JP4416861B2

JP4416861B2 - Gear surface hardening method

Info

Publication number: JP4416861B2
Application number: JP11315999A
Authority: JP
Inventors: 勝幸松井; 洋仁衛藤; 柱安藤
Original assignee: Isuzu Motors Ltd
Current assignee: Isuzu Motors Ltd
Priority date: 1999-04-21
Filing date: 1999-04-21
Publication date: 2010-02-17
Anticipated expiration: 2019-04-21
Also published as: JP2000301458A

Description

【０００１】
【発明の属する技術分野】
本発明は、機械部品である鋼材製の歯車の表面の改質硬化方法に関する。
【０００２】
【従来の技術】
自動車用歯車等の機械部品の表面改質方法として、現在、浸炭法浸炭＋ショットピーニング法、軟窒化法が用いられている。これらの技術は、例えば、特開平９−８５６２４号公報、特開平９−５７６２９号公報、特開平５−５１６２９号公報に開示されている。
【０００３】
しかし、これらの表面改質法は、下記の問題を持っている。
▲１▼浸炭法……９００℃以上の高温での長時間処理のため、熱処理歪みが大きい。
かつ、粒界酸化層や不完全焼入層等の表面異常層が発生するため、疲労強度を低下させる。
▲２▼浸炭＋ショットピーニング法……ショットピーニング法で、▲１▼の欠点の１つである表面異常層の除去や圧縮残留応力の付与で疲労強度低下をカバーできるが、熱処理歪みの問題は解決できない。
▲３▼軟窒化法……熱処理歪みは浸炭より小さいが、疲労限は浸炭以下である。
【０００４】
【発明が解決しようとする課題】
上記の問題を解決するため、本発明は輪郭高周波焼入れとダブルショットピーニングとを組み合わせた表面硬化改質方法を提案するものである。
【０００５】
【課題を解決するための手段】
本発明の歯車の表面を硬化して前記歯車の機械的強度を向上させる方法は、鋼材製の加工対象歯車の表面を硬化して前記歯車の機械的強度を向上させる方法であって、前記歯車を低周波用コイル内に位置決めし、前記歯車の輪郭に沿って低周波熱を加える輪郭低周波予熱工程と、前記輪郭低周波予熱工程の停止後における熱拡散工程と、前記熱拡散工程に引き続いて前記歯車を高周波用コイル内に位置決めし、前記歯車の輪郭に沿って高周波熱を加えた後、水溶性焼入剤を用いて前記輪郭低周波予熱工程における予熱開始温度と同程度まで急冷する焼入れ処理を行い、前記歯車の表面に表面硬化層を形成する輪郭高周波焼入れ処理工程と、前記輪郭高周波焼入れ処理工程の後に前記予熱開始温度から低温焼戻し処理を行う工程と、前記低温焼戻し処理の完了に引続いて前記歯車の表面硬化層に２段階のショットピーニング加工を施す２段階のショットピーニング処理工程と、を順次工程として実施することを特徴とするものである。
【０００８】
【発明の実施の形態】
図１は、本発明の歯車の表面硬化改質方法に使用される輪郭高周波焼入れ装置の概要を示す説明図、図２は輪郭高周波焼入れの加熱温度と焼入れの加熱サイクルを示す説明図である。
全体を符号１で示す輪郭高周波焼入れ装置は、焼入れ対象である歯車１０を囲む第１のコイル２０と、第１のコイル２０に低周波を供給する低周波電源３０を有する。
【０００９】
第１のコイル２０の下部には、第２のコイル４０が配設され、第２のコイル４０は高周波電源５０に接続される。
第２のコイル４０の下方には、焼入れタンク６０が配設され、水溶性の焼入剤によりスプレー焼入れが行われる。
【００１０】
ワークである歯車１０は、支持部材７０を介して支持装置８０に支持され、第１のコイル２０と焼入れタンク６０の間を移動する。
第１のコイル２０内に位置決めされた歯車１０は、電源３０から供給される数ＫＨｚ、１，０００ＫＷ級の低周波により、１〜２秒間予熱される。
この予熱後に、約１秒間加熱を停止し、熱拡散を行なう。
【００１１】
次に、歯車１０を第２のコイル４０に挿入し、電源５０から１００〜数百ＫＨｚの高周波を供給し、０．１〜０．３秒間歯車の輪郭に沿って本加熱する。
その後に、歯車１０を焼入れタンク６０内で水溶性焼入剤を用いて、スプレー焼入れを行なう。
焼入れ後に、低温焼戻し処理を行なう。
【００１２】
図２は、この低周波による予加熱から高周波本加熱スプレー焼入れ、低温焼戻しまでの加熱サイクルによる歯車表面の絶対温度と時間経過の関係を示している。
焼入れ処理された歯車１０は、図３に示すように表面に沿って硬化層Ｈ_１が形成されている。
【００１３】
次に、この表面に向けてショットピーニング加工を施す。
ショットピーニング加工は、２段階にわけて施される。ショットピーニング加工は、ノズル１００から投射材１１０を空気圧力により歯車及び歯底全体に投射して、表面硬化改質を施す加工である。
【００１４】
本発明にあっては、第１段のショットピーニングは直径が約０．６ｍｍで、歯車と同程度の硬さ（約６０ＨＲＣ程度）を有する鋼球を投射材として使用し、数Ｋｇ／ｃｍ^２の空気圧でショットピーニング処理を行なう。
【００１５】
次に、第２段目のショットピーニング処理として、粒径寸法が約０．０８ｍｍの鋼球を投射材として使用し、数Ｋｇ／ｃｍ^２の空気圧でショットピーニング処理を施した。
この処理により、歯車１０の歯先１２と歯元１４を含む表面直下に硬化層Ｈ_１を形成することができる。
【００１６】
図４は、以上に説明した輪郭高周波焼入れに加えて２段階のショットピーニングを施した歯車と、従来の焼入れ処理を施した歯車の硬化層の残留応力を比較したグラフである。
丸印は、ＪＩＳ機械構造用炭素鋼であるＳ５０Ｃの歯車に、本発明の処理を施したもの、三角印は、Ｓ５０Ｃの歯車に調質と輪郭高周波焼入れを施したもの、四角印は、機械構造用合金鋼であるＳＣｒ４２０Ｈの歯車に焼なまし処理と浸炭焼入れ処理を施したものを示す。
グラフは、横軸に歯車表面からの深さを、たて軸に残留応力をとったもので、本発明の処理によれば、大きな残留圧縮応力を得ることができ、歯車の疲労強度を向上することができる。
【００１７】
図５は、同様の試料による焼入れ硬化層の硬度を比較したグラフである。
横軸に硬化層の表面からの深さを、たて軸にビッカース硬度をとったものである。本発明により硬度の向上を図ることができることが示されている。
特に、歯車の強度上重要な要因である歯車表面から０．１ｍｍ程度の深さまでの硬度が向上し、強度向上の硬化を得ることができる。
次に、本発明の処理を施した歯車の寿命に対する効果向上を説明する。
【００１８】
図６は、歯車の疲労試験装置を示す。
歯車１０を支持シャフト２１０に取り付け、歯山１２を固定部材２３０と可動部材２２０の間に挾む。可動部材２２０は油圧サーボ機構により、くり返し荷重Ｖが加えられる。可動部材２２０の先端には応力検知器２２２が取り付けてある。
【００１９】
図７は、横軸にくり返し荷重Ｖのサイクル回数を、たて軸に応力範囲を示したものである。
本発明の処理を施すことで、歯車の強度と寿命が格段に向上することが判明した。
【００２０】
本発明は以上のように、鋼材製の加工対象歯車の表面を硬化して前記歯車の機械的強度を向上させる方法であって、前記歯車を低周波用コイル内に位置決めし、前記歯車の輪郭に沿って低周波熱を加える輪郭低周波予熱工程と、前記輪郭低周波予熱工程の停止後における熱拡散工程と、前記熱拡散工程に引き続いて前記歯車を高周波用コイル内に位置決めし、前記歯車の輪郭に沿って高周波熱を加えた後、水溶性焼入剤を用いて前記輪郭低周波予熱工程における予熱開始温度と同程度まで急冷する焼入れ処理を行い、前記歯車の表面に表面硬化層を形成する輪郭高周波焼入れ処理工程と、前記輪郭高周波焼入れ処理工程の後に前記予熱開始温度から低温焼戻し処理を行う工程と、前記低温焼戻し処理の完了に引続いて前記歯車の表面硬化層に２段階のショットピーニング加工を施す２段階のショットピーニング処理工程と、を順次工程として実施するものであるため、ショットピーニング加工時に歯車の歯面が欠けるようなことはなくなり、従来技術に比べて、より一層歯車表面の硬度を向上するとともに、表面直下の硬化層に大きな残留圧縮応力を生ずることができるものである。この加工により、歯車の表面硬度を向上して、小型の歯車で大きなトルクを伝達することができ、また、寿命を向上させることができる。
【図面の簡単な説明】
【図１】本発明に使用する輪郭高周波焼入れ装置の説明図。
【図２】輪郭高周波焼入れの熱サイクルの説明図。
【図３】本発明に使用するショットピーニング加工の説明図。
【図４】本発明と従来の加工を比較する硬化層の深さと残留応力を示す図。
【図５】本発明と従来の加工を比較する硬化層の深さとビッカース硬度を示す図。
【図６】歯車の耐久試験装置の説明図。
【図７】本発明と従来の加工を比較する歯車にかかる応力と寿命を示す図。
【符号の説明】
１輪郭高周波焼入れ装置
１０歯車
１２歯先
１４歯元
１００ノズル
１１０投射材[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for reforming and hardening the surface of a steel gear, which is a mechanical component.
[0002]
[Prior art]
Currently, carburizing method carburizing + shot peening method and soft nitriding method are used as surface modification methods for machine parts such as automobile gears. These techniques are disclosed in, for example, JP-A-9-85624, JP-A-9-57629, and JP-A-5-51629.
[0003]
However, these surface modification methods have the following problems.
(1) Carburizing method: The heat treatment distortion is large because of long-time treatment at a high temperature of 900 ° C. or higher.
In addition, an abnormal surface layer such as a grain boundary oxide layer or an incompletely hardened layer is generated, so that the fatigue strength is reduced.
(2) Carburizing + shot peening method: The shot peening method can cover the fatigue strength reduction by removing the abnormal surface layer and applying compressive residual stress, which is one of the disadvantages of (1). It cannot be solved.
(3) Soft nitriding method: heat treatment strain is smaller than carburizing, but fatigue limit is less than carburizing.
[0004]
[Problems to be solved by the invention]
In order to solve the above problems, the present invention proposes a surface hardening reforming method that combines contour induction hardening and double shot peening.
[0005]
[Means for Solving the Problems]
The method for hardening the surface of the gear of the present invention to improve the mechanical strength of the gear is a method for improving the mechanical strength of the gear by hardening the surface of the gear to be machined made of steel. Is positioned in the low frequency coil, and the contour low frequency preheating step of applying low frequency heat along the contour of the gear, the heat diffusion step after stopping the contour low frequency preheating step, and the heat diffusion step are continued. the gear Te was positioned in the high-frequency coil, after the high-frequency Naminetsu was pressurized example along the contour of the gear, to the same extent as the preheat start temperature in the contour low frequency preheating process using a water-soluble sintered Irizai performs quenching and quenching, the contour induction hardening treatment step of forming a surface hardened layer on the surface of the gear, and performing low-temperature tempering from the preheating starting temperature after the contour induction hardening process, the low temperature co Is characterized in that to implement a sequentially step and two-step shot peening process, the that subsequent to completion subjected to shot peening in two stages on a surface hardening layer of the gear processing.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an explanatory diagram showing an outline of a contour induction hardening apparatus used in the method for surface hardening of a gear according to the present invention, and FIG. 2 is an explanatory diagram showing a heating temperature of contour induction hardening and a heating cycle of quenching.
The contour induction hardening apparatus denoted as a whole by reference numeral 1 includes a first coil 20 surrounding a gear 10 to be quenched, and a low frequency power supply 30 for supplying a low frequency to the first coil 20.
[0009]
A second coil 40 is disposed below the first coil 20, and the second coil 40 is connected to a high frequency power supply 50.
A quenching tank 60 is disposed below the second coil 40, and spray quenching is performed with a water-soluble quenching agent.
[0010]
The gear 10, which is a workpiece, is supported by the support device 80 via the support member 70 and moves between the first coil 20 and the quenching tank 60.
The gear 10 positioned in the first coil 20 is preheated for 1 to 2 seconds by a low frequency of several KHz and 1,000 KW class supplied from the power supply 30.
After this preheating, heating is stopped for about 1 second to perform thermal diffusion.
[0011]
Next, the gear 10 is inserted into the second coil 40, a high frequency of 100 to several hundred KHz is supplied from the power source 50, and the main heating is performed along the contour of the gear for 0.1 to 0.3 seconds.
Thereafter, the gear 10 is spray-quenched in the quenching tank 60 using a water-soluble quenching agent.
After quenching, a low temperature tempering treatment is performed.
[0012]
FIG. 2 shows the relationship between the absolute temperature of the gear surface and the passage of time due to the heating cycle from preheating by this low frequency to high frequency main heating spray quenching and low temperature tempering.
Quenching the treated wheel 10, the hardened layer H ₁ along the surface as shown in FIG. 3 is formed.
[0013]
Next, a shot peening process is performed toward this surface.
Shot peening is performed in two stages. The shot peening process is a process in which the projection material 110 is projected from the nozzle 100 onto the entire gear and the bottom of the tooth by air pressure to perform surface hardening modification.
[0014]
In the present invention, the first stage shot peening uses a steel ball having a diameter of about 0.6 mm and a hardness similar to that of a gear (about 60 HRC) as a projection material, and is several Kg / cm ^2. The shot peening process is performed with the air pressure.
[0015]
Next, as a second-stage shot peening treatment, a steel ball having a particle size of about 0.08 mm was used as a projection material, and the shot peening treatment was performed with an air pressure of several kg / cm ² .
By this treatment, the hardened layer H ₁ can be formed immediately below the surface including the tooth tip 12 and the tooth root 14 of the gear 10.
[0016]
FIG. 4 is a graph comparing the residual stress of the hardened layer of a gear subjected to two-stage shot peening in addition to the contour induction hardening described above and a gear subjected to a conventional quenching process.
Circle marks are S50C gears, JIS carbon steel for machine structural use, processed according to the present invention. Triangle marks are S50C gears subjected to tempering and contour induction hardening. Square marks are machine A gear of SCr420H, which is a structural alloy steel, is subjected to annealing treatment and carburizing and quenching treatment.
The graph shows the depth from the gear surface on the horizontal axis and the residual stress on the vertical axis. According to the process of the present invention, a large residual compressive stress can be obtained and the fatigue strength of the gear is improved. can do.
[0017]
FIG. 5 is a graph comparing the hardness of the quenched and hardened layer of the same sample.
The horizontal axis represents the depth from the surface of the cured layer, and the vertical axis represents Vickers hardness. It has been shown that the present invention can improve hardness.
In particular, the hardness from the gear surface, which is an important factor in the strength of the gear, to a depth of about 0.1 mm is improved, and hardening with improved strength can be obtained.
Next, improvement in the effect on the life of the gear subjected to the processing of the present invention will be described.
[0018]
FIG. 6 shows a gear fatigue testing apparatus.
The gear 10 is attached to the support shaft 210, and the tooth 12 is sandwiched between the fixed member 230 and the movable member 220. A repetitive load V is applied to the movable member 220 by a hydraulic servo mechanism. A stress detector 222 is attached to the tip of the movable member 220.
[0019]
FIG. 7 shows the number of cycles of the repeated load V on the horizontal axis and the stress range on the vertical axis.
It has been found that the strength and life of the gears are remarkably improved by applying the treatment of the present invention.
[0020]
As described above, the present invention is a method of improving the mechanical strength of the gear by hardening the surface of the gear to be machined made of steel , wherein the gear is positioned in a low frequency coil, and the contour of the gear is determined. A contour low-frequency preheating process for applying low-frequency heat along the contour, a heat diffusion process after stopping the contour low-frequency preheating process, and positioning the gear in the high-frequency coil following the heat diffusion process, After applying high-frequency heat along the contour of the above, a quenching treatment is performed using a water-soluble quenching agent to rapidly cool to the same level as the preheating start temperature in the contour low-frequency preheating step, and a surface hardened layer is formed on the surface of the gear A contour induction hardening process to be formed, a step of performing a low temperature tempering process from the preheating start temperature after the contour induction hardening process, and a surface hardened layer of the gear following completion of the low temperature tempering process Because it is intended to implement the two-stage shot peening treatment step of performing shot peening step, successively as a step, no longer possible, such as tooth surfaces of the gear lack during the shot peening process, compared to the prior art, and more In addition to improving the hardness of the single-layer gear surface, a large residual compressive stress can be generated in the hardened layer immediately below the surface. By this processing, the surface hardness of the gear can be improved, a large torque can be transmitted with a small gear, and the life can be improved.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a contour induction hardening apparatus used in the present invention.
FIG. 2 is an explanatory diagram of a thermal cycle of contour induction hardening.
FIG. 3 is an explanatory diagram of shot peening used in the present invention.
FIG. 4 is a diagram showing the depth and residual stress of a hardened layer comparing the present invention with conventional processing.
FIG. 5 is a diagram showing the depth and Vickers hardness of a hardened layer comparing the present invention with conventional processing.
FIG. 6 is an explanatory diagram of a gear durability test apparatus.
FIG. 7 is a diagram showing stress and life applied to a gear for comparing the present invention with conventional machining.
[Explanation of symbols]
1 Contour Induction Hardening Device 10 Gear 12 Tooth Tip 14 Tooth Base 100 Nozzle 110 Projection Material

Claims

It is a method for improving the mechanical strength of the gear by hardening the surface of the gear to be processed made of steel ,
Positioning the gear in the low frequency coil and applying low frequency heat along the contour of the gear, a contour low frequency preheating step, a heat diffusion step after stopping the contour low frequency preheating step, and the heat diffusion step said gear is positioned within the RF coil subsequently, after the addition of high frequency Naminetsu along the contour of the gear, the preheating initiation temperature in the contour low frequency preheating process using a water-soluble sintered Irizai A contour induction hardening process for forming a hardened surface on the surface of the gear, quenching to a degree , a step of performing a low temperature tempering process from the preheating start temperature after the contour induction hardening process, and the low temperature and two-step shot peening process step of performing the shot peening two steps on the surface hardening layer of the gears subsequent to completion of the tempering process, to implement as a sequential process of Surface hardening method for gears according to symptoms.