JPH07185663A - Press molding method and molded product - Google Patents

Abstract

PURPOSE:To obtain a press forming method and a press formed article in which forming can be performed without generating spring back. CONSTITUTION:A step shape recessed stage part (d) recessed in a direction opposite to a forming bending direction is formed simultaneously when a bending shoulder part (t) is formed to prevent the spring back generated at the bending shoulder part (t) in the forming of the press formed article W, which keeps balance by generating a reverse moment against the spring back. An emposs shape recessed stage part (d) can be formed locally instead of the step shape recessed stage part (d).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a press-molding method and a press-molded product which are molded without causing springback.

[0002]

2. Description of the Related Art Heretofore, a molding method has been known in which spring back caused by press molding is prevented during press molding. As an example of such a molding method,
For example, in Japanese Examined Patent Publication No. 4-4047, a method of pressing the bending shoulder with a slight forging is adopted.

[0003]

However, in the case of the above technique, the spring back stress is reduced by pressing the bending shoulder portion to reduce the plate thickness of the bending shoulder portion and obtain a certain effect. However, there is a problem that it is difficult to obtain a further effect.

[0004]

In order to solve the above problems, the present invention provides a press forming method for preventing springback which occurs in a bending shoulder portion during press forming. At the bending shoulder portion, a concave step portion that is recessed in the direction opposite to the forming bending direction is formed at the same time.

[0005]

Operation: By forming a concave stepped portion that is recessed in the direction opposite to the forming bending direction on the bending shoulder, a springback moment in the opposite direction is positively generated to achieve balance.

[0006]

Embodiments of the press molding method of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view of a molded product in which a step-shaped concave step portion is molded, and FIG. 2 is an experimental data table showing improvement of springback when the step-shaped concave step portion is molded.

Generally, when bending is performed by press working as shown in FIG. 5, the springback moment M _R acts in a direction in which the bending angle decreases when released from the mold.

The springback amount Δθ _R is
If it is assumed that the material is a work-hardened material having a relationship of plastic stress σ and strain ε represented by σ = Fε ⁿ (F is a work-hardening coefficient) and is in a plane strain state (two-dimensional problem), for example, the curvature When bent at a bending angle θ _R with a radius R, it is expressed by the following general formula.

[0009]

[Equation 1]

Here, n is a work hardening index (n value), F is a work hardening coefficient (F value), E is a Young's modulus, and t ₀ is a plate thickness.

Therefore, according to the present invention, in the press molding stage, as shown in FIG.
As shown in (a), a stepped concave step portion d is formed in the center of the bending shoulder portion t of the molded product W, and a moment in a direction opposite to the springback moment M _R is generated by the concave step portion d. Let me balance it.

The recessed step portion d not only reduces the plate thickness by recessing the surface, but also, for example, as shown in FIG.
As shown in, the entire shape is recessed in the direction opposite to the forming and bending direction.

In the case of such a molding, for example, in the case of molding a cross section such as (B), R3 (or R0)
The punch having the curved convex portions of No. 2 and the die having the curved convex portions of R5 on both sides of the concave portion corresponding thereto are formed.

The recessed step portion d recessed in the direction opposite to the forming direction causes springback in the direction opposite to the forming bending direction and balances the springback.

The springback of the molded product molded by the above method is compared with the springback of the molded product molded by the conventional method as shown in FIG.

FIG. 2 shows a springback amount (°) when a steel plate (SPC) and an aluminum plate are formed under a processing condition of a drawing depth of 30 mm and a processing speed of 25 SPM, and a circle indicates a conventional conventional method. In FIG. 3, a triangle mark is formed by a punch having a curvature of R3, and a square mark is formed by a punch having a curvature of R0.

As a result, it has been clarified that both the steel plate (SPC) and the aluminum plate are very effective.

Here, as is clear from the equation for obtaining the springback amount Δθ _R , originally, the larger the R of the punch, the larger the reverse moment, so the springback should be smaller, but this experiment In the case of, the opposite result is shown. It is considered that this is deviated from the theoretical value because the die is correcting the R stop portion.

As shown in FIG. 6, the sectional shape is r
_1, r _2, provided with a bending radius of a total of 3 locations having a radius of curvature r _3, when the opposite bending direction of the center of the bending R portions to bending direction of the bending R portions of both sides two locations , The theoretical value of the springback amount Δθ at the point B when the point A is constrained in the vertical direction is calculated by the following equation.

[0020]

[Equation 2]

Next, FIG. 3 shows an example in which an embossed concave step portion d is locally added to the bending shoulder portion t.

Also, in this molding, the bending shoulder portion t and the embossed concave step portion d are simultaneously formed.

As shown in FIG. 4, the springback of the molded product molded using the φ5 punch and the φ3 punch was compared with the springback of the molded product molded by the conventional method. It can be seen that the effect is great in this case as well. In addition, the fact that the springback is negative indicates that the reverse moment is larger.

[0024]

As described above, in the press-molding method and the molded product of the present invention, since the concave step portion which is recessed in the opposite direction is formed in the bending shoulder portion, the reverse moment is generated and the balance is achieved. Springback can be effectively prevented. Therefore, the dimensional accuracy of the press-formed product can be improved.

[Brief description of drawings]

FIG. 1 is a perspective view of a molded product in which a stepped concave step is molded.

FIG. 2 is an experimental data table showing an improvement in springback when a step-like concave step is formed.

FIG. 3 is a perspective view of a molded product in which an embossed concave step is molded.

FIG. 4 is an experimental data table showing an improvement in springback when an embossed concave step is formed.

FIG. 5 is an explanatory diagram for explaining spring back of simple bending.

FIG. 6 is an explanatory view for explaining a springback of bead-shaped bending.

[Explanation of symbols]

 W Molded product t Bent shoulder d Concave step

Front page continued (72) Inventor Kei Kiyama 1-10-1 Shin-Sayama, Sayama-shi, Saitama Honda Engineering Co., Ltd. (72) Inventor Tetsuya Wakabayashi 1-10-1 Shin-Sayama, Sayama-shi, Saitama Honda Engineering Co., Ltd. In the company

Claims (2)

[Claims] 1. A press forming method for preventing springback from occurring in a bending shoulder portion during press forming, wherein when forming the bending shoulder portion, the bending shoulder portion is recessed in a direction opposite to a forming bending direction. A press molding method characterized in that a concave step is formed at the same time. 2. A press-formed product, which is a press-formed product, in which a bent shoulder is formed with a recessed step portion for preventing springback which is recessed in a direction opposite to the bending direction.