JP7494883B2 - Press molding method and method for manufacturing press molded product - Google Patents
Press molding method and method for manufacturing press molded product Download PDFInfo
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- 238000009966 trimming Methods 0.000 claims description 22
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Description
本発明は、天板部と縦壁部を有し、平面視で長手方向に湾曲する湾曲部を有するコ字断面形状のプレス成形品をプレス成形するプレス成形方法およびプレス成形品の製造方法に関する。 The present invention relates to a press molding method for press molding a press molded product having a U-shaped cross section with a top plate portion and a vertical wall portion, and a curved portion that is curved in the longitudinal direction when viewed from above, and a method for manufacturing the press molded product.
近年、自動車車体の衝突安全性向上と軽量化とを両立させるため、引張強度590MPa級以上の高強度鋼板（以下、ハイテン材とも称する）の車体構造部品への適用が進んでいる。
また、ハイテン材は、シート骨格部品等の車体構造部品への適用も検討されているが、引張強度が高いため、プレス成形後のスプリングバックによる形状不良が課題となっている。
In recent years, in order to simultaneously improve the collision safety of automobile bodies and reduce their weight, high-strength steel sheets with tensile strengths of 590 MPa or higher (hereinafter also referred to as high-tensile steel) have been increasingly used in vehicle body structural parts.
The use of high tensile steel is also being considered for use in vehicle body structural components such as seat frames, but because of its high tensile strength, there is an issue of shape defects caused by springback after press forming.
車体構造部品の中で例えばシート骨格部品等には、縮みフランジ変形部位を有するコ字断面形状のプレス成形品が用いられる。このようなプレス成形品をプレス成形して成形下死点から離型すると、プレス成形品の天板部が長手方向に凸状に反るスプリングバックが発生する。このようなプレス成形品に対して、ハイテン材を適用した場合、成形下死点での応力がさらに大きくなり、スプリングバックが増加するという課題が発生する。 For example, seat frame parts and other vehicle body structural parts use press-formed products with a U-shaped cross section that has shrink flange deformation areas. When such press-formed products are press-formed and released from the bottom dead point of the press, springback occurs, in which the top plate of the press-formed product warps convexly in the longitudinal direction. If high tensile steel is used for such press-formed products, the stress at the bottom dead point of the press is even greater, resulting in the problem of increased springback.
このようなスプリングバックを防止する先行技術として、例えば特許文献１、２に開示されたプレス成形方法が挙げられる。
特許文献１に開示のプレス成形方法は、長手方向に延びる溝形状部を有し、該溝形状部を形成する一対の縦壁部の少なくとも一方に長手方向に沿って湾曲するフランジ部を有する製品形状の成形品を成形するプレス成形方法である。そして、第１成形工程で縮みフランジ変形を受けるフランジ部に対しては長手方向の線長が前記製品形状のフランジ部の線長よりも短くなるように、フランジ部全体が傾斜した形状に成形する。さらに、前記第１成形工程で成形され傾斜したフランジ部に第２成形工程でひずみの戻りを与えて、前記フランジ部を製品形状に成形しスプリングバックを抑制する方法である。
Prior art techniques for preventing such springback include press forming methods disclosed in Patent Documents 1 and 2, for example.
The press forming method disclosed in Patent Document 1 is a press forming method for forming a formed product having a groove-shaped portion extending in the longitudinal direction and a flange portion curved along the longitudinal direction on at least one of a pair of vertical walls forming the groove-shaped portion. Then, for the flange portion that is subjected to shrink flange deformation in a first forming step, the entire flange portion is formed into an inclined shape so that the longitudinal line length is shorter than the line length of the flange portion in the product shape. Furthermore, in a second forming step, the inclined flange portion formed in the first forming step is given a return of strain, so that the flange portion is formed into the product shape and springback is suppressed.
また、特許文献２に開示のものは、長手方向へ連続する略ハット型断面を有し、そのハット頂上部を挟んで対向する位置に伸びフランジ成形部と縮みフランジ成形部とが形成されたプレス部品について、展開抜きされた素材を冷間で曲げ加工する方法である。そして、前記伸びフランジ成形部及び前記縮みフランジ成形部を形成する素材部分を、上型ダイにより下型ポンチに対して縮みフランジ成形側から伸びフランジ成形側へ回転移動させてから、下型ポンチに押圧し、スプリングバックを抑制するものである。 Patent Document 2 discloses a method of cold bending a blank that has been developed for a press part that has a roughly hat-shaped cross section that continues in the longitudinal direction, with a stretch flange forming portion and a shrink flange forming portion formed at opposing positions across the hat apex. The blank portion that forms the stretch flange forming portion and the shrink flange forming portion is rotated by an upper die from the shrink flange forming side to the stretch flange forming side relative to a lower punch, and then pressed against the lower punch to suppress springback.
しかしながら、特許文献１のプレス成形方法は、第１成形工程で天板部と縦壁部を目標形状（製品形状）に成形し、その後にフランジ部を成形するため、本発明が対象とする天板部と縦壁部からなりフランジ部を有していないコ字断面形状のプレス成形品に適用することはできない。
また、本発明のプレス成形品で発生するスプリングバックの要因となる応力部位は、後述するとおり、上面視で湾曲していない領域であるため、特許文献１のように湾曲部位のスプリングバック抑制方法を適用しても効果を奏することはできない。
However, the press molding method of Patent Document 1 molds the top plate portion and vertical wall portion into the target shape (product shape) in the first molding process, and then molds the flange portion, and therefore cannot be applied to the press-molded product of the present invention that has a U-shaped cross-section and consists of a top plate portion and vertical wall portion but does not have a flange portion.
Furthermore, as described below, the stress areas that cause springback in the press-formed products of the present invention are areas that are not curved when viewed from above, so applying a method of suppressing springback in curved areas as in Patent Document 1 will not be effective.
また、特許文献２に記載のプレス成形方法は、伸びフランジ成形部及び縮みフランジ成形部を形成する素材部分を、上型ダイにより下型ポンチに対して縮みフランジ成形側から伸びフランジ成形側へ回転移動させる方法である。
一方、本発明においては、縮みフランジ変形部とその周囲のみを対象としているため、特許文献２の方法を適用することはできない。
また、特許文献２のプレス成形品は、捻り変形のスプリングバックを抑制するものであり、本発明が対象としている天板部が長手方向凸状に反るスプリングバックとは変形形態が異なっている。
In addition, the press molding method described in Patent Document 2 is a method in which the material portion that forms the stretch flange molding portion and the shrink flange molding portion is rotated and moved by an upper die from the shrink flange molding side to the stretch flange molding side relative to a lower punch.
On the other hand, since the present invention is directed only to the shrink flange deformation portion and its surroundings, the method of Patent Document 2 cannot be applied.
Furthermore, the press-formed product of Patent Document 2 suppresses springback due to torsional deformation, and the deformation form is different from the springback that is the subject of the present invention, in which the top plate portion is warped convexly in the longitudinal direction.
以上のように、特許文献１、２においては、天板部と縦壁部からなるコ字断面形状のプレス成形品における天板部が長手方向凸状に反るスプリングバックを抑制することができないという課題を有していた。 As described above, Patent Documents 1 and 2 had the problem that they were unable to suppress springback, in which the top plate portion of a press-formed product having a U-shaped cross section consisting of a top plate portion and a vertical wall portion is warped in a longitudinally convex shape.
本発明は、かかる課題を解決するためになされたものであり、天板部と縦壁部からなるコ字断面形状のプレス成形品における天板部が長手方向凸状に反るスプリングバックを効果的に抑制できるプレス成形方法およびプレス成形品の製造方法を提供することを目的としている。 The present invention has been made to solve these problems, and aims to provide a press-molding method and a manufacturing method for press-molded products that can effectively suppress springback, in which the top plate portion of a press-molded product having a U-shaped cross section consisting of a top plate portion and a vertical wall portion is warped in a longitudinally convex shape.
（１）本発明に係るプレス成形方法は、天板部と縦壁部を有し、平面視で長手方向に湾曲する湾曲部を有するコ字断面形状のプレス成形品であって、前記湾曲部における縮みフランジ変形部となる縦壁部Ａの縦壁高さＨaと、前記縦壁部Ａを挟む両側の縦壁の一方である縦壁部Ｂの縦壁高さＨbと、前記縦壁部Ａを挟む両側の縦壁の他方である縦壁部Ｃの縦壁高さＨcとの関係が、Ｈa＞Ｈb＞Ｈcとなっているプレス成形品をプレス成形するプレス成形方法であって、
パンチとパッドとダイによって金属板を、前記縦壁部Ｂの縦壁高さが前記縦壁部Ａの縦壁高さ以上の中間成形品にプレス成形する中間成形品プレス成形工程と、
前記中間成形品をトリミング用金型で挟んで、前記縦壁部Ｂの縦壁高さが前記プレス成形品の縦壁高さであるＨｂになるように前記縦壁部Ｂをトリミングするトリミング工程とを備えたことを特徴とするものである。
(1) A press molding method according to the present invention is a press molding method for press molding a press-molded product having a U-shaped cross section having a top plate portion and a vertical wall portion and a curved portion that is curved in the longitudinal direction in a plan view, wherein a relationship between a vertical wall height Ha of a vertical wall portion A that becomes a shrink flange deformation portion in the curved portion, a vertical wall height Hb of a vertical wall portion B that is one of the vertical walls on both sides sandwiching the vertical wall portion A, and a vertical wall height Hc of a vertical wall portion C that is the other of the vertical walls on both sides sandwiching the vertical wall portion A is Ha>Hb>Hc,
an intermediate product press forming process in which a metal plate is press-formed by a punch, a pad, and a die into an intermediate product having a vertical wall height of the vertical wall portion B equal to or greater than the vertical wall height of the vertical wall portion A;
and a trimming process in which the intermediate molded product is clamped with a trimming die and the vertical wall portion B is trimmed so that the vertical wall height of the vertical wall portion B becomes Hb, which is the vertical wall height of the press-molded product.
（２）また、上記（１）に記載のものにおいて、前記金属板を引張強度590MPa級以上の鋼板とすることを特徴とするものである。
（３）また、本発明に係るプレス成形品の製造方法は、天板部と縦壁部を有し、平面視で長手方向に湾曲する湾曲部を有するコ字断面形状のプレス成形品であって、前記湾曲部における縮みフランジ変形部となる縦壁部Ａの縦壁高さＨaと、前記縦壁部Ａを挟む両側の縦壁の一方である縦壁部Ｂの縦壁高さＨbと、前記縦壁部Ａを挟む両側の縦壁の他方である縦壁部Ｃの縦壁高さＨcとの関係が、Ｈa＞Ｈb＞Ｈcとなっているプレス成形品の製造方法であって、
パンチとパッドとダイによって金属板を、前記縦壁部Ｂの縦壁高さが前記縦壁部Ａの縦壁高さ以上の中間成形品にプレス成形する中間成形品プレス成形工程と、
前記中間成形品をトリミング用金型で挟んで、前記縦壁部Ｂの縦壁高さが前記プレス成形品の縦壁高さであるＨｂになるように前記縦壁部Ｂをトリミングするトリミング工程とを備えたことを特徴とするものである。
（４）また、上記（３）に記載のものにおいて、前記金属板を引張強度590MPa級以上とすることを特徴とするものである。
(2) In the above (1), the metal plate is a steel plate having a tensile strength of 590 MPa or more.
(3) The manufacturing method of the press-molded product according to the present invention is a press-molded product having a U-shaped cross section having a top plate portion and a vertical wall portion and a curved portion curved in the longitudinal direction in a plan view, wherein a relationship between a vertical wall height Ha of a vertical wall portion A which becomes a shrink flange deformation portion in the curved portion, a vertical wall height Hb of a vertical wall portion B which is one of the vertical walls on both sides sandwiching the vertical wall portion A, and a vertical wall height Hc of a vertical wall portion C which is the other of the vertical walls on both sides sandwiching the vertical wall portion A is Ha>Hb>Hc,
an intermediate product press forming process in which a metal plate is press-formed by a punch, a pad, and a die into an intermediate product having a vertical wall height of the vertical wall portion B equal to or greater than the vertical wall height of the vertical wall portion A;
and a trimming process in which the intermediate molded product is clamped with a trimming die and the vertical wall portion B is trimmed so that the vertical wall height of the vertical wall portion B becomes Hb, which is the vertical wall height of the press-molded product.
(4) In the above (3), the metal plate has a tensile strength of 590 MPa or more.
本発明によれば、縮みフランジ変形部位を有するコ字断面形状のプレス成形品のスプリングバックを低減することができて、その結果、寸法精度の高い部品が得られる。
さらに、本発明に係るプレス成形方法およびプレス成形品の製造方法で得られたプレス成形品を車体部品に用いることにより、容易に部品の組み立てを行なうことが可能となり、車体の生産能率を向上できる。
According to the present invention, it is possible to reduce springback in a press-formed product having a U-shaped cross section and a shrink flange deformation portion, and as a result, a part with high dimensional accuracy can be obtained.
Furthermore, by using the press-molded products obtained by the press molding method and manufacturing method for press-molded products according to the present invention as vehicle body parts, it becomes possible to easily assemble the parts, thereby improving the production efficiency of the vehicle body.
本実施の形態に係るプレス成形方法は、図２に示すように、天板部３と縦壁部５を有し、平面視で長手方向に湾曲する湾曲部を有するコ字断面形状のプレス成形品１であって、湾曲部における縮みフランジ変形部となる縦壁部５Ａの縦壁高さＨaと、縦壁部５Ａを挟む両側の縦壁の一方である縦壁部５Ｂの縦壁高さＨbと、縦壁部５Ａを挟む両側の縦壁の他方である縦壁部５Ｃの縦壁高さＨcとの関係が、Ｈa＞Ｈb＞Ｈcとなっているプレス成形品１をプレス成形するプレス成形方法である。
なお、該プレス成形方法を実行することによって、プレス成形品１が製造されるので、プレス成形方法の発明は、プレス成形品の製造方法の発明として構成することができる。したがって、以下に説明するプレス成形方法の実施の形態は、プレス成形品の製造方法の実施の形態と共通するものである。
The press molding method according to the present embodiment is a press molding method for press-molding a press-molded product 1 having a U-shaped cross-sectional shape with a curved portion that is curved in the longitudinal direction in a plan view, as shown in FIG. 2, in which the relationship between the vertical wall height Ha of the vertical wall portion 5A, which is the shrink flange deformation portion in the curved portion, the vertical wall height Hb of the vertical wall portion 5B, which is one of the vertical walls on both sides sandwiching the vertical wall portion 5A, and the vertical wall height Hc of the vertical wall portion 5C, which is the other of the vertical walls on both sides sandwiching the vertical wall portion 5A, is Ha > Hb > Hc.
In addition, since the press-molded product 1 is manufactured by carrying out the press-molding method, the invention of the press-molding method can be configured as the invention of the manufacturing method of the press-molded product. Therefore, the embodiment of the press-molding method described below is common to the embodiment of the manufacturing method of the press-molded product.
本発明の実施の形態を説明するのに先立って本発明に至った経緯について図２～図４に基づいて説明する。
図２に示すような目標形状のプレス成形品１を展開したブランク形状を求め（図３（ａ）参照）、該形状のブランク（従来例）７をプレス成形解析し、スプリングバック成形解析したプレス成形品（従来例）９における成形下死点からの乖離量をコンター表示したものを図３（ｂ）に示す。なお、目標形状のプレス成形品１の展開は、解析モデルから逆成形解析するとよい。
Prior to describing the embodiments of the present invention, the background to how the present invention was arrived at will be described with reference to FIGS.
A blank shape is obtained by developing a press-formed product 1 having a target shape as shown in Fig. 2 (see Fig. 3(a)), and a blank (conventional example) 7 having that shape is subjected to press forming analysis. Fig. 3(b) shows a contour plot of the deviation from the bottom dead center of a press-formed product (conventional example) 9 obtained by springback forming analysis. The development of the press-formed product 1 having the target shape may be performed by performing a reverse forming analysis from an analytical model.
図３（ｂ）に一例を示すように、プレス成形品（従来例）９を天板部１１の方向から見て、長手方向両端部がプレス成形方向（紙面奥）に0.8mm凹み(-0.8mm)、長手方向中央部がプレス成形方向と逆方向（紙面手前）に0.2mm凸状(+0.2mm)を成して、プレス成形品（従来例）９の天板部１１が長手方向に凸状に反るスプリングバック（キャンバーバック）が発生する。 As shown in an example in Figure 3 (b), when the press-formed product (conventional example) 9 is viewed from the direction of the top plate 11, both ends in the longitudinal direction are recessed by 0.8 mm (-0.8 mm) in the press-forming direction (into the page), and the longitudinal center portion is convex by 0.2 mm (+0.2 mm) in the opposite direction to the press-forming direction (toward the page), resulting in springback (camber back) in which the top plate 11 of the press-formed product (conventional example) 9 is warped in a convex shape in the longitudinal direction.
このスプリングバックについて、有限要素解析を行ってプレス成形下死点における応力分布を求め、コンター表示したものを図４に示す。図４（ａ）は平面図であり、図４（ｂ）は湾曲外側の縦壁方向からみた側面図である。
図４（ｂ）に示すように、縮みフランジ変形部位の縦壁部１３Ａでは長手方向（Ｘ方向）に圧縮応力が作用するが、縮みフランジ変形部位の縦壁部１３Ａに隣接し、縦壁部１３Ａの高さより低くなる紙面左側の縦壁部１３Ｂの長手方向（Ｘ方向）に引張応力が作用することがわかる。その結果、プレス成形後に離型すると、この引張応力によってプレス成形品（従来例）９の天板部１１が長手方向に凸状に反るスプリングバックが生じるわけである。さらに、ブランク７の材料強度が増加すると、この引張応力も増加し、スプリングバック量もより大きくなる。
Regarding this springback, a finite element analysis was performed to obtain the stress distribution at the bottom dead center of press forming, and the resulting contour plot is shown in Figure 4. Figure 4(a) is a plan view, and Figure 4(b) is a side view seen from the direction of the vertical wall on the outer side of the curve.
As shown in Fig. 4(b), compressive stress acts in the longitudinal direction (X direction) on the vertical wall portion 13A of the shrink flange deformation portion, but tensile stress acts in the longitudinal direction (X direction) on the vertical wall portion 13B on the left side of the drawing, which is adjacent to the vertical wall portion 13A of the shrink flange deformation portion and is lower in height than the vertical wall portion 13A. As a result, when the press-molded product (conventional example) 9 is released from the mold after press molding, this tensile stress causes springback in which the top plate portion 11 of the press-molded product (conventional example) 9 warps convexly in the longitudinal direction. Furthermore, if the material strength of the blank 7 increases, this tensile stress also increases, and the amount of springback also becomes larger.
縮みフランジ変形部位の縦壁部１３Ａに隣接し、この縦壁部１３Ａより高さの低い縦壁部１３Ｂに引張応力が発生する要因は、主に二つ挙げられる。
一つ目の要因は、図４（ｂ）に示すように、縦壁方向からの側面視において縮みフランジ変形部位が圧縮変形となることである。また、紙面右側の短軸部位である縦壁部１３Ｃは縦壁高さが極端に低くて、長軸部位である紙面左側の縦壁部１３Ｂは縦壁高さが相対的に高い。その結果、プレス成形すると縮みフランジ変形部位の縦壁部１３Ａの圧縮変形に伴って周囲から材料を引き込もうとするため、縦壁高さが相対的に高くて材料が相対的に多い長軸部位である紙面左側の縦壁部１３Ｂが引っ張られて、引張応力が発生する。
There are two main factors that cause tensile stress to occur in the vertical wall portion 13B that is adjacent to the vertical wall portion 13A of the shrink flange deformation portion and is lower in height than this vertical wall portion 13A.
The first factor is that the shrink flange deformation portion is compressed when viewed from the vertical wall direction as shown in Fig. 4(b). Also, the vertical wall height of the vertical wall portion 13C, which is the short axis portion on the right side of the paper, is extremely low, while the vertical wall height of the vertical wall portion 13B, which is the long axis portion on the left side of the paper, is relatively high. As a result, when press-molded, the vertical wall portion 13A, which is the shrink flange deformation portion, is compressed and deformed, so that the vertical wall portion 13B, which is the long axis portion with a relatively high vertical wall height and a relatively large amount of material, is pulled, generating tensile stress.
二つ目の要因は、長軸部位である紙面左側の縦壁部１３Ｂの高さが、縮みフランジ変形部位の縦壁部１３Ａの高さより低いことである。上述の図４（ｂ）に示すとおり、長軸部位である紙面左側の縦壁部１３Ｂに引張応力が作用するが、天板部１１は同じ高さで、縦壁高さが縦壁部１３Ａより低いことにより、引張応力が縦壁部１３Ｂの下端から上端近くまで集中しやすく、この引張応力が残存する。 The second factor is that the height of the vertical wall portion 13B on the left side of the paper, which is the long axis portion, is lower than the height of the vertical wall portion 13A in the shrink flange deformation portion. As shown in FIG. 4(b) above, tensile stress acts on the vertical wall portion 13B on the left side of the paper, which is the long axis portion, but because the top plate portion 11 is the same height and the vertical wall height is lower than the vertical wall portion 13A, the tensile stress tends to concentrate from the bottom end to near the top end of the vertical wall portion 13B, and this tensile stress remains.
上記２つの要因のうち、一つ目の要因である引張応力は、縮みフランジ変形に伴って必然的に生じてしまう。そこで、二つ目の要因である引張応力を軽減して、かつ、引張応力を縦壁部１３Ｂの下端に集中させる方法を検討し、本発明に至ったものであり、具体的には以下に示すものである。
一例として図２に示すような、湾曲部における縮みフランジ変形部となる縦壁部５Ａの縦壁高さＨaと、縦壁部５Ａを挟む両側の縦壁の一方である縦壁部５Ｂの縦壁高さＨbと、縦壁部５Ａを挟む両側の縦壁の他方である縦壁部５Ｃの縦壁高さＨcとの関係が、Ｈa＞Ｈb＞Ｈcとなっているプレス成形品１をプレス成形する方法であって、パンチとパッドとダイによって金属板を、縦壁部５Ｂ（１７Ｂ）の縦壁高さが前記縦壁部５Ａ（１７Ａ）の縦壁高さ以上の中間成形品１５（図５参照、図５は縦壁高さが同じ場合）にプレス成形する中間成形品プレス成形工程と、中間成形品をトリミング用金型で挟んで、縦壁部５Ｂの縦壁高さが前記プレス成形品１の縦壁高さであるＨｂになるように縦壁部５Ｂをトリミングするトリミング工程とを備えたものである（図１参照）。
以下、各工程を説明する。
Of the above two factors, the first factor, tensile stress, is inevitably generated by the shrink flange deformation. Therefore, a method for reducing the second factor, tensile stress, and concentrating the tensile stress at the lower end of the vertical wall portion 13B was studied, and the present invention was arrived at. Specifically, the following is shown.
As an example, as shown in FIG. 2, a method for press-molding a press-molded product 1 in which the relationship between the vertical wall height Ha of the vertical wall portion 5A, which becomes the shrink flange deformation portion in the curved portion, the vertical wall height Hb of the vertical wall portion 5B, which is one of the vertical walls on both sides sandwiching the vertical wall portion 5A, and the vertical wall height Hc of the vertical wall portion 5C, which is the other of the vertical walls on both sides sandwiching the vertical wall portion 5A, is Ha > Hb > Hc, includes an intermediate product press-molding process in which a metal plate is press-molded by a punch, a pad, and a die into an intermediate product 15 (see FIG. 5, FIG. 5 shows the case where the vertical wall heights are the same) in which the vertical wall portion 5B (17B) is equal to or greater than the vertical wall height of the vertical wall portion 5A (17A), and a trimming process in which the intermediate product is sandwiched between a trimming die and the vertical wall portion 5B is trimmed so that the vertical wall height of the vertical wall portion 5B becomes Hb, which is the vertical wall height of the press-molded product 1 (see FIG. 1).
Each step will be described below.
＜中間成形品プレス成形工程＞
中間成形品プレス成形工程は、パンチとパッドとダイによって金属板を、縦壁部１７Ｂの縦壁高さが縦壁部１７Ａの縦壁高さ以上の中間成形品１５にプレス成形する工程である。
以下、中間成形品プレス成形工程の意義について、以下に説明する。
<Intermediate product press molding process>
The intermediate product press forming process is a process in which a metal plate is press-formed by a punch, a pad, and a die into an intermediate product 15 in which the vertical wall height of vertical wall portion 17B is equal to or greater than the vertical wall height of vertical wall portion 17A.
The significance of the intermediate product press molding step will be explained below.
プレス成形品（従来例）９において縮みフランジ変形部位の縦壁部１３Ａより高さの低い縦壁部１３Ｂに引張応力が集中する原因は、図４（ｂ）に示すように、縦壁部１３Ｂの高さが縮みフランジ変形部位の縦壁部１３Ａの高さより低いことにある。そこで、縦壁部１３Ｂの縦壁高さを縦壁部１３Ａと同等以上になるように（図５参照）、縮みフランジ変形部位に対応する縦壁相当部分のブランク幅Ｗａに対して長軸部位である紙面左側の縦壁部１７Ｂに対応する縦壁相当部分のブランク幅Ｗｂが同等以上になるブランク１９を用いることを考えた（図６参照、図６はＷａとＷｂが同じ場合）。
なお、ブランクである金属板として引張強度５９０ＭＰａ級以上の鋼板が好ましい。
In the press-molded product (conventional example) 9, the tensile stress is concentrated in the vertical wall portion 13B, which is lower in height than the vertical wall portion 13A in the shrink flange deformation region, because the height of the vertical wall portion 13B is lower than the height of the vertical wall portion 13A in the shrink flange deformation region, as shown in Fig. 4(b). Therefore, it was considered to use a blank 19 in which the blank width Wb of the vertical wall equivalent portion corresponding to the vertical wall portion 17B on the left side of the paper surface, which is the long axis portion, is equal to or greater than the blank width Wa of the vertical wall equivalent portion corresponding to the shrink flange deformation region (see Fig. 6, where Wa and Wb are equal in Fig. 6).
The metal blank is preferably a steel plate having a tensile strength of 590 MPa or more.
このようなブランク１９を用いてプレス成形すると、図５に示すように、引張応力発生領域は長軸部位の縦壁高さを高くした縦壁部１７Ｂの下端近傍に生ずる。
この部分は前述のブランク幅Ｗｂの一部に対応し、目標形状においては不要となる部分であるため、次のトリミング工程で切り落とすことで残存応力を無くすることができる。
When such a blank 19 is press-molded, as shown in FIG. 5, a tensile stress region is generated in the vicinity of the lower end of the vertical wall portion 17B in which the vertical wall height of the major axis portion is increased.
This portion corresponds to a part of the blank width Wb described above, and is unnecessary in the target shape, so that the remaining stress can be eliminated by cutting it off in the next trimming process.
＜トリミング工程＞
トリミング工程は、中間成形品１５をトリミング用金型で挟んで、縦壁部Ｂの縦壁高さがプレス成形品１の縦壁高さであるＨｂになるように縦壁部１７Ｂをトリミングする工程である。
トリミングすることで、図５に示した中間成形品１５が、図７に示す目標形状のプレス成形品１となる。
<Trimming process>
The trimming process is a process in which the intermediate molded product 15 is sandwiched between trimming dies and the vertical wall portion 17B is trimmed so that the vertical wall height of the vertical wall portion B becomes the vertical wall height Hb of the press-molded product 1.
By trimming, the intermediate product 15 shown in FIG. 5 becomes the press-formed product 1 having the target shape shown in FIG.
トリミング工程により、プレス成形後に長軸部位の縦壁延長部のエッジ近傍に広がった引張応力が存在する部位を切り落とすため、結果として、目標形状となるプレス成形品１には長軸部位の引張応力が存在しなくなり、本発明で課題となっていたプレス成形品１の天板部が長手方向に凸状に反るスプリングバックを防止できるわけである。 The trimming process cuts off the area where tensile stress spreads near the edge of the vertical wall extension of the long axis area after press forming. As a result, the press-formed product 1 with the target shape does not have tensile stress in the long axis area, and springback, in which the top plate of the press-formed product 1 warps convexly in the longitudinal direction, which was an issue in this invention, can be prevented.
図７は、トリム工程を施したプレス成形品１について、有限要素解析によりトリム用金型に挟み込んで求めた成形下死点での応力分布を示したものである。プレス成形品（従来例）９の天板部に長手方向凸状に反るスプリングバックが生じていた図４（ｂ）の成形下死点での応力分布と比較すると、本実施の形態のプレス成形方法で成形したプレス成形品１では、図７に示すように、長軸部位である縦壁部分の引張応力が著しく低減して、スプリングバックが抑制されたことがわかる。
また、上述のプレス成形方法の各工程を実行することで、プレス成形品１が製造でき、製造されたプレス成形品は上述の通り、スプリングバックが抑制されたものとなる。
Fig. 7 shows the stress distribution at the bottom dead point of the press-formed product 1 that has been subjected to the trimming process, which was obtained by clamping the product between trimming dies using finite element analysis. Compared with the stress distribution at the bottom dead point of the press-formed product 1 (conventional example) 9, in which springback occurred in the top plate portion of the press-formed product 9, which was warped in a convex shape in the longitudinal direction, it can be seen that in the press-formed product 1 formed by the press forming method of this embodiment, as shown in Fig. 7, the tensile stress in the vertical wall portion, which is the long axis portion, is significantly reduced, and springback is suppressed.
Furthermore, by carrying out each step of the above-described press forming method, the press-formed product 1 can be manufactured, and the manufactured press-formed product has suppressed springback as described above.
本発明に係るプレス成形方法およびプレス成形品の製造方法によるスプリングバック低減効果を確認するため、有限要素法（FEM）によるプレス成形解析およびスプリングバック解析を行なったので、その結果について以下に説明する。
本実施例では図２に示す上面視で湾曲し縮みフランジ変形部位を有するコ字断面形状のプレス成形品１を対象にプレス成形解析を実施した。
なお、プレス成形に使用するブランク（金属板）は板厚t=1.2mmであって、引張強度が590MPa級～1180MPa級の鋼板とした。目標プレス成形品との精度差として、プレス成形品の各部位について、成形下死点での部品形状を基準としてスプリングバックした後の各部位との相対距離について、プレス成形方向をマイナスの値、逆方向をプラスの値として求め図８～図１０に示した。プレス成形方向における最大差の絶対値と逆方向における最大差の絶対値との和を目標形状との精度差として求めた。表１に評価結果をまとめて示す。
In this embodiment, a press molding analysis was performed on a press-formed product 1 having a U-shaped cross section that is curved when viewed from above and has a shrink flange deformation portion as shown in FIG.
The blank (metal plate) used for press forming was a steel plate with a plate thickness t = 1.2 mm and a tensile strength of 590 MPa to 1180 MPa. As the accuracy difference from the target press-formed product, for each part of the press-formed product, the relative distance from each part after springback was determined based on the part shape at the bottom dead center of forming, with the press forming direction being a negative value and the reverse direction being a positive value, and these are shown in Figures 8 to 10. The sum of the absolute value of the maximum difference in the press forming direction and the absolute value of the maximum difference in the reverse direction was determined as the accuracy difference from the target shape. The evaluation results are summarized in Table 1.
表１のNo.１とNo.２は590MPa級鋼板であり、従来例１と発明例１のスプリングバックによる乖離量の分布をそれぞれ図８（ａ）、（ｂ）に示した。従来例１のNo.1(図８（ａ）)では目標形状との精度差が、プレス成形方向に0.8mm（-0.8mm）、逆方向に0.1mm（+0.1mm）であり、これらの絶対値の和が0.9mmであったのに対し、発明例１のNo.2（図８（ｂ））では、プレス成形方向に0.6mm（-0.6mm）、逆方向に0.1mm（+0.1mm）であり、これらの絶対値の和が0.7mmまで低減した。 No. 1 and No. 2 in Table 1 are 590 MPa class steel sheets, and the distribution of deviation due to springback for Conventional Example 1 and Invention Example 1 is shown in Figures 8(a) and (b), respectively. For Conventional Example 1 No. 1 (Figure 8(a)), the accuracy difference from the target shape was 0.8 mm (-0.8 mm) in the press forming direction and 0.1 mm (+0.1 mm) in the reverse direction, with the sum of these absolute values being 0.9 mm, whereas for Invention Example 1 No. 2 (Figure 8(b)), the accuracy difference was 0.6 mm (-0.6 mm) in the press forming direction and 0.1 mm (+0.1 mm) in the reverse direction, with the sum of these absolute values being reduced to 0.7 mm.
表１のNo.３と４は980MPa級鋼板であり、従来例２と発明例２のスプリングバックによる乖離量の分布をそれぞれ図９（ａ）、（ｂ）に示した。従来例２のNo.３（図９（ａ））では目標形状との精度差が、プレス成形方向に1.0mm（-1.0mm）、逆方向に0.2mm（+0.2mm）であり、これらの絶対値の和が1.2mmであったのに対し、発明例２のNo.４(図９（ｂ）)では、プレス成形方向に0.7mm（-0.7mm）、逆方向に0.2mm（+0.2mm）であり、これらの絶対値の和が0.9mmまで低減した。 Nos. 3 and 4 in Table 1 are 980 MPa class steel sheets, and the distribution of deviation due to springback for Conventional Example 2 and Invention Example 2 is shown in Figures 9(a) and (b), respectively. For Conventional Example 2 No. 3 (Figure 9(a)), the accuracy difference from the target shape was 1.0 mm (-1.0 mm) in the press forming direction and 0.2 mm (+0.2 mm) in the reverse direction, with the sum of these absolute values being 1.2 mm, whereas for Invention Example 2 No. 4 (Figure 9(b)), the accuracy difference was 0.7 mm (-0.7 mm) in the press forming direction and 0.2 mm (+0.2 mm) in the reverse direction, with the sum of these absolute values reduced to 0.9 mm.
表１のNo.５と６は1180MPa級鋼板であり、従来例３と発明例３のスプリングバックによる乖離量の分布をそれぞれ図１０（ａ）、（ｂ）に示した。従来例３のNo.５(図１０（ａ）)では目標形状との精度差が、プレス成形方向に1.3mm（-1.3mm）、逆方向に0.3mm（+0.3mm）であり、これらの絶対値の和が1.6mmであったのに対し、発明例３のNo.６(図１０（ｂ）)では、プレス成形方向に0.9mm（-0.9mm）、逆方向に0.3mm（+0.3mm）であり、これらの絶対値の和が1.2mmまで低減した。
以上から、発明例が従来例に比べて、スプリングバックを低減できて、形状精度の良好なプレス成形を実現できること、及び形状精度の良好なプレス成形品を製造できることを実証できた。
Nos. 5 and 6 in Table 1 are 1180 MPa class steel sheets, and the distribution of deviation due to springback for Conventional Example 3 and Inventive Example 3 is shown in Figures 10(a) and (b), respectively. For Conventional Example 3 No. 5 (Figure 10(a)), the accuracy difference from the target shape was 1.3 mm (-1.3 mm) in the press forming direction and 0.3 mm (+0.3 mm) in the reverse direction, with the sum of these absolute values being 1.6 mm, whereas for Inventive Example 3 No. 6 (Figure 10(b)), the accuracy difference was 0.9 mm (-0.9 mm) in the press forming direction and 0.3 mm (+0.3 mm) in the reverse direction, with the sum of these absolute values being reduced to 1.2 mm.
From the above, it has been demonstrated that the examples of the invention can reduce springback compared to the conventional examples, realize press forming with good shape accuracy, and produce press-formed products with good shape accuracy.
１ プレス成形品
３ 天板部
５ 縦壁部
５Ａ 縮みフランジ変形部となる縦壁部
５Ｂ 縦壁部５Ａに隣接する一方の縦壁部
５Ｃ 縦壁部５Ａに隣接する他方の縦壁部
７ ブランク（従来例）
９ プレス成形品（従来例）
１１ 天板部
１３ 縦壁部
１３Ａ 縮みフランジ変形部となる縦壁部
１３Ｂ 縦壁部１３Ａに隣接する一方の縦壁部
１３Ｃ 縦壁部１３Ａに隣接する他方の縦壁部
１５ 中間成形品
１７ 縦壁部
１７Ａ 縮みフランジ変形部となる縦壁部
１７Ｂ 縦壁部１７Ａに隣接する一方の縦壁部
１７Ｃ 縦壁部１７Ａに隣接する他方の縦壁部
１９ ブランク
1 Press-molded product 3 Top plate portion 5 Vertical wall portion 5A Vertical wall portion that becomes a shrink flange deformation portion 5B One vertical wall portion adjacent to the vertical wall portion 5A 5C The other vertical wall portion adjacent to the vertical wall portion 5A 7 Blank (conventional example)
9. Press-molded products (conventional examples)
REFERENCE SIGNS LIST 11 Top plate portion 13 Vertical wall portion 13A Vertical wall portion that becomes a shrink flange deformation portion 13B One vertical wall portion adjacent to vertical wall portion 13A 13C The other vertical wall portion adjacent to vertical wall portion 13A 15 Intermediate molded product 17 Vertical wall portion 17A Vertical wall portion that becomes a shrink flange deformation portion 17B One vertical wall portion adjacent to vertical wall portion 17A 17C The other vertical wall portion adjacent to vertical wall portion 17A 19 Blank
Claims (4)
パンチとパッドとダイによって金属板を、前記縦壁部Ｂの縦壁高さが前記縦壁部Ａの縦壁高さ以上の中間成形品にプレス成形する中間成形品プレス成形工程と、
前記中間成形品をトリミング用金型で挟んで、前記縦壁部Ｂの縦壁高さが前記プレス成形品の縦壁高さであるＨｂになるように前記縦壁部Ｂをトリミングするトリミング工程とを備えたことを特徴とするプレス成形方法。 A press-molded product having a U-shaped cross section, the press-molded product having a top plate portion and a vertical wall portion, and a curved portion that is curved in the longitudinal direction in a plan view, wherein a vertical wall height Ha of a vertical wall portion A that becomes a shrink flange deformation portion in the curved portion, a vertical wall height Hb of a vertical wall portion B that is one of the vertical walls on both sides sandwiching the vertical wall portion A, and a vertical wall height Hc of a vertical wall portion C that is the other of the vertical walls on both sides sandwiching the vertical wall portion A are such that Ha>Hb>Hc,
an intermediate product press forming process in which a metal plate is press-formed by a punch, a pad, and a die into an intermediate product having a vertical wall height of the vertical wall portion B equal to or greater than the vertical wall height of the vertical wall portion A;
and a trimming step of clamping the intermediate molded product with a trimming die and trimming the vertical wall portion B so that the vertical wall height of the vertical wall portion B becomes Hb, which is the vertical wall height of the press-molded product.
パンチとパッドとダイによって金属板を、前記縦壁部Ｂの縦壁高さが前記縦壁部Ａの縦壁高さ以上の中間成形品にプレス成形する中間成形品プレス成形工程と、
前記中間成形品をトリミング用金型で挟んで、前記縦壁部Ｂの縦壁高さが前記プレス成形品の縦壁高さであるＨｂになるように前記縦壁部Ｂをトリミングするトリミング工程とを備えたことを特徴とするプレス成形品の製造方法。 A method for manufacturing a press-molded product having a U-shaped cross section having a top plate portion and a vertical wall portion, and a curved portion that is curved in the longitudinal direction in a plan view, wherein a relationship between a vertical wall height Ha of a vertical wall portion A that becomes a shrink flange deformation portion in the curved portion, a vertical wall height Hb of a vertical wall portion B that is one of the vertical walls on both sides sandwiching the vertical wall portion A, and a vertical wall height Hc of a vertical wall portion C that is the other of the vertical walls on both sides sandwiching the vertical wall portion A is Ha>Hb>Hc,
an intermediate product press forming process in which a metal plate is press-formed by a punch, a pad, and a die into an intermediate product having a vertical wall height of the vertical wall portion B equal to or greater than the vertical wall height of the vertical wall portion A;
and a trimming process for clamping the intermediate molded product with a trimming die and trimming the vertical wall portion B so that the vertical wall height of the vertical wall portion B becomes Hb, which is the vertical wall height of the press-molded product.
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| WO2019068345A1 (en) | 2017-10-06 | 2019-04-11 | Thyssenkrupp Steel Europe Ag | Method and device for producing shaped sheet-metal components by means of preshaped components |
| US20210162480A1 (en) | 2018-08-21 | 2021-06-03 | Jfe Steel Corporation | Press forming method |
| JP2023046870A (en) | 2021-09-24 | 2023-04-05 | 日本製鉄株式会社 | Molded article, blank, manufacturing method of molded article, and metal mold |
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