JP7006666B2 - Design method for press-molded products, manufacturing method for press-molded products and press-molded products - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention is a method for designing a press-molded product that reduces springback that occurs when a molded product is released from a die in press-molding of a plate-shaped material mainly made of a metal plate, and enhances the dimensional accuracy of the press-molded product. , Press-molded products and methods for manufacturing press-molded products.

In recent years, there has been an increasing demand for weight reduction of automobile bodies for the purpose of improving fuel efficiency due to energy problems and global environmental problems, while demands for improving collision characteristics, for example, body rigidity, for occupant protection in the event of a collision. Is increasing year by year. In order to meet these two conflicting demands, the application of high-strength steel sheets is expanding. By applying a high-strength steel plate, it is possible to increase the strength and rigidity of the automobile body and the absorbed energy at the time of a collision without increasing the plate thickness.

However, in press molding, which is generally used frequently for processing vehicle body parts, a shape freezing defect called springback becomes a problem. Springback occurs when a press-molded product press-molded from a steel plate as a plate-like material is released from a die, and increases as the material strength of the steel plate increases. Since springback not only impairs the appearance quality but also causes welding defects during assembly, it is indispensable to take measures against springback in order to expand the application of high-strength steel sheets.

The cause of the springback is the elastic recovery due to the bending moment caused by the non-uniformity of the residual stress being released at the time of mold release of the press-molded product. Therefore, conventionally, as a measure against springback, a method of alleviating the non-uniformity of residual stress has been proposed. However, since the shape rigidity of a low-rigidity component is low and springback occurs even at a low stress, it is considered more effective to improve the component rigidity than to reduce the residual stress.

In Patent Document 1, an intermediate product in which an emboss is arranged in an elongated flange portion and a surplus bead is arranged in a contracted flange portion is formed, and in the molding of a final molded product, compressive stress is applied to the elongated flange portion by crushing the embossing. A technique has been proposed for leveling the residual stress distribution of a press-formed product by applying tensile stress to the shrinking flange portion by means of a surplus bead.

Patent Document 2 proposes a technique for preventing warpage of a panel by providing a convex bead inside the container in the vicinity of the bottom corner portion of the bottom panel portion in a square drawing container.

In Patent Document 3, flatness is corrected by forming a plurality of triangular beads along the edge of the flange portion of a press-molded product having a flange portion bent at a substantially right angle at least a part of the peripheral edge of the flat surface portion. The technology to do is proposed.

In Patent Document 4, as a springback suppression countermeasure component, a stress state that causes springback is set in each element of an analysis model of a press-formed product, shape optimization analysis is performed, and a portion having a high contribution to rigidity is detected. A technique for taking measures for improving the rigidity of a specific part of a press-molded product based on the detected part has been proposed.

Japanese Unexamined Patent Publication No. 2009-255117 Japanese Unexamined Patent Publication No. 2008-105088 Japanese Unexamined Patent Publication No. 11-277155 Japanese Unexamined Patent Publication No. 2014-46349

As a method for leveling the residual stress, Patent Document 1 proposes a method of forming an embossing on the extension flange portion and forming a surplus bead on the contraction flange portion, but the low rigidity which is the main object of the present invention is proposed. Since springback occurs in parts even at low stress, it may not be sufficient to reduce the stress in a specific part. In addition, another form of springback may occur in a new stress state resulting from reducing the stress in a particular portion.

Patent Document 2 proposes a technique for preventing the panel from warping by providing a convex bead inside the container near the bottom corner of the bottom panel portion, but among the automobile frame parts mainly targeted by the present invention. There are also low-rigidity parts with complicated shapes, and a method of increasing the rigidity only near the bottom corner may not be sufficient as a countermeasure.

Patent Document 3 targets parts having a bent flange portion, but some low-rigidity parts have edges that do not have a bent flange portion, and the low rigidity of such a portion is the low rigidity of the entire panel. Since the flatness may be deteriorated, it may not be sufficient as a countermeasure.

Patent Document 4 proposes a technique for improving the dimensional accuracy of a panel by taking measures to improve rigidity at a part specified by optimization analysis, but optimization analysis requires a large amount of time for analysis and is not applicable. It may have a possible shape and may not be available in the actual product development phase.

That is, the problems to be solved by the conventional technology are listed below.
(1) Shape The shape of the part is effective for suppressing springback for parts with low rigidity.
(2) The bead arrangement and component shape that are effective in suppressing springback can be easily designed.

The present invention has been made in view of the above problems, and is a product having an effective part shape, a small amount of springback after press forming, and excellent shape freezing property in a springback suppression measure by improving the rigidity of the part. It is an object of the present invention to propose a design method of a press-molded product that can be easily designed, to provide the press-molded product, and to propose a manufacturing method of the press-molded product.

As a result of diligent studies, the inventors should appropriately arrange rigidity-added shapes with excellent shape freezing properties such as beads, overhanging shapes, and step shapes against the distortion of the molded product panel due to the springback of low-rigidity parts. It was found that springback can be reduced.
The method for designing a press-molded product of the present invention that advantageously solves the above problems has a first rigidity-added shape in the longitudinal direction of the press-molded product when designing the shape of the press-molded product that is press-molded from a plate-shaped material. Is arranged, and the second rigidity-added shape is arranged in a direction intersecting the longitudinal direction.

Further, the press-molded product of the present invention that advantageously solves the above-mentioned problems is a press-molded product in which a plate-shaped material is press-molded and a rigidity-added shape is arranged, and the first press-molded product in the longitudinal direction of the press-molded product. It is characterized in that the rigidity-added shape is arranged and the second rigidity-added shape is arranged in the direction intersecting the longitudinal direction.

Further, in the method for manufacturing a press-molded product of the present invention, which advantageously solves the above-mentioned problems, when a press-molded product in which a rigidity-added shape is arranged is manufactured from a plate-shaped material by press molding, the first method is in the longitudinal direction of the press-molded product. It includes a step of forming the rigidity-added shape of No. 1, and is characterized in that the second rigidity-added shape is formed at the same time as or in another step of the first rigidity-added shape in a direction intersecting the longitudinal direction.

According to the method for designing a press-molded product of the present invention, a press-molded product in which a rigidity-added shape that improves the shape rigidity of a part, for example, a bead, a step shape, or an overhang shape is arranged, and the rigidity-added shape is incorporated. Springback can be reduced by molding a press-molded product.

Moreover, according to the design method of the press-molded product of the present invention, by arranging the bead, the step shape, and the overhanging shape, which are the first rigidity-added shapes, in the longitudinal direction, it is a form of the spring back in the longitudinal direction. By suppressing camber back and further arranging the second rigidity-added shape in the direction intersecting the longitudinal direction, it is possible to suppress twisting about the longitudinal direction of the component.

According to the press-molded product and the method for manufacturing the press-molded product of the present invention, the press-molded product incorporates the rigidity-added shape arranged in the shape design of the press-molded product, so that springback is reduced and the molding accuracy is high. It can be a press-molded product.

It is a perspective view of an example of the press-molded article of a plate-shaped material. It is a contour line diagram which shows the displacement in the Z direction after the spring back of the press-molded article by the conventional method. It is a perspective view of the press-molded article which shows the arrangement of the bead which concerns on one Embodiment of this invention. FIG. 3 is a sectional view taken along the line AA ′ according to an embodiment of the present invention. It is a contour line diagram which shows the displacement in the Z direction after the spring back of the press-molded article which concerns on one Embodiment of this invention. It is a perspective view of the press-molded article which arranged the step shape and the overhang shape which concerns on other embodiment of this invention in combination.

In the method for designing a press-molded product according to an embodiment of the present invention, a rigidity-added shape that is expected to improve rigidity is arranged to design a component shape of the press-molded product. For example, when arranging a bead as a "stiffness-added shape", it is preferable to design as follows.

First, as a measure against camber back, which is a form of spring back in the longitudinal direction of the component, a first bead linear in the longitudinal direction is arranged. In order to enhance the effect of suppressing camber back, it is preferable to arrange the first bead at a length of 80% or more of the total length in the longitudinal direction of the component. More preferably, it is in the range of 90% or more and 95% or less in length. Here, the longitudinal direction of the part means a direction parallel to the long side when the press-molded product is projected onto a plane and circumscribed by a rectangle having the minimum area, and the short direction is the longitudinal direction in the same plane. A direction that is orthogonal to the direction. Further, it is preferable that the first bead is in a direction in which a bead as long as possible can be formed even if the direction does not completely coincide with the longitudinal direction.

Next, as a countermeasure against twisting about the longitudinal direction, the second bead is arranged in the direction intersecting the longitudinal direction. The second bead is preferably arranged at a position where the position in the longitudinal direction is near both ends or the component rigidity changes significantly in the longitudinal direction. Further, the intersecting direction is preferably a lateral direction orthogonal to the longitudinal direction or a direction in which the component rigidity changes significantly. Examples of the position and direction in which the rigidity changes significantly include a position where the shape of the part is constricted and a flat flat surface portion having no overhang shape. Further, the moment of inertia of area may be calculated to strictly calculate the position and direction in which the rigidity changes.

If the first bead in the longitudinal direction and the second bead in the direction intersecting the longitudinal direction are connected and integrated, the rigidity of the intersecting portion is reduced, so that the second bead is separated from the first bead. It is preferable to arrange them. The distance d between the first bead and the start point of the second bead at the intersection is preferably equal to or less than the height h of the bead.

As the rigidity-added shape, in addition to the above-mentioned linear bead, a continuous linear structure such as another overhang shape or a step shape can be applied. Moreover, you may apply them in combination. In addition, in order to avoid the generation of stress due to the additional forming of beads, it is desirable to design a part shape in which an overhang shape or a step shape that is expected to improve rigidity is woven in advance.

The press-molded product according to the embodiment of the present invention is press-molded from a plate-shaped material and intersects with the arranged first rigidity-added shape in the longitudinal direction and the longitudinal direction by the design method of the press-molded product. It has a second rigidity-added shape in the direction.

In the method for manufacturing a press-molded product according to an embodiment of the present invention, when a press-molded product having a rigidity-added shape is manufactured from a plate-shaped material by press molding, the press-molded product is arranged in the longitudinal direction according to the above-mentioned design method for the press-molded product. A process of forming a first rigidity-added shape into a plate-like material, and forming a second rigidity-added shape at the same time as or in another process of the first rigidity-added shape in a direction intersecting the longitudinal direction. Is.

(Example 1)
The present invention has been applied to the molding of the front pillar lower inner of an actual part. It is a component with an approximate length of 700 mm and a width of 400 mm. The material is a 980 MPa class cold-rolled steel sheet (HITEN) with a plate thickness of 1.2 mm, and the mechanical properties are yield point (YP) of 620 MPa, tensile strength (TS) of 1030 MPa, and elongation (El) of 15. %Met.

FIG. 1 shows the shape of the press-molded product 1 in a perspective view. The flat plate portion 2 is set as the XY surface, the longitudinal direction is the X axis in the right direction (direction from the lower side to the upper side of the component), and the lateral direction is the Y axis in the direction away from the step portion 3, and Z is perpendicular to the flat plate surface 2. The coordinate system is the axis. Same below. A step portion 3 having a Z-shaped cross section is provided along a curve on the front side (the side on the side having a small Y value). When this part is press-molded by the conventional method, the lower side of the part (left side in FIG. 1) is displaced to the negative side in the Z direction due to springback, and twisting is generated about the vertical direction of the part (left and right direction in FIG. 1). ..

FIG. 2 is a contour diagram showing the Z-direction displacement of the press-molded product by the conventional method after springback. In FIG. 2, only the flat plate portion 2 is shown in a top view. The numerical value of each corner in FIG. 2 represents the amount of displacement of each corner portion in the Z direction.

FIG. 3 shows a perspective view of a press-molded product according to an embodiment of the present invention. A linear bead 4 is arranged as a first rigidity-added shape in the longitudinal direction of the component, and a linear bead 5 is arranged as a second rigidity-added shape in a direction intersecting the longitudinal direction. The first bead 4 is arranged at a position where it can be effectively arranged over the entire length in the longitudinal direction, and the second bead 5 is arranged at a position where the shape of the part is constricted and the rigidity is greatly changed. FIG. 4 shows a cross-sectional view taken along the line AA'of the second bead 5. The second bead 5 is separated at the intersection with the first bead 4 in the longitudinal direction. The distance d between the first bead and the start point of the second bead and the height h of the bead are equivalent.

FIG. 5 is a contour diagram showing the displacement in the Z direction of the press-molded product to which the present invention is applied after springback. Similar to FIG. 2, FIG. 5 also shows only the flat plate portion 2 in a top view. In addition, the positions of the first and second beads 4 and 5 are shown. The numerical value of each corner in FIG. 5 represents the amount of displacement of each corner portion in the Z direction, and is the same unit as in FIG. From this result, it can be seen that by applying the present invention, the camber back in the longitudinal direction and the twist about the longitudinal direction are significantly improved, and the spring back can be reduced.

(Example 2)
FIG. 6 shows a perspective view of a press-molded product according to another embodiment of the present invention. A linear step 6 is arranged as a first rigidity-added shape in the longitudinal direction of the component, and a linear overhang 7 is arranged as a second rigidity-added shape in a direction intersecting the longitudinal direction. Similar to the first embodiment, the step 6 is arranged at a position where it can be effectively arranged over the entire length in the longitudinal direction, and the overhang 7 is arranged at a position where the shape of the part is constricted and the rigidity is greatly changed. The interval d from the end of the step to the start of overhang and the overhang height h are almost the same. In other embodiments as well, it was confirmed that the camber back in the longitudinal direction and the twist about the longitudinal direction were significantly improved and the spring back could be reduced as in the first embodiment.

Although the above description has been made based on the illustrated example, the method for designing the press-molded product and the method for manufacturing the press-molded product and the press-molded product of the present invention are not limited to the above examples, and are within the scope of the claims. The shape of the press-molded product may be other than that shown in FIG. 3, and the shape with added rigidity may be other than the bead shown in FIG.

Thus, according to the press-molded product design method, the press-molded product, and the press-molded product manufacturing method of the present invention, springback can be efficiently suppressed. The technique of the present invention is suitable for application to low-rigidity parts with a small amount of processing of a flat plate portion.

1 Press-molded product 2 Flat plate part 3 Step part 4 First rigidity-added shape (bead)
5 Second rigidity-added shape (bead)
6 First rigidity-added shape (step)
7 Second rigidity-added shape (overhang)

Claims (3)

When designing the shape of a press-molded product that is press-molded from a plate-shaped material,
The feature is that the first rigidity-added shape is arranged in the longitudinal direction of the press-molded product, and the second rigidity-added shape is arranged separately from the first rigidity-added shape in the direction intersecting the longitudinal direction. How to design a press-molded product. In a press-molded product that is press-molded from a plate-shaped material and has an added rigidity shape.
The first rigidity-added shape was arranged in the longitudinal direction of the press-molded product, and the second rigidity-added shape was arranged separately from the first rigidity-added shape in the direction intersecting the longitudinal direction. A press-molded product characterized by. When manufacturing a press-molded product with an additional rigidity shape from a plate-shaped material by press molding,
The step of forming the first rigidity-added shape in the longitudinal direction of the press-molded product is included, and the second rigidity-added shape is formed by separating from the first rigidity-added shape in the direction intersecting the longitudinal direction. A method for manufacturing a press-molded product, which comprises molding at the same time as the shape with added rigidity or in another process.

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