JPS5938050B2 - Method for preventing torsional deformation of pressed parts - Google Patents

Description

[Detailed Description of the Invention] In press working of thin plates, torsional deformation may occur in the molded product when it is released from the mold after processing, and as a result, positioning becomes impossible when proceeding to the next press process, etc. This causes the inconvenience of not being able to be processed, and even if press processing is possible, problems such as deformation of the assembled product occur.

In particular, torsional deformation frequently occurs in recent press forming of high-strength steel sheets, and this has become a major problem because no countermeasures have been established. Additionally, the increase in torsional deformation is due to an increase in material strength, and as long as high-tensile steel plates are used, there is no material-based countermeasure. Conventionally, when torsion occurs during press working, the torsional deformation is removed or reduced manually by partially heating or hitting the part, and in the case of mild torsion, spot welding during assembly is performed. If the order is selected appropriately, the negative effects of twisting after assembly can be reduced, but since it is not possible to remove these twisting deformations in the middle of the press processing line, if the twisting deformation is significant, it is necessary to move on to the next press die. Such countermeasures are of no use since the material cannot be loaded or positioned, making subsequent processing impossible.

Further, since such countermeasures are based on empirical know-how, the effectiveness may vary depending on the skill and experience of the worker, and sufficient effects may not be obtained depending on the shape of the part. Through numerous studies, the inventors have clarified that the occurrence of torsional deformation in repress molded products is due to the residual stress distribution present in the press molded product. In other words, the residual stress that exists in press-formed products generally has a unique pattern, with tensile residual stress existing in the part corresponding to the bottom of the punch, and compressive residual stress existing in the flange part. , such residual stress distribution is the main cause.From this point of view, the present invention reduces the above-mentioned residual stress, and in particular, forms the plate in a manner that locally reduces the thickness during one press forming process. The purpose of this invention is to provide a new method for obtaining a molded product in which torsional deformation is sufficiently reduced during demolding by adding a coining process to the blank plate at the end of the process.

The mold used for molding in the method of the present invention is similar to conventional molds, with a lower mold having a structure facing the punch, and molding is performed by the punch hitting the lower mold at the end of the press stroke. However, the feature of the present invention is that a protrusion with an appropriate height and width is provided on the surface of the lower die or punch, or a plurality of these protrusions are arranged at an appropriate pitch to perform one press stroke. The idea is to add a coining effect to the material to be formed so that a locally reduced thickness occurs at the final stage of the process.

As mentioned above, tensile residual stress exists in the portion of the molded product corresponding to the punch bottom, but the coining process added at the final stage partially reduces the plate thickness, resulting in elongation deformation.

As a result, the tensile residual stress decreases, and the compressive residual stress also decreases correspondingly, so that the magnitude of the residual stress decreases as a whole, and torsional deformation decreases. This coining process creates a local uneven pattern on the part corresponding to the punch bottom of the molded product, but if it is an interior part, there is no problem in terms of appearance.

Furthermore, since the reduction in plate thickness is local, it poses little problem in terms of structural strength as a whole. Example Comparison of torsion angle during mold release using a mold as shown in the cross-sectional view in Fig. 2, with a lower mold having protrusions on the surface of the present invention and a conventional lower mold without protrusions. did.

The molding conditions at this time were as follows. For a molded product as shown in FIG. 1 made by the conventional method, a second
As shown in the cross-sectional view of the figure, the blank 1 is placed on the die 2, and then the blank plate 1 is pressed against the die 2 by applying appropriate pressure around the periphery with the wrinkle presser plate 3. Next, the punch 4 is pressed. It descends and molding is performed, but as it progresses, it hits the lower mold 5 and the punch 4
At the same time as the molding stops, a product with the molding depth is obtained, and molding is completed in the state shown in FIG. Since the lower mold 5 has a protrusion 6 as shown in Fig. 5, the coining process is added to the blank plate at the end of the pressing process, and the plate thickness at the protrusion part decreases, causing elongation and reducing residual stress. As a result, the desired molded product with little torsional deformation was obtained. The size, shape, number, and arrangement of the protrusions may be determined experimentally so as to obtain the desired effect.

In this example, an example of a linear protrusion is shown, but the protrusion is not limited to this, and any type of protrusion that causes a partial reduction in the plate thickness is effective. Table 1 shows a comparison example of the twist angle, and shows that the method of the present invention sufficiently reduced twist at various formation depths and showed a remarkable effect compared to the conventional method that does not add coining processing. .

As mentioned above, according to the prevention method of the present invention, residual stress can be sufficiently reduced in one stroke of pressing, so a molded product with small torsional deformation can be obtained. Since it is incorporated, there is no particular increase in complexity, and correction work for removing twisting deformation is omitted, and the transition to the next processing step after demolding is facilitated.

In addition, a constant product can always be obtained regardless of the experience and skill of the worker. Therefore, it is suitable for use in labor-saving factories such as automatic press lines or fully automatic assembly lines. Furthermore, it exhibits great power in forming high-strength steel sheets.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a molded product similar to the example produced by the conventional method, FIG. The figure also shows the state after processing. Figure 4 is a partially cut-out enlarged cross-sectional view of the molded product after processing.
FIG. 5 is an enlarged perspective view of the lower die provided with protrusions for coining processing. 1: Raw board, 2: Dice, 3: Wrinkle press plate,
4: Punch, 5: Lower die, 6: Protrusion.

Claims (1)

[Claims] 1. When press-molding a blank plate, use a punch and a lower die that have a protrusion capable of coining on at least one of the punch or lower die surfaces that are in contact with the blank plate, and press a wrinkle presser plate on the die surface. A pressed part characterized in that a coining process is performed to produce a locally reduced thickness part at the final stage of a process in which the blank plate is held down and pressed by the punch with the blank plate facing a lower die. Method for preventing torsional deformation.