JP5036449B2 - Pipe bending method - Google Patents

Pipe bending method Download PDF

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JP5036449B2
JP5036449B2 JP2007211463A JP2007211463A JP5036449B2 JP 5036449 B2 JP5036449 B2 JP 5036449B2 JP 2007211463 A JP2007211463 A JP 2007211463A JP 2007211463 A JP2007211463 A JP 2007211463A JP 5036449 B2 JP5036449 B2 JP 5036449B2
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pipe
bending
press
press bending
material pipe
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JP2009045631A (en
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治 園部
裕二 橋本
孝司 鈴木
正雄 岡田
幸司 齋藤
裕英 吉田
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JFE Steel Corp
Taiyo Corp
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Taiyo Corp
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Description

本発明は、自動車の足回り、バンパ、ボディ等の部材用として好適なパイプである、高強度薄肉鋼管の曲げ加工方法に係り、とくにハイドロフォーミングの予成形曲げ加工を施されるパイプのプレス曲げ加工方法に関する。   The present invention relates to a bending method of a high-strength thin-walled steel pipe, which is a pipe suitable for a member such as an automobile undercarriage, a bumper, a body, and the like, and in particular, press bending of a pipe subjected to hydroforming preforming bending. It relates to a processing method.

パイプのプレス曲げ加工方法は、例えば非特許文献１に示されるように、パイプをその長さ方向の二つの支持点に当接させたパイプ支持子で支持し、該二つの支持点の間のパイプ部分をプレス曲げ金型で押し込むことにより、パイプを曲げる加工方法である。パイプのプレス曲げ加工製品の形状は、パイプの材料特性にばらつきがない場合、プレス曲げ金型の曲げ型形状と、押し込みのストローク量（すなわち最終押し込み量）によって決まるとされる。なお、同じ曲げ型形状のプレス曲げ金型を用いる場合は、製品曲げ角度がストローク量によって決まるとされる。
日本塑性加工学会編「チューブフォーミング」コロナ社、１９９２年１０月３０日、Ｐ３８−３９ For example, as shown in Non-Patent Document 1, a pipe is bent and supported by a pipe support member that is in contact with two support points in the length direction, and between the two support points. This is a processing method of bending a pipe by pushing the pipe portion with a press bending die. If there is no variation in the material characteristics of the pipe, the shape of the pipe press-bending product is determined by the bending shape of the press bending mold and the stroke amount (that is, the final pressing amount) of the pressing. In addition, when using the press bending die of the same bending die shape, the product bending angle is determined by the stroke amount.
Edited by Japan Society for Technology of Plasticity “Tube Forming” Corona, October 30, 1992, P38-39

しかし、パイプが高強度鋼管（引張強さが780MPa以上の鋼管）であると、同一のプレス曲げ金型を用いて同一のストローク量で曲げた後のパイプのスプリングバック量が、鋼管製造ロットの違いから生じる材料特性のばらつき等によって比較的大きく変化し、曲げ精度が低下して、目標曲げ角度や目標のプロファイルを達成できない場合が多々ある。
また、プレス曲げ加工されたパイプを、さらにハイドロフォーミング用の型に装入してハイドロフォーミング加工を施す場合に、プレス曲げ精度が悪いと、ハイドロフォーミング用の型に投入した際に、型による噛み込みが発生し、成形不具合となる場合が多々ある。また、プレス曲げ加工されたパイプを、さらに、例えば金型に装入してハイドロフォーミング加工を施す場合等では、従来から、パイプを金型に装入しやすいように、プレス曲げ加工されたパイプの曲げ部を、断面が扁平形状となるように潰す工程を付加する場合もあった。 However, if the pipe is a high-strength steel pipe (steel pipe with a tensile strength of 780 MPa or more), the amount of springback of the pipe after bending with the same stroke amount using the same press bending mold will be There are many cases in which the target bending angle or the target profile cannot be achieved due to a relatively large change due to variations in material properties resulting from the difference, and the bending accuracy is lowered.
In addition, when a pipe that has been press-bent is further inserted into a hydroforming mold and subjected to hydroforming, if the press bending accuracy is poor, when the pipe is put into the hydroforming mold, it is bitten by the mold. In many cases, this may cause molding defects. In addition, when a pipe that has been press-bent is further inserted into a mold and subjected to hydroforming, for example, conventionally, a pipe that has been press-bent so that the pipe can be easily inserted into the mold. In some cases, a step of crushing the bent portion of the material so as to have a flat cross section is added.

しかし、プレス曲げ加工に加えて、さらにこのようなパイプの曲げ部断面を扁平形状とする工程を付加することは、工程が複雑となり、製造コストが上がるという問題があった。
本発明は、かかる従来技術の問題を有利に解決し、余分な工程を付加することなく、パイプ、好ましくは高強度薄肉鋼管を、プレス曲げ加工のみで、曲げ部の断面が扁平形状を呈するパイプとする、パイプのプレス曲げ加工方法を提供することを目的とする。なお、ここでいう「高強度薄肉鋼管」とは、引張強さTSが780MPa以上で、肉厚が3.2mm以下の鋼管をいう。 However, in addition to the press bending process, adding a process of making the cross section of the bent portion of the pipe flat has a problem that the process becomes complicated and the manufacturing cost increases.
The present invention advantageously solves the problems of the prior art, and without adding an extra step, a pipe, preferably a high-strength thin-walled steel pipe, is formed by only press bending, and the cross section of the bent portion exhibits a flat shape. An object of the present invention is to provide a method for press bending a pipe. As used herein, “high-strength thin-walled steel pipe” refers to a steel pipe having a tensile strength TS of 780 MPa or more and a wall thickness of 3.2 mm or less.

本発明者らは、上記した目的を達成するために、パイプ、とくに高強度薄肉鋼管の、パイプ曲げ部の断面形状に及ぼすプレス曲げ加工条件の影響について鋭意研究した。その結果、パイプ曲げ部の断面の扁平率は、プレス曲げ金型のカリバ径と素材パイプの外径との関係を適切にすること、さらにはプレス曲げ加工時にパイプに張力を付加すること、により調整可能であることを知見した。さらに、本発明者らは、プレス曲げ金型のカリバ径が素材パイプの外径より大きいとプレス曲げ加工時に座屈が発生する場合があるが、プレス曲げ金型のカリバ径を素材パイプの外径より大きくし、プレス曲げ加工時にパイプの管軸方向に張力、好ましくは素材パイプの降伏強さの３％以上の張力を、付加することにより、座屈の発生や、曲げ部内側にしわ疵の発生を防止して、パイプの曲げ部断面が所定の扁平率となるように曲げ加工することができることを見出した。   In order to achieve the above-mentioned object, the present inventors diligently studied the influence of press bending process conditions on the cross-sectional shape of a pipe bending portion of a pipe, particularly a high-strength thin-walled steel pipe. As a result, the flatness of the cross section of the pipe bending part is achieved by making the relationship between the caliber diameter of the press bending mold and the outer diameter of the material pipe appropriate, and by applying tension to the pipe during press bending. It was found that it can be adjusted. Furthermore, the present inventors have found that when the caliber diameter of the press bending die is larger than the outer diameter of the material pipe, buckling may occur during the press bending process. By making the diameter larger than the diameter and applying tension in the pipe axis direction of the pipe during press bending, preferably more than 3% of the yield strength of the material pipe, buckling occurs and wrinkles occur inside the bent part. It has been found that the bending can be performed so that the cross section of the bent portion of the pipe has a predetermined flatness.

本発明は、上記した知見に基づき、さらに検討を加えて完成されたものである。すなわち、本発明の要旨は次のとおりである。
（１） 高強度鋼管を素材パイプとして、該素材パイプにプレス曲げ金型を押し込み、プレス曲げ加工を施すに当たり、前記プレス曲げ金型を、カリバ径が前記素材パイプの外径の１．１〜２．０倍であるプレス曲げ金型とし、前記プレス曲げ加工を前記素材パイプの管軸方向に該素材パイプの降伏強さの20％以上の張力を負荷しながら施し、曲げ部の断面形状を前記張力に依存しないほぼ一定の扁平率で然も効率的に扁平化させることを特徴とするパイプの曲げ加工方法。 The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
(1) Using a high-strength steel pipe as a raw material pipe, a press bending die is pressed into the raw material pipe, and the press bending die is subjected to a press bending die with a caliber diameter of 1.1 to an outer diameter of the raw material pipe. A press-bending mold of 2.0 times is applied , and the press-bending process is performed while applying a tension of 20% or more of the yield strength of the material pipe in the tube axis direction of the material pipe, and the cross-sectional shape of the bent part is bending method of a pipe, characterized in Rukoto natural also efficiently is flattened at a substantially constant aspect ratio that does not depend on the tension.

本発明によれば、高強度薄肉鋼管を、所望の曲げ角度でかつ曲げ部断面が所定の扁平率で扁平化したパイプに、精度高く容易に、かつ効率よく、プレス曲げ加工することができ、産業上格段の効果を奏する。本発明によれば、パイプの曲げ加工と断面扁平化加工とを同時に行うことができ、従来の工程の一部を省略することが可能となり、プレス曲げ加工の効率化に顕著に寄与するという効果もある。   According to the present invention, a high-strength thin-walled steel pipe can be press-bended with high accuracy, easily, and efficiently into a pipe with a desired bending angle and a bent section section flattened at a predetermined flattening ratio, There are remarkable effects in the industry. According to the present invention, the pipe bending process and the cross-section flattening process can be performed at the same time, part of the conventional process can be omitted, and the effect of contributing significantly to the efficiency of the press bending process. There is also.

本発明は、パイプのプレス曲げ加工方法であり、使用する素材パイプは、高強度薄肉鋼管とする。本発明では、素材パイプにプレス曲げ金型を押し込み、プレス曲げ加工を施す。本発明におけるプレス曲げ加工方法の概略を図１に示す。
加工開始前、パイプ１０は、その長さ方向の二点をパイプ支持子４で支持される。パイプ支持子４はコロあるいはシューなどで構成される（図１ではコロである）。パイプ支持子４に支持される二点間の距離（支持点間距離Ｌ）のほぼ２等分点にあたるパイプ部分に、プレス曲げ金型１が当接する（図１（ａ））。プレス曲げ金型１の曲げ型部のパイプ当接面は、長さ方向に、例えば曲率半径Ｒ1の、曲がり形状を有し、また幅方向にはパイプ径ｄ0に適合したカリバ径、例えばＤを有する孔型１ａ内面と同じ曲がり形状を有する（図１Ａ−Ａ矢視図）。 The present invention is a method of press bending a pipe, and a material pipe to be used is a high-strength thin-walled steel pipe. In the present invention, a press bending die is pushed into the material pipe to perform press bending. An outline of the press bending method in the present invention is shown in FIG.
Before starting the processing, the pipe 10 is supported by the pipe support 4 at two points in the length direction. The pipe support 4 is composed of a roller or a shoe (in FIG. 1, it is a roller). The press-bending die 1 is brought into contact with a pipe portion corresponding to approximately a bisector of a distance between two points supported by the pipe support 4 (distance L between support points) (FIG. 1A). The pipe contact surface of the bending die portion of the press bending die 1 has a curved shape with a radius of curvature R 1 , for example, in the length direction, and a caliber diameter suitable for the pipe diameter d 0 in the width direction, for example, It has the same bent shape as the inner surface of the hole mold 1a having D (FIG. 1A-A arrow view).

曲げ加工が始まると、プレス曲げ金型１はシリンダ２により付勢されてパイプ１０を押し込んでいく。なお、３はロードセルである。ストローク量に初期設定値を与えて加工を開始し、押し込み途上で押し込み量がストローク量（初期設定値）に達した時にシリンダ２による付勢を停止して加工を終える（図１（ｂ））。曲げ角度θは、図１（ｂ）で示す角度θで定義される値である。パイプをプレス曲げ金型１から取り外すと、スプリングバックによってθは小さくなる。とくに、高強度鋼管の場合には、この変化量が大きく、目標の曲げ角度を達成するためにはプレス曲げ加工直後のパイプをプレス曲げ金型１から取り外す前のθを目標曲げ角度より大きくする必要がある。なお、プレス曲げ加工に際しては、予め、曲げ角度θとストローク量との関係を素材パイプ（パイプ強度）に応じて求めておくことは言うまでもない。   When the bending process starts, the press bending die 1 is urged by the cylinder 2 and pushes the pipe 10. Reference numeral 3 denotes a load cell. Machining is started by giving an initial setting value to the stroke amount, and when the pushing amount reaches the stroke amount (initial setting value) in the course of pushing, the urging by the cylinder 2 is stopped and the machining is finished (FIG. 1B). . The bending angle θ is a value defined by the angle θ shown in FIG. When the pipe is removed from the press bending mold 1, θ is reduced by the spring back. In particular, in the case of a high-strength steel pipe, the amount of change is large, and in order to achieve the target bending angle, θ before removing the pipe immediately after press bending from the press bending mold 1 is made larger than the target bending angle. There is a need. Needless to say, in press bending, the relationship between the bending angle θ and the stroke amount is obtained in advance according to the material pipe (pipe strength).

本発明では、パイプの曲げ部断面の扁平率は、カリバ径Ｄと素材パイプ外径ｄ0との関係で適切に調整する。本発明のプレス曲げ加工方法では、使用するプレス曲げ金型１のカリバ径Ｄを、図２（ａ）に示すように、被加工材である素材パイプ１０の外径ｄ0より大きくする。これにより、図２（ｂ）に示すように、パイプの曲げ部断面の形状を扁平化することができる。所望の扁平率の曲げ部断面とするために、使用するプレス曲げ金型のカリバ径Ｄは、鋼種ごとに、予め求めておいた加工後の曲げ部断面の扁平率と、カリバ径Ｄ、素材パイプ外径ｄ0、付与する張力との関係に基づき決定する。なお、プレス曲げ金型のカリバ径Ｄは、素材パイプの外径ｄ0 の1.1倍以上とすることが曲げ部を効率的に扁平化する観点から好ましい。カリバ径Ｄが1.1ｄ0未満では、扁平が小さく非効率的である。なお、カリバ径Ｄは、1.5〜2.0ｄ0とすることがより好ましい。 In the present invention, flattening of the bent portion the cross section of the pipe, appropriately adjusted in relation to the caliber diameter D and the material pipe outer diameter d 0. In the press bending method of the present invention, the caliber diameter D of the press bending mold 1 to be used is made larger than the outer diameter d 0 of the material pipe 10 which is a workpiece as shown in FIG. Thereby, as shown in FIG.2 (b), the shape of the bending part cross section of a pipe can be flattened. In order to obtain a bending portion cross section having a desired flatness ratio, the caliber diameter D of the press bending die used is the flatness ratio of the bending portion cross section after processing, the caliber diameter D, and the material obtained in advance for each steel type. It is determined based on the relationship between the pipe outer diameter d 0 and the applied tension. In addition, it is preferable that the caliber diameter D of the press bending die is 1.1 times or more the outer diameter d 0 of the material pipe from the viewpoint of efficiently flattening the bent portion. If the caliber diameter D is less than 1.1 d 0 , the flatness is small and inefficient. The caliber diameter D is more preferably 1.5 to 2.0 d 0 .

なお、カリバ径Ｄが素材パイプの外径ｄ0より大きいプレス曲げ金型を用いて、所定の曲げ角度までプレス曲げ加工を行うと、パイプが座屈する。このため、本発明では、素材パイプの管軸方向に張力を付与する。素材パイプの管軸方向に張力を負荷しながらプレス曲げ加工を施すと、座屈を生じることなく、プレス曲げ加工を行うことができ、しかもパイプの曲げ部断面を扁平化することができる。なお、負荷する張力は、素材パイプの降伏強さYSの３％以上とすることが好ましい。負荷される張力が、素材パイプのYSの３％未満ではプレス曲げ加工に際し、座屈の発生を完全に防止することができない。 In addition, when a press bending process is performed to a predetermined bending angle using a press bending die having a caliber diameter D larger than the outer diameter d 0 of the material pipe, the pipe buckles. For this reason, in this invention, tension | tensile_strength is provided to the pipe-axis direction of a raw material pipe. When press bending is performed while applying tension in the tube axis direction of the material pipe, the press bending can be performed without causing buckling, and the cross section of the bent portion of the pipe can be flattened. The tension to be applied is preferably 3% or more of the yield strength YS of the material pipe. If the applied tension is less than 3% of YS of the material pipe, buckling cannot be completely prevented during press bending.

なお、素材パイプの管軸方向に負荷される張力は、素材パイプの降伏強さYSの20％以上とすることがより好ましい。負荷張力Ｐを素材パイプの降伏強さYSの20％以上（（負荷張力Ｐ）／（パイプの降伏強さYS）：0.20以上）とすることにより、次式
扁平率ｆ（％）＝｛（ｄmax−ｄmin）／ｄmax｝×100
で定義される扁平率ｆが、図３に示すように、ほぼ一定となる。負荷張力Ｐが素材パイプの降伏強さの20％以上である場合には、曲げ部断面の扁平率ｆは、カリバ径Ｄ、素材パイプ外径ｄ0との関係のみで決定され、張力依存性がなくなる。このため、素材パイプの管軸方向に負荷する張力Ｐを素材パイプの降伏強さの20％以上としてプレス曲げ加工を行うことにより、プレス曲げ加工後の曲げ部断面の扁平率の変動がなく、安定したパイプのプレス曲げ加工を行うことができることになる。なお、負荷する張力Ｐが、素材パイプの降伏強さの20％未満では、負荷される張力に依存して、扁平率ｆが変化する。このため、プレス曲げ加工後の曲げ部断面の扁平率と、負荷される張力との関係を予め、調査しておくことが、プレス曲げ加工後の曲げ部断面の扁平率を適正値に調整するうえで重要となる。 The tension applied in the tube axis direction of the material pipe is more preferably 20% or more of the yield strength YS of the material pipe. By setting the load tension P to 20% or more of the yield strength YS of the material pipe ((load tension P) / (yield strength of pipe YS): 0.20 or more), the following formula flatness f (%) = {( dmax−dmin) / dmax} × 100
The flat rate f defined by is substantially constant as shown in FIG. When the load tension P is 20% or more of the yield strength of the material pipe, the flattening ratio f of the bent section is determined only by the relationship between the caliber diameter D and the material pipe outer diameter d 0, and is dependent on the tension. Disappears. For this reason, there is no fluctuation in the flatness of the cross section of the bent part after press bending by performing press bending with the tension P applied in the pipe axis direction of the material pipe being 20% or more of the yield strength of the material pipe, Stable pipe bending can be performed. Note that when the applied tension P is less than 20% of the yield strength of the material pipe, the flattening ratio f changes depending on the applied tension. For this reason, investigating in advance the relationship between the flattening ratio of the bending section after press bending and the applied tension adjusts the flatness of the bending section after press bending to an appropriate value. Is important.

780MPa級高強度薄肉鋼管（引張強さTS：780MPa以上）（鋼管寸法：外径70mmφ×肉厚2.6mm）を素材パイプとして、プレス曲げ加工を実施した。プレス曲げ加工では、カリバ径Ｄ：114.3mm、曲げ半径Ｒ：1000mmのプレス曲げ金型を用い、支持点間距離をＬ＝1000mmとして、曲げ角度θ：35度、曲げ部の曲率半径がほぼ1150mmとなるように行った。プレス曲げ加工に際し、素材パイプの管軸方向に、素材パイプの降伏強さYSの３％および20％の張力を負荷し、本発明例とした。なお、張力負荷なしを比較例とした。また、カリバ径Ｄ：70.0mm、曲げ半径Ｒ：1000mmのプレス曲げ金型を用いて、曲げ角度θ：35度、曲げ部の曲率半径がほぼ1150mmとなるようにプレス曲げ加工を行い、従来例とした。従来例では、張力の負荷は行わなかった。従来例では、プレス曲げ加工後に、曲げ部断面の扁平化工程を行った。なお、曲げ部断面の扁平化工程は、プレス曲げ加工後のパイプを半径方向に25mm程度押し潰す加工とした。   Press bending was performed using 780 MPa class high-strength thin-walled steel pipe (tensile strength TS: 780 MPa or more) (steel pipe dimensions: outer diameter 70 mmφ x wall thickness 2.6 mm) as a material pipe. In press bending, a press bending die with a caliber diameter D of 114.3 mm and a bending radius R of 1000 mm is used, the distance between support points is set to L = 1000 mm, the bending angle θ is 35 degrees, and the curvature radius of the bending portion is approximately 1150 mm. It went so that it might become. At the time of press bending, a tension of 3% and 20% of the yield strength YS of the material pipe was applied in the tube axis direction of the material pipe to obtain an example of the present invention. Note that no tension load was used as a comparative example. Also, using a press bending mold with a caliber diameter D of 70.0 mm and a bending radius R of 1000 mm, press bending is performed so that the bending angle θ is 35 degrees and the bending radius of curvature is approximately 1150 mm. It was. In the conventional example, no tension was applied. In the conventional example, the flattening process of the cross section of the bent part was performed after the press bending process. The step of flattening the cross section of the bent part was a process of crushing the pipe after the press bending process by about 25 mm in the radial direction.

プレス曲げ加工は、各条件について2000本づつ、実施し、各条件の平均加工時間および総時間、さらに、パイプの曲げ部断面の扁平率を抜き取りで各条件につき各100本調査した。なお、各パイプの曲げ部断面の扁平率は、曲げ部断面の寸法を図２（ｂ）に示すように測定し、次式
扁平率ｆ（％）＝｛（ｄmax−ｄmin）／ｄmax｝×100
を用いて算出し、その算術平均を求めた。 The press-bending process was carried out in 2000 for each condition, and the average machining time and total time for each condition, and the flatness of the cross section of the bent part of the pipe were extracted, and 100 were investigated for each condition. In addition, the flatness of the cross section of the bent portion of each pipe is measured by measuring the cross section of the bent portion as shown in FIG. 2B, and the following formula: flat rate f (%) = {(dmax−dmin) / dmax} × 100
And the arithmetic average was obtained.

得られた結果を表１に示す。   The obtained results are shown in Table 1.

Figure 0005036449
Figure 0005036449

本発明例では、曲げ部断面で所望の扁平率を有するパイプを、従来例に比べ、短い加工時間でプレス曲げ加工することができ、顕著に曲げ加工効率を向上できる。   In the example of the present invention, a pipe having a desired flatness in the cross section of the bent part can be press-bended in a shorter processing time than the conventional example, and the bending efficiency can be significantly improved.

本発明のプレス曲げ加工方法の概略を模式的に示す説明図である。It is explanatory drawing which shows typically the outline of the press bending method of this invention. （ａ）本発明におけるプレス曲げ金型１のカリバ径Ｄと素材パイプの外径ｄ0との関係、および（ｂ）本発明におけるプレス曲げ加工後のパイプ１０の扁平形状、を模式的に示す説明図である。(A) The relationship between the caliber diameter D of the press bending die 1 in the present invention and the outer diameter d 0 of the material pipe, and (b) the flat shape of the pipe 10 after press bending in the present invention are schematically shown. It is explanatory drawing. 曲げ部断面の扁平率ｆと負荷張力Ｐ／降伏強さYSとの関係を示すグラフである。It is a graph which shows the relationship between flatness f of a bending part cross section, and load tension P / yield strength YS.

符号の説明Explanation of symbols

１ プレス曲げ金型
１ａ 孔型
２ シリンダ
３ ロードセル
４ パイプ支持子（コロ）
１０ パイプ（素材パイプ）
Ｐ 負荷張力 1 Press bending mold 1a Hole mold 2 Cylinder 3 Load cell 4 Pipe support (roller)
10 Pipe (material pipe)
P Load tension

Claims (1)

高強度鋼管を素材パイプとして、該素材パイプにプレス曲げ金型を押し込み、プレス曲げ加工を施すに当たり、前記プレス曲げ金型を、カリバ径が前記素材パイプの外径の１．１〜２．０倍であるプレス曲げ金型とし、前記プレス曲げ加工を前記素材パイプの管軸方向に該素材パイプの降伏強さの20％以上の張力を負荷しながら施し、曲げ部の断面形状を前記張力に依存しないほぼ一定の扁平率で然も効率的に扁平化させることを特徴とするパイプの曲げ加工方法。 When a high-strength steel pipe is used as a raw material pipe, a press bending die is pushed into the raw material pipe, and the press bending die is subjected to the press bending die, and the caliber diameter is 1.1 to 2.0 of the outer diameter of the raw material pipe. A press bending die that is doubled, and the press bending process is performed while applying a tension of 20% or more of the yield strength of the material pipe in the tube axis direction of the material pipe, and the cross-sectional shape of the bent portion is set to the tension. bending method of a pipe, characterized in Rukoto natural also efficiently is flattened at a substantially constant aspect ratio that is independent.
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