JP3617763B2

JP3617763B2 - Molding method for green compacts used as sintered materials

Info

Publication number: JP3617763B2
Application number: JP36827197A
Authority: JP
Inventors: 毅大場; 好美菅谷
Original assignee: Hitachi Powdered Metals Co Ltd
Current assignee: Hitachi Powdered Metals Co Ltd
Priority date: 1997-12-26
Filing date: 1997-12-26
Publication date: 2005-02-09
Anticipated expiration: 2017-12-26
Also published as: JPH11193403A

Description

【０００１】
【発明の属する技術分野】
本発明は、焼結品の素材とされる圧粉体の成形方法に係り、特に異種粉末材料を複合させた圧粉体を成形する方法に関する。
【０００２】
【従来の技術】
例えば、楕円状の板カム等の摺動部材は、その摺動面を形成する外周部（特に強い圧力を受けるカムトップ部）に高い耐摩耗性が要求される一方、内側の肉部の耐摩耗性はそれほど高くなくてもよく、よって、外周部と内側の肉部の材料を異ならせた複合構造としてコストダウンを図ることが行われている。複合構造の部材を製造するには粉末冶金法が製法上有利である。例えば、特開昭５５−１００９０３号、特開昭５７−１６９００３号および特開昭５７−２００５０３号には、金型のキャビティを仕切板等で分割し、各分割キャビティ内に異種粉末をそれぞれ充填し、次いで仕切板を除外して各粉末を接触させた後に圧縮して圧粉体を得る方法が開示されている。ところが、このような方法では、仕切板を要するとともに仕切板のセットや除外といった操作に手間がかかる不利な面があった。
【０００３】
そこで、仕切板を用いない方法として、特開昭５８−１４１８９５号には、互いに摺動する２つの金型のキャビティ内に異種粉末をそれぞれ充填し、一方の金型を動かして双方のキャビティを合わせることにより各粉末を接触させた後に圧縮する方法が開示されている。また、特開昭５７−１２０６０１号には、複数種の粉末のうちの一部を予成形してその予成形体を金型のキャビティ内に挿入し、このキャビティ内に他の粉末を充填してから、予成形体と粉末とを圧縮する方法が開示されている。
【０００４】
【発明が解決しようとする課題】
上記の仕切板を用いない方法のうちの前者の方法にあっては、金型の構造が複雑化してコストがかかるとともに、２つの金型のキャビティどうしを合わせて最終的に形成するキャビティの精度が不安定になりやすく、その制御が難しいことが想定される。また、後者の方法では、２層構造の部材は形成することができるものの、３層以上の複雑な部材には適用しにくいといった欠点がある。
したがって本発明は、特殊な金型を要することなく、かつ複雑な層構造の部材であっても容易に圧粉体を得ることのできる圧粉体の成形方法を提供することを目的としている。
【０００５】
【課題を解決するための手段】
本発明は上記目的を達成するためになされたものであり、複数の予圧粉体をハンドリングが可能な密度に成形し、次いで、これら予圧粉体を、前記圧粉体を成形し得る成形型のキャビティ内にセットし、この後、前記複数の予圧粉体を押し型で圧縮して相互に接合させることを特徴としている。
【０００６】
この方法によれば、はじめから圧粉体を成形する成形型のキャビティ内に粉末を充填せず、まず、成形すべき圧粉体を適宜に分割した形状の予圧粉体を、ハンドリングが可能な密度に成形する。ここで言うハンドリングが可能な密度とは、手に持って取り扱うことができ、その際に損壊しない状態を可能とする密度を指す。そして、これら予圧粉体を、圧粉体を成形し得る成形型のキャビティ内に組み合わせてセットする。この後、予圧粉体を本圧縮して隣接する予圧粉体どうしの接合を行わしめるとともに成形し、成形型から抜き出して圧粉体を得る。
【０００７】
ここで、予め成形しておく予圧粉体の密度は、上記のようにハンドリングが可能であることが前提であるが、これに加えて、圧縮時に、隣接する予圧粉体どうしが接合され得るような密度が求められる。予圧粉体どうしの接合は、密度が低ければ低いほど十分になされるものであるが、密度が低すぎると、今度はハンドリングが不可能となってしまう。接合が可能な条件としては、密度比（同一組成の金属の真密度に対する成形体で得られた密度の比）が７６％未満の場合と知られており、７６％超の場合には、接合界面にクラックが生じる確率が高くなり好ましくない。したがって、予圧粉体の密度としては、密度比が７６％未満で、なおかつハンドリングが可能な範囲内で選択され、その範囲としては、６０〜７５％の密度比が実現される密度が好適である。例えば、粉末がＦｅ系の場合は４．７〜５．９ｇ／ｃｍ^３、Ａｌの場合は１．６〜２ｇ／ｃｍ^３、Ｃｕ系の場合は５．３〜６．６ｇ／ｃｍ^３が好適とされる。
【０００８】
また、予圧粉体の密度を上記の値より低く設定しておき、その予圧粉体を圧縮成形した最終的な圧粉体を焼結する温度の約３０〜６５％程度の温度で脱ろうおよび仮焼結すると、予圧粉体の強度が高くなり、例えば予圧粉体を移送機械を用いて成形型に供給する際に好都合となる。仮焼結の温度が高い場合には強度が高まる反面、成形型で圧縮したときの接合が不十分となりやすい。例えば、鉄粉を主とする予圧粉体では、７５０℃程度を仮焼結の最高温度とするのが好ましい。
【０００９】
本発明によれば、粉末を充填して圧縮する通常の成形型をそのまま流用することができるので特殊な成形型を必要とせず、しかも層を隔てるための仕切板をキャビティにセットする必要もない。また、層の数が多くて複雑な構造の圧粉体であっても、それに応じた形状の予圧粉体を組み合わせて圧縮することにより、目的とする圧粉体の成形が容易化する。さらに、予め予圧粉体を多量に作ってストックしておき、必要に応じて本圧縮して圧粉体を得るようにすれば、圧粉体を成形するたびに粉末の調整や充填を行う手間が省け、生産性の向上が図られる。
【００１０】
さて、本発明における複数の予圧粉体は、本圧縮の際に変形し、かつ相互に接合されて所望の圧粉体形状に成形される。ここでその形状（特に圧縮方向からみた場合の平面形状）は、キャビティ内にセット可能であれば圧縮後の最終形状に近いものでなくともよく、ある程度ラフな形状であってかまわない。その場合、圧縮時には予圧粉体に大きな崩壊が伴うことがあるが、崩壊の過程を経て最終的に圧縮・成形される。しかしながら、勿論最終形状に近いものであれば有利であり、したがって、予圧粉体は、互いに組み合わせることにより本圧縮後の圧粉体の形状に相似するよう成形され、その組み合わせ状態で、キャビティ内にセットされることが好ましい。
【００１１】
また、本発明における予圧粉体は、求められる特性が異なる部位別に、密度や形状を異ならせて成形される形態を特徴している。すなわち、例えば圧粉体が前述したような楕円状の板カムの素材である場合、予圧粉体を、高い耐摩耗性が要求される外周部と、それほど耐摩耗性を要求されない内側の肉部の２つとする。そして、外周部の予圧粉体を密度を高いものとし、かつ加工度が高まるように余肉部が大きい形状とし、一方、内側の肉部の予圧粉体の密度を低くする。このように複数の予圧粉体を部位に応じて成形し、組み合わせて本圧縮すれば、自動的に各部位の特性が求められるものとなり得る。
【００１２】
さらに、本発明では、隣接する予圧粉体どうしの接合強度を高めるために、予圧粉体の互いの接合面が、互いに噛み合う凹凸面に形成されているか、もしくは少なくとも一方の接合面が凹凸面に形成されていることを好ましい形態としている。
【００１３】
【発明の実施の形態】
以下、図面を参照して本発明の実施形態について説明する。
（１）第１の実施形態
図１は、第１の実施形態に係る圧粉体１を示している。この圧粉体１は、自動車のエンジンに組み込まれる円筒状のバルブガイドの素材であり、焼結工程を経て製品とされる。製品であるバルブガイドとしては、端部２，２に高い耐久性が要求され、一方、中央部３は端部２，２よりも耐久性に劣っていてもよいとされている。以下に、この圧粉体１を成形する工程を説明する。
【００１４】
「工程１−予圧粉体の成形」
図示せぬ所定の成形型により、図２に示す３つ１組の予圧粉体２ａ，３ａ，２ａを成形する。これら予圧粉体２ａ，３ａ，２ａは、圧粉体１の端部２，２に対応する円筒状の２つの端部２ａ，２ａおよび中央部３に対応する円筒状の中央部３ａであり、中央部３ａの両端に端部２ａ，２ａをそれぞれ同軸的に組み合わせることにより、圧粉体１に相似する形状となる。端部２ａ，２ａおよび中央部３ａは、圧縮後の圧粉体１における端部２，２および中央部３よりも軸方向長さがそれぞれ長く、かつ直径は僅かに小さく設定される。いずれの予圧粉体２ａ，３ａ，２ａも、その密度比が６０〜７５％の範囲内になるように粉末が圧縮されて成形されてなり、ハンドリングが可能で、かつ後の本圧縮で互いに接合され得る密度を有している。しかしながらこの範囲内で、高い耐久性が要求される端部２ａ，２ａの密度は高く、中央部３ａの密度は端部２ａ，２ａよりも低く設定される。また、このような密度の設定に加えて、粉末は端部２，２および中央部３に応じたものが選択される。なお、予圧粉体２ａ，３ａ，２ａは本圧縮よりも圧力が低いので、粉末中への潤滑剤の添加を省略することができる。なお、圧粉体１は、後に焼結されるので、予圧粉体２ａ，３ａ，２ａの粉末材料は同じものか、あるいは液相が生じる異種元素もしくは固相拡散する異種元素が望ましい。
【００１５】
「工程２−成形装置への予圧粉体のセット」
工程１で得た３つの予圧粉体２ａ，３ａ，２ａを、図３（ａ）に示すようにして成形装置にセットする。成形装置は、金型（成形型）４、上下のパンチ（押し型）５，６およびコアロッド７を備えており、まず、金型４、下パンチ６およびコアロッド７によって形成されるキャビティ８内に、端部２ａ、中央部３ａ、端部２ａの順に、内部の空洞部をコアロッド７に通して挿入する。
【００１６】
「工程３−本圧縮」
図３（ｂ）に示すように、上パンチ５をキャビティ８内に下降させ、次いで、上下のパンチ５，６により予圧粉体２ａ，３ａ，２ａを縦方向に圧縮する。予圧粉体２ａ，３ａ，２ａはキャビティ８の形状にならって変形するとともに、互いに接合して圧粉体１とされる。なお、圧縮による接合強度を高めるために、予圧粉体２ａ，３ａ，２ａの互いの接合面に、互いに噛み合う凹凸面を形成しておくか、もしくは少なくとも一方の接合面に凹凸面を形成しておくと好ましい。
この後、上パンチ５を上昇させ、さらに下パンチ６を上昇させて圧縮・成形された圧粉体１を金型４内から取り出す。このようにして得られた圧粉体１は、予圧粉体２ａ，３ａ，２ａの粉末材料、密度または形状が反映されて中央部３よりも端部２，２の方が高い耐久性を有するものとなる。
【００１７】
（２）第２の実施形態
次に、本発明を板カムの成形に適用した第２の実施形態を説明する。
図４は、板カムの素材となる圧粉体１０を示している。板カムとしては、外周部１１に高い耐摩耗性が要求され、一方、内側の内周部１２は適度な強度が要求される。内周部１２の中央には、カムシャフトが嵌合される円形の嵌合孔１３が形成される。この嵌合孔１３は、カムシャフトの回り止めとなるキー溝１３ａを有している。以下に、この圧粉体１０を成形する工程を説明する。
【００１８】
「工程１−予圧粉体の成形」
図示せぬ所定の成形型により、図５に示す２つ１組の予圧粉体１１ａ，１２ａを成形する。これら予圧粉体１１ａ，１２ａは、圧粉体１０の外周部１１に対応するリング状の外周部１１ａおよび内周部１２に対応する内周部１２ａであり、外周部１１ａの中に内周部１２ａを入れた組み合わせ状態で、圧粉体１０に相似する形状となる。内周部１２ａには嵌合孔１３に対応する孔１３ｂが形成されている。これら外周部１１ａおよび内周部１２ａの厚さは圧粉体１０よりも厚く、かつ径方向の大きさは僅かに小さく設定される。いずれの予圧粉体１１ａ，１２ａも、その密度比が６０〜７５％の範囲内になるように粉末が圧縮されて成形されてなり、ハンドリングが可能で、かつ後の本圧縮で互いに接合され得る密度を有している。しかしながらこの範囲内で、高い耐摩耗性が要求される外周部１１ａの密度は高く、内周部１２ａの密度は外周部１１ａよりも低く設定される。また、このような密度の設定に加えて、粉末は外周部１１および内周部に１２に応じたものが選択される。
【００１９】
「工程２−成形装置への予圧粉体のセット」
工程１で得た２つの予圧粉体１１ａ，１２ａを、図６（ａ）に示すように、金型（成形型）１４、上下のパンチ（押し型）１５，１６およびコアロッド１７を備えた成形装置にセットする。コアロッド１７の外周面には、前記キー溝１３ａを形成するための凸条（図示略）が形成されている。セットの仕方は、まず、金型１４、下パンチ１６およびコアロッド１７によって形成されるキャビティ１８内に、内周部１２ａの空洞部をコアロッド１７に通して挿入し、次いで外周部１１ａを内周部の周囲に置く。
【００２０】
「工程３−本圧縮」
図６（ｂ）に示すように、上パンチ１５をキャビティ１８内に下降させ、次いで、上下のパンチ１５，１６により予圧粉体１１ａ，１２ａを圧縮する。予圧粉体１１ａ，１２ａはキャビティ１８の形状にならって変形するとともに、互いに接合して圧粉体１０とされる。この後、上パンチ１５を上昇させ、さらに下パンチ１６を上昇させて圧縮・成形された圧粉体１０を金型１４内から取り出す。このようにして得られた圧粉体１０は、予圧粉体１１ａ，１２ａの粉末材料、密度または形状が反映されて内周部１２よりも外周部１１の方が高い耐摩耗性を有するものとなる。
【００２１】
（３）第３の実施形態
次に、本発明をギヤの成形に適用した第２の実施形態を説明する。
図７は、ギヤの素材となる圧粉体２０を示している。ギヤとしては、多数の歯２１ｘを有する外周部２１に高い耐摩耗性が要求され、一方、内側の内周部２２には適度な耐震性が要求される。内周部２２の中央には軸孔２３が形成され、さらにこの軸孔２３の周囲にはボス２３ｘが形成される。以下に、この圧粉体２０を成形する工程を説明する。
【００２２】
「工程１−予圧粉体の成形」
図示せぬ所定の成形型により、図８に示す２つ１組の予圧粉体２１ａ，２２ａを成形する。これら予圧粉体２１ａ，２２ａは、圧粉体２０の外周部２１に対応するリング状の外周部２１ａおよび内周部２２に対応する内周部２２ａであり、外周部２１ａの中に内周部２２ａを入れて組み合わせられる。外周部２１ａは単なるリング状で、歯２１ｘに対応する部分は形成されていない。また、内周部２２ａには軸孔２３に対応する孔２３ａが形成されているが、ボス２３ｘに対応する部分は形成されていない。これら外周部２１ａおよび内周部２２ａの厚さは圧粉体２０よりも厚く、かつ径方向の大きさは僅かに小さく設定される。いずれの予圧粉体２１ａ，２２ａも、その密度比が６０〜７５％の範囲内になるように粉末が圧縮されて成形されてなり、ハンドリングが可能で、かつ後の本圧縮で互いに接合され得る密度を有している。しかしながらこの範囲内で、高い耐摩耗性が要求される外周部２１ａの密度は高く、内周部２２ａの密度は外周部２１ａよりも低く設定される。また、このような密度の設定に加えて、粉末は外周部２１および内周部２２に応じたものが選択される。
【００２３】
「工程２−成形装置への予圧粉体のセット」
工程１で得た２つの予圧粉体２１ａ，２２ａを、図９（ａ）に示すように、金型（成形型）２４、上下のパンチ（押し型）２５，２６およびコアロッド２７を備えた成形装置にセットする。金型２４の内周面には、前記歯２１ｘを形成するための内歯（図示略）が形成されている。また、上パンチ２５には、前記ボス２３ｘを形成するための凹所２５ａが形成されている。セットの仕方は、まず、金型２４、下パンチ２６およびコアロッド２７によって形成されるキャビティ２８内に、内周部２２ａの空洞部をコアロッド２７に通して挿入し、次いで外周部２１ａを内周部２２ａの周囲に配する。
【００２４】
「工程３−本圧縮」
図９（ｂ）に示すように、上パンチ２５をキャビティ２８内に下降させ、次いで、上下のパンチ２５，２６により予圧粉体２１ａ，２２ａを圧縮する。予圧粉体２１ａ，２２ａはキャビティ２８の形状にならって変形するとともに、互いに接合して圧粉体２０とされる。この後、上パンチ２５を上昇させ、さらに下パンチ２６を上昇させて圧縮・成形された圧粉体２０を金型２４内から取り出す。このようにして得られた圧粉体２０は、予圧粉体２１ａ，２２ａの粉末材料、密度または形状が反映されて内周部２２よりも外周部２１の方が高い耐摩耗性を有し、かつ内周部２２は適度な耐震性を有するものとなる。
【００２５】
上記第１〜第３の実施形態によれば、粉末を充填して圧縮する通常の成形装置をそのまま流用することができ、しかも層を隔てるための仕切板をキャビティ内にセットすることなく複合構造の圧粉体（１，１０，２０）を成形することができる。また、予め予圧粉体を多量に作ってストックしておき、必要に応じて本圧縮して圧粉体を得るようにすれば、圧粉体を成形するたびに粉末の調整や充填を行う手間が省け、生産性の向上が図られる。さらに、予圧粉体の形状（圧縮方向からみた場合の平面形状）を、組み合わせ状態で圧粉体の最終形状に相似したものとしているので、本圧縮時の圧力を大幅に高くする必要がなく成形が容易となる。しかしながら、予圧粉体の形状はキャビティ内にセット可能であって、本圧縮により圧粉体の最終形状に成形される範囲であれば、ある程度ラフな形状であってかまわない。また、複数の予圧粉体を部位に応じて成形し、組み合わせて本圧縮するので、自動的に各部位の特性が求められるものとなる。
【００２６】
なお、上記第１〜第３の実施形態では、いずれも横断面が円形で、中心に孔を有する圧粉体を成形するものであり、その孔を形成するためのコアロッド（７，１７，２７）を圧縮方向に沿って立てているが、コアロッドを圧縮方向に対して直交してセットする形式の成形装置にも適用できる。また、圧縮する際には、通常、被圧縮体（この場合予圧粉体）が圧縮により摺動する金型（４，１４，２４）の内面に潤滑剤を塗布するが、本発明の場合は、予圧粉体をハンドリングできることにより、その予圧粉体の表面にに潤滑剤を塗布することができる。これは、金型によっては、その内面に潤滑剤を塗布する作業が困難な場合もあるので、作業上有利となる。さらに、第２および第３の実施形態では、圧粉体を焼結したときに、内周部と外周部とが互いに締まり合う寸法変化が生じる粉末材料を選択すると、接合強度が増大して好ましい。
【００２７】
なお、本発明は、複数の予圧粉体を組み合わせ、これを圧縮・成形して圧粉体を得る方法であり、上記第１〜第３の実施形態は、その方法および部材を具体化した例である。本発明により成形される部材は上記各実施形態に限定されるものでは勿論なく、いかなる圧粉体にも適用は可能である。そのような部材の例を、以下に説明する。
【００２８】
図１０（ａ）はリング状のバルブシートであり、図示せぬバルブフェースが密着する座面部３０と、その他の部分の主部３１とに分けられて予圧粉体が成形される。この場合、座面部３０が高い耐摩耗性を有するように予圧粉体が設定される。
図１０（ｂ）は回動自在に設けられるラチェット爪であり、爪部４０と、軸受部４１と、その他の部分の主部４２とに分けられて予圧粉体が成形される。この場合、爪部４０には高い耐摩耗性が要求され、また、軸受部に４１には潤滑油の保持機能を有するように多孔質が要求され、さらに主部４２には高い強度が要求される。したがって、これら部位となる各予圧粉体は、各特性を満足し得るよう設定される。
図１０（ｃ）は軸受であり、軸が摺動する内面部５０と、その他の部分の主部５１とに分けられて予圧粉体が成形される。この場合、内面部５０が高い耐摩耗性を有するように予圧粉体が設定される。
図１０（ｄ）はボールベアリングのレースであり、多数のボールが摺動する内面部６０と、これよりも外側の外面部６１とに分けられて予圧粉体が成形される。この場合、内面部６０が高い耐摩耗性を有するように予圧粉体が設定される。
図１０（ｅ）は板カムであり、高い圧力を受けるトップ部７０と、その他の部分のボトム部７１とに分けられて予圧粉体が成形される。この場合、トップ部７０が高い耐摩耗性を有するように予圧粉体が設定される。
【００２９】
【発明の効果】
以上説明したように本発明によれば、複数の予圧粉体をハンドリングが可能な密度に成形し、次いで、これら予圧粉体を押し型で圧縮して相互に接合させることにより所望の圧粉体を成形することを特徴とするから、特殊な金型を要することなく、かつ複雑な層構造の部材であっても容易に圧粉体を得ることのできるといった効果を奏する。
【図面の簡単な説明】
【図１】本発明の第１の実施形態に係る圧粉体の斜視図である。
【図２】本発明の第１の実施形態に係る予圧粉体の斜視図である。
【図３】本発明の第１の実施形態に係る圧粉体を成形する工程を順に示す断面図である。
【図４】本発明の第２の実施形態に係る圧粉体の斜視図である。
【図５】本発明の第２の実施形態に係る予圧粉体の斜視図である。
【図６】本発明の第２の実施形態に係る圧粉体を成形する工程を順に示す断面図である。
【図７】本発明の第３の実施形態に係る圧粉体の斜視図である。
【図８】本発明の第３の実施形態に係る予圧粉体の斜視図である。
【図９】本発明の第３の実施形態に係る圧粉体を成形する工程を順に示す断面図である。
【図１０】本発明を適用して成形することのできる部材の例を示す斜視図である。
【符号の説明】
１，１０，２０…圧粉体、
２ａ，３ａ，１１ａ，１２ａ，２１ａ，２２ａ…予圧粉体、
４，１４，２４…金型（成形型）、
５，１５，２５…上パンチ（押し型）、
６，１６，２６…下パンチ（押し型）、
８，１８，２８…キャビティ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a green compact used as a material for a sintered product, and more particularly to a method for forming a green compact in which different powder materials are combined.
[0002]
[Prior art]
For example, a sliding member such as an elliptical plate cam is required to have high wear resistance at the outer peripheral portion (particularly a cam top portion that receives a strong pressure) that forms the sliding surface, while the inner flesh portion is resistant to wear. Abrasion does not have to be so high. Therefore, cost reduction is being achieved as a composite structure in which materials of the outer peripheral portion and the inner meat portion are different. The powder metallurgy method is advantageous in terms of manufacturing method for producing a member having a composite structure. For example, in Japanese Patent Laid-Open Nos. 55-100903, 57-169003 and 57-200003, the mold cavity is divided by a partition plate or the like, and each divided cavity is filled with a different type of powder. Then, a method is disclosed in which a compact is obtained by excluding the partition plate and bringing the powders into contact with each other and then compressing them. However, such a method has a disadvantage in that it requires a partition plate and takes time and effort to set and remove the partition plate.
[0003]
Therefore, as a method that does not use a partition plate, Japanese Patent Laid-Open No. 58-141895 describes that cavities of two molds that slide with each other are filled with different types of powder, and one mold is moved to move both cavities. A method is disclosed in which the powders are brought into contact and then compressed after being brought together. Japanese Patent Application Laid-Open No. 57-120601 discloses that a part of a plurality of types of powders is preformed, the preform is inserted into a cavity of a mold, and another powder is filled in the cavity. Since then, a method of compressing a preform and a powder has been disclosed.
[0004]
[Problems to be solved by the invention]
In the former method that does not use the partition plate, the mold structure is complicated and expensive, and the accuracy of the cavity finally formed by combining the cavities of the two molds is high. Is likely to become unstable and difficult to control. In the latter method, a member having a two-layer structure can be formed, but there is a drawback that it is difficult to apply to a complicated member having three or more layers.
Accordingly, an object of the present invention is to provide a method for forming a green compact that can easily obtain a green compact even with a member having a complicated layer structure without requiring a special mold.
[0005]
[Means for Solving the Problems]
The present invention has been made in order to achieve the above-mentioned object, and a plurality of pre-compressed powders are molded to a density that can be handled, and then these pre-compressed powders are molded molds that can form the green compacts. It is characterized in that it is set in a cavity, and thereafter, the plurality of pre-pressed powders are compressed with a pressing die and joined together.
[0006]
According to this method, it is possible to handle a pre-compacted powder having a shape obtained by appropriately dividing the compact to be molded without first filling the cavity of the molding die for molding the compact from the beginning. Mold to density. The density that can be handled here refers to a density that can be handled by hand and that does not break down. Then, these pre-compressed powders are set in combination in a cavity of a mold that can form the green compact. Thereafter, the pre-pressurized powder is subjected to main compression, the adjacent pre-pressurized powders are joined to each other and molded, and then extracted from the mold to obtain the green compact.
[0007]
Here, the density of the pre-compacted powder to be preliminarily formed is premised on handling as described above, but in addition to this, adjacent pre-compressed powders can be joined together during compression. High density is required. The lower the density, the better the bonding between the preloaded powders. However, if the density is too low, handling becomes impossible this time. It is known that the density ratio (ratio of the density obtained by the molded body to the true density of the metal having the same composition) is less than 76% as a condition for joining. The probability that a crack will occur at the interface increases, which is not preferable. Therefore, the density of the pre-pressed powder is selected within a range in which the density ratio is less than 76% and can be handled, and a density that realizes a density ratio of 60 to 75% is preferable as the range. . For example, if the powder is 3, Cu-based 1.6~2g / ^cm in the case when the Fe-based 4.7~5.9g / ^cm 3, Al preferably 5.3~6.6g / cm ³ It is said.
[0008]
Further, the density of the pre-pressed powder is set lower than the above value, and dewaxing is performed at a temperature of about 30 to 65% of the temperature at which the final green compact obtained by compression-molding the pre-pressed powder is sintered. Pre-sintering increases the strength of the pre-pressurized powder, which is convenient when, for example, the pre-pressurized powder is supplied to the mold using a transfer machine. When the pre-sintering temperature is high, the strength is increased, but on the other hand, bonding when compressed with a mold tends to be insufficient. For example, in the pre-compressed powder mainly composed of iron powder, it is preferable to set the maximum temperature for pre-sintering at about 750 ° C.
[0009]
According to the present invention, a normal mold for filling and compressing powder can be used as it is, so no special mold is required, and there is no need to set a partition plate for separating layers in the cavity. . Further, even if the green compact has a large number of layers and has a complicated structure, the compacting of the target green compact is facilitated by combining and compressing the pre-compressed powder having a corresponding shape. In addition, if a large amount of pre-compressed powder is prepared and stocked in advance and then compressed as necessary to obtain a compact, the effort to adjust and fill the powder each time the compact is formed. Can be saved and productivity can be improved.
[0010]
Now, the plurality of pre-compacted powders in the present invention are deformed during the main compression and are joined to each other to be formed into a desired green compact shape. Here, the shape (particularly, the planar shape when viewed from the compression direction) does not have to be close to the final shape after compression as long as it can be set in the cavity, and may be somewhat rough. In this case, the pre-compacted powder may be largely collapsed during compression, but is finally compressed and molded through the process of collapse. However, of course, it is advantageous if it is close to the final shape. Therefore, the pre-compacted powder is shaped so as to resemble the shape of the compact after the main compression by combining with each other, and in the combined state, it is placed in the cavity. It is preferably set.
[0011]
In addition, the pre-pressurized powder according to the present invention is characterized in that it is molded with different densities and shapes for each part having different required characteristics. That is, for example, when the green compact is a material of an elliptical plate cam as described above, the pre-pressed powder is divided into an outer peripheral portion that requires high wear resistance and an inner meat portion that does not require so much wear resistance. Two of these. Then, the pre-pressed powder in the outer peripheral portion is made to have a high density and a shape having a large surplus portion so that the degree of processing is increased, while the density of the pre-pressed powder in the inner meat portion is reduced. In this way, if a plurality of pre-compressed powders are formed according to a part, combined and subjected to main compression, the characteristics of each part can be automatically obtained.
[0012]
Furthermore, in the present invention, in order to increase the bonding strength between adjacent preloaded powders, the bonding surfaces of the preloaded powders are formed as uneven surfaces that mesh with each other, or at least one of the bonding surfaces is formed into a rugged surface. It is preferred that it is formed.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(1) First embodiment Fig. 1 shows a green compact 1 according to a first embodiment. The green compact 1 is a material of a cylindrical valve guide incorporated in an automobile engine, and is made into a product through a sintering process. As a valve guide which is a product, the end portions 2 and 2 are required to have high durability, while the central portion 3 may be less durable than the end portions 2 and 2. Below, the process of shape | molding this green compact 1 is demonstrated.
[0014]
"Step 1-Molding of pre-pressed powder"
A set of three pre-pressurized powders 2a, 3a, 2a shown in FIG. 2 is formed by a predetermined mold (not shown). These pre-compacted powders 2a, 3a, 2a are two cylindrical end portions 2a, 2a corresponding to the end portions 2, 2 of the green compact 1, and a cylindrical central portion 3a corresponding to the central portion 3. A shape similar to the green compact 1 is obtained by coaxially combining the end portions 2a and 2a with both ends of the central portion 3a. The end portions 2a, 2a and the center portion 3a are set to have axial lengths that are longer than those of the end portions 2, 2 and the center portion 3 in the green compact 1 after compression, and slightly smaller in diameter. Any of the pre-pressurized powders 2a, 3a, 2a is formed by compressing the powder so that the density ratio is in the range of 60 to 75%, and can be handled and joined to each other by subsequent main compression. Has a density that can be achieved. However, within this range, the density of the end portions 2a and 2a that require high durability is high, and the density of the central portion 3a is set lower than that of the end portions 2a and 2a. In addition to setting the density, powders corresponding to the end portions 2 and 2 and the central portion 3 are selected. In addition, since the pre-pressurized powders 2a, 3a, 2a have a lower pressure than the main compression, the addition of a lubricant to the powder can be omitted. Since the green compact 1 is sintered later, the powder material of the pre-pressed powders 2a, 3a, 2a is preferably the same, or a different element that causes a liquid phase or a different element that causes solid phase diffusion.
[0015]
"Step 2-Setting the pre-loaded powder to the molding equipment"
Three pre-pressurized powders 2a, 3a, 2a obtained in step 1 are set in a molding apparatus as shown in FIG. The molding apparatus includes a mold (molding mold) 4, upper and lower punches (pushing molds) 5, 6 and a core rod 7. First, in a cavity 8 formed by the mold 4, the lower punch 6 and the core rod 7. The internal cavity is inserted through the core rod 7 in the order of the end 2a, the center 3a, and the end 2a.
[0016]
"Step 3-Main compression"
As shown in FIG. 3 (b), the upper punch 5 is lowered into the cavity 8, and the pre-pressurized powders 2a, 3a, 2a are then compressed in the vertical direction by the upper and lower punches 5, 6. The pre-compacted powders 2a, 3a, 2a are deformed according to the shape of the cavity 8, and are joined together to form the compact 1. In order to increase the bonding strength by compression, an uneven surface that meshes with each other is formed on the bonding surfaces of the pre-loaded powders 2a, 3a, 2a, or an uneven surface is formed on at least one of the bonding surfaces. It is preferable.
Thereafter, the upper punch 5 is raised and the lower punch 6 is further raised, and the green compact 1 compressed and molded is taken out from the mold 4. The green compact 1 thus obtained has higher durability at the end portions 2 and 2 than at the central portion 3 reflecting the powder material, density or shape of the pre-pressed powders 2a, 3a and 2a. It will be a thing.
[0017]
(2) Second embodiment Next, a second embodiment in which the present invention is applied to the formation of a plate cam will be described.
FIG. 4 shows a green compact 10 as a material for the plate cam. As a plate cam, the outer peripheral portion 11 is required to have high wear resistance, while the inner peripheral portion 12 is required to have an appropriate strength. A circular fitting hole 13 into which the camshaft is fitted is formed at the center of the inner peripheral portion 12. The fitting hole 13 has a key groove 13a that prevents the camshaft from rotating. Below, the process of shape | molding this green compact 10 is demonstrated.
[0018]
"Step 1-Molding of pre-pressed powder"
A set of two pre-compressed powders 11a and 12a shown in FIG. 5 is formed by a predetermined mold (not shown). These pre-compacted powders 11a and 12a are a ring-shaped outer peripheral part 11a corresponding to the outer peripheral part 11 of the green compact 10 and an inner peripheral part 12a corresponding to the inner peripheral part 12, and the inner peripheral part in the outer peripheral part 11a. It becomes a shape similar to the green compact 10 in the combined state including 12a. A hole 13b corresponding to the fitting hole 13 is formed in the inner peripheral portion 12a. The outer peripheral portion 11a and the inner peripheral portion 12a are thicker than the green compact 10, and the radial size is set slightly smaller. Any of the pre-pressurized powders 11a and 12a is formed by compressing the powder so that the density ratio is in the range of 60 to 75%, can be handled, and can be joined to each other in the subsequent main compression. It has a density. However, within this range, the density of the outer peripheral part 11a requiring high wear resistance is high, and the density of the inner peripheral part 12a is set lower than that of the outer peripheral part 11a. In addition to the density setting, powders corresponding to the outer peripheral portion 11 and the inner peripheral portion 12 are selected.
[0019]
"Step 2-Setting the pre-loaded powder to the molding equipment"
As shown in FIG. 6 (a), the two pre-pressurized powders 11a and 12a obtained in step 1 are molded with a die (molding die) 14, upper and lower punches (pushing die) 15 and 16, and a core rod 17. Set in the device. On the outer peripheral surface of the core rod 17, a protrusion (not shown) for forming the key groove 13a is formed. The setting method is as follows. First, the cavity portion of the inner peripheral portion 12a is inserted through the core rod 17 into the cavity 18 formed by the die 14, the lower punch 16, and the core rod 17, and then the outer peripheral portion 11a is inserted into the inner peripheral portion. Put around.
[0020]
"Step 3-Main compression"
As shown in FIG. 6B, the upper punch 15 is lowered into the cavity 18, and then the pre-pressurized powders 11 a and 12 a are compressed by the upper and lower punches 15 and 16. The pre-compacted powders 11 a and 12 a are deformed according to the shape of the cavity 18 and are joined together to form the compact 10. Thereafter, the upper punch 15 is lifted, and the lower punch 16 is further lifted to take out the green compact 10 that has been compressed and molded from the mold 14. The green compact 10 thus obtained has higher wear resistance in the outer peripheral portion 11 than in the inner peripheral portion 12 reflecting the powder material, density or shape of the pre-pressed powder 11a, 12a. Become.
[0021]
(3) Third embodiment Next, a second embodiment in which the present invention is applied to gear molding will be described.
FIG. 7 shows a green compact 20 that is a material of the gear. As the gear, high wear resistance is required for the outer peripheral portion 21 having a large number of teeth 21x, while moderate inner earthquake resistance is required for the inner peripheral portion 22 inside. A shaft hole 23 is formed at the center of the inner peripheral portion 22, and a boss 23 x is formed around the shaft hole 23. Below, the process of shape | molding this green compact 20 is demonstrated.
[0022]
"Step 1-Molding of pre-pressed powder"
A set of two precompressed powders 21a and 22a shown in FIG. 8 is formed by a predetermined mold (not shown). These pre-compacted powders 21a and 22a are a ring-shaped outer peripheral part 21a corresponding to the outer peripheral part 21 of the green compact 20 and an inner peripheral part 22a corresponding to the inner peripheral part 22, and the inner peripheral part in the outer peripheral part 21a. Can be combined with 22a. The outer peripheral part 21a is a mere ring shape, and the part corresponding to the tooth | gear 21x is not formed. Moreover, although the hole 23a corresponding to the shaft hole 23 is formed in the inner peripheral part 22a, the part corresponding to the boss | hub 23x is not formed. The outer peripheral portion 21a and the inner peripheral portion 22a are thicker than the green compact 20, and the radial size is set slightly smaller. Each of the pre-pressurized powders 21a and 22a is formed by compressing and molding the powder so that the density ratio is in the range of 60 to 75%, can be handled, and can be joined to each other in the subsequent main compression. It has a density. However, within this range, the density of the outer peripheral portion 21a requiring high wear resistance is high, and the density of the inner peripheral portion 22a is set lower than that of the outer peripheral portion 21a. Further, in addition to the density setting, powder corresponding to the outer peripheral portion 21 and the inner peripheral portion 22 is selected.
[0023]
"Step 2-Setting the pre-loaded powder to the molding equipment"
As shown in FIG. 9 (a), the two preloaded powders 21a and 22a obtained in step 1 are molded with a die (molding die) 24, upper and lower punches (pushing die) 25 and 26, and a core rod 27. Set in the device. Inner teeth (not shown) for forming the teeth 21 x are formed on the inner peripheral surface of the mold 24. The upper punch 25 has a recess 25a for forming the boss 23x. The setting method is as follows. First, the cavity of the inner peripheral portion 22a is inserted through the core rod 27 into the cavity 28 formed by the mold 24, the lower punch 26 and the core rod 27, and then the outer peripheral portion 21a is inserted into the inner peripheral portion. Arranged around 22a.
[0024]
"Step 3-Main compression"
As shown in FIG. 9B, the upper punch 25 is lowered into the cavity 28, and then the pre-pressurized powders 21 a and 22 a are compressed by the upper and lower punches 25 and 26. The pre-compacted powders 21 a and 22 a are deformed according to the shape of the cavity 28 and are joined together to form a compact 20. Thereafter, the upper punch 25 is raised, and the lower punch 26 is further raised, and the green compact 20 that has been compressed and molded is taken out from the mold 24. The green compact 20 thus obtained has higher wear resistance in the outer peripheral portion 21 than in the inner peripheral portion 22 reflecting the powder material, density or shape of the pre-pressed powder 21a, 22a. And the inner peripheral part 22 has moderate earthquake resistance.
[0025]
According to the first to third embodiments, it is possible to use a normal molding apparatus that fills and compresses powder as it is, and without having to set a partition plate for separating layers in the cavity. The green compact (1, 10, 20) can be formed. In addition, if a large amount of pre-compacted powder is prepared and stocked in advance and then compressed as necessary to obtain a compact, the effort to adjust and fill the powder each time the compact is formed Can be saved and productivity can be improved. In addition, the shape of the pre-compressed powder (planar shape when viewed from the compression direction) is similar to the final shape of the green compact in the combined state, so there is no need to significantly increase the pressure during main compression. Becomes easy. However, the shape of the pre-pressed powder can be set in the cavity, and may be a rough shape to some extent as long as it is within the range that can be formed into the final shape of the green compact by the main compression. In addition, since a plurality of pre-compressed powders are molded according to the part, combined and subjected to main compression, the characteristics of each part are automatically obtained.
[0026]
In each of the first to third embodiments, a green compact having a circular cross section and having a hole in the center is formed, and core rods (7, 17, 27 for forming the hole) are formed. However, the present invention can also be applied to a molding apparatus in which the core rod is set orthogonally to the compression direction. Further, when compressing, a lubricant is usually applied to the inner surface of the mold (4, 14, 24) on which the object to be compressed (pre-pressurized powder in this case) slides by compression. Since the preloaded powder can be handled, a lubricant can be applied to the surface of the preloaded powder. This is advantageous in terms of operation because depending on the mold, the operation of applying the lubricant to the inner surface may be difficult. Furthermore, in the second and third embodiments, it is preferable to select a powder material that causes a dimensional change in which the inner peripheral portion and the outer peripheral portion are tightened when the green compact is sintered, which increases the bonding strength. .
[0027]
The present invention is a method of obtaining a green compact by combining a plurality of pre-compressed powders and compressing and molding them, and the first to third embodiments are examples in which the method and members are embodied. It is. The member molded by the present invention is not limited to the above-described embodiments, and can be applied to any green compact. Examples of such members are described below.
[0028]
FIG. 10A shows a ring-shaped valve seat, which is divided into a seat surface portion 30 to which a valve face (not shown) is closely attached and a main portion 31 of the other portion, and the precompressed powder is formed. In this case, the preloaded powder is set so that the seat surface portion 30 has high wear resistance.
FIG. 10B shows a ratchet claw that is rotatably provided. The preloaded powder is formed by being divided into a claw portion 40, a bearing portion 41, and a main portion 42 of other portions. In this case, the claw portion 40 is required to have high wear resistance, the bearing portion 41 is required to be porous so as to have a lubricating oil retaining function, and the main portion 42 is required to have high strength. The Therefore, each pre-pressurized powder serving as these parts is set so as to satisfy each characteristic.
FIG. 10C shows a bearing, which is divided into an inner surface portion 50 on which the shaft slides and a main portion 51 of the other portion, and the precompressed powder is formed. In this case, the preloaded powder is set so that the inner surface portion 50 has high wear resistance.
FIG. 10D shows a ball bearing race, in which a pre-loaded powder is formed by being divided into an inner surface portion 60 on which a large number of balls slide and an outer surface portion 61 on the outer side. In this case, the preloaded powder is set so that the inner surface portion 60 has high wear resistance.
FIG. 10E shows a plate cam, which is divided into a top portion 70 that receives a high pressure and a bottom portion 71 of the other portion, and pre-pressurized powder is formed. In this case, the preloaded powder is set so that the top portion 70 has high wear resistance.
[0029]
【The invention's effect】
As described above, according to the present invention, a plurality of pre-compacted powders are molded to a density that can be handled, and then the pre-compacted powders are compressed with a pressing die and bonded together to form a desired compact. Therefore, it is possible to easily obtain a green compact without using a special mold and even a member having a complicated layer structure.
[Brief description of the drawings]
FIG. 1 is a perspective view of a green compact according to a first embodiment of the present invention.
FIG. 2 is a perspective view of a pre-loaded powder according to the first embodiment of the present invention.
FIG. 3 is a cross-sectional view sequentially illustrating steps of molding a green compact according to the first embodiment of the present invention.
FIG. 4 is a perspective view of a green compact according to a second embodiment of the present invention.
FIG. 5 is a perspective view of a pre-pressurized powder according to a second embodiment of the present invention.
FIGS. 6A and 6B are cross-sectional views sequentially showing steps of forming a green compact according to the second embodiment of the present invention. FIGS.
FIG. 7 is a perspective view of a green compact according to a third embodiment of the present invention.
FIG. 8 is a perspective view of a pre-pressurized powder according to a third embodiment of the present invention.
FIG. 9 is a cross-sectional view sequentially illustrating steps of molding a green compact according to a third embodiment of the present invention.
FIG. 10 is a perspective view showing an example of a member that can be molded by applying the present invention.
[Explanation of symbols]
1, 10, 20 ... green compact,
2a, 3a, 11a, 12a, 21a, 22a ... pre-pressed powder,
4, 14, 24 ... Mold (molding die),
5,15,25 ... Upper punch (push type),
6, 16, 26 ... lower punch (push type),
8, 18, 28 ... cavity.

Claims

A plurality of pre- compressed powders are molded to a density ratio of 60 to 75%, and then these pre-compressed powders are set in a cavity of a molding die capable of forming the green compacts. A method for forming a green compact used as a material for a sintered product, characterized in that the two are compressed with a pressing die and bonded together.

A plurality of pre-compacted powders are molded at a density ratio of 60 to 75%, and then dewaxed and pre-sintered at a temperature corresponding to 30 to 65% of the sintering temperature, Molding of a green compact as a material for a sintered product, which is set in a cavity of a mold that can be molded, and thereafter, the plurality of pre-pressed powders are compressed with a pressing die and bonded together Method.

The pressure used as the material of the sintered product according to claim 2, wherein the pre-pressurized powder has the highest content of iron powder, and the maximum temperature of the dewaxing and pre-sintering is 750 ° C or less. Powder molding method.

The plurality of pre-compacted powders are shaped so as to resemble the shape of the compacted powder by being combined with each other, and are set in the cavity in the combined state . A method for forming a green compact as a material for the sintered product described in 1.

The green compact has a plurality of parts having different required characteristics, and the pre-compacted powder is formed by a powder material, a shape, or a density corresponding to each part. A method for forming a green compact as a material for the sintered product according to any one of 1 to 4 .

Bonding surfaces to each other of said preload powder, according to any one of claims 1 to 5, characterized in that if it were formed on uneven surfaces mutually meshing, or at least one of the bonding surfaces is formed on the uneven surface A method for forming green compacts that are used as materials for sintered products .