Press-forming tool and method for manufacturing press-formed product

A press-forming tool comprising: a punch including a punch portion and a plate portion transferring shape to a blank material; a die paired with the punch and opposes the punch portion; a wrinkle suppression mold including a first surface opposing the plate portion and comes into contact with the plate portion at a press-forming ending point, a second surface opposing the die and holds the blank material along with the die, and a third surface continued between the first and second surface and opposes the punch portion, and disposed between the third surface and the punch portion via a gap; a pressure receiving portion including a groove portion on the first surface of the wrinkle suppression mold; and a wrinkle suppression force increasing portion disposed on a surface opposing the first surface of the plate portion, protrudes toward the pressure receiving portion, and generates a reaction force opposed to a pressing direction when pressed in the pressing direction in end-phase of a press-forming.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a press-forming tool for a metal plate, and a method for manufacturing a press-formed product which is press-formed using the press-forming tool. Particularly, the present invention relates to a press-forming tool and a method for manufacturing a press-formed product for securing improved shape freezing properties by decreasing springback which is generated after the press forming is performed.

RELATED ART

It is possible to form members having various shapes by performing press forming using a metal plate such as a steel sheet or aluminum alloy plate. Accordingly, many press-formed products are used in members for an automobile and the like.

In the press-formed product, there is a problem relating to a dimension accuracy defect (a shape freezing defect) due to an angular change or bending of the press-formed product, which is called springback, generated after the metal plate is press-formed.

The springback is generated since the press-formed product is deformed by elastic recovery after the press forming due to residual stress introduced into the metal plate during the press forming. When the residual stress introduced into the metal plate is non-uniformly distributed in a plate thickness direction or an in-plane direction of the metal plate, the springback is easily generated.

In order to decrease the springback and improve the dimension accuracy of the press-formed product, in the end phase of the press forming, it is effective to increase a wrinkle suppression force with respect to a blank material during the press forming.

However, in order to increase the wrinkle suppression force during the press forming, a press forming apparatus, which includes a variable die cushion device using a servo valve or the like, is generally required.

With respect to this problem, Patent Document 1 discloses a press-forming tool in which an elastic body such as a spring is disposed in the press-forming tool. In this press-forming tool, it is possible to increase the wrinkle suppression force in the end phase of the press forming without the variable die cushion device.

Patent Document 2 discloses a press-forming tool in which the disc spring is disposed in the press-forming tool. In this press-forming tool, since the disc spring which can generate a high load even by a low stroke is used, it is possible to make the wrinkle suppression force which is increased in the end phase of the press forming be larger even without the variable die cushion device.

Patent Document 3 discloses a press-forming tool in which a wrinkle suppression mold is divided into a corner portion and a straight side portion. In this press-forming tool, it is possible to increase the wrinkle suppression force at every position in which the press forming is performed.

PRIOR ART DOCUMENT

Patent Document

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

In the press-forming tool disclosed in Patent Document 1, even when the portion which is added an increased the wrinkle suppression force is a part of the entire wrinkle suppression portion, it is necessary to increase the wrinkle suppression force in the entire wrinkle suppression portion. That is to say, in order to suppress the springback of the press-formed product, it is necessary to increase the size of the spring disposed in the press-forming tool or to increase the number of the springs. However, a site capable of disposing the spring in the press-forming tool is limited. Accordingly, when a metal plate having a larger springback such as high tensile strength steel or high tensile strength aluminum alloy is press-formed as the blank material, it is difficult to sufficiently increase the wrinkle suppression force.

In the press-forming tool disclosed in Patent Document 2, as the spring for increasing the wrinkle suppression force, the disc spring capable of obtaining the reaction force of the high load by the low stroke is used. Accordingly, in the end phase of the press forming at which the increase of the wrinkle suppression force is needed, it is possible to effectively increase the wrinkle suppression force by a slight stroke. However, also in this press-forming tool, even when the portion which is added the increased wrinkle suppression force is a part of the entire wrinkle suppression portion, it is also necessary to increase the wrinkle suppression force of the entire wrinkle suppression portion. Therefore, in recent years, when a metal plate which is further high-strengthened is press-formed as the blank material, even if the disc spring is used, the increase of the wrinkle suppression force is not sufficient.

In the press-forming tool disclosed in Patent Document 3, in order to suppress occurrence of wrinkles (springback) in the corner portion of the press-formed product which becomes a shrinkage flange deformation region, the wrinkle suppression force in the early phase of the press-forming is increased. In addition, in order to avoid occurrence of breakage in the corner portion, the wrinkle suppression force during the press-forming is decreased. Moreover, in order to remove a shape freezing defect in the corner portion, the wrinkle suppression force is increased again immediately before a bottom dead center (press-forming ending point) of the press-forming.

However, in this press-forming tool, in order to change the wrinkle suppression force in a part of the entire wrinkle suppression portion, the wrinkle suppression mold is set as a split-type. Since the wrinkle suppression mold is the split-type, a large spring force is not required, and only the wrinkle suppression force in the required region is increased.

However, generally, compared to an integral-type mold, the split mold has many problems with respect to manufacturing, operation, maintenance, repair, replacement, life span, or the like of the mold. Accordingly, since the split mold is adopted, management of the manufacturing process of the press-formed product becomes complicated, and the manufacturing cost of the press-formed product may be increased. Therefore, in a mass production process of press-forming members for an automobile or the like, it is more preferable to change the wrinkle suppression force in a part of the entire wrinkle suppression portion not using the split-type wrinkle suppression mold but using the integral-type wrinkle suppression mold.

In addition, the integral wrinkle suppression mold refers to a wrinkle suppression mold constituted of the minimum number of components difficult to be further split, from the viewpoint of the manufacturing of the press mold and the shape of the press-formed product.

Moreover, the press-forming tool disclosed in Patent Document 3 is a press-forming tool for a drawing of the metal plate and is not suitable to press-form a high-strength metal plate. Specifically, in the press-forming tool disclosed in Patent Document 3, a steel sheet is mainly drawn in a deep cylindrical shape.

Accordingly, the shape of the press-formed product obtained by this press-forming tool is different from the shape of the press-formed product in which the high-strength metal plate is mainly press-formed. In the press mold in which the high-strength metal plate is used as the blank material drawing and bending processing is often performed to obtain a press-formed product in which both ends in the longitudinal direction are opened (hat-shaped cross-section).

When such the high strength metal plate is performed drawing and bending processing, there are problems which are different from the problems generated when the metal plate is drawn in a deep cylindrical shape.

In the drawing processing of making the metal plate into a deep cylindrical shape, the drawn corner portion of the press-formed product becomes a shrinkage flange deformation region. On the other hand, in the drawing and bending processing of making the high-strength metal plate into the shape (for example, a member part) having both ends opened in the longitudinal direction, a portion (for example, a flange portion corresponding to an inner side of a bent portion) of the corner portion of the press-formed product becomes an extension flange deformation region.

Here, the shrinkage flange deformation refers to deformation in which extension and shrinkage are simultaneously generated in two axes an in-plane, and the extension flange deformation refers to deformation in which the extension is generated in both two axes of the in-plane. That is to say, in the press-formed product drawn by the press-forming tool disclosed in Patent Document 3, the corner portion which becomes the extensions flange deformation region such as the member part does not exist. Moreover, in the drawn press-formed product, the plate thickness of the flange portion at which the shrinkage flange deformation is generated is not changed or is increased.

On the other hand, in the press-formed product after the drawing and bending processing, the plate thickness of the flange portion at which the extension flange deformation is generated is significantly decreased. In the region in which the plate thickness is significantly decreased during the press forming, the wrinkle suppression force is not easily transmitted to the blank material, and as a result, dimension accuracy defects such as wall warpage of the press-formed product or waviness of a vertical wall are easily generated.

Here, the drawing processing refers to press forming (processing) to obtain a vessel-shaped (cylindrical) press-formed product which does not have the region being generated the extension flange deformation and which does not have opening portions on both ends in a direction perpendicular to an advancement direction (pressing direction) of a punch. Moreover, the drawing and bending processing refers to press forming (processing) to obtain a member-shaped press-formed product which has the region being generated the extension flange deformation and has openings on both ends in the longitudinal direction (the extension direction of the flange portion to which the wrinkle suppression force is applied).

In the manufacturing process in which the high-strength metal plate is press-formed in a member part or the like, development of a press-forming tool capable of suppressing springback at a portion which becomes the extension flange deformation region in addition to the shrinkage flange deformation region is significantly required.

In consideration of the above-described circumferences, an object of the present invention is to provide a press-forming tool in which a wrinkle suppression mold is not a split-type but an integral-type and springback can be suppressed in a portion which becomes an extension flange deformation region even when a high-strength metal plate is press-formed as a blank material, and a method for manufacturing a press-formed product which is press-formed using the press-forming tool.

That is to say, the present invention provides a press-forming tool and a method for manufacturing a press-formed product in which a general press forming apparatus is used without a press forming apparatus having a variable die cushion device, and a press-formed product having high dimension accuracy can be obtained by sufficiently increasing a wrinkle suppression force with respect to a blank material in the end phase of the press forming when a metal plate such as high tensile strength steel or high strength aluminum alloy in which springback easily occurs is press-formed as a blank material.

Particularly, another object of the present invention is to provide a press-forming tool and a method for manufacturing a press-formed product in which a press-formed product having an extension flange deformation region in addition to a shrinkage flange deformation region can be press-formed with high dimension accuracy by a press-forming tool by which a metal plate is performed drawing and bending processing.

Means for Solving the Problem

The inventors earnestly reviewed a mold structure in which a wrinkle suppression force is effectively increased at a portion which is added the increased wrinkle suppression force, in a press-formed product having an extension flange deformation region such as a member part. As a result, the inventors found a providing of a pressure receiving portion on a portion of a wrinkle suppression mold of the press-forming tool and providing of a wrinkle suppression force increasing portion on a portion of a punch of the press-forming tool.

According to this configuration, in the end phase of the press forming, the pressure receiving portion and the wrinkle suppression force increasing portion come into contact with each other, the wrinkle suppression mold is elastically deformed and bent, and thus, the wrinkle suppression force can be locally added to a portion of the blank material which is added the increased wrinkle suppression force. Springback of a press-formed product having the extension flange deformation region such as a member part can be significantly decreased.

Here, the part having the extension flange deformation region such as the member part refers to a press-formed product having a hat-shaped cross section shape in which both ends in the longitudinal direction are opened.

The gist of the present invention is as follows.

(1) According to an aspect of the present invention, there is provided a press-forming tool comprising: a punch which includes a punch portion and a plate portion which are configured to transfer a shape to a blank material; a die which is paired with the punch and opposes the punch portion; a wrinkle suppression mold which includes a first surface which opposes the plate portion and comes into contact with the plate portion at a press-forming ending point, a second surface which opposes the die and holds the blank material along with the die, and a third surface which is continuous between the first surface and the second surface and opposes the punch portion, and is disposed between the third surface and the punch portion via a gap; a pressure receiving portion which includes a groove portion and which is disposed on the first surface of the wrinkle suppression mold; and a wrinkle suppression force increasing portion which is disposed on the plate portion so as to oppose the first surface, protrudes toward the pressure receiving portion, and generates a reaction force in a direction opposite to a pressing direction when being pressed in the pressing direction in an end phase of a press forming.

(2) In the press-forming tool according to (1), when a region in which a plate thickness is maximum in a flange portion of a press-formed product is defined as a plate thickness maximum portion and a region in which the plate thickness is more than 0% and less than or equal to 97% with respect to the plate thickness maximum portion is defined as a plate thickness decreasing portion, based on a case where the pressure receiving portion and the wrinkle suppression force increasing portion are removed from the press-forming tool, the pressure receiving portion may overlap with a portion of a region corresponding to the plate thickness decreasing portion in the blank material when viewed along the pressing direction.

(3) In the press-forming tool according to (1) or (2), the pressure receiving portion is consisted of the groove portion, wherein when a thickness of the wrinkle suppression mold in a position of the groove portion is defined as L in mm units and a minimum value of the thickness of the wrinkle suppression mold in a position which excludes the groove portion and comes into contact with the blank material is defined as H in mm units, the wrinkle suppression mold may satisfy a following Expression 1 or 2, and when a protruding height of the wrinkle suppression force increasing portion is defined as G in mm units and a press stroke distance from a press-forming starting point to the press-forming ending point is defined as PS in mm units, and the protruding height G of the wrinkle suppression force increasing portion may satisfy a following Expression 3:
20≦L≦0.8×Hwhen 40≦H≦50  (Expression 1)
20≦L≦40 when 50<H≦80  (Expression 2)
0.02×PS+H−L≦G≦0.3×PS+H−L(Expression 3).

(4) In the press-forming tool according to (1) or (2), a portion of a boundary which partitions the pressure receiving portion may be the groove portion.

(5) In the press-forming tool according to any one of (1) to (4), the wrinkle suppression force increasing portion may include an elastic body which applies the reaction force.

(6) In the press-forming tool according to any one of (1) to (5), the elastic body may be at least one of a disc spring, a helical spring, and a rubber.

(7) According to another aspect of the present invention, there is provided a method for manufacturing a press-formed product which is press-formed using the press-forming tool according to any one of (1) to (6), including a step of increasing a wrinkle suppression force with respect to a portion of a blank material in an end phase of a press forming, which is started from a position at which a press stroke is 2% to 30% and which is ended at a forming end position, when a forming start position of the press stroke is defined as 100% and the forming end position of the press stroke is defined as 0% during the press forming of the blank material.

Effects of the Invention

According to the above-described aspects of the present invention, a pressure receiving portion is provided on a portion of a wrinkle suppression mold, and a wrinkle suppression force increasing portion is provided on a portion of a punch. The pressure receiving portion and the wrinkle suppression force increasing portion come into contact with each other in the end phase of the press forming, and thus, the wrinkle suppression mold is elastically deformed. As a result, the wrinkle suppression force generated from the wrinkle suppression force increasing portion is sufficiently transmitted to the portion of a blank material which is added the increased wrinkle suppression force in the end phase of press forming.

That is to say, even when the press-formed product includes an extension flange deformation region in addition to a shrinkage flange deformation region, springback of the press-formed product can be effectively decreased.

In a press-formed product which is press-formed using a press-forming tool of the related art in which the pressure receiving portion and the wrinkle suppression force increasing portion are removed from the press-forming tool, when a portion in which a plate thickness of a flange portion is thinned is defined as a plate thickness decreasing portion, according to the above-described aspects of the present invention, a portion (a portion which is added an increased the wrinkle suppression force) of a region corresponding to the plate thickness decreasing portion of the blank material and the pressure receiving portion overlap with each other when viewed along the pressing direction.

Accordingly, the wrinkle suppression force at the portion which is added the increased wrinkle suppression force is preferably increased in the end phase of the press forming. As a result, even when the press-formed product includes the extension flange deformation region in addition to the shrinkage flange deformation region, springback of the press-formed product can be further decreased.

In addition, according to the above-described aspects of the present invention, even when a metal plate, in which the springback easily occurs, such as high tensile strength steel or high strength aluminum alloy, is used as the blank material, an integral-type wrinkle suppression mold, which is a general press forming apparatus which does not include a variable die cushion device and which is not a split-type is used, and even when the press-formed product includes the extension flange deformation region in addition to the shrinkage flange deformation region, it is possible to obtain a press-formed product having high dimension accuracy.

EMBODIMENTS OF THE INVENTION

Hereinafter, each embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to only the configurations of the following embodiments, and various modifications may be applied to the present invention within a scope which does not depart from the gist of the present invention. Moreover, in the drawings used for the following description, in order to make the description easier to be understood, for convenience, a portion becoming a main portion may be shown to be enlarged, and it is not limited that a dimension ratio of each component or the like is the same as the actual condition.

FIGS. 1A and 1Bare views showing a schematic configuration of a press-forming tool according to a first embodiment of the present invention.FIG. 1Ais a perspective view showing the entirety thereof andFIG. 1Bis a plan view of a punch configuring the press-forming tool. InFIG. 1A, a reference numeral1indicates the press-forming tool according to the present embodiment.

The press-forming tool1according to the present embodiment includes a punch10, a die20, and wrinkle suppression molds25aand25b. The punch10includes a punch portion12and a plate portion14configured to transfer a shape to a blank material. The punch portion12and the plate portion14are fixed to each other by a fastening member (not shown) and become the punch10. Alternatively, the punch portion12and the plate portion14may integrally form the punch10.

As shown inFIG. 1B, wrinkle suppression force increasing portions16aand16bare disposed on a surface of the plate portion14opposing the wrinkle suppression molds25aand25b. The wrinkle suppression force increasing portions16aand16bprotrude toward the wrinkle suppression molds25aand25band generate a reaction force in a direction opposite to a pressing direction when the wrinkle suppression force increasing portions are pressed in the pressing direction in the end phase of press forming.

The die20is paired with the punch10and is disposed so as to oppose the punch portion12. The wrinkle suppression molds25aand25bare disposed between the punch10and the die20. The wrinkle suppression molds25aand25baccording to the present embodiment are constituted of the minimum number of components, which is difficult to divide it further, from the viewpoint of a structure of a press mold and a shape of a press-formed product. That is to say, the wrinkle suppression molds25aand25bare not split-type wrinkle suppression molds but integral-type wrinkle suppression molds.

The wrinkle suppression molds25aand25binclude first surfaces31aand31bwhich oppose the plate portion14of the punch10and which come into contact with the plate portion14at a press-forming ending point. In addition, the wrinkle suppression molds25aand25binclude second surfaces32aand32bwhich oppose the die20and which hold the blank material along with the die20.

A side surface (third surface)33awhich is continuous between the first surface31aand the second surface32aoppose the punch portion12via a predetermined gap (clearance). Similarly, a side surface (third surface)33bwhich is continuous between the first surface31band the second surface32boppose the punch portion12via a predetermined gap (clearance). By setting the gap appropriately, occurrence of wrinkles of the press-formed product or cracks of the press-formed product can be preferably prevented. The setting of the gap may be determined according to a routine procedure.

FIG. 2is a perspective view when the wrinkle suppression molds25aand25bare viewed from the first surfaces31aand31bsides. As shown inFIG. 2, the wrinkle suppression molds25aand25binclude pressure receiving portions (groove portions)30aand30b, which receive the reaction force to elastically deform the wrinkle suppression molds25aand25bin the end phase of the press forming, on the first surfaces31aand31b. In the press-forming tool1according to the present embodiment, each of the pressure receiving portions30aand30bis formed of a groove portion. In the end phase of the press forming, the wrinkle suppression force increasing portions16aand16bcome into contact with the pressure receiving portions30aand30band are pressed in the pressing direction. If the reaction force is generated in a direction opposite to the pressing direction, the wrinkle suppression molds25aand25breceive the reaction force and are elastically deformed.

FIGS. 3A and 3Bare explanatory views schematically showing the movements of the punch10, the die20, and the wrinkle suppression molds25aand25bwhen the blank material5is press-formed.FIG. 3Ais a perspective view when the press forming starts, andFIG. 3Bis a perspective view during the press forming.

A blank material5is disposed on the second surfaces32aand32bof the wrinkle suppression molds25aand25bin a state where the second surfaces32aand32bof the wrinkle suppression molds25aand25band a tip surface13of the punch portion12are flush with each other.

As shown inFIG. 3A, the die20is lowered in the pressing direction, and a flange portion of the blank material5is held by a constant load by the die20and the wrinkle suppression molds25aand25b.

Moreover, as shown inFIG. 3B, in the state where the blank material5is held by the die20and the wrinkle suppression molds25aand25b, the die20moves in the pressing direction, that is to say, a direction of the plate portion14of the punch10(downward inFIG. 3B), and thus, the press forming of the blank material5is performed by the punch portion12.

At a predetermined position in the end phase of the press forming, the pressure receiving portions30aand30bprovided on the first surfaces31aand31bof the wrinkle suppression molds25aand25bcome into contact with the wrinkle suppression force increasing portions16aand16b. Moreover, the pressure receiving portions30aand30bpress the wrinkle suppression force increasing portions16aand16bin the pressing direction in conjunction with the press forming from the predetermined position of the end phase of the press forming to the press-forming ending point.

As a result, the reaction force in the direction opposite to the pressing direction is generated from the wrinkle suppression force increasing portions16aand16b. The pressure receiving portions30aand30breceive the reaction force, and the wrinkle suppression force with respect to the blank material5in the end phase of the press forming is increased.

FIGS. 4A and 4Bare vertical cross-sectional views showing when a plurality of disc springs overlap with each other as the wrinkle suppression force increasing portions.FIG. 4Ashows a state where the wrinkle suppression force is not increased, andFIG. 4Bshows a state where the wrinkle suppression force is increased.

As shown inFIG. 4A, the wrinkle suppression force increasing portion16aincludes a pin40aand a disc spring42a. In this way, the wrinkle suppression force increasing portion16aincludes an elastic body which applies the reaction force. In the present embodiment, 12 disc springs42apile in parallel and in series. However, the number and arrangement of the disc springs42aare not limited to this. For example, 4 disc springs42amay pile in series. Although it is not shown, the wrinkle suppression force increasing portion16bis similar to the above-described configuration.

Instead of the disc spring42a, an elastic body such as a helical spring or a rubber may be used. It is preferable that the disc spring42ais used since it is possible to obtain a high load even by a low stroke.

As shown inFIG. 4B, the pressure receiving portion30aprovided on the first surface31aof the wrinkle suppression mold25apresses the pin40ain the pressing direction, and thus, the disc spring42ais compressed. The wrinkle suppression mold25areceives the reaction force in the direction opposite to the pressing direction from the disc spring42a.

As a result, the reaction force is transmitted to the blank material5which is held between the second surface32aof the wrinkle suppression mold25aand the die20, and thus, the wrinkle suppression force with respect to the blank material5can be increased in the end phase of the press forming.

The wrinkle suppression mold25awhich receives the reaction force from the disc spring42aincludes the pressure receiving portion30awhich is constituted of a groove portion, and thus, the wrinkle suppression mold25ais convexly and elastically deformed to the blank material5side and is bent. That is to say, when viewed along the pressing direction, a portion which is convexly and elastically deformed on the second surface32acorresponding to the pressure receiving portion30aeffectively transmits the reaction force to the blank material5. Here, the pressure receiving portion30ais formed on the first surface31aof the wrinkle suppression mold25a.

If the wrinkle suppression mold25adoes not include the pressure receiving portion30a, the reaction force from the disc spring42ais distributed to the entire wrinkle suppression mold25a. Accordingly, since the reaction force cannot be locally applied to the blank material5, the transmission efficiency of the reaction force is decreased.

FIG. 5is a view explaining a thickness of the wrinkle suppression mold25a, and is a vertical cross-sectional view when the wrinkle suppression mold25ais viewed from an arrow I direction shown inFIG. 2. As shown inFIG. 5, the thickness of the wrinkle suppression mold25aon the pressure receiving portion30awhich is constituted of a groove portion is defined as L in mm units. Moreover, the thickness of the wrinkle suppression mold25aon the region which excludes the pressure receiving portion30aand which comes into contact with the blank material5is defined as H in mm units.

In the press-forming tool1according to the present embodiment, the thickness H is constant. However, when the thickness is not constant, the minimum value of the thickness on the region which excludes the pressure receiving portion30aand comes into contact with the blank material5may be set to H. For example, as the case where the thickness H is not constant, there is a case where a press-formed product in which the height of the flange surface is not constant is formed, as shown inFIG. 27.

The lower limit of the thickness L is preferably set to 20 mm. If the thickness L is less than 20 mm, the wrinkle suppression mold25amay be plastically deformed or damaged during drawing and bending processing (during press forming).

On the other hand, in the case of 40≦H≦50, the upper limit of the thickness L is preferably set to 0.8×H. If the thickness L exceeds 0.8×H, even when the pressure receiving portion30areceives the reaction force from the wrinkle suppression force increasing portion16a, the wrinkle suppression mold25ais not elastically deformed, and thus, the reaction force may not be effectively transmitted to the blank material5.

In the case of 40≦H≦50, the preferable upper limit of the thickness L is 0.6×H. If the upper limit of the thickness L is 0.6×H, even when capability of the wrinkle suppression force increasing portion16ais small, the reaction force generated by the wrinkle suppression force increasing portion16acan be effectively transmitted to the blank material5.

In the case of 50<H≦80, the upper limit of the thickness L is preferably set to 40 mm regardless of the thickness H. The maximum value of the reaction force, which is received from the wrinkle suppression force increasing portion16ato the pressure receiving portion30a, is 6.5 MPa. Accordingly, if the thickness L exceeds 40 mm, stiffness of the pressure receiving portion30ais increased, and the wrinkle suppression mold25may not be elastically deformed even by the maximum value of the reaction force.

If the thickness H is less than 40 mm, the stiffness of the entire wrinkle suppression mold25ais not sufficient. On the other hand, if the thickness H exceeds 80 mm, the stiffness of the wrinkle suppression mold25ais increased more than necessary, and a material cost of the wrinkle suppression mold25ais also increased.

In summary about the thicknesses of the wrinkle suppression mold25a, a relationship between the thickness L and the thickness H preferably satisfies the relationship of the following Expression 1 or 2. Moreover, although it is not shown, the wrinkle suppression mold25bis also similar to the above.
20≦L≦0.8×Hwhen 40≦H≦50  (Expression 1)
20≦L≦40 when 50<H≦80  (Expression 2)

The reaction force from the wrinkle suppression force increasing portion16ais generated from contacting the pressure receiving portion30aprovided on the wrinkle suppression mold25awith the pin40a, until the pressure receiving portion30areaches the press-forming ending point. The position of contacting the pressure receiving portion30aprovided on the wrinkle suppression mold25awith the pin40amay be a predetermined position in the end phase of the press forming. The position of contacting the pressure receiving portion30awith the pin40amay be controlled by changing the protruding length (height) of the tip of the pin40afrom the surface of the plate14.

As shown inFIG. 4A, a protruding height G of the tip of the pin40afrom the surface of the plate14may be a height which adds a groove depth (a value which is obtained by subtracting L from H) of the pressure receiving portion30awhich is constituted of a groove portion and a distance from the surface of the plate portion14to the above-described predetermined position which is added the increased wrinkle suppression force in the end phase of the press forming.

The protruding height of the tip of the pin40aof the wrinkle suppression force increasing portion16afrom the surface of the plate14is defined as G in mm units. A press stroke distance from a press-forming starting point, which is a press stroke position at which the plastic deformation of the blank material5starts, to the press-forming ending point is defined as PS in mm units. At this time, the protruding height G of the wrinkle suppression force increasing portion16amay preferably satisfy the following Expression 3. Moreover, although it is not shown, the wrinkle suppression force increasing portion16bis also similar to the above.
0.02×PS+H−L≦G≦0.3×PS+H−L(Expression 3)

The protruding height G of the pin40ais preferably equal to or more than a value which adds the groove depth (H−L) of the pressure receiving portion30ato 2% of the press stroke distance PS (0.02×PS). That is to say, the interval of the press stroke which increase the wrinkle suppression force in the end phase of the press forming is preferably equal to or more than 2% of the press stroke distance PS.

If the protruding height G is less than the value (0.02×PS+H−L), the increase of the wrinkle suppression force is not sufficient, and the effects which is exerted by decreasing the springback may be unstable. In order to further decrease the springback, the value of the protruding height G is preferably equal to or more than (0.05×PS+H−L).

On the other hand, it is preferable that the protruding height G of the pin40abe less than or equal to a value which adds the groove depth (H−L) of the pressure receiving portion30ato 30% of the press stroke distance PS (0.3×PS). That is to say, the interval of the press stroke which increases the wrinkle suppression force in the end phase of the press forming is preferably less than or equal to 30% of the press stroke distance PS.

If the protruding height G exceeds the value (0.3×PS+H−L), since the interval of increasing the wrinkle suppression force becomes too long, a difference in the wrinkle suppression force becomes smaller between the press-forming starting point and the press-forming ending point. Accordingly, the effect which is exerted by increasing the wrinkle suppression force is decreased only in the end phase of the press forming is decreased, and thus, the springback may occur to the contrary. In order to further decrease the springback, the value of the protruding height G is preferably less than or equal to (0.15×PS+H−L).

So far, it is mainly described regarding the wrinkle suppression mold25aand the wrinkle suppression force increasing portion16a. However, the wrinkle suppression mold25band the wrinkle suppression force increasing portion16aare similar to the above.

FIGS. 6A and 6Bshow the press-formed product which is formed by the press-forming tool1according to the present embodiment.FIG. 6Ais a perspective view, andFIG. 6Bis a vertical cross-sectional view when viewed from an arrow A direction inFIG. 6A. InFIGS. 6A and 6B, a reference numeral50indicates the press-formed product.

The press-formed product50includes flange portions54aand54b, vertical wall portions55aand55b, and a top portion55c. Moreover, straight side portions51aand51band a bent portion52interposed between the straight side portions51aand51bare provided on both ends of the press-formed product50.

When viewed from the cross section perpendicular to the longitudinal direction, the press-formed product50has a so-called hat-shaped cross section, and both ends in the longitudinal direction of the press-formed product50are opened. Here, when viewed from an arrow A direction inFIG. 6A, the hat-shaped cross section is a shape which includes the top portion55cprovided on the center portion in the width direction, the vertical wall portions55aand55bprovided to be inclined from both ends of the top portion55ctoward one surface side of the top portion55c, and the flange portions54aand54bprovided to be parallel with the top portion55cfrom the tips of the vertical wall portions55aand55b.

When the press forming is performed, according to the shape of the press-formed product50, it is generated that a portion in which a plastic flow of the blank material5is easily occurred and a portion in which the plastic flow is not easily occurred. According to a difference in ease of the generation of the plastic flow, non-uniformity of residual stress in a plate thickness direction or an in-plane direction of the press-formed product50occurs.

Moreover, due to the non-uniformity of the residual stress, for example, springback such as warpage, twist, or waviness of the vertical wall portions55aand55boccurs on the press-formed product50. Particularly, when the shape of the press-formed product50has a curved portion, shrinkage flange deformation or extension flange deformation is applied in the longitudinal direction of the press-formed product50. Accordingly, the non-uniformity of the residual stress in the plate thickness direction or the in-plane direction is increased.

In general, after the drawing and bending processing is performed, finishing processing (restriking processing) is performed to the press-formed product50. According to the restriking processing, when the press-formed product50is processed to the shape of a press-formed product57shown inFIGS. 16A and 16Bdescribed below, remarkable waviness occurs on the vertical wall portion55aor the like of the bent portion52.

In order to decrease dimension accuracy defects of the press-formed product57, in general, an advanced estimation of a deformation amount generated by the springback into mold dimensions at the time of design is often performed. However, when the springback is waviness, it is difficult to estimate the deformation amount in advance.

In addition, since correction of the mold in order to solve the waviness of the press-formed product57includes trial and error, a lot of time and costs are required for the correction of the mold.

The waviness is generated since the vertical wall portion55aof the bent portion52becomes the extension flange deformation region by the drawing and bending processing (press forming). Accordingly, tensile stress in the longitudinal direction of the press-formed product50is increased, and the non-uniformity of the residual stress in the plate thickness direction or the in-plane direction of the press-formed product50is promoted.

Due to the non-uniformity of the residual stress of the press-formed product after drawing and bending processing50, waviness occurs on the press-formed product after restriking processing57. Accordingly, in order to remove the waviness of the bent portion52, the wrinkle suppression force applied to the bent portion52is preferably increased in the end phase of the press forming of the draw-bending processing.

In order to increase the wrinkle suppression force applied to the bent portion52in the end phase of the press forming compared to the straight side portions51aand51b, as shown inFIGS. 1A to 2, the pressure receiving portion30ais provided on the wrinkle suppression mold25aand the pressure receiving portion30bis provided on the wrinkle suppression mold25b. In order to elastically deform the wrinkle suppression molds25aand25bin the end phase of the press forming, the wrinkle suppression force increasing portions16aand16bare disposed on the plate portion14.

As described above, the wrinkle suppression force is increased in the end phase of the press forming, and thus, tension of the vertical wall portion55aof the bent portion52, which is the region in which the extension flange deformation occurs, is increased. As a result, the non-uniformity of the residual stress in the plate thickness direction or the in-plane direction, which occurs the springback, of the press-formed product50is decreased.

The region in which the shrinkage flange deformation occurs is also similar to the above. That is to say, as described above, the wrinkle suppression force is increased in the end phase of the press forming, and thus, tension of the vertical wall portion55bof the bent portion52which is the region in which the shrinkage flange deformation occurs is also increased. As a result, the springback at the region in which the shrinkage flange deformation occurs is also decreased.

When the pressure receiving portions30aand30bare not provided on the wrinkle suppression molds25aand25b, the wrinkle suppression molds25aand25bare not elastically deformed. The reaction force from the wrinkle suppression force increasing portions16aand16bis distributed on the entire wrinkle suppression molds25aand25b. Accordingly, the wrinkle suppression force cannot be locally increased on the bent portion52in the end phase of the press forming, and thus, the wrinkle suppression force needed in the bent portion52cannot be applied.

As a result, tension which is necessary to suppress the springback cannot be applied on the vertical wall portions55aand55bof the bent portion52. Accordingly, effects which is exerted by decreasing the springback of the press-formed product50are significantly decreased.

In order to decrease the distribution of the reaction force from the above-described wrinkle suppression force increasing portions16aand16bby increasing capability of the wrinkle suppression force increasing portions16aand16b, for example, it is necessary to increase the diameter of the disc spring42aor increase the number of the disc springs42. In this case, the sizes of the wrinkle suppression force increasing portions16aand16bare increased.

On the other hand, in order to press-form a metal plate having a large plastic flow resistance and large springback such as high tensile strength steel or high strength aluminum alloy, since the shape of the press-formed product50is curved, it is particularly necessary to increase the wrinkle suppression force in the end phase of the press forming on the region in which the extension flange deformation or the shrinkage flange deformation occurs, or the like.

Accordingly, when the high tensile strength steel, the high strength aluminum alloy, or the like is press-formed, and in the case of decreasing the distribution of the reaction force by increasing the capability of the wrinkle suppression force increasing portions16aand16b, it is necessary to significantly increase the sizes of the wrinkle suppression force increasing portions16aand16b. Accordingly, it is difficult to dispose the wrinkle suppression force increasing portions16aand16bon the press-forming tool1.

Next, a press-forming tool according to a second embodiment of the present invention will be described.FIGS. 7A and 7Bare views showing a schematic configuration of the press-forming tool according to the second embodiment of the present invention.FIG. 7Ais a perspective view showing the entirety thereof andFIG. 7Bis a plan view of a punch configuring the press-forming tool.

FIG. 8is a perspective view of a wrinkle suppression mold of the press-forming tool according to the present embodiment when viewed from a first surface side.

A press-forming tool2of the present embodiment is the same as the press-forming tool1of the first embodiment except that only the wrinkle suppression force increasing portion16bis provided on the plate14, the pressure receiving portion30bformed of a groove portion is disposed only on the wrinkle suppression mold25b, and a wrinkle suppression mold25edoes not include the pressure receiving portion.

In the press-forming tool2according to the present embodiment, the wrinkle suppression force with respect to the blank material5can be increased only on the region (only the portion which is particularly added the increased wrinkle suppression force) in which the extension flange deformation occurs. That is to say, when the tensile strength of the blank material5is not so high, each of the pressure receiving portion30band the wrinkle suppression force increasing portion16bmay be disposed according to curvature or the like of the bent portion52of the press-formed product50.

Next, a press-forming tool according to a third embodiment of the present invention will be described.FIGS. 9A and 9Bare views showing a schematic configuration of the press-forming tool according to the third embodiment of the present invention.FIG. 9Ais a perspective view showing the entirety thereof andFIG. 9Bis a plan view of a punch configuring the press-forming tool.

A press-forming tool3according to the present embodiment is the same as the press-forming tool1according to the first embodiment except that wrinkle suppression force increasing portions16a,16b,16c,16d,16e, and16fare disposed on the plate portion14.

Moreover, the wrinkle suppression molds25aand25bof the press-forming tool3according to the present embodiment shown inFIG. 9Aare the same as the wrinkle suppression molds25aand25bof the press-forming tool1according to the first embodiment shown inFIG. 2.

As shown inFIGS. 9A and 9B, the press-forming tool3according to the present embodiment includes the wrinkle suppression force increasing portions16cto16fin addition to the wrinkle suppression force increasing portions16aand16bwhich come into contact with the pressure receiving portions30aand30bin the end phase of the press forming. Accordingly, it is possible to precisely control the wrinkle suppression force with respect to the blank material5in the end phase of the press forming.

However, compared to the wrinkle suppression force increasing portions16aand16bwhich come into contact with the pressure receiving portions30aand30b, in the wrinkle suppression force increasing portions16cto16fwhich come into contact with the first surfaces31aand31bnot the pressure receiving portions30aand30b, the effect which is exerted by increasing the wrinkle suppression force with respect to the blank material5is smaller. That is to say, whether or not disposing the wrinkle suppression force increasing portions16cto16fwhich come into contact with the first surface31aand31b, which is not the pressure receiving portions30aand30b, may be determined according to the shape of the press-formed product or the structure of the press mold.

Next, a press-forming tool according to a fourth embodiment of the present invention will be described.FIGS. 10A and 10Bare views showing a schematic configuration of the press-forming tool according to the fourth embodiment of the present invention.FIG. 1OA is a perspective view showing the entirety thereof andFIG. 10Bis a plan view of a punch configuring the press-forming tool.

FIG. 11is a perspective view when a wrinkle suppression mold of the press-forming tool according to the fourth embodiment is viewed from a first surface side.FIG. 12is a view explaining the wrinkle suppression mold according to the present embodiment and is a vertical cross-sectional view of the wrinkle suppression mold when viewed from an arrow C direction shown inFIG. 11.

A press-forming tool4according to the present embodiment is the same as the press-forming tool1according to the first embodiment except that the pressure receiving portions30cand30dof the wrinkle suppression molds25cand25dinclude groove portions35cand35dand the groove portions35cand35d, become a portion of the boundary portion and partition the pressure receiving portions30cand30d.

In addition, the punch10according to the present embodiment shown inFIG. 10Bis the same as the punch10according to the first embodiment.

The wrinkle suppression molds25cand25daccording to the present embodiment are constituted of the minimum number of components which is difficult to divide it further, from the viewpoint of the structure of the press mold and the shape of the press-formed product. That is to say, the wrinkle suppression molds25cand25dare not split-type wrinkle suppression molds but integral-type wrinkle suppression molds.

The wrinkle suppression molds25cand25dinclude first surfaces31cand31dwhich oppose the plate portion14of the punch10and come into contact with the plate portion14at the press-forming ending point. In addition, the wrinkle suppression molds25cand25dincludes second surfaces32cand32dwhich oppose the die20and hold the blank material5along with the die20.

In the wrinkle suppression molds25cand25d, the pressure receiving portions30cand30dwhich receive the reaction force for elastically deforming the wrinkle suppression molds25cand25din the end phase of the press forming are provided on the first surfaces31cand31d. The pressure receiving portions30cand30dinclude the groove portions35cand35d. The groove portions35cand35dbecome a portion of the boundary portion, and the pressure receiving portions30cand30dare partitioned on the first surfaces31cand31d.

Specifically, as shown inFIG. 11, the pressure receiving portions30cand30dare partitioned by the groove portions35cand35dand partial edges of the first surfaces31cand31don the first surfaces31cand31d.

In the end phase of the press forming, the pressure receiving portions30cand30dand the wrinkle suppression force increasing portions16aand16bcome into contact with each other, and thus, the wrinkle suppression molds25cand25dare elastically deformed. As a result, it is possible to locally add the wrinkle suppression force to the portion of the blank material5which is added the increased wrinkle suppression force.

Accordingly, the wrinkle suppression force in the shrinkage flange deformation region or the extension flange deformation region can be locally increased in the end phase of the press forming, and thus, it is possible to effectively suppress the springback.

In the end phase of the press forming, the wrinkle suppression molds25cand25dreceive the reaction force from the wrinkle suppression force increasing portions16aand16bby the pressure receiving portions30cand30d, the wrinkle suppression molds25cand25dinclude the groove portions35cand35d. Accordingly, the reaction force is not distributed to the entire wrinkle suppression molds25cand25d.

If the wrinkle suppression molds25cand25dreceive the reaction force from the wrinkle suppression force increasing portions16aand16b, the wrinkle suppression molds25cand25dare convexly and elastically deformed to the die20(blank material5) side with the groove portions35cand35das the boundary portion. As a result, it is possible to locally and intensively increase the wrinkle suppression force with respect to the blank material5.

The depths, widths, or the like of the groove portions35cand35dof the present embodiment are not particularly limited. The groove portions35cand35dmay have appropriate dimensions according to the shape of the press-formed product50and the structure of the press mold4. The thickness L of each of the wrinkle suppression mold25cand25din the pressure receiving portions30cand30dexcluding the groove portions35cand35d, and the thickness H of each of the wrinkle suppression mold25cand25din the region which excludes the pressure receiving portions30cand30dand comes into contact with the blank material5are not particularly limited.

In the present embodiment, although it is shown that the aspect in which the thickness L and the thickness H are the same as each other, it is sufficient that the thickness L is 20≦L≦H. Moreover, if the thickness L satisfies 20≦L≦H, similar to the first embodiment, it is sufficient that the protruding height G of each of the wrinkle suppression force increasing portions16aand16bis 0.02×PS+H−L≦G≦0.3×PS+H−L.

The press-forming tools1to4according to the first to fourth embodiments of the present invention are described above. Next, effective positions to dispose the wrinkle suppression force increasing portions16ato16fand the pressure receiving portions30ato30dwill be described.

FIGS. 13A and 13Bare views showing a schematic configuration of a press-forming tool of the related art which does not include the pressure receiving portion and the wrinkle suppression force increasing portion.FIG. 13Ais a perspective view showing the entirety thereof, andFIG. 13Bis a plan view showing a punch configuring the press-forming tool of the related art. InFIG. 13A, a reference numeral91indicates the press-forming tool of the related art.

FIG. 14is an explanatory view showing a plate thickness distribution of a flange portion in a press-formed product when the blank material5having the plate thickness of 1.0 mm is performed drawing and bending processing (press-forming) using the press-forming tool of the related art shown inFIG. 13A.

That is to say,FIG. 14is a view showing the state of the press-formed product50after the blank material5is performed drawing and bending processing (press-forming) using the press-forming tool91shown inFIG. 13A, and is plan view when viewed along the pressing direction in a state where the die20is omitted.

InFIG. 14, the measurement results of the plate thickness of the flange portions54aand54bare shown. As shown inFIG. 14, the flange portions54aand54binclude a curved outside portion6a, a curved inside portion6b, and straight line portions6c,6d,6e, and6f.

As shown inFIG. 14, the plate thickness of the curved outside portion6ais thick. The curved outside portion6abecomes a plate thickness maximum portion in which the plate thickness is the maximum in the flange portions54aand54bof the press-formed product50. On the other hand, the plate thickness of the curved inside portion6bis thin.

In this way, in the press-formed product50which is press-formed using the press-forming tool91of the related art, the plate thicknesses in respective portions in the flange portions54aand54bare not the same as one another. The second surfaces32eand32fof wrinkle suppression molds25eand25fand the die20which hold the blank material5are flat.

Accordingly, in the wrinkle suppression mold91in which the pressure receiving portions30ato30dare not provided like the wrinkle suppression molds25eand25f, when the plate thickness of each position in the flange portions54aand54bis changed during the press forming, a portion to which the wrinkle suppression force is strongly applied and a portion to which the wrinkle suppression force is weakly applied exist.

If the magnitude of the wrinkle suppression force is changed according to the portion during the press forming, a balance in the plastic flow of the blank material5during the plastic deformation is lost. As a result, dimension accuracy of the press-formed product50after the press forming is decreased.

In order to suppress the decrease in the dimension accuracy of the press-formed product50due to the above-described coexistence of the portion to which the wrinkle suppression force is strongly applied and the portion to which the wrinkle suppression force is weakly applied, it is preferable to increase the wrinkle suppression force at the portion at which the plate thickness in the flange portions54aand54bis decreased during the press forming, in the end phase of the press forming.

Specifically, the press-forming tool91of the related art in which the pressure receiving portions30ato30dand the wrinkle suppression force increasing portions16ato16fare removed from the press-forming tools1to4is set as a reference. A region in which the plate thickness becomes the maximum in the flange portions54aand54bof the press-formed product50is defined as a plate thickness maximum portion, and a region in which the plate thickness is more than 0% and less than or equal to 97% with respect to the plate thickness maximum portion is defined as a plate thickness decreasing portion. In this case, when viewed along the pressing direction, the pressure receiving portions30ato30dof the wrinkle suppression molds25ato25dare preferably disposed to overlap with a portion of the plate thickness decreasing portion on the blank material5.

As a result, the wrinkle suppression force at the portion at which the plate thickness in the flange portions54aand54bis decreased during the press forming can be preferably increased in the end phase of the press forming. The wrinkle suppression force on the plate thickness decreasing portion, in which the plate thickness is more than 0% and less than or equal to 97% with respect to the plate thickness maximum portion, is preferably increased in the end phase of the press forming, and thus, the springback of the press-formed product50can be effectively decreased.

FIG. 15is an explanatory view exemplifying preferable positions at which the pressure receiving portion and the wrinkle suppression force increasing portion are disposed in the view showing the plate thickness distribution of the flange portion in the press-formed product which is formed by the press-forming tool of the related art shown inFIG. 13A. That is to say, as an example,FIG. 15is an explanatory view in which the disposition positions of the pressure receiving portions30band30dand the wrinkle suppression force increasing portion16bare overlapped inFIG. 14.

As shown inFIG. 15, the pressure receiving portions30band30dare preferably disposed so that a portion of the curved inside portion6b(the portion which becomes the plate thickness decreasing portion having the plate thickness of more than 0% and less than or more than 97% with respect to the plate thickness maximum portion) overlaps with the curved outside portion6a(the portion which becomes the plate thickness maximum portion in the flange portions54aand54bof the press-formed product50press-formed by the press-forming tool91of the related art).

The wrinkle suppression force increasing portion16bis preferably disposed such that the wrinkle suppression force increasing portion16bprotrudes toward the pressure receiving portions30band30d, and generate the reaction force opposite to the pressing direction when the wrinkle suppression force increasing portion is pressed in the pressing direction, and elastically deform the wrinkle suppression molds25band25d.

As a result, it is possible to preferably increase the wrinkle suppression force of the curved inside portion6bin which the plate thickness is decreased in the flange portions54aand54bduring the press forming, in the end phase of the press forming.

In this way, by disposing the pressure receiving portions30band30dand the wrinkle suppression force increasing portions16b, the wrinkle suppression molds25band25dare convexly and elastically deformed to the blank material5side by the pressure receiving portions30band30din the end phase of the press forming, and thus, it is possible to locally and intensively increase the wrinkle suppression force on the curved inside portion6b.

The press-forming tools according to each aspect of the present invention described above are summarized as follows.

(1) The press-forming tools1to4according to each aspect of the present invention include the punch10which includes the punch portion12and the plate portion14configured to transfer a shape to the blank material5, the die20which is paired with the punch10and opposes the punch portion12, and wrinkle suppression molds25ato25d.

The wrinkle suppression molds25ato25dinclude the first surfaces31ato31d, the second surfaces32ato32d, and the side surfaces (third surfaces)33aand33bwhich are continuous between the first surface31ato31dand the second surface32ato32dand which oppose the punch portion12. The wrinkle suppression molds25ato25dare disposed between the side surfaces (third surfaces)33aand33band the punch portion12via a gap.

The first surfaces31ato31doppose the plate portion14and come into contact with the plate portion14at the press-forming ending point. The second surfaces32ato32doppose the die20and hold the blank material5along with the die20.

The press-forming tools1to4according to each aspect of the present invention include: pressure receiving portions30ato30dwhich include the groove portion, which receives the reaction force to elastically deform the wrinkle suppression molds25ato25din the end phase of the press forming, on the first surfaces31ato31dof the wrinkle suppression molds25ato25d; and wrinkle suppression force increasing portions16aand16bwhich are disposed on surfaces opposing the first surfaces31ato31dof the plate portion14, protrude toward the pressure receiving portions30ato30d, and generate the reaction force in a direction opposite to the pressing direction when the wrinkle suppression force increasing portions are pressed in the pressing direction in the end phase of press forming.

(2) Based on a case where the pressure receiving portions30ato30dand the wrinkle suppression force increasing portions16aand16bare removed from the press-forming tools1to4, the region in which the plate thickness is maximum in the flange portions54aand54bof the press-formed product50is defined as the plate thickness maximum portion. The region in which the plate thickness is more than 0% and less than and equal to 97% with respect to the plate thickness maximum portion is defined as the plate thickness decreasing portion. In this case, the pressure receiving portion30ato30dmay overlap with a portion of the region corresponding to the plate thickness decreasing portion in the blank material5when viewed along the pressing direction.

(3) The pressure receiving portions30aand30bis constituted of a groove portion, the thickness of each of the wrinkle suppression molds25aand25bin the positions of the pressure receiving portions (groove portions)30aand30bis defined as L in mm units. The minimum value of the thickness of each of the wrinkle suppression molds25aand25bin the position which excludes the pressure receiving portions (groove portions)30aand30band comes into contact with the blank material5is defined as H in mm units. In this case, each of the wrinkle suppression molds25aand25bmay satisfy the following Expressions 1 and 2, and when the protruding height of each of the wrinkle suppression force increasing portions16aand16bfrom the surface of the plate portion14is defined as G in mm units and the press stroke distance from the press-forming starting point to the press-forming ending point is defined as PS in mm units, the protruding height G of each of the wrinkle suppression force increasing portions16aand16bmay satisfy the following Expression 3.
20≦L≦0.8×Hwhen 40≦H≦50  (Expression 1)
20≦L≦40 when 50<H≦80  (Expression 2)
0.02×PS+H−L≦G≦0.3×PS+H−L(Expression 3)

(4) A portion of the boundary which partitions the pressure receiving portions30cand30dmay be the groove portions35cand35d. Specifically, the pressure receiving portions30cand30dmay include the groove portions35cand35d, the groove portions35cand35dbecome a portion of the boundary portion, and thus, the pressure receiving portions30cand30dmay be partitioned on the first surfaces31cand31d.

(5) The wrinkle suppression force increasing portions16aand16bmay include an elastic body which applies the reaction force.

(6) The elastic body may be at least one of the disc spring42a, a helical spring, and rubber.

Next, a method for manufacturing the press-formed product50which is press-formed using the press-forming tools1to4according to the embodiments of the present invention will be described.

A method for manufacturing the press-formed product50according to an aspect of the present invention, including: a step of increasing the wrinkle suppression force with respect to a portion of the blank material5during the press forming in the end phase of the press forming from the position at which the press stroke is 2% to 30% to the forming end position using the press-forming tools1to4according the above-described aspects, and when the forming start position of the press stroke when the blank material5is press-formed is defined as 100% and the forming end position of the press stroke is defined as 0%.

According to the method of manufacturing the press-formed product50, the springback is suppressed, and thus, the press-formed product50having high dimension accuracy can be obtained. In the method for manufacturing, if the position of the press stroke which is a starting position of increasing the wrinkle suppression force is less than 2%, the increase in the wrinkle suppression force is not sufficient, and thus, the effect which is exerted by decreasing the springback may be unstable.

On the other hand, if the position of the press stroke which is a starting position of increasing the wrinkle suppression force is more than 30%, the interval of increasing the wrinkle suppression force becomes too long. Accordingly, the difference in the wrinkle suppression force is decreased between the forming starting position of the press stroke and the forming ending position of the press stork.

Therefore, the effect which is exerted by increasing the wrinkle suppression force only in the end phase of the press forming is decreased, and thus, the springback may occur to the contrary. Moreover, in order to further decrease the springback, the position of the press stroke which is a starting position of increasing the wrinkle suppression force is preferably 5% to 15%.

Effects of the aspects of the present invention will be further described according to Examples. However, conditions of Examples are conditions adopted to confirm feasibility and effects of the present invention, and the present invention is not limited to the conditions. The present invention adopts various conditions if achieving the object of the present invention without departing from the gist of the present invention.

The blank material5was obtained by laser-cutting the high tensile strength steel sheet in a predetermined shape. The blank material5was performed drawing and bending processing (press-forming) so that the shape became a hat-shaped cross section. Moreover, after the drawing and bending processing, the blank material was performed finishing processing (restriking processing). Conditions or the like for each process are described below.

The high tensile strength steel sheet having 1.0 mm in the plate thickness and 590 MPa in the tensile strength was used as the material, the high tensile strength steel sheet was laser-cut so that the shape after the finishing processing (restriking processing) became a cross-section width of 60 mm and a height of 80 mm as shown inFIGS. 16A and 16B, and thus, the blank material5was obtained.

The blank material5was performed drawing and bending processing (press-forming) to have the shape (hat-shaped cross section) shown inFIGS. 6A and 6Busing the press-forming tool1FIGS. 1A to 2(the press-forming tool1according to the first embodiment), the press-forming tool2shown inFIGS. 7A to 8(the press-forming tool2according to the second embodiment), and the press-forming tool3shown inFIGS. 9A and 9B(the press-forming tool3according to the third embodiment).

As the wrinkle suppression force increasing portions16ato16f, the disc spring unit which is a combination of disc springs42ashown inFIG. 4Awas used. The load (reaction force) to which the wrinkle suppression force increasing portions16ato16fwere applied to the wrinkle suppression molds25aand25bin the end phase of the press forming and were changed according to the number and the combination method (parallel, series, and parallel series) of the disc springs42a.

In the press-forming tool3(the press-forming tool3according to the third embodiment) shown inFIGS. 9A and 9B, in addition to the pressure receiving portions30aand30b, the wrinkle suppression force increasing portions16cto16fwere disposed.

The thicknesses H of the wrinkle suppression molds25aand25bon the region which exclude the pressure receiving portions30aand30band come into contact with the blank material5, the thicknesses L of the wrinkle suppression molds25aand25bon the pressure receiving portion30aand30b, and the thickness ratio L/H are shown in Table 1.

The load (reaction force) of the wrinkle suppression force increasing portions16ato16fapplied to the wrinkle suppression molds25aand25bare also shown in Table 1. The load is indicated in the total value of the loads of the disc spring unit disposed on the press-forming tools1to3.

For example, the press-forming tool3shown inFIGS. 9A and 9Bwas used in the Example of the present invention No. 6. In this case, six wrinkle suppression force increasing portions16ato16fare disposed. The load (reaction force) which is applied to the wrinkle suppression molds25aand25bby one disc spring unit in the wrinkle suppression force increasing portions16ato16fis 100 kN. Accordingly, the total of the loads (reaction forces) is 600 kN (100 kN×6).

In Conventional Example No. 14, the press-forming tool91shown inFIGS. 13A and 13B, which did not have the pressure receiving portions30aand30band the wrinkle suppression force increasing portions16ato16f, was used. In Reference Example 1, the press-forming tool1in which the thickness H and the thickness L of the wrinkle suppression molds25aand25bwere the same as each other was used.

That is to say, the press-forming tool1used in the Reference Example 1 was a press-forming tool in which the wrinkle suppression molds25eand25fwhich did not have the pressure receiving portion and the punch10which had the wrinkle suppression force increasing portions16aand16bwere combined.

The drawing and bending processing (press forming) was performed using a press forming apparatus having a capability of 1960 kN (200 tons). Press forming was performed until the height of the press-formed product50became 60 mm as shown inFIG. 6Bwhile 196 kN (20 tons) in the wrinkle suppression load (total value of the loads applied to the wrinkle suppression molds25aand25b) was applied. Conventional Example No. 14 was also performed similarly.

The press forming apparatus used was a general press forming apparatus which did not have a variable die cushion device or the like.

In No. 1 to No. 10 in the Examples of the present invention and the Reference Examples, the increase in the wrinkle suppression force in the end phase of the press forming started from the height of 9 mm before the press-forming ending point. That is to say, the protruding height G of each of the wrinkle suppression force increasing portions16aand16bcoming into contact with the pressure receiving portions30aand30bin the end phase of the press forming was set to the value which added 9 mm to the depth (H-L) of each of the pressure receiving portions30aand30b.

The press stroke distance PS from the press-forming starting point to the press-forming ending point was 60 mm. That is to say, when the forming start position of the press stroke was defined as 100% and the forming end position of the press stroke was defined as 0% during the press-forming of the blank materials, the position of the press stroke which is a starting position of increasing the wrinkle suppression force was positioned at the position of 15%.

Here, the wrinkle suppression force increasing portions16aand16bcoming into contact with the pressure receiving portions30aand30bin the end phase of the press forming is described. However, in the wrinkle suppression force increasing portions16cto16fwhich did not come into contact with the pressure receiving portions30aand30bin the end phase of the press forming, the protruding height G was set to 9 mm.

In No. 11 to No. 13 in the Examples of the present invention and the Reference Examples, the increase in the wrinkle suppression force in the end phase of the press forming was controlled as follows. That is to say, as shown in Table 1, the starting position of increasing the wrinkle suppression force was controlled by setting the depth (H-L) of each of the pressure receiving portions30aand30bto be constant and changing the value of the protruding height G.

In Example No. 11 of the present invention, the increase in the wrinkle suppression force started from the height (the position in which the press stroke is 33%) of 20 mm before the press-forming ending point. In Example No. 12 of the present invention, the increase in the wrinkle suppression force started from the height (the position in which the press stroke is 2.5%) of 1.5 mm before the press-forming ending point. In Example No. 13 of the present invention, the increase in the wrinkle suppression force started from the height (the position in which the press stroke is 1.8%) of 1.1 mm before the press-forming ending point.

The finishing processing (restriking processing) was performed using the press-formed product50obtained by the above-described drawing and bending processing (press forming).

FIGS. 16A and 16Bare views showing the press-formed product after the finishing processing (restriking processing).FIG. 16Ais a perspective view andFIG. 16Bis a vertical cross-sectional view when viewed from an arrow B direction inFIG. 16A. InFIGS. 16A and 16B, a reference numeral57indicates the press-formed product after the finishing processing (restriking processing).

FIG. 17is a view showing a schematic configuration of a restriking processing mold which performs the finishing processing (restriking processing) and is a perspective view showing the entirety thereof. InFIG. 17, a reference numeral92indicates the restriking processing mold.

In the press-formed product50obtained by the drawing and bending processing (press forming), a hat portion surrounded by the vertical wall portions55aand55band the top portion55cwas fitted into the punch portion12of the restriking processing mold92, and the top portion55cwas pressed by a pad18. The finishing processing (restriking processing) was performed by the punch portion12and the die20. In the finishing processing (restriking processing), the wrinkle suppression was not performed.

The finishing processing (restriking processing) was performed using a press-forming apparatus having a capability of 1960 kN (200 tons). As shown inFIG. 16B, the restriking processing was performed until the height of the press-formed product57was 80 mm as shown inFIG. 16B. According to the finishing processing (restriking processing), the press-formed product50having the hat-shaped cross section became the press-formed product57having the shape shown inFIGS. 16A and 16B.

The press-forming apparatus used was a general press-forming apparatus which did not include the variable die cushion device or the like.

Next, an evaluation method of the springback with respect to the press-formed product50after the drawing and bending processing and the press-formed product after the finishing processing (restriking processing)57will be described.

FIG. 18is a vertical cross-sectional view perpendicular to a longitudinal direction of the press-formed product after the drawing and bending processing, and an explanatory view showing a generation state of wall warpage (springback). InFIG. 18, Whindicates the gap between the vertical wall portion55aand the vertical wall portion55bwhen the springback is not generated. Wh′ indicates the gap between the vertical wall portion55a′ and the vertical wall portion55b′ when the springback is generated. ΔWhindicates the difference between Wh′ and Wh.

Specifically, as shown inFIG. 18, when an intersection point of the vertical wall portion55aand the flange portion54ais defined as P and an intersection point of the vertical wall portion55band the flange portion54bis defined as Q, a line segment PQ is defined as Wh. Moreover, when an intersection point of the vertical wall portion55a′ and the flange portion54a′ is defined as P′ and an intersection point of the vertical wall portion55b′ and the flange portion54b′ is defined as Q′, a line segment P′Q′ is defined as Wh′.

Wh′, Wh, and ΔWhmay be obtained as follows. Coordinate values of a point group on the outer surface of the press-formed product50after the drawing and bending processing are acquired using a non-contact type CCD three-dimensional measurement apparatus. In the cross-sectional view when viewed from the arrow A direction inFIG. 6A, the gap Wh′ between the vertical wall portion55a′ and the vertical wall portion55b′ when the springback is generated is measured. The gap Wh′ is compared with the gap Whbetween the vertical wall portion55aand the vertical wall portion55bin CAD data (design shape) when the press-formed product50is designed. Accordingly, ΔWh=Wh′−Whis obtained.

Based on ΔWhobtained in the above-described way, the wall warpage (springback) after the drawing and bending processing (press forming) was evaluated according to the following reference.

Good (G): ΔWhis less than or equal to 10 mm

Not Bad (NB): ΔWhis more than 10 mm and less than 15 mm

Bad (B): ΔWhis equal to or more than 15 mm

FIG. 19is a vertical cross-sectional view perpendicular to a longitudinal direction of the press-formed product after the finishing processing (restriking processing), and an explanatory view showing a generation state of wall warpage (springback). InFIG. 19, Wcindicates the gap between the vertical wall portion55aand the vertical wall portion55bwhen the springback is not generated. Wc′ indicates the gap between the vertical wall portion55a′ and the vertical wall portion55b′ when the springback is generated. ΔWcindicates the difference between Wc′ and Wc.

Specifically, as shown inFIG. 19, when an end of the vertical wall portion55ais defined as a point R and an end of the vertical wall portion55bis defined as a point S, the line segment RS becomes Wc. Moreover, when an end of the vertical wall portion55a′ is defined as a point R′ and an end of the vertical wall portion55b′ is defined as a point S′, the line segment R′S′ becomes Wc′.

Wc′, Wc, and ΔWcmay be obtained as follows. Coordinate values of a point group on the outer surface of the press-formed product after the finishing processing (restriking processing)57are acquired using a non-contact type CCD three-dimensional measurement apparatus. In the cross-sectional view when viewed from the arrow B direction inFIG. 16A, the gap Wc′ between the vertical wall portion55a′ and the vertical wall portion55b′ when the springback is generated is measured. The gap Wc′ is compared with the gap Wcbetween the vertical wall portion55aand the vertical wall portion55bin CAD data (design shape) when the press-formed product57is designed. Accordingly, ΔWc=Wc′−Wcis obtained.

Based on ΔWcobtained in the above-described way, the wall warpage (springback) after the finishing processing (restriking processing) was performed was evaluated according to the following reference.

Good (G): ΔWcis less than or equal to 7 mm

Not Bad (NB): ΔWcis more than 7 mm and less than 15 mm

Bad (B): ΔWcis equal to or more than 15 mm

Moreover,FIG. 20is a perspective view showing the press-formed product after the finishing processing (restriking processing) and an explanatory view showing a generation state of waviness (springback). InFIG. 20, a state where waviness61occurs on a curved face60of the bent portion52of the press-formed product57is shown.

FIG. 21Ais a perspective view showing the press-formed product after the finishing processing (restriking processing) and an explanatory view showing a measurement position of the waviness (springback). The generation state of the waviness61is evaluated at a line segment62shown by a dotted line inFIG. 21A.

FIG. 21Bis a graph showing an example of the measured result of the waviness (springback). InFIG. 21B, a horizontal axis corresponds to the line segment62shown inFIG. 21Aand a vertical axis indicates the generation state (a difference between an actual measured value and a design shape value) of the waviness61.

The waviness61of the press-formed product57may be evaluated as follows. Coordinate values of a point group on the outer surface of the press-formed product after the finishing processing (restriking processing)57are acquired using a non-contact type CCD three-dimensional measurement apparatus. The measured results of the coordinate values in the line segment62in the curved face60are compared with the CAD data (design shape) when the press-formed product57is designed, and thus, the graph shown inFIG. 21Bis prepared.

An absolute value ΔYWof the difference between the maximum value and the minimum value in the graph in the curved face60is obtained as shown inFIG. 21B. The line segment62which is the measurement position of the waviness61is parallel with an intersection line formed by the top portion55cand the vertical wall portion55a(having a U shaped cross-section) of the press-formed product57, and the distance between the parallel lines is 70 mm.

Based on ΔYwobtained in this way, the waviness61(springback) after the finishing processing (restriking processing) was evaluated according to the following reference.

Very Good (VG): ΔYwis less than or equal to 3 mm

Good (G): ΔYwis more than 3 mm and less than 7 mm

Not Bad (NB): ΔYwis more than 7 mm and less than 15 mm

Bad (B): ΔYwis equal to or more than 15 mm

Evaluation results of the springback with respect to the press-formed product50after the drawing and bending processing and the press-formed product57after the finishing processing (restriking processing) are shown in Table 2. After performing the drawing and bending processing and the restriking processing, cracks were not confirmed in the press-formed product50or the press-formed product57under any conditions.

First, the evaluation result of the springback with respect to the press-formed product50after the drawing and bending processing is described. As shown in Table 2, in any one of the Examples No. 3 to No. 7 and No. 9 to No. 12 of the present invention, it was confirmed that ΔWhafter the drawing-bending processing was performed was good and the wall warpage (springback) was small.

On the other hand, in any one of Reference Examples No. 1, No. 2, No. 8, and No. 13, and Conventional Example No. 14, ΔWh, after the drawing and bending processing was performed was not better than ΔWhof the Example of the present invention.

By comparing the Examples No. 3 and No. 6 of the present invention, when only the wrinkle suppression force increasing portions16aand16bwere disposed, it was confirmed that the effect which is exerted by decreasing the springback was higher than when the wrinkle suppression force increasing portions16ato16fwere disposed. That is to say, when only the wrinkle suppression force increasing portions16aand16bwere disposed, the wrinkle suppression molds25aand25bwere remarkably bent in the end phase of the press forming, compared to when the wrinkle suppression force increasing portions16cto16fare disposed.

As a result, it could be confirmed that the springback in the press-formed product50could be further decreased.

By comparing No. 1 to No. 4 in the Examples of the present invention and the Reference Examples, it could be confirmed that the thickness H and the thickness L preferably satisfy the above-described Expressions 1 and 2. In No. 1 to No. 4, only the thickness L of each of the wrinkle suppression molds25aand25bwas changed, and other press-forming conditions were the same as one another.

In No. 1 to No. 4, the values of the protruding heights G were different from one another. However, above all, the position of the press stroke which is a starting position of increasing the wrinkle suppression force was 15% in these Examples, which was the same as one another.

Among No. 1 to No. 4, the thickness L exceeded 0.8×H in No. 1 and No. 2, and the thickness L was less than or equal to 0.8×H in No. 3 and No. 4. That is to say, in No. 3 and No. 4 which were examples satisfying Expression 1 or 2 in No. 1 to No. 4, the springback could be preferably decreased.

Here,FIGS. 22 to 25show contact pressure distributions on the second surfaces32aand32bwhen the wrinkle suppression molds25aand25breceive the reaction force from the wrinkle suppression force increasing portions16aand16bin the end phase of the press forming.

FIGS. 22 to 25correspond to No. 1 to No. 4 which are the Examples of the present invention and the Reference Examples. That is to say,FIG. 22shows the contact pressure distribution on the second surface of the wrinkle suppression mold when the thickness ratio L/H of the wrinkle suppression mold is 100%.FIG. 23shows the contact pressure distribution on the second surface of the wrinkle suppression mold when the thickness ratio L/H of the wrinkle suppression mold is 90%.FIG. 24shows the contact pressure distribution on the second surface of the wrinkle suppression mold when the thickness ratio L/H of the wrinkle suppression mold is 80%.FIG. 25shows the contact pressure distribution on the second surface of the wrinkle suppression mold when the thickness ratio L/H of the wrinkle suppression mold is 70%.

InFIGS. 22 to 25, reference numerals71,72,73, and74indicate the regions in which the contact pressures on the second surfaces32aand32bbecome the maximum values. Moreover, in the regions of the reference numerals71,72,73, and74, the contact pressures were 1.5 MPa, 2.5 MPa, 6.5 MPa, and 8.7 MPa, respectively.

As shown inFIGS. 22 to 25, when the thickness H is 50 mm, the contact pressures on the regions corresponding to portions on which the pressure receiving portions30aand30bare provided on the second surfaces32aand32bof the wrinkle suppression molds25aand25bare increased as the thickness ratio L/H is decreased. As described above, the flange portions54aand54bof the press-formed product50is held between the die20and the second surfaces32aand32bof the wrinkle suppression molds25aand25b, and the wrinkle suppression force is applied to the flange portions.

Accordingly, the portion which is particularly added the increased wrinkle suppression force on the flange portions54aand54band a portion of the region (the region on which the pressure receiving portions30aand30bare provided) in which the contact pressure is preferably increased on the second surfaces32aand32boverlap with each other when viewed along the pressing direction.

By comparing No. 4, No. 11 to No. 13 which are the Examples of the present invention and the Reference Examples, it could be confirmed that the protruding height G of each of the wrinkle suppression force increasing portions16aand16bpreferably satisfy the above-described Expression 3. In No. 4, No. 11 to No. 13, only the position of the press stroke which is a starting position of increasing the wrinkle suppression force is changed by changing the value of the protruding height G, and other press forming conditions are the same as one other.

Among No. 4, No. 11 to No. 13, in No. 11, the position of the press stroke which is a starting position of increasing the wrinkle suppression force is 33%. In No. 13, the position of the press stroke which is a starting position of increasing the wrinkle suppression force is 1.8%.

On the other hand, among No. 4, No. 11 to No. 13, in No. 4, the position of the press stroke which is a starting position of increasing the wrinkle suppression force is 15%. In No. 12, the position of the press stroke which is a starting position of increasing the wrinkle suppression force is 2.5%.

That is to say, among No. 4, No. 11 to No. 13, the protruding height G satisfies Expression 3 in No. 4 and No. 12. In this way, in No. 4 and No. 12 which are the examples satisfying Expression 3 among No. 4, No. 11 to No. 13, it could be confirmed that the springback could be preferably decreased.

On the other hand, as described above, in Reference Example No. 1 and No. 2, since the thickness L exceeded 0.8×H, the springback could not be decreased. In Reference Example No. 8, since the thickness L exceeded 40 mm, the springback could not be decreased.

As described above, in Reference Example No. 13, since the position of the press stroke which is a starting position of increasing the wrinkle suppression force was 1.8% and the increase of the wrinkle suppression force in the end phase of the press forming was not sufficient, the springback could not be decreased. In Conventional Example No. 14, since the pressure receiving portions30aand30band the wrinkle suppression force increasing portions16aand16bwere not provided, the springback could not be decreased.

Next, the evaluation method of the springback with respect to the press-formed product after the finishing processing (restriking processing)57will be described. As shown in Table 2, in any one of the Examples No. 3 to No. 7 of the present invention, it could be confirmed that No. 9 to No. 12, ΔWcand ΔYwafter the finishing processing (restriking processing) were good and the wall warpage and the waviness61were small.

It could be confirmed that the dimension accuracy of the press-formed product after the finishing processing (restriking processing)57was improved as the springback of the press-formed product after the drawing and bending processing50was decreased. This is because the tensile stress in the longitudinal direction of the press-formed product50on the vertical wall surfaces55aand55bof the bent portion52is decreased by increasing the wrinkle suppression force of the bent portion52in the end phase of the press forming in the drawing and bending processing.

As a result, the non-uniformity of the residual stress in the plate thickness direction or the in-plane direction of the press-formed product50is decreased, and thus, the dimension accuracy of the press-formed product after the finishing processing (restriking processing)57is also improved.

On the other hand, in any one of Reference Examples No. 1, No. 2, No, 8, and No. 13 and Conventional Example No. 14, ΔWcand ΔYwafter the restriking processing were not better than ΔWcand ΔYwof the Example of the present invention. In this way, if the springback of the press-formed product after the drawing and bending processing50was large, even when the finishing processing (restriking processing) was performed, it could be confirmed that the dimension accuracy of the press-formed product57was not improved.

FIG. 26is a view showing disposed positions of the pressure receiving portion and the wrinkle suppression force increasing portion of the press-forming tool. As shown inFIG. 26, the disposition positions of the pressure receiving portions30a,30b, and30gto30jand the wrinkle suppression force increasing portions16ato16fwere changed, and the blank material5was performed the drawing and bending processing (press forming).

Specifically, a high tensile strength steel sheet having 1.0 mm in the plate thickness and 590 MPa in the tensile strength was used as the material, and similar to the Example 1, the high tensile strength steel sheet was laser-cut, and thus, the blank material5was obtained. The blank material5was performed the drawing and bending processing (press forming) to have the shape (hat-shaped cross section) shown inFIGS. 6A and 6B.

Table 3 shows combinations of the disposed positions of the pressure receiving portions30a,30b, and30gto30jand the wrinkle suppression force increasing portions16ato16f. For example, the press-forming tool of Example No. 16 of the present invention is the same as the press-forming tool2of Example No. 5 of the present invention of the Example 1 except for the thickness H, the thickness L, and the thickness ratio L/H.

The load (reaction force) applied to the wrinkle suppression molds25aand25bby the disc spring unit of the wrinkle suppression force increasing portions16ato16fwas set to 150 kN. Moreover, the protruding height G was set to 19 mm. The press stroke distance PS from the press-forming starting point to the press-forming ending point was set to 60 mm. That is to say, when the forming start position of the press stroke was set to 100% and the forming end position of the press stroke was set to 0% during the press-forming of the blank material5, the position of the press stroke which is a starting position of increasing the wrinkle suppression force was set to 6.7%.

After the drawing and bending processing, the finishing processing (restriking processing) was performed. The conditions of the drawing and bending processing, the conditions of the restriking processing, and the evaluation method of the springback were similar to those of the Example 1.

The evaluation results of the springback with respect to the press-formed product after the drawing and bending processing50and the press-formed product after the finishing processing (restriking processing)57are shown in Table 4. After the drawing and bending processing and the restriking processing were performed, in any condition, cracks were not confirmed in the press-formed product50or the press-formed product57.

As shown in Table 4, in Example No. 16 of the present invention, ΔWhafter the drawing and bending processing, and ΔWcand ΔYwafter the finishing processing were good, and it could be confirmed that the springback was small.

In Example No. 16 of the present invention, the pressure receiving portion30bwas disposed so that the pressure receiving portion overlapped with a portion of the curved inside portion6bwhich becomes the plate thickness decreasing portion having the plate thickness more than 0% and less than or equal to 97% with respect to the curved outside portion6awhich becomes the plate thickness maximum portion on the flange portion54aand54bof the press-formed product50press-formed by the press-forming tool91of the related art.

That is to say, in Example No. 16 of the present invention, the wrinkle suppression force could be locally and intensively increased to the curved inside portion6bwhich is necessary to increase the wrinkle suppression force in the end phase of the press forming, which was difficult to be achieved by the press-forming tool91of the related art.

On the other hand, in any one of Reference Example No. 15 and No. 17 to No. 20, ΔWh, ΔWc, and ΔYwwere not better than Example No. 16 of the present invention. As shown in Table 4, in Reference Example No. 15 and No. 17 to No. 20, the pressure receiving portions30aand30gto30jwere disposed so that the pressure receiving portions overlapped with not the curved inside portion6bwhich becomes the plate thickness decreasing portion but at least a portion of the curved outside portion6aor the straight line portions6cto6f.

Accordingly, the wrinkle suppression force could not be increased to the curved inside portion6bwhich is necessary to increase the wrinkle suppression force in the end phase of the press forming. In general, in the press-formed product57, it is required that the dimensions on the entire region of the press-formed product57are within a permitted range.

That is to say, the press-formed product57in which the dimensions are outside the permitted range even at one site, for example, the press-formed products57of the Reference Examples No. 15 and Nos. 17 to 20 are not preferable.

As described above, if the wrinkle suppression force on the plate thickness decreasing portion which is necessary to increase the wrinkle suppression force was increased in the end phase of the press forming, it could be confirmed that the dimension accuracy of the press-formed product after the drawing and bending processing50and the press-formed product after the finishing processing (restriking processing)57could be preferably improved.

INDUSTRIAL APPLICABILITY

As described above, according to an aspect of the present invention, a pressure receiving portion is provided on a portion of a wrinkle suppression mold, and a wrinkle suppression force increasing portion is provided on a portion of a punch. The pressure receiving portion and the wrinkle suppression force increasing portion come into contact with each other in the end phase of the press forming, and thus, the wrinkle suppression mold is elastically deformed.

As a result, the wrinkle suppression force generated from the wrinkle suppression force increasing portion is sufficiently transmitted to the portion of a blank material which is added the increased wrinkle suppression force in the end phase of press forming.

That is to say, even when the press-formed product includes an extension flange deformation region in addition to a shrinkage flange deformation region, springback of the press-formed product can be effectively decreased. Accordingly, the industrial applicability thereof is high.

BRIEF DESCRIPTION OF THE REFERENCE SYMBOLS

5: blank material

6cto6f: straight line portion

14: plate portion

30cand30d: pressure receiving portion

31ato31f: first surface

32ato32f: second surface

50: press-formed product after drawing and bending processing

51aand51b: straight side portion

55c: top portion

57: press-formed product after the finishing processing (restriking processing)

62: line segment

H and L: thickness

PS: press stroke distance