JP7131076B2 - How to produce pressed products - Google Patents

Description

The present invention relates to a method of producing pressed products. More particularly, it relates to a method of producing a pressed product including a stretch flange portion by bending.

A vehicle body frame is required to have high strength. For this reason, metals such as high-strength steel plates are often used as materials for body frames. Parts forming the vehicle body frame made of such high-strength metal are formed by pressing.

The cross-sectional shape of the parts constituting the vehicle body frame is often U-shaped or hat-shaped including the top plate portion and the vertical wall portion. Also, the body frame often has a curved portion. The curved portions are, for example, the T-shaped upper and lower ends of a vertically extending center pillar of a four-wheeled vehicle. When a part having a curved portion is formed by pressing, the curved portion receives tensile stress as the material deforms. The curved portion subjected to this tensile stress is called a "stretch flange". When the stretch-flange portion is subjected to molding in which excessive tensile stress is applied, the stretch-flange portion is likely to break.

A method of producing a pressed product that suppresses breakage is disclosed, for example, in Japanese Patent Application Laid-Open No. 2017-136624 (Patent Document 1).

The method for producing a pressed product described in Patent Document 1 includes a die, a pressing member protruding from the die, a blank holder facing the die and the pressing member, and a punch facing the die and arranged outside the blank holder. The blank is bent using a press. Specifically, the blank is sandwiched between the blank holder and the pressing member. After that, the blank is bent by the pressing member and the convex portion of the die arranged outside the pressing member. Patent Literature 1 describes that this suppresses defective molding of the pressed product.

JP 2017-136624 A

However, in general, if a pressed product including a stretch flange portion is bent, wrinkles are likely to occur. In particular, wrinkles are likely to occur on the top plate of a press product having a cross-sectional shape such as a hat. If an attempt is made to suppress the occurrence of such wrinkles, breakage is likely to occur at the ends of the press product including the stretch flange portion. Therefore, in forming a press product including a stretch flange portion, it is often difficult to avoid both occurrence of wrinkles and breakage while forming a desired shape.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a pressed product having a desired shape while suppressing the occurrence of wrinkles and breakage.

In the method of producing a pressed product of the present embodiment, a pressed product including a stretch flange portion is produced by bending using a pressing device including a punch, a die facing the punch, and a pad facing the punch. A method of producing a pressed product includes a placement step, a third region constraining step, a first region pushing step, and a second region machining step. In the arranging step, a blank including a first region including the end portion of the stretch flange portion of the pressed product, a second region located inside the first region, and a third region located inside the second region Place in a press. In the third area constraining step, after the arranging step, the pad and the punch are brought close to each other, and a gap is created between the blank and the pad by the pad and the punch to constrain the third region. In the first region pushing step, after the third region constraining step, the die and the punch are brought closer together to bring the die and the first region into contact, and the die pushes the first region toward the punch side. In the second region processing step, after the first region pressing step is started, the punch and the second region are brought into contact and the die and the second region are brought into contact to process the second region with the punch and the die.

According to the method of producing a pressed product according to the present invention, it is possible to produce a pressed product having a desired shape while suppressing the occurrence of wrinkles and breakage.

FIG. 1 is a cross-sectional view showing bending. FIG. 2 is a cross-sectional view showing pad bending. FIG. 3 is a perspective view of a press product including a stretch flange portion. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. FIG. 5 is a cross-sectional view showing the press device of the first embodiment. FIG. 6 is a plan view of the blank. FIG. 7 is a cross-sectional view showing the placement process of the first embodiment. FIG. 8 is a cross-sectional view showing the third region constraining step of the first embodiment. FIG. 9 is a cross-sectional view showing the first region pressing step of the first embodiment. FIG. 10 is a cross-sectional view showing the second region processing step of the first embodiment. FIG. 11 is a cross-sectional view showing the end of the second area processing step in the first embodiment. FIG. 12 is a cross-sectional view showing the press device of the second embodiment. FIG. 13 is a cross-sectional view showing an arrangement process of the second embodiment. FIG. 14 is a cross-sectional view showing a third region constraining step of the second embodiment. 15A and 15B are cross-sectional views showing a first region pressing step according to the second embodiment. FIG. 16 is a cross-sectional view showing the second region processing step of the second embodiment. FIG. 17 is a cross-sectional view showing the end of the second region processing step of the second embodiment. FIG. 18 is a cross-sectional view showing the pressing device of the third embodiment. FIG. 19 is a cross-sectional view showing the placement process of the third embodiment. FIG. 20 is a cross-sectional view showing a third region constraining step of the third embodiment. FIG. 21 is a cross-sectional view showing a first region pressing step according to the third embodiment. FIG. 22 is a cross-sectional view showing the second region processing step of the third embodiment. FIG. 23 is a cross-sectional view showing the end of the second area processing step in the third embodiment. FIG. 24 is a perspective view of a model of the pressed product molded in this example.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same reference numerals are given to the same or corresponding parts in the drawings, and the description thereof will not be repeated.

[Bending and pad bending]
First, general bending and general pad bending are described.

FIG. 1 is a cross-sectional view showing bending. Hereinafter, "cross section" means a cross section along the pressing direction unless otherwise specified. Referring to FIG. 1, typical bending is performed by punch 101 and die 102 . Blank 10 is placed on punch 101 and die 102 is lowered. The die top 103 closest to the punch of the die contacts one end of the blank 10 . As die top 103 contacts one end of blank 10 , the other end of the blank on punch top 104 moves away from punch top 104 . Since the other end of blank 10 is away from punch top 104 , there is excess material between die 102 and punch top 104 . When the die 102 reaches the bottom dead center from this state, this surplus material becomes wrinkles. As a method for suppressing the occurrence of wrinkles due to this bending, there is pad bending.

FIG. 2 is a cross-sectional view showing pad bending. Referring to FIG. 2, typical pad bending is performed by punch 101, die 102 and pad 110. FIG. As noted above, in simple bending, the other end of blank 10 separates from punch top 104 as die top 103 begins to work one end of blank 10 . Thus, in pad bending, the pad 110 presses the punch top 104 against the other end of the blank. The die top 103 then begins working one end of the blank. Therefore, during bending, the other end of the blank does not separate from the punch top 104, thereby suppressing the occurrence of wrinkles.

However, in pad bending, blank 10 is sandwiched between punch 101 and pad 110 during forming. Therefore, in the area of the blank sandwiched between the punch 101 and the pad 110 during pad bending, material flow is suppressed. Therefore, when a pressed product including a stretch flange portion is subjected to pad bending, breakage may occur in the stretch flange portion of the blank.

[Stretch flange]
FIG. 3 is a perspective view of a press product including a stretch flange portion. FIG. 3 shows a lower end portion of a center pillar of a four-wheeled vehicle as an example of a pressed product including a stretch flange portion. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3 and 4, the cross section perpendicular to the extending direction of the center pillar 105, that is, the horizontal cross section, has a hat shape. Center pillar 105 includes top plate portion 107 , vertical wall portion 108 , and flange portion 109 . Since the lower end of the center pillar 105 is connected to the side step 106, it has a T shape. Therefore, the lower end of the center pillar 105 is curved substantially at right angles. During the molding of this curved portion, the curved vertical wall portion 108 and curved flange portion 109 move in the direction of the arrows in FIG. Therefore, tensile stress is generated in the curved vertical wall portion 108 and the curved flange portion 109 . In this specification, such a curved portion subjected to tensile stress during forming is referred to as a stretch flange portion. If this tensile stress becomes too great, the blank will break.

The present inventors have studied pad bending that suppresses wrinkles and fractures at the stretch flange portion. As described above, in pad bending, the blank is sandwiched between the pad and the punch, making it difficult for the material to flow. Therefore, during pad bending, the material does not flow into the stretch flange portion, and the tensile stress increases, making it easier to break.

Therefore, the present inventors came up with the idea of pinching (restraining) the blank between the pad and the punch with a slight gap in pad bending. As a result, the blank is not completely sandwiched between the pad and the punch during pad bending, so the material flows more easily than in typical pad bending. Therefore, the material tends to flow into the stretch flange portion during pad bending, and breakage of the stretch flange portion can be suppressed. Moreover, since the distance between the pad and the punch is only slightly larger than the plate thickness of the blank, the blank does not largely separate from the punch during pad bending, and the occurrence of wrinkles can be suppressed.

Furthermore, the inventors have come up with the idea to move the area where the die first begins to shape further away from where the pad and punch constrain the blank. In other words, the region from the end of the stretch flange portion of the blank to the position of the blank that first contacts the die (first region) and the blank region (third region) restrained by the pad and punch A region (second region) that does not contact the die for a certain period of time after the start of pad bending is provided between them. As a result, the second area of the blank begins to be pushed toward the punch after a certain period of time after the first area of the blank begins to be pushed toward the punch by the die. This means that the molding stroke of the portion of the die in contact with the first region is greater than the molding stroke of the portion of the die in contact with the second region. Increasing the forming stroke of the first region of the blank increases the time that the first region of the blank is being formed. Further, while the blank regions (first region and second region) not sandwiched between the pad and the punch are pushed toward the punch side, the blank region (third region) sandwiched between the pad and the punch material flows. Therefore, the longer the first region is molded, the longer the material in the third region of the blank flows. This makes it easier for the material to flow from the third region of the blank into the stretch-flange portion during molding, thereby suppressing breakage of the stretch-flange portion.

(1) A method for producing a pressed product of the present embodiment based on the above knowledge is a press device including a punch, a die facing the punch and a pad facing the punch, and a pressed product including a stretch flange portion by bending. to produce. A method of producing a pressed product includes a placement step, a third region constraining step, a first region pushing step, and a second region machining step. In the arranging step, a blank including a first region including the end portion of the stretch flange portion of the pressed product, a second region located inside the first region, and a third region located inside the second region Place in a press. In the third area constraining step, after the arranging step, the pad and the punch are brought close to each other, and a gap is created between the blank and the pad by the pad and the punch to constrain the third region. In the first region pushing step, after the third region constraining step, the die and the punch are brought closer together to bring the die and the first region into contact, and the die pushes the first region toward the punch side. In the second region processing step, after the first region pressing step is started, the punch and the second region are brought into contact and the die and the second region are brought into contact to process the second region with the punch and the die.

In the placement process, the distance between the pad and the punch in the pressing direction is slightly greater than the thickness of the blank. That is, a slight gap is provided between the third region of the blank and the pad. This facilitates the flow of the material of the third region of the blank, and facilitates the flow of the material of the third region of the blank into the stretch flange portion during bending. Therefore, breakage at the stretch flange portion is suppressed. Also, since the gap between the third region of the blank and the pad is so small, the third region of the blank does not separate greatly from the punch during bending. Therefore, the occurrence of wrinkles in the pressed product is suppressed. Further, in the first region pressing step, the first region of the blank on the end side of the stretch flange portion is first pressed toward the punch by the die. A second region of the blank is machined by the punch and die after a period of time from when the first region begins to be indented. That is, the molding stroke of the portion of the die blank that contacts the first region is increased compared to using only the pad (conventional pad bending). As the molding stroke increases as described above, more material flows from the third region of the blank into the stretch flange portion during molding. Therefore, the material is easily supplied to the stretch-flange portion, and breakage at the stretch-flange portion is suppressed.

(2) In the method of producing pressed products of (1) above, in the third region constraining step, the gap is preferably 120% or less of the plate thickness of the blank. Further, the gap is more preferably 110% or less of the plate thickness of the blank.

If the gap is too large, the third region of the blank will be too far away from the punch during bending, so the gap should be less than the predetermined value. The gap means the distance along the pressing direction between the area of the punch that constrains the third area of the blank and the area of the pad.

(3) In the method of producing a pressed product according to (1) or (2) above, in the second region machining step, the die or punch reaches the bottom dead center, and the first region It is preferable to terminate the processing of .

If bending is performed using an integral punch and an integral die, the first and second regions of the blank are finished at the same time. The use of an integral punch and integral die simplifies the construction of the press.

(4) In the method of producing pressed products of (3) above, the blank is preferably preheated before starting the step of pressing in the first region.

Heating the blank increases the ductility of the blank, making it easier to form press products that are difficult to form. In addition, in the method of producing a pressed product of the present embodiment, the second region does not contact the die for a certain period of time after the first region is pressed and before the second region is processed. As a result, the contact time and contact area between the blank and the die before reaching the bottom dead center of the die can be reduced as much as possible, so the occurrence of local deformation and unevenness in characteristics can be avoided. It is possible to improve the formability of bending at.

(5) In the method of producing pressed products of (4) above, it is preferable that the blank is made of steel and the blank is heated to a temperature of 700° C. or higher.

In many steels, heating to 700° C. or higher causes the metallographic structure to austenite. When a blank heated to 700° C. or higher is press-molded, the blank is quenched by contact between the blank and the die. Thereby, a high-strength pressed product can be obtained. Such a method is called hot stamping.

(6) The method of producing pressed products described in (1) to (5) above can be realized with the following configuration. The die includes protrusions that project toward the punch beyond the die top of the die. In the first region pushing step, the protrusion and the first region are brought into contact with each other, and the protrusion pushes the first region toward the punch side.

(7) The method of producing pressed products described in (1) to (6) above can also be realized with the following configuration. The punch includes an inner pad that protrudes toward the die from the tip processed portion of the punch and is accommodated in the recess of the punch when the die or punch reaches the bottom dead center. In the arranging step, the blank is arranged such that the third region is located at a position corresponding to the inner pad. In the third area constraining step, the pad and the inner pad are brought closer to each other, and a gap is provided between the pad and the inner pad to constrain the third area.

A method for producing the pressed product of this embodiment will be described in detail below. A method of producing a pressed product includes a placement step, a third region constraining step, a first region pressing step, and a second region machining step. The method of producing a pressed product of the present embodiment is a method of producing a pressed product including a stretch flange portion by bending.

[First embodiment]
[Press device]
A press device according to the first embodiment will be described. The press apparatus of the first embodiment is an apparatus for carrying out a method of producing pressed products of the first embodiment, which will be described later.

FIG. 5 is a cross-sectional view showing the press device of the first embodiment. Referring to FIG. 5 , press device 1 includes punch 3 , die 2 , pad 4 and distance block 5 .

The punch 3 is arranged as a lower die and faces the die 2 in the pressing direction. The punch 3 is fixed, for example, to a bolster plate. The punch 3 includes a punch top 31 , a punch shoulder 30 , a punch vertical wall 32 and a punch bottom 33 . The punch top 31 protrudes toward the die 2 from the punch bottom 33 in the pressing direction. In other words, the punch top 31 is arranged above the punch bottom 33 in the vertical direction. The punch top portion 31 has a shape corresponding to the shape of the top plate portion of the pressed product. The punch shoulder 30 is provided between the punch top 31 and the punch vertical wall 32 to connect them. In cross-section, the punch shoulder 30 has a curved shape.

The punch bottom 33 is arranged outside the punch top 31 . In other words, the punch bottom 33 is arranged around the punch top 31 in plan view. In other words, the term “outside” as used herein means the direction of the outer frame of the press device 1 . The punch bottom 33 is arranged below the punch top 31 in the vertical direction. The punch bottom 33 has a shape corresponding to the shape of the flange of the pressed product.

The punch vertical wall portion 32 is arranged between the punch top portion 31 and the punch bottom portion 33 and connects the punch top portion 31 and the punch bottom portion 33 . The punch vertical wall portion 32 extends vertically. Here, the punch vertical wall portion 32 is not limited to extending strictly in the vertical direction, and may extend in a direction inclined by 0 to 45 degrees from the vertical direction. The same applies to the die vertical wall portion 22, which will be described later. The punch vertical wall portion 32 has a shape corresponding to the shape of the vertical wall portion of the pressed product.

A die 2 is arranged as an upper mold. The die 2 is for example mounted on a slide. The slides are mounted in a well-known configuration such that moving the slides toward and away from the punch 3 moves the die 2 toward and away from the punch 3 .

Die 2 includes projection 6 , die top 23 , die shoulder 20 , die vertical wall 22 and recess 21 . The recess 21 can accommodate the pad 4 . The recess 21 faces the punch top 31 .

A die top 23 is positioned outside the recess 21 . Die top 23 faces punch bottom 33 . The die top 23 protrudes toward the punch 3 from the recess 21 in the pressing direction. That is, the die top portion 23 is arranged below the recess portion 21 in the vertical direction. The die top portion 23 has a shape corresponding to the shape of the flange portion of the pressed product. A die shoulder 20 is provided between a die top 23 and a die vertical wall 22 to connect them. In cross-section, the die shoulder 20 has a curved shape.

The die vertical wall 22 is arranged between the recess 21 and the die top 23 and connects the recess 21 and the die top 23 . The die vertical wall portion 22 extends vertically. The die vertical wall portion 22 has a shape corresponding to the shape of the vertical wall portion of the pressed product.

The protrusions 6 are arranged outside the die top 23 . Projection 6 includes tip 25 . A tip portion 25 of the protrusion protrudes toward the punch 3 from the die top portion 23 in the pressing direction. That is, the tip portion 25 of the protrusion 6 is arranged below the die top portion 23 in the vertical direction. A tip portion 25 of the projecting portion 6 protrudes toward the punch 3 side most among the portions of the die. The tip 25 of the protrusion 6 does not have a shape corresponding to the shape of the pressed product. This is because, as will be described later, when the die 2 reaches the bottom dead center, the protrusion 6 does not come into contact with the blank.

Pad 4 is attached to recess 21 of die 2 via elastic member 7 . The elastic member 7 is, for example, a spring, a die cushion, a hydraulic cylinder, or the like. Pad 4 includes a pad tip 41 . The pad tip portion 41 faces the punch top portion 31 in the pressing direction. When the die 2 is at the top dead center, the pad tip 41 protrudes toward the punch 3 in the pressing direction than the tip 25 of the projection 6 of the die. Therefore, when the die 2 is lowered, the pad tip 41 and the punch top 31 can initially constrain the third region of the blank.

The distance block 5 is placed on the punch top 31 of the punch. The distance block 5 is arranged at a position facing the pad 4 in the pressing direction. However, the distance block 5 is not placed at the position where the blank is placed. The distance block 5 keeps the distance between the pad 4 and the punch top 31 larger than the thickness of the third region of the blank. Therefore, the material of the distance block 5 is not particularly limited as long as it has this function. However, after the pad 4 contacts the distance block 5 , when the die 2 is further lowered, the pad 4 exerts force on the distance block 5 due to the elastic function of the elastic member 7 . Therefore, in order to maintain the distance between the pad 4 and the punch 3, the distance block 5 is preferably made of high strength metal such as steel.

[Method of producing pressed products]
A method for producing the pressed product of the first embodiment will be described. In the method of producing the pressed product of the first embodiment, the press apparatus of the first embodiment described above is used. The method of producing the pressed product of the first embodiment is performed cold.

[Placement process]
FIG. 6 is a plan view of the blank. FIG. 6 shows a blank molded into the center pillar as an example. The blank 10 includes a first region 11 including an edge 15 , a second region 12 located inside the first region 11 , and a third region 13 located inside the second region 12 . The end 15 of the first region 11 of the blank 10 is the end of the stretch flange portion of the pressed product. For example, the portion indicated by reference numeral 111 in FIG. 4 corresponds to the end portion of the stretch flange portion of the press product. By inner side of the blank is meant the area directed away from the edge 15 of the stretch flange portion of the blank. The first region 11 is the region at a predetermined distance from the edge 15 of the stretch flange portion of the blank. This predetermined distance depends on the shape of the pressed product. That is, as will be described later, the first region 11 is the region from the end 15 of the stretch flange to the position of the blank that first comes into contact with the die. The third area 13 is a blank area bounded by pads and punches, as will be described later. The second area 12 is an area between the first area 11 and the third area 13 .

The blank 10 is a metal plate such as a steel plate molded into a predetermined shape. Before the arranging step, the metal plate is formed into a predetermined shape by stamping or the like to obtain a blank. The predetermined shape of the blank corresponds to the shape of the press to be formed. In addition, in this embodiment, it demonstrates on the premise that the material of a blank is steel. However, the blank is not limited to this. The blanks may be aluminum, aluminum alloys, copper, copper alloys, carbon fiber reinforced plastics (CFRP), and the like.

FIG. 7 is a cross-sectional view showing the placement process of the first embodiment. Referring to FIG. 7, in the placement step, blank 10 is placed on press device 1 . More specifically, the third region 13 of the blank 10 is placed over the punch top 31 . The first region 11 and the second region 12 of the blank are not in contact with the punch 3 during the placement process.

[Third Region Constraint Step]
FIG. 8 is a cross-sectional view showing the third region constraining step of the first embodiment. Referring to FIG. 8, the third area constraining step is performed after the arranging step. In the third area constraining step, the pad 4 and the punch 3 are brought close to each other. More specifically, the pad 4 is attached to the die 2 via an elastic member 7 such as a spring. Therefore, by lowering the die 2 toward the punch 3, the pad 4 also approaches the punch. In the pressing direction, the pad tip portion 41 protrudes toward the punch 3 side more than the tip portion 25 of the protrusion 6 . Therefore, when the die 2 is lowered, the blank can be restrained by the pad 4 and the punch 3 before the protrusion 6 contacts the blank.

The approximation of pad 4 and punch 3 stops before the pad contacts blank 10 on the punch. That is, in the third area constraining step, the pad 4 and the punch 3 constrain the blank third area 13 with a gap SP. In other words, pad 4 does not contact blank 10 and there is a gap SP between pad 4 and blank 10 . In short, in the third region restraining step, the distance between the pad tip portion 41 and the punch top portion 31 along the pressing direction is greater than the plate thickness of the third region 13 of the blank. A distance block 5 is provided on the punch top 31 to prevent contact between the pad 4 and the blank 10 . The distance block 5 has a thickness greater than the plate thickness of the blank third region 13 and protrudes toward the pad 4 side from the pad 4 side surface of the blank third region 13 . As a result, the approach between the pad 4 and the punch 3 is stopped. This gap is maintained until the molding of the pressed product is completed, that is, until the die 2 reaches the bottom dead center.

Even if the blank is bent after the third region constraining step, the material of the third region of the blank is more likely to flow than when the blank is completely sandwiched between the pad and the punch due to the gap SP. Therefore, even if a pressed product including a stretch-flanged portion is formed, the material of the third region of the blank tends to flow into the stretch-flanged portion during forming, and breakage of the stretch-flanged portion can be suppressed. Further, in the third region constraining step, the gap between the pad 4 and the blank third region 13 is a predetermined distance or less, which is small. Therefore, the third region 13 of the blank does not move far from the punch top 31 during bending. Therefore, it is possible to suppress the occurrence of wrinkles in the press product, particularly in the top plate portion.

Preferably, when the blank third region 13 is restrained by the pad 4 and the punch 3, the distance between the pad tip 41 and the punch top 31 is 120% or less of the plate thickness of the blank third region 13. be. As described above, the suppression of wrinkles in pad bending is realized by suppressing separation of the blank 10 from the punch top 31 during forming. The larger the gap between the pad 4 and the blank 10, the more likely the blank will separate from the pad during molding, increasing the possibility of wrinkling. Therefore, it is preferable that the gap between the pad 4 and the blank 10 is small. Therefore, the upper limit of the distance between the pad tip portion 41 and the punch top portion 31 when the blank is constrained is 120% or less of the plate thickness of the third region 13 of the blank. More preferably, the upper limit of the distance between the pad 4 and the punch top 31 when the blank is constrained is 110% or less of the plate thickness of the third region 13 of the blank. More preferably, the upper limit of the distance between the pad 4 and the punch top 31 when the blank is constrained is 105% or less of the plate thickness of the third region 13 of the blank.

On the other hand, when the blank third region 13 is restrained by the pad 4 and the punch 3, the lower limit of the distance between the pad tip portion 41 and the punch top portion 31 is not particularly limited. When the blank is constrained, any gap between the pad 4 and the blank 10 makes it easier for the material in the third region of the blank to flow into the stretch flange portion during bending. Therefore, the lower limit of the distance between the pad 4 and the punch top 31 when the blank is constrained is not particularly limited.

[First Area Pushing Step]
FIG. 9 is a cross-sectional view showing the first region pressing step of the first embodiment. Referring to FIG. 9, the first region pressing step is performed after the third region restraining step. In the first region pushing step, the die 2 is further lowered to bring the die 2 and the punch 3 closer together. At this time, since the pad 4 is attached to the die 2 via the elastic member 7, the distance between the pad 4 and the die 2 is shortened by contraction of the elastic member 7. FIG. A distance block 5 is provided on the punch top 31 . Therefore, only the die 2 approaches the punch 3 while the distance between the pad 4 and the punch top 31 is maintained at the distance in the third region restraining step.

A protrusion 6 is provided on the die 2 . In the pressing direction, the tips 25 of the protrusions 6 protrude most towards the punch 3 compared to the rest of the die 2 . Therefore, when the die 2 is lowered, the protrusion 6 comes into contact with the blank 10 first. Also, the protrusion 6 is provided on the outermost side of the die 2 . The protrusion 6 thus contacts the first region 11 at a predetermined distance from the edge 15 of the blank. As the die 2 descends further, the protrusion 6 of the die pushes the first area of the blank toward the punch 3 . As a result, starting from the boundary between the third region 13 and the second region 12 of the blank (portion in contact with the punch shoulder 30), the first region 11 and the second region 12 of the blank are bent by the protrusion 6 of the die. be done.

The second region 12 of the blank does not come into contact with the die 2 and punch 3 during the first region pressing process. More specifically, the protrusion 6 protrudes toward the punch 3 from the die top portion 23 provided adjacent to the inside of the protrusion 6 of the die (on the pad 4 side). Therefore, a space exists between the die top portion 23 and the punch bottom portion 33 inside the protrusion 6 . In the first region pressing step, the second region 12 exists within this space, so the second region 12 does not come into contact with the die 2 and the punch 3 . Further, when the first region 11 and the second region 12 of the blank begin to bend, the contact portion between the first region 11 and the protrusion 6 gradually moves relatively toward the edge 15 of the blank.

In the first region pressing step, the portion of the blank in contact with the protrusion 6 of the first region 11 gradually moves relatively toward the edge 15 of the blank. The end (end 15 of the stretch flange portion) on the side of the first region 11 is pulled out from the projecting portion 6 of the die. More specifically, the end 15 of the stretch flange portion moves closer to the third region 13 (toward the pad 4 ) than the inner end 24 of the protrusion 6 . This completes the first region pressing step. The die 2 has not reached the bottom dead center when the first region pushing process is completed. That is, the first area pressing process ends before the second area machining process, which will be described later.

[Second Region Machining Step]
FIG. 10 is a cross-sectional view showing the second region processing step of the first embodiment. Referring to FIG. 10, the second area machining process is performed after the first area pressing process is started. That is, the second area processing step may be performed after the first area pressing process is started and before the first area pressing process is completed (that is, before the end 15 of the stretch flange portion is removed from the protrusion 6). The second region processing step may be performed after the first region pressing step is completed. In the second region machining step, the punch 3 and die 2 are brought into contact with the second region 12 of the blank.

After the protrusion 6 of the die 2 contacts the first area 11 of the blank, the die top 23 of the die 2 contacts the second area 12 of the blank after a certain period of time as the die 2 continues to descend. As the die 2 descends further, the blank second region 12 is pushed toward the punch 3 by the die top 23 . As mentioned above, before the die 2 reaches bottom dead center, the first region 11 of the blank moves inside the projection 6, i.e. into the space between the die top 23 and the punch bottom 33. Therefore, after the first area 11 of the blank moves to the area facing the die top 23, the first area 11 and the second area 12 of the blank are punched 3 by the die top 23 until the die 2 reaches the bottom dead center. pushed to the side.

FIG. 11 is a cross-sectional view showing the end of the second area processing step in the first embodiment. Referring to FIG. 11, when the die 2 reaches the bottom dead center, the first region 11 and the second region 12 of the blank are formed into the vertical wall portion and the flange portion of the pressed product having the hat cross-sectional shape. As a result, the second area processing step is completed, and a pressed product is obtained.

As described above, in the method of producing the pressed product of the first embodiment, the pad and the punch constrain the third region of the blank with a gap in the third region constraining step. Since this gap is a small gap of a predetermined distance or less, the third region of the blank does not leave the punch significantly during bending. As a result, surplus material is less likely to occur between the pad and the punch, and wrinkles are suppressed. In addition, the material of the third region tends to flow into the first region and the second region (that is, the stretch flange portion side) during bending. Therefore, breakage due to insufficient flow of material at the stretch flange portion is suppressed. Further, prior to the second region processing step, which is the main step of press bending, the blank is bent by pressing the first region of the blank in advance in the first region pressing step. As a result, the height of the protrusion 6 in the first region pressing step can be added as a forming stroke to the punch (or die) forming stroke in the second region processing step. In this case, since bending is started in advance in the step of pressing the first region by the height of the protrusion 6, the time during which the blank is bent during forming is long. Thus, a greater flow of material from the third region of the blank in one molding stroke can be achieved. As a result, the amount of material that flows into the stretch flange portion increases, and the plate thickness reduction rate is suppressed. Therefore, breakage of the stretch flange portion is further suppressed.

The first embodiment of the present invention has been described above. However, embodiments of the invention are not so limited. Other embodiments of the present invention will be described below.

[Second embodiment]
[Press device]
A press device according to the second embodiment will be described. A press apparatus of the second embodiment is an apparatus for carrying out a method of producing a pressed product of the second embodiment, which will be described later. Unlike the press device of the first embodiment, the press device of the second embodiment does not have projections and has an inner pad on the punch. In addition, in the following description, description overlapping with that of the first embodiment will be omitted.

FIG. 12 is a cross-sectional view showing the press device of the second embodiment. Referring to FIG. 12 , press device 1 includes punch 3 , die 2 , pad 4 and distance block 5 .

The punch 3 includes a punch top 31 , a punch vertical wall 32 , a punch bottom 33 , an inner pad 34 and a recess 26 . The inner pad 34 includes an inner pad tip portion 35 . The inner pad tip portion 35 protrudes toward the die 2 from the punch top portion 31 in the pressing direction. That is, the inner pad distal end portion 35 is arranged above the punch top portion 31 in the vertical direction. The inner pad tip portion 35 and the punch top portion 31 have a shape corresponding to the shape of the top plate portion of the pressed product.

The inner pad 34 is attached to the recess 26 via the elastic member 7 . The elastic member 7 is, for example, a spring, a die cushion, a hydraulic cylinder, or the like. The inner pad tip portion 35 faces the pad tip portion 41 of the pad 4 in the pressing direction. When the die 2 is at the top dead center position, the pad tip 41 of the pad 4 protrudes toward the punch 3 from the die top 23 of the die. Therefore, when the die 2 is lowered, the pad tip 41 and the inner pad tip 35 can initially constrain the third region of the blank.

The distance block 5 is arranged on the inner pad tip portion 35 of the inner pad. The distance block 5 is arranged at a position facing the pad 4 in the pressing direction.

[Method of producing pressed products]
A method for producing the pressed product of the second embodiment will be described. In the second embodiment, the inner pad restrains the blank on the die side of the punch. Since the restraint position of the blank is closer to the die side, the molding stroke of the punch (or die) that contacts the first region of the blank can be increased. Therefore, as in the first embodiment, breakage of the stretch flange portion can be suppressed. The method of producing the pressed product of the second embodiment is performed cold.

[Placement process]
FIG. 13 is a cross-sectional view showing an arrangement process of the second embodiment. Referring to FIG. 13 , in the placement step, third region 13 of blank 10 is placed on inner pad 34 projecting from punch top 31 toward pad 4 . The blank third region 13 contacts the inner pad 34 .

[Third Region Constraint Step]
FIG. 14 is a cross-sectional view showing a third region constraining step of the second embodiment. Referring to FIG. 14, in the third region restraining step, die 2 is lowered toward punch 3 to bring pad 4 and inner pad 34 of punch 3 closer together. The pad tip portion 41 protrudes from the die top portion 23 toward the punch 3 side. Therefore, when the die 2 is lowered, the blank can be restrained by the pad 4 and the inner pad 34 before the die top 23 contacts the blank.

A distance block 5 is provided on the inner pad 34 of the punch. Therefore, in the third region restraining step, the blank third region 13 is restrained with the gap SP between the pad 4 and the inner pad 34 of the punch. Therefore, even if a pressed product including a stretch-flange portion is formed, the material of the third region 13 of the blank can easily flow into the stretch-flange portion during forming, and breakage of the stretch-flange portion can be suppressed. Further, the gap SP between the pad 4 and the blank third region 13 is smaller than the predetermined distance. Therefore, the blank third region 13 does not greatly separate from the inner pad tip portion 35 of the punch 3 during bending. Therefore, it is possible to suppress the occurrence of wrinkles in the press product, particularly in the top plate portion.

[First Area Pushing Step]
15A and 15B are cross-sectional views showing a first region pressing step according to the second embodiment. Referring to FIG. 15, the die 2 is further lowered in the first region pushing step. The distance block 5 allows only the die 2 to approach the punch 3 while maintaining the distance between the pad 4 and the inner pad 34 at the distance in the third region constraint step.

The die top 23 of the die 2 protrudes most towards the punch 3 compared to the rest of the die 2 in the pressing direction. Also, the die top portion 23 is provided on the outermost side of the die 2 . Thus, the die top 23 contacts the first region 11 at a predetermined distance from the edge of the blank (stretch flange edge 15). As the die 2 descends further, the die top 23 pushes the blank first region 11 toward the punch 3 .

The inner pad tip portion 35 protrudes toward the die 2 from the punch top portion 31 in the pressing direction. Also, the punch top portion 31 is arranged outside the inner pad tip portion 35 . Thus, the blank's third region 13 contacts the inner pad tip 35 and the blank's second region 12 does not contact the punch top 31 and the die 2 . Also, when the first region 11 and the second region 12 of the blank begin to bend, the first region 11 of the blank comes into contact with the inner edge of the die top 23 and the contact area between the first region 11 and the die top 23 is decreases. The contact portion of the first region 11 with the die top 23 gradually moves relatively toward the edge 15 of the blank.

[Second Region Machining Step]
FIG. 16 is a cross-sectional view showing the second region processing step of the second embodiment. Referring to FIG. 16, when the die top 23 contacts the first region 11 of the blank 10 and then the die 2 is further lowered, the second region of the blank bends after a certain period of time starting from the shoulder of the die. Thereby, the second area processing process is started. Then, the die vertical wall portion 22 of the die and the second region 12 of the blank are brought into contact. Also, the punch top 31 of the punch and the second region 12 of the blank are in contact.

FIG. 17 is a cross-sectional view showing the end of the second region processing step of the second embodiment. Referring to FIG. 17, when the die 2 reaches the bottom dead center, the first region 11 and the second region 12 of the blank are formed into the vertical wall portion and the flange portion of the press product having a hat cross section. As a result, the second area processing step is completed, and a pressed product is obtained.

As described above, also in the method of producing the pressed product of the second embodiment, the pad and the punch (inner pad) constrain the third region of the blank with a gap in the third region constraining step. Since this gap is a small gap less than or equal to a predetermined distance, the third region of the blank does not separate greatly from the inner pad during bending. As a result, surplus material is less likely to occur between the pad and the inner pad, and wrinkles are suppressed. Further, during the bending of the first and second regions of the blank, the material of the third region tends to flow into the first and second regions (that is, the stretch flange portion side). Therefore, breakage due to insufficient flow of material at the stretch flange portion is suppressed. Furthermore, the first region of the blank is pushed forward by the die towards the punch side. A second region of the blank contacts the die after a period of time from the contact of the die and the first region. Thus, in the present embodiment, the height of the inner pad (the distance between the inner pad tip portion 35 and the punch top portion 31) in the first region pressing step is used as the forming stroke of the punch in the second region processing step. can be added. As a result, as in the first embodiment, the amount of material that flows into the stretch flange portion increases, and the plate thickness reduction rate is suppressed. Therefore, breakage of the stretch flange portion is further suppressed.

[Third Embodiment]
[Press device]
A press device according to the third embodiment will be described. A press apparatus according to the third embodiment is an apparatus for carrying out a method for producing a pressed product according to a third embodiment, which will be described later. The pressing device of the third embodiment is provided with both the protrusion of the pressing device of the first embodiment and the inner pad of the punch of the second embodiment. In addition, in the following description, description overlapping with the first embodiment and the second embodiment will be omitted.

FIG. 18 is a cross-sectional view showing the pressing device of the third embodiment. Referring to FIG. 18 , press device 1 includes punch 3 , die 2 , pad 4 and distance block 5 .

The punch 3 includes a punch top 31 , a punch vertical wall 32 , a punch bottom 33 and an inner pad 34 . The distance block 5 is arranged on the inner pad tip portion 35 of the inner pad.

Die 2 includes protrusion 6 , die top 23 , die vertical wall 22 , and recess 21 . The protruding portion 6 is arranged outside the die top portion 23 and protrudes most toward the punch 3 side among the portions of the die. When the die 2 is at the top dead center position, the pad tip portion 41 protrudes toward the punch 3 from the protrusion 6 of the die.

[Method of producing pressed products]
A method for producing the pressed product of the third embodiment will be described. In the third embodiment, a pressing device including both the protrusions of the first embodiment and the inner pad of the second embodiment is used. The method of producing the pressed product of the third embodiment is performed cold.

[Placement process]
FIG. 19 is a cross-sectional view showing the placement process of the third embodiment. Referring to FIG. 19 , in the placement step, third region 13 of blank 10 is placed on inner pad 34 .

[Third Region Constraint Step]
FIG. 20 is a cross-sectional view showing a third region constraining step of the third embodiment. Referring to FIG. 20, in the third area constraining step, die 2 is lowered toward punch 3 to bring pad 4 and inner pad 34 of punch 3 closer together. The pad tip portion 41 protrudes toward the punch 3 side from the projection portion 6 . Therefore, when the die 2 is lowered, the blank can be restrained by the pad 4 and the inner pad 34 before the protrusion 6 contacts the blank 10. - 特許庁

A distance block 5 is provided on the inner pad 34 of the punch. Therefore, in the third region restraining step, the blank third region 13 is restrained with the gap SP between the pad 4 and the inner pad 34 of the punch. Therefore, even if a pressed product including a stretch-flange portion is formed, the material of the third region of the blank tends to flow into the stretch-flange portion during forming, and breakage of the stretch-flange portion can be suppressed. Further, the gap SP between the pad 4 and the blank third region 13 is smaller than the predetermined distance. Therefore, the blank third region 13 does not largely separate from the inner pad tip portion 35 during bending. Therefore, it is possible to suppress the occurrence of wrinkles in the press product, particularly in the top plate portion.

[First Area Pushing Step]
FIG. 21 is a cross-sectional view showing a first region pressing step according to the third embodiment. Referring to FIG. 21, in the first region pushing step, die 2 is further lowered to bring die 2 and punch 3 closer together. The distance block 5 allows only the die 2 to approach the punch 3 while maintaining the distance between the pad 4 and the inner pad 34 at the distance in the third region constraint step.

When the die 2 descends, the protrusion 6 protruding toward the punch 3 first contacts the first region 11 of the blank 10 . When the die 2 is further lowered, the first region 11 and the second region 12 of the blank are bent by the projections 6 of the die starting from the boundary between the second region 12 and the third region 13 .

[Second Region Machining Step]
FIG. 22 is a cross-sectional view showing the second region processing step of the third embodiment. Referring to FIG. 22, in the second region processing step, the die top 23 of the die and the second region 12 of the blank are brought into contact. Moreover, in the second region processing step, the punch top portion 31 of the punch and the second region 12 of the blank are brought into contact with each other. As described above, the provision of the projections 6 increases the molding stroke of the die 2 in contact with the first region 11 of the blank 10 . In addition, since the inner pad 34 is provided, the molding stroke of the die 2 in contact with the first region 11 of the blank 10 is further increased. Therefore, the fixed time during which the second region 12 of the blank does not come into contact with the punch 3 and the die 2 after the start of the first region pressing step until the processing of the second region 12 of the blank is started becomes longer. This lengthens the time during which the material flows from the third region 13 of the blank to the stretch-flange portion during molding, thereby suppressing breakage at the stretch-flange portion.

FIG. 23 is a cross-sectional view showing the end of the second area processing step in the third embodiment. Referring to FIG. 23, when the die 2 reaches the bottom dead center, the second region machining step is completed and a pressed product is obtained.

In short, in the method of producing the pressed product of the third embodiment, in addition to the effect of the material flowing into the stretch flange portion by the protrusion 6, the inner pad 34 also adds the effect of the material flowing into the stretch flange portion. Therefore, breakage at the stretch flange portion is further suppressed as compared with the first embodiment and the second embodiment.

[Fourth embodiment]
In a fourth embodiment, a pressed product is formed from the heated blank. That is, the method of producing the pressed product of the fourth embodiment is performed hot or warm. For example, in hot stamping, a press machine bends a heated blank, and when the die reaches the bottom dead center, the formed pressed product is rapidly cooled and quenched. As a result, a pressed product containing a martensitic structure, ie, a high-strength pressed product can be obtained. Therefore, when forming a press product by hot stamping and quenching it, the blank must be made of steel.

[Press device]
A press device according to the fourth embodiment will be described. Any of the press apparatuses of the first to third embodiments described above can be used as the press apparatus of the fourth embodiment.

Preferably, the projections 6 have a lower heat transfer coefficient than the die 2 and punch 3 . In the case of hot stamping, when the die 2 reaches the bottom dead center, the molded blank (pressed product) is quenched, so the die 2 and the punch 3 preferably have high heat transfer coefficients. On the other hand, as mentioned above, when the die 2 begins to descend after the placement step, the protrusions 6 are the first to contact the blank. Therefore, from the viewpoint of ensuring the ease of flow of the material of the blank during bending, it is desirable that the protrusion 6 does not cool the blank. Also, when the die 2 reaches the bottom dead center, the protrusion 6 does not come into contact with the pressed product. Taking hot stamping as an example, since the protrusions 6 do not harden the pressed product, the heat transfer coefficient may be low.

[Method of producing pressed products]
A method for producing the pressed product of the fourth embodiment will be described.

In any one of the above-described first to third embodiments, a heated blank, such as hot stamping, warm stamping, or hot stamping, can be processed. In the following description of the fourth embodiment, as an example, a method of producing pressed products by hot stamping using the press apparatus of the first embodiment will be described. The method of producing the pressed product of the fourth embodiment includes a heating step and a cooling step in addition to the method of producing the pressed product of the first embodiment.

[Blank heating]
The blank is heated by a heating device (not shown). A heating device is not particularly limited. Examples of the heating device include a continuous heating furnace and a batch heating furnace. The heating method is also not particularly limited. Heating methods include, for example, gas heating and induction heating.

For example, in the case of hot stamping, the heating step may heat the blank above the A1 transformation point of the material. In this case, the heating temperature is, for example, 700.degree. C. to 900.degree. By heating a blank made of steel to the A1 transformation point or higher, the structure of the pressed product becomes martensite after the blank (pressed product) is quenched. Therefore, the strength of the pressed product is increased. In addition, when hot stamping (that is, quenching) is not performed, the heating temperature is not particularly limited. In this case, the blank heating temperature may be appropriately set in consideration of the material of the blank, the strength of the blank, the shape of the pressed product to be molded, and the like. After the blank is heated, the heated blank is placed in the pressing device using a transport path, a robot arm, or the like, that is, a placement step is performed. Description of the arrangement process is omitted.

4th Embodiment demonstrates the case where a blank is heated before an arrangement|positioning process. However, heating the blank is not limited to this case. For example, the heating of the blank may be performed after the placement step and before the third region constraining step, or may be performed simultaneously with or after the start of the third region constraining step and before the third region constraining step ends. Alternatively, it may be performed at the same time as or after the completion of the third region restriction step. In short, it is sufficient that the heating process is performed before the blank starts to be deformed by the mold. When the blank is heated after the placement step, the blank may be heated using an induction heating device or the like.

The heating temperature should be higher than the room temperature, for example, 200° C. or higher at the time when the die 2 starts to descend. The heating temperature of such a blank is measured with a radiation thermometer.

[Third Region Constraint Step]
Referring to FIG. 8 , in the third region restraining step, distance block 5 creates gap SP between blank third region 13 and pad tip portion 41 . The effect of this third region constraining step in hot stamping will be described.

As described at the beginning, when a pressed product including a stretch-flanged portion is drawn, the vertical wall portion and the flange portion of the stretch-flanged portion are likely to break. On the other hand, when a pressed product including a stretch flange portion is formed by general bending in order to suppress breakage, wrinkles are likely to occur in the top plate portion. Hot or warm press forming is known as a method for forming such difficult-to-form press products. However, if the shape of the pressed product is more complicated, even in hot or warm press forming, the stretch flange portion may break or the top plate portion may wrinkle.

In the third area constraining step of the fourth embodiment, the pad 4 and the punch 3 constrain the blank third area 13 with a gap. Therefore, the material of the third region of the blank flows more easily than when the blank is completely sandwiched between the pad 4 and the punch 3 without any gap. This effect can also be obtained in hot or warm press molding as in the cold (first to third embodiments) described above. Further, in the third region constraining step, the gap between the pad 4 and the blank third region 13 is a predetermined distance or less, which is small. Therefore, it is possible to suppress the occurrence of wrinkles in the top plate portion of the pressed product even in hot or warm press molding.

A third region 13 of the heated blank contacts the punch top 31 . Since the third region 13 of the blank is heat-extracted by the contact with the punch top 31, the third region 13 of the blank can be cooled (quenched in the case of hot stamping).

[First Area Pushing Step]
Referring to FIG. 9, when bending by the die 2 is started after the third region constraining step, the first region 11 and the second region 12 of the blank are formed with the boundary between the second region 12 and the third region 13 as a starting point. bend. At this time, since the third region of the blank is not completely sandwiched between the pad 4 and the punch 3, the third region 13 of the blank is also slightly separated from the punch top 31 and may come into contact with the tip 41 of the pad. This contact provides resistance to the flow of blank material. However, due to the high ductility of the heated blank, the blank's third region 13 is less likely to separate from the punch top 31 when the blank's first region 11 and the blank's second region 12 bend. Contact between the heated third region 13 of the blank and the punch top 31 is suppressed. Therefore, even if a difficult-to-form pressed product including a stretch-flange portion is formed, the material of the third region of the blank tends to flow into the stretch-flange portion during forming, and breakage of the stretch-flange portion can be suppressed.

Further, as described above, in the first region pushing step, the die 2 (projection 6) pushes the first region 11 of the blank toward the punch 3, so that the second region 12 of the blank is formed by the die 2, the pad 4 and the punch 3. do not come into contact with Therefore, the second region 12 is difficult to cool in the first region pushing step. Therefore, in the subsequent second region processing step, the material of the second region 12 of the blank is more likely to flow, and breakage of the stretch flange portion can be suppressed.

Furthermore, as will be explained later, the mold may be cooled in order to cool the pressed product, but the protrusion 6 in contact with the first region 11 of the blank is not cooled even in this case. That is, even if the projecting portion 6 comes into contact with the first region 11 of the blank, the first region 11 of the blank is less likely to be cooled. This is because, as mentioned above, when the die 2 reaches the bottom dead center, the protrusion 6 does not come into contact with the blank. The temperature drop in the first region of the blank is small during the first region pressing step because the protrusions cool the blank very little. Therefore, local deformation of the high-temperature region of the blank due to the removal of heat from the first region of the blank is suppressed. That is, breakage of the blank is suppressed.

[Second Region Machining Step]
Referring to FIG. 9, as in the first embodiment described above, after the protrusion 6 of the die 2 contacts the first region 11 of the blank, if the die 2 continues to descend, after a certain period of time, the die 2 Die top 23 contacts second region 12 of the blank. In this way, by delaying the timing at which the second region 12 of the blank contacts the mold, the difference in cooling time between the second region 12 of the blank and the first region 11 is reduced, resulting in uneven cooling (quenching in hot stamping). unevenness) can be reduced. As the die 2 descends further, the blank second region 12 is pushed toward the punch 3 by the die top 23 . After that, the die 2 reaches the bottom dead center.

Since the punch 3 and the die 2 are cooler than the blank 10 in the first zone pressing step and the second zone machining step, the blank 10 is cooled when the punch 3 and/or the die 2 come into contact with the blank 10 . In addition, the punch 3 and/or the die 2 (that is, the mold) may be cooled in order to positively cool the pressed product. For example, a cooling channel for flowing a cooling medium may be provided in the mold, or the blank may be directly water-cooled. In the case of hot stamping, a high-strength pressed product can be obtained after quenching. Note that the cooling rate of the pressed product is appropriately set according to the material.

The effect of the method for producing pressed products according to the present embodiment was investigated by numerical calculation. As examples of the present invention, three patterns of Inventive Examples 1 to 3 were calculated. As comparative examples, five patterns of comparative examples 1 to 5 were calculated.

In Example 1 of the present invention, a press product was molded assuming the press apparatus of the first embodiment. In Example 2 of the present invention, a press product was molded assuming the press apparatus of the second embodiment. In Example 3 of the present invention, a press product was molded assuming the press apparatus of the third embodiment. All of Inventive Examples 1 to 3 assumed hot pressing.

In Comparative Example 1, a pressed product was formed by assuming a press apparatus in which the distance block was removed from Example 1 of the present invention. In Comparative Example 2, a pressed product was formed by assuming a press apparatus in which the distance block was removed from Example 2 of the present invention. In Comparative Example 3, a pressed product was formed assuming a general pad bending press machine (see FIG. 2). All of Comparative Examples 1 to 3 assumed hot pressing.

[Calculation condition]
Calculation conditions common to Inventive Examples 1 to 3 and Comparative Examples 1 to 3 will be described. Numerical calculations were performed using software LS-DYNA from Livermore Software Technology Corporation. The finite element method (FEM) was used as the calculation method. The blank was a steel plate having a thickness of 1.6 mm and a tensile strength of 600 MPa at room temperature. The heating temperature of the blank was 900°C. The punch was fixed as a lower die, and the lowering speed of the die was 4000 mm/sec. The load applied from the elastic member to the pad when the die reached the bottom dead center was 49000N.

FIG. 24 is a perspective view of a model of the pressed product molded in this example. Referring to FIG. 24, in the present embodiment, it is assumed that a press product that includes a top plate portion 16, a vertical wall portion 17 and a flange portion 18 and is curved 90 degrees in an L shape is formed. The L-shaped curved region of the pressed product, that is, the stretch flange portion 14 was a quarter circle with a radius of 30 mm.

Calculation conditions that are different in Examples 1 to 3 of the present invention and Comparative Examples 1 to 3 will be described.

Referring to FIG. 5, in Example 1 of the present invention and Comparative example 1, when the die 2 is at the top dead center position, the pad tip 41 of the pad 4 in the pressing direction is a projection positioned on the pad 4 side in the pressing direction. It was closer to the 66 mm punch 3 than the tip 25 of the part. In Inventive Example 1 and Comparative Example 1, when the die 2 was at the top dead center, the tip 25 of the protrusion was closer to the 25 mm punch 3 than the die top 23 in the pressing direction.

Referring to FIG. 12 , in Inventive Example 2 and Comparative Example 2, when the die 2 is at the top dead center, the pad tip 41 of the pad 4 is closer to the 66 mm punch 3 than the die top 23 in the pressing direction. rice field. When the die 2 was at the top dead center, the inner pad tip 35 of the inner pad 34 was 10 mm closer to the die 2 than the punch top 31 in the pressing direction. The load applied from the elastic member to the inner pad when the die reached the bottom dead center was 98000N.

Referring to FIG. 18, in Example 3 of the present invention, when the die 2 was at the top dead center, the pad tip 41 of the pad 4 was closer to the 66 mm punch 3 than the tip 25 of the protrusion in the pressing direction. . In Inventive Example 3, when the die 2 was at the top dead center, the tip 25 of the protrusion was closer to the 25 mm punch 3 than the die top 23 in the pressing direction. In Inventive Example 3, when the die 2 was at the top dead center, the inner pad tip 35 of the inner pad 34 was 10 mm closer to the die 2 than the punch top 31 in the pressing direction. The load applied from the elastic member to the inner pad when the die reached the bottom dead center was 98000N.

In Comparative Example 3, when the die 2 was at the top dead center, the pad tip 41 of the pad 4 was closer to the 66 mm punch 3 than the die top 23 of the die 2 in the press direction.

In Inventive Examples 1 to 3, the length of the distance block in the pressing direction was 1.8 mm. That is, a gap of 0.2 mm was provided between the blank and the tip of the pad.

[Calculation result]
With reference to FIG. 24, the plate thickness reduction rate in the stretch flange portion 14 was calculated in Inventive Examples 1 to 3 and Comparative Examples 1 to 3. It means that the larger the numerical value of the plate thickness reduction rate, the more the plate thickness is reduced and the easier it is to break. The sheet thickness reduction rate was calculated by the following formula.
(Plate thickness reduction rate [%]) = (plate thickness before molding - plate thickness after molding) x 100 / (plate thickness before molding)

As evaluation of breakage, the plate thickness reduction rate at the boundary between the vertical wall portion 17 and the flange portion 18 at the center of the curve of the stretch flange portion 14 where breakage is most likely to occur was calculated. In addition, as an evaluation of the difficulty of breaking, the area of the region where the plate thickness reduction rate is 17% or more in the vertical wall portion 17 and the flange portion 18 of the stretch flange portion 14 was calculated. From the calculated values, the ratios of Inventive Examples 1 to 3 and Comparative Examples 1 to 3 were calculated with the value of Comparative Example 1 set to 100.

Table 1 shows the calculation results.

In Inventive Examples 1 to 3, the plate thickness reduction rate at the center of the curve of the stretch flange portion 14 was below the value in the comparative example. That is, in Examples 1 to 3 of the present invention, breakage of the stretch flange portion was suppressed more than in the comparative example. Further, in Examples 1 to 3 of the present invention, the area of the regions where the plate thickness reduction rate was 17% or more was smaller than that of the comparative example. That is, in Examples 1 to 3 of the present invention, the range in which the vertical wall portion and the flange portion are likely to break was suppressed as compared with the comparative example. In Examples 1 to 3 of the present invention, the plate thickness reduction rate of the top plate portion 16 was not large enough to cause wrinkles.

The embodiments of the present invention have been described above. However, the above-described embodiments are merely examples for implementing the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit of the present invention.

In the above-described embodiment, the case where the die is arranged as the upper mold and the punch is arranged as the lower mold has been described. However, the punch may be the upper die and the die may be the lower die. In short, the press device of the embodiment described above may be turned upside down.

In the embodiments described above, the pressed product need not be the product. That is, the pressed product obtained by the method of producing the pressed product of the present embodiment may be further subjected to bending, drawing, cutting, or the like.

In the above-described embodiment, a case where one side of a pressed product having a hat cross-sectional shape is formed in a cross-sectional view has been described. However, in the method of producing the pressed product of the present embodiment, it goes without saying that both sides of the pressed product having a hat cross-sectional shape may be formed in a cross-sectional view. Also, the pressed product does not have to include stretch flanges on both sides in a cross-sectional view. That is, the pressed product may include the stretch flange portion only on one side in a cross-sectional view.

The method for producing a pressed product according to this embodiment is used for producing a pressed product including a stretch flange portion. Pressed products including a stretch flange portion are, for example, parts constituting a vehicle body such as a front pillar, a center pillar, a rear pillar, a front bumper, a rear bumper and a lower arm of a four-wheeled vehicle.

1: Press device 2: Die 3: Punch 4: Pad 5: Distance block 6: Projection 7: Elastic member 10: Blank 11: First region 12: Second region 13: Third region 14: Stretch flange 15: End of stretch flange portion 21: recessed portion 22: die vertical wall portion 23: die top portion 24: inner end of projection portion 25: tip portion of projection portion 31: punch top portion 32: punch vertical wall portion 33: punch bottom portion 34: inner pad 35: Inner pad tip 41: Pad tip

Claims (6)

A method for producing a pressed product including a stretch flange portion by bending using a press device including a punch, a die facing the punch, and a pad facing the punch, the method comprising:
A blank containing a first region including a portion that will be the end of the stretch flange portion of the pressed product, a second region located inside the first region, and a third region located inside the second region An arrangement step of arranging in a press device;
a third region constraining step of, after the arranging step, bringing the pad and the punch close to each other to create a gap between the blank and the pad by the pad and the punch to constrain the third region;
After the third region constraining step, a first region pushing step of bringing the die and the punch closer together to bring the die and the first region into contact and pushing the first region toward the punch side with the die;
After the start of the first region pushing step, the punch and the second region are brought into contact, and the die and the second region are brought into contact to process the second region with the punch and the die. a region processing step;
the die includes a protrusion that protrudes toward the punch from the die top of the die;
In the first area pushing step, the protrusion and the first area are brought into contact, the first area is pushed into the punch side by the protrusion, and the end of the stretch flange portion is pushed into the inner end of the protrusion. A method of producing a pressed product, in which the press product is moved to the third area side . A method for producing a pressed product including a stretch flange portion by bending using a press device including a punch, a die facing the punch, and a pad facing the punch, the method comprising:
A blank containing a first region including a portion that will be the end of the stretch flange portion of the pressed product, a second region located inside the first region, and a third region located inside the second region An arrangement step of arranging in a press device;
a third region constraining step of, after the arranging step, bringing the pad and the punch close to each other to create a gap between the blank and the pad by the pad and the punch to constrain the third region;
After the third region constraining step, a first region pushing step of bringing the die and the punch closer together to bring the die and the first region into contact and pushing the first region toward the punch side with the die;
After the start of the first region pushing step, the punch and the second region are brought into contact, and the die and the second region are brought into contact to process the second region with the punch and the die. a region processing step;
The punch includes an inner pad that protrudes toward the die from the tip processed portion of the punch and is accommodated in the recess of the punch when the die or the punch reaches the bottom dead center,
In the arranging step, arranging the blank so that the third region corresponds to the inner pad;
In the third region constraining step, the pad and the inner pad are brought close to each other, and a gap is provided between the pad and the inner pad to constrain the third region. A method for producing a pressed product according to claim 1 or claim 2,
A method of producing a pressed product, wherein in the third region constraining step, the gap between the pad and the punch is 120% or less of the plate thickness of the blank. A method for producing a pressed product according to any one of claims 1 to 3,
In the second area machining step, the die or the punch reaches the bottom dead center, and the machining of the first area is completed simultaneously with the completion of machining of the second area. A method for producing a pressed product according to claim 4,
A method of producing a pressed product, wherein said blank is preheated prior to commencing said first zone pressing process. A method for producing a pressed product according to claim 5,
the blank is made of steel,
A method for producing a pressed product, wherein the heating temperature of the blank is 700° C. or higher.

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