JPH039805B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of bending a metal blank into a flange or the like using a press die.

"Background of the Invention and Prior Art" When a metal blank is bent, spring back θ occurs in the metal blank due to its own elasticity, as shown by the imaginary line in FIG.
This needs to be corrected somehow. Conventionally, as a means for correcting the spring back, a correction step is added after the bending process shown in FIG. 8. For example, as shown in Fig. 9, the product is bent again by taking into account the spring back amount α in the bending angle, and this re-bending process employs a cam mechanism A, The machining force is applied to the mold from the

[Problems to be Solved by the Invention] The estimated cutting amount of the mold to obtain the springback amount α is extremely uncertain, and it is complicated to determine it by repeating molding trials. In addition, the cam mechanism complicates the mold structure and raises the cost of mold production, which is an economical problem.

Therefore, an object of the present invention is to adopt a bending method in which a bead is formed in advance along the bending line on the bent part of a metal blank, and this bead is crushed during the bending process to plastically deform it, and The purpose is to obtain a highly accurate bending angle with corrected back. At the same time, we have minimized the need for complicated operations such as re-bending and preparing the molding surface for spring back, which were previously required, and we have simplified the mold structure to reduce mold production costs. The aim is to provide a method for achieving this goal.

[Means for Solving the Problems] The structure of the present invention that solves the problems of the prior art is to form a continuous bead or an interrupted bead along the bending line in the bending portion of the metal blank. A bead is formed in advance, and this bead is crushed during the bending process of the metal blank, and the spring back in the bent portion of the metal blank is corrected by plastic deformation of the bead due to the crushing.

[Example] As shown in FIG. 1, a bead 2 having a semicircular arc cross section is formed in advance on a bent portion of a metal blank 1.

The metal blank 1 is bent by a die 3 as shown in FIG.
The bead 2 is clamped between the blank holder 4 and the bead 2 so as to face the arcuate shoulder 5 of the bending die 3. In the state shown in FIG.
As shown in FIG. 3, the movable punch 6 is lowered to press and bend the die, and the bending die 3 and the movable punch 6 are introduced perpendicularly between the sides of the die, and then the movable punch 6 is lowered to bend the die. An arcuate pressing surface 7 provided on the die 3 that fits the shoulder 5 crushes the bead 2 located on the shoulder 5 as shown in FIG.
Due to the plastic deformation of the bead 2 due to this crushing, the residual stress that causes springback is divided and reduced, and the springback is corrected.

3a to 5a are stress distribution diagrams corresponding to each bending stage shown in FIGS. 3 to 5 described above and simply modeling and explaining the stress state of the bent portion of a metal blank.

First, as shown in FIG. 3, when the bead 2 has not yet been crushed, the bead portion C and the bent portions A and B that continue from side to side with this bead portion C as a boundary are as shown in FIG. 3a. As shown, tensile stress acts on the outside and compressive stress acts on the inside, bordering on the neutral plane of the metal blank.

Next, as shown in FIG. 4, when the bead 2 is being crushed, as shown in FIG. Similarly, there is a tensile stress on the outside, and
Compressive stress is acting on the inside.

Next, as shown in FIG. 5, at the release stage when the bead 2 is completely crushed and the bending process is completed and the movable die 6 rises and separates from the metal blank 1, the bead portion C is shown as shown in FIG. 5a. As shown, the compressive stress reaches the plastic region and undergoes plastic deformation, whereby the stress state that causes spring back disappears. Further, the outward stress remaining in the bent portions A and B is separated by the plastic deformation of the bead portion C. This reduces the amount of spring back.

The above explanation is based on a simple model to facilitate understanding of the present invention, but in this explanation, in particular, the actual bending process of the present invention at the bending stage shown in FIGS. 4a and 5a above, The bent part of a metal blank exhibits the following behavior.

That is, Fig. 4b shows the actual behavior of the bent portion of the metal blank 1 corresponding to the bending stage shown in Fig. 4 above, and as shown in the figure, during the crushing of the bead 2, the left and right sides of the bead 2 are deformed into a bead shape, and
As shown in Fig. 5b, which corresponds to Fig. 5, the bead 2 is essentially completely crushed, and due to the plastic deformation of the bead 2, the small bead-shaped deformed part that occurred in Fig. 4b is also finally is crushed, and as shown in Fig. 5C, the stress is divided by plastic deformation at the bead part C.
Further, unlike the stress distribution in FIG. 5a, tensile stress remains on the outside and compressive stress remains on the inside of the bent portions A and B, that is, inward force remains.

As a result, the outward residual stress that causes springback caused by bending is reduced or canceled out by the above-mentioned stress effect caused by the crushing of the bead, and the springback at the bend is corrected. is to be done.

In the above embodiment, an example was shown in which the groove of the bead 2 faces downward to the shoulder portion 5 and the bead is crushed.
Even if it is crushed with the groove facing upward, the effect is the same. In addition, as shown in FIG. 6, for example, a metal blank 1
When bent along a curved line when viewed from above, it is difficult to form a continuous bead, so it is also possible to add a single bead interrupted along the bending line, as shown in the figure. .

[Effects of the Invention] As described above, according to the configuration of the present invention, the following effects can be obtained.

(a) One continuous bead or one intermittent bead is formed in advance along the bending line on the bending part of the metal blank, and this bead is crushed during the bending process. A predetermined bending angle with corrected spring back can be obtained by a simple method of correcting spring back at a bent portion of a metal blank through plastic deformation.

(b) However, according to the method of the present invention, by adjusting the bead height, it is possible to correspond to an arbitrary amount of spring back. At the same time, it eliminates as much as possible the complicated work that was required in the past, such as re-bending and machining the mold forming surface for spring back, and it is a simple method that does not require the cam mechanism of the conventional technology. Since the mold structure can be used, the manufacturing cost of the mold can be greatly reduced.
There is an economical effect that cannot be expected with conventional bending methods of this type.

[Brief explanation of the drawing]

Fig. 1 is a partial perspective view of a blank metal plate on which beads have been formed in advance to be used in carrying out the method of the present invention, Figs. 2 to 5 are process explanatory views showing the bending process, and Figs. 3a to 3 Figure 5a is a simplified stress distribution diagram for explaining how springback is corrected, and Figures 4b and 5b are diagrams for explaining the behavior of a metal blank during actual bending. , Fig. 5C is a stress distribution diagram after completion of actual bending processing, Fig. 6 is a plan view of a metal blank showing a modified example, Fig. 7 is a side view of the same, and Figs. 8 and 9 are FIG. 2 is an explanatory diagram of a conventional example. 1... Metal plate, 2... Bead, 3... Bending die, 4... Blank presser, 5... Shoulder, 6... Bending punch, 7... Arc-shaped pressing surface.

Claims (1)

[Claims] 1 A continuous bead or an interrupted bead is formed in advance along the bending line on the bending part of the metal blank, and this bead is crushed during the bending process of the metal blank, A method for bending a blank metal plate, characterized in that spring back at a bent portion of the blank metal plate is corrected by plastic deformation of the bead due to the crushing.