JP3674437B2

JP3674437B2 - Boss gear forming method

Info

Publication number: JP3674437B2
Application number: JP2000016506A
Authority: JP
Inventors: 真義小倉
Original assignee: Sumitomo Metal Industries Ltd
Current assignee: Nippon Steel Corp
Priority date: 2000-01-26
Filing date: 2000-01-26
Publication date: 2005-07-20
Anticipated expiration: 2020-01-26
Also published as: JP2001205384A

Description

【０００１】
【発明の属する技術分野】
本発明は、歯車、より具体的には一方の端面にボスを有する平歯車やはすば歯車（以下、単にボス付き歯車という）の密閉金型を用いた冷間または温間による成形方法に関する。
【０００２】
【従来の技術】
上記のボス付き歯車は、一般に、熱間鍛造でブランクを成形し、このブランクに切削加工を施して製品とされていた。しかし、この方法は、旋削→ホブ切り→面取り→シェービング→浸炭焼入→ホーニングと製造工程が長く、コスト高につく。このため、製造工程の短縮化の要望が強く、これに応えるために、従来から金型を用いた冷間鍛造による種々の歯車成形方法の開発がなされてきた。
【０００３】
図３は、その代表的な方法の１つで、低い工具面圧での成形が可能な不完全密閉金型を用いた１段階捨て軸法と称される方法を説明するための図である。
【０００４】
すなわち、この１段階捨て軸法は、図に示すように、ダイス孔の内周面に得るべき製品の外歯に対応する歯型１ａが形成され、この歯型１ａに歯合する歯型４ａが外周面に形成された下パンチ４が歯合されたダイ１内に中空の被加工材料２を配置するとともに、被加工材料２の軸心部にその大径部が位置するようにマンドレル５を配置する。そして、この状態で内径がマンドレル５の大径部の外径よりも大きい上パンチ３により加圧し、加工中にマンドレル５と上パンチ３の内径で画成される空隙部に被加工材料２を流入させるようにした方法である。
【０００５】
この１段階捨て軸法によれば、マンドレル５と上パンチ３の内径で画成される空隙部に流入した材料６の部分をボスと見なすことができ、ボス付き歯車が成形可能である。しかし、この１段階捨で軸法は、ボス径が歯車全体の横断面積に対する面積率で約４０％以下で、しかもボス高さがボス径に応じた一定高さのボス付き歯車しか成形できないという欠点を有している。このことは、図４に示す実験結果から明らかである。
【０００６】
図４は、表１に示す化学組成を有する２鋼種のうちの鋼種Ｓ１０Ｃ製で、その寸法諸元が表２に示すヘリカル歯車を、前述した図３の上パンチ３の内径を種々変化させて室温下で成形した際における結果の一例を示す図で、横軸に平均工具面圧、縦軸にボス高さを採って示してある。
【０００７】
なお、横軸の平均工具面圧は下パンチに作用する荷重をその受圧面積で除して求められる値（ＭＰａ）、縦軸のボス高さはボスを含む全高さに対するボス高さ率（％）であり、図中の（）内値はダイ１の歯型に対する材料の充満率（％）である。
【０００８】
また、図４は、被加工材料２として、その質量がいずれも切削加工後の製品の質量の１．１倍のものを用いた場合の結果である。
【０００９】
【表１】

【表２】

この図４からわかるように、ボス径が歯車全体の横断面積に対する面積率で３３％と４０％の場合には、ダイ１の歯型１ａに対する材料の充満率が１００％になる平均工具面圧が存在する。したがって、完全な外歯を有するボス（図３中の６部分）付き歯車の成形が可能である。しかし、そのボス高さは、ボスの面積率が３３％の場合にはボスを含む全高さの４０％、４０％の場合には４７％と一定であり、これよりも高さの低いボスや高いボスは成形できない。
【００１０】
これに対し、ボスの面積率が５０％と６５％の場合には、ダイ１の歯型１ａに対する材料の充満率が１００％になる平均工具面圧が存在しない。したがって、ボスは成形されるが製品の外歯が成形されず、完全な外歯を有するボス付き歯車の成形は不可能である。なお、ボスの面積率６５％とは、ボス径が外歯の溝底径に等しいことを意味している。
【００１１】
ここで、ボスの面積率が４０％を超えると完全な外歯を有するボス付き歯車の成形が不可能になるのは、マンドレル５と上パンチ３の内径で画成される空隙部の断面積が大きすぎ、この空隙部への材料流入抵抗が不足するためである。
【００１２】
なお、図示は省略するが、表１に示す鋼種ＳＣｒ４２０Ｈの場合も、横軸の平均工具面圧がＳ１０Ｃの場合よりも変形抵抗が大きい分だけ増大するが、図４と同じ結果であった。すなわち、Ｓ１０Ｃの変形抵抗は、ひずみが１の時、４８２ＭＰａであり、ＳＣｒ４２０Ｈでは６２３ＭＰａで、その比１．３倍だけ、平均工具面圧が増大した結果であった。
【００１３】
ところが、実際に要求されるボス付き歯車には、ボスの面積率が４０％を超えるものや、４０％以下でもその高さが種々異なるものがある。具体的に例示すると、例えば自動車の手動変速機用のボス付き歯車には、表３に示すような寸法範囲のものが多い。また、その軸孔の内周面にはスプラインと称される内歯を有するものもあり、このようなボス付き歯車を高い材料歩留まりで成形することが可能な方法の開発が強く望まれていた。
【００１４】
【表３】

【発明が解決しようとする課題】
本発明の第１の目的は、ボスの面積率が６５％以下、すなわちボス径が外歯の溝底径以下で、かつその高さが種々異なるボス付き歯車を高い材料歩留まりで成形することが可能な方法を提供することにある。また、第２の目的は、得るべき製品が内歯を備えた軸孔を有する場合、全高さにわたって十分な深さを有する内歯を備えたボス付き歯車を成形することが可能な方法を提供することにある。
【００１５】
【発明が解決しようとする課題】
本発明者は、上記の課題を達成するために数多くの実験を行った。その結果、以下のことを知見した。
【００１６】
上パンチには、得るべき製品のボス径に等しい径で分割された内パンチと外パンチとからなるものを用いる必要がある。
【００１７】
内パンチと外パンチによる加圧は、内パンチの加圧面を得るべき製品のボス高さに等しい寸法だけ外パンチの加圧面から後退させた位置に初期設定して加圧する方法では不十分で、下記のいずれかに初期設定して内外パンチの両方で加圧を開始する必要がある。
【００１８】
すなわち、その１つは、内パンチの加圧面を外パンチの加圧面から所定の距離だけ後退させた位置、具体的には得るべき製品のボス高さの９０％以下の範囲内で後退させた位置に設定する。他の１つは、内外パンチの加圧面を一致させるか、または内パンチの加圧面を外パンチの加圧面から所定の距離だけ前進させた位置、具体的には得るべき製品のボス高さの３０％以下の範囲内で前進させた位置に設定する。
【００１９】
そして、内外パンチの両方による加圧開始後は、外パンチによる加圧はそのまま加工終了まで継続してよいが、内パンチによる加圧はその加圧面が初期設定位置から一定の距離だけ後退する間、所定の工具面圧に維持し、しかる後に内パンチによる加圧を解除する必要がある。
【００２０】
また、得るべきボス付き歯車が内歯を備えた軸孔を有する場合は、外径が前記の軸孔径に等しく、その外周面に製品の内歯に対応する歯型が形成されたマンドレルを被加工材料の軸心部に配置する。しかし、それだけでは不十分で、上記の内パンチによる加圧解除後における外パンチのみでの加圧による加工終了後、所定の工具面圧で内パンチによる再加圧を行う必要がある。
【００２１】
上記の知見に基づく本発明の要旨は、下記（１）〜（３）のボス付き歯車の成形方法にある。
（１）ダイス孔の内周面に製品の外歯に対応する歯型が形成されたダイと、ダイのダイス孔を閉塞する上パンチと下パンチとを具備する密閉金型を用い、ダイのダイス孔に配置された被加工材料を主に上パンチで加圧してダイス孔の隅々にまで被加工材料を完全充満させることによって一方の端面にボスを有するボス付き歯車を成形する際、前記の上パンチとして得るべき製品のボス外径と等しい径で外パンチと内パンチとに分割された分割パンチを用いるとともに、内パンチの加圧面を得るべき製品のボス高さの９０％以下の範囲内で外パンチの加圧面よりも後退させた初期設定状態で内外パンチの両方による加圧を開始し、その後外パンチによる加圧はそのまま継続する一方、内パンチによる加圧はその加圧面が前記の初期設定位置から一定の距離だけ後退するまでの間、所定の工具面圧に維持した後に内パンチによる加圧を解除し、この内パンチの加圧解除後もさらに外パンチによる加圧を継続するボス付き歯車の成形方法。
（２）ダイス孔の内周面に製品の外歯に対応する歯型が形成されたダイと、ダイのダイス孔を閉塞する主パンチと下パンチとを具備する密閉金型を用い、ダイのダイス孔に配置された被加工材料を主に主パンチで加圧してダイス孔の隅々にまで被加工材料を完全充満させることによって一方の端面にボスを有するボス付き歯車を成形する際、前記の上パンチとして得るべき製品のボス外径と等しい径で外パンチと内パンチとに分割された分割パンチを用いるとともに、内外パンチの加圧面を一致させるか、または内パンチの加圧面を得るべき製品のボス高さの３０％以下の範囲内で外パンチの加圧面よりも前進させた初期設定状態で内外パンチの両方による加圧を開始し、その後外パンチによる加圧は継続する一方、内パンチによる加圧はその加圧面が前記の初期設定位置から一定の距離だけ後退するまでの間、所定の工具面圧に維持した後に内パンチによる加圧を解除し、この内パンチの加圧解除後もさらに外パンチによる加圧を継続するボス付き歯車の成形方法。
（３）上記（１）または（２）に記載のボス付き歯車の成形方法において、得るべき製品が内歯を備えた軸孔を有する場合、被加工材料の軸心部に内パンチと下パンチの軸深部を貫通する外径が前記の軸孔径に等しく、その外周面に得るべき製品の内歯に対応する歯型が形成された形成されたマンドレルを配置する一方、内パンチによる加圧解除後における外パンチによる加圧終了後、外パンチを後退させた後に被加工材料の変形抵抗の２．７〜３．３倍の工具面圧で内パンチによる再加圧を行うボス付き歯車の成形方法。
【００２２】
上記（１）の方法においては、内外パンチによる加圧開始の前に、内パンチの加圧面を外パンチの加圧面よりも前進させた状態で加圧を行うのが好ましい。
【００２３】
また、（１）と（２）の方法における前記所定の工具面圧は、前者の場合には被加工材料の変形抵抗の２．５倍または下パンチに加わる荷重を下パンチの受圧面積で除して求められる平均工具面圧の０．８０倍以下、後者の場合には被加工材料の変形抵抗の２．１５倍または下パンチに加わる荷重を下パンチの受圧面積で除して求められる平均工具面圧の０．８０倍以下とするのが好ましい。
【００２４】
さらに、（３）の方法における内パンチによる再加圧は、被加工材料の変形抵抗の２．８〜３．１倍の工具面圧で行うのがより好ましい。
【００２５】
【発明の実施の形態】
以下、本発明のボス付き歯車の成形方法について、得るべき製品がはすば歯車の場合を例に挙げて、添付図面を参照して詳細に説明する。
【００２６】
まず始めに、本発明で用いる完全密閉型の金型について説明する。なお、従来の一段階捨て軸法で用いられる不完全密閉金型と同様の部材には、従来と同じ符号を付して説明する。
【００２７】
図１は、本発明の方法で用いる完全密閉型の金型の一例を示す模式的縦断面である。図に示すように、金型は、軸長方向の全長にわたってはすば歯車の外歯を成形するための歯型１ａがその全周面に形成されたダイス孔を有するダイ１、前記の歯型１ａに歯合する歯型４ａが外周面に形成されていてその一部が前記の歯型１ａに歯合された中空の下パンチ４、この下パンチ４の中空部に配置された中実の軸長方向に同一外径のマンドレル５０、得るべき製品のボス径と等しい径で２分割され、その内径がマンドレル５０の外径と実質的に等しい内パンチ３ａと、外径がダイ１のダイス孔径よりも大きい外パンチ３ｂで構成されている。
【００２８】
上記のダイ１は、複動プレスの基台７に対し、スラストベアリングなどの適宜な手段を介してスプリングなどの伸縮自在な部材８により、その下面が支持されている。
【００２９】
金型を構成する上記各工具のうち、下パンチ４、マンドレル５０、内パンチ３ａおよび外パンチ３ｂは、複動プレス（図示は省略するが、下方が２シリンダー、上方が３シリンダーの複動プレス）の各ラムに対して個別に連結されている。
【００３０】
なお、プレスは油圧ダイセット付きの機械式プレスであってもよい。また、内パンチ３ａが連結されたラムには、荷重計と距離計が取り付けられており、内パンチ３ａに作用する工具面圧（加圧力）と外パンチ３ｂに対する内パンチ３ａの相対移動距離が測定可能で、その工具面圧を所定の値に一定の時間保持できるようになっている。なお、荷重計は各工具に取り付けてもよく、距離計は外パンチ３ｂにも取り付けるのが望ましい。
【００３１】
次に、上記のように構成された金型によるはすば歯車の成形方法のうち、第１の方法（特許請求の範囲の欄の請求項１に記載の方法）について説明する。
【００３２】
すなわち、第１の方法においては、図１の（ａ）に示すように、内パンチ３ａの加圧面を外パンチ３ｂの加圧面よりも距離Ａだけ後退させた位置に初期設定する。また、この初期設定前または後に、被加工材料２をダイ１のダイス孔内に装入して下パンチ４上に載置する。この時、被加工材料２としては、外径がダイス孔内径と同一またはそれよりも若干小さく、内径がマンドレル５０の外径と同一またはそれよりも若干大きく、かつ質量が得るべき製品の質量に成形後の切削代に相当する質量を加えた質量のものを用いる。
【００３３】
次いで、内パンチ３ａと外パンチ３ｂを同時に下降させて両パンチの相互の位置関係を変えずに加圧を行い、内パンチ３ａの工具面圧が所定の値になるまで継続する。その後、外パンチ３ｂは外歯の高さが得るべき製品の高さに達するまで加圧を継続する。
【００３４】
一方、内パンチ３ａは、外パンチ３ｂとの一体の加圧により所定の工具面圧の値に到達してから、加圧の進行に伴って被加工材料２が塑性変形して図１（ｂ）を経て図１（ｃ）に示す状態、すなわち、内パンチ３ａの加圧面が初期設定位置から一定の距離Ｂだけ後退するまでの間、その工具面圧を所定の値に保持して加圧し、内パンチ３ａの加圧面が距離Ｂだけ後退した時点で内パンチによる加圧を解除する。
【００３５】
上記のようにして外パンチ３ｂと内パンチ３ａで被加工材料２を加圧する場合には、ボスの面積率が４０％を超える場合でも、マンドレル５０に沿った上方への材料流入量が内パンチ３ａの加圧面によって規制されるので、図１（ｃ）に示すように、ダイ１の歯型１ａに対する材料の充満率が１００％となる。
【００３６】
また、ボスの高さは、図１（ｄ）に示すように、上記内ダイス３ａによる加圧解除後も継続する外パンチ３ｂによる加圧により、材料が内ダイス３ａの抵抗を受けることなくマンドレル５０に沿って上方へ流入するので確保される。
【００３７】
この第１の方法において、上記の距離ＡとＢおよび内パンチ３ａが距離Ｂだけ後退する間保持する内パンチ３ａの工具面圧は、得るべきボス付き歯車の鋼種によっては、ひずみが１の時の変形抵抗の大きさの比で決まるだけであるが、その寸法および歯車諸元によって異なる。したがって、これらの値は、予め実験を行って適宜定める必要があるが、例えば、鋼種が前述の表１に示すＳ１０Ｃ製、歯車本体が同じく前述の表２に示すはすば歯車で、かつボスの面積率が４０％と５０％であり、ボス高さがいずれもボスを含む全高さの４０〜５０％のボス付きはすば歯車の場合、上記の距離Ａは１０ｍｍ、距離Ｂは１ｍｍとし、内パンチ３ａの加圧面が距離Ｂだけ後退する間保持する内パンチ３ａの工具面圧はボスの面積率に応じて表４に示す範囲とするのがよい。
【００３８】
【表４】

ただし、距離Ａは、得るべき製品のボス高さの９０％以下の値とする必要がある。その理由は、距離Ａが得るべき製品のボス高さの９０％を超えると、実質的に距離Ｂが確保できなくなり、下パンチ４に作用する平均工具面圧が過大になって金型が破損する恐れがある。このため、上記第１の方法では、距離Ａを得るべき製品のボス高さの９０％以下の範囲内とした。
【００３９】
なお、以上に述べた第１の方法は、ボスの面積率が大きい場合、成形途中において上部の外歯は十分に成形されるが下部の外歯が十分に成形されず、加工途中でダイ１の上部のダイス孔が大きくなることがある。その結果、得られた製品のオーバーボールダイアが上部で大きく、下部で小さくなり、用途によっては要求される寸法仕様を満たさなくなるものや、著しい場合には外歯の部分に被さり疵と称される欠陥が生じることがある。
【００４０】
例えば、上記のボスの面積率が５０％のボス付き歯車の場合、上下のオーバーボールダイア差が０．０７〜０．０９ｍｍにもなって自動車のトランスミッション用には不適なものになったり、ボスの面積率が６５％のボス付き歯車の場合、上記の欠陥が生じることがある。
【００４１】
第１の方法において生じる上記のような問題は、次の手段を講じることにより解決することができる。すなわち、その手段は、上記の初期設定状態での内外パンチの両方による加圧開始の前に、内パンチ３ａの加圧面を外パンチ３ｂの加圧面よりも前進させた状態で予備加圧を行う方法である。この予備加圧を行う場合には、被加工材料２の中央部分が主として圧縮変形し、長手方向の中央部が外側に膨らんだ形状になる。その結果、その後の加工において上記のような変形態様が生じなくなり、上下のオーバーボールダイア差の小さな製品が得られるようになる。
【００４２】
したがって、第１の方法においては、上記の初期設定状態での内外パンチの両方による加圧開始の前に、内パンチ３ａの加圧面を外パンチ３ｂの加圧面よりも前進させた状態で予備加圧を行うのが好ましい。なお、その際の予備加圧量としては、加圧前の被加工材料２の高さをＨ₀、製品の外歯の高さをＨ₁とした時、下式で定義される据込み率で１５〜２５％程度とするのがよい。
【００４３】
据込み率＝（１−Ｈ₁／Ｈ₀）×１００（％）
しかし、この予備加圧工程の付加は加工時間の増加を招くが、この問題は次に説明する第２の方法（特許請求の範囲の欄の請求項４に記載の方法）により解決できる。
【００４４】
図２は、第２の方法を説明するための図であり、この第２の方法は、図２の（ａ）に示すように、内パンチ３ａの加圧面を外パンチ３ｂの加圧面よりも距離Ｃだけ前進させた位置に初期設定した状態で内パンチ３ａと外パンチ３ｂの両方による加圧を開始し、その後は実質的に第１の方法と同じ工程を採る方法である。具体的には、外パンチ３ｂによる加圧は、第１の方法と同じく、外歯の高さが得るべき製品の高さに達するまでそのまま継続する。これに対し、内パンチ３ａによる加圧は、外パンチ３ｂと一体の加圧の進行に伴ってその工具面圧が所定の値にまで上昇した時点から被加工材料２が塑性変形して図２（ｂ）を経て図２（ｃ）に示す状態、すなわち、内パンチ３ａの加圧面が初期設定位置から一定の距離Ｄだけ後退するまでの間、その工具面圧を所定の値に保持して加圧し、内パンチ３ａの加圧面が距離Ｄだけ後退して時点で内パンチによる加圧を解除する。
【００４５】
上記のようにして外パンチ３ｂと内パンチ３ａで被加工材料２を加圧する場合には、第１の方法の場合と同様に、ボスの面積率が４０％を超える場合でも、マンドレル５０に沿った上方への材料流入量が内パンチ３ａの加圧面によって規制されるので、図２（ｃ）に示すように、ダイ１の歯型１ａに対する材料の充満率が１００％となる。
【００４６】
また、ボスの高さは、図２（ｄ）に示すように、上記内ダイス３ａによる加圧解除後も継続する外パンチ３ｂによる加圧により、材料が内ダイス３ａの抵抗を受けることなくマンドレル５０に沿って上方へ流入するので確保される。
【００４７】
さらに、加圧の初期に内パンチ３ａによる加圧を受けて被加工材料２の中央部分が圧縮変形し、その材料形状が長手方向の中央部が外側に膨らんだ形状になるので、上下のオーバーボールダイア差の小さな製品が得られる。
【００４８】
この第２の方法においても、第１の方法の場合同様に、上記の距離ＣとＤおよび内パンチ３ａが距離Ｄだけ後退する間保持する内パンチ３ａの工具面圧は、得るべきボス付き歯車の鋼種によっては、ひずみが１の時の変形抵抗の大きさの比で決まるだけであるが、その寸法および歯車諸元によって異なる。したがって、これらの値は、予め実験を行って適宜定める必要があるが、例えば、鋼種が前述の表１に示すＳ１０Ｃ製、歯車本体が同じく前述の表２に示すはすば歯車で、かつボスの面積率が４０％、５０％および６５％であり、ボス高さがボスを含む全高さの３０〜５０％のボス付きはすば歯車の場合、上記の距離ＣとＤはいずれも１ｍｍとし、内パンチ３ａの加圧面が距離Ｄだけ後退する間保持する内パンチ３ａの工具面圧はボスの面積率に応じて表５に示す範囲とするのがよい。
【００４９】
【表５】

ただし、距離Ｃは、得るべき製品のボス高さの３０％以下の値とする必要がある。その理由は、距離Ｃが得るべき製品のボス高さの３０％を超えると、必要なボス高さが確保できなくなる。このため、この第２の方法では、距離Ｃを得るべき製品のボス高さの３０％以下の範囲内とした。
【００５０】
なお、この第２の方法においては、内外パンチの加圧面の初期位置を上記のように設定する必要は必ずしもなく、外パンチ３ｂの加圧面と内パンチ３ａの加圧面を一致させて両パンチによる加圧を開始しするようにしてもよい。しかし、この場合には、得られた製品の上下のオーバーボールダイア差が、第１の方法によった場合よりも小さいものの若干大きくなる。このため、その初期設定位置は上記のようにするのが好ましい。
【００５１】
次に、第３の方法（特許請求の範囲の欄の請求項６に記載の方法）について説明する。この第３の方法は、上記の第１の方法または第２の方法により、軸孔の内周面にスプラインと称される軸長方向に平行な内歯が形成されたボス付き歯車を成形する方法である。
【００５２】
したがって、この第３の方法においては、図１と図２に示すマンドレル５０に代えて、図示は省略するが、その外周面に得るべき製品の内歯に対応する歯型が形成されたマンドレルを用いる。しかし、この場合、上記の第１の方法または第２の方法によっただけでは、外歯に対向する部分の内歯は成形されるものの、ボスに対向する部分の内歯、なかでもボスの上部に対向する部分の内歯は成形されない。これは、内パンチ３ａによる加圧解除後も継続される外パンチ３ｂによる加圧時における被加工材料２の軸方向への変形量が径方向への変形量よりも大きく、マンドレルに形成された歯型の凹部に対して材料が十分に充満しないためである。
【００５３】
このため、この第３の方法では、内パンチ３ａによる加圧解除後も継続される外パンチ３ｂによる加圧終了（図１と図２の（ｄ））後、外パンチ３ｂを後退させ、しかる後に内パンチ３ａによる再加圧を行うこととした。
【００５４】
しかし、この内パンチ３ａによる再加圧時の加圧力、すなわち内パンチ３ａの工具面圧が適切でないと、必要とされる内歯は成形されない。したがって、内パンチ３ａによる再加圧時におけるその工具面圧は所定の値に設定する必要があるが、この値は必要とされる内歯の材料充満率によって異なる。
【００５５】
このため、その工具面圧は、予め実験を行って適宜定める必要があるが、例えば、鋼種が前述の表１に示すＳ１０Ｃ製、歯車本体が同じく前述の表２に示すはすば歯車で、内歯の大径（内歯の溝底径）が３５ｍｍ、小径（軸孔径）が３３ｍｍ、歯数が２４であり、かつボスの面積率が４０％、５０％および６５％で、ボス高さがボスを含む全高さの３０〜５０％の内歯を有すボス付きはすば歯車の場合、その工具面圧は要求される内歯の材料充満率に応じて表６に示す値以上とするのがよい。
【００５６】
ただし、金型の寿命を考慮した場合、その上限は３．３倍以下、より好ましくは３．１倍以下とするのがよい。これは、前述の表１に示す２鋼種のうち、鋼種ＳＣｒ４２０Ｈの場合、その工具面圧がＳＣｒ４２０Ｈの変形抵抗の３．３倍を超えると金型が破損する恐れがあるからである。
【００５７】
【表６】

なお、以上の説明は、外歯がはすば歯車の場合であるが、外歯が平歯車の場合にはダイ１と下パンチ４に形成する歯型を平歯車用にすることにより、成形可能である。
【００５８】
【実施例】
《実施例１》
鋼種が前述の表１に示すＳ１０Ｃ、歯車本体が前述の表２に示す寸法、ボスの面積率が４０％と５０％で、ボス高さがボスを含む全高さの４０〜５０％のボス付きはすば歯車を第１の方法によって成形した。
【００５９】
その際、内パンチ３ａの加圧面は外パンチ３ｂの加圧面よりも１０ｍｍ後退した位置に初期設定した。また、内パンチ３ａによる加圧は、工具面圧を種々変え、その加圧面が初期設定位置から１ｍｍ後退する間、一定に保持して加圧した。
【００６０】
なお、被加工材料２には、いずれの場合も、外径５５．１ｍｍ、内径３５．２ｍｍ、高さ３０．５ｍｍのものを用いた。
【００６１】
そして、各条件のもとに成形して得られたボス付きはすば歯車の外歯の材料充満率、ボス高さを調べる一方、各条件下での据込み率と下パンチ４の平均工具面圧も併せて調べた。
【００６２】
以上の調査結果を、成形条件と合わせて表７に示した。
【００６３】
【表７】

表７からわかるように、ボスの面積率が４０％のものは、いずれの条件においても外歯の材料充満率１００％、ボス高さ４０％以上のものが得られたが、試番３は下パンチ４の平均工具面圧が被加工材料の変形抵抗の３．３倍と過大なため、鋼種がＳ１０Ｃの場合には問題ないが、ＳＣｒ４２０Ｈの場合では金型破損の恐れがあった。
【００６４】
また、ボスの面積率が５０％のものは、いずれの条件においてもボス高さ４０％以上のものが得られた。しかし、試番４〜６では外歯の材料充満率が６０％以下のものしか得られず、試番１４と１５では外歯の材料充満率は１００％であるが、下パンチ４の平均工具面圧が被加工材料の変形抵抗の３．３倍と過大なため、金型破損の恐れがあった。
【００６５】
以上のことは、第１の方法によって上記の鋼種、寸法のボス付きはすば歯車を成形する場合における内パンチ３ａの工具面圧としては、前述した表４に示す範囲に設定するのがよいことを意味している。
【００６６】
なお、表７中への記載は省略したが、各試番のうち、良否判定結果が良の製品の上下のオーバーボールダイア差は、０．０７〜０．０９ｍｍであった。
【００６７】
《実施例２》
鋼種が前述の表１に示すＳ１０Ｃ、歯車本体が前述の表２に示す寸法、ボスの面積率が４０％、５０％および６５％で、ボス高さがボスを含む全高さの３０〜５０％のボス付きはすば歯車を第２の方法によって成形した。
【００６８】
その際、内パンチ３ａの加圧面は外パンチ３ｂの加圧面よりも１ｍｍ前進した位置に初期設定した。また、内パンチ３ａによる加圧は、工具面圧を種々変え、その加圧面が初期設定位置から１ｍｍ後退する間、一定に保持して加圧した。
【００６９】
ただし、試番２６は０．５ｍｍ、試番２７は０．３ｍｍ、試番２８は０．２ｍｍ、試番２９と３０は０．１ｍｍ、試番３１〜３５は４ｍｍ、内パンチの加圧面が初期設定位置から後退する間、その工具面圧を一定に保持して加圧した。これは、ボス成形前に外歯の材料充満率を高めながらボス高さ率を上昇させることを意図したものである。
【００７０】
なお、被加工材料２には、いずれの場合も、外径５５．１ｍｍ、内径３５．２ｍｍ、高さ３０．５ｍｍのものを用いた。
【００７１】
そして、各条件のもとに成形して得られたボス付きはすば歯車の外歯の材料充満率、ボス高さを調べる一方、各条件下での据込み率と下パンチ４の平均工具面圧も併せて調べた。
【００７２】
以上の調査結果を、成形条件と合わせて表８に示した。
【００７３】
【表８】

表８からわかるように、ボスの面積率が４０％のものは、いずれの条件においても外歯の材料充満率は１００％のものが得られるが、試番１９と２０は目標の３０％以上のボス高さは得られなかった。
【００７４】
また、ボスの面積率が５０％のものは、試番２１〜２９ではボス高さ３０％以上のものが得られたが、そのうち試番２１と２２は外歯の材料充満率が８５％以下のものしか得られなかった。また、試番３０は外歯の材料充満率は１００％であるが、目標の３０％以上のボス高さは得られなかった。
【００７５】
さらに、ボスの面積率が６５％のものは、試番３１〜３８ではボス高さ３０％以上のものが得られたが、そのうち試番３１と３２は外歯の材料充満率が６０％以下のものしか得られなかった。また、試番３９は外歯の材料充満率は１００％であるが、目標の３０％以上のボス高さは得られなかった。
【００７６】
以上のことは、第２の方法によって上記の鋼種、寸法のボス付きはすば歯車を成形する場合における内パンチ３ａの工具面圧としては、前述した表５に示す範囲に設定するのがよいことを意味している。
【００７７】
なお、表８中への記載は省略したが、各試番のうち、良否判定結果が良の製品の上下のオーバーボールダイア差は、０．０２〜０．０４ｍｍであり、第１の方法によった場合に比べ大幅に小さく、自動車のトランスミッション用として十分な寸法精度を有していた。
【００７８】
《実施例３》
鋼種が前述の表１に示すＳ１０Ｃ、歯車本体が前述の表２に示す寸法、ボスの面積率が４０％、５０％および６５％で、ボス高さがボスを含む全高さの３０〜５０％であり、内径（小径）３３ｍｍの軸孔の内周面に溝底径（大径）が３５ｍｍ、歯数が２４の内歯を有するボス付きはすば歯車を第３の方法によって成形した。
【００７９】
その際、内パンチ３ａによる再加圧までの工程は、上記の実施例２における試番２４と同じとし、外パンチ３ｂを後退させた後、種々異なる工具面圧で再加圧した。
【００８０】
そして、各条件のもとに成形して得られたボス付きはすば歯車の内歯全体とボスに対向する部分の内歯の材料充満率を調べた。その結果、内歯全体とボスに対向する部分の内歯の材料充満率は、ボスの面積率にかかわらず同じであり、表９に示す通りであった。
【００８１】
【表９】

この表９から明らかなように、内歯の材料充満率は再加圧時の内パンチの工具面圧によって異なり、例えば、一般に、製品として許容される内歯全体の材料充満率が８０％以上のものを得るためには、被加工材料の変形抵抗の２．７倍以上の工具面圧で加圧する必要があり、１００％のものを得るためには２．８倍以上の工具面圧で加圧する必要があることがわかる。
【００８２】
このことは、第３の方法によって上記の鋼種、寸法の内歯を有するボス付きはすば歯車を成形する場合における再加圧時の内パンチ３ａの工具面圧としては、前述した表６に示す範囲に設定するのがよいことを意味している。
【００８３】
なお、表６の説明おける上限値３．３は、前述の実施例１で述べたように、これを超えると鋼種がＳＣｒ４２０Ｈの場合に金型破損の恐れあり、金型破損を確実に避ける観点からは３．１倍以下であることが望ましいことから定めた値である。
【００８４】
以上の実施例１〜３の結果から明らかなように、本発明によれば、ボスの面積率が４０％を超えるものは勿論、４０％以下のものであっても、製品のボスの面積率に応じて内パンチの工具面圧を適正に設定することにより、高さの異なるボスを有し、さらには適正な材料充満率の内歯を有するボス付き歯車を成形することが可能なことがわかる。
【００８５】
【発明の効果】
本発明によれば、外径が外歯の溝底径以下で高さが種々異なるボス、さらにはその軸孔の内周面に内歯を有する高寸法精度のボス付き歯車を高い材料歩留まりで高能率に製造することができる。
【図面の簡単な説明】
【図１】本発明の第１の方法を説明するための図である。
【図２】本発明の第２の方法を説明するための図である。
【図３】従来の一段階捨て軸法を説明するための図である。
【図４】従来の一段階捨て軸法により面積率が異なるボス付き歯車を成形した場合における結果の一例を示す図である。
【符号の説明】
１：ダイ、
２：被加工材料、
３：上パンチ、
３ａ：内パンチ、
３ｂ：外パンチ、
４：下パンチ、
５、５０：マンドレル、
６：材料（ボスに相当）、
７：基台、
８：伸縮自在な部材。[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a cold or warm forming method using a gear, more specifically, a spur gear or a helical gear having a boss on one end face (hereinafter simply referred to as a bossed gear). .
[0002]
[Prior art]
The above bossed gear is generally made into a product by forming a blank by hot forging and cutting the blank. However, this method requires a long process of turning, hobbing, chamfering, shaving, carburizing and quenching, honing, and high cost. For this reason, there is a strong demand for shortening the manufacturing process, and in order to meet this demand, various gear forming methods by cold forging using a mold have been conventionally developed.
[0003]
FIG. 3 is a diagram for explaining a method called a one-stage scraping shaft method using an incompletely sealed mold capable of forming with a low tool surface pressure as one of the representative methods. .
[0004]
That is, in this one-stage scraping shaft method, as shown in the figure, a tooth mold 1a corresponding to the external teeth of the product to be obtained is formed on the inner peripheral surface of the die hole, and the tooth mold 4a meshing with this tooth mold 1a. The hollow workpiece material 2 is disposed in the die 1 meshed with the lower punch 4 formed on the outer peripheral surface, and the mandrel 5 is positioned so that the large diameter portion is positioned at the axial center portion of the workpiece material 2. Place. In this state, pressure is applied by the upper punch 3 whose inner diameter is larger than the outer diameter of the large-diameter portion of the mandrel 5, and the workpiece 2 is placed in the gap defined by the inner diameter of the mandrel 5 and the upper punch 3 during processing. This is a method of making it flow.
[0005]
According to this one-stage scraping shaft method, the portion of the material 6 that has flowed into the gap defined by the inner diameter of the mandrel 5 and the upper punch 3 can be regarded as a boss, and a gear with a boss can be formed. However, with this one-stage shaft method, the boss diameter is about 40% or less in terms of the area ratio relative to the cross-sectional area of the entire gear, and the boss height can only be formed with a boss-equipped gear whose height corresponds to the boss diameter. Has drawbacks. This is clear from the experimental results shown in FIG.
[0006]
4 is made of steel grade S10C of the two steel grades having the chemical composition shown in Table 1, the dimensions of the helical gear shown in Table 2 are changed by changing the inner diameter of the upper punch 3 in FIG. It is a figure which shows an example of the result at the time of shape | molding at room temperature, and has shown taking the average tool surface pressure on the horizontal axis, and the boss height on the vertical axis | shaft.
[0007]
The average tool surface pressure on the horizontal axis is a value (MPa) obtained by dividing the load acting on the lower punch by the pressure receiving area, and the boss height on the vertical axis is the boss height ratio (% The value in parentheses in the figure is the material filling rate (%) with respect to the tooth type of the die 1.
[0008]
FIG. 4 shows the results when the material 2 to be processed has a mass that is 1.1 times the mass of the product after cutting.
[0009]
[Table 1]

[Table 2]

As can be seen from FIG. 4, when the boss diameter is 33% and 40% in terms of the area ratio relative to the cross-sectional area of the entire gear, the average tool surface pressure at which the filling ratio of the material to the tooth mold 1a of the die 1 is 100%. Exists. Therefore, it is possible to form a gear with a boss (six parts in FIG. 3) having complete external teeth. However, the height of the boss is constant at 40% of the total height including the boss when the area ratio of the boss is 33% and 47% when the area ratio of the boss is 40%. High bosses cannot be molded.
[0010]
On the other hand, when the area ratio of the boss is 50% and 65%, there is no average tool surface pressure at which the filling ratio of the material with respect to the tooth mold 1a of the die 1 becomes 100%. Accordingly, the boss is formed but the external teeth of the product are not formed, and it is impossible to form a bossed gear having complete external teeth. The boss area ratio of 65% means that the boss diameter is equal to the groove bottom diameter of the external teeth.
[0011]
Here, when the area ratio of the boss exceeds 40%, it becomes impossible to form a gear with a boss having complete external teeth because the cross-sectional area of the gap defined by the inner diameter of the mandrel 5 and the upper punch 3 is not possible. This is because the material inflow resistance to the gap is insufficient.
[0012]
In addition, although illustration is abbreviate | omitted, also in the case of steel type SCr420H shown in Table 1, although the deformation | transformation resistance increases by the amount of deformation resistance larger than the case where the average tool surface pressure of a horizontal axis is S10C, it was the same result as FIG. That is, the deformation resistance of S10C was 482 MPa when the strain was 1, and 623 MPa for SCr420H, which was a result of increasing the average tool surface pressure by 1.3 times the ratio.
[0013]
However, bossed gears that are actually required include those with an area ratio of boss exceeding 40%, and those with different heights even when the ratio is 40% or less. Specifically, for example, there are many boss-equipped gears for a manual transmission of an automobile, for example, in the size range shown in Table 3. Also, some of the inner peripheral surfaces of the shaft holes have internal teeth called splines, and development of a method capable of forming such bossed gears with a high material yield has been strongly desired. .
[0014]
[Table 3]

[Problems to be solved by the invention]
A first object of the present invention is to form gears with bosses having a boss area ratio of 65% or less, that is, boss diameters being less than or equal to the groove bottom diameters of external teeth and having different heights with high material yield. It is to provide a possible method. In addition, the second object is to provide a method capable of forming a bossed gear with internal teeth having a sufficient depth over the entire height when the product to be obtained has a shaft hole with internal teeth. There is to do.
[0015]
[Problems to be solved by the invention]
The inventor conducted a number of experiments in order to achieve the above-described problem. As a result, the following was found.
[0016]
For the upper punch, it is necessary to use an upper punch composed of an inner punch and an outer punch divided by a diameter equal to the boss diameter of the product to be obtained.
[0017]
Pressing with the inner punch and the outer punch is insufficient in the method of initially setting and pressing at a position retracted from the pressing surface of the outer punch by a dimension equal to the boss height of the product to obtain the pressing surface of the inner punch, It is necessary to initially set to one of the following and start pressurization with both internal and external punches.
[0018]
That is, one of them is that the pressure surface of the inner punch is retracted by a predetermined distance from the pressure surface of the outer punch, specifically within a range of 90% or less of the boss height of the product to be obtained. Set to position. The other one is that the pressure surfaces of the inner and outer punches are made to coincide, or that the pressure surface of the inner punch is advanced by a predetermined distance from the pressure surface of the outer punch, specifically the boss height of the product to be obtained. Set to a position advanced within 30% or less.
[0019]
After pressurization by both the inner and outer punches, pressurization by the outer punch may continue as it is until the end of processing, but pressurization by the inner punch is performed while the pressurization surface is retracted by a certain distance from the initial setting position. It is necessary to maintain a predetermined tool surface pressure and then release the pressurization by the inner punch.
[0020]
In addition, when the bossed gear to be obtained has a shaft hole with inner teeth, the outer diameter is equal to the shaft hole diameter, and a mandrel having a tooth shape corresponding to the inner teeth of the product formed on the outer peripheral surface thereof is covered. Arranged at the axial center of the workpiece. However, that alone is not sufficient, and it is necessary to perform re-pressurization with the inner punch at a predetermined tool surface pressure after the completion of pressurization with only the outer punch after releasing the pressure with the inner punch.
[0021]
The gist of the present invention based on the above knowledge is the following (1) to (3) bossed gear forming method.
(1) Using a die having a die having a tooth die corresponding to the external teeth of the product formed on the inner peripheral surface of the die hole, and an upper punch and a lower punch for closing the die hole of the die. When forming a boss-equipped gear having a boss on one end face by pressurizing the work material arranged in the die hole mainly with an upper punch and completely filling the work material to every corner of the die hole, Use a split punch divided into an outer punch and an inner punch with a diameter equal to the outer diameter of the boss of the product to be obtained as the upper punch, and a range of 90% or less of the boss height of the product to obtain the pressure surface of the inner punch In the initial setting state where the inner punch is retreated from the pressure surface of the outer punch, pressurization by both the inner and outer punches is started, and then pressurization by the outer punch is continued as it is, while pressurization by the inner punch From the default setting position The boss-equipped gear that releases the pressure by the inner punch after maintaining the predetermined tool surface pressure until it retreats by a certain distance, and continues the pressure by the outer punch after releasing the pressure of the inner punch. Molding method.
(2) Using a die having a die having a tooth mold corresponding to the external teeth of the product formed on the inner peripheral surface of the die hole, a main punch for closing the die hole of the die, and a lower punch. When forming a boss-equipped gear having a boss on one end surface by pressurizing the work material arranged in the die hole mainly with a main punch and completely filling the work material to every corner of the die hole, Use a split punch divided into an outer punch and an inner punch with a diameter equal to the outer diameter of the boss of the product to be obtained as an upper punch, and make the pressure surfaces of the inner and outer punches coincide or obtain the pressure surface of the inner punch Pressing by both the inner and outer punches is started in the initial setting state advanced from the pressing surface of the outer punch within a range of 30% or less of the boss height of the product, and then pressing by the outer punch continues while Pressing with a punch The pressure applied by the inner punch is released after maintaining the predetermined tool surface pressure until the pressure surface is retracted by a certain distance from the initial setting position. After the pressure release of the inner punch is further released by the outer punch. A method of forming a gear with a boss that continues pressurization.
(3) In the method for forming a gear with a boss described in (1) or (2) above, when the product to be obtained has a shaft hole provided with internal teeth, an inner punch and a lower punch are formed in the shaft center portion of the work material. An outer diameter penetrating the deep part of the shaft is equal to the shaft hole diameter, and a mandrel formed with a tooth mold corresponding to the inner teeth of the product to be obtained is arranged on the outer peripheral surface, while pressure release by the inner punch is arranged. After completion of pressurization by the outer punch, forming a gear with a boss that performs repressurization by the inner punch with a tool surface pressure of 2.7 to 3.3 times the deformation resistance of the work material after the outer punch is retracted Method.
[0022]
In the above method (1), it is preferable to perform pressurization in a state in which the pressurization surface of the inner punch is advanced from the pressurization surface of the outer punch before the start of pressurization by the inner and outer punches.
[0023]
In the former case, the predetermined tool surface pressure in the methods (1) and (2) is 2.5 times the deformation resistance of the material to be processed or the load applied to the lower punch is divided by the pressure receiving area of the lower punch. 0.80 times or less of the average tool surface pressure obtained by the above, in the latter case, 2.15 times the deformation resistance of the work material or the average obtained by dividing the load applied to the lower punch by the pressure receiving area of the lower punch It is preferably 0.80 times or less of the tool surface pressure.
[0024]
Furthermore, it is more preferable that the re-pressurization by the inner punch in the method (3) is performed at a tool surface pressure that is 2.8 to 3.1 times the deformation resistance of the work material.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the method for forming a boss-equipped gear according to the present invention will be described in detail with reference to the accompanying drawings, taking as an example the case where the product to be obtained is a helical gear.
[0026]
First, a completely sealed mold used in the present invention will be described. In addition, the same code | symbol as the past is attached | subjected and demonstrated to the member similar to the incomplete sealing metal mold | die used with the conventional one-stage scraping shaft method.
[0027]
FIG. 1 is a schematic longitudinal section showing an example of a completely sealed mold used in the method of the present invention. As shown in the figure, the die is a die 1 having a die hole in which a tooth die 1a for forming external teeth of a helical gear is formed on the entire peripheral surface over the entire length in the axial length direction, and the tooth A hollow lower punch 4 in which a tooth mold 4a meshing with the mold 1a is formed on the outer peripheral surface and a part thereof is meshed with the tooth mold 1a, and a solid disposed in the hollow portion of the lower punch 4 The mandrel 50 having the same outer diameter in the axial direction of the inner punch 3a is divided into two parts with a diameter equal to the boss diameter of the product to be obtained, the inner punch 3a having an inner diameter substantially equal to the outer diameter of the mandrel 50, and the outer diameter of the die 1 The outer punch 3b is larger than the die hole diameter.
[0028]
The lower surface of the die 1 is supported on a base 7 of a double-acting press by a stretchable member 8 such as a spring through an appropriate means such as a thrust bearing.
[0029]
Of the above-mentioned tools constituting the mold, the lower punch 4, the mandrel 50, the inner punch 3a and the outer punch 3b are double-acting presses (not shown, but a double-acting press with two cylinders below and three cylinders above) ) Individually connected to each ram.
[0030]
The press may be a mechanical press with a hydraulic die set. Further, a load meter and a distance meter are attached to the ram to which the inner punch 3a is connected. The tool surface pressure (pressing force) acting on the inner punch 3a and the relative movement distance of the inner punch 3a with respect to the outer punch 3b are determined. The tool surface pressure can be kept at a predetermined value for a certain period of time. The load meter may be attached to each tool, and the distance meter is preferably attached to the outer punch 3b.
[0031]
Next, a description will be given of a first method (a method according to claim 1 in the column of claims) of a method for forming a helical gear by a metal mold configured as described above.
[0032]
That is, in the first method, as shown in FIG. 1A, the pressure surface of the inner punch 3a is initially set to a position that is set back by the distance A from the pressure surface of the outer punch 3b. Further, before or after the initial setting, the work material 2 is inserted into the die hole of the die 1 and placed on the lower punch 4. At this time, the workpiece 2 has an outer diameter equal to or slightly smaller than the inner diameter of the die hole, an inner diameter equal to or slightly larger than the outer diameter of the mandrel 50, and a mass to be obtained. A mass having a mass corresponding to a cutting allowance after molding is added.
[0033]
Next, the inner punch 3a and the outer punch 3b are lowered at the same time to perform pressurization without changing the positional relationship between the two punches, and continue until the tool surface pressure of the inner punch 3a reaches a predetermined value. Thereafter, the outer punch 3b continues to be pressurized until the height of the outer teeth reaches the height of the product to be obtained.
[0034]
On the other hand, the inner punch 3a reaches a predetermined tool surface pressure value by integral pressurization with the outer punch 3b, and then the workpiece 2 is plastically deformed with the progress of pressurization, and FIG. ) Through the state shown in FIG. 1C, that is, until the pressing surface of the inner punch 3a is retracted by a certain distance B from the initial setting position, the tool surface pressure is maintained at a predetermined value and pressed. When the pressure surface of the inner punch 3a is retracted by the distance B, the pressure applied by the inner punch is released.
[0035]
In the case where the workpiece 2 is pressurized with the outer punch 3b and the inner punch 3a as described above, even if the area ratio of the boss exceeds 40%, the amount of material flowing upward along the mandrel 50 is increased. Since it is regulated by the pressing surface of 3a, as shown in FIG. 1 (c), the filling rate of the material with respect to the tooth mold 1a of the die 1 is 100%.
[0036]
Further, as shown in FIG. 1 (d), the height of the boss is adjusted so that the material is not subjected to the resistance of the inner die 3a due to the pressure applied by the outer punch 3b which continues even after the pressure release by the inner die 3a. This is ensured because it flows upward along the line 50.
[0037]
In this first method, the tool surface pressure of the inner punch 3a held while the distances A and B and the inner punch 3a are retracted by the distance B depends on the steel type of the bossed gear to be obtained. It depends only on the ratio of the magnitude of the deformation resistance of the motor, but varies depending on its dimensions and gear specifications. Therefore, these values need to be determined as appropriate by conducting experiments in advance. For example, the steel grade is S10C shown in Table 1 above, the gear body is a helical gear shown in Table 2 above, and the boss In the case of a helical gear with a boss whose area ratio is 40% and 50% and the boss height is 40 to 50% of the total height including the boss, the distance A is 10 mm and the distance B is 1 mm. The tool surface pressure of the inner punch 3a held while the pressure surface of the inner punch 3a is retracted by the distance B is preferably in the range shown in Table 4 according to the area ratio of the boss.
[0038]
[Table 4]

However, the distance A needs to be 90% or less of the boss height of the product to be obtained. The reason is that if the distance A exceeds 90% of the boss height of the product to be obtained, the distance B cannot be secured substantially, the average tool surface pressure acting on the lower punch 4 becomes excessive, and the die is damaged. There is a fear. Therefore, in the first method, the distance A is set within a range of 90% or less of the boss height of the product to be obtained.
[0039]
In the first method described above, when the area ratio of the boss is large, the upper external teeth are sufficiently formed in the middle of forming, but the lower external teeth are not sufficiently formed, and the die 1 is processed in the middle of processing. The die hole at the top of the may become large. As a result, the overball diamond of the obtained product is large at the upper part and smaller at the lower part, so that it does not meet the required dimensional specification depending on the application, and in the case of remarkable, it is called the covering tooth. Defects may occur.
[0040]
For example, in the case of a gear with a boss where the area ratio of the boss is 50%, the difference between the upper and lower overball diamonds is 0.07 to 0.09 mm, which is not suitable for an automobile transmission. In the case of a bossed gear with an area ratio of 65%, the above defects may occur.
[0041]
The above-mentioned problem that occurs in the first method can be solved by taking the following measures. That is, the means performs pre-pressurization in a state where the pressure surface of the inner punch 3a is advanced from the pressure surface of the outer punch 3b before the pressurization by both the inner and outer punches in the initial setting state is started. Is the method. When this pre-pressurization is performed, the central portion of the work material 2 is mainly compressed and deformed, and the central portion in the longitudinal direction swells outward. As a result, the above-described deformation mode does not occur in subsequent processing, and a product with a small difference between the upper and lower overball diamonds can be obtained.
[0042]
Therefore, in the first method, prior to the start of pressurization by both the inner and outer punches in the above-described initial setting state, preliminary pressurization is performed with the pressure surface of the inner punch 3a advanced from the pressure surface of the outer punch 3b. It is preferable to apply pressure. In addition, as the pre-pressurization amount at that time, the height of the work material 2 before pressurization is H ₀ The height of the external teeth of the product is H ₁ In this case, the upsetting rate defined by the following formula is preferably about 15 to 25%.
[0043]
Upsetting rate = (1-H ₁ / H ₀ ) X 100 (%)
However, the addition of this pre-pressurization step leads to an increase in processing time, but this problem can be solved by the second method described below (the method described in claim 4 in the claims).
[0044]
FIG. 2 is a diagram for explaining the second method. In the second method, as shown in FIG. 2A, the pressure surface of the inner punch 3a is set to be higher than the pressure surface of the outer punch 3b. This is a method in which pressurization by both the inner punch 3a and the outer punch 3b is started in a state initially set at a position advanced by a distance C, and thereafter, substantially the same process as the first method is taken. Specifically, the pressurization by the outer punch 3b is continued as it is until the height of the outer teeth reaches the height of the product to be obtained, as in the first method. On the other hand, pressurization by the inner punch 3a is caused by plastic deformation of the work material 2 from the time when the tool surface pressure rises to a predetermined value as the pressurization integrated with the outer punch 3b proceeds. 2B, the tool surface pressure is maintained at a predetermined value until the state shown in FIG. 2C, that is, until the pressure surface of the inner punch 3a is retracted by a certain distance D from the initial setting position. When the pressure is applied and the pressure surface of the inner punch 3a is retracted by the distance D, the pressure applied by the inner punch is released.
[0045]
When pressurizing the workpiece 2 with the outer punch 3b and the inner punch 3a as described above, even when the area ratio of the boss exceeds 40%, as in the case of the first method, it follows the mandrel 50. Since the material inflow amount to the upper side is regulated by the pressing surface of the inner punch 3a, the filling rate of the material with respect to the tooth mold 1a of the die 1 is 100% as shown in FIG.
[0046]
Further, as shown in FIG. 2 (d), the height of the boss is adjusted so that the material is not subjected to the resistance of the inner die 3a due to the pressure applied by the outer punch 3b which continues after the pressure release by the inner die 3a. This is ensured because it flows upward along the line 50.
[0047]
Furthermore, since the central portion of the work material 2 is compressed and deformed by the pressurization by the inner punch 3a in the initial stage of pressurization, and the material shape becomes a shape in which the central portion in the longitudinal direction bulges outward, A product with a small ball diamond difference is obtained.
[0048]
Also in this second method, as in the case of the first method, the above-mentioned distances C and D and the tool surface pressure of the inner punch 3a held while the inner punch 3a is retracted by the distance D are the bossed gears to be obtained. Depending on the type of steel, it is only determined by the ratio of the magnitude of the deformation resistance when the strain is 1, but it depends on the dimensions and specifications of the gear. Therefore, these values need to be determined as appropriate by conducting experiments in advance. For example, the steel grade is S10C shown in Table 1 above, the gear body is a helical gear shown in Table 2 above, and the boss In the case of a helical gear with a boss having an area ratio of 40%, 50% and 65% and a boss height of 30 to 50% of the total height including the boss, the above distances C and D are both 1 mm. The tool surface pressure of the inner punch 3a held while the pressure surface of the inner punch 3a is retracted by the distance D is preferably in the range shown in Table 5 according to the area ratio of the boss.
[0049]
[Table 5]

However, the distance C needs to be 30% or less of the boss height of the product to be obtained. The reason is that if the distance C exceeds 30% of the boss height of the product to be obtained, the necessary boss height cannot be secured. Therefore, in the second method, the distance C is set within a range of 30% or less of the boss height of the product to be obtained.
[0050]
In the second method, it is not always necessary to set the initial position of the pressure surface of the inner and outer punches as described above, and the pressure surface of the outer punch 3b and the pressure surface of the inner punch 3a are made to coincide with each other. Pressurization may be started. However, in this case, the upper and lower overball diamond differences of the obtained product are slightly larger than those obtained by the first method. For this reason, the initial setting position is preferably as described above.
[0051]
Next, a third method (method according to claim 6 in the claims) will be described. In this third method, a boss-equipped gear in which inner teeth parallel to the axial length direction called a spline are formed on the inner peripheral surface of the shaft hole is formed by the first method or the second method described above. Is the method.
[0052]
Therefore, in this third method, instead of the mandrel 50 shown in FIGS. 1 and 2, a mandrel having a tooth shape corresponding to the inner teeth of the product to be obtained on its outer peripheral surface is omitted. Use. However, in this case, only the first method or the second method described above forms the internal teeth of the portion facing the external teeth, but the internal teeth of the portion facing the boss, especially the boss The internal teeth of the portion facing the upper part are not molded. This is because the deformation amount in the axial direction of the work material 2 during pressurization by the outer punch 3b continued even after release of the pressurization by the inner punch 3a is larger than the deformation amount in the radial direction, and is formed on the mandrel. This is because the material does not sufficiently fill the concave portion of the tooth mold.
[0053]
For this reason, in the third method, after the pressurization by the outer punch 3b is continued even after the pressure release by the inner punch 3a is released ((d) in FIGS. 1 and 2), the outer punch 3b is moved backward. Later, re-pressurization by the inner punch 3a was performed.
[0054]
However, if the pressurizing force at the time of re-pressurization by the inner punch 3a, that is, the tool surface pressure of the inner punch 3a is not appropriate, the required internal teeth are not molded. Therefore, the tool surface pressure at the time of re-pressurization by the inner punch 3a needs to be set to a predetermined value, but this value varies depending on the required material filling rate of the inner teeth.
[0055]
For this reason, the tool surface pressure needs to be determined appropriately by conducting an experiment in advance. For example, the steel grade is made of S10C shown in Table 1 above, and the gear body is a helical gear shown in Table 2 above. The boss height is 35 mm, the small diameter (shaft hole diameter) is 33 mm, the number of teeth is 24, the boss area ratio is 40%, 50% and 65%. In the case of a helical gear with a boss having 30 to 50% of internal teeth including the boss, the tool surface pressure is not less than the value shown in Table 6 according to the required material filling rate of the internal teeth. It is good to do.
[0056]
However, when considering the life of the mold, the upper limit is 3.3 times or less, more preferably 3.1 times or less. This is because, among the two steel types shown in Table 1 above, in the case of steel type SCr420H, if the tool surface pressure exceeds 3.3 times the deformation resistance of SCr420H, the mold may be damaged.
[0057]
[Table 6]

The above description is for the case where the external teeth are helical gears, but when the external teeth are spur gears, the tooth molds formed on the die 1 and the lower punch 4 are formed for the spur gears. Is possible.
[0058]
【Example】
Example 1
Steel grade S10C shown in Table 1 above, gear body dimensions shown in Table 2 above, boss area ratio 40% and 50%, boss height 40% to 50% of total height including boss A helical gear was formed by the first method.
[0059]
At that time, the pressure surface of the inner punch 3a was initially set at a position retracted 10 mm from the pressure surface of the outer punch 3b. Further, pressurization by the inner punch 3a was performed by changing the tool surface pressure in various ways and holding it constant while the pressurization surface was retracted 1 mm from the initial setting position.
[0060]
In all cases, the material 2 to be processed was an outer diameter of 55.1 mm, an inner diameter of 35.2 mm, and a height of 30.5 mm.
[0061]
And while checking the material filling rate and the boss height of the external teeth of the helical gear with boss obtained by molding under each condition, the upsetting rate under each condition and the average tool of the lower punch 4 The surface pressure was also examined.
[0062]
The above investigation results are shown in Table 7 together with the molding conditions.
[0063]
[Table 7]

As can be seen from Table 7, when the area ratio of the boss was 40%, the material filling ratio of the external teeth was 100% and the boss height was 40% or more under any condition. Since the average tool surface pressure of the lower punch 4 is excessively 3.3 times the deformation resistance of the material to be processed, there is no problem when the steel type is S10C, but there is a risk of damage to the mold when the steel type is SCr420H.
[0064]
In addition, when the boss area ratio was 50%, a boss height of 40% or more was obtained under any conditions. However, in the trial numbers 4 to 6, only the material filling rate of the outer teeth was 60% or less, and in the trial numbers 14 and 15, the material filling rate of the outer teeth was 100%. Since the surface pressure was excessively 3.3 times the deformation resistance of the work material, there was a risk of damage to the mold.
[0065]
As for the above, the tool surface pressure of the inner punch 3a in the case of forming a helical gear with a boss of the above steel type and dimensions by the first method is preferably set within the range shown in Table 4 described above. It means that.
[0066]
In addition, although description in Table 7 was abbreviate | omitted, the overball diamond difference of the upper and lower sides of the product with a favorable quality determination result was 0.07-0.09 mm among each trial number.
[0067]
Example 2
Steel type is S10C shown in Table 1 above, gear body is the size shown in Table 2 above, boss area ratio is 40%, 50% and 65%, and boss height is 30-50% of total height including boss A helical gear with a boss was formed by the second method.
[0068]
At that time, the pressure surface of the inner punch 3a was initially set at a position advanced by 1 mm from the pressure surface of the outer punch 3b. Further, pressurization by the inner punch 3a was performed by changing the tool surface pressure in various ways and holding it constant while the pressurization surface was retracted 1 mm from the initial setting position.
[0069]
However, the trial number 26 is 0.5 mm, the trial number 27 is 0.3 mm, the trial number 28 is 0.2 mm, the trial numbers 29 and 30 are 0.1 mm, the trial numbers 31 to 35 are 4 mm, and the pressure surface of the inner punch is While retreating from the initial set position, the tool surface pressure was kept constant and pressurized. This is intended to increase the height ratio of the boss while increasing the material filling ratio of the external teeth before forming the boss.
[0070]
In all cases, the material 2 to be processed was an outer diameter of 55.1 mm, an inner diameter of 35.2 mm, and a height of 30.5 mm.
[0071]
And while checking the material filling rate and the boss height of the external teeth of the helical gear with a boss obtained by molding under each condition, the upsetting rate under each condition and the average tool of the lower punch 4 The surface pressure was also examined.
[0072]
The results of the above investigation are shown in Table 8 together with the molding conditions.
[0073]
[Table 8]

As can be seen from Table 8, when the area ratio of the boss is 40%, the material filling ratio of the external teeth is 100% under any condition, but the test numbers 19 and 20 are 30% or more of the target. The boss height was not obtained.
[0074]
In addition, when the area ratio of the boss was 50%, the boss height of 30% or more was obtained in the trial numbers 21 to 29, but among them, the trial material 21 and 22 had an external tooth material filling rate of 85% or less. Only the thing of was obtained. Further, in the trial No. 30, the material filling rate of the external teeth was 100%, but the target boss height of 30% or more was not obtained.
[0075]
Furthermore, those with a boss area ratio of 65% were obtained with the boss height of 30% or more in the trial numbers 31 to 38, of which the trial numbers 31 and 32 had an external tooth material filling rate of 60% or less. Only the thing of was obtained. Further, in Test No. 39, the material filling rate of the external teeth was 100%, but the target boss height of 30% or more was not obtained.
[0076]
As for the above, the tool surface pressure of the inner punch 3a when forming a helical gear with a boss of the above steel type and dimensions by the second method is preferably set within the range shown in Table 5 above. It means that.
[0077]
In addition, although description in Table 8 was omitted, among the trial numbers, the upper and lower overball diamond differences of the products with good and bad judgment results were 0.02 to 0.04 mm, and the first method Therefore, it was much smaller than the case, and had sufficient dimensional accuracy for automobile transmissions.
[0078]
Example 3
Steel type S10C shown in Table 1 above, gear body dimensions shown in Table 2 above, boss area ratio 40%, 50% and 65%, boss height 30-30% of total height including boss A bossed helical gear having an inner tooth with a groove bottom diameter (large diameter) of 35 mm and 24 teeth on the inner peripheral surface of a shaft hole having an inner diameter (small diameter) of 33 mm was molded by the third method.
[0079]
At that time, the process up to the re-pressurization by the inner punch 3a was the same as the trial number 24 in the above-described Example 2, and after the outer punch 3b was retracted, the pressure was re-pressurized with various tool surface pressures.
[0080]
And the material filling rate of the internal teeth of the helical gear with a boss | hub obtained by shape | molding on each condition and the internal tooth of the part facing a boss | hub was investigated. As a result, the material filling rate of the entire internal teeth and the internal teeth of the portion facing the boss was the same regardless of the area ratio of the boss, as shown in Table 9.
[0081]
[Table 9]

As is apparent from Table 9, the material filling rate of the inner teeth varies depending on the tool surface pressure of the inner punch at the time of re-pressurization. For example, the material filling rate of the entire inner teeth allowed as a product is generally 80% or more. In order to obtain the product, it is necessary to pressurize with a tool surface pressure of 2.7 times or more of the deformation resistance of the work material. To obtain 100%, the tool surface pressure must be 2.8 times or more. It turns out that it is necessary to pressurize.
[0082]
This indicates that the tool surface pressure of the inner punch 3a at the time of re-pressurization in the case of forming a bossed helical gear having internal teeth of the above steel types and dimensions by the third method is shown in Table 6 above. This means that it should be set within the range shown.
[0083]
In addition, as described in Example 1 above, the upper limit value 3.3 in the description of Table 6 exceeds the above value. If the steel type is SCr420H, there is a risk of damage to the mold. Is a value determined from the fact that it is preferably 3.1 times or less.
[0084]
As is clear from the results of Examples 1 to 3 above, according to the present invention, the area ratio of the boss of the product is not limited to the area ratio of the boss exceeding 40%, but also the area ratio of 40% or less. It is possible to form a gear with a boss that has bosses with different heights and internal teeth with an appropriate material filling rate by setting the tool surface pressure of the inner punch appropriately according to Understand.
[0085]
【The invention's effect】
According to the present invention, a boss gear with an outer diameter that is equal to or less than the groove bottom diameter of the outer tooth and various heights, and a high dimensional accuracy bossed gear having an inner tooth on the inner peripheral surface of the shaft hole with a high material yield. It can be manufactured with high efficiency.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a first method of the present invention.
FIG. 2 is a diagram for explaining a second method of the present invention.
FIG. 3 is a diagram for explaining a conventional one-stage discarded axis method;
FIG. 4 is a diagram showing an example of a result in the case where bossed gears having different area ratios are formed by a conventional one-stage scraping shaft method.
[Explanation of symbols]
1: Die,
2: Work material
3: Top punch,
3a: inner punch,
3b: outside punch,
4: Bottom punch,
5, 50: Mandrel,
6: Material (equivalent to boss),
7: Base,
8: Stretchable member.

Claims

Use a die with a die formed on the inner peripheral surface of the die hole corresponding to the external teeth of the product, and an upper die and a lower punch to close the die hole of the die. When forming a bossed gear having a boss on one end surface by pressurizing the arranged work material mainly with the upper punch and completely filling the work material to every corner of the die hole, the upper punch Use a split punch that is divided into an outer punch and an inner punch with a diameter equal to the outer diameter of the boss of the product to be obtained, and within a range of 90% or less of the boss height of the product to obtain the pressure surface of the inner punch. Pressing with both the inner and outer punches is started in an initial setting state that is retracted from the pressing surface of the punch, and then pressing with the outer punch is continued as it is. Constant from position A method for forming a gear with a boss that releases the pressurization by the inner punch after maintaining the predetermined tool surface pressure until it is retracted by a distance, and further continues the pressurization by the outer punch even after releasing the pressurization of the inner punch. .

The method for forming a gear with a boss according to claim 1, wherein the pressurization is performed in a state where the pressurization surface of the inner punch is advanced from the pressurization surface of the outer punch before the start of pressurization by the inner and outer punches.

The predetermined tool surface pressure is 2.5 times the deformation resistance of the work material or 0.80 times or less of the average tool surface pressure obtained by dividing the load applied to the lower punch by the pressure receiving area of the lower punch. Item 3. A method for forming a gear with a boss according to Item 1 or 2.

A die having a tooth mold corresponding to the external teeth of the product formed on the inner peripheral surface of the die hole, and a closed mold having a main punch and a lower punch for closing the die hole of the die are used as the die hole of the die. When forming a bossed gear having a boss on one end face by pressurizing the arranged work material mainly with a main punch and completely filling the work material to every corner of the die hole, the upper punch Use a split punch divided into an outer punch and an inner punch with a diameter equal to the outer diameter of the boss of the product to be obtained, and make the pressing surfaces of the inner and outer punches coincide with each other, or obtain the pressing surface of the inner punch Pressing by both the inner and outer punches is started in an initial setting state advanced from the pressing surface of the outer punch within a range of 30% or less of the height, and then pressing by the outer punch continues, while pressing by the inner punch continues. Pressure is the pressurization Is maintained at a predetermined tool surface pressure until it is retracted by a certain distance from the initial setting position, and then pressurization by the inner punch is released, and further pressurization by the outer punch after releasing the pressurization of the inner punch. A method of forming a gear with a boss that continues the process.

The predetermined tool surface pressure is 2.15 times the deformation resistance of the workpiece material or 0.80 times or less of the average tool surface pressure obtained by dividing the load applied to the lower punch by the pressure receiving area of the lower punch. Item 5. A method for forming a gear with a boss according to Item 4.

The method for forming a gear with a boss according to any one of claims 1 to 5, wherein when the product to be obtained has a shaft hole provided with internal teeth, the shaft deep portion of the inner punch and the lower punch is formed in the shaft center portion of the work material. A mandrel having an outer diameter that penetrates the shaft is equal to the shaft hole diameter, and a tooth mold corresponding to the inner teeth of the product is disposed on the outer peripheral surface, and pressurization by the outer punch is terminated after release of pressure by the inner punch. After that, after the outer punch is retracted, a boss-equipped gear is formed by re-pressurization with the inner punch at a tool surface pressure of 2.7 to 3.3 times the deformation resistance of the work material.

The method for forming a gear with a boss according to claim 6, wherein the re-pressurization with the inner punch is performed at 2.8 to 3.1 times the deformation resistance of the workpiece.