JP6652092B2 - Press molding method - Google Patents

Description

  The present invention relates to a method for press-forming a metal plate such as a steel plate.

  Panels having a hat-shaped cross section are often used as frame parts of automobiles. From the viewpoint of reducing the weight of the vehicle body, the strength of the panel has been increased, and this increased strength has caused a problem that springback after press molding is increased.

  As a technology for reducing the springback of hat-shaped components, for example, Patent Document 1 discloses that “wrinkle pressing force is applied at the time of press forming and punch release, and pad pressure is applied at the initial stage of the release, and the material is die-bonded. A press forming method characterized by releasing a punch while overrunning inside a groove ”(see claim 2 of Patent Document 1).

JP 2005-296968 A

  However, the method of Patent Literature 1 has a problem that the shape tends to vary because the overrun portion is free during molding, and the product shape after springback also tends to vary.

  The present invention has been made in order to solve such a problem, and in press forming of a metal plate such as a steel plate, in particular, a press in which a vertical wall portion is prevented from springback that opens and a product shape has little variation. It is intended to provide a molding method.

(1) The press forming method according to the present invention is a press forming method for press forming a metal plate into a shape having at least a top plate portion and a vertical wall portion by a die and a punch,
The vertical wall forming portion of the punch is provided with a movable convex portion that can appear and disappear, and a die and a punch are relatively close to each other to form the vertical wall portion, and before the bottom dead center, the movable convex portion is protruded. The metal plate is brought into a three-point bending state constrained by the punch shoulder, the movable projection and the die shoulder, and then the movable projection is immersed in the vertical wall forming portion of the punch and the die is moved to the bottom dead center. The vertical wall portion is formed by moving.

(2) In the device according to (1), the movable convex portion is provided closer to the punch shoulder than the center in the height direction of the vertical wall forming portion. .

  In the present invention, a movable convex portion that can protrude and retract in a vertical wall forming portion of a punch is provided. Then, the metal plate is brought into a three-point bending state restrained by the punch shoulder, the movable projection, and the die shoulder. Thereafter, the movable projection is immersed in the vertical wall forming portion of the punch, and the die is lowered. By moving to the point and forming the vertical wall portion, the spring back generated in the opening direction of the vertical wall portion can be offset by the spring go generated at the position where the movable convex portion abuts, and the spring back is suppressed and the target is suppressed. It can approach the product shape. In addition, since the three-point bending state is performed while the metal plate is restrained by the punch shoulder, the movable projection, and the die shoulder, variation in the product shape can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram illustrating a press forming die used in a press forming method according to one embodiment of the present invention. FIG. 2 is an explanatory diagram illustrating a state in the middle of molding in the press molding method according to one embodiment of the present invention. FIG. 3 is an explanatory diagram illustrating a state of a molding bottom dead center in a press molding method according to an embodiment of the present invention. It is a figure explaining distance measurement between both ends of a flange of a press-formed product section by shape measurement after press-forming.

Prior to describing a press molding method according to an embodiment of the present invention, a press molding die to be used will be described.
The press-molding die 1 used in the present embodiment is for forming a hat-shaped press-formed product having vertical walls on both sides of a top plate, and includes a punch 3, a die 5, and a pad 7. ing.
The punch 3 can be protruded and retracted from the vertical wall forming section 9, that is, can be in a state of protruding from the surface of the vertical wall forming section 9, and in a state of being flush with the surface of the vertical wall forming section 9 or being immersed therein. The movable projection 11 is provided. In the example of FIG. 1, the movable convex portion 11 can move in and out of the vertical wall forming portion 9 by moving in the horizontal direction in the figure.

The shape of the movable protrusion 11 is not particularly limited, but may be any as long as it can support a metal plate during molding. However, in order to prevent the metal plate from being bent, it is desirable that the metal plate has a smooth arc shape.
The position where the movable convex portion 11 is provided in the vertical wall forming portion 9 is preferably higher than the center in the height direction of the vertical wall forming portion 9, that is, a position close to the punch shoulder portion 13.
This is because, as will be described later, a spring go is generated at a position where the movable convex portion 11 abuts to cancel the spring back generated at the punch shoulder 13. Is effective.

The movable convex portion 11 is supported by the movable convex portion operation portion 15, and the movement of the movable convex portion 11 is controlled by the movable convex portion operation portion 15.
There are various modes for controlling the emergence, but it can be realized by, for example, supporting the movable convex portion 11 with a spring having a predetermined urging force. Specifically, the metal plate has a strength enough to maintain the three-point bending state of the metal plate even when the metal plate abuts during the molding, and has an urging force enough to be pushed in when the die 5 moves to the bottom dead center. Apply a spring.

  As another control method of the emergence, there is a mode in which the movable convex portion 11 is supported by a gas cylinder. Before the bottom dead center, the gas pressure is increased to support the movable projection 11 so as not to be immersed, and then the gas pressure is released when the die 5 moves to the bottom dead center. Further, a hydraulic cylinder may be used instead of the gas cylinder.

  Next, a press forming method using the above press forming die 1 will be described with reference to FIGS.

  A metal plate 17 such as a steel plate is placed on the top plate forming portion 19 of the punch 3, pressed by the pad 7, and the die 5 and the punch 3 are relatively moved to form a vertical wall portion. At this time, as shown in FIG. 2, before the bottom dead center, the metal plate 17 is formed at three places (see A, B, and C in the figure) by the punch shoulder 13, the movable projection 11, and the die shoulder 21. It becomes a three-point bending state that is constrained and protrudes outward. Rather than being bent freely as in the overrun portion of Patent Document 1, the present invention is restrained and bent at three places, so that the variation in shape during molding is small, and therefore the shape after springback is achieved. Is also stable.

  Forming the three-point bending state that is outwardly convex as shown in FIG. 2 immediately before the bottom dead center is performed by forming the portion bent by the movable protrusion 11 when the mold is released to the bottom dead center and released from the mold. This is for deforming (spring go) so as to protrude outward from the state. In order to cause such deformation at the time of mold release, it is desirable that the die 5 be bent in a three-point state at least 1 mm to 5 mm before the bottom dead center.

  FIG. 3 shows a state in which the die 5 further moves from the state shown in FIG. At this time, the movable convex portion 11 is immersed (stored) in the vertical wall forming portion 9 of the punch 3, and the vertical wall forming portion 9 has no projecting portion, and the vertical wall forming portion 9 has a flat surface.

  When the mold is released in the state shown in FIG. 3, the metal plate 17 springs back in the direction in which the vertical wall opens at the boundary between the top plate and the vertical wall (corresponding to the punch shoulder R). As described above, the portion convex by the movable convex portion 11 is deformed (spring-go) so as to protrude outward from the straight line as described above. Since the spring go is a deformation that closes the vertical wall portion, the spring go cancels the above-mentioned spring back and suppresses the spring back, thereby making it possible to approach a target product shape.

  As described above, according to the present embodiment, the spring back generated in the direction in which the vertical wall portion opens can be offset by the spring go generated at the position where the movable convex portion abuts, and the spring back is suppressed to approach the target product shape. be able to. Further, since the three-point bending state is performed while the metal plate 17 is restrained by the punch shoulder portion 13, the movable convex portion 11, and the die shoulder portion 21, variation in the product shape can be reduced.

An experiment for confirming the effect of the present invention was conducted, and will be described below.
A straight part having a thickness of 1.2 mm and a length of 500 mm was press-formed using a hat cross section having a punch bottom flat width of 55 mm, punch shoulder R5 mm, die shoulder R6.5 mm, height 40 mm and flange width 12 mm as a target shape.
The material is 980MPa class high strength steel sheet. A punch 3, a die 5, and a pad 7 as shown in FIG. 1 were used as a mold. The pad pressure was kept constant during molding at 10 tonf, and foam molding was performed.

The shape of the formed steel sheet was measured, and as shown in FIG. 4, the distance between the front ends of the flanges on both sides was measured for a cross section obtained by cutting the shape data at the center in the longitudinal direction and perpendicular to the central axis. The difference (L'-L) between the flange end distance L 'measured in this way and the flange end distance L of the target shape (equivalent to the bottom dead center shape) was defined as the springback amount.
When the movable convex portion 11 was housed inside the vertical wall forming portion 9 during molding and foam-formed (corresponding to the prior art), the springback amount was 15 mm.
On the other hand, in the initial stage of the molding, the movable convex portion 11 is formed into a foam by projecting 2 mm from the vertical wall forming portion 9 so that the movable convex portion 11 is completely housed in the vertical wall forming portion 9 at the bottom dead center ( The springback amount of the present invention) was halved to 7 mm.
Thus, it was confirmed that the springback amount can be suppressed by applying the present invention.

DESCRIPTION OF SYMBOLS 1 Press molding die 3 Punch 5 Die 7 Pad 9 Vertical wall forming part 11 Movable convex part 13 Punch shoulder part 15 Movable convex part operating part 17 Metal plate 19 Top plate forming part 21 Die shoulder

Claims (2)

A press forming method for press forming a metal plate into a shape having at least a top plate portion and a vertical wall portion by a die, a punch, and a pad ,
The vertical wall forming part of the punch is provided with a movable protruding part that can appear and disappear, the metal plate placed on the top plate forming part of the punch is pressed by the pad, and a die and a punch are relatively brought close to each other to form the vertical wall part. Before the bottom dead center in the process of molding the metal plate, the movable convex portion is projected to bring the metal plate into a three-point bending state restrained by the punch shoulder portion, the movable convex portion, and the die shoulder portion. A press forming method comprising: immersing a part into a vertical wall forming part of the punch; and moving the die to a bottom dead center to form the vertical wall part.   The press molding method according to claim 1, wherein the movable convex portion is provided closer to the shoulder of the punch than the center in the height direction of the vertical wall forming portion.

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