JP3728148B2

JP3728148B2 - Drawing bending method for hat-shaped cross-section members with excellent shock absorption characteristics

Info

Publication number: JP3728148B2
Application number: JP20375199A
Authority: JP
Inventors: 憲一渡辺
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 1999-07-16
Filing date: 1999-07-16
Publication date: 2005-12-21
Anticipated expiration: 2019-07-16
Also published as: JP2001030020A

Description

【０００１】
【発明が属する技術分野】
本発明は、例えば自動車車体、自動車用部品などに使用される、衝撃吸収用ハット型断面構造部材の衝撃吸収特性を向上させる絞り曲げ成形方法に関する。
【０００２】
【従来の技術】
自動車の耐衝突安全性向上の要求が強まるとともに、地球環境の保護の観点から自動車の燃費向上のため、車体重量の軽量化の要求が強まっている。このような要求を満足させるために、自動車の衝突時の衝撃吸収用部材を形成する材料として、高強度鋼板が用いられるようになってきた。衝撃吸収用部材の形状としては、図４に示すように、対向配置された側壁部５２、５２を備えた、Ｕ形断面を有するハット型断面構造部材５１が多い。
【０００３】
前記ハット型断面構造部材５１は、通常、プレス成形による絞り曲げ成形よって成形される。前記絞り曲げ成形は、図１に示すように、一対の平面部が対向配置された凹状成形面２を有し、該凹状成形面２の外側に板押さえ面３が延設された下型（ダイ）１と、前記下型１に対して昇降自在に設けられ、下型１側に下降することによって前記凹状成形面２と共働して金属板Ｗを成形する凸状成形面５を有する上型４と、前記板押さえ面３との間で金属板Ｗを押圧状態で挟持する板押さえ部材６とを備えた金型１０を用い、前記板押さえ面３と板押さえ部材６との間に金属板Ｗを押圧状態で挟持し、上型４の凸状成形面５の下面を金属板Ｗに当接させつつ下方へ下降させて金属板Ｗを凸状成形面５と凹状成形面２との間で断面Ｕ形に成形する方法である。図中のＳは、凸状成形面５の下面が金属板Ｗに当接してから、上型４が成形のために移動する移動量であり、成形ストロークと呼ぶ。なお、板押さえ面３と板押さえ部材６とによって金属板Ｗを挟持する際の押圧力（板押さえ圧）は、成形の際に板押さえ面３と板押さえ部材６とによって挟持された金属板Ｗの成形面への流入を妨げず、板押さえ面３上において金属板Ｗにしわが発生しないように設定される。
【０００４】
成形対象の金属板として鋼板を用い、これを絞り曲げ成形すると、鋼板が下型１の凹状成形面２から板押さえ面３に移行する肩部７を通過する際に曲げ・曲げ戻し変形を受けて加工硬化し、これにより降伏点が上昇し、あるいはさらにその後の塗装焼き付け処理（ＢＨ処理と呼ぶ。）によってさらに降伏点が向上し、ハット型断面構造部材の衝撃吸収特性は向上する。
【０００５】
【発明が解決しようとする課題】
鋼板を用いてハット型断面構造部材を絞り曲げ成形した場合、図２に示すように、成形後、弾性回復現象によって曲げ・曲げ戻し変形を受けたハット型断面構造部材５１の側壁部５２に寸法精度不良（反り）が発生しやすいという問題があり、この反りは鋼板の強度が高いほど著しい。
【０００６】
この側壁部５２の反りを防止するためには、基本的には成形の際に曲げ・曲げ戻し変形を受ける側壁部に引っ張り力を作用させることが有効である。側壁部に引っ張り力を作用させるには、成形中の押圧力を高くしたり、あるいは板押さえ面３に凹部を設け、一方板押さえ部材６に前記凹部に係合する凸部を設けることにより、鋼板の流入抵抗を増大する方法がとられる。
【０００７】
しかしながら、この様な方法では、側壁部５２での反りが防止されるものの、側壁部５２の板厚がかなり減少するため、耐衝撃特性という観点から見れば、成形部材の衝撃吸収特性が却って低下してしまうという問題がある。
【０００８】
なお、ハット型断面構造部材５１は、Ｖ曲げ成形によっても成形される。前記Ｖ曲げ成形は、図７に示すように、Ｖ溝成形面２２を有する下型２１と、前記下型２１側に下降して前記Ｖ溝成形面２２と共働して金属板ＷをＶ溝成形面２２に沿って曲げ成形する凸状成形面２５とを有する上型２４とを備えた金型３１を用い、前記Ｖ溝成形面２２の上に金属板Ｗを置き、上型２４を下降させて金属板Ｗに凸状成形面２５の頂部を当接させ、さらに押し下げてＶ溝成形面２２に沿って曲げ成形する方法である。このＶ曲げ成形によって成形した場合、ハット型断面構造部材５１の側壁部５２には、反りが発生せず、また板厚の減少も生じないが、側壁部５２は変形を受けないため、加工硬化、ＢＨ処理による衝撃吸収特性の向上は期待できない。
【０００９】
本発明はかかる問題に鑑みてなされたもので、金属板で形成されたハット型断面構造部材の絞り曲げ成形において、成形型の移動方向に成形された側壁部に反りが生じにくく、しかも衝撃吸収特性に優れた部材を成形することができる成形方法を提供するものである。
【００１０】
【課題を解決するための手段】
本発明のハット型断面構造部材の絞り曲げ成形方法は、請求項１に記載したように、凹状成形面およびこの凹状成形面の外側に連成された板押さえ面を有する第１成形型と、前記第１成形型側に相対移動することにより前記板押さえ面の上に供給された金属板を前記凹状成形面と共働して成形する凸状成形面を有する第２成形型と、成形の際に金属板を前記板押さえ面に押圧する板押さえ部材とを備え、前記凹状成形面から前記板押さえ面に移行する肩部はその曲率半径Ｒが金属板の板厚をｔとしたときＲ＝１．５ｔ〜３．５ｔとされた金型を用い、金属板を成形する際の前記第１成形型あるいは前記第２成形型が相対移動する成形ストロークをＳとし、成形に要する全成形ストロークをＳＴとしたとき、Ｓが０．９８×ＳＴ〜０．９９×ＳＴの間にあるときに金属板を前記板押さえ部材と前記板押さえ面とによって拘束し、その状態でＳＴの残部を成形するものである。
【００１１】
本発明の成形方法によれば、第１成形型の凹状成形面から板押さえ面に移行する肩部の曲率半径Ｒが金属板の板厚ｔに対して１．５ｔ〜３．５ｔとされた金型を用いて絞り曲げ成形し、成形する際に、成形に要する全成形ストロークをＳＴとしたとき、成形ストロークＳが０．９８×ＳＴ〜０．９９×ＳＴの間にあるときに金属板を前記板押さえ部材と前記板押さえ面とによって拘束し、その状態でＳＴの残部を成形するので、金属板の拘束後の成形後段において、成形型の移動方向に成形されたハット型断面構造部材の側壁部に、ほとんど板厚変化を生じさせることなく、伸び歪を導入することができる。このため、板厚減少による衝撃吸収特性の劣化を防止しつつ、ハット型断面構造部材の側壁部の反りを改善することができる。
【００１２】
前記肩部の曲率半径Ｒを１．５ｔ〜３．５ｔとしたのは、金属板が肩部を通過する際に曲げ・曲げ戻し変形により、板厚を減少させることなく適度な加工硬化を付与するためである。すなわち、後述の実施例から明らかなとおり、肩部の曲率半径Ｒが１．５ｔ未満では金属板が肩部を通過する際の曲げ・曲げ戻し変形による加工硬化による降伏点は十分に上昇するが、変形量が大きくなるために成形部材の側壁部における板厚が減少し、衝撃吸収特性が低下するようになる。一方、Ｒが３．５ｔを超えると金属板が肩部を通過する際の曲げ・曲げ戻し変形量が小さいため、降伏点の上昇が不足し、衝撃吸収特性が向上しないようになる。
【００１３】
また、金属板の拘束の開始時点すなわち成形前段から成形後段への切り換え時点を成形ストロークＳが０．９８×ＳＴ〜０．９９×ＳＴの間にあるときとしたのは、後述の実施例から明らかなとおり、Ｓが０．９８ＳＴ未満では反りは軽減するものの、成形後段における金属板の拘束後の残部の成形ストローク（ＳＴ−Ｓ）が長いため、側壁部の伸びひずみが大きくなり、板厚が減少して衝撃吸収特性が低下するようになり、一方Ｓが０．９９ＳＴを超えると、拘束後の成形ストローク（ＳＴ−Ｓ）が短いため、側壁部に十分な伸びが加えられず、反りの低減効果が不足するようになるからである。
【００１４】
本発明の成形対象となる金属板は、鋼板に限らず、Ａｌ又はＡｌ合金板、Ｔｉ又はＴｉ合金板等を用いることができ、強度の高いものほど効果的である。金属板として、自動車部材として使用される板厚１〜３mm程度の鋼板を用いる場合、成形前段における鋼板の板押さえ部材による押圧力Ｐは、通常、成形前段の成形終了時点における板押さえ面と板押さえ部材とによって挟持された鋼板に作用する面圧が１０〜３０kgf/cm² になるように設定され、成形後段に入る前に鋼板を拘束して、凹状成形面への流入を阻止するには、押圧力を４．０×Ｐ以上に設定すればよい。
【００１５】
また、本発明に用いる金型の第１成形型、第２成形型はそれぞれ図１の下型１、上型４に相当するものであるが、下型１と上型４との配置を上下反転し、下型１を上型４側に移動して成形を行うようにしてもよい。
【００１６】
【実施例】
強度５９０Ｎクラスの鋼板（板厚ｔ＝１．６０mm、降伏点ＹＳ＝３７６Ｎ／mm²、引張強さＴＳ＝６０３Ｎ／mm²、伸びＥｌ＝２６．５％）を図１および図７に示した金型を用いて、表１の条件にしたがって絞り曲げ成形、Ｖ曲げ成形によりハット型断面部材を製作した。
【００１７】
絞り曲げ成形については、全成形ストロークＳＴは８０mmであり、板押さえ部材６による成形前段における押圧力Ｆ１を５tonf（成形前段の成形終了時点における鋼板に作用する面圧２７kgf/cm² ）として成形した。また、成形ストロークＳが全成形ストロークＳＴ（＝８０mm）に対して表中のＳ／ＳＴとなった時点で押圧力をＦ２に上昇して、鋼板を板押さえ面３上で拘束するようにして、ＳＴの残部（ＳＴ−Ｓ）を成形した。表中のＲは図１に示す肩部７、あるいは図７に示す凸状成形面２５の先端アール部の曲率半径である。
【００１８】
成形後、ハット型断面部材５１の側壁部５２の反りを測定した。反りの大きさδは、図２に示すように、ハット型断面部材５１の角部のＲ止まり（アール末端）を結ぶ直線から各側壁部５２、５２における最大離間量δ１、δ２を測定し、δ＝（δ１＋δ２）／２から算出した。また、側壁部５２から引張試験片を採取し、その平均の板厚ｔ′を求めた。また、引張試験により降伏点を測定し、成形前の素材鋼板との降伏点差（ΔＹＳ）を求めた。
【００１９】
また、図３に示すように、ハット型断面構造部材５１の開口部に同材質、同厚の平板６１をスポット溶接し、両端に端板６２、６２を溶接して衝撃試験部材６３を製作し、これを用いて下記要領で衝撃圧壊試験を行い、高速変形時の衝撃吸収特性を調べた。前記衝撃圧壊試験は、試験部材６３の一端を固定し、他端に１４ｍ／ｓで試験部材の軸方向から衝突体を衝突させ、ハット型断面構造部材５１の変位量が１５０mmまでの吸収エネルギーを測定した。なお、図３には各部の寸法（mm）も示した。
【００２０】
これらの測定結果を表１に併せて示す。また、試料No. ２〜９についてＲ／ｔと吸収エネルギーとの関係を整理したグラフを図５に、試料No. １４〜１７についてＳ／ＳＴと吸収エネルギーとの関係を整理したグラフを図６に示す。
【００２１】
【表１】

【００２２】
試料No. ２〜９および図５より、下型肩部７のＲを変化させると、成形後の板厚ｔ′が大きく変化し、発明条件（Ｒ／ｔ＝１．５〜３．５）を満足するもの（No. ４〜６）ではＶ曲げ成形したNo. １に比較して、吸収エネルギーが約１０％向上していることがわかる。
【００２３】
また、試料No. １４〜１８および図６より、本発明の鋼板拘束タイミングを満足する試料No. １６、１７では反りも小さく、吸収エネルギーも大きく、成形精度および衝撃吸収特性に優れることがわかる。一方、成形ストロークＳが０．９８×ＳＴより小さいときに鋼板を拘束し、成形面への流入を阻止した場合、板厚が０．１０mm以上減少し、吸収エネルギーが低下した。また、Ｓが０．９９×ＳＴより大きいときに鋼板を拘束した場合、成形時に大きな反りが発生して、試験部材の製作ができなかった。
【００２４】
また、Ｆ２／Ｆ１が３．５以下のNo. １０、１１では、鋼板が拘束されておらず、成形面への鋼板の流入が認められたため、成形時に大きな反りが発生し、このため試験部材の製作ができなかった。
【００２５】
【発明の効果】
本発明のハット型断面構造部材の絞り曲げ成形方法によれば、第１成形型の肩部の曲率半径を成形対象である金属板の板厚ｔに対して１．５ｔ〜３．５ｔとし、また金属板を拘束して成形面への流入を阻止するタイミングを０．９８ＳＴ〜０．９９ＳＴ（全成形ストロークＳＴ）の範囲で行うので、成形の際に曲げ・曲げ戻し変形を受けるハット型断面構造部材の側壁部にその板厚の減少を防止しつつ、加工硬化による降伏強度の上昇を図り、しかも十分な伸び歪を導入することができ、前記側壁部の反りの発生を防止するとともに優れた衝撃吸収特性を備えたハット型断面構造部材を得ることができる。
【図面の簡単な説明】
【図１】絞り曲げ成形を行うための金型の断面図である。
【図２】側壁部に反りが形成されたハット型断面構造部材の斜視図である。
【図３】ハット型断面構造部材を備えた衝撃圧壊試験部材の全体斜視図である。
【図４】ハット型断面構造部材の斜視図である。
【図５】実施例におけるＲ（肩部の曲率半径）／ｔ（成形前板厚）と吸収エネルギーとの関係を整理したグラフである。
【図６】実施例におけるＳ（成形ストローク）／ＳＴ（全成形ストローク）と吸収エネルギーとの関係を整理したグラフである。
【図７】Ｖ曲げ成形を行うための金型の断面図である。
【符号の説明】
１下型（本発明における第１成形型）
２凹状成形面
３板押さえ面
４上型（本発明における第２成形型）
５凸状成形面
６板押さえ部材
７肩部
Ｗ金属板[0001]
[Technical field to which the invention belongs]
The present invention relates to a drawing and bending method for improving impact absorption characteristics of a shock-absorbing hat-type cross-sectional structural member used for, for example, an automobile body or an automotive part.
[0002]
[Prior art]
There is an increasing demand for improving the collision safety of automobiles, and there is an increasing demand for lighter body weight in order to improve automobile fuel efficiency from the viewpoint of protecting the global environment. In order to satisfy such requirements, high-strength steel sheets have been used as a material for forming a shock absorbing member at the time of automobile collision. As the shape of the shock absorbing member, as shown in FIG. 4, there are many hat-shaped cross-section structural members 51 having U-shaped cross sections provided with

side wall portions

52, 52 arranged to face each other.
[0003]
The hat-shaped cross-section structural member 51 is usually formed by drawing and bending by press molding. As shown in FIG. 1, the drawing bending molding has a concave molding surface 2 in which a pair of flat portions are opposed to each other, and a lower mold (a plate pressing surface 3 is extended outside the concave molding surface 2). A die) 1 and a convex molding surface 5 which is provided so as to be movable up and down with respect to the lower mold 1 and which forms the metal plate W in cooperation with the concave molding surface 2 by descending to the lower mold 1 side. Between the plate pressing surface 3 and the plate pressing member 6, a mold 10 having a plate pressing member 6 that holds the metal plate W in a pressed state between the upper mold 4 and the plate pressing surface 3 is used. The metal plate W is sandwiched in a pressed state, and the lower surface of the convex molding surface 5 of the upper mold 4 is brought into contact with the metal plate W while being lowered to bring the metal plate W into the convex molding surface 5 and the concave molding surface 2. Is formed into a U-shaped cross section. S in the drawing is a movement amount that the upper mold 4 moves for molding after the lower surface of the convex molding surface 5 contacts the metal plate W, and is called a molding stroke. The pressing force (plate pressing pressure) when the metal plate W is clamped by the plate pressing surface 3 and the plate pressing member 6 is a metal plate clamped by the plate pressing surface 3 and the plate pressing member 6 during molding. It is set so that the metal plate W is not wrinkled on the plate pressing surface 3 without hindering the inflow of W into the molding surface.
[0004]
When a steel plate is used as the metal plate to be formed and is drawn and bent, the steel plate undergoes bending / bending-back deformation when passing through the shoulder portion 7 that transitions from the concave forming surface 2 of the lower mold 1 to the plate pressing surface 3. Thus, the yield point is increased, or the yield point is further improved by the subsequent coating baking process (referred to as BH process), and the impact-absorbing characteristics of the hat-type cross-sectional structure member are improved.
[0005]
[Problems to be solved by the invention]
When a hat-shaped cross-section structural member is drawn and formed using a steel plate, as shown in FIG. 2, the dimension is given to the side wall portion 52 of the hat-type cross-section structural member 51 that has undergone bending and bending back deformation due to an elastic recovery phenomenon after forming. There is a problem that inaccuracy (warp) is likely to occur, and this warp becomes more significant as the strength of the steel plate increases.
[0006]
In order to prevent the side wall 52 from warping, it is basically effective to apply a tensile force to the side wall which undergoes bending / bending deformation during molding. In order to apply a tensile force to the side wall portion, by increasing the pressing force during molding, or by providing a concave portion on the plate pressing surface 3, while providing a convex portion that engages with the concave portion on the plate pressing member 6, A method of increasing the inflow resistance of the steel sheet is taken.
[0007]
However, in such a method, although the warp at the side wall portion 52 is prevented, the thickness of the side wall portion 52 is considerably reduced. From the viewpoint of impact resistance, the shock absorbing property of the molded member is rather lowered. There is a problem of end up.
[0008]
Note that the hat-shaped cross-section structural member 51 is also formed by V-bending. As shown in FIG. 7, the V-bending is performed by lowering the lower die 21 having a V-groove forming surface 22 and descending toward the lower die 21 to cooperate with the V-groove forming surface 22 to form a metal plate W. A metal plate W is placed on the V-groove forming surface 22 using a mold 31 having an upper mold 24 having a convex molding surface 25 that is bent along the groove forming surface 22. In this method, the metal plate W is lowered to bring the top of the convex molding surface 25 into contact with the metal plate W, and further pressed down to bend along the V-groove molding surface 22. When molded by this V-bending, the side wall 52 of the hat-shaped cross-section member 51 is not warped and the plate thickness is not reduced, but the side wall 52 is not deformed, so that it is work hardened. The improvement of shock absorption characteristics by BH treatment cannot be expected.
[0009]
The present invention has been made in view of such problems, and in draw bending of a hat-shaped cross-sectional structure member formed of a metal plate , the side wall portion formed in the moving direction of the mold is unlikely to warp and absorbs shock. A molding method capable of molding a member having excellent characteristics is provided.
[0010]
[Means for Solving the Problems]
A drawing bending method for a hat-shaped cross-section structural member according to the present invention includes a first molding die having a concave molding surface and a plate pressing surface coupled to the outside of the concave molding surface. A second molding die having a convex molding surface for molding the metal plate supplied on the plate pressing surface by moving relative to the first molding die side in cooperation with the concave molding surface; A plate pressing member that presses the metal plate against the plate pressing surface, and the shoulder portion that transitions from the concave forming surface to the plate pressing surface has a radius of curvature R when the thickness of the metal plate is t. = A molding stroke of 1.5t to 3.5t, and the molding stroke in which the first molding die or the second molding die moves relative to each other when molding the metal plate is S, and the total molding stroke required for molding Where S is 0.98 × ST to 0.99 × ST In this state, the metal plate is constrained by the plate pressing member and the plate pressing surface, and the remaining portion of the ST is formed in that state.
[0011]
According to the molding method of the present invention, the curvature radius R of the shoulder portion that transitions from the concave molding surface of the first molding die to the plate pressing surface is 1.5 t to 3.5 t with respect to the plate thickness t of the metal plate. When drawing and bending using a mold and forming, when the forming stroke S is between 0.98 × ST and 0.99 × ST, the metal plate Is restrained by the plate pressing member and the plate pressing surface, and the remaining portion of the ST is molded in that state. Therefore, the hat-shaped cross-sectional structure member molded in the moving direction of the molding die in the latter stage after the molding of the metal plate Elongation strain can be introduced in the side wall portion of the steel plate with almost no plate thickness change. For this reason, it is possible to improve the warpage of the side wall portion of the hat-shaped cross-sectional structure member while preventing the deterioration of the shock absorption characteristics due to the reduction in the plate thickness.
[0012]
The reason why the radius of curvature R of the shoulder portion is set to 1.5t to 3.5t is that when the metal plate passes through the shoulder portion, bending and unbending deformation imparts appropriate work hardening without reducing the plate thickness. It is to do. That is, as will be apparent from the examples described later, when the curvature radius R of the shoulder is less than 1.5 t, the yield point due to work hardening by bending / unbending deformation when the metal plate passes through the shoulder is sufficiently increased. Since the amount of deformation increases, the plate thickness at the side wall portion of the molded member decreases, and the impact absorption characteristics deteriorate. On the other hand, when R exceeds 3.5 t, the bending / unbending deformation amount when the metal plate passes through the shoulder is small, so that the yield point is insufficiently increased and the shock absorption characteristics are not improved.
[0013]
Also, the time when the metal plate is restrained, that is, when the molding stroke S is between 0.98 × ST and 0.99 × ST, is the time when switching from the pre-molding stage to the post-molding stage. As is apparent, warpage is reduced when S is less than 0.98 ST, but the remaining forming stroke (ST-S) after restraint of the metal plate in the post-forming stage is long, so that the elongation strain of the side wall portion increases and the plate thickness When the S exceeds 0.99ST, the molding stroke after restraint (ST-S) is short, so that the side wall is not sufficiently stretched and warped. This is because the effect of reducing this becomes insufficient.
[0014]
The metal plate to be formed according to the present invention is not limited to a steel plate, and an Al or Al alloy plate, Ti or Ti alloy plate, or the like can be used. The higher the strength, the more effective. When a steel plate having a thickness of about 1 to 3 mm used as an automobile member is used as the metal plate, the pressing force P by the plate pressing member of the steel plate in the pre-forming stage is usually the plate pressing surface and the plate at the end of forming in the pre-forming stage. To prevent the inflow to the concave forming surface by setting the surface pressure acting on the steel plate sandwiched between the pressing members to be 10 to 30 kgf / cm ² and restraining the steel plate before entering the post-forming stage. The pressing force may be set to 4.0 × P or more.
[0015]
The first mold and the second mold of the mold used in the present invention correspond to the lower mold 1 and the upper mold 4 in FIG. 1, respectively, but the arrangement of the lower mold 1 and the upper mold 4 is up and down. Inversion may be performed by moving the lower mold 1 to the upper mold 4 side.
[0016]
【Example】
FIG. 1 and FIG. 7 show a steel plate having a strength of 590 N class (plate thickness t = 1.60 mm, yield point YS = 376 N / mm ² , tensile strength TS = 603 N / mm ² , elongation El = 16.5%). Using a mold, a hat-shaped cross-section member was manufactured by drawing bending and V bending according to the conditions shown in Table 1.
[0017]
For the drawing bending, the total forming stroke ST is 80 mm, and the pressing force F1 in the pre-forming stage by the plate pressing member 6 is set to 5 tons (the surface pressure acting on the steel sheet at the end of forming in the pre-forming stage is 27 kgf / cm ² ). . Further, when the forming stroke S becomes S / ST in the table with respect to the entire forming stroke ST (= 80 mm), the pressing force is increased to F2, and the steel plate is restrained on the plate pressing surface 3. The remainder of ST (ST-S) was molded. R in the table is the radius of curvature of the shoulder portion 7 shown in FIG. 1 or the tip radius portion of the convex molding surface 25 shown in FIG.
[0018]
After molding, the warpage of the side wall 52 of the hat-shaped cross-section member 51 was measured. As shown in FIG. 2, the amount of warping δ is determined by measuring the maximum distances δ1 and δ2 at the

side wall portions

52 and 52 from the straight line connecting the R-stops (R-ends) of the corners of the hat-shaped cross-section member 51, Calculation was performed from δ = (δ1 + δ2) / 2. Further, a tensile test piece was collected from the side wall portion 52, and the average thickness t ′ was obtained. Moreover, the yield point was measured by a tensile test, and the yield point difference (ΔYS) with the raw steel plate before forming was determined.
[0019]
Further, as shown in FIG. 3, a flat plate 61 of the same material and thickness is spot welded to the opening of the hat-shaped cross-section structural member 51, and

end plates

62 and 62 are welded to both ends to produce an impact test member 63. Using this, an impact crushing test was conducted in the following manner, and the impact absorption characteristics during high-speed deformation were investigated. In the impact crushing test, one end of the test member 63 is fixed, and the other end is caused to collide with a collision body from the axial direction of the test member at 14 m / s. It was measured. FIG. 3 also shows the dimensions (mm) of each part.
[0020]
These measurement results are also shown in Table 1. FIG. 5 is a graph in which the relationship between R / t and absorbed energy is arranged for sample Nos. 2 to 9, and FIG. 6 is a graph in which the relationship between S / ST and absorbed energy is arranged for sample Nos. 14 to 17. Shown in
[0021]
[Table 1]

[0022]
From Sample Nos. 2 to 9 and FIG. 5, when the R of the lower mold shoulder 7 is changed, the plate thickness t ′ after forming changes greatly, and the invention conditions (R / t = 1.5 to 3.5) It can be seen that the absorbed energy is improved by about 10% in comparison with No. 1 formed by V-bending (No. 4 to 6) satisfying the above.
[0023]
Also, from Sample Nos. 14 to 18 and FIG. 6, it can be seen that Sample Nos. 16 and 17 satisfying the steel plate restraint timing of the present invention have small warpage, large absorption energy, and excellent molding accuracy and impact absorption characteristics. On the other hand, when the steel sheet was restrained when the forming stroke S was smaller than 0.98 × ST and the flow into the forming surface was prevented, the plate thickness decreased by 0.10 mm or more, and the absorbed energy decreased. Further, when the steel plate was restrained when S was larger than 0.99 × ST, a large warp occurred during forming, and the test member could not be manufactured.
[0024]
In Nos. 10 and 11 with F2 / F1 of 3.5 or less, the steel plate was not constrained and the inflow of the steel plate to the forming surface was observed, so that a large warp occurred during forming. Could not be made.
[0025]
【The invention's effect】
According to the drawing and bending method of the hat-shaped cross-section structural member of the present invention, the radius of curvature of the shoulder of the first mold is 1.5t to 3.5t with respect to the thickness t of the metal plate to be molded, Moreover, since the timing for restricting the metal plate and preventing the inflow to the forming surface is in the range of 0.98ST to 0.99ST (total forming stroke ST), the hat-shaped cross section that undergoes bending / unbending deformation during forming. It is possible to increase the yield strength by work hardening while preventing the reduction of the plate thickness on the side wall portion of the structural member, and to introduce sufficient elongation strain, and to prevent the occurrence of warpage of the side wall portion and excellent Thus, a hat-shaped cross-sectional structural member having shock absorbing characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a mold for performing drawing bending molding.
FIG. 2 is a perspective view of a hat-shaped cross-sectional structure member having a warp formed on a side wall portion.
FIG. 3 is an overall perspective view of an impact crushing test member provided with a hat-shaped cross-sectional structural member.
FIG. 4 is a perspective view of a hat-shaped cross-sectional structural member.
FIG. 5 is a graph in which the relationship between R (curvature radius of shoulder) / t (plate thickness before molding) and absorbed energy in an example is organized.
FIG. 6 is a graph in which the relationship between S (molding stroke) / ST (total molding stroke) and absorbed energy in an example is arranged.
FIG. 7 is a cross-sectional view of a mold for performing V-bending molding.
[Explanation of symbols]
1 Lower mold (first mold in the present invention)
2 concave molding surface 3 plate pressing surface 4 upper mold (second molding mold in the present invention)
5 Convex forming surface 6 Plate pressing member 7 Shoulder portion W Metal plate

Claims

A drawing bending method of a hat-shaped cross-sectional structure member having oppositely disposed side wall portions,
A first molding die having a concave molding surface and a plate pressing surface coupled to the outside of the concave molding surface, and a metal plate supplied on the plate pressing surface by moving relatively to the first molding die side A second molding die having a convex molding surface that cooperates with the concave molding surface to mold the side wall portion, and a plate pressing member that presses the metal plate against the plate pressing surface during molding, The shoulder that transitions from the concave molding surface to the plate pressing surface uses a mold having a radius of curvature R of R = 1.5t to 3.5t, where t is the thickness of the metal plate,
When the molding stroke in which the first molding die or the second molding die moves relative to each other when the metal plate is molded is S, and the total molding stroke required for molding is ST, S is 0.98 × ST-0. The metal plate is constrained by the plate pressing member and the plate pressing surface when it is between 99 × ST, and the bending bending molding of the hat-shaped cross-sectional structure member having excellent shock absorption characteristics that forms the remainder of the ST in that state. Method.