0.95, the change in the opening angle Δθ was 1.9°, which was significantly smaller than that in No. 20. In No. 35, where CL/t is 0.85, the change in the opening angle Δθ was 1.9°, which was significantly smaller than that in No. 20. In No. 36, the change in the opening angle Δθ was even smaller at 1.2°. Therefore, in the case of the straight-line type die 10A, as in the curved-line type die 10, in order to further improve the dimensional accuracy of the press-molded 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 the clearance CL is 0.85 times or more and 0.95 times or less than the plate thickness t.

[Second embodiment]
CAE analysis was performed on the molds 10 and 10A under the same basic conditions as in the first embodiment to verify the difference in effect due to the presence or absence of the pad 13 and the presence or absence of the die top surface. The analysis results are shown in Table 3.

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 the conditions of No. 2, except that the pad 13 was not provided on the mold 10. The conditions of No. P20 are the same as the conditions of No. 20, except that the pad 13 was not provided on the mold 10A. The conditions of No. D2 are the same as the conditions of No. 2, except that the die top surface was provided on the dies 12L and 12R instead of the pad 13. The conditions of No. D20 are the same as the conditions of No. 20, except that the die top surface was provided on the dies 12L and 12R instead of the pad 13. No. 2, No. P2, No. In D2, the line length L of the middle part 122e of the die lower side surface 122b of the left and right die sides 122L and 122R was set to 1.08 x A.

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

However, in No. P2, which does not have a pad 13, Δθ is larger than in No. 2, which has a pad 13. In addition, in No. P20, which does not have a pad 13, Δθ is larger than in No. 20, which has a 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 pads 13 for pressing the material between the left and right dies 12L and 12R.

In addition, in No. D2, in which the die top surface was provided on the dies 12L and 12R instead of the pad 13, Δθ was larger than in No. 2, in which the pad 13 was provided, but Δθ was smaller than in No. P2, in which the pad 13 and the die top surface were not provided. In addition, in No. D20, in which the die top surface was provided on the dies 12L and 12R instead of the pad 13 was provided, Δθ was larger than in No. 20, in which the pad 13 was provided, but Δθ was smaller than in No. P20, in which the pad 13 and the die top surface were not provided. 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 to hold down the material, and it is even more preferable to have a pad 13.

[Third Example]
A CAE analysis was performed on the die 10 under the same basic conditions as in the first embodiment to verify the difference in effect depending on the length of the line L of the middle portion 122e of the die lower side surface 122b. The analysis results are shown in Table 4. Table 4 lists the values obtained by dividing the line length L by the parameter A expressed by the following formula.
A=((H2-Rd2-Rd3) ² +(W2-Rd2-Rd3) ² ) ^0.5

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 conditions of No. 200 are the same as No. 2, with the line length L being 1.08 times the parameter A, but H2/W2 is different from No. 2. The conditions of No. 201 are that the line length L is 1.01 times the parameter A, and the recess in the middle part 122e (side surface of the lower part of the die) is smaller than that of No. 200 and is almost linear. The conditions of No. 202 are that the line length L is 1.03 times the parameter A, and the recess in the middle part 122e (side surface of the lower part of the die) is smaller than that of No. 200. The conditions of No. 203 are that the line length L is 1.06 times the parameter A, and the recess in the middle part 122e (side surface of the lower part of the die) is larger than that of No. 202 but smaller than that of No. 2. The condition for No. 204 is that the line length L is 1.10 times the parameter A, and the depression in the middle part 122e (lower side of the die) is the largest in Table 4.

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

Since Δθ is smallest in the order of the largest line length L, that is, No. 204, No. 200, No. 203, No. 202, and No. 201, it can be said that the larger the line length L, the more preferable it is. In other words, the larger the line length L, the larger the recess in the middle part 122e (lower die side surface) and the greater the deflection of the material M during press processing. The greater the deflection of the material M during press processing, the more effectively the stress of the bent parts 33L and 33R generated during press processing and the moment generated during demolding can be counteracted by bending back when the material M is firmly clamped between each upper die side surface 122a and the punch side surfaces 113L and 113R.

As shown in Table 4, in No. 200 and No. 202 to 204, in which the line length L is 1.03 times or more the parameter A, the change in the opening angle Δθ is significantly smaller than in the comparative examples. In No. 200 and No. 204, in which the line length L is 1.08 times or more the parameter A, Δθ is even smaller. Therefore, it is preferable that the line length L is 1.03 times or more the parameter A, and it is more preferable that it is 1.08 times or more the parameter A.

In No. 2, like No. 200, the line length L is 1.08 times the parameter A, but No. 2 has a smaller H2/W2 than No. 200. In No. 2, the change in the opening angle Δθ is smaller than in No. 200.

10, 10A: Die 11: Punch 111: Punch top surface 112L, 112R: Punch shoulder 113L, 113R: Punch side surface 12L, 12R: Die 121L, 121R: Die shoulder 122L, 122R: Die side surface 122a: Die upper side surface 122b: Die lower side surface 122c, 122d: Connection portion 122e: Middle portion 122f: Inclined surface 123L, 123R: Die flange surface 13: Pad 20: Press device 30: Press-molded product

Claims (14)

A die for performing press working on a plate-shaped material,
a punch including a punch top surface, a punch side surface, and a punch shoulder defining 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 from the die side surface in the width direction of the die;
Equipped with
The die side is
a die upper side surface provided continuously with the die shoulder and 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 shape that is concave 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;
having
A mold in which H1 is 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 of the die, and H2 is the length in the vertical direction from the lower end of the upper side of the die to the lower end of the lower side of the die, and 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. The mold according to claim 1,
The die lower side surface is
a first connection portion provided continuously with the lower end of the die upper side surface and connecting the die lower side surface to the die upper side surface;
a second connection portion including the lower end of the die lower side surface and connecting the die lower side surface to the die flange surface;
an intermediate portion disposed between the first connection portion and the second connection portion and positioned outwardly of the first connection portion in the width direction;
Including the mould. The mold according to claim 2,
A mold, wherein the first connection portion has an arc shape having a radius of curvature of 1.0 mm or more and 10.0 mm or less when viewed in a cross-section of the die. The mold according to claim 2 or 3,
The mold, wherein the intermediate portion includes a curved surface having a concave shape extending outward in the width direction relative to the first connection portion. The mold according to claim 4,
A mold in which H2/W2 is 1.0 or more and 5.0 or less, when W2 is 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. The mold according to claim 2 or 3,
The mold, wherein the intermediate portion includes an inclined surface that is inclined with respect to a horizontal plane. The mold according to claim 6,
The angle that the inclined surface forms with a horizontal plane is (50-θ)° or more and (78-θ)° or less, where θ° is the angle that the punch side surface forms with a vertical plane. A mold according to any one of claims 1 to 7,
A die, wherein a clearance between a side surface of the punch and a side surface of an upper portion of the die when the punch and the die are in a closed state is smaller than a plate thickness of the material. The mold according to claim 8,
The clearance is 0.85 to 0.95 times the plate thickness. The mold according to any one of claims 1 to 9, further comprising:
A die including a pad corresponding to the top surface of the punch. A press device for forming a press-formed product from a plate-shaped material,
The mold according to claim 10,
The press device is configured so that the material placed on the punch top surface is clamped between the punch top surface and the pad, and molding of the material by the punch and the die is started. The pressing device according to claim 11, further comprising:
a die holder that supports the die and the pad so as to be movable together;
A press apparatus, wherein the pad is connected to the die holder by an expandable elastic member. A method for manufacturing a press-molded product, comprising the steps of:
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 molding step of molding the material into the press-molded product using the die;
Equipped with
The molding step includes:
a step of placing the material on the top surface of the punch, and then moving the die relatively close to the punch and bringing a lower side surface of the die into contact with the material to bend the material;
a step of moving the die closer to the punch while the material is bent, and bringing the upper side surface of the die into contact with the material;
a step of bending the material back by the side surface of the upper part of the die by further approaching the die to the punch while keeping the side surface of the upper part of the die in contact with the material;
closing the punch and the die to clamp the material between the punch shoulder and the die shoulder and between the punch side and the upper side of the die;
Including,
The manufacturing method, wherein the blank assumes a shape that conforms to the punch top surface, the punch shoulder, and the punch side surface when the punch and the die are completely closed. The method according to claim 13, further comprising the steps of:
In the first preparation step, the mold according to claim 10 is prepared,
In the forming step, the material placed on the top surface of the punch is bent by a lower side surface of the die while being sandwiched between the top surface of the punch and the pad.