JP2009270150A - Method for manufacturing coil spring - Google Patents

Method for manufacturing coil spring Download PDF

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JP2009270150A
JP2009270150A JP2008121197A JP2008121197A JP2009270150A JP 2009270150 A JP2009270150 A JP 2009270150A JP 2008121197 A JP2008121197 A JP 2008121197A JP 2008121197 A JP2008121197 A JP 2008121197A JP 2009270150 A JP2009270150 A JP 2009270150A
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coil spring
residual stress
shot peening
manufacturing
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Satoru Kondo
覚 近藤
Takaaki Nishimura
隆昭 西村
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Togo Seisakusho Corp
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Togo Seisakusho Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a coil spring which can stably show high fatigue characteristics. <P>SOLUTION: The method for manufacturing the coil spring includes: a forming step of forming the coil spring by employing an oil-tempered alloy-steel wire as a raw material; a nitriding treatment step of enhancing the surface hardness of the coil spring; and a shot peening step of imparting residual stress to the coil spring. The method further includes electrolytically polishing the coil spring after the shot peening step to remove the surface layer of the coil spring, control the thickness of a white layer formed in the nitriding treatment step to 5 μm or less, simultaneously control the surface roughness to 4 μm or less by Rc and also control the compressive residual stress of the outermost surface to 1,800 MPa or higher. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

本発明はコイルばねの製造方法に関する。   The present invention relates to a method of manufacturing a coil spring.

高強度高耐疲労ばねを製造する方法として、引張強度の高い線材を使用して所定形状にコイリング成形し、窒化処理により表面硬化させた後に高い圧縮残留応力を付与するために高エネルギのショットピーニングを施す方法が知られている(例えば、特許文献1)。   High energy shot peening as a method of manufacturing high strength and high fatigue resistance springs by applying high tensile strength wire to coiling into a predetermined shape and applying high compressive residual stress after surface hardening by nitriding treatment The method of applying is known (for example, Patent Document 1).

しかし、さらに高強度で高い疲労特性を要求されるようになると、従来よりもさらに高エネルギのショットピーニング処理を施さなければ、要求される疲労特性に見合う高い圧縮残留応力をばね表面に付与することができない。窒化処理後にこのように強いショットピーニングを施すと、ばね表面が著しく粗面化するとともに表面全体に微細な表面欠陥を発生させる。このため、ばねはキズ感受性が高くなって結果的に疲労特性が低下するという問題があった。
特開平10−118930号公報
However, when higher strength and higher fatigue properties are required, high compressive residual stress that matches the required fatigue properties can be applied to the spring surface unless shot peening treatment with higher energy than before is applied. I can't. When such strong shot peening is performed after nitriding, the spring surface becomes extremely rough and fine surface defects are generated on the entire surface. For this reason, the spring has a problem that the sensitivity to scratches is increased, resulting in a decrease in fatigue characteristics.
Japanese Patent Laid-Open No. 10-118930

本発明は上記の問題を解決するためになされたものであり、コイルばねに窒化処理を施して表面を高硬度化するとともに、従来よりも高強度のショットピーニングを施して高い圧縮残留応力を付与しても、安定して高い疲労特性を発揮できるコイルばねの製造方法を提供することを課題とする。   The present invention has been made to solve the above-mentioned problems. The surface of the coil spring is subjected to nitriding treatment to increase the hardness, and the shot peening is applied with higher strength than before to give high compressive residual stress. Even so, it is an object to provide a method of manufacturing a coil spring that can stably exhibit high fatigue characteristics.

本発明のコイルばねの製造方法は、合金鋼オイルテンパー線を素材としてコイルばねを成形する成形工程と、このコイルばねの表面硬度を向上させる窒化処理工程と、このコイルばねに残留応力を付与するショットピーニング工程とを有するコイルばねの製造方法において、前記ショットピーニング工程の後に電解研磨を施すことによりコイルばねの表層を除去して、前記窒化処理により生成した白層の厚さを5μm以下にするとともに、表面粗さをRcで4μm以下とし、かつ最表面の圧縮残留応力を1800MPa以上とすることを特徴とする。   The method for manufacturing a coil spring according to the present invention includes a forming step of forming a coil spring using an alloy steel oil temper wire as a raw material, a nitriding treatment step for improving the surface hardness of the coil spring, and applying residual stress to the coil spring. In a method for manufacturing a coil spring having a shot peening process, the surface layer of the coil spring is removed by performing electropolishing after the shot peening process, so that the thickness of the white layer generated by the nitriding treatment is 5 μm or less. In addition, the surface roughness is 4 μm or less in terms of Rc, and the compressive residual stress on the outermost surface is 1800 MPa or more.

本発明のコイルばねの製造方法において、前記窒化処理後のコイルばねの表面硬度は850〜1400HVであることが望ましく、電解研磨によりコイルばねの表層を3〜20μm除去するようにするとよい。   In the coil spring manufacturing method of the present invention, the surface hardness of the coil spring after the nitriding treatment is desirably 850 to 1400 HV, and the surface layer of the coil spring is preferably removed by 3 to 20 μm by electrolytic polishing.

また、本発明のコイルばねの製造方法において、前記合金鋼オイルテンパー線は、質量%でC:0.55〜0.75%、Si:1.00〜2.70%、Mn:0.10〜1.50%、Cr:0.4〜2.50%、V:0.05〜0.50%を含み、残部Feと不可避的不純物とからなることが好ましく、さらにMo:0.05〜2.0%、Co:0.05〜0.40%、のいずれか1種を含むことができる。   Moreover, in the manufacturing method of the coil spring of this invention, the said alloy steel oil temper wire is C: 0.55-0.75% in mass%, Si: 1.00-2.70%, Mn: 0.10. -1.50%, Cr: 0.4-2.50%, V: 0.05-0.50%, preferably consisting of the balance Fe and unavoidable impurities, Mo: 0.05- Any one of 2.0% and Co: 0.05 to 0.40% can be included.

本発明ではショットピーニング後に電解研磨を施すことにより、窒化処理工程でコイルばね表面に形成される有害な白層について、その厚さが5μm以下となるようにコイルばねの表層部を除去する。従って、本発明によればコイルばねの耐衝撃性や疲労特性を向上することができる。   In the present invention, by performing electropolishing after shot peening, the surface layer portion of the coil spring is removed so that the thickness of the harmful white layer formed on the surface of the coil spring in the nitriding process is 5 μm or less. Therefore, according to the present invention, the impact resistance and fatigue characteristics of the coil spring can be improved.

また、本発明では電解研磨を施すことによりショットの圧痕による微細な表面欠陥を除去してばね表面の表面粗さをRcで4μm以下とする。また、ばねの作用応力は表面で最大となる。従って、本発明によれば、コイルばねの切り欠きもしくは疵を低減して耐衝撃性や疲労特性を向上することができる。   Further, in the present invention, fine surface defects due to shot indentation are removed by performing electropolishing so that the surface roughness of the spring surface is set to 4 μm or less in terms of Rc. The working stress of the spring is maximized on the surface. Therefore, according to the present invention, the notch or wrinkle of the coil spring can be reduced to improve the impact resistance and fatigue characteristics.

一般にショットピーニングで付与される圧縮残留応力は、ばねの表面から幾分内部で最大となる。本発明では電解研磨処理によりコイルばねの表層部を除去するので、コイルばねの最表面での圧縮残留応力を最大値に近づけることができる。また、ばねの作用応力は表面が最大となるので、本発明によれば付与した圧縮残留応力を最も有効化してコイルばねの疲労特性を向上することができる。   In general, the compressive residual stress applied by shot peening is maximized somewhat inside from the surface of the spring. In the present invention, since the surface layer portion of the coil spring is removed by electrolytic polishing, the compressive residual stress on the outermost surface of the coil spring can be brought close to the maximum value. In addition, since the surface of the working stress of the spring is maximized, according to the present invention, the applied compressive residual stress can be most effectively used to improve the fatigue characteristics of the coil spring.

以下、本発明の好適な一実施の形態を詳細に説明する。本実施の形態においては、質量%でC:0.55〜0.75%、Si:1.00〜2.70%、Mn:0.10〜1.50%、Cr:0.4〜2.50%、V:0.05〜0.50%を含み、残部Feと不可避的不純物とからなる合金鋼オイルテンパー線を素材とするとよい。このような組成を有するオイルテンパー線としては、特開平2−107746に開示されているものなどが知られている。   Hereinafter, a preferred embodiment of the present invention will be described in detail. In the present embodiment, C: 0.55 to 0.75%, Si: 1.00 to 2.70%, Mn: 0.10 to 1.50%, Cr: 0.4 to 2% by mass%. An alloy steel oil tempered wire containing 50%, V: 0.05 to 0.50%, and the balance Fe and unavoidable impurities may be used as a material. As an oil tempered wire having such a composition, those disclosed in JP-A-2-107746 are known.

また、係る組成にさらにMoを0.05〜2.0%含有する合金鋼オイルテンパー線(特開2003−3241で開示されているもの)やCoを0.05〜0.40%含有する合金鋼オイルテンパー線(特開2004−190116で開示されているもの)も好適に用いることができる。これらの合金鋼オイルテンパー線は、引張強度が1900〜2300MPa、絞りが35%以上のものを用いるとよい。   Further, an alloy steel oil tempered wire containing 0.05 to 2.0% of Mo in the composition (disclosed in Japanese Patent Laid-Open No. 2003-3241) and an alloy containing 0.05 to 0.40% of Co. A steel oil tempered wire (disclosed in JP-A No. 2004-190116) can also be suitably used. As these alloy steel oil tempered wires, those having a tensile strength of 1900 to 2300 MPa and a drawing of 35% or more may be used.

まず所望の化学成分組成と引張強度とを有する合金鋼オイルテンパー線を冷間コイリングして所望のばね形状に成形する。その後大気雰囲気中で350〜500℃で3〜60分の低温熱処理を施してコイル成形時に生じた残留応力や残留歪みを除去する。   First, an alloy steel oil temper wire having a desired chemical composition and tensile strength is cold-coiled and formed into a desired spring shape. Thereafter, a low-temperature heat treatment is performed at 350 to 500 ° C. for 3 to 60 minutes in an air atmosphere to remove residual stress and residual strain generated during coil forming.

次に、窒化処理に先立ってディスケール処理を施す。ディスケール処理とは、コイル成形されたばね素材表面の酸化皮膜を除去する工程で、酸化皮膜を取り除くことにより均一な窒化を可能とするものである。このディスケール処理ではばね素材の表面の最大高さRzが5μm以下になるようにするとよい。ばね素材表面の最大高さRzが5μmを超えると、窒化の均一性が得られないことがあるので好ましくない。ディスケール処理としては、ばね素材の表面粗さを増大させないように、比較的弱くブラストされるような条件、例えば、マイクロショットを用いたショットピーニングを施す。マイクロショットとしては、比較的軟らかいガラスビーズや砥粒、直径0.3mm以下のカットワイヤ、あるいは直径0.3mm以下のスティールショットなどを例示することができる。これらのマイクロショットにより、ばね素材表面の最大高さRzを5μm以下にすることができる。   Next, a descale process is performed prior to the nitriding process. The descaling process is a process of removing the oxide film on the surface of the spring material that has been coil-formed, and enables uniform nitriding by removing the oxide film. In this descale process, the maximum height Rz of the surface of the spring material is preferably 5 μm or less. If the maximum height Rz of the spring material surface exceeds 5 μm, nitriding uniformity may not be obtained, which is not preferable. As the descaling process, conditions such that the spring material is relatively weakly blasted, for example, shot peening using micro shots, are applied so as not to increase the surface roughness of the spring material. Examples of the micro shot include relatively soft glass beads and abrasive grains, a cut wire having a diameter of 0.3 mm or less, or a steel shot having a diameter of 0.3 mm or less. By these micro shots, the maximum height Rz of the spring material surface can be reduced to 5 μm or less.

窒化処理は、窒素ガス又はアンモニアガスなどの雰囲気中で行うことができるが、400〜500℃で2〜48時間のアンモニアガスによるガス窒化処理が望ましい。窒化処理温度が400℃未満では、コイルばねの表面層が硬化不足となり、一方、500℃を超えると内部硬さが低下して疲労特性に優れた高強度コイルばねを得ることができない。さらに、窒化処理時間が2時間未満では窒化処理に伴う硬化層の形成が不均一となり、また、48時間を超えても硬化が飽和してしまい長時間処理に見合うより有効な窒化層を得ることはできないので不経済である。   The nitriding treatment can be performed in an atmosphere such as nitrogen gas or ammonia gas, but gas nitriding treatment with ammonia gas at 400 to 500 ° C. for 2 to 48 hours is desirable. When the nitriding temperature is less than 400 ° C., the surface layer of the coil spring becomes insufficiently cured, while when it exceeds 500 ° C., the internal hardness is lowered and a high-strength coil spring having excellent fatigue characteristics cannot be obtained. Furthermore, if the nitriding time is less than 2 hours, the formation of a hardened layer accompanying the nitriding treatment becomes non-uniform, and even if it exceeds 48 hours, the hardening is saturated and a more effective nitrided layer suitable for long-time processing can be obtained. It is uneconomical because it cannot be done.

以上のような窒化処理を施すことにより窒化処理後のコイルばねの表面(表面から0.02mm付近まで)硬度を850〜1400HVとする。窒化処理後の表面硬度が850HV未満では次工程のショットピーニングで充分な圧縮残留応力を形成することができないので、所望の疲労強度を付与することができない。一方、1400HVを超えると靱性が低下して所望の耐衝撃性を得ることができない。より好ましくは、850〜1200HVである。   By performing the nitriding treatment as described above, the hardness (from the surface to the vicinity of 0.02 mm) of the coil spring after the nitriding treatment is set to 850 to 1400 HV. If the surface hardness after the nitriding treatment is less than 850 HV, a sufficient compressive residual stress cannot be formed by shot peening in the next step, and thus a desired fatigue strength cannot be imparted. On the other hand, if it exceeds 1400 HV, the toughness decreases and the desired impact resistance cannot be obtained. More preferably, it is 850-1200HV.

次に、窒化処理後のコイルばねにショットピーニングを施す。本実施形態では、圧縮残留応力を表層部分で高くかつ内部深くまで付与するためにショット方法の異なる2段以上の多段ショットピーニングを施す。   Next, shot peening is applied to the coil spring after nitriding. In this embodiment, two or more stages of multi-step shot peening with different shot methods are applied in order to impart a high compressive residual stress at the surface layer and deep inside.

例えば、1段目のショットピーニング工程では、まず粒径の大きいショットを高速でコイルばねに投射して表面から内部の深い位置まで残留応力を付与する。そして2段目のショットピーニング工程では、1段目のショットピーニング工程で使用したショットより粒径が小さいショットを使用して投射し、極表層部にさらに大きな残留応力を付与する。この工程では1段目のショットピーニング工程で使用したショットより硬度の高いものを使用したり、あるいはショットを高速で投射することでその効果をより高めることができる。   For example, in the first-stage shot peening process, first, a shot having a large particle size is projected onto a coil spring at a high speed to apply a residual stress from the surface to a deep position inside. In the second-stage shot peening process, a shot having a particle size smaller than that used in the first-stage shot peening process is used for projection, and a larger residual stress is applied to the extreme surface layer portion. In this step, the effect can be further enhanced by using one having a higher hardness than the shot used in the first shot peening step, or by projecting the shot at a high speed.

第1ショットピーニング工程で使用されるショットとしては、内部の深い位置まで残留応力を付与するために、0.4〜1.0mmの径で、硬さが500〜800HVの範囲のもの、例えば、コンディションドカットワイヤーなどが好ましい。   As a shot used in the first shot peening step, in order to give a residual stress to a deep position inside, a shot having a diameter of 0.4 to 1.0 mm and a hardness of 500 to 800 HV, for example, Conditioned cut wires are preferred.

また、第2ショットピーニング工程では表面部の残留応力を高めるために、第1ショットピーニング工程で用いるショットと比べて小径でかつ硬さが硬いショットを用いることが好ましい。具体的には、径が0.05〜0.3mm程度で、硬さが700〜1500HVのショット、例えば、コンディションドカットワイヤーや超硬ショット等を使用することが好ましい。この場合には高圧エアーによるショットの投射が望ましく、この高圧での投射で表面付近に著しく高い残留応力を形成することができる。さらに必要に応じて第3段目のショットピーニングを施してもよい。このような多段ショットピーニングを施すことで表面に高い圧縮残留応力を付与してコイルばねの疲労特性を向上することができる。   In the second shot peening process, it is preferable to use a shot having a smaller diameter and a higher hardness than the shot used in the first shot peening process in order to increase the residual stress on the surface portion. Specifically, it is preferable to use a shot having a diameter of about 0.05 to 0.3 mm and a hardness of 700 to 1500 HV, such as a conditioned cut wire or a carbide shot. In this case, it is desirable to project a shot with high-pressure air, and a remarkably high residual stress can be formed near the surface by this high-pressure projection. Further, third-stage shot peening may be performed as necessary. By performing such multi-stage shot peening, a high compressive residual stress can be applied to the surface and the fatigue characteristics of the coil spring can be improved.

続いて、ショットピーニング後のコイルばねに低温焼き鈍しを施す。この低温焼き鈍しはショットピーニングによる異常に大きな内部歪みを除去する目的で行うものであり、一般的には200〜300℃で3〜60分程度の加熱処理である。   Subsequently, the coil spring after shot peening is annealed at a low temperature. This low-temperature annealing is performed for the purpose of removing abnormally large internal strain caused by shot peening, and is generally a heat treatment at 200 to 300 ° C. for about 3 to 60 minutes.

次いで、低温焼き鈍し後のコイルばねに電解研磨処理を施す。本実施形態では前記のようにディスケーリング後のコイルばねに窒化処理を施して、表層部に窒化による硬化層を形成することでコイルばねをより高強度化するようにしている。しかし、窒化処理を施すとコイルばねの表面に窒化物や炭窒化物を主体とする白層が形成される。形成される白層の厚さは窒化処理条件や部位によって異なるが、概ね1〜10μm程度である。この白層は非常に硬くて脆いという性質を有するために、コイルばねの耐衝撃性や疲労特性を低下させる原因となる。従って、電解研磨を施すことによりこの有害な白層の厚さが5μm以下(好ましくは3μm以下)となるようにコイルばねの表層部を除去する。白層の厚さを5μm以下にすることでコイルばねの耐衝撃性や疲労特性を向上することができる。   Next, the coil spring after the low-temperature annealing is subjected to electrolytic polishing. In the present embodiment, as described above, the coil spring after descaling is subjected to nitriding treatment, and a hardened layer by nitriding is formed on the surface layer portion, so that the strength of the coil spring is further increased. However, when nitriding is performed, a white layer mainly composed of nitride or carbonitride is formed on the surface of the coil spring. The thickness of the white layer to be formed is about 1 to 10 μm, although it varies depending on the nitriding conditions and the site. Since this white layer has the property of being very hard and brittle, it causes a reduction in the shock resistance and fatigue characteristics of the coil spring. Therefore, the surface layer portion of the coil spring is removed by electropolishing so that the thickness of the harmful white layer is 5 μm or less (preferably 3 μm or less). By making the thickness of the white layer 5 μm or less, the impact resistance and fatigue characteristics of the coil spring can be improved.

また、高強度なショットピーニング処理のためにピーニング後のコイルばねの表面は表面の最大高さRzが7μm以上と著しく粗面化されている。また、同時にショットの圧痕による微細な表面欠陥が多数発生している。このため、電解研磨を施すことによりこの表面欠陥を除去して表面粗さをRcで4μm以下(好ましくは3μm以下)としてコイルばねのキズ感受性を低減させる。表面粗さを示すパラメータとしてはJIS B 0601に平均粗さRa、最大高さRz、平均高さRcなどが規定されている。ここで平均高さRcで評価するようにしたのは、Rcは高さを平均して算出されるパラメータであるので、全体的な表面粗さを表現するには最適と考えられるからである。   Further, the surface of the coil spring after peening is extremely roughened with a maximum surface height Rz of 7 μm or more because of high-intensity shot peening. At the same time, many fine surface defects are generated due to shot indentations. For this reason, this surface defect is removed by electropolishing, and the surface roughness is set to 4 μm or less (preferably 3 μm or less) in terms of Rc to reduce the scratch sensitivity of the coil spring. As parameters indicating the surface roughness, JIS B 0601 defines an average roughness Ra, a maximum height Rz, an average height Rc, and the like. The reason why the average height Rc is evaluated here is that Rc is a parameter calculated by averaging the heights, and is considered optimal for expressing the overall surface roughness.

また、ショットピーニングで付与される圧縮残留応力は、ショットの硬さ、大きさ、速度、ピーニング回数などにより異なるが、概ねばねの表面から2〜10μm内部で最大となる。そこで、好ましくは最表面でより最大値に近い圧縮残留応力になるように電解研磨処理によりコイルばねの表層を除去する。   The compressive residual stress imparted by shot peening varies depending on the hardness, size, speed, number of peenings, etc. of the shot, but is generally maximum within 2 to 10 μm from the spring surface. Therefore, the surface layer of the coil spring is preferably removed by electrolytic polishing so that the compressive residual stress is closer to the maximum value on the outermost surface.

以上のように、有害な白層の除去、ショットの圧痕による微細な表面欠陥の除去、および低圧縮残留応力部分の除去を実現するために、ショットピーニング工程後に電解研磨を施してコイルばねの表層を3〜20μm除去することが好ましい。表層部の除去量が3μm未満では5μm以上の白層が残存することがあるので好ましくない。また、20μm以上除去すると最表面における圧縮残留応力がかえって低下することがあるので好ましくない。より好ましくは、3〜10μm除去する。なお、上記のようにコイルばねにはショットピーニング工程のあとで低温焼き鈍しやさらにセッティングなどが施されるが、この電解研磨処理工程は、ショットピーニング工程の後であれば任意の段階で実施することができる。   As described above, the surface layer of the coil spring is subjected to electropolishing after the shot peening process in order to realize removal of harmful white layers, removal of minute surface defects due to shot indentations, and removal of low compressive residual stress portions. Is preferably removed by 3 to 20 μm. If the removal amount of the surface layer is less than 3 μm, a white layer of 5 μm or more may remain, which is not preferable. Further, if it is removed by 20 μm or more, the compressive residual stress on the outermost surface may be lowered, which is not preferable. More preferably, 3 to 10 μm is removed. In addition, as described above, the coil spring is subjected to low-temperature annealing and further setting after the shot peening process, but this electrolytic polishing treatment process should be performed at any stage after the shot peening process. Can do.

(実施例1)
コイルばねの素材として、C:0.65質量%(以下、同様)、Si:2.23%、Mn:0.54%、Cr:1.18%、V:0.15%、Co:0.20%で残部がFeと不可避不純物とからなり、引張強さが2252MPa、絞りが50%の合金鋼オイルテンパー線を用いた。
Example 1
As a material of the coil spring, C: 0.65 mass% (hereinafter the same), Si: 2.23%, Mn: 0.54%, Cr: 1.18%, V: 0.15%, Co: 0 An alloy steel oil tempered wire having a balance of Fe and inevitable impurities at 20%, tensile strength of 2252 MPa, and drawing of 50% was used.

このオイルテンパー線をコイリングし、線径:3.2mm、コイル外径:23.2mm、総巻数:5.9巻、有効巻数:3.9巻、自由高さ:47mm、ばね定数:32N/mmのコイルばねを成形した。   The oil temper wire is coiled, and the wire diameter is 3.2 mm, the coil outer diameter is 23.2 mm, the total number of windings is 5.9, the effective number of windings is 3.9, the free height is 47 mm, and the spring constant is 32 N / A coil spring of mm was formed.

次に、これらのコイルばねを450℃で7分間均熱処理してコイル成形時に生じた残留応力や残留歪みを除去した。その後、0.2mmのスティールボールを使用して20分間のマイクロショットを施して表面の酸化膜を除去した。   Next, these coil springs were soaked at 450 ° C. for 7 minutes to remove residual stress and residual strain generated during coil forming. Thereafter, a micro-shot for 20 minutes was performed using a 0.2 mm steel ball to remove the oxide film on the surface.

次に、アンモニアガス雰囲気下で500℃×4時間の窒化処理を施し、コイル表面に窒化層を形成した。窒化後の表面硬度は850〜950HVであった。   Next, nitriding treatment was performed at 500 ° C. for 4 hours in an ammonia gas atmosphere to form a nitrided layer on the coil surface. The surface hardness after nitriding was 850 to 950 HV.

窒化処理後に直径0.8mmのコンディションドカットワイヤーを使用して60分間の第1ショットピーニングを行った。続いて、直径0.25mmのコンディションドカットワイヤーをエアーで5分間投射して第2ショットピーニングを施しコイル表面に圧縮残留応力を付与した。   The first shot peening was performed for 60 minutes using a conditioned cut wire having a diameter of 0.8 mm after the nitriding treatment. Subsequently, a conditional cut wire having a diameter of 0.25 mm was projected with air for 5 minutes to give a second shot peening, thereby applying a compressive residual stress to the coil surface.

次いで、225℃×30分の低温焼き鈍しで異常に大きな内部歪みを除去した。コイルばね成形工程以後、この低温焼き鈍し工程までは成形したコイルばね全部に同様の処理を施したが、ここでは半数を電解研磨前試料として採取した。   Subsequently, abnormally large internal strain was removed by low-temperature annealing at 225 ° C. × 30 minutes. After the coil spring forming process, the same treatment was applied to all the formed coil springs until the low-temperature annealing process, but half of them were collected as samples before electropolishing.

残り半数にさらに表1の条件で電解研磨を施して表層部を5μm除去して電解研磨後試料とした。なお、電解研磨による表層部の除去厚さは、電解研磨前後のコイルばねの重量変化から計算で求めた。   The remaining half was further electropolished under the conditions shown in Table 1 to remove the surface layer portion by 5 μm, and a sample after electropolishing was obtained. In addition, the removal thickness of the surface layer part by electropolishing was calculated | required by calculation from the weight change of the coil spring before and behind electropolishing.

Figure 2009270150
Figure 2009270150

[評価]
(評価方法)
上記で得られた電解研磨前後の試料について、白層の厚さ、表面粗さ(Ra、Rz、Rc)、圧縮残留応力の分布及び疲労特性を測定した。なお、白層の厚さ、表面粗さは、コイルばねの内周側で各々数点を測定した。測定方法は以下の通りである。
(a)白層の厚さは、得られた各試料の断面を研磨し、ナイタールでエッチングして白層を明確にしてから金属顕微鏡で測定した。
(b)表面粗さ(Ra、Rz、Rc)は、JIS B 0601(2001年版)に準拠して測定した。
(c)圧縮残留応力は、X線応力測定装置(リガク社製 PSPC型)を用いてCr管球、45kV、40mAの条件で測定した。
(d)疲労特性は、星形ばね疲労試験機を用いて、平均応力:750MPa、応力振幅:700MPa、回転数:1800rpmで試験し、同時に試験に供した8個の試料のうち1×10回までに折損する試料の個数を折損確率として評価した。
[Evaluation]
(Evaluation methods)
About the sample before and behind electropolishing obtained above, the thickness of the white layer, surface roughness (Ra, Rz, Rc), distribution of compressive residual stress, and fatigue characteristics were measured. In addition, the thickness and surface roughness of the white layer were measured at several points on the inner peripheral side of the coil spring. The measuring method is as follows.
(A) The thickness of the white layer was measured with a metal microscope after the cross section of each obtained sample was polished and etched with nital to clarify the white layer.
(B) The surface roughness (Ra, Rz, Rc) was measured according to JIS B 0601 (2001 edition).
(C) The compressive residual stress was measured under the conditions of a Cr tube, 45 kV, and 40 mA using an X-ray stress measuring device (PSPC type manufactured by Rigaku Corporation).
(D) Fatigue characteristics were tested using a star spring fatigue tester at an average stress of 750 MPa, a stress amplitude of 700 MPa, and a rotation speed of 1800 rpm, and 1 × 10 7 out of 8 samples subjected to the test at the same time. The number of samples that broke by the time was evaluated as the breakage probability.

測定結果を表2に示す。   The measurement results are shown in Table 2.

Figure 2009270150
Figure 2009270150

(評価結果)
白層厚さは電解研磨前では2〜10μmとかなり厚い層として観察された。しかし電解研磨を施すことで5μm未満(0〜3μm)となり、コイルばねの耐衝撃性や疲労特性に対して無害化できた。また、表面粗さRcは電解研磨を施すことにより4.5μmから2.9μmに減少し、コイル表面が平滑化されたことが分かる。
(Evaluation results)
The white layer thickness was observed as a considerably thick layer of 2 to 10 μm before electropolishing. However, by electropolishing, the thickness was less than 5 μm (0 to 3 μm), and it was made harmless to the impact resistance and fatigue characteristics of the coil spring. Further, it can be seen that the surface roughness Rc was reduced from 4.5 μm to 2.9 μm by electrolytic polishing, and the coil surface was smoothed.

図1は電解研磨前後における表面からの深さ方向の残留応力分布を示すグラフである。A(●)は電解研磨前、B(○)は電解研磨後の残留応力分布を示す。図1に示すように電解研磨前の圧縮残留応力は表面では約1500MPaであるが、表面から5〜10μm深い位置では約1950MPaで最大となっている。ところが電解研磨により表層部の5μmが除去されたので、電解研磨後にはコイル表面が約2000MPaで最大圧縮残留応力部位となった。従って、電解研磨を施すことにより最表面の圧縮残留応力は約500MPa改善されたわけである。   FIG. 1 is a graph showing the residual stress distribution in the depth direction from the surface before and after electropolishing. A (●) represents the residual stress distribution before electropolishing and B (◯) represents the residual stress distribution after electropolishing. As shown in FIG. 1, the compressive residual stress before electropolishing is about 1500 MPa at the surface, but is maximum at about 1950 MPa at a position 5 to 10 μm deep from the surface. However, since 5 μm of the surface layer portion was removed by electropolishing, the coil surface became the maximum compressive residual stress site at about 2000 MPa after electropolishing. Therefore, the compressive residual stress on the outermost surface was improved by about 500 MPa by applying electropolishing.

疲労試験は平均応力:750MPa、応力振幅:700MPa、1×10回という苛酷な試験条件で実施したところ、コイルばねの折損確率は電解研磨前のものでは2/8であった。ところが電解研磨を施したコイルばねの折損確率は0/8であり、極めて優れた疲労特性を有することが確認できた。 The fatigue test was carried out under severe test conditions of average stress: 750 MPa, stress amplitude: 700 MPa, 1 × 10 7 times, and the breakage probability of the coil spring was 2/8 before electropolishing. However, the breakage probability of the electropolished coil spring was 0/8, and it was confirmed that the coil spring had extremely excellent fatigue characteristics.

本発明は、オートマティック車における自動変速機のクラッチとーションのダンパースプリングやエンジンの弁ばねの製造に適用して有用である。   INDUSTRIAL APPLICABILITY The present invention is useful when applied to the manufacture of a damper spring for an automatic transmission clutch and a valve spring for an engine in an automatic vehicle.

電解研磨前後における表面からの深さ方向の残留応力分布を示すグラフである。It is a graph which shows the residual stress distribution of the depth direction from the surface before and behind electropolishing.

Claims (5)

合金鋼オイルテンパー線を素材としてコイルばねを成形する成形工程と、該コイルばねの表面硬度を向上させる窒化処理工程と、該コイルばねに残留応力を付与するショットピーニング工程とを有するコイルばねの製造方法において、
前記ショットピーニング工程の後に電解研磨を施すことにより前記コイルばねの表層を除去して、前記窒化処理により生成した白層の厚さを5μm以下にするとともに、表面粗さをRcで4μm以下とし、かつ最表面の圧縮残留応力を1800MPa以上とすることを特徴とするコイルばねの製造方法。
Production of a coil spring comprising a forming step of forming a coil spring using an alloy steel oil tempered wire, a nitriding treatment step for improving the surface hardness of the coil spring, and a shot peening step for imparting residual stress to the coil spring In the method
The surface layer of the coil spring is removed by electropolishing after the shot peening process, the thickness of the white layer generated by the nitriding treatment is 5 μm or less, and the surface roughness is 4 μm or less with Rc, And the compression residual stress of the outermost surface shall be 1800 Mpa or more, The manufacturing method of the coil spring characterized by the above-mentioned.
前記窒化処理後のコイルばねの表面硬度は850〜1400HVである請求項1に記載のコイルばねの製造方法。   The method of manufacturing a coil spring according to claim 1, wherein the surface hardness of the coil spring after nitriding is 850 to 1400 HV. 前記電解研磨によりコイルばねの表層を3〜20μm除去する請求項1に記載のコイルばねの製造方法。   The method for manufacturing a coil spring according to claim 1, wherein a surface layer of the coil spring is removed by 3 to 20 μm by the electrolytic polishing. 前記合金鋼オイルテンパー線は、質量%でC:0.55〜0.75%、Si:1.00〜2.70%、Mn:0.10〜1.50%、Cr:0.4〜2.50%、V:0.05〜0.50%を含み、残部Feと不可避的不純物とからなる請求項1〜3のいずれかに記載のコイルばねの製造方法。   The alloy steel oil tempered wire is C: 0.55-0.75%, Si: 1.00-2.70%, Mn: 0.10-1.50%, Cr: 0.4-% by mass. The manufacturing method of the coil spring in any one of Claims 1-3 which contains 2.50% and V: 0.05-0.50%, and consists of remainder Fe and an unavoidable impurity. さらにMo:0.05〜2.0%、Co:0.05〜0.40%、のいずれか1種を含む請求項4に記載のコイルばねの製造方法。   Furthermore, the manufacturing method of the coil spring of Claim 4 containing any 1 type of Mo: 0.05-2.0%, Co: 0.05-0.40%.
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Cited By (3)

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CN102834540A (en) * 2010-04-14 2012-12-19 日本发条株式会社 Spring and method for producing same
JP2020159704A (en) * 2019-03-25 2020-10-01 新東工業株式会社 Method for manufacturing reference piece for measuring x-ray residual stress and reference piece for measuring x-ray residual stress
CN116463483A (en) * 2023-03-29 2023-07-21 宁波北仑博优模具技术有限公司 Shot peening strengthening method for die casting die surface

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Publication number Priority date Publication date Assignee Title
CN102834540A (en) * 2010-04-14 2012-12-19 日本发条株式会社 Spring and method for producing same
CN102834540B (en) * 2010-04-14 2015-05-27 日本发条株式会社 Spring and method for producing same
JP2020159704A (en) * 2019-03-25 2020-10-01 新東工業株式会社 Method for manufacturing reference piece for measuring x-ray residual stress and reference piece for measuring x-ray residual stress
WO2020194909A1 (en) * 2019-03-25 2020-10-01 新東工業株式会社 Method for manufacturing reference piece for x-ray measurement of residual stress and reference piece for x-ray measurement of residual stress
CN113574368A (en) * 2019-03-25 2021-10-29 新东工业株式会社 Method for manufacturing reference sheet for measuring X-ray residual stress and reference sheet for measuring X-ray residual stress
JP7059974B2 (en) 2019-03-25 2022-04-26 新東工業株式会社 Manufacturing method of reference piece for X-ray residual stress measurement and reference piece for X-ray residual stress measurement
CN116463483A (en) * 2023-03-29 2023-07-21 宁波北仑博优模具技术有限公司 Shot peening strengthening method for die casting die surface

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