JP3781172B2

JP3781172B2 - Gear manufacturing method

Info

Publication number: JP3781172B2
Application number: JP2000307687A
Authority: JP
Inventors: 原裕二郎小; 野裕高
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 2000-10-06
Filing date: 2000-10-06
Publication date: 2006-05-31
Anticipated expiration: 2020-10-06
Also published as: JP2002113544A

Description

【０００１】
【発明の属する技術分野】
本発明は、例えば、自動車の差動装置に用いられる歯車の製造方法に関するものである。
【０００２】
【従来の技術】
一般に、自動車の差動装置に用いる歯車は、鋼材等のブランクにセンタ穴を成形すると共に、同ブランクに削り出しや鍛造などにより歯形を成形した後、浸炭処理を行っており、全体的にほぼ均一の深さの浸炭層が形成される。
【０００３】
一方、この種の歯車では、部位毎の特性として、歯形の歯面部には相手の歯車との噛み合いのために耐摩耗性が要求され、歯形の歯元部には繰り返しの衝撃入力に対する衝撃疲労強度が要求され、また、センタ穴の内壁部には同センタ穴に挿入する軸との接触のために耐摩耗性や耐焼付き性が要求される。
【０００４】
このような特性要求に対して、歯形等の成形後に浸炭処理を行った場合、図４（ａ）に示すように浸炭層Ｃの深さが全体的に均一であるため、歯面部Ｇａにおいては浸炭層Ｃの深さが充分に得られて耐摩耗性が向上するものの、歯元部Ｇｂにおいては浸炭層Ｃの深さが過大となり、近年の動力伝達系の高出力化に伴う入力の増大に対して歯元部Ｇｂの衝撃疲労強度が低下するという問題がある。この問題を解決するために、歯元部に防炭処理を施し、図４（ｂ）に示すように、歯面部Ｇａの浸炭層Ｃの深さをそのままにして、歯元部Ｇｂの浸炭層Ｃを薄くすることが試みられた。しかし、この場合には、防炭処理の費用が高く、また、浸炭層Ｃの深さのコントロールを正確に行うことが困難であった。
【０００５】
そこで、特開平９−３８７４７号公報に開示されているように、中空状に成形したブランクに浸炭処理を施し、このブランクを温間鍛造して歯車に成形する方法が提案されている。この方法によれば、鍛造による材料の流れにより、図４（ｃ）に示すように、歯面部Ｇａの浸炭層Ｃの深さを保ちつつ歯元部Ｇｂの浸炭層Ｃを薄くすることが可能になった。
【０００６】
【発明が解決しようとする課題】
ところで、上記したような従来の歯車の製造方法では、ブランクを鍛造した際の歯元部の塑性変形量が大きく、これにより歯面部の浸炭層の深さを保ちつつ歯元部の浸炭層を薄くし得るのであるが、歯面部および歯元部の浸炭層の深さはブランクに形成した浸炭層の深さと塑性加工の変形量により決まることから、双方の浸炭層の形成パターンすなわち歯面部の浸炭層の深さと歯元部の浸炭層の深さの比率がほぼ限られている。このため、歯元部の浸炭層の深さを適正なものにしようとすると、歯面部の浸炭層の深さが過大になる場合があり、逆に、歯面部の浸炭層の深さを意図的に大きくしようとすると、歯元部の浸炭層の深さが過大になる場合があることから、従来にあっては、歯面部および歯元部の夫々により適正の深さの浸炭層を得るうえでさらなる改善が要望されていた。
【０００７】
【発明の目的】
本発明は、上記従来の状況に鑑みて成されたもので、とくに、歯形の歯面部および歯元部の夫々により適正な深さの浸炭層を得ることができる歯車の製造方法を提供することを目的としている。
【０００８】
【課題を解決するための手段】
本発明に係わる歯車の製造方法は、請求項１として、センタ穴を有する歯車を製造するに際し、第１鍛造工程で円柱状のブランクを初期形状と最終の歯車形状との間の中間形状に成形すると共にブランクのセンタ穴の両側に対応する部分に凹部を成形し、この中間成形体に浸炭処理を施したのち、第２鍛造工程で中間成形体を歯車形状に成形すると共に両側の凹部を双方の間に内ばりを有するセンタ穴に成形するのに続いて、センタ穴の内ばりを除去する構成とし、請求項２として、中間成形体の中間形状の歯面が、最終の歯車形状に近似し且つ外側に滑らかに連続する曲面形状である構成とし、請求項３として、第１鍛造工程の前に、ブランクに浸炭処理を施す構成としており、上記の構成をもって従来の課題を解決するための手段としている。
【０００９】
【発明の作用】
本発明の請求項１に係わる歯車の製造方法は、歯形の歯面部には耐摩耗性を得るために所定の深さの浸炭層を確保し、歯元部には衝撃疲労強度を得るために歯面部の浸炭層よりも薄い浸炭層を確保しようとするものであって、その工程としては、ブランクを適宜加熱し、第１鍛造工程でブランクを初期形状と最終の歯車形状との間の中間形状に成形し、これを中間成形体とする。このとき、中間成形体は、未完の歯形を有する概略歯車形状を成すものとすることができる。この中間成形体の成形に際して、ブランクのセンタ穴の両側に対応する部分に凹部を成形する。次に、中間成形体に浸炭処理を施し、中間成形体の全体に均一な深さの浸炭層を形成する。そして、中間成形体を適宜再加熱し、第２鍛造工程で中間成形体を歯車形状に成形することにより、歯形の歯面部には所定の深さの浸炭層を確保し、歯元部には歯面部の浸炭層よりも薄い浸炭層を確保する。この第２鍛造工程で中間成形体を歯車形状に成形するに際しては、両側の凹部を双方の間に内ばりを有するセンタ穴に成形する。このとき、当該歯車の製造方法では、とくに、両側の凹部に均一な深さの浸炭層を形成し、その両凹部を内ばり付のセンタ穴に成形するので、センタ穴の内壁部の浸炭層がセンタ穴の一方から内ばりを介してセンタ穴の他方へほぼ連続した状態となる。したがって、その後に内ばりを除去することにより、貫通したセンタ穴の内壁部に沿って浸炭層が良好に保たれ、この浸炭層により、センタ穴に挿入される軸に対する耐摩耗性や耐焼付け性が確保される。なお、第２鍛造工程で成形した歯車には、必要に応じて、焼入れ、ショットブラストおよび機械加工などが施される。
【００１０】
ここで、ブランクを歯車形状に成形する過程では、とくに歯形の歯元部の塑性変形量が大きいので、浸炭処理を施したブランクを１回の鍛造で歯車形状に形成すると、浸炭層の変形量も大きくなって歯元部の浸炭層が薄くなり過ぎる場合があり、また、歯元部の浸炭層を確保するために初期の浸炭層を深めに形成することで歯面部の浸炭層の深さが過大になる場合がある。
【００１１】
これに対して、当該歯車の製造方法では、ブランクを中間成形体に成形し、この中間成形体に浸炭処理を施してから同中間成形体を歯車形状に成形するので、浸炭処理後の第２鍛造工程における歯元部の塑性変形量が少なく、これに伴って浸炭層の変形量が少ないものとなる、したがって、歯元部の浸炭層が薄くなり過ぎるのが防止され、また、初期の浸炭層を深めに形成しなくても歯元部の浸炭層が確保されるので、歯面部の浸炭層の深さが過大になることもなく、歯面部および歯元部の夫々に適正な深さの浸炭層が確保される。
【００１３】
本発明の請求項２に係わる歯車の製造方法では、中間成形体の中間形状の歯面を最終の歯車形状に近似したものとし、且つ同歯面を外側に滑らかに連続する曲面形状としているので、その後に行われる浸炭処理および第２鍛造工程を経ることで、歯面部には所定の深さの浸炭層がより容易に且つ確実に確保され、歯元部には歯面部の浸炭層よりも薄い浸炭層がより容易に且つ確実に確保される。
【００１４】
本発明の請求項３に係わる歯車の製造方法では、第１鍛造工程の前にブランクに浸炭処理を施し、その後、第１鍛造工程でブランクを中間成形体に成形し、この中間成形体に浸炭処理を施し、第２鍛造工程で中間成形体を歯車形状に成形するので、歯形の歯面部および歯元部における浸炭層の形成パターンをコントロールする機会が増し、例えば、歯元部の浸炭層が薄くなり過ぎるのを防止しつつ歯面部の浸炭層の深さを意図的に増大させることも可能になる。
【００１５】
すなわち、ブランクに浸炭処理を施した後に第１鍛造工程を行うと、歯面部の浸炭層の深さを保ちつつ歯元部の浸炭層を薄くすることが可能であるから、この際に、歯元部の浸炭層を適正な深さよりも薄く成形する。こののち、中間成形体に浸炭処理を施して第２鍛造工程を行えば、歯面部の浸炭層の深さはさらに増すこととなり、歯元部の浸炭層は適正な深さとなる。
【００１６】
【発明の効果】
本発明の請求項１に係わる歯車の製造方法によれば、第１鍛造工程でブランクを中間成形体に成形し、中間成形体に浸炭処理を施した後、第２鍛造工程で中間成形体を歯車形状に成形する方法としたことにより、歯形の歯面部には耐摩耗性を得るために所定の深さの浸炭層を確保して、歯元部には衝撃疲労強度を得るために歯面部の浸炭層よりも薄い浸炭層を確保する場合に、歯元部の浸炭層が薄くなり過ぎるのを防止することができ、中間成形体における初期の浸炭層を深めに形成しなくても歯元部の浸炭層が確保されるので、浸炭処理費の低減を実現すると共に、歯面部の浸炭層の深さが過大になるのを防止することができ、歯面部および歯元部の夫々により適正な深さの浸炭層を確保することができる。また、中間成形体の形状を選択すれば、歯元部の浸炭層を適正な深さにしつつ歯面部の浸炭層の深さを意図的に増大させることも可能である。そして、自動車の差動装置に用いる歯車を製造する場合には、歯面部および歯元部に個々の特性を備えて動力伝達系の高出力化に充分に対応し得る歯車を得ることができる。
【００１７】
加えて、本発明の請求項１に係わる歯車の製造方法では、中実のブランクに予めセンタ穴を成形する工程が不要であって、その分工数や製造コストの低減を実現することができ、また、センタ穴の内壁部には、浸炭層切れがほとんど無い良好な浸炭層を得ることができ、その浸炭層によりセンタ穴に挿入する軸に対して充分な耐摩耗性や耐焼付き性を確保することができる。
【００１８】
本発明の請求項２に係わる歯車の製造方法によれば、請求項１と同様の効果を得ることができるうえに、中間成形体の中間形状の歯面を最終の歯車形状に近似し且つ外側に滑らかに連続する曲面形状としたことにより、その後に行われる浸炭処理および第２鍛造工程を経ることで、歯面部には所定の深さの浸炭層をより容易に且つ確実に確保することができ、歯元部には歯面部の浸炭層よりも薄い浸炭層をより容易に且つ確実に確保することができる。
【００１９】
本発明の請求項３に係わる歯車の製造方法によれば、請求項１および２と同様の効果を得ることができるうえに、ブランクに浸炭処理を施した後、第１鍛造工程、浸炭処理および第２鍛造工程を経ることから、歯面部および歯元部の浸炭層の形成パターンをより広く変化させることが可能になると共に、歯面部および歯元部の夫々に所望の深さの浸炭層を得ることができ、例えば、歯面部と歯元部とで浸炭層を大きく変化させた歯車を製造することもできる。
【００２０】
【実施例】
図１および図２は、本発明に係わる歯車の製造方法の一実施例を説明する図である。なお、この実施例において図１（ｇ）に示す歯車Ｇは、自動車の差動装置に用いられる傘歯車であって、小径部から大径部に至る歯形Ａを有すると共に、軸線方向に沿ってセンタ穴Ｈを有し、大径側には背球面Ｒを有している。
【００２１】
上記の歯車Ｇを製造するには、図１（ａ）に示すような中実の円柱状ブランクＢを使用し、ブランクＢを９００〜１１００℃程度に加熱した後、同ブランクＢを第１鍛造工程において初期形状と最終の歯車形状との間の中間形状に成形し、図１（ｂ）に示すように、未完の歯形を有する概略歯車形状の中間成形体Ｆを得る。この中間成形体Ｆの中間形状は、歯面が最終の歯車形状に近似したものとなり、且つ同歯面が外側に滑らかに連続する曲面形状を成している。
【００２２】
第１鍛造工程では、図２（ａ）に示すような鍛造型が用いられる。鍛造型は、中心に上側ポンチ１を挿設した上側ダイ２と、同じく中心に下側ポンチ３を挿設した下側ダイ４を備えている。上側ダイ２は歯形Ａの成形部５を有し、下側４ダイは背球面Ｒの成形部６を有している。また、上下の各ポンチ１，３は、先端に半球状の凸部１ａ，３ａを有している。そして、第１鍛造工程では、上記の鍛造型を用いて、歯形Ａや背球面Ｒを一次成形すると共に、各ポンチ１，３により、ブランクＢのセンタ穴Ｈの両側に対応する部分に凹部７，８を成形し、中間成形体Ｆを得る。このとき、各凹部７，８は、ポンチ１，３の凸部によって底部が半球面に成形され、また、開口部付近は外側に滑らかに連続する曲面に成形されている。
【００２３】
上記の如く成形された中間成形体Ｆには、浸炭処理を施し、図１（ｃ）および（ｄ）に示すように、全体に均一な浸炭層Ｃを形成する。この際の浸炭深さは、部品としての浸炭要求深さや第２鍛造工程での塑性変形量の大きさなどに応じて適宜設定する。その後、中間成形体Ｆを９００〜１１００℃程度に再加熱し、第２鍛造工程において中間成形体Ｆを図１（ｅ）および（ｆ）に示す歯車形状に成形する。
【００２４】
この第２鍛造工程では、図２（ｂ）に示すような鍛造型が用いられる。鍛造型は、中心に上側ポンチ１１を挿設した上側ダイ１２と、同じく中心に下側ポンチ１３を挿設した下側ダイ１４を備えている。上側ダイ１２は歯形Ａの成形部１５を有し、下側１４ダイは背球面Ｒの成形部１６を有している。また、上下の各ポンチ１１，１３は、平坦な先端部を有している。そして、第２鍛造工程では、上記の鍛造型を用いて、歯形Ａや背球面Ｒを二次成形すると共に、各ポンチ１１，１３により、両側の凹部７，８を双方の間に内ばりＶを有する有底円筒形状のセンタ穴７Ｈ，８Ｈに成形する。
【００２５】
このとき、センタ穴７Ｈ，８Ｈは、第１鍛造工程で中間成形体Ｆに凹部７，８を成形し、浸炭処理を施した後、第２鍛造工程で内ばりＶ付の状態に成形する過程を経ることにより、内壁部の浸炭層Ｃが、一方のセンタ穴７Ｈから内ばりＶを介して他方のセンタ穴８Ｈにほぼ連続した状態となる。
【００２６】
その後、当該歯車の製造方法では、ピアス型等を用いてセンタ穴７Ｈ，８Ｈの内ばりＶを打抜いて除去し、図１（ｇ）に示す歯車Ｇを得る。これにより、貫通したセンタ穴Ｈの内壁部に沿って浸炭層Ｃが良好に保たれる。こののち、歯車Ｇには、図１（ｈ）に示すように焼入れ（ブロックＢ１）が施され、次いでショットブラスト（Ｂ２）が施され、さらに適宜の機械加工（Ｂ３）が施される。
【００２７】
このようにして、上記した歯車の製造方法では、従来技術の項で説明した図６（ｃ）に示す理想的な浸炭層Ｃを有する歯形と同様に、歯面部（Ｇａ）には所定の深さの浸炭層Ｃを確保し、歯元部（Ｇｂ）には歯面部の浸炭層Ｃよりも薄い浸炭層Ｃを確保し、センタ穴Ｈの内壁部にも良好な浸炭層Ｃを確保する。
【００２８】
つまり、ブランクＢを歯車形状に成形する過程では、とくに歯形の歯元部の塑性変形量が大きくなり、歯元部の浸炭層Ｃが薄くなり過ぎるなどの不具合が生じることがあるため、当該歯車の製造方法では、ブランクＢを中間成形体Ｆに成形し、とくに、中間成形体Ｆの中間形状の歯面が最終の歯車形状に近似し且つ外側に滑らかに連続する曲面形状を成すものとし、この中間成形体Ｆに浸炭処理を施してから同中間成形体Ｆを歯車形状に成形するようにして、浸炭処理後の第２鍛造工程における歯元部の塑性変形量を少ないものにし、これに伴って浸炭層Ｃの変形量を少なくしている。したがって、歯元部の浸炭層Ｃが薄くなり過ぎることはなく、また、初期の浸炭層Ｃを深めに形成しなくても歯元部の浸炭層Ｃが確保されるので、歯面部の浸炭層のＣ深さが過大になることもなく、歯面部および歯元部の夫々に適正な深さの浸炭層Ｃが確保される。
【００２９】
そして、歯車Ｇは、相手の歯車と噛み合う歯面部には浸炭層Ｃの深さを保つことで耐摩耗性が確保され、回転時に衝撃入力を受ける歯元部には浸炭層を薄くすることで衝撃疲労強度が確保され、さらに、センタ穴の内壁部に挿入された軸と接触する同センタ穴の内壁部には浸炭層Ｃを良好に保って耐摩耗性や耐焼付け性が確保されることとなり、自動車の差動装置に用いる歯車として、各部位毎の特性を備えて動力伝達系の高出力化に充分対応し得るものとなる。
【００３０】
本発明に係わる歯車の製造方法は、上記実施例で説明したほかに、第１鍛造工程の前にブランクＢに浸炭処理を施すようにしても良い。すなわち、図１（ａ）に示すブランクＢに浸炭処理を施し、その後、第１鍛造工程でブランクＢを中間成形体Ｆに成形し、この中間成形体Ｆに浸炭処理を施し、第２鍛造工程で中間成形体Ｆを歯車形状に成形する。
【００３１】
このような歯車の製造方法では、先の実施例と同様の効果が得られるのに加えて、歯形の歯面部および歯元部における浸炭層Ｃの形成パターンをコントロールする機会が増し、例えば、歯元部の浸炭層Ｃが薄くなり過ぎるのを防止しつつ歯面部の浸炭層Ｃの深さを意図的に増大させることも可能になる。つまり、ブランクＢに浸炭処理を施した後に第１鍛造工程を行うと、歯面部の浸炭層Ｃの深さを保ちつつ歯元部の浸炭層Ｃを薄くすることが可能であるから、この際に、歯元部の浸炭層Ｃを適正な深さよりも薄く成形する。こののち、中間成形体Ｆに浸炭処理を施して第２鍛造工程を行えば、歯面部の浸炭層Ｃの深さはさらに増し、歯元部の浸炭層Ｃは適正な深さとなる。
【図面の簡単な説明】
【図１】本発明に係わる歯車の製造方法の一実施例において、製造過程を説明する断面図（ａ）〜（ｇ）およびブロック図（ｈ）である。
【図２】図１に示す歯車の製造方法の第１鍛造工程に用いる鍛造型の一例を示す断面図（ａ）および第２鍛造工程に用いる鍛造型の一例を示す断面図（ｂ）である。
【図３】歯形成形後に浸炭処理をした場合の歯形の断面図（ａ）、歯形成形後に歯元部に防炭処理をして浸炭処理をした場合の歯形の断面図（ｂ）、および浸炭処理後に歯形を鍛造成形した場合の歯形の断面図（ｃ）である。
【符号の説明】
Ｂブランク
Ｃ浸炭層
Ｆ中間成形体
Ｇ歯車
Ｈセンタ穴
Ｖ内ばり
７８凹部
７Ｈ８Ｈ内ばり除去前のセンタ穴[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a gear used for, for example, a differential of an automobile.
[0002]
[Prior art]
In general, gears used in automobile differentials are formed with a center hole in a blank made of steel, etc., and a carburizing process is performed on the blank after forming a tooth profile by cutting or forging. A carburized layer having a uniform depth is formed.
[0003]
On the other hand, in this type of gear, as a characteristic of each part, the tooth surface portion of the tooth profile is required to have wear resistance for meshing with the other gear, and the tooth root portion of the tooth profile has impact fatigue due to repeated impact input. Strength is required, and the inner wall portion of the center hole is required to have wear resistance and seizure resistance for contact with the shaft inserted into the center hole.
[0004]
In response to such a characteristic request, when carburizing treatment is performed after forming a tooth profile or the like, the depth of the carburized layer C is uniform as a whole as shown in FIG. Although the depth of the carburized layer C is sufficiently obtained and wear resistance is improved, the depth of the carburized layer C is excessive in the tooth root portion Gb, and the input increases with the recent increase in output of the power transmission system. On the other hand, there is a problem that the impact fatigue strength of the tooth root portion Gb is lowered. In order to solve this problem, carburizing treatment is applied to the tooth base part, and as shown in FIG. 4B, the carburized layer of the tooth base part Gb without changing the depth of the carburized layer C of the tooth surface part Ga. An attempt was made to make C thinner. However, in this case, the cost of the carburizing treatment is high, and it is difficult to accurately control the depth of the carburized layer C.
[0005]
Therefore, as disclosed in Japanese Patent Application Laid-Open No. 9-38747, a method has been proposed in which a carburized blank is subjected to a carburizing process, and the blank is warm-forged and formed into a gear. According to this method, it is possible to make the carburized layer C of the tooth base part Gb thin while maintaining the depth of the carburized layer C of the tooth surface part Ga, as shown in FIG. Became.
[0006]
[Problems to be solved by the invention]
By the way, in the conventional gear manufacturing method as described above, the amount of plastic deformation of the tooth root when the blank is forged is large, whereby the carburized layer of the tooth root is maintained while maintaining the depth of the carburized layer of the tooth surface. Although the thickness of the carburized layer at the tooth surface and the root portion is determined by the depth of the carburized layer formed on the blank and the amount of deformation of the plastic working, the formation pattern of both carburized layers, i.e. The ratio between the depth of the carburized layer and the depth of the carburized layer at the root is almost limited. For this reason, if the depth of the carburized layer of the tooth root part is made appropriate, the depth of the carburized layer of the tooth surface part may become excessive, and conversely, the depth of the carburized layer of the tooth surface part is intended. Therefore, since the depth of the carburized layer at the tooth base portion may become excessive if it is attempted to increase the size, conventionally, a carburized layer having an appropriate depth is obtained by each of the tooth surface portion and the tooth root portion. Further improvement has been demanded.
[0007]
OBJECT OF THE INVENTION
The present invention has been made in view of the above-described conventional situation, and in particular, provides a gear manufacturing method capable of obtaining a carburized layer having an appropriate depth by each of a tooth surface portion and a tooth root portion of a tooth profile. It is an object.
[0008]
[Means for Solving the Problems]
Method of manufacturing a gear according to the present invention, the intermediate shape between a claim 1, when preparing a tooth wheel having a center hole, and a cylindrical blank in the first forging step initial shape and the final gear shape shaping the recess in the portion corresponding to both sides of the blank center hole of the well as formed shape to, after carburized to this intermediate product, Rutotomoni both sides to mold the preform into a gear shape in the second forging step Following a recess for molding the center hole having an inner burr during both the configuration you remove the inner beams of the center hole, as claimed in claim 2, the tooth surface of the intermediate shape of the medium between the molded body, a structure is a curved surface smoothly continuous to and outwardly similar to a gear shape of the final, as a third aspect, before the first forging step, has a structure carburized blank, with the construction of the As a means to solve the conventional problems That.
[0009]
[Effects of the Invention]
In the gear manufacturing method according to claim 1 of the present invention, a carburized layer having a predetermined depth is secured in the tooth surface portion of the tooth profile to obtain wear resistance, and an impact fatigue strength is obtained in the tooth base portion. It is intended to secure a carburized layer thinner than the carburized layer of the tooth surface part. As the process, the blank is appropriately heated, and the blank is intermediate between the initial shape and the final gear shape in the first forging process. It shape | molds in a shape and makes this an intermediate molded object. At this time, the intermediate molded body may have a substantially gear shape having an incomplete tooth profile . At the time of forming this intermediate formed body, concave portions are formed in portions corresponding to both sides of the center hole of the blank. In the following, carburize the intermediate molded body to form a carburized layer of uniform depth throughout the preform. Then, the intermediate formed body is appropriately reheated, and the intermediate formed body is formed into a gear shape in the second forging step, thereby securing a carburized layer having a predetermined depth on the tooth surface portion of the tooth profile, and on the tooth base portion. A carburized layer thinner than the carburized layer on the tooth surface is secured . When the intermediate formed body is formed into a gear shape in the second forging step, the concave portions on both sides are formed into a center hole having an inner beam between both sides. At this time, in the gear manufacturing method, in particular, a carburized layer having a uniform depth is formed in the concave portions on both sides, and both the concave portions are formed into a center hole with an inner flash, so the carburized layer on the inner wall portion of the center hole. Is substantially continuous from one center hole to the other center hole through the inner beam. Therefore, by subsequently removing the inner beam, the carburized layer is kept well along the inner wall portion of the center hole that has penetrated, and this carburized layer makes it possible to wear and seize the shaft inserted into the center hole. Is secured. Na us, the gear was molded by the second forging step, if necessary, hardening, etc. shot blasting and machining is performed.
[0010]
Here, in the process of forming the blank into a gear shape, since the amount of plastic deformation of the tooth root portion of the tooth profile is particularly large, when the blank subjected to carburizing treatment is formed into a gear shape by one forging, the deformation amount of the carburized layer The carburization layer at the tooth root may become too thin, and the depth of the carburization layer at the tooth surface may be increased by forming a deep initial carburization layer to secure the carburization layer at the tooth root. May become excessive.
[0011]
On the other hand, in the gear manufacturing method, the blank is formed into an intermediate formed body, and the intermediate formed body is subjected to carburizing treatment and then the intermediate formed body is formed into a gear shape. The amount of plastic deformation of the tooth root in the forging process is small, and accordingly, the amount of deformation of the carburized layer is small. Therefore, it is prevented that the carburized layer of the tooth root is too thin, and the initial carburizing is performed. Since the carburized layer of the tooth root is secured without forming a deep layer, the depth of the carburized layer of the tooth surface does not become excessive, and the appropriate depth for each of the tooth surface and the tooth root A carburized layer is secured.
[0013]
In the gear manufacturing method according to claim 2 of the present invention, the intermediate tooth surface of the intermediate molded body is approximated to the final gear shape, and the tooth surface is formed into a curved surface shape that smoothly continues outward. Then, through the carburizing process and the second forging process performed thereafter, a carburized layer having a predetermined depth is more easily and reliably secured in the tooth surface portion, and the tooth base portion than the carburized layer of the tooth surface portion. A thin carburized layer is more easily and reliably ensured.
[0014]
In the gear manufacturing method according to claim 3 of the present invention, the blank is carburized before the first forging step, and then the blank is formed into an intermediate formed body in the first forging step, and the intermediate formed body is carburized. Since the intermediate formed body is formed into a gear shape in the second forging process, the opportunity to control the formation pattern of the carburized layer in the tooth surface portion and the tooth root portion of the tooth profile is increased. For example, the carburized layer in the tooth root portion It is also possible to intentionally increase the depth of the carburized layer of the tooth surface portion while preventing it from becoming too thin.
[0015]
That is, when the first forging process is performed after carburizing the blank, the carburized layer of the tooth root portion can be made thin while maintaining the depth of the carburized layer of the tooth surface portion. Form the carburized layer of the base part thinner than the appropriate depth. Thereafter, if the carburizing treatment is performed on the intermediate formed body and the second forging step is performed, the depth of the carburized layer at the tooth surface portion is further increased, and the carburized layer at the tooth base portion becomes an appropriate depth.
[0016]
【The invention's effect】
According to the gear manufacturing method according to claim 1 of the present invention, the blank is formed into an intermediate formed body in the first forging step, and the intermediate formed body is subjected to carburizing treatment, and then the intermediate formed body is formed in the second forging step. By adopting a method of forming a gear shape, a carburized layer of a predetermined depth is secured on the tooth surface portion of the tooth profile to obtain wear resistance, and a tooth surface portion is obtained on the tooth base portion to obtain impact fatigue strength. When a carburized layer that is thinner than the carburized layer is secured, it is possible to prevent the carburized layer at the tooth root portion from becoming too thin, and even if the initial carburized layer in the intermediate formed body is not deeply formed, As the carburized layer is secured, the carburization cost can be reduced, and the carburized layer depth of the tooth surface can be prevented from becoming excessive. A carburized layer with a sufficient depth can be secured. Further, if the shape of the intermediate formed body is selected, it is possible to intentionally increase the depth of the carburized layer at the tooth surface while making the carburized layer at the tooth base portion appropriate. And when manufacturing the gear used for the differential of a motor vehicle, it is possible to obtain a gear having individual characteristics in the tooth surface portion and the tooth root portion and capable of sufficiently responding to high output of the power transmission system.
[0017]
In addition, the gear manufacturing method according to claim 1 of the present invention does not require a step of forming a center hole in advance in a solid blank, and can reduce the number of man-hours and the manufacturing cost. In addition, a good carburized layer with almost no carburized layer breakage can be obtained on the inner wall of the center hole, and the carburized layer ensures sufficient wear resistance and seizure resistance for the shaft inserted into the center hole. can do.
[0018]
According to the manufacturing method of the gear according to claim 2 of the present invention, on top that can obtain the same effect as claim 1, to approximate the tooth surface of the intermediate shape of the preform into the final gear shape and outer By making the curved surface shape smoothly continuous, a carburized layer having a predetermined depth can be more easily and surely secured on the tooth surface portion through a carburizing process and a second forging process performed thereafter. In addition, a carburized layer that is thinner than the carburized layer on the tooth surface can be more easily and reliably secured at the tooth base.
[0019]
According to the gear manufacturing method according to claim 3 of the present invention, the same effects as in claims 1 and 2 can be obtained, and after carburizing the blank, the first forging step, carburizing treatment and Through the second forging process, the formation pattern of the carburized layer of the tooth surface portion and the tooth root portion can be changed more widely, and a carburized layer having a desired depth is formed on each of the tooth surface portion and the tooth root portion. For example, a gear in which the carburized layer is greatly changed between the tooth surface portion and the tooth root portion can be manufactured.
[0020]
【Example】
1 and 2 are diagrams for explaining an embodiment of a gear manufacturing method according to the present invention. In this embodiment, the gear G shown in FIG. 1 (g) is a bevel gear used for a differential of an automobile, and has a tooth profile A from a small diameter portion to a large diameter portion, and along the axial direction. A center hole H is provided, and a back spherical surface R is provided on the large diameter side.
[0021]
In order to manufacture the gear G, a solid cylindrical blank B as shown in FIG. 1A is used, and the blank B is heated to about 900 to 1100 ° C., and then the blank B is first forged. In the process, an intermediate shape between the initial shape and the final gear shape is formed, and as shown in FIG. 1B, a substantially gear-shaped intermediate formed body F having an incomplete tooth shape is obtained. The intermediate shape of the intermediate molded body F has a curved surface shape in which the tooth surface approximates the final gear shape and the tooth surface smoothly continues to the outside.
[0022]
In the first forging step, a forging die as shown in FIG. The forging die includes an upper die 2 having an upper punch 1 inserted in the center and a lower die 4 having a lower punch 3 inserted in the center. The upper die 2 has a molded part 5 of a tooth profile A, and the lower 4 die has a molded part 6 of a back spherical surface R. Each of the upper and lower punches 1 and 3 has hemispherical convex portions 1a and 3a at the tip. In the first forging step, the tooth profile A and the back spherical surface R are primarily formed using the forging die described above, and the punches 1 and 3 are used to form recesses 7 in portions corresponding to both sides of the center hole H of the blank B. , 8 are molded to obtain an intermediate molded body F. At this time, the concave portions 7 and 8 are formed into a hemispherical bottom by the convex portions of the punches 1 and 3, and the vicinity of the opening is formed into a curved surface that is smoothly continuous to the outside.
[0023]
The intermediate molded body F molded as described above is subjected to carburizing treatment to form a uniform carburized layer C as shown in FIGS. 1C and 1D. The carburization depth at this time is appropriately set according to the required carburization depth as a part, the amount of plastic deformation in the second forging process, and the like. Thereafter, the intermediate formed body F is reheated to about 900 to 1100 ° C., and the intermediate formed body F is formed into a gear shape shown in FIGS. 1E and 1F in the second forging step.
[0024]
In the second forging step, a forging die as shown in FIG. 2B is used. The forging die includes an upper die 12 having an upper punch 11 inserted at the center and a lower die 14 having a lower punch 13 inserted at the center. The upper die 12 has a molded part 15 of a tooth profile A, and the lower 14 die has a molded part 16 of a back spherical surface R. Each of the upper and lower punches 11 and 13 has a flat tip portion. In the second forging step, the tooth profile A and the back spherical surface R are secondarily formed using the forging die described above, and the concave portions 7 and 8 on both sides are inserted between the two by the punches 11 and 13. The bottomed cylindrical center holes 7H and 8H are formed.
[0025]
At this time, the center holes 7H and 8H are formed by forming the recesses 7 and 8 in the intermediate formed body F in the first forging process, carburizing, and then forming the center holes 7H and 8H into the state with the inner flash V in the second forging process. As a result, the carburized layer C on the inner wall portion is in a state of being substantially continuous from the one center hole 7H to the other center hole 8H through the inner flash V.
[0026]
Thereafter, in the gear manufacturing method, the inner beam V of the center holes 7H and 8H is punched and removed using a piercing die or the like to obtain the gear G shown in FIG. Thereby, the carburized layer C is well maintained along the inner wall portion of the penetrating center hole H. Thereafter, the gear G is quenched (block B1) as shown in FIG. 1 (h), then shot blasted (B2), and further subjected to appropriate machining (B3).
[0027]
Thus, in the gear manufacturing method described above, the tooth surface portion (Ga) has a predetermined depth as in the tooth profile having the ideal carburized layer C shown in FIG. The carburized layer C is secured, the carburized layer C thinner than the carburized layer C of the tooth surface portion is secured at the tooth base portion (Gb), and a good carburized layer C is secured also at the inner wall portion of the center hole H.
[0028]
That is, in the process of forming the blank B into a gear shape, the amount of plastic deformation of the tooth root portion of the tooth profile is particularly large, and a problem such as the carburized layer C of the tooth root portion becoming too thin may occur. In this manufacturing method, the blank B is formed into an intermediate formed body F, and in particular, the intermediate-shaped tooth surface of the intermediate formed body F has a curved surface shape that approximates the final gear shape and smoothly continues to the outside. The intermediate formed body F is subjected to carburizing treatment, and then the intermediate formed body F is formed into a gear shape so that the amount of plastic deformation of the tooth root portion in the second forging step after the carburizing treatment is reduced. Accordingly, the deformation amount of the carburized layer C is reduced. Therefore, the carburized layer C of the tooth base portion does not become too thin, and the carburized layer C of the tooth root portion is ensured without forming the initial carburized layer C deeply. Therefore, the carburized layer C having an appropriate depth is ensured in each of the tooth surface portion and the tooth root portion.
[0029]
And the gear G has a wear resistance secured by maintaining the depth of the carburized layer C at the tooth surface portion meshing with the gear of the other, and the carburized layer is thinned at the tooth base portion that receives impact input during rotation. The impact fatigue strength is ensured, and furthermore, the carburized layer C is well maintained on the inner wall portion of the center hole that comes into contact with the shaft inserted in the inner wall portion of the center hole, so that wear resistance and seizure resistance are ensured. Therefore, as a gear used for a differential of an automobile, it has characteristics for each part and can sufficiently cope with a high output of a power transmission system.
[0030]
The gear manufacturing method according to the present invention may be carburized on the blank B before the first forging step, as described in the above embodiment. That is, the blank B shown in FIG. 1A is subjected to carburizing treatment, and then the blank B is formed into an intermediate formed body F in the first forging step, and the intermediate formed body F is subjected to carburizing treatment, and then the second forging step. Then, the intermediate formed body F is formed into a gear shape.
[0031]
In such a gear manufacturing method, the same effects as in the previous embodiment can be obtained, and in addition, the opportunity to control the formation pattern of the carburized layer C in the tooth surface portion and the tooth root portion of the tooth profile is increased. It is also possible to intentionally increase the depth of the carburized layer C at the tooth surface while preventing the carburized layer C at the base from becoming too thin. That is, when the first forging process is performed after the blank B is subjected to the carburizing process, the carburized layer C of the tooth base portion can be made thin while maintaining the depth of the carburized layer C of the tooth surface portion. In addition, the carburized layer C of the tooth base is formed thinner than an appropriate depth. After that, if the carburizing treatment is performed on the intermediate formed body F and the second forging process is performed, the depth of the carburized layer C in the tooth surface portion further increases, and the carburized layer C in the tooth root portion has an appropriate depth.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view (a) to (g) and a block diagram (h) illustrating a manufacturing process in an embodiment of a gear manufacturing method according to the present invention.
2 is a cross-sectional view (a) showing an example of a forging die used in the first forging step of the method for manufacturing the gear shown in FIG. 1, and a cross-sectional view (b) showing an example of the forging die used in the second forging step. .
FIG. 3 is a cross-sectional view of a tooth profile when carburizing is performed after the tooth formation (a), a cross-sectional view of the tooth profile when carburizing is performed after the tooth formation is carburized and carburized (b), and carburizing. It is sectional drawing (c) of a tooth profile at the time of forging a tooth profile after a process.
[Explanation of symbols]
B Blank C Carburized layer F Intermediate compact G Gear H Center hole V Inner beam 7 8 Recess 7H 8H Center hole before removing inner beam

Claims

Upon manufacturing a tooth wheel having a center hole, the portion corresponding to both sides of the blank center hole of the well as formed form an intermediate shape between the cylindrical blank the initial shape and the final gear shape in the first forging step in molding the recess, then subjected to carburizing treatment to the intermediate product, forming an intermediate formed body in a second forging step in the center hole having an inner burr between both recesses Rutotomoni sides be molded to the gear shape to Following the method of manufacturing a gear which is characterized that you remove the inner beams of the center hole.

The gear manufacturing method according to claim 1, wherein the intermediate-shaped tooth surface of the intermediate formed body has a curved surface shape that approximates the final gear shape and smoothly continues to the outside.

The gear manufacturing method according to claim 1 or 2, wherein the blank is subjected to a carburizing process before the first forging step.