WO2022038836A1

WO2022038836A1 - Method for predicting shape variation in press-formed article

Info

Publication number: WO2022038836A1
Application number: PCT/JP2021/017283
Authority: WO
Inventors: 亮伸石渡; 祐輔藤井; 正樹卜部
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2020-08-17
Filing date: 2021-04-30
Publication date: 2022-02-24
Also published as: JP2022033452A; JP6939962B1

Abstract

This method for predicting shape variation in a press-formed article predicts shape variation wherein a lengthwise direction end section side of the press-formed article twists due to stress relaxation occurring over time after the press-formed article has been released from a die and springback has occurred, said press-formed article including a shape that has a hat-shaped cross-section obtained by having a top plate portion, a side wall portion, and a flange portion, and is curved along the lengthwise direction in top plane view. This method for predicting shape variation in a press-formed article includes: a step (S1) of acquiring the shape and the residual stress of the press-formed article as of immediately after springback; a step (S3) of setting, for at least a curve inner side flange portion and/or a curve outer side flange portion of the press-formed article as of immediately after springback, a stress value that is reduced due to relaxation in comparison to the residual stress as of immediately after springback; and a step (S5) of calculating, for the press-formed article for which the relaxation-reduced stress value was set, a shape in which the moments of forces are balanced.

Description

プレス成形品の形状変化予測方法Method for predicting shape change of press-molded products

　本発明は、プレス成形品（press　formed　part）の形状変化予測方法（prediction　method　for　shape　variation）に関し、特に、天板部（top　portion）と縦壁部（side　wall　portion）とフランジ部（flange　portion）を有してなるハット型断面形状（hat-shaped　cross　section）であり上面視で長手方向に沿って湾曲した形状を含むプレス成形品について、金型（tool　of　press　forming）から離型（die　release）してスプリングバック（springback）した後の時間経過に伴って生じる形状変化（shape　variation）を予測するプレス成形品の形状変化予測方法に関する。 The present invention relates to a method for predicting a shape change (prediction method for shape variation) of a press-formed part, and in particular, a top plate portion (top portion), a vertical wall portion (side wall portion), and a flange portion (flange portion). ), Which is a hat-shaped cross section and includes a shape curved along the longitudinal direction in the top view, from the die (tool of press forming). The present invention relates to a method for predicting a shape change of a press-formed product that predicts a shape variation that occurs with the passage of time after the release) and springback.

　プレス成形は金属部品（metal　part）を低コストかつ短時間に製造することができる製造方法であり、多くの自動車部品（automotive　part）の製造に用いられている。近年では、自動車の衝突安全性（collision　safety）と車体（automotive　body）の軽量化（weight　reduction）を両立するため、より高強度な金属板（high-strength　metal　sheet）が自動車部品のプレス成形（press　forming）に利用されている。 Press molding is a manufacturing method that can manufacture metal parts at low cost and in a short time, and is used in the manufacture of many automobile parts. In recent years, in order to achieve both collision safety of automobiles and weight reduction of the automobile body, higher-strength metal sheets have been press-molded for automobile parts (high-strength metal sheet). It is used for press forming).

　高強度な金属板をプレス成形する場合の主な課題の一つにスプリングバックによる寸法精度（dimensional　accuracy）の低下がある。プレス成形により金属板を変形させる際にプレス成形品に発生した残留応力（residual　stress）が駆動力となり、金型から離型したプレス成形品がプレス成形前の金属板（metal　sheet）の形状にバネのように瞬間的に戻ろうとする現象をスプリングバックと呼ぶ。 One of the main issues when press-molding a high-strength metal plate is a decrease in dimensional accuracy due to springback. Residual stress generated in the press-molded product when deforming the metal plate by press molding becomes the driving force, and the press-molded product released from the mold becomes the shape of the metal sheet before press molding. The phenomenon of momentarily returning like a spring is called springback.

　プレス成形時に発生する残留応力は高強度な金属板（例えば、高張力鋼板（high-tensile　steel　sheet））ほど大きくなるため、スプリングバックによる形状変化も大きくなる。したがって、高強度な金属板ほどスプリングバック後の形状を規定の寸法内におさめることが難しくなる。そこで、スプリングバックによるプレス成形品の形状変化を精度良く予測する技術が重要となる。 Since the residual stress generated during press forming increases as the metal plate has higher strength (for example, high-tensile steel sheet), the shape change due to springback also increases. Therefore, the higher the strength of the metal plate, the more difficult it is to keep the shape after springback within the specified dimensions. Therefore, a technique for accurately predicting the shape change of a press-molded product due to springback is important.

　スプリングバックによる形状変化の予測には、有限要素法（finite　element　method）によるプレス成形シミュレーション（press　forming　simulation）の利用が一般的である。当該プレス成形シミュレーションにおける手順としては、まず、金属板を成形下死点（the　bottom　dead　center　of　forming）までプレス成形する過程のプレス成形解析（press　forming　analysis）を行い、プレス成形下死点での残留応力を予測する第１段階（例えば特許文献１）と、金型から離型した（取り出した）プレス成形品がスプリングバックにより形状が変化する過程のスプリングバック解析を行い、離型したプレス成形品における力のモーメント（moment）と残留応力との釣り合いがとれる形状を予測する第２段階（例えば特許文献２）に分けられる。 For prediction of shape change by springback, it is common to use press forming simulation by the finite element method. As a procedure in the press forming simulation, first, a press forming analysis in the process of press forming a metal plate to the bottom dead center of forming is performed, and then the press forming analysis is performed at the press forming bottom dead point. The first step of predicting residual stress (for example, Patent Document 1) and the springback analysis of the process in which the shape of the press-formed product released (taken out) from the die changes due to springback are performed, and the press-formed product is released from the mold. It is divided into the second stage (for example, Patent Document 2) of predicting a shape in which the moment of force and the residual stress in the product can be balanced.

特許第５７９５１５１号公報Japanese Patent No. 5795151 特許第５８６６８９２号公報Japanese Patent No. 5866892 特開２０１３－１１３１４４号公報Japanese Unexamined Patent Publication No. 2013-11344

　これまでに、前述した第１段階のプレス成形解析と第２段階のスプリングバック解析（spring-back　analysis）とを統合したプレス成形シミュレーションを行うことにより、金型から離型してスプリングバックした直後のプレス成形品の形状が予測されてきた。しかしながら、発明者らは、プレス成形シミュレーションにより予測されたプレス成形品の形状と実際にプレス成形されたプレス成形品の形状とを比較した際、プレス成形シミュレーションによる形状予測精度が低くなるプレス成形品があることに気づいた。 By performing a press forming simulation that integrates the above-mentioned first-stage press forming analysis and second-stage spring-back analysis, the die is removed from the mold and immediately after springback. The shape of the press-formed product has been predicted. However, when the inventors compare the shape of the press-molded product predicted by the press-form simulation with the shape of the press-molded product actually press-molded, the shape prediction accuracy by the press-form simulation becomes low. I noticed that there is.

　そこで、プレス成形シミュレーションによる形状予測精度が低くなるプレス成形品に関して調査したところ、一例として図２に示すような、天板部３と縦壁部５とフランジ部７とを有してなるハット型断面形状（hat-shaped　cross　section）であり、上面視で長手方向に沿って湾曲したプレス成形品１においては、離型して数日経過した後では、長手方向中央部に対して長手方向端部側が捩れ（twist）るような変形が生じてしまい、プレス成形直後と数日経過後とではプレス成形品１の形状が異なることを発見した。 Therefore, when a press-formed product having a low shape prediction accuracy by press-forming simulation was investigated, as an example, a hat type having a top plate portion 3, a vertical wall portion 5, and a flange portion 7 as shown in FIG. In the press-formed product 1 which has a cross section and is curved along the longitudinal direction in the top view, after several days have passed since the mold was released, the longitudinal end with respect to the central portion in the longitudinal direction. It was discovered that the shape of the press-molded product 1 was different immediately after the press molding and after several days had passed due to the deformation such that the portion side was twisted.

　このようなプレス成形品の時間単位の経過に伴う経時変化は、クリープ現象（creep　phenomenon）のように外部から高い荷重を受け続ける構造部材（structure　member）が徐々に変形する現象（例えば、特許文献３）と類似しているように思われるが、外部から荷重を受けていないプレス成形品において起こる形状の変化はこれまでに知られていなかった。 Such a change over time with the passage of time of a press-molded product is a phenomenon in which a structural member that continues to receive a high load from the outside, such as a creep phenomenon (creep phenomenon), is gradually deformed (for example, Patent Documents). Although it seems to be similar to 3), the change in shape that occurs in the press-formed product that is not subjected to an external load has not been known so far.

　さらに、従来のプレス成形シミュレーションにおける第２段階（スプリングバック解析）は、金型から取り出した瞬間にスプリングバックした直後のプレス成形品の形状を予測するものである。そのため、本願が目的とするスプリングバックしたプレス成形品について、例えば数日経過した後の形状変化を予測することに関しては、これまでに何ら検討されていなかった。その上、スプリングバックしたプレス成形品の時間単位の経過による形状変化は、前述したように、外部からの荷重を受けずに生じるものである。そのため、プレス成形品の時間単位の経過による形状変化の予測を試みたとしても、クリープ現象による形状変化を取り扱う解析手法を適用することはできなかった。 Furthermore, the second stage (springback analysis) in the conventional press molding simulation predicts the shape of the press molded product immediately after springback at the moment of taking out from the die. Therefore, for the spring-backed press-molded product, which is the object of the present application, for example, the prediction of the shape change after several days has not been studied. Moreover, the shape change of the spring-backed press-molded product over time occurs without receiving an external load, as described above. Therefore, even if an attempt was made to predict the shape change of the press-molded product over time, it was not possible to apply an analysis method that handles the shape change due to the creep phenomenon.

　本発明は、上記のような課題を解決するためになされたものであり、天板部と該天板部から連続する縦壁部と該縦壁部から連続するフランジ部とを有してなるハット型断面形状であり上面視（天板部方向から見た場合）で長手方向に沿って湾曲した形状を含むプレス成形品について、金型から離型した瞬間にスプリングバックした後の時間単位の経過による前記プレス成形品の形状変化を予測するプレス成形品の形状変化予測方法を提供することを目的とする。 The present invention has been made to solve the above-mentioned problems, and includes a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion. For press-molded products that have a hat-shaped cross-sectional shape and include a shape that is curved along the longitudinal direction when viewed from above (when viewed from the top plate), the unit of time after springing back at the moment of mold release from the mold. It is an object of the present invention to provide a method for predicting a shape change of a press-molded product that predicts a shape change of the press-molded product over time.

　本発明に係るプレス成形品の形状変化予測方法は、天板部と該天板部から連続する縦壁部と該縦壁部から連続するフランジ部とを有してなるハット型断面形状であり、上面視で長手方向に沿って湾曲した形状を含むプレス成形品について、金型から離型した瞬間にスプリングバックした後の時間経過に伴う応力緩和による長手方向端部側が捩れる形状変化を予測するものであって、前記プレス成形品のスプリングバック解析により、スプリングバックした直後の前記プレス成形品の形状及び残留応力を取得するスプリングバック直後の形状・残留応力取得工程と、スプリングバックした直後の前記プレス成形品の少なくとも湾曲内側フランジ部及び／又は湾曲外側フランジ部に対し、スプリングバックした直後の残留応力よりも緩和減少した応力の値を設定する残留応力緩和（residual　stress　relaxation）減少設定工程と、緩和減少した応力の値を設定した前記プレス成形品について力のモーメントが釣り合う形状を求める残留応力緩和形状解析工程と、を含む。 The method for predicting a shape change of a press-molded product according to the present invention is a hat-shaped cross-sectional shape having a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion. Predicts a shape change in which the end side in the longitudinal direction is twisted due to stress relaxation over time after springing back at the moment of removal from the mold for a press-molded product containing a shape curved along the longitudinal direction in top view. The shape / residual stress acquisition step immediately after springback and the shape / residual stress acquisition step immediately after springback to acquire the shape and residual stress of the press-molded product immediately after springback by the springback analysis of the press-molded product, and immediately after springback. A residual stress relaxation reduction setting step for setting a stress value that is relaxed and reduced from the residual stress immediately after springback with respect to at least the curved inner flange portion and / or the curved outer flange portion of the press-molded product. The present invention includes a residual stress relaxation shape analysis step of obtaining a shape in which the moments of force are balanced for the press-molded product in which the value of the stress reduced by relaxation is set.

　前記残留応力緩和減少設定工程において、スプリングバックした直後の残留応力よりも10%以上緩和減少した応力の値を設定するとよい。 In the residual stress relaxation reduction setting step, it is preferable to set the value of the stress whose relaxation is reduced by 10% or more from the residual stress immediately after springback.

　前記プレス成形品のプレス成形に供するブランク（blank）は、引張強度（tensile　strength）が150MPa級（MPa-class）以上2000MPa級以下の金属板であるとよい。 The blank used for press molding of the press-molded product is preferably a metal plate having a tensile strength of 150 MPa class (MPa-class) or more and 2000 MPa class or less.

　本発明においては、天板部と該天板部から連続する縦壁部と該縦壁部から連続するフランジ部とを有してなるハット型断面形状であり上面視で長手方向に沿って湾曲した形状を含むプレス成形品について、該プレス成形品のスプリングバック解析により、スプリングバックした直後の前記プレス成形品の形状及び残留応力を取得するスプリングバック直後の形状・残留応力取得工程と、該取得したスプリングバックした直後のプレス成形品の少なくとも湾曲内側フランジ部及び／又は湾曲外側フランジ部に対し、スプリングバックした直後の残留応力よりも緩和減少した応力の値を設定する残留応力緩和減少設定工程と、緩和減少した応力の値を設定した前記プレス成形品について力のモーメントが釣り合う形状を求める残留応力緩和形状解析工程と、を含むことにより、金型から離型してスプリングバックした後の時間経過に伴う前記プレス成形品の形状変化を精度良く予測することができる。その結果、自動車部品や車体等の製造工程において、従来よりもさらに寸法精度の優れたプレス成形品を得て、製造能率を大幅に向上できる。 In the present invention, it is a hat-shaped cross-sectional shape having a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion, and is curved along the longitudinal direction in a top view. For the press-molded product including the formed shape, the shape / residual stress acquisition step immediately after springback and the acquisition of the shape and residual stress of the press-molded product immediately after springback by the springback analysis of the press-molded product. Residual stress relaxation reduction setting step for setting at least the value of the stress that is relaxed and reduced from the residual stress immediately after springback for at least the curved inner flange portion and / or the curved outer flange portion of the press-formed product immediately after springback. , Residual stress relaxation shape analysis step to obtain a shape in which the moment of force is balanced for the press-formed product in which the value of the stress reduced by relaxation is set, and the time elapsed after the mold is removed from the mold and springed back. It is possible to accurately predict the shape change of the press-molded product due to the above. As a result, in the manufacturing process of automobile parts, car bodies, etc., a press-molded product having higher dimensional accuracy than the conventional one can be obtained, and the manufacturing efficiency can be significantly improved.

図１は、本発明の実施の形態に係るプレス成形品の形状変化予測方法の処理の流れを示すフロー図である。FIG. 1 is a flow chart showing a processing flow of a method for predicting a shape change of a press-molded product according to an embodiment of the present invention. 図２は、本発明の実施の形態で対象とした上面視で長手方向に沿って湾曲したハット型断面形状のプレス成形品を示す図である（（ａ）斜視図、（ｂ）上面図）。FIG. 2 is a view showing a press-molded product having a hat-shaped cross-sectional shape curved along the longitudinal direction in a top view, which is the object of the embodiment of the present invention ((a) perspective view, (b) top view). .. 図３は、ひずみ（strain）を付与した後に一定に保持した状態で時間の経過とともに応力が緩和して減少する応力緩和現象（stress　relaxation　phenomenon）を説明する図である。FIG. 3 is a diagram for explaining a stress relaxation phenomenon (stress relaxation phenomenon) in which stress is relaxed and decreased with the passage of time in a state of being held constant after applying strain. 図４は、上面視で長手方向に沿って湾曲したハット型断面形状のプレス成形品の湾曲内側フランジ部及び湾曲外側フランジ部における応力緩和による形状変化を説明する図である（（ａ）プレス成形直後の成形下死点、（ｂ）スプリングバック直後、（ｃ）時間経過後）。FIG. 4 is a diagram illustrating a shape change due to stress relaxation in a curved inner flange portion and a curved outer flange portion of a press-molded product having a hat-shaped cross-sectional shape curved along the longitudinal direction in a top view ((a) press molding). Immediately after molding bottom dead center, (b) immediately after springback, (c) after time elapses). 図５は、実施例で対象とした上面視で長手方向に沿って湾曲したハット型断面形状のプレス成形品を示す図である。FIG. 5 is a diagram showing a press-molded product having a hat-shaped cross-sectional shape curved along the longitudinal direction in a top view, which is the target of the embodiment.

＜発明に至るまでの検討＞
　発明者らは、前述の課題を解決するために、図２に一例として示すプレス成形品１について、金型から離型した瞬間にスプリングバックした後のさらなる時間経過に伴う応力緩和による形状変化を予測する手法を確立するために、その前段階として、プレス成形品１の形状が時間経過に伴って変化する原因について検討した。 <Examination leading up to the invention>
In order to solve the above-mentioned problems, the inventors have made a change in the shape of the press-molded product 1 shown as an example in FIG. In order to establish a prediction method, as a preliminary step, the cause of the change in the shape of the press-molded product 1 with the passage of time was examined.

　検討の対象としたプレス成形品１は、図２に一例を示すように、天板部３と、天板部３から連続する一対の縦壁部５と、一対の縦壁部５のそれぞれから連続するフランジ部７とを有してなるハット型断面形状であり、上面視で長手方向に沿って湾曲した形状を含み、天板部３と縦壁部５とはパンチ肩Ｒ部（shoulder　part　of　a　punch）９を介して連続し、縦壁部５とフランジ部７とはダイ肩Ｒ部（shoulder　part　of　a　die）１１を介して連続する。また、フランジ部７には、湾曲の内側に位置する湾曲内側フランジ部７ａと、湾曲の外側に位置する湾曲外側フランジ部７ｂとがある。なお、湾曲の内側とは、上面視において湾曲の曲率中心（curvature　center）と同じ側とし、湾曲の外側とは、上面視において湾曲の曲率中心と反対側とする。 As shown in FIG. 2, the press-molded product 1 to be examined is from each of the top plate portion 3, the pair of vertical wall portions 5 continuous from the top plate portion 3, and the pair of vertical wall portions 5. It is a hat-shaped cross-sectional shape having a continuous flange portion 7, including a shape curved along the longitudinal direction in a top view, and the top plate portion 3 and the vertical wall portion 5 are punch shoulder R portions (shoulder part). It is continuous via the punch) 9, and the vertical wall portion 5 and the flange portion 7 are continuous via the die shoulder R portion (shoulder part of a die) 11. Further, the flange portion 7 includes a curved inner flange portion 7a located inside the curve and a curved outer flange portion 7b located outside the curve. The inside of the curve is the same side as the curvature center of the curve in the top view, and the outside of the curve is the opposite side of the curvature center of the curve in the top view.

　そして、このようなプレス成形品１について上記を検討した結果、発明者らは、図３の応力―ひずみ線図（stress-strain　curve）に示すように、ひずみを付与した後に一定に保持したまま時間の経過とともに応力が徐々に緩和する応力緩和現象に着目した。そして、スプリングバックした後のプレス成形品１においても、湾曲内側フランジ部７ａと湾曲外側フランジ部７ｂの残留応力が時間の経過とともに徐々に緩和することで、プレス成形品１の力のモーメントと釣り合う形状が変化することを突き止めた。 Then, as a result of examining the above for such a press-molded product 1, the inventors, as shown in the stress-strain curve of FIG. 3, keep the strain constant after applying the strain. We focused on the stress relaxation phenomenon in which the stress gradually relaxes over time. Further, even in the press-molded product 1 after springback, the residual stress of the curved inner flange portion 7a and the curved outer flange portion 7b is gradually relaxed with the passage of time, so that the residual stress is balanced with the moment of the force of the press-molded product 1. I found that the shape changed.

　プレス成形品１における残留応力の緩和による形状変化について、図４に示す模式図を用いて説明する。なお、図４（ａ）（ii）、図４（ｂ）（ii）及び図４（ｃ）（ii）中の破線は、プレス成形品１の長手方向端部の断面における天板部３の傾きを示す線である。 The shape change due to the relaxation of the residual stress in the press-molded product 1 will be described with reference to the schematic diagram shown in FIG. The broken lines in FIGS. 4 (a) (ii), 4 (b) (ii) and 4 (c) (ii) indicate the top plate portion 3 in the cross section of the longitudinal end portion of the press-molded product 1. It is a line showing the inclination.

　プレス成形品１のプレス成形において、金属板（ブランク）は図２に示すように上面視で湾曲した形状に曲げられるため、成形下死点では、図４（ａ）（i）に示すように、湾曲内側フランジ部７ａではブランク端部の線長が伸びる伸びフランジ変形（stretch　flanging）が生じて引張応力（tensile　stress）が発生し、湾曲外側フランジ部７ｂではブランク端部の線長が縮まる縮みフランジ変形（shrinkage　flanging）が生じて圧縮応力（compressive　stress）が発生する。 In the press molding of the press-molded product 1, the metal plate (blank) is bent into a curved shape in the top view as shown in FIG. 2, so that the bottom dead point of molding is as shown in FIGS. 4 (a) and 4 (i). In the curved inner flange portion 7a, the line length of the blank end is extended, stretch flangeing occurs to generate tensile stress, and in the curved outer flange portion 7b, the line length of the blank end is shortened. Flange deformation (shrinkage flangeing) occurs and compressive stress occurs.

　次に、金型からプレス成形品１を取り外すと、プレス成形時に発生した残留応力を駆動力としてスプリングバックが発生する。このスプリングバックにおいて、湾曲内側フランジ部７ａは縮もうとし、湾曲外側フランジ部７ｂは伸びようとする。しかしながら、湾曲内側フランジ部７ａ及び湾曲外側フランジ部７ｂの面内での縮みや伸びといった変形は剛性（rigidity）が大きくて生じにくいため、図４（ｂ）に示すように面外変形（out-of-plane　deformation）となる長手方向端部側の捩れが生じる。そして、成形下死点での湾曲内側フランジ部７ａ及び湾曲外側フランジ部７ｂの残留応力（引張応力及び圧縮応力）は、絶対値が小さくなるか、場合によっては、図４（ｂ）（i）に示すように残留応力が反転した状態となり力のモーメントが釣り合う形状となる。 Next, when the press-molded product 1 is removed from the die, springback is generated using the residual stress generated during press molding as a driving force. In this springback, the curved inner flange portion 7a tends to shrink, and the curved outer flange portion 7b tends to expand. However, deformation such as shrinkage and elongation in the plane of the curved inner flange portion 7a and the curved outer flange portion 7b has a large rigidity and is unlikely to occur. Therefore, as shown in FIG. 4 (b), out-of-plane deformation (out- A twist on the end side in the longitudinal direction, which is an of-plane deformation), occurs. The residual stresses (tensile stress and compressive stress) of the curved inner flange portion 7a and the curved outer flange portion 7b at the bottom dead point of molding have small absolute values, or in some cases, FIGS. 4 (b) and 4 (i). As shown in, the residual stress is reversed and the force moments are balanced.

　その後、スプリングバックした直後の湾曲内側フランジ部７ａにおける圧縮応力と湾曲外側フランジ部７ｂにおける引張応力は、図４（ｂ）（i）から図４（ｃ）（i）に示すように、時間経過とともに外部からの強制を受けないまま緩和して減少する。これにより、力のモーメントと釣り合う形状が変化するため、プレス成形品１の長手方向端部においてはさらに捩れが発生し、成形下死点形状からさらに乖離する。 After that, the compressive stress in the curved inner flange portion 7a and the tensile stress in the curved outer flange portion 7b immediately after springback are over time as shown in FIGS. 4 (b) (i) to 4 (c) (i). At the same time, it relaxes and decreases without being forced from the outside. As a result, the shape that balances with the moment of force changes, so that further twisting occurs at the longitudinal end of the press-molded product 1, further deviating from the shape of the bottom dead center of molding.

　このように、上面視で湾曲した形状のハット型断面形状のプレス成形品１においては、プレス成形してスプリングバックした後のさらなる時間の経過に伴って湾曲内側フランジ部７ａと湾曲外側フランジ部７ｂの残留応力が緩和することに起因して、長手方向端部側に捩れが発生し、成形下死点からさらに乖離した形状になるという知見が得られた。 As described above, in the press-molded product 1 having a hat-shaped cross-sectional shape that is curved in the top view, the curved inner flange portion 7a and the curved outer flange portion 7b with the lapse of further time after press-molding and springing back. It was found that twisting occurs on the end side in the longitudinal direction due to the relaxation of the residual stress of the molding, and the shape is further deviated from the bottom dead center of molding.

　そこで、発明者らは、上記の新たな知見に基づいて、例えば、図２に示すようなプレス成形品１についてスプリングバックした後の時間経過に伴う応力緩和による形状変化を予測する方法について検討をすすめた。その結果、前述したプレス成形シミュレーションの第２段階（スプリングバック解析）で得られるスプリングバックした直後のプレス成形品１の少なくとも湾曲内側フランジ部７ａ及び／又は湾曲外側フランジ部７ｂの残留応力を緩和させ、プレス成形品１の力のモーメントと釣り合う形状を求める第３段階の解析をさらに行うことで、前述したようなプレス成形品１の時間経過に伴う形状変化（長手方向端部の捩れ）を予測できるということを見い出した。 Therefore, based on the above-mentioned new findings, the inventors have studied, for example, a method for predicting a shape change due to stress relaxation with the passage of time after springing back the press-molded product 1 as shown in FIG. I recommended it. As a result, the residual stress of at least the curved inner flange portion 7a and / or the curved outer flange portion 7b of the press-formed product 1 immediately after springback obtained in the second stage (springback analysis) of the above-mentioned press forming simulation is relaxed. By further performing the third stage analysis to obtain the shape that balances with the moment of the force of the press-formed product 1, the shape change (twist of the end portion in the longitudinal direction) with the passage of time of the press-formed product 1 as described above is predicted. I found that I could do it.

　本発明は、このような検討及び知見に基づいてなされたものであり、以下に具体的な構成の一例を説明する。 The present invention has been made based on such studies and findings, and an example of a specific configuration will be described below.

＜プレス成形品の形状変化予測方法＞
　本発明の実施の形態に係るプレス成形品の形状変化予測方法は、一例として図２に示すように、天板部３と天板部３から連続する縦壁部５と縦壁部５から連続するフランジ部７とを有してなるハット型断面形状であり、上面視で長手方向に沿って湾曲した形状を含むプレス成形品１について、金型から離型しスプリングバックした後の時間経過に伴う応力緩和による長手方向端部側が捩れる形状変化を予測するものであって、図１に示すように、スプリングバック直後の形状・残留応力取得工程Ｓ１と、残留応力緩和減少設定工程Ｓ３と、残留応力緩和形状解析工程Ｓ５と、を備えるものである。以下、上記の各工程について説明する。 <Method for predicting shape change of press-molded products>
As an example, as shown in FIG. 2, the method for predicting a shape change of a press-molded product according to an embodiment of the present invention is continuous from a top plate portion 3 and a vertical wall portion 5 continuous from the top plate portion 3 and a vertical wall portion 5. A press-molded product 1 having a hat-shaped cross-sectional shape having a flange portion 7 and having a shape curved along the longitudinal direction in a top view is separated from the mold and springed back in time. As shown in FIG. 1, the shape / residual stress acquisition step S1 immediately after springback, the residual stress relaxation reduction setting step S3, and the shape change in which the end side in the longitudinal direction is twisted due to the accompanying stress relaxation are predicted. It includes a residual stress relaxation shape analysis step S5. Hereinafter, each of the above steps will be described.

≪スプリングバック直後の形状・残留応力取得工程≫
　スプリングバック直後の形状・残留応力取得工程Ｓ１は、プレス成形品１のスプリングバック解析により、スプリングバックした直後のプレス成形品１の形状及び残留応力を取得する工程である。 ≪Shape and residual stress acquisition process immediately after springback≫
The shape / residual stress acquisition step S1 immediately after springback is a step of acquiring the shape and residual stress of the press-molded product 1 immediately after springback by the springback analysis of the press-molded product 1.

　スプリングバックした直後のプレス成形品１の形状及び残留応力を取得する具体的な処理の一例としては、実際のプレス成形品１のプレス成形に用いる金型をモデル化した金型モデル（tool　model　of　press　forming）を用いて、金属板を成形下死点までプレス成形する過程のプレス成形解析を行い、成形下死点におけるプレス成形品１の形状及び残留応力を求める第１段階と、該求めた成形下死点におけるプレス成形品１を金型モデルから離型した後のプレス成形品１の力のモーメントの釣り合いが取れる形状及び残留応力を求めるスプリングバック解析を行う第２段階と、を有する有限要素法によるプレス成形シミュレーションが挙げられる。 As an example of a specific process for acquiring the shape and residual stress of the press-formed product 1 immediately after springback, a die model (tool model of) that models the mold used for the actual press-forming of the press-formed product 1 is performed. Press forming) is used to perform a press forming analysis in the process of press-forming a metal plate to the bottom dead point of molding, and the first step of determining the shape and residual stress of the press-formed product 1 at the bottom dead point of molding, and the determination. A finite shape having a shape in which the moments of the forces of the press-molded product 1 after the press-molded product 1 at the bottom dead point of molding are released from the die model, and a second stage of springback analysis for obtaining residual stress. Press forming simulation by the element method can be mentioned.

≪残留応力緩和減少設定工程≫
　残留応力緩和減少設定工程Ｓ３は、スプリングバック直後の形状・残留応力取得工程Ｓ１において取得したスプリングバックした直後のプレス成形品１の少なくとも湾曲内側フランジ部７ａ及び／又は湾曲外側フランジ部７ｂに対し、スプリングバックした直後の残留応力よりも緩和減少させた応力の値を設定する工程である。 ≪Residual stress relaxation reduction setting process≫
The residual stress relaxation reduction setting step S3 is performed with respect to at least the curved inner flange portion 7a and / or the curved outer flange portion 7b of the press-formed product 1 immediately after springback acquired in the shape / residual stress acquisition step S1 immediately after springback. This is a step of setting the value of the stress relaxed and reduced from the residual stress immediately after springback.

　残留応力緩和減少設定工程Ｓ３における残留応力とは、スプリングバックした直後のプレス成形品１に残留する引張応力及び圧縮応力のことをいう。さらに、残留応力緩和減少設定工程Ｓ３において残留応力を緩和減少させた応力の値を設定するとは、スプリングバックした直後のプレス成形品１に残留する引張応力（正の値）及び圧縮応力（負の値）の絶対値を緩和減少させることをいう。 The residual stress in the residual stress relaxation reduction setting step S3 means the tensile stress and the compressive stress remaining in the press-formed product 1 immediately after springback. Further, setting the stress value for which the residual stress is relaxed and reduced in the residual stress relaxation reduction setting step S3 means that the tensile stress (positive value) and the compressive stress (negative value) remaining in the press-formed product 1 immediately after springback are used. Value) means to relax and reduce the absolute value.

≪残留応力緩和形状解析工程≫
　残留応力緩和形状解析工程Ｓ５は、残留応力緩和減少設定工程Ｓ３で緩和減少した応力の値を設定したプレス成形品１について、力のモーメントが釣り合う形状を求める解析を行う工程である。 ≪Residual stress relaxation shape analysis process≫
The residual stress relaxation shape analysis step S5 is a step of performing an analysis to obtain a shape in which the moments of force are balanced with respect to the press-formed product 1 in which the value of the stress reduced by relaxation in the residual stress relaxation reduction setting step S3 is set.

　残留応力緩和形状解析工程Ｓ５における解析には、スプリングバック直後の形状・残留応力取得工程Ｓ１におけるスプリングバック解析と同様の解析手法を適用することにより、残留応力を緩和減少させた後のプレス成形品１の形状及び残留応力を得ることができる。 For the analysis in the residual stress relaxation shape analysis step S5, the press-formed product after the residual stress is relaxed and reduced by applying the same analysis method as the springback analysis in the shape / residual stress acquisition step S1 immediately after the springback. The shape and residual stress of 1 can be obtained.

　このように、本実施の形態に係るプレス成形品の形状変化予測方法によれば、スプリングバック解析により取得した、スプリングバックした直後のプレス成形品１の少なくとも湾曲内側フランジ部７ａ及び／又は湾曲外側フランジ部７ｂに対し、スプリングバックした直後の残留応力よりも緩和減少した応力の値を設定し、緩和減少した応力の値を設定したプレス成形品１について力のモーメントと釣り合う形状を求める解析を行うことで、実際のプレス成形品１における時間経過による応力緩和と形状変化を模擬し、金型から離型してスプリングバックした後のプレス成形品１の時間経過に伴う長手方向端部側が捩れる形状変化を予測することができる。 As described above, according to the method for predicting the shape change of the press-molded product according to the present embodiment, at least the curved inner flange portion 7a and / or the curved outer side of the press-molded product 1 immediately after springback obtained by the springback analysis. For the flange portion 7b, a stress value that is relaxed and reduced compared to the residual stress immediately after springback is set, and an analysis is performed to obtain a shape that balances the moment of force for the press-formed product 1 that is set with the stress value that is relaxed and reduced. As a result, the stress relaxation and shape change with the passage of time in the actual press-molded product 1 are simulated, and the end side in the longitudinal direction is twisted with the passage of time after the press-molded product 1 is separated from the mold and springed back. Shape changes can be predicted.

　なお、上記の説明において、残留応力緩和減少設定工程Ｓ３は、プレス成形品１における少なくとも湾曲内側フランジ部７ａ及び／又は湾曲外側フランジ部７ｂに対し、それら各部位の残留応力を緩和減少させた応力の値を設定するものであった。 In the above description, in the residual stress relaxation reduction setting step S3, the residual stress of each portion of the press-formed product 1 is relaxed and reduced with respect to at least the curved inner flange portion 7a and / or the curved outer flange portion 7b. Was to set the value of.

　もっとも、本発明は、プレス成形品１における湾曲内側フランジ部７ａや湾曲外側フランジ部７ｂ以外の他の部位に対しても残留応力を緩和減少させるものであってもよいし、プレス成形品１の全部に対して残留応力を緩和減少させた値を設定してもよい。さらには、湾曲内側フランジ部７ａや湾曲外側フランジ部７ｂ等の部位ごとに残留応力を緩和減少させる割合や値を変えてもよい。 However, according to the present invention, the residual stress may be relaxed and reduced with respect to other portions other than the curved inner flange portion 7a and the curved outer flange portion 7b in the press-molded product 1, and the press-molded product 1 may be used. A value in which the residual stress is relaxed and reduced may be set for all of them. Further, the ratio or value of relaxing and reducing the residual stress may be changed for each portion such as the curved inner flange portion 7a and the curved outer flange portion 7b.

　なお、上記の説明は、長手方向の全長にわたって上面視で湾曲した形状のプレス成形品を対象とするものであったが、本発明は、長手方向における一部の部位が上面視で長手方向に沿って湾曲した形状のプレス成形品であればよく、例えば、湾曲した湾曲部（curved　portion）と、該湾曲部の湾曲の端から長手方向の外方の両側又は片側に直線状に延出する辺部（linear　portion）とを含むプレス成形品を対象とすることができる。 In addition, although the above description was intended for a press-molded product having a shape curved in the top view over the entire length in the longitudinal direction, the present invention has a part of a portion in the longitudinal direction in the longitudinal direction in the longitudinal direction. It may be a press-molded product having a curved shape along, for example, a curved portion and a linear extension from the curved end of the curved portion to both sides or one side outward in the longitudinal direction. Press-molded products including a linear portion can be targeted.

　また、本発明は、残留応力緩和減少設定工程において、スプリングバックした直後の残留応力よりも10%以上緩和減少させることにより、時間経過した後の形状変化を良好に予測できて好ましい。 Further, it is preferable that the present invention can satisfactorily predict the shape change after the lapse of time by reducing the residual stress by 10% or more from the residual stress immediately after springback in the residual stress relaxation reduction setting step.

　本発明に係るプレス成形品の形状変化予測方法において、プレス成形に供するブランク（金属板）や、プレス成形品の形状、種類には特に制限はないが、プレス成形品の残留応力が高くなる金属板を用いてプレス成形した自動車部品に対してより効果がある。 In the method for predicting the shape change of a press-molded product according to the present invention, the blank (metal plate) to be used for press molding and the shape and type of the press-molded product are not particularly limited, but the metal having a high residual stress in the press-molded product. It is more effective for automobile parts press-molded using a plate.

　具体的には、ブランクの板厚については、0.5mm以上4.0mm以下であることが好ましい。また、ブランクの引張強度については、150MPa級以上2000MPa級以下であることが好ましく、440MPa級以上1470MPa級以下であることがより好ましい。 Specifically, the thickness of the blank is preferably 0.5 mm or more and 4.0 mm or less. The tensile strength of the blank is preferably 150 MPa class or more and 2000 MPa class or less, and more preferably 440 MPa class or more and 1470 MPa class or less.

　引張強度が150MPa級未満の金属板は、プレス成形品に利用されることが少ないため、本発明に係るプレス成形品の形状変化予測方法を用いる利点が少ない。引張強度150MPa級以上の金属板を用いた自動車の外板部品等の剛性が低いものについては、残留応力の変化による形状変化を受けやすいため、本発明を適用する利点が多くなるので本発明を好適に適用できる。 Since a metal plate having a tensile strength of less than 150 MPa class is rarely used for press-molded products, there is little advantage in using the method for predicting shape change of press-molded products according to the present invention. The present invention has many advantages to apply the present invention because the outer plate parts of automobiles using metal plates with a tensile strength of 150 MPa class or higher and having low rigidity are susceptible to shape changes due to changes in residual stress. It can be suitably applied.

　一方、引張強度が2000MPa級を超える金属板は延性（ductility）が乏しいため、例えば、図２に示すようなハット型断面形状のプレス成形品１のプレス成形過程においてはパンチ肩Ｒ部９やダイ肩Ｒ部１１で割れ（fracture）が発生しやすく、プレス成形することができない場合がある。 On the other hand, since a metal plate having a tensile strength exceeding 2000 MPa class has poor ductility, for example, in the press forming process of the press-formed product 1 having a hat-shaped cross-sectional shape as shown in FIG. 2, the punch shoulder R portion 9 and the die Fracture is likely to occur at the shoulder R portion 11, and press molding may not be possible.

　さらに、プレス成形品の種類としては、ルーフサイドレール（roof　side　rail）やフロントピラーアッパ（front　pillar　upper）などの上面視で湾曲したハット型断面形状の骨格部品（body　frame　parts）を対象とすることが好ましいが、ハット型断面形状であって上面視で湾曲した形状を含み、プレス成形した後の時間経過により長手方向端部側の捩れが発生して寸法精度が低下する自動車部品に本発明を広く用いることができる。 Furthermore, as a type of press-molded product, a hat-shaped cross-sectional skeleton part (body frame parts) that is curved from the top view, such as a roof side rail and a front pillar upper, is targeted. It is preferable, but the present invention is used for an automobile part having a hat-shaped cross-sectional shape and curved in a top view, and twisting on the end side in the longitudinal direction occurs with the lapse of time after press molding to reduce dimensional accuracy. Can be widely used.

　なお、本発明で対象とするプレス成形品のプレス成形方法についても、曲げ成形（bend-forming）、フォーム成形（crash　forming）又はドロー成形（deep　drawing）等、特に問わない。 The press forming method of the press-formed product targeted in the present invention is not particularly limited to bend-forming, foam forming (crash forming), draw forming (deep drawing), and the like.

　実施例では、まず、金属板の一例として、以下の表１に一例を示す機械的特性を持つ鋼板（steel　sheet）Ａを用い、図５に示す、天板部２３と天板部２３から連続する縦壁部２５と縦壁部２５から連続するフランジ部２７とを有してなるハット型断面形状であり、上面視で長手方向に沿って湾曲した自動車部品であるプレス成形品２１のプレス成形を行った。プレス成形品２１の成形下死点形状は、湾曲の曲率半径（curvature　radius）を170mm、プレス成形方向における縦壁部２５の縦壁高さを40mmとした。なお、鋼板Ａの板厚は、1.2mmであり、降伏強度（yield　strength）は、690MPaであり、引張強度は、1030MPaであり、伸びは、15%である。 In the embodiment, first, as an example of the metal plate, a steel sheet A having mechanical characteristics shown in Table 1 below is used, and the top plate portion 23 and the top plate portion 23 shown in FIG. 5 are continuous. Press molding of a press-molded product 21 which is a hat-shaped cross-sectional shape having a vertical wall portion 25 and a flange portion 27 continuous from the vertical wall portion 25, and is an automobile part curved along the longitudinal direction in a top view. Was done. The shape of the bottom dead center of the press-molded product 21 has a radius of curvature (curvature radius) of 170 mm and a vertical wall height of the vertical wall portion 25 in the press-molding direction of 40 mm. The thickness of the steel plate A is 1.2 mm, the yield strength is 690 MPa, the tensile strength is 1030 MPa, and the elongation is 15%.

　そして、成形下死点までプレス成形した後に金型から離型してスプリングバックした直後と、スプリングバックして３日経過した後において、プレス成形品２１の形状を測定し、長手方向中央の天板部２３を基準とする長手方向端部の天板部２３の傾きを捩れ角として実測した。 Then, the shape of the press-molded product 21 was measured immediately after press-molding to the bottom dead center of molding, then released from the mold and springed back, and after 3 days from springback, and the top of the center in the longitudinal direction was measured. The inclination of the top plate portion 23 at the end in the longitudinal direction with respect to the plate portion 23 was actually measured as the twist angle.

　次に、プレス成形品２１の時間経過による長手方向端部の捩れを予測する解析を行った。解析では、まず、プレス成形に用いる金型をモデル化した金型モデルを用いて、鋼板Ａを成形下死点までプレス成形する過程のプレス成形解析を行い、成形下死点におけるプレス成形品２１の形状及び残留応力を求めた。 Next, an analysis was performed to predict the twist of the end portion in the longitudinal direction over time of the press-molded product 21. In the analysis, first, a press molding analysis in the process of press forming the steel plate A to the bottom dead point of molding is performed using a die model that models the mold used for press molding, and the press molded product 21 at the bottom dead point of molding is performed. Shape and residual stress were determined.

　続いて、成形下死点におけるプレス成形品２１を金型モデルから離型した直後のプレス成形品２１の形状及び残留応力を求めるスプリングバック解析を行った。 Subsequently, a springback analysis was performed to determine the shape and residual stress of the press-molded product 21 immediately after the press-molded product 21 at the bottom dead center of molding was released from the die model.

　さらに、スプリングバック解析により求めた、スプリングバックした直後のプレス成形品２１の湾曲内側フランジ部２７ａ及び／又は湾曲外側フランジ部２７ｂに対し、残留応力の絶対値を所定の割合で低下させた応力の値を設定した。そして、残留応力を低下させたプレス成形品２１について力のモーメントが釣り合う形状を求める解析を行い、長手方向中央の天板部２３を基準とする長手方向端部の天板部２３の傾きである捩れ角を求めた。 Further, the stress obtained by reducing the absolute value of the residual stress with respect to the curved inner flange portion 27a and / or the curved outer flange portion 27b of the press-formed product 21 immediately after springback, which is obtained by the springback analysis, by a predetermined ratio. Set the value. Then, an analysis is performed to obtain a shape in which the moments of force are balanced for the press-molded product 21 in which the residual stress is reduced, and the inclination of the top plate portion 23 at the end portion in the longitudinal direction with respect to the top plate portion 23 in the center in the longitudinal direction. The twist angle was calculated.

　実施例では、スプリングバック解析により取得したプレス成形品２１の湾曲内側フランジ部２７ａのみ、又は、湾曲内側フランジ部２７ａ及び湾曲外側フランジ部２７ｂの双方に対し、スプリングバックした直後の残留応力を所定の割合（応力緩和減少率（stress　relaxation　rate））で低下した応力の値を設定したものを発明例１～発明例３とした。 In the embodiment, the residual stress immediately after springback is predetermined for only the curved inner flange portion 27a of the press-formed product 21 obtained by springback analysis, or for both the curved inner flange portion 27a and the curved outer flange portion 27b. The values in which the values of the stress decreased by the ratio (stress relaxation rate) were set were designated as Invention Example 1 to Invention Example 3.

　また、比較対象として、発明例１～発明例３と同様にプレス成形品２１のプレス成形解析及びスプリングバック解析を行ったものの、残留応力を緩和減少した応力の値を設定して力のモーメントが釣り合う形状を求める解析を行わなかったものを比較例１とした。 Further, as a comparison target, although the press molding analysis and the springback analysis of the press molded product 21 were performed in the same manner as in the inventions 1 to 3, the residual stress was relaxed and the stress value was set and the force moment was increased. Comparative Example 1 was obtained in which the analysis for obtaining the balanced shape was not performed.

　表２に、発明例１～発明例３及び比較例１における応力緩和減少率と、実験値からの天板部２３の長手方向端部における捩れ角の乖離量の結果をまとめて示す。長手方向中央の天板部２３を基準とする長手方向端部の天板部２３の傾きである捩れ角の実測値は6.7°であった。 Table 2 summarizes the results of the stress relaxation reduction rate in Invention Examples 1 to 3 and Comparative Example 1 and the amount of deviation of the twist angle at the longitudinal end of the top plate 23 from the experimental values. The measured value of the twist angle, which is the inclination of the top plate portion 23 at the end portion in the longitudinal direction with respect to the top plate portion 23 in the center in the longitudinal direction, was 6.7 °.

　表２において、予測値は、長手方向中央の天板部２３を基準とする長手方向端部の天板部２３の傾きである捩れ角を予測した値である。また、実測値と予測値との差分及び実測値に対する予測値の誤差を算出し、合わせて記載した。 In Table 2, the predicted value is a value that predicts the twist angle which is the inclination of the top plate portion 23 at the end portion in the longitudinal direction with respect to the top plate portion 23 in the center in the longitudinal direction. In addition, the difference between the measured value and the predicted value and the error of the predicted value with respect to the measured value were calculated and described together.

　比較例１においては、捩れ角の予測値は5.8°であり、実測値と予測値との差分は0.9°であり、予測値の誤差は13.4%であった。 In Comparative Example 1, the predicted value of the twist angle was 5.8 °, the difference between the measured value and the predicted value was 0.9 °, and the error of the predicted value was 13.4%.

　発明例１は、湾曲外側フランジ部７ｂのみに対して応力緩和減少率10%で低下させた応力の値を設定したものであり、予測値は6.0°と増加し、実測値と予測値との差分は0.7°、予測値の誤差は10.4%となり、比較例１よりも実測値に近づく結果となった。 In Invention Example 1, the value of the stress reduced by the stress relaxation reduction rate of 10% is set only for the curved outer flange portion 7b, the predicted value increases to 6.0 °, and the measured value and the predicted value are set. The difference was 0.7 ° and the error of the predicted value was 10.4%, which was closer to the measured value than in Comparative Example 1.

　発明例２は、湾曲外側フランジ部７ｂと湾曲内側フランジ部７ａの双方に対して応力緩和減少率10%で低下させた応力の値を設定したものであり、予測値は6.4°に増加し、実測値と予測値との差分は0.3°、予測値の誤差は4.5%となり、比較例１及び発明例１よりも実測値に近づく結果となり、良好であった。 In Invention Example 2, the stress values reduced by the stress relaxation reduction rate of 10% are set for both the curved outer flange portion 7b and the curved inner flange portion 7a, and the predicted value increases to 6.4 °. The difference between the measured value and the predicted value was 0.3 °, and the error of the predicted value was 4.5%, which was closer to the measured value than in Comparative Example 1 and Invention Example 1, which was good.

　発明例３は、湾曲外側フランジ部７ｂと湾曲内側フランジ部７ａの双方に対して応力緩和減少率20%で低下させた応力の値を設定したものであり、予測値は7.0°に増加し、実測値と予測値との差分は-0.3°、予測値の誤差は-4.5%となり、いずれも負の値であるが、絶対値で比較すると比較例１及び発明例１よりも改善し、発明例３と同じく良好であった。 In Invention Example 3, the stress value reduced by the stress relaxation reduction rate of 20% is set for both the curved outer flange portion 7b and the curved inner flange portion 7a, and the predicted value increases to 7.0 °. The difference between the measured value and the predicted value is -0.3 °, and the error of the predicted value is -4.5%, both of which are negative values. It was as good as Example 3.

　本発明によれば、天板部と該天板部から連続する縦壁部と該縦壁部から連続するフランジ部とを有してなるハット型断面形状であり上面視（天板部方向から見た場合）で長手方向に沿って湾曲した形状を含むプレス成形品について、金型から離型した瞬間にスプリングバックした後の時間単位の経過による前記プレス成形品の形状変化を予測するプレス成形品の形状変化予測方法を提供することができる。 According to the present invention, it is a hat-shaped cross-sectional shape having a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion, and is viewed from above (from the direction of the top plate portion). For press-molded products that include a shape that is curved along the longitudinal direction in (when viewed), press-molding that predicts the shape change of the press-molded product over time after springing back at the moment of mold release from the mold. It is possible to provide a method for predicting a change in the shape of an article.

　　１　プレス成形品
　　３　天板部
　　５　縦壁部
　　７　フランジ部
　　７ａ　湾曲内側フランジ部
　　７ｂ　湾曲外側フランジ部
　　９　パンチ肩Ｒ部
　１１　ダイ肩Ｒ部
　２１　プレス成形品（実施例）
　２３　天板部
　２５　縦壁部
　２７　フランジ部
　２７ａ　湾曲内側フランジ部
　２７ｂ　湾曲外側フランジ部　
　 1 Press-molded product 3 Top plate part 5 Vertical wall part 7 Flange part 7a Curved inner flange part 7b Curved outer flange part 9 Punch shoulder R part 11 Die shoulder R part 21 Press-molded product (Example)
23 Top plate part 25 Vertical wall part 27 Flange part 27a Curved inner flange part 27b Curved outer flange part

Claims

　天板部と該天板部から連続する縦壁部と該縦壁部から連続するフランジ部とを有してなるハット型断面形状であり、上面視で長手方向に沿って湾曲した形状を含むプレス成形品について、金型から離型した瞬間にスプリングバックした後の時間経過に伴う応力緩和による長手方向端部側が捩れる形状変化を予測するプレス成形品の形状変化予測方法であって、
　前記プレス成形品のスプリングバック解析により、スプリングバックした直後の前記プレス成形品の形状及び残留応力を取得するスプリングバック直後の形状・残留応力取得工程と、
　スプリングバックした直後の前記プレス成形品の少なくとも湾曲内側フランジ部及び／又は湾曲外側フランジ部に対し、スプリングバックした直後の残留応力よりも緩和減少した応力の値を設定する残留応力緩和減少設定工程と、
　緩和減少した応力の値を設定した前記プレス成形品について力のモーメントが釣り合う形状を求める残留応力緩和形状解析工程と、を含む、プレス成形品の形状変化予測方法。 It is a hat-shaped cross-sectional shape having a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion, and includes a shape curved along the longitudinal direction in a top view. A method for predicting a shape change of a press-molded product, which predicts a shape change in which the end side in the longitudinal direction is twisted due to stress relaxation with the passage of time after springing back at the moment when the die is released from the die.
The shape / residual stress acquisition process immediately after springback to acquire the shape and residual stress of the press-molded product immediately after springback by the springback analysis of the press-molded product, and the process of acquiring the shape / residual stress immediately after springback.
A residual stress relaxation reduction setting step for setting at least a value of stress that is relaxed and reduced from the residual stress immediately after springback with respect to at least the curved inner flange portion and / or the curved outer flange portion of the press-formed product immediately after springback. ,
A method for predicting a shape change of a press-molded product, which comprises a residual stress relaxation shape analysis step of obtaining a shape in which a force moment is balanced for the press-molded product in which a value of the stress reduced by relaxation is set.
　前記残留応力緩和減少設定工程において、スプリングバックした直後の残留応力よりも10%以上緩和減少した応力の値を設定する、請求項１に記載のプレス成形品の形状変化予測方法。 The method for predicting shape change of a press-molded product according to claim 1, wherein in the residual stress relaxation reduction setting step, a value of stress whose relaxation is reduced by 10% or more from the residual stress immediately after springback is set.
　前記プレス成形品のプレス成形に供するブランクは、引張強度が150MPa級以上2000MPa級以下の金属板である、請求項１又は２に記載のプレス成形品の形状変化予測方法。 The method for predicting a shape change of a press-molded product according to claim 1 or 2, wherein the blank used for press-molding the press-molded product is a metal plate having a tensile strength of 150 MPa class or more and 2000 MPa class or less. The