阅读说明：本技术 冲压成型品的设计方法、冲压成型模具、冲压成型品以及冲压成型品的制造方法 (Method for designing press-molded article, press-molding die, press-molded article, and method for manufacturing press-molded article ) 是由 仮屋崎祐太 山崎雄司 于 2019-02-25 设计创作，主要内容包括：本发明涉及冲压成型品的设计方法、冲压成型模具、冲压成型品以及冲压成型品的制造方法。将抑制由回弹引起的冲压成型品的端部的下降或者跳起、冲压成型品的扭曲,抑制由回弹导致的冲压成型品的形状不良的作为课题,在设计由板状材料冲压成型的冲压成型品的形状时,使配置于上述冲压成型品的附加形状具有的、凹曲部与凸曲部连续的凹凸弯曲形状中的、凹曲部的曲率半径(R1)与凸曲部的曲率半径(R2)相同。(The present invention relates to a method of designing a press-formed article, a press-forming die, a press-formed article, and a method of manufacturing a press-formed article. In designing the shape of a press-formed article to be press-formed from a plate-like material, the radius of curvature (R1) of a concave curved portion in a concave-convex curved shape in which the concave curved portion and the convex curved portion are continuous, which is provided in an additional shape of the press-formed article, is made to be the same as the radius of curvature (R2) of the convex curved portion.)

1. A method for designing a press-formed article, characterized in that,

when designing the shape of a press-formed article press-formed from a plate-like material,

the curvature radius of the concave curved portion and the curvature radius of the convex curved portion are the same in the concave-convex curved shape having the concave curved portion and the convex curved portion which are continuous with each other and arranged in the additional shape of the press-formed product.

2. The method of designing a press-formed article according to claim 1,

the additional shape is added to improve the rigidity of the press-molded article.

3. A press-forming die for press-forming a press-formed product having an additional shape of a concave-convex curved shape in which a concave curved portion and a convex curved portion are continuous from each other from a plate-like material, the press-forming die comprising:

a die member having a shoulder portion for molding a concave curved portion and a convex curved portion of a convex curved shape provided in an additional shape to be disposed in the press-molded article,

the radius of curvature of the shoulders of the mould parts is the same.

4. The punch forming die according to claim 3,

the additional shape is added to improve the rigidity of the press-molded article.

5. A press-molded article which is press-molded from a plate-like material and has an additional shape having a concave-convex curved shape in which a concave curved portion and a convex curved portion are continuous,

the radius of curvature of the concave curved portion in the above concave-convex curved shape is the same as the radius of curvature of the convex curved portion.

6. The punch molding according to claim 5,

the additional shape is added to improve the rigidity of the press-molded article.

7. A method for producing a press-molded article, characterized in that,

when a press-formed article having an additional shape in which a concave-convex curved shape having a concave curved portion continuous with a convex curved portion is disposed is produced from a plate-like material by press-forming,

the radius of curvature of the concave curve in the concavely and convexly curved shape is the same as the radius of curvature of the convex curve.

8. The method of producing a press-molded article according to claim 7, wherein,

the additional shape is added to improve the rigidity of the press-molded article.

Technical Field

The present invention relates to a method of designing a press-formed article, a press-forming die, a press-formed article, and a method of manufacturing a press-formed article, in order to suppress a shape defect such as a drop, a jump, or a twist of an end portion of a press-formed article due to springback at the time of releasing from the press-forming die, in a press-formed article press-formed from a plate-like material.

Background

In recent years, high-strength steel sheets have been increasingly used to reduce the weight of automobile bodies for the purpose of improving fuel efficiency. By applying the high-strength steel sheet, the strength, rigidity, or energy absorption at the time of collision of the automobile body can be improved without increasing the sheet thickness.

However, in press forming which is generally used for processing automobile body parts in many cases, a shape freezing defect called springback becomes a problem. Springback occurs when a press-formed product press-formed from a steel plate as a plate-shaped material is released from a press-forming die, and increases as the material strength of the steel plate increases. The shape defect caused by springback not only impairs the appearance quality but also causes a welding defect at the time of vehicle body assembly, and therefore, measures against springback are required for the application and enlargement of high-strength steel sheets.

The reason for the springback is elastic recovery due to the bending moment generated by the unevenness of the residual stress being released at the time of the die release of the press-formed article. Therefore, conventionally, as a measure against springback, a method of alleviating unevenness of residual stress and a method of increasing the rigidity of a press-formed product to reduce springback have been proposed. In addition, for the purpose of reducing the bending moment, improving the rigidity of the press-formed article, controlling the material flow rate, and the like, there is proposed a technique of disposing an additional shape in an intermediate formed article or a final formed article, and effectively disposing the additional shape to thereby achieve the reduction of the crack and the wrinkle of the press-formed article and the improvement of the dimensional accuracy.

For example, patent document 1 proposes a technique in which, as an additional shape, embossments are arranged on an extended flange portion, an intermediate molded product in which extra beads are formed on a contracted flange portion is molded, and in the subsequent molding of a final molded product, the extended flange portion is flattened by the embossments to apply a compressive stress, and the contracted flange portion is applied with a tensile stress via the extra beads, thereby equalizing the distribution of residual stress in the press-molded product.

Patent document 2 proposes, as an additional shape, a technique of reducing a bending/bending return deformation moment received when a metal sheet passes through a die shoulder and a residual stress in the metal sheet after passing, and reducing a buckling deformation caused by springback after unloading, by arranging a plurality of groove shapes having a rectangular or circular cross section in the longitudinal direction of the die shoulder in the metal sheet.

Patent document 3 proposes a technique of absorbing a longitudinal compressive force generated in a flange by forming a plurality of convex shapes in the flange aligned in the longitudinal direction thereof as an additional shape when forming a bent flange which is bent from an end of a bent panel to be a contracted flange, and suppressing a surface of the panel from being lowered due to springback of the flange.

Patent document 1: japanese patent No. 5380890

Patent document 2: japanese laid-open patent publication No. H08-281335

Patent document 3: japanese laid-open patent publication No. H07-112219

Patent document 1 proposes a method of reducing springback by forming embossings in an extended flange portion and forming extra beads in a contracted flange portion as additional shapes to equalize residual stress, but a low-rigidity press-molded product to which the present invention is mainly directed is insufficient in reducing stress in a specific portion because springback occurs even at low stress. In addition, in a new stress state generated as a result of reducing the stress of the specific portion, springback of another form may occur. Therefore, it is difficult to efficiently perform a springback countermeasure by stress control in a press-formed product having a low rigidity shape.

Patent document 2 proposes a technique of arranging a groove shape having a rectangular or circular cross section in a metal plate to reduce residual stress in the metal plate and reduce buckling deformation after unloading, and patent document 3 proposes a technique of forming a convex shape in a flange to suppress surface lowering of the panel in molding a panel having a curved flange which is a shrink flange, but a curvature radius of the curved portion of an additional shape is not particularly specified. In the case of the additional shape, which is projected or recessed from the flat surface, the concave-convex curved shape having a substantially S-shaped cross section in which the concave curved portion and the convex curved portion are continuous is provided at the peripheral edge portion, and the spring back of these curved portions generally varies depending on the radius of curvature, and therefore, when the additional shape is applied to the press-formed product, it is necessary to design the curved portion of the concave-convex curved shape in the additional shape with an appropriate radius of curvature, but patent documents 2 and 3 do not describe a method of designing the radius of curvature of the concave-convex curved portion in the additional shape.

That is, the problems to be solved by the prior art are listed below.

(1) A molded article shape effective for measures against springback of a press-molded article having a low rigidity shape is obtained.

(2) In order to reduce the shape defect caused by springback of the press-formed product with a low rigidity shape, an effective additional shape can be designed.

However, in the conventional art, it is known that, in designing the shape of a press-molded product, the radius of curvature of the curved portion is changed such that the radius of curvature is decreased in order to increase the area of the seat surface at a portion where high surface accuracy is required, such as a joint portion, or the radius of curvature of the curved portion is increased in order to avoid breakage.

Regarding the correlation between the radius of curvature of the curved portion and the amount of springback, when the inventors studied a countermeasure against springback for a press-formed product having a low rigidity shape, it was found that, in a concave-convex curved shape having a substantially S-shaped cross section in which a concave curved portion and a convex curved portion are continuous, if the radii of curvature of the concave curved portion and the convex curved portion are different, the amount of springback occurring in the concave curved portion is different from the amount of springback occurring in the convex curved portion, and therefore, the flat portions on both sides across the concave-convex curved shape are not parallel after springback, and displacement in the height direction occurs.

Fig. 5 (a) to (c) are explanatory views of a cross section of the flat portions on both sides across the concave-convex curved shape, showing a state at the time of press bottom dead center by a broken line and showing a state after springback by a solid line, (a) shows a case where a curvature radius R1 of the concave curved portion is the same as a curvature radius R2 of the convex curved portion, (b) shows a case where a curvature radius R1 of the concave curved portion is larger than a curvature radius R2 of the convex curved portion, and (c) shows a case where a curvature radius R1 of the concave curved portion is smaller than a curvature radius R2 of the convex curved portion.

As shown in fig. 5 (a), when the radius of curvature R1 of the concave curve portion is the same as the radius of curvature R2 of the convex curve portion, the spring back amounts (spring back angles) of the concave curve portion and the convex curve portion are the same as indicated by arrows. On the other hand, as shown in fig. 5 (b), when the curvature radius R1 of the concave curved portion is larger than the curvature radius R2 of the convex curved portion, the spring back amount (spring back angle) of the concave curved portion is larger than the spring back amount (spring back angle) of the convex curved portion as indicated by an arrow. In addition, as shown in fig. 5 c, when the curvature radius R1 of the concave curved portion is smaller than the curvature radius R2 of the convex curved portion, the spring back amount (spring back angle) of the concave curved portion is larger than the spring back amount (spring back angle) of the convex curved portion as indicated by an arrow.

Since the displacement in the height direction due to the difference in the springback amount (springback angle) becomes larger as the distance from the concavo-convex curved shape increases, the distribution of the displacement in the height direction causes the end portion of the press-formed article to descend or jump up, and the distribution of the displacement in the height direction becomes a cause of the warpage of the press-formed article if the distribution of the displacement in the height direction is inclined with respect to the longitudinal direction of the press-formed article. This tendency is remarkable in a press-molded article having a high strength material and low rigidity, which has a large spring back.

Disclosure of Invention

The present invention has been made in view of the above-described findings of the present inventors to solve the problems of the prior art, and an object of the present invention is to provide a method for designing a press-formed article capable of designing an effective concavo-convex curved shape in order to reduce a shape defect after springback of the press-formed article having a low rigidity shape, and a press-forming die, a press-formed article, and a method for manufacturing a press-formed article using the designing method.

The method for designing a press-formed article according to the present invention is characterized in that, in order to suppress a shape defect of the press-formed article due to springback at the time of releasing the press-formed article, when designing the shape of the press-formed article press-formed from a plate-like material, the curvature radius of a concave curved portion and the curvature radius of a convex curved portion in a concave-convex curved shape which is continuous with the concave curved portion and is provided in an additional shape of the press-formed article are made to be the same.

The press-forming die of the present invention using the above design method is a press-forming die in which a press-formed product having an additional shape of a concave-convex curved shape in which a concave curved portion and a convex curved portion are continuous is press-formed from a plate-shaped material in order to suppress a shape defect of the press-formed product due to springback at the time of releasing the press-formed product, and the press-forming die is characterized by including die members having shoulder portions of the concave curved portion and the convex curved portion respectively formed and arranged in the convex curved shape of the additional shape of the press-formed product, and the radius of curvature of the shoulder portions of the die members are the same.

The press-formed article of the present invention using the above-described design method is a press-formed article which is press-formed from a plate-like material and has an additional shape having a concave-convex curved shape in which a concave curved portion and a convex curved portion are continuous, and in which the curvature radius of the concave curved portion is the same as the curvature radius of the convex curved portion, in order to suppress a shape defect of the press-formed article due to springback at the time of releasing the press-formed article.

In the method for producing a press-formed article according to the present invention, in order to suppress a shape defect of the press-formed article due to springback at the time of releasing the press-formed article from a die, when a press-formed article in which an additional shape having an uneven curved shape in which an uneven curved portion and a convex curved portion are continuous is produced by press-forming from a plate-shaped material, a curvature radius of the uneven curved portion in the uneven curved shape is the same as a curvature radius of the convex curved portion.

In the present specification, "the same" means that the other radius of curvature is preferably within a range of ± 10%, more preferably within a range of ± 5%, with respect to the one radius of curvature.

Effects of the invention

According to the method of designing a press-formed article of the present invention, since the additional shape having the concavely and convexly curved shape in which the concavely curved portion and the convexly curved portion are continuous is disposed on the press-formed article and the radius of curvature of the concavely curved portion in the concavely and convexly curved shape is made to be the same as the radius of curvature of the convexly curved portion, the flat portions on both sides sandwiching the concavely and convexly curved shape of the press-formed article are parallel to each other after springback regardless of the amount of springback, and therefore, lowering or jumping of the end portion of the press-formed article and twisting of the press-formed article can be suppressed, and defective shape of the press-formed article due to springback can be suppressed.

Further, according to the press-forming die of the present invention, since the die member having the shoulder portions for respectively forming the concave curved portion and the convex curved portion in the concave-convex curved shape of the die member of the press-forming die in which the additional shape of the concave-convex curved shape having the concave curved portion continuous with the convex curved portion is press-formed and arranged from the plate-like material has the same radius of curvature of the cross section of the shoulder portions, the flat portions of the press-forming product on both sides of the concave curved portion and the convex curved portion formed by the shoulder portions are parallel to each other after the spring-back regardless of the amount of the spring-back, the lowering or the jumping of the end portion of the press-forming product and the twisting of the press-forming product can be suppressed, and the shape defect of the press-forming product due to the spring-.

Further, according to the press-formed article and the method of manufacturing the press-formed article of the present invention, since the additional shape of the concave-convex curved shape in which the concave curved portion and the convex curved portion are continuous is provided and the curvature radius of the concave curved portion in the concave-convex curved shape is made to be the same as the curvature radius of the convex curved portion, the flat portions on both sides sandwiching the concave-convex curved shape of the press-formed article are parallel to each other after springback regardless of the springback amount, and therefore, the lowering or jumping of the end portion of the press-formed article and the twisting of the press-formed article can be suppressed, and the shape defect of the press-formed article due to the springback can.

In the method of designing a press-formed article, the press-forming die, the press-formed article, and the method of manufacturing a press-formed article according to the present invention, the additional shape having the concave-convex curved shape in which the concave curved portion and the convex curved portion are continuous may be added to improve the rigidity of the press-formed article. In this way, the rigidity of the press-formed article can be improved by the additional shape to reduce the amount of springback, and the shape defect of the press-formed article due to springback can be suppressed.

Drawings

Fig. 1 is a perspective view showing a press-formed article according to an embodiment of the present invention designed by a method of designing a press-formed article according to an embodiment of the present invention.

Fig. 2 (a) and (B) are cross-sectional views taken along the line a-a and the line B-B in fig. 1, respectively, of the rigid shape of the press-molded article according to the above embodiment.

Fig. 3 is a plan view showing the height direction displacement distribution by springback analysis of a press-formed product of a comparative example by displacement contour lines (contour lines).

Fig. 4 is a plan view showing the height direction displacement distribution by springback analysis of the press-formed product according to the above embodiment by displacement contour lines (contour lines).

Fig. 5 (a) to (c) are explanatory views of a cross section of the flat portions on both sides across the concave-convex curved shape, showing a state at the time of press bottom dead center by a broken line and showing a state after springback by a solid line, (a) shows a case where a curvature radius R1 of the concave curved portion is the same as a curvature radius R2 of the convex curved portion, (b) shows a case where a curvature radius R1 of the concave curved portion is larger than a curvature radius R2 of the convex curved portion, and (c) shows a case where a curvature radius R1 of the concave curved portion is smaller than a curvature radius R2 of the convex curved portion.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, fig. 1 is a perspective view showing a press-formed product according to an embodiment of the present invention designed by a method of designing a press-formed product according to an embodiment of the present invention, fig. 2 (a) and 2 (B) are cross-sectional views of a rigid shape of the press-formed product according to the embodiment along lines a-a and B-B in fig. 1, fig. 3 is a plan view showing a height-direction displacement distribution by springback analysis of an original-shaped press-formed product as a comparative example with displacement contour lines (contour lines), fig. 4 is a plan view showing a height-direction displacement distribution by springback analysis of the press-formed product according to the embodiment with displacement contour lines (contour lines), and in the drawings, reference numeral 1 denotes a press-formed product.

The method of designing a press-formed product according to the above-described embodiment is used to design a press-formed product 1 provided as a front pillar ring member that is a kind of a vehicle body member of an automobile, and the press-formed product 1 has a thin trapezoidal shape that is easily bent and easily twisted, that is, a shape with low rigidity, without the additional shapes 2 and 3 shown in fig. 1. In addition, as a press-molded product of an automobile body member, such a shape having low rigidity is often provided. Therefore, in the press-molded article 1, two additional shapes 2 and 3 having a long circular shape in plan view and a flat top surface are added to the flat surface of the thin trapezoidal shape in order to improve rigidity.

The shapes 2 and 3 of the press-formed article 1 have concave-convex curved shapes 4 each having a substantially S-shaped cross section in which a concave curved portion and a convex curved portion are continuous in the peripheral edge portion, as in the cross-sectional shapes shown in fig. 2 (a) and (b), and when designing the shape of the press-formed article 1, the radius R1 of the concave curved portion and the radius R2 of the convex curved portion in the concave-convex curved shape 4 are set to values different from each other, i.e., R1 > R2, as shown in fig. 5 (b), for example. When the press-forming analysis and the springback analysis are performed on the press-formed product 1 of the original shape by using known software by a computer, as shown by a displacement contour line having the point O of the reference numeral as a reference height in fig. 3, the Z-direction displacement on the negative side becomes large on the left side of the additional shape 3, and therefore, a large drop is recognized, and the Z-direction displacement on the negative side becomes further large on the left upper side of the additional shape 2, and therefore, the press-formed product 1 is recognized to be distorted.

Therefore, in the method of designing a press-formed product according to the present embodiment, for example, as shown in fig. 5 (a), the press-formed product 1 according to the above-described embodiment is designed by setting the radius R1 of the concave curved portion and the radius R2 of the convex curved portion in the concave-convex curved shape 4 having a substantially S-shaped cross section in which the concave curved portion and the convex curved portion are continuous in the peripheral edge portions of the additional shapes 2 and 3 to the same value, that is, R1 is equal to R2.

When the press-forming analysis and the springback analysis are performed on the press-formed product 1 of the present embodiment in which the radius R1 of the concave curved portion and the radius R2 of the convex curved portion have the same value by using known software by a computer in the same manner as the original shape, as shown by the displacement contour line of the height with reference to the point O in fig. 4, it is found that the Z-direction displacement on the negative side is reduced on the left side of the additional shape 3, so that the drop is smaller than the original shape, and the Z-direction displacement on the negative side is reduced in the left-up direction from the additional shape 2, so that the warpage of the press-formed product 1 is reduced as compared with the original shape. Therefore, according to the design method of the present embodiment and the press-formed product 1 of the present embodiment, it is possible to suppress the end portion of the press-formed product from dropping or jumping, and the distortion of the press-formed product, and to suppress the shape defect of the press-formed product due to springback.

The plate-like material forming the press-molded article 1 of the present embodiment can be, for example, a 980 MPa-level high-tensile steel plate, a plate thickness t: 0.9mm, yield point YP: 620MPa, tensile strength TS: 1030MPa, elongation El: 15%, the method of manufacturing a press-formed article according to an embodiment of the present invention is a method of press-forming the steel sheet using the press-forming die according to an embodiment of the present invention, thereby forming the press-formed article 1 according to the above-described embodiment.

Therefore, the press forming die of the above embodiment includes, as die members, a normal punch having a concave portion having a shape corresponding to the thin trapezoidal shape upward from the outward flanges located at the upper and lower end portions in fig. 1 of the press formed product 1 and the additional shapes 2, 3 protruding from the flat surface of the trapezoidal shape, a die, and a blank holder, the blank holder sandwiching a steel plate between the die and the flat surface outside the concave portion of the die, the punch press-pressing the steel plate sandwiched between the die and the blank holder into the concave portion of the die to form the thin trapezoidal shape, and the punch press-pressing the convex portion at the tip of the punch into the concave portion of the die to press-form the additional shapes 2, 3 on the flat surface of the trapezoidal shape.

Here, in the press forming die of the above embodiment, the radius of the cross-sectional shape of the shoulder portion of the concave portion of the die for forming the concave curved portion of the additional shape 2, 3 is substantially equal to the radius R1 of the concave curved portion, the radius of the cross-sectional shape of the shoulder portion of the convex portion of the punch tip for forming the convex curved portion of the additional shape 2, 3 is substantially equal to the radius R2 of the convex curved portion, and the radii of the cross-sectional shapes of these shoulder portions are equal to each other.

With the method of manufacturing a press-formed article according to the above-described embodiment, the press-formed article 1 press-formed using the press-forming die according to the above-described embodiment has the same radius R1 of the concave curved portion and the same radius R2 of the convex curved portion of the additional shapes 2 and 3, and according to the press-formed article and the method of manufacturing the same according to the present embodiment, it is possible to suppress lowering or jumping of the end portion of the press-formed article and twisting of the press-formed article due to springback of the press-formed article, and it is possible to suppress shape defects of the press-formed article due to springback.

While the embodiments have been described above, the design method of the press-formed article, the press-forming die, the press-formed article, and the manufacturing method of the press-formed article according to the present invention are not limited to the above-described embodiments, and can be appropriately changed within the scope of the description of the technical means, and for example, the shape and the additional shape of the press-formed article may be other than those shown in fig. 1, and the concave-convex curved shape having a substantially S-shaped cross section in which the concave curved portion and the convex curved portion are continuous may be an additional shape for improving the rigidity, or may be an additional shape for reducing the bending moment, controlling the material flow rate, or the like.

Possibility of industrial utilization

Thus, according to the method of designing a press-formed article, the press-forming die, the press-formed article, and the method of manufacturing a press-formed article of the present invention, it is possible to suppress the lowering or jumping of the end portion of the press-formed article and the twisting of the press-formed article due to the springback, and to suppress the shape defect of the press-formed article due to the springback.

Description of reference numerals

1 … press molding, 2, 3 … additional shape, 4 … concave-convex curved shape, radius of R1 … concave curved portion, radius of R2 … convex curved portion.