JP3860065B2 - Compression bending method for metal strip - Google Patents

Description

【００１０】
式（５）に示す基本曲げモーメントＭ_C ′と曲げ角度θの関係の例を、推進力Ｐを小さくした場合と大きくした場合を例にとって円グラフに示すと、図２に示す曲線１５（推進力Ｐが小さい場合）、１６（推進力Ｐが大きい場合）のようになる。なお、図中、円弧１７は正方向の許容曲げモーメント＋Ｍ_P を、円弧１８は逆方向の許容曲げモーメント−Ｍ_P を、円弧１９は曲げモーメント０を示している。図２の曲線１５，１６から良く分かるように、アームクランプ根元に作用する基本曲げモーメントＭ_C ′は、曲げ開始時には、正方向に作用しているが、曲げの進行に伴って減少し、途中から逆方向に変わり且つ増大してゆく。そして、その基本曲げモーメントＭ_C ′は、推進力Ｐが小さい場合には、曲線１５で示すように、正逆の許容曲げモーメントの範囲内（＋Ｍ_P 〜−Ｍ_P ）にあるが、推進力Ｐを大きくした場合には、曲線１６で示すように、曲げ角度θ_C で許容曲げモーメント−Ｍ_P を越えてしまう。このため、この曲げ角度θ_C を越えて曲げ加工した場合には、首折れが生じてしまう。そこで、本発明では、荷重付与装置１１によって正方向の曲げモーメントを加え、アームクランプ根元に作用する曲げモーメントが逆方向の許容曲げモーメント−Ｍ_P を越えないようにするものである。本明細書では、基本曲げモーメントＭ_C ′が逆方向の許容曲げモーメント−Ｍ_P に達する曲げ角度θ_C を限界曲げ角度と称し、且つ荷重Ｆによって加える曲げモーメントを付加曲げモーメントと称する。
【００１１】
本発明において、荷重付与装置１１が金属条材１に荷重を付与する位置は、金属条材１のアームクランプ根元に正方向の曲げモーメントを付与しうる位置であればよく、従って、図１において、ガイドロール６から曲げアーム３に至る領域内とすればよく、好適には、ガイドロール６から曲げ先端側の曲げ境界点Ｂまでの領域内とすればよい。荷重付与装置１１による荷重付与位置は１個所に限らず、複数個所としてもよく、また、その荷重付与位置も一定位置に固定する必要はなく、曲げ加工中、変化させてもよい。但し、荷重Ｆの付与は、少なくとも基本曲げモーメントＭ_C ′が負側の許容曲げモーメントに達する前に、即ち曲げ角度が限界曲げ角度θ_C に達する前に開始しなければならないので、少なくとも１個の荷重付与装置１１は、図１に示すように、曲げアーム３が限界曲げ角度θ_C に対応する位置を占めている時に、その曲げアーム３とガイドローラ６との間で金属条材１に荷重Ｆを付与しうる位置に配置している。荷重Ｆの付加期間は、少なくとも、基本曲げモーメントＭ_C ′が負側の許容曲げモーメントを越えている期間を含むものであれぱよく、具体的には、荷重付与を、上記した限界曲げ角度θ_C に達する前に開始すればよい。
【００１２】
限界曲げ角度θ_C は、上記したように、基本曲げモーメントＭ_C ′が逆方向の許容曲げモーメント−Ｍ_P に一致する曲げ角度であるので、上記の式（５）の絶対値が許容曲げモーメントＭ_P に等しいとして、計算することで求めることができる。すなわち、限界曲げ角度θ_C は、数４に示す式（６）から計算で求めることができる。
【数４】

【００１３】
なお、限界曲げ角度θ_C は上記式（６）から計算で求めることはできるが、かなりの計算量が必要となる。そこで、近似式を作っておくことが好ましい。上記（６）式において、曲げモーメントＭ_A は、金属条材１の曲げ温度における引張強さσ_h 、断面係数Ｚ及び圧縮率の関数、推進力Ｐは圧縮率の関数、圧縮率は、曲げ加工後の金属条材１の減肉率αの関数、許容曲げモーメントＭ_P は許容曲げ応力σ_a 及び断面係数Ｚの関数である。これらを考慮すると、限界曲げ角度θ_C は、主として、素材の許容曲げ応力σ_a 、曲げ温度における引張強さσ_h 及び減肉率αの関数である。そこで、金属条材１が円管である場合について、これらをファクターとする近似式を求め、数５に示す式（１）を得た。従って、円管に対して曲げ加工を行う場合には、式（１）を用いて、限界曲げ角度θ_C を求め、少なくとも、その限界曲げ角度θ_C に到達する前に荷重Ｆの付与を開始すればよい。なお、荷重Ｆの付与開始は、限界曲げ角度θ_C に到達する前であればよいので、必ずしも限界曲げ角度θ_C を求めておく必要はなく、限界曲げ角度θ_C の前であると思われる適当な時期に荷重付与開始を行っても良い。
【数５】

【００１４】
荷重付与装置１１によって付与する荷重の大きさは、曲げ加工中、金属条材１のアームクランプ根元に作用する全曲げモーメントＭ_C （基本曲げモーメントと付加曲げモーメントの総和）の絶対値が許容曲げモーメントＭ_P を越えないように、曲げ加工の条件（具体的には基本曲げモーメントＭ_C ′）に応じて、適切に定めれば良い。以下、荷重付与装置１１による荷重付与の位置、タイミング、荷重の大きさ等の具体例を説明する。
【００１５】
まず、一定位置に配置した１個の荷重付与装置１１を用いる場合を説明する。図１に示すように、荷重付与装置１１を金属条材１の曲げ部の角度φの位置に、曲げ中心Ｏに向かって荷重Ｆを加えるように配置するものとすると、曲げ角度がθとなった時点での、荷重Ｆによるアームクランプ根元への付加曲げモーメントＭ_crは、数６に示す式（８）のようになる。
【数６】

【００１６】
アームクランプ根元に作用する全曲げモーメントＭ_C は、
Ｍ_C ＝Ｍ_C ′＋Ｍ_cr ……（９）
であるので、この式（９）を計算することにより、全曲げモーメントＭ_C を求めることができ、その全曲げモーメントＭ_C の絶対値が許容曲げモーメントＭ_P を越えないように、荷重Ｆの大きさ及びその付与位置の角度φを求めることができる。
【００１７】
今、９０度の曲げ加工を行う場合において、アームクランプ根元の基本曲げモーメントＭ_C ′が図３の円グラフに曲線２１で示すように、曲げの終わり近傍において、許容曲げモーメント−Ｍ_P を少し越えるものとする。この場合には、付加曲げモーメントＭ_crをあまり大きくする必要がないので、荷重Ｆの付与位置を、図１のＡ点（角度φ＝０の位置、具体的には、加熱部の前又は後）とし、曲げ開始時から連続的に小さい荷重Ｆを付加する方法を採ることで首折れを防止できる。例えば、図３において、曲げ角度θ＝９０度の時に、全曲げモーメントＭ_C の絶対値が許容曲げモーメントＭ_P に一致するような荷重Ｆを、上記した式（８）、（９）から求めておき、その荷重Ｆを曲げ開始時から付加する。すると、その荷重Ｆによる付加曲げモーメントＭ_crは、曲線２２で示すようになり、全曲げモーメントＭ_C は曲線２３で示すように、全曲げ範囲内で許容曲げモーメント範囲内（＋Ｍ_P 〜−Ｍ_P の範囲内）に保持される。かくして、首折れを生じることなく曲げ加工を行うことができる。なお、荷重付与位置及び期間はこれに限らず適宜変更可能であり、例えば、荷重Ｆの付与位置を角度φ＝０の位置としたままで、荷重付与開始のタイミングを、曲げがある程度進行した時点（但し、限界曲げ角度θ_C に到達する前）とするように変更してもよいし、荷重Ｆの付与位置を、限界曲げ角度θ_C 以下の任意の位置に変更してもよい。
【００１８】
次に、９０度の曲げ加工を行う場合ではあるが、アームクランプ根元の基本曲げモーメントＭ_C ′が図４の円グラフに曲線２６で示すように、比較的早く許容曲げモーメント−Ｍ_P を越え、曲げ終わり（曲げ角度θ＝９０度）には、かなり大きく許容曲げモーメント−Ｍ_P を越えてしまう場合がある。この場合、荷重Ｆの付与位置を角度φ＝０の位置とし、曲げ角度θ＝９０度の時に、全曲げモーメントＭ_C の絶対値が許容曲げモーメントＭ_P に一致するような荷重Ｆを曲げ開始時から付加する方法を採ると、その荷重Ｆによる付加曲げモーメントＭ_crは、曲線２７で示すようになり、全曲げモーメントＭ_C が曲線２８で示すように変化し、曲げの初期領域では、正側の許容曲げモーメントＭ_P を越えてしまい、正方向の首折れを生じてしまう。そこでこれを防ぐため、荷重Ｆを加えるタイミングを、全曲げモーメントＭ_C が許容曲げモーメントＭ_P より適当に小さくなる時点からとする。例えば、図５（ａ）に示すように、曲げ角度がθ_S に到達した時点で荷重Ｆの付与を開始する。これにより、全曲げモーメントＭ_C は、曲げ角度θ＝０〜θ_S の領域では、曲線２６のように変化し、曲げ角度θ＝θ_S 〜９０度の領域では、曲線２８のように変化することとなり、全曲げ範囲内で許容曲げモーメント範囲内（＋Ｍ_P 〜−Ｍ_P の範囲内）に保持され、首折れを防止できる。
【００１９】
なお、図５（ａ）に示すように、曲げ角度θがθ_S に達した時点で所定の大きさの荷重Ｆの付与を開始すると、その時点で全曲げモーメントＭ_C が急激に増加し、曲げに悪い影響を与える場合がある。そのような恐れのある場合には、金属条材１に付与する荷重を０から徐々に所定の荷重Ｆにまで増加させる方法を採ることが好ましい。この方法を採用することで、図５（ｂ）に示すように、付加曲げモーメントＭ_crは、曲線２７Ａで示すように増加し、荷重が所定の大きさＦに到達した後は、曲線２７で示すようになり、それに伴い全曲げモーメントＭ_C も、曲線２８Ａで示すように変化し、次いで曲線２８で示すように変化し、急激な曲げモーメントの変化を無くすことができる。なお、付与する荷重Ｆは、必ずしも、曲げの途中から一定とする必要はなく、付与する全期間に渡って変化させる形態としてもよい。
【００２０】
図５に示す実施形態では、荷重Ｆの付与位置を角度φ＝０の位置としているが、これに代えて、図５に示すように、荷重Ｆの付与位置（角度φ）を、０と限界曲げ角度θ_C の範囲内の適当な位置とするように変更してもよい。この場合にも、例えば、曲げ角度θ＝９０度の時に、全曲げモーメントＭ_C の絶対値が許容曲げモーメントＭ_P に一致するような荷重Ｆを計算で求めておき、図６（ａ）に示すように、その荷重Ｆを角度φの位置に、曲げ角度がその角度φより適度に進んだ角度θ_S に達した時点で付加すると、その荷重Ｆによる付加曲げモーメント Ｍ_crは、曲線３１で示すようになり、それ以後の全曲げモーメントＭ_C は曲線３２で示すように変化する。かくして、全曲げ範囲内で許容曲げモーメント範囲内（＋Ｍ_P 〜−Ｍ_P の範囲内）に保持でき、首折れを生じることなく曲げ加工を行うことができる。なお、この場合においても、金属条材１に付与する荷重Ｆを０から徐々に所定の荷重Ｆにまで増加させる方法を採ることができ、その場合には、図６（ｂ）に示すように、付加曲げモーメントＭ_crと全曲げモーメントＭ_C が、それぞれ曲線３１Ａ、３２Ａに示すように変化することとなり、全曲げモーメントＭ_C の急激な変化を生じさせない利点が得られる。
【００２１】
次に、曲げ角度を１８０度まで行う場合を説明する。今、基本曲げモーメントＭ_C′が図７の円グラフで曲線３６のように変化するものとする。荷重Ｆをφ＝０の位置（図１のＡ点）に付与するものとし、その荷重Ｆを曲げ角度θ_C に達した時点から付与を始めると、その荷重Ｆによる付加曲げモーメントＭ_crは、曲線３７で示すようになり、荷重付与位置からの曲げ角度が９０度を越えるあたりから急激に小さくなり、１８０度よりもかなり小さい或る角度θ _D で０になり、それ以後は逆方向の曲げモーメントとなってしまう。このため、全曲げモーメントＭ_C は曲線３８のように変化し、例え荷重Ｆを大きく選定しても、逆方向の首折れを防止するという初期の目的を達成できないばかりか、逆に首折れを助長してしまう。そこで、この場合には、荷重Ｆの付与位置（角度φ）を、図８，図１０に示すように、曲げの進行方向に大きく進んだ位置とし、曲げ終わり（１８０度）に達した時点でも、付加曲げモーメントＭ_crを正の値に保つことができるようにする。そして、荷重Ｆの大きさを適切に、例えば、曲げ角度が１８０度に達した時に全曲げモーメントＭ_C が負側の許容曲げモーメント−Ｍ_P に等しくなるように設定することで、その荷重Ｆによる付加曲げモーメントＭ_crは、曲線４０で示すように変化し、その付加曲げモーメントＭ_crを加えた全曲げモーメントＭ_C を、曲線４１で示すように変化させ、全曲げ範囲内で許容曲げモーメント範囲内（＋Ｍ_P 〜−Ｍ_P の範囲内）に保持でき、首折れを生じることなく曲げ加工を行うことができる。
【００２２】
ここで、荷重Ｆを付与する位置は、最終曲げ角度（図８の実施形態では曲げ角度１８０度）に達するまで付加曲げモーメントＭ_crを正の値に保持しうる位置であればよい。図８、図１０において、荷重Ｆを付加する領域の下限を角度θ_E とすると、この角度θ_E の位置は、その位置に荷重Ｆを作用させて曲げ加工を行い、曲げ終わり（曲げ角度１８０度）に達した時点での付加曲げモーメントＭ_crが０となる位置である。この角度θ_E は上記した付加曲げモーメントＭ_crを求める式（８）を用いて求めることができる。具体的には、図７において荷重Ｆの付与位置から付加曲げモーメントＭ_crが０になる位置までの角度θ_D を求めると、その角度θ_D は数７に示す式（１０）のようになるので、その角度θ_D の位置が曲げ終わりの位置に一致するように荷重Ｆの付与位置を進めておけばよい。又、荷重Ｆの付与範囲の下限角度θ_E は、数７の式（２）のようになる。従って、θ_D を越える曲げ角度の曲げ加工を行う場合、金属条材１に対して荷重Ｆを加える位置を、式（２）に示す角度θ_E 以上の領域としておけばよく、これによって曲げ終わりまで、首折れを生じることなる曲げ加工することができる。なお、荷重Ｆを加える領域の上限は、上記したように荷重Ｆを曲げ角度が限界曲げ角度θ_C に達するまでに付与する必要があることから、限界曲げ角度θ_C に達した時点における曲げアーム位置であり、好適には、限界曲げ角度θ_C である。従って、９０度を越えるような大きい角度の曲げ加工を行う場合には、荷重Ｆを付与する領域は、図１０に示すように、角度θ_E 〜θ_C 内の領域とすればよい。
【数７】

【００２３】
図８に示す場合においても、金属条材１に付与する荷重を０から徐々に所定の荷重Ｆにまで適当な角度範囲内で増加させる方法を採ることが好ましく、この方法を採ることにより、図９に示すように、付加曲げモーメントＭ_cr及び全曲げモーメントＭ_C を曲線４４，４５で示すようになだらかに変化させて行くことができる。なお、図９の実施形態では、荷重Ｆの付与位置を限界曲げ角度θ_C よりもある程度小さい角度とし、その角度θ_C を少し越えた角度θ_S に達した時点で荷重付加を開始している。
【００２４】
図８，図９の実施形態で示したように、１８０度曲げを行う場合において、荷重Ｆを１点に加えることで、曲げの全範囲において全曲げモーメントＭ_C を許容曲げモーメント範囲内（＋Ｍ_P 〜−Ｍ_P の範囲内）に保持することは可能である。しかしながら、荷重付与位置からの曲げ角度が或る程度以上に大きくなると、荷重Ｆによる付加曲げモーメントが小さくなってしまうため、首折れを防止するには、荷重Ｆとしてかなり大きい荷重を加える必要があり、これによって曲げ半径の精度が悪くなる場合がある。これを防ぐには、曲げが進行した時点で荷重Ｆを付与する位置をアームクランプ根元に近い位置に変えるとか、追加することが有効となる。以下、その場合の実施形態を説明する。
【００２５】
図１１に示す曲げ加工装置では、荷重付与装置１１（以下第一荷重付与装置という）に加えて、その第一荷重付与装置１１と同様な構造の第二荷重付与装置５１を備えている。第一荷重付与装置１１は、曲げ角度が限界曲げ角度θ_C に達する前に荷重Ｆを付加することができるように設けるものであり、その第一荷重付与装置１１による荷重付与位置（第一荷重付与位置という）は、ガイドローラ６から限界曲げ角度θ_C の位置までの間に設定される。第二荷重付与装置５１は、荷重付与位置（第二荷重付与位置という）が、第一荷重付与位置から曲げアーム３に至る領域内に設定されるように設けられる。なお、図面の実施形態では、第一荷重付与位置を角度φ₁ ＝３０度の位置とし、第二荷重付与位置を角度φ₂ ＝９０度の位置としている。
【００２６】
次に、図１１に示す曲げ加工装置による曲げ加工中の荷重付与及び曲げモーメント変化を、図１２の円グラフを用いて説明する。図中、３６は基本曲げモーメントＭ_C ′の変化を示す曲線である。曲げ加工を開始した後、曲げ角度が第一荷重付与位置（角度φ₁ ＝３０度）を少し越えた時点（曲げ角度θ_S1）で第一荷重付与位置への第一荷重Ｆ₁ の付加を開始する。この時、第一荷重Ｆ₁ は０から徐々に増加させてゆく。これにより、曲線５３Ａで示すように付加曲げモーメントＭ_crが加えられ、全曲げモーメントＭ_C は曲線５４Ａのように変化し、許容曲げモーメントの範囲内に保たれる。そして、曲げが進行し、曲げ角度が９０度を少し越え、第二荷重付与装置５１による荷重付加が可能となった時点（曲げ角度 θ _S2 ）で、第一荷重付与位置に加えていた第一荷重Ｆ₁ を無くすと同時に、第二荷重付与位置に第二荷重Ｆ₂ を付加し始め、その後は一定の第二荷重Ｆ₂ を付加し続ける。ここで加える第二荷重Ｆ₂ は、例えば、曲げ終了時（曲げ角度θ＝１８０度）の時に、全曲げモーメントＭ_C が負側の許容曲げモーメント−Ｍ_P に等しくなるように設定しておく。また、第一荷重付与位置への第一荷重Ｆ₁ は、荷重付与を切り替える時点において、第一荷重Ｆ₁ による付加曲げモーメントＭ_crが第二荷重Ｆ₂ による付加曲げモーメントＭ_crに等しくなるように設定しておく。これにより、荷重付与切り替え後は、曲線５３Ｂで示すように付加曲げモーメントＭ_crが加えられ、全曲げモーメントＭ_C は曲線５４Ｂのように変化し、許容曲げモーメントの範囲内に保たれる。かくして、全曲げ範囲に渡って全曲げモーメントＭ_C は許容曲げモーメントの範囲内に保たれ、首折れを生じることなく曲げ加工を行うことができる。この実施形態のように、曲げ角度の大きい位置に第二荷重付与位置を設定し、その位置に第二荷重Ｆ₂ を加える構成とすると、その第二荷重Ｆ₂ によってアームクランプ根元に作用させる付加曲げモーメントＭ_crを大きくすることができ、換言すれば、小さい第二荷重Ｆ₂ で首折れ防止を図ることができる。かくして、比較的小さい荷重Ｆ₁ 、Ｆ₂ を加えることで、全曲げモーメントＭ_C を許容範囲内に保持でき、曲げ半径の精度を高く保ちながら、首折れを防止した曲げ加工を行うことができる。
【００２７】
なお、上記の説明では、第一荷重付加位置への第一荷重Ｆ₁ の付加と第二荷重付加位置への第二荷重Ｆ₂ の付与を切り替えているが、第一荷重Ｆ₁ の付与を継続しながら、それに並行して第二荷重Ｆ₂ 追加する構成としてもよく、また、その場合、第一荷重Ｆ₁ を徐々に低下させ、第二荷重Ｆ₂ を徐々に増加させる構成としてもよい。更に、上記の説明では、荷重Ｆ₁ を０から徐々に増加するように変化させているが、これに限らず付与開始時から一定の大きさの荷重Ｆ₁ を加えるように変更してもよく、同様に、荷重Ｆ₂ についても、最初から一定の大きさの荷重を付与する場合に限らず、適当に変化させながら、付与してもよい。
【００２８】
以上に説明した実施形態は、いずれも、荷重付与装置１１、５１を定まった位置に設置し、曲げ加工中、一定の曲げ角度位置に荷重を付与しているが、これを曲げの進行に伴って移動する構成とすることも可能である。図１３はその場合の実施形態を示すものである。この実施形態では、曲げアーム３の旋回中心Ｏを中心として旋回するように旋回アーム６１を設け、その旋回アーム６１に荷重付与装置１１を保持させている。この曲げ加工装置においては、荷重付与装置１１を作動させない状態で曲げ加工を開始し、曲げ角度が限界曲げ角度θ_C に達する前の適当な時期に、限界曲げ角度θ_C より小さい角度位置に荷重付与装置１１を位置させて作動させ荷重Ｆを付与し始める。その後、曲げの進行に伴い、旋回アーム６１も曲げアーム３の旋回方向に旋回させ、荷重付与位置を進める。これにより、荷重Ｆによる曲げモーメントを、曲げ角度が大きくなった時点でも有効にクランプ根元に作用させることができ、比較的小さい荷重Ｆを加えることで、全曲げモーメントＭ_C を許容範囲内に保持でき、曲げ半径の精度を高く保ちながら、首折れを防止した曲げ加工を行うことができる。なお、曲げ加工中、旋回アーム６１を、曲げアーム３と同期させて連続的に旋回させてもよいし、曲げ加工中の或る期間は一つの位置に停止し、曲げ加工が進行した時点で次の位置に旋回して停止するといった間欠的な旋回を行うようにしてもよい。また、この実施形態で加える荷重Ｆも、一定の大きさのものであっても、変化するものであってもよい。
【００２９】
【発明の効果】
以上に説明したように、本発明は、曲げ加工期間中の少なくとも、曲げアームの旋回及び推進力Ｐによって金属条材のアームクランプ根元に作用する曲げモーメントＭ_C ′の絶対値が前記金属条材の許容曲げモーメントＭ_P を越える期間は、前記金属条材のアームクランプ根元に作用する全曲げモーメントＭ_C の絶対値が前記許容曲げモーメントＭ_P を越えないように、前記金属条材の加熱部近傍の直線部を含み、その直線部から前記曲げアームに至る領域の金属条材に、曲げ平面内で前記曲げアームの旋回中心のある側に向かう方向の荷重を加えてアームクランプ根元に付加曲げモーメントを作用させながら曲げ加工する構成としたことで、小曲げ半径の圧縮曲げを行う場合に生じがちな首折れを防止でき、首折れのない製品を得ることができるといった効果を有している。
【００３０】
ここで、金属条材に対して荷重を加える期間を、少なくとも前記曲げアームの旋回角度が、上記した式（１）に示す限界曲げ角度θ_C に到達する前に開始させる構成とすると、アームクランプ根元に作用する全曲げモーメントＭ_C の絶対値が許容曲げモーメントＭ_P を越える前に、荷重の付与を開始して首折れ発生を防止でき、簡単な計算によって、荷重付加のタイミングを求めることができるという効果が得られる。
【００３１】
また、曲げ角度が９０度を越えるような曲げ加工を行う際には、金属条材に対して荷重を加える位置を、上記した式（２）に示す角度θ_E 以上の領域とすると、曲げ角度が大きくなった場合にも、アームクランプ根元に正方向の付加曲げモーメントを作用させることができ、例えば、曲げ角度が１８０度といった大きい曲げ角度の曲げ加工においても、首折れを防止できるという効果が得られる。
【００３２】
また、金属条材に対して荷重を加える位置を、その荷重を加え始める時点では金属条材の加熱部近傍の直管部からその時点での前記曲げアームに至る領域内に設定した第一荷重付与位置とし、その後、所定量の曲げ加工が進行した時点で、前記第一荷重付与位置よりも曲げ方向に前進した第二荷重付与位置に変更若しくは追加する構成とすると、比較的小さい荷重を付加することで、アームクランプ根元に作用する全曲げモーメントを許容曲げモーメント内に保持でき、曲げ半径の精度を悪くすることなく首折れを防止できるという効果が得られる。
【００３３】
また、金属条材に対して前記荷重を加える位置を、曲げ加工の進行につれて前記曲げアームの旋回方向に移動させる構成とすると、比較的小さい荷重を付加することで、アームクランプ根元に作用する全曲げモーメントを許容曲げモーメント内に保持でき、曲げ半径の精度を悪くすることなく首折れを防止できるという効果が得られる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る曲げ加工装置の概略平面図
【図２】曲げ加工中に金属条材のアームクランプ根元に作用する曲げモーメントの、曲げ角度に対する変化を示す円グラフ
【図３】図１の装置を用いた、本発明の一実施形態に係る曲げ加工方法において、曲げ加工中に金属条材のアームクランプ根元に作用する曲げモーメントの、曲げ角度に対する変化を示す円グラフ
【図４】曲げ開始位置に大きい荷重Ｆを加えた状態で、金属条材のアームクランプ根元に作用する曲げモーメントの、曲げ角度に対する変化を示す円グラフ
【図５】（ａ），（ｂ）はそれぞれ、本発明の他の実施形態に係る曲げ加工方法において金属条材のアームクランプ根元に作用する曲げモーメントの、曲げ角度に対する変化を示す円グラフ
【図６】（ａ），（ｂ）はそれぞれ、本発明の更に他の実施形態に係る曲げ加工方法において金属条材のアームクランプ根元に作用する曲げモーメントの、曲げ角度に対する変化を示す円グラフ
【図７】曲げ角度を１８０度とした場合において、曲げ開始位置に荷重Ｆを加えた状態で、金属条材のアームクランプ根元に作用する曲げモーメントの、曲げ角度に対する変化を示す円グラフ
【図８】本発明の更に他の実施形態に係る曲げ加工方法において金属条材のアームクランプ根元に作用する曲げモーメントの、曲げ角度に対する変化を示す円グラフ
【図９】本発明の更に他の実施形態に係る曲げ加工方法において金属条材のアームクランプ根元に作用する曲げモーメントの、曲げ角度に対する変化を示す円グラフ
【図１０】大きい曲げ角度での曲げ加工を行う場合における荷重付与領域を示す、曲げ加工装置の概略平面図
【図１１】本発明の他の実施形態に係る曲げ加工装置の概略平面図
【図１２】図１１の装置を用いた、本発明の実施形態に係る曲げ加工方法において金属条材のアームクランプ根元に作用する曲げモーメントの、曲げ角度に対する変化を示す円グラフ
【図１３】本発明の更に他の実施形態に係る曲げ加工装置の概略平面図
【図１４】従来の曲げ加工装置の概略平面図
【図１５】従来の装置で曲げ加工した金属条材（鋼管）を示す概略平面図
【符号の説明】
１ 金属条材
２ 加熱装置
３ 曲げアーム
４ アームクランプ
５ 冷却水
６ ガイドローラ
１１ 荷重付与装置（第一荷重付与装置）
１２ 押しローラ
１３ 油圧シリンダ
５１ 第二荷重付与装置[0001]
BACKGROUND OF THE INVENTION
  The present invention is a method for continuously bending metal strips such as steel pipes and section steels.To the lawRelated.
[0002]
[Prior art]
Conventionally, as a method of bending a metal strip such as a steel pipe, as shown in FIG. 14, the metal strip 1 to be bent is passed through a heating device 2 such as an induction coil for heating a short section in the longitudinal direction. The distal end side is fixed to an arm clamp 4 provided on a bending arm 3 that can rotate around a fulcrum O, and the metal strip 1 is heated by a heating device 2 while being elongated by a strip propulsion device (not shown). By moving the heating unit 2 in the longitudinal direction of the metal strip 1 by propelling in the direction, a bending moment generated by the turning of the bending arm 3 is applied to the heating unit and deformed. A bending method is known in which cooling water 5 is sprayed from the heating device 2 to cool it. In this bending method, a force P in the direction opposite to the turning direction of the bending arm 3 as the bending process proceeds is applied to the bending arm 3._bIs applied to the metal strip 1, and the bending force is applied to the metal strip 1 in a state where the longitudinal compression force is applied to the metal strip 1 (compression bending method). Also known as). The compression bending method has an advantage that the thinning on the outer periphery side of the bending can be suppressed. In the figure, 6 is a guide roller.
[0003]
[Problems to be solved by the invention]
Recently, there has been a demand for reducing the bending radius as much as possible. For example, a need has arisen for a small R-bending with a bending radius R of 1.5 D or less for a steel pipe having an outer diameter D. However, when such a small R-bending is performed by the compression bending method, as shown in an exaggerated manner in FIG. 15, the portion 1Aa grasped by the arm clamp of the steel pipe 1A after the bending is formed by the arm clamp root (C The phenomenon of bending in the direction opposite to the bending direction (referred to as neck breakage) occurred at the position of the point, resulting in a problem that the product could not be produced.
[0004]
The present invention has been made in view of such a situation, and when bending a metal strip such as a steel pipe, even when a small R-bending is performed by compression bending, it is an object to prevent neck breakage from occurring. And
[0005]
[Means for Solving the Problems]
As a result of examining the cause of the neck break, the present inventors have found the following matters. That is, as shown in FIG. 14, the metal strip 1 is propelled to turn the bending arm 3, thereby causing a bending moment M having a magnitude that causes bending deformation in the heated portion (point A) of the metal strip 1._AIs bent in a clockwise direction, the bending moment M in the counterclockwise direction is applied to the metal strip 1 at the base of the arm clamp (point C) by the reaction._AIs working. Further, at the base of the arm clamp, a bending moment M due to the propulsive force P applied to the metal strip 1 is provided._GThis bending moment M_GIs acting clockwise. Therefore, during the bending process, when the counterclockwise direction is the positive direction, the bending moment represented by the following formula (4) is applied to the arm clamp root (point C) of the metal strip 1 due to the turning and propulsive force P of the bending arm 3. M_C ′ Is acting.
M_C'= M_A-M_G    ...... (4)
Hereinafter, this bending moment M_C 'Is called the basic bending moment. In the case of normal bending (when no compressive force is applied, or when the bending is performed, the bending radius is not very small, and therefore the applied compressive force is small, etc.), the bending moment M due to the propulsive force M_GHowever, when performing small R-bending, the thinning rate on the outer periphery of the bending is large, so to reduce the thinning, the thrust P is greatly increased to increase the amount of compression. As a result, the bending moment M due to the thrust P_GBecomes extremely large, and a large bending moment acts on the arm clamp root (point C) in the reverse direction (clockwise), which causes permanent distortion at the arm clamp root and causes neck breakage. Therefore, when the bending moment due to the propulsive force P increases and the possibility of neck breakage occurs, the neck breakage can be prevented by applying a positive bending moment to the arm clamp base of the metal strip. In order to apply a positive bending moment to the base of the arm clamp, the metal strip being bent includes a straight portion in the vicinity of the heating portion, and the region extending from the straight portion to the bending arm is within the bending plane. Therefore, it is effective to apply a load in a direction toward the side where the turning center of the bending arm is located.
[0006]
  The present invention has been made based on such findings,A compression bending method in which bending force is applied to a bending arm while applying a force in the direction opposite to the turning direction of the bending arm as the bending process proceeds to apply a compressive force to the metal strip. The bending moment M acting on the base of the arm clamp of the metal strip by the turning and propulsive force P of the bending arm _C The absolute value of ′ is the allowable bending moment M of the metal strip _P Compression with a period exceedingIn the bending method, a bending moment, that is, a basic bending moment M that acts on the base of the arm clamp of the metal strip by at least the bending arm turning and propulsion force P during the bending period._C The absolute value of ′ is the allowable bending moment M of the metal strip_PThe period exceedingIn order to prevent neck breakage from occurring in the metal strip due to the bending moment acting on the arm clamp base of the metal strip,Total bending moment M acting on the arm clamp base of the metal strip_CIs the allowable bending moment M_PIn the metal strip in the region extending from the straight section to the bending arm, on the side where the turning center of the bending arm is located in the bending plane. It is characterized by bending while applying an additional bending moment to the arm clamp base by applying a load in the direction toward the neck, thereby preventing neck breakage.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to embodiments of the drawings. FIG. 1 is a schematic plan view showing an example of a bending apparatus used for carrying out the method of the present invention in the middle of bending. The bending apparatus shown in FIG. 1 also heats a short section in the longitudinal direction of the metal strip 1 such as a steel pipe and sprays cooling water 5 on one side (right side in the drawing) of the heating portion, similarly to the conventional bending apparatus. A bending device 3 having a heating device 2 such as an induction coil and the like, an arm clamp 4 for clamping the processing tip side of the metal strip 1, and capable of turning about a fulcrum O, The force P in the direction opposite to the turning direction of the bending arm 3 as it progresses_b, A strip material propulsion device (not shown) for applying a longitudinal propulsive force P to the metal strip 1 and moving it forward toward the bending arm 3, a guide roller 6 and the like. ing. Further, this bending apparatus is provided with a load applying device 11 for applying a bending moment in the positive direction (counterclockwise in the drawing) to the arm clamp root C of the metal strip 1 unlike the conventional one. The load applying device 11 includes a pressing roller 12 and a hydraulic cylinder 13 that presses the pressing roller 12 against the metal strip 1. A bending arm is attached to the metal strip 1 being bent in a direction perpendicular to the axis and within a bending plane. By applying a load F in a direction toward the side of the center 3 of rotation 3, a positive (counterclockwise) bending moment can be applied to the arm clamp root C of the metal strip 1. Here, the installation position of the load applying device 11 includes a straight line portion (specifically, a straight line portion from the guide roller 6 to the heating device 2) in the vicinity of the heating portion (point A) of the metal strip 1, and the straight line. It is determined so that the load F can be applied to a desired position in the region extending from the part to the bending arm 3 (described in detail later). In addition, as shown in FIG. 1, when arrange | positioning the load provision apparatus 11 so that the load F can be provided to the bending part (area | region bent in the circular arc shape) of the metal strip 1, the revolving arm 3 changes the position. The entire load applying device 11 or the pressing roller 12 can be retracted so that it can pass without any trouble.
[0008]
Also in this bending apparatus, the metal strip 1 to be bent is passed through the heating device 2 and the processing tip side is fixed to the arm clamp 4 of the bending arm 3 and the metal strip 1 is heated as in the prior art. The heating unit is continuously moved in the longitudinal direction of the metal strip 1 by being propelled in the longitudinal direction while being heated by the apparatus 2, and at the same time, the bending arm 3 is swung to deform the heating unit by applying a bending moment. Then, a continuous bending process of cooling the part immediately after that is performed. During a predetermined period during the bending process, the load applying device 11 operates to apply the load F to the metal strip 1 and the total bending moment M acting on the base of the arm clamp._CIs the allowable bending moment M of the metal strip 1_PDo not exceed. Hereinafter, the position where the load F is applied by the load applying device 11, the period during which the load F is applied, the magnitude of the load F, and the like will be described. In this specification, when the position in the bent portion of the metal strip 1 is indicated by an angle, a straight line OA connecting the turning center O of the bending arm 3 and the heating center point A by the heating device 2 is used as a reference line, and the point O is The angle with respect to the reference line is used as the center. When the position of the bending arm 3 is indicated by an angle, a turning angle from the reference line (equal to the bending angle) is used with the position occupied by the bending arm 3 at the start of bending as a reference line.
[0009]
If the load applying device 11 is not operated during bending, the basic bending moment M is applied to the arm clamp base (point C)._C Only 'works, and its size is
M_C'= M_A-M_G    ...... (4)
It is. Here, bending moment M due to propulsive force P_GIs a function of the angle (bending angle) θ of the bending arm 3, so rewriting equation (4) yields equation (5) shown in equation (3).
[Equation 3]

[0010]
Basic bending moment M shown in equation (5)_C2 is shown as a pie chart taking the case where the propulsive force P is reduced and the case where the propulsive force P is increased as an example, curves 15 (when the propulsive force P is small), 16 (propulsive force) When P is large). In the figure, the arc 17 indicates the allowable bending moment + M in the positive direction._PThe arc 18 is the allowable bending moment -M in the reverse direction._PThe arc 19 indicates a bending moment 0. As can be seen from the curves 15 and 16 in FIG. 2, the basic bending moment M acting on the base of the arm clamp._C′ Acts in the forward direction at the start of bending, but decreases with the progress of bending, and changes and increases in the opposite direction from the middle. And its basic bending moment M_CWhen the propulsive force P is small, ′ is within the range of the allowable bending moment (+ M_P~ -M_P), When the driving force P is increased, the bending angle θ is_CAllowable bending moment -M_PWill be exceeded. For this reason, this bending angle θ_CIf it is bent beyond the range, neck breakage will occur. Therefore, in the present invention, a bending moment in the forward direction is applied by the load applying device 11, and the bending moment acting on the base of the arm clamp is the allowable bending moment -M in the reverse direction._PIs not to exceed. In this specification, the basic bending moment M_C'Is the allowable bending moment in the reverse direction -M_PBending angle θ reaching_CIs called the limit bending angle, and the bending moment applied by the load F is called the additional bending moment.
[0011]
In the present invention, the position where the load applying device 11 applies the load to the metal strip 1 may be any position where a positive bending moment can be applied to the base of the arm clamp of the metal strip 1. The area from the guide roll 6 to the bending arm 3 may be set, and the area from the guide roll 6 to the bending boundary point B on the bending tip side may be preferably set. The load application position by the load application device 11 is not limited to one, and may be a plurality of positions. Also, the load application position does not need to be fixed at a fixed position, and may be changed during bending. However, the load F is applied at least to the basic bending moment M_CBefore ′ reaches the negative allowable bending moment, that is, the bending angle is the critical bending angle θ_CSince at least one load applicator 11 has a bending arm 3 as shown in FIG._CIs disposed at a position where the load F can be applied to the metal strip 1 between the bending arm 3 and the guide roller 6. The additional period of load F is at least the basic bending moment M_CIt may be sufficient to include a period when ′ exceeds the allowable bending moment on the negative side. Specifically, the load is applied to the above-mentioned limit bending angle θ._CYou can start before you reach.
[0012]
Limit bending angle θ_CAs mentioned above, the basic bending moment M_C'Is the allowable bending moment in the reverse direction -M_PTherefore, the absolute value of the above equation (5) is the allowable bending moment M._PIt can be calculated by calculating that it is equal to. That is, the limit bending angle θ_CCan be calculated from Equation (6) shown in Equation 4.
[Expression 4]

[0013]
The critical bending angle θ_CCan be calculated from the above equation (6), but requires a considerable amount of calculation. Therefore, it is preferable to create an approximate expression. In the above equation (6), the bending moment M_AIs the tensile strength σ at the bending temperature of the metal strip 1_h, Section modulus Z and compression rate function, propulsive force P is compression rate function, compression rate is a function of the metal thinning ratio α of the metal strip 1 after bending, allowable bending moment M_PIs the allowable bending stress σ_aAnd a function of the section modulus Z. Considering these, the critical bending angle θ_CIs mainly the allowable bending stress σ of the material_a, Tensile strength at bending temperature σ_hAnd a function of the thinning rate α. Therefore, when the metal strip 1 is a circular pipe, an approximate expression using these as factors was obtained, and Expression (1) shown in Equation 5 was obtained. Therefore, when bending a circular pipe, the limit bending angle θ is obtained using the equation (1)._CAnd at least its critical bending angle θ_CWhat is necessary is just to start the application of the load F before reaching. It should be noted that the application of the load F starts with the limit bending angle θ_CIt is only necessary to reach before the critical bending angle θ._CIt is not necessary to obtain the limit bending angle θ_CThe load application may be started at an appropriate time which is considered to be before.
[Equation 5]

[0014]
The magnitude of the load applied by the load applying device 11 is the total bending moment M acting on the arm clamp root of the metal strip 1 during bending._CThe absolute value of the sum of the basic bending moment and the additional bending moment is the allowable bending moment M_PBending conditions (specifically, the basic bending moment M_CAccording to ′), it may be determined appropriately. Hereinafter, specific examples of the load application position, timing, and load magnitude by the load application device 11 will be described.
[0015]
First, the case where the one load application apparatus 11 arrange | positioned in the fixed position is used is demonstrated. As shown in FIG. 1, when the load applying device 11 is arranged at the position of the angle φ of the bending portion of the metal strip 1 so as to apply the load F toward the bending center O, the bending angle becomes θ. Additional bending moment M at the base of the arm clamp due to the load F_crIs as shown in Equation (8) shown in Equation 6.
[Formula 6]

[0016]
Total bending moment M acting on the arm clamp root_CIs
M_C= M_C'+ M_cr            ...... (9)
Therefore, by calculating this equation (9), the total bending moment M_CAnd its total bending moment M_CThe absolute value of is the allowable bending moment M_PThus, the magnitude of the load F and the angle φ of the applied position can be obtained.
[0017]
Now, when bending 90 degrees, the basic bending moment M at the base of the arm clamp_CAs shown by a curve 21 in the pie chart of FIG._PA little over. In this case, the additional bending moment M_cr1 is set to point A in FIG. 1 (the position at the angle φ = 0, specifically, before or after the heating portion), and continuously from the start of bending. Neck breakage can be prevented by adopting a method of applying a small load F. For example, in FIG. 3, when the bending angle θ = 90 degrees, the total bending moment M_CThe absolute value of is the allowable bending moment M_PIs obtained from the above equations (8) and (9), and the load F is added from the start of bending. Then, the additional bending moment M due to the load F_crIs as shown by curve 22 and the total bending moment M_CIs within the allowable bending moment range within the entire bending range (+ M_P~ -M_PWithin the range). Thus, bending can be performed without causing neck breakage. Note that the load application position and the period are not limited to this, and can be changed as appropriate. For example, the load application start timing is kept at the position of the angle φ = 0, and the load application start timing is when the bending progresses to some extent. (However, limit bending angle θ_COr the position where the load F is applied can be changed to the limit bending angle θ._CYou may change to the following arbitrary positions.
[0018]
Next, in the case of performing bending at 90 degrees, the basic bending moment M at the base of the arm clamp_CAs shown by a curve 26 in the pie chart of FIG._POver the bending end (bending angle θ = 90 degrees), the allowable bending moment −M_PMay be exceeded. In this case, the position where the load F is applied is a position where the angle φ = 0, and when the bending angle θ = 90 degrees, the total bending moment M_CThe absolute value of is the allowable bending moment M_PIf a method of adding a load F that coincides with the load F from the beginning of bending, an additional bending moment M due to the load F is obtained._crIs as shown by curve 27 and the total bending moment M_CChanges as shown by the curve 28, and in the initial region of bending, the allowable bending moment M on the positive side is_PWill cause the neck to break in the positive direction. Therefore, in order to prevent this, the timing of applying the load F is determined by the total bending moment M_CIs the allowable bending moment M_PFrom the point of time when it becomes smaller appropriately. For example, as shown in FIG._SThe application of the load F is started at the time of reaching. As a result, the total bending moment M_CIs the bending angle θ = 0 to θ_SIn the region of, the curve changes like a curve 26 and the bending angle θ = θ_SIn the region of ~ 90 degrees, the curve changes as shown by curve 28, and within the allowable bending moment range within the entire bending range (+ M_P~ -M_PIn the range of (1) and can prevent neck breakage.
[0019]
As shown in FIG. 5A, the bending angle θ is θ_SWhen the application of the load F having a predetermined magnitude is started at the time of reaching the total bending moment M_CMay increase sharply and adversely affect bending. In such a case, it is preferable to adopt a method in which the load applied to the metal strip 1 is gradually increased from 0 to a predetermined load F. By adopting this method, as shown in FIG. 5B, the additional bending moment M_crIncreases as shown by the curve 27A, and after the load reaches a predetermined magnitude F, it becomes as shown by the curve 27, and accordingly, the total bending moment M_CCan also be changed as shown by the curve 28A, and then changed as shown by the curve 28, so that a sudden bending moment change can be eliminated. The applied load F does not necessarily have to be constant from the middle of bending, and may be changed over the entire period of application.
[0020]
In the embodiment shown in FIG. 5, the position where the load F is applied is the position where the angle φ = 0. Instead, as shown in FIG. 5, the position where the load F is applied (angle φ) is limited to 0. Bending angle θ_CYou may change so that it may become an appropriate position in the range of this. Also in this case, for example, when the bending angle θ = 90 degrees, the total bending moment M_CThe absolute value of is the allowable bending moment M_P6 is obtained by calculation, and as shown in FIG. 6A, the load F is placed at the position of the angle φ, and the angle θ where the bending angle is appropriately advanced from the angle φ._SWhen added, the additional bending moment M due to the load F is added._crIs as shown by curve 31 and the total bending moment M thereafter_CChanges as shown by curve 32. Thus, within the allowable bending moment range within the entire bending range (+ M_P~ -M_PAnd can be bent without causing neck breakage. In this case as well, a method of gradually increasing the load F applied to the metal strip 1 from 0 to a predetermined load F can be adopted, and in that case, as shown in FIG. , Additional bending moment M_crAnd total bending moment M_CWill change as indicated by curves 31A and 32A, respectively, and the total bending moment M_CThe advantage of not causing a drastic change of is obtained.
[0021]
Next, a case where the bending angle is performed up to 180 degrees will be described. Now, basic bending moment M_CIt is assumed that 'changes as shown by a curve 36 in the pie chart of FIG. The load F is applied to the position of φ = 0 (point A in FIG. 1), and the load F is applied to the bending angle θ._CWhen the application is started from the point of time, the additional bending moment M due to the load F is obtained._crIs as shown by the curve 37, and the angle from which the bending angle from the load application position suddenly becomes smaller when it exceeds 90 degrees, is an angle that is considerably smaller than 180 degrees.θ _D 0, and after that, the bending moment is in the opposite direction. For this reason, the total bending moment M_C Changes as shown by a curve 38. Even if the load F is selected to be large, not only the initial purpose of preventing neck breakage in the reverse direction can be achieved, but also neck breakage is promoted. Therefore, in this case, the application position (angle φ) of the load F is set to a position greatly advanced in the bending direction as shown in FIGS. 8 and 10, and even when the bending end (180 degrees) is reached. , Additional bending moment M_crCan be kept positive. Then, when the magnitude of the load F is appropriately set, for example, when the bending angle reaches 180 degrees, the total bending moment M_CIs the negative allowable bending moment -M_PThe additional bending moment M due to the load F is set to be equal to_crChanges as shown by curve 40 and its additional bending moment M_crTotal bending moment M with_CAs shown by the curve 41, and within the allowable bending moment range (+ M_P~ -M_PAnd can be bent without causing neck breakage.
[0022]
Here, the position where the load F is applied is the additional bending moment M until the final bending angle (the bending angle of 180 degrees in the embodiment of FIG. 8) is reached._crAny position can be used as long as it can be held at a positive value. 8 and 10, the lower limit of the region to which the load F is applied is the angle θ_EThen this angle θ_EThe position of is subjected to bending by applying a load F to the position, and the additional bending moment M when the bending end (bending angle 180 degrees) is reached._crIs a position where 0 becomes zero. This angle θ_EIs the above-mentioned additional bending moment M_crCan be determined using Equation (8). Specifically, in FIG. 7, the additional bending moment M from the position where the load F is applied._crThe angle θ until the position becomes 0_D, The angle θ_DIs expressed by the equation (10) shown in Equation 7, so that the angle θ_DWhat is necessary is just to advance the provision position of the load F so that the position of may coincide with the position of the end of bending. Also, the lower limit angle θ of the load F application range_EIs given by Equation (2) in Equation 7. Therefore, θ_DIn the case of bending with a bending angle exceeding the angle θ, the position where the load F is applied to the metal strip 1 is expressed by the angle θ shown in the equation (2)._EWhat is necessary is just to set it as the above area | region, and by this, the bending process which produces neck breakage to the end of bending can be performed. The upper limit of the region to which the load F is applied is that the bending angle of the load F is the limit bending angle θ as described above._CThe critical bending angle θ_CThe bending arm position at the point of time, preferably the critical bending angle θ_CIt is. Therefore, when bending at a large angle exceeding 90 degrees, the region to which the load F is applied is an angle θ as shown in FIG._E~ Θ_CThe inner region may be used.
[Expression 7]

[0023]
Also in the case shown in FIG. 8, it is preferable to adopt a method of gradually increasing the load applied to the metal strip 1 from 0 to a predetermined load F within an appropriate angle range. As shown in FIG. 9, the additional bending moment M_crAnd total bending moment M_CCan be gradually changed as shown by the curves 44 and 45. In the embodiment of FIG. 9, the application position of the load F is the limit bending angle θ._CThe angle is somewhat smaller than the angle θ_CAn angle slightly beyond_SWhen it reaches, load addition is started.
[0024]
As shown in the embodiment of FIGS. 8 and 9, when bending 180 degrees, by applying the load F to one point, the total bending moment M in the entire bending range_CWithin the allowable bending moment range (+ M_P~ -M_PIt is possible to keep it within the range. However, if the bending angle from the load application position becomes larger than a certain level, the additional bending moment due to the load F becomes small. Therefore, in order to prevent neck breakage, it is necessary to apply a considerably large load as the load F. As a result, the accuracy of the bending radius may deteriorate. In order to prevent this, it is effective to change or add the position to which the load F is applied when the bending progresses to a position close to the arm clamp root. Hereinafter, an embodiment in that case will be described.
[0025]
The bending apparatus shown in FIG. 11 includes a second load applying device 51 having a structure similar to that of the first load applying device 11 in addition to the load applying device 11 (hereinafter referred to as the first load applying device). The first load applying device 11 has a bending angle that is a limit bending angle θ._CThe load F is provided so that the load F can be applied before the load reaches the position, and the load application position (referred to as the first load application position) by the first load application device 11 is determined from the guide roller 6 by the limit bending angle θ._CIt is set up to the position of. The second load applying device 51 is provided such that a load applying position (referred to as a second load applying position) is set in a region from the first load applying position to the bending arm 3. In the embodiment of the drawing, the first load application position is set to the angle φ.₁= 30 degree position and second load application position is angle φ₂= 90 degrees.
[0026]
Next, load application and bending moment change during bending by the bending apparatus shown in FIG. 11 will be described using the pie chart of FIG. In the figure, 36 is a basic bending moment M._CIt is a curve which shows the change of '. After starting the bending process, the bending angle is the first load application position (angle φ₁= 30 degrees) (bending angle θ)_S1) First load F to the first load application position₁Start adding. At this time, the first load F₁Gradually increases from zero. As a result, as shown by the curve 53A, the additional bending moment M_crAnd the total bending moment M_CChanges like a curve 54A and is kept within the range of the allowable bending moment. Then, when the bending progresses, the bending angle slightly exceeds 90 degrees, and the load can be applied by the second load applying device 51 (the bending angleθ _S2 ), The first load F applied to the first load application position₁At the same time, the second load F is applied to the second load application position.₂And then a constant second load F₂Continue to add. Second load F applied here₂For example, at the end of bending (bending angle θ = 180 degrees), the total bending moment M_CIs the negative allowable bending moment -M_PIs set to be equal to. Also, the first load F to the first load application position₁Is the first load F at the time of switching the load application.₁Additional bending moment M due to_crIs the second load F₂Additional bending moment M due to_crIs set to be equal to. Thus, after switching the load application, as shown by the curve 53B, the additional bending moment M_crAnd the total bending moment M_CChanges like a curve 54B and is kept within the range of the allowable bending moment. Thus, the total bending moment M over the entire bending range._CIs maintained within the range of the allowable bending moment, and bending can be performed without causing neck breakage. As in this embodiment, the second load application position is set at a position where the bending angle is large, and the second load F is set at the position.₂The second load F₂Added bending moment M acting on the arm clamp base_crIn other words, a small second load F₂Can prevent neck breakage. Thus, a relatively small load F₁, F₂To add a total bending moment M_CCan be held within an allowable range, and bending that prevents neck breakage can be performed while keeping the accuracy of the bending radius high.
[0027]
In the above description, the first load F to the first load application position.₁And second load F to the second load application position₂Is switched, but the first load F₁In parallel with the second load F₂A configuration may be added, and in that case, the first load F₁The second load F is gradually reduced.₂It is good also as a structure which increases gradually. Furthermore, in the above description, the load F₁However, the present invention is not limited to this, but the load F having a certain magnitude from the start of the application is not limited to this.₁The load F may be changed as well.₂As for the above, it is not limited to the case of applying a constant load from the beginning, but may be applied while appropriately changing the load.
[0028]
In any of the embodiments described above, the load applying devices 11 and 51 are installed at fixed positions, and a load is applied to a certain bending angle position during the bending process. It is also possible to adopt a configuration in which the robot moves. FIG. 13 shows an embodiment in that case. In this embodiment, the turning arm 61 is provided so as to turn about the turning center O of the bending arm 3, and the load applying device 11 is held by the turning arm 61. In this bending apparatus, bending is started in a state where the load applying device 11 is not operated, and the bending angle is the limit bending angle θ._CAt an appropriate time before reaching the critical bending angle θ_CThe load applying device 11 is positioned and operated at a smaller angular position to start applying the load F. Thereafter, as the bending progresses, the turning arm 61 also turns in the turning direction of the bending arm 3 to advance the load application position. As a result, the bending moment due to the load F can be effectively applied to the clamp root even when the bending angle increases, and by applying a relatively small load F, the total bending moment M_CCan be held within an allowable range, and bending that prevents neck breakage can be performed while keeping the accuracy of the bending radius high. During the bending process, the swivel arm 61 may be continuously swung in synchronism with the bending arm 3, or when it is stopped at one position for a certain period during the bending process and the bending process proceeds. You may make it perform intermittent turning, such as turning to the next position and stopping. Also, the load F applied in this embodiment may be of a constant magnitude or may vary.
[0029]
【The invention's effect】
As described above, according to the present invention, the bending moment M acting on the base of the arm clamp of the metal strip by the turning and propulsion force P of the bending arm at least during the bending process._C The absolute value of ′ is the allowable bending moment M of the metal strip_PThe period exceeding the total bending moment M acting on the arm clamp root of the metal strip_CIs the allowable bending moment M_PIn the metal strip in the region extending from the straight section to the bending arm, on the side where the turning center of the bending arm is located in the bending plane. By applying a load in the direction of the head and bending while applying an additional bending moment to the base of the arm clamp, neck bending that tends to occur when performing compression bending with a small bending radius can be prevented, and there is no neck bending. It has the effect that a product can be obtained.
[0030]
Here, the period during which the load is applied to the metal strip is set so that at least the turning angle of the bending arm is the limit bending angle θ shown in the above equation (1)._CIf the configuration is started before reaching, the total bending moment M acting on the arm clamp root_CThe absolute value of is the allowable bending moment M_PBefore the load is exceeded, the application of a load can be started to prevent the neck from being broken, and the load application timing can be obtained by a simple calculation.
[0031]
Further, when performing a bending process in which the bending angle exceeds 90 degrees, the position at which the load is applied to the metal strip is determined by the angle θ shown in the above equation (2)._EWith the above region, even when the bending angle becomes large, an additional bending moment in the positive direction can be applied to the arm clamp base. For example, in bending with a large bending angle of 180 degrees, The effect that neck breakage can be prevented is obtained.
[0032]
In addition, the position where the load is applied to the metal strip, the first load set in the region from the straight pipe portion in the vicinity of the heated portion of the metal strip to the bending arm at the time when the load starts to be applied. When the configuration is such that the applied position is changed to or added to the second load applying position that is advanced in the bending direction from the first load applying position when a predetermined amount of bending is performed thereafter, a relatively small load is applied. By doing so, the total bending moment acting on the arm clamp root can be maintained within the allowable bending moment, and the effect of preventing neck breakage without deteriorating the accuracy of the bending radius can be obtained.
[0033]
In addition, when the position where the load is applied to the metal strip is configured to move in the turning direction of the bending arm as the bending process proceeds, all the forces acting on the arm clamp base can be obtained by applying a relatively small load. The bending moment can be maintained within the allowable bending moment, and the effect of preventing neck breakage without deteriorating the accuracy of the bending radius can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic plan view of a bending apparatus according to an embodiment of the present invention.
FIG. 2 is a pie chart showing the change of the bending moment acting on the arm clamp root of the metal strip during bending, with respect to the bending angle.
3 is a circle showing a change in bending moment of a bending moment acting on an arm clamp root of a metal strip during bending in the bending method according to an embodiment of the present invention using the apparatus of FIG. 1; Graph
FIG. 4 is a pie chart showing the change of the bending moment acting on the arm clamp root of the metal strip with respect to the bending angle with a large load F applied to the bending start position.
FIGS. 5 (a) and 5 (b) are pie charts showing changes in bending moment acting on the arm clamp root of a metal strip with respect to the bending angle in a bending method according to another embodiment of the present invention.
FIGS. 6A and 6B are pie charts showing changes of a bending moment acting on a base of an arm clamp of a metal strip with respect to a bending angle in a bending method according to still another embodiment of the present invention.
FIG. 7 is a pie chart showing the change of the bending moment acting on the base of the arm clamp of the metal strip with respect to the bending angle when the bending angle is 180 degrees and the load F is applied at the bending start position.
FIG. 8 is a pie chart showing a change of a bending moment acting on a base of an arm clamp of a metal strip with respect to a bending angle in a bending method according to still another embodiment of the present invention.
FIG. 9 is a pie chart showing a change of a bending moment acting on a base of an arm clamp of a metal strip with respect to a bending angle in a bending method according to still another embodiment of the present invention.
FIG. 10 is a schematic plan view of a bending apparatus showing a load application area when bending is performed at a large bending angle.
FIG. 11 is a schematic plan view of a bending apparatus according to another embodiment of the present invention.
12 is a pie chart showing a change of a bending moment acting on a base of an arm clamp of a metal strip with respect to a bending angle in the bending method according to the embodiment of the present invention using the apparatus of FIG.
FIG. 13 is a schematic plan view of a bending apparatus according to still another embodiment of the present invention.
FIG. 14 is a schematic plan view of a conventional bending apparatus.
FIG. 15 is a schematic plan view showing a metal strip (steel pipe) bent by a conventional apparatus.
[Explanation of symbols]
1 Metal strip
2 Heating device
3 Bending arm
4 Arm clamp
5 Cooling water
6 Guide roller
11 Load applying device (first load applying device)
12 Push roller
13 Hydraulic cylinder
51 Second load applying device

Claims (5)

The metal strip to be bent is passed through a heating device that heats a short section in the longitudinal direction, and the processing tip side is fixed to an arm clamp provided on a rotatable bending arm, and the metal strip is fixed by the heating device. By propelling in the longitudinal direction while heating, the heating part by the heating device is moved in the longitudinal direction of the metal strip, and the bending part caused by the turning of the bending arm is applied to the heating part and deformed. The metal strip material is compressed and bent by applying a force in the direction opposite to the turning direction of the bending arm as the bending process proceeds to the bending arm. A bending method M _C acting on the arm clamp root of the metal strip by the turning and propulsive force P of the bending arm during the bending process. In the compression bending method in which there is a period in which the absolute value of ′ exceeds the allowable bending moment M _P of the metal strip, the arm of the metal strip by the turning and propulsion force P of the bending arm at least during the bending period period the absolute value of the moment M _C 'bending acting on the clamp base exceeds an allowable bending moment M _P of the metal strip material is broken neck to the metal strip material by the bending moment acting on the arm clamp base of the metal strip material for but to prevent the occurrence, such that the absolute value of the total bending moment M _C acting on the arm clamp base of the metal strip material does not exceed the permissible bending moment M _P, heating the vicinity of the metal strip material In the direction from the straight line portion to the bending arm in a direction toward the side with the pivot center of the bending arm in the bending plane. Compression bending method for a metal strip material, characterized by bending while applying an additional bending moment at the root arm clamp added heavy. 2. The method for compressing and bending a metal strip according to claim 1, wherein the period during which the load is applied is started at least before the bending angle reaches [theta] _C shown in Formula (1) within the following equation (1). .

The compression bending of the metal strip according to claim 1 or 2, wherein the position at which the load is applied to the metal strip is set to a position equal to or larger than an angle θ _E shown in the following equation (2). Processing method.

The position where the load is applied to the metal strip is set at a point in the region from the straight pipe portion in the vicinity of the heating portion of the metal strip to the bending arm at that time when the load starts to be applied. The load application position is changed to a second load application position set at a position advanced from the first load application position in the advancing direction of the bending arm at the time when a predetermined amount of bending processing proceeds, or the second load application position is set. The method of compressing and bending a metal strip according to any one of claims 1 to 3, wherein a load is applied to the load application position. 4. The metal strip compression according to claim 1, wherein a position at which the load is applied to the metal strip is moved in a turning direction of the bending arm as a bending process proceeds. 5. Bending method.

Images