JP3763796B2

JP3763796B2 - Manufacturing method of sintered member with inner hole with excellent coaxiality accuracy

Info

Publication number: JP3763796B2
Application number: JP2002091798A
Authority: JP
Inventors: 浩行高村
Original assignee: Nippon Piston Ring Co Ltd
Current assignee: Nippon Piston Ring Co Ltd
Priority date: 2002-03-28
Filing date: 2002-03-28
Publication date: 2006-04-05
Anticipated expiration: 2022-03-28
Also published as: JP2003286504A

Description

【０００１】
【発明の属する技術分野】
本発明は、複数回の圧縮成形を含む、内孔を有する焼結部材の製造方法に係り、とくに内外周の同軸度精度の向上に関する。
【０００２】
【従来の技術】
粉末冶金製品は部品形状に近い形状に加工でき、切削加工費の削減が可能であることから、近年、内燃機関の製造コスト低減という観点から、内燃機関用部品として、数多く使用されている。内燃機関用部品には、かなりの負荷がかかるため、高強度でかつ摺動性に優れた材料が要求されている。
【０００３】
高強度、すなわち高密度な材料を得る方法として、温間成形、２回圧縮２回焼結法（２Ｐ２Ｓ法）、あるいは焼結鍛造法等が一般的に知られている。しかし、例えば、２Ｐ２Ｓ法を用いて製造された粉末冶金製品では、切削加工を完全に省略するには寸法精度が不十分であり、このためサイジング処理等を付加して寸法精度を向上させている。しかし、サイジング処理による変形量には自ずと限界があり、サイジング処理前の寸法精度によっては製品の寸法精度が不十分となる場合があった。
【０００４】
例えば、内孔を有する焼結体は、成形型の型孔（ダイ孔）にコアロッドを挿入した型を用い、コアロッドの周囲のダイ孔に原料粉末を充填し、この原料粉末をパンチを用いてコアロッドの長さ方向に圧縮して、仮内孔を有する成形体としたのち、さらにサイジング処理を施して形を矯正し、焼結して製造されてきた。しかし、このような技術で製造された焼結体で、内孔径にくらべ高さが大きい場合には、開口部近傍の内孔径が中央部の内孔径よりも小さくなるという問題があった。
【０００５】
このような問題に対し、例えば、特開昭61-210102 号公報には、外周壁に中空孔（内孔）の開口部側に向かって広がるテーパを付けたコアロッドを使用する内孔（中空孔）を有する焼結体の高精度製造方法が提案が提案されている。特開昭61-210102 号公報に記載された技術で製造された焼結体は、真円度の高い内孔（中空孔）を有するとされている。
【０００６】
また、特開昭61-210106 号公報には、原料粉末を圧粉して得られた成形体に、高周波焼入れ処理を施して成形体の表層部に焼入れ層を形成したのち、サイジング処理を施す、高精度の焼結体を得る方法が提案されている。特開昭61-210106 号公報に記載された技術では、サイジング処理により生じる変形を焼入れ層の内側の多孔質部分で吸収でき、寸法精度が向上するとしている。しかしながら、多孔質部分の気孔率の増加には限界があり、特開昭61-210106 号公報に記載された技術による中空孔 (内孔）の高精度化には自ずから限界があった。
【０００７】
上記したような技術により、内孔を有する焼結体の内径、外径の寸法精度はかなり向上するが、内径基準の軸心と外径基準の軸心との差（内外周の同軸度精度）は、通常、成形時の精度で決定されている。
複数の内孔付き焼結体 (カム）を軸に組み付けるカムシャフトの製造においては、焼結体 (カム）の内径の寸法精度に加えてさらに、焼結体 (カム）の外周部の外径を基準とした軸心と、焼結体 (カム）の内周部の内径を基準とした軸心との同軸度精度を向上させることが要求されている。とくに、最近では同一軸に異種材料の焼結体 (カム）を組み付ける場合があり、同軸度精度の更なる向上が要望されている。
【０００８】
このような要望に対し、例えば、特開2001-293531 号公報には、孔を区画する内周部と外周部とを備えるワーク (焼結体）について、ダイス孔およびダイス孔内に配置されたコアロッドをもつダイスを用い、ダイス孔内にワークを装入し、、ワークの外周部をダイス孔の内周部で拘束するとともに、ワークの内周部をコアロッドの外周部でしごく、ワーク内周部の内径を基準とした軸心と外周部の外径を基準とした軸心との同軸性を高めるためのしごき工程を含むワークの内径精度向上方法が提案されている。
【０００９】
また、特開2001-198645 号公報には、製造されるべきカムロブの厚さより大きい厚さと、小さい外形と、軸方向孔の形状よりわずかに大きい軸方向孔を有する素材を、製造されるべきカムロブの輪郭形状と相補形状の壁面を有する外型と、カムロブの軸方向孔の形状と相補形状の壁面を有する中型と、底面と中型が係合する受け孔を有する下型とからなる金型内に置き、カムロブと同じ断面形状を有する押型にて、厚さ方向に冷間で押圧する組立て式カムシャフト用カムロブの製造方法が提案されている。
【００１０】
【発明が解決しようとする課題】
しかしながら、特開2001-198645 号公報に記載された技術では、製造されたカムロブ（焼結体）の同軸度精度が不足して、仕上げ加工を必要とする場合が多くあり、工程が複雑化し製造コストの高騰を招くという問題があった。また、特開2001-293531 号公報に記載された技術では、焼結体の内周面しごき加工を必要とするうえ、必ずしも所望の同軸度精度が得られない場合があり、仕上げ加工を必要とする場合が多く、製造工程が複雑化し製造コストの高騰を招くという問題があった。
【００１１】
本発明は、上記した従来技術の問題を有利に解決し、内外周の同軸度精度に優れた内孔付き焼結部材の製造方法を提案することを目的とする。なお、本発明でいう「同軸度精度に優れた」とは、外周部の外径を基準とした軸心と、焼結体 (カム）の内周部の内径を基準とした軸心とのずれ（差）が、平均で0.04mm以内である状態をいうものとする。
【００１２】
【課題を解決するための手段】
本発明者は、上記した課題を達成するために、同軸度精度に影響する要因についてさらに鋭意研究した。その結果、再圧縮工程を含む焼結体の製造方法では、再圧縮時に金型と仮焼結体（ワーク）との間にクリアランスを必要とするため、そのクリアランスの範囲内で、仮焼結体（ワーク）の装入位置に自由度があり、外径を基準とした軸心と内径を基準とした軸心とにずれ（差）が生じる原因となり、同軸度精度が低下することを見出した。本発明者は、再圧縮時に仮焼結体（ワーク）が一定位置に装入されるように金型形状を調整することにより、同軸度精度が顕著に向上することに想到し、本発明を完成した。
【００１３】
すなわち、本発明は、ダイと、該ダイのダイ孔内の中心部に挿入したコアロッドと、上パンチと、下パンチとからなる成形用金型を用い、少なくとも一次圧縮成形と二次圧縮成形とを含む工程からなる内孔付き焼結部材の製造方法において、前記成形用金型を、上パンチおよび／または下パンチが、内周部側および／または外周部側に面取り突起を有し、かつ前記二次圧縮成形に用いる上または下パンチの面取り突起が前記一次圧縮成形に用いる上または下パンチの面取り突起と同一または大きい金型とすることを特徴とする内外周の同軸度精度に優れた内孔付き焼結部材の製造方法である。
【００１４】
また、本発明は、ダイと、該ダイのダイ孔内の中心部に挿入したコアロッドと、上パンチと、下パンチとからなる一次成形用金型を用い、該一次成形用金型の前記ダイと前記コアロッドとの間のダイ孔内に原料粉末を充填し、前記上パンチと前記下パンチとにより前記原料粉末を一次圧縮成形したのち、仮焼結を施して内孔を有する仮焼結体とする一次成形工程と、該仮焼結体を、ダイと、該ダイのダイ孔内の中心部に挿入したコアロッドと、上パンチと、下パンチとからなる二次成形用金型のダイ孔内に装入し、前記上パンチと前記下パンチとにより前記仮焼結体を二次圧縮成形したのち本焼結を施して、内孔を有する焼結体とする二次成形工程とからなる内孔付き焼結部材の製造方法において、前記一次成形用金型の上パンチおよび／または前記一次成形用金型の下パンチ、および、前記二次成形用金型の上パンチおよび／または前記二次成形用金型の下パンチが、内周部側および／または外周部側に面取り突起を有し、かつ前記二次圧縮成形に用いる上または下パンチの面取り突起が前記一次圧縮成形に用いる上または下パンチの面取り突起と同一または大きいことを特徴とする内外周の同軸度精度に優れた内孔付き焼結部材の製造方法である。
【００１５】
【発明の実施の形態】
本発明は、ダイと、該ダイのダイ孔内の中心部に挿入したコアロッドと、上パンチと、下パンチとからなる成形用金型を用い、原料粉末に、少なくとも一次圧縮成形を施す一次成形工程と該一次成形工程を経た一次成形体に二次圧縮成形（再圧縮成形）を施す二次成形工程と、を含む工程からなる内孔付き焼結部材の製造方法である。なお、本発明では、一次成形工程において、一次圧縮成形を施し一次成形体とした後に仮焼結を施し仮焼結体とする工程を含み、さらに二次成形工程においては、一次成形工程で得られた仮焼結体に再圧縮成形（二次圧縮成形）を施し、さらに本焼結を施し焼結体とする工程からなる、いわゆる２Ｐ２Ｓ法とすることが好ましい。以下、２Ｐ２Ｓ法を用いた場合をもとに説明するが、本発明はこれに限定されるものではないことは言うまでもない。
【００１６】
まず、本発明では、内孔付き焼結部材を製造するために、ダイ11と、該ダイ11のダイ孔内の中心部に挿入したコアロッド14と、上パンチ12と、下パンチ13とからなる成形用金型を用いる。原料粉末１を、コアロッド14の周囲のダイ孔内に充填し、上パンチ12と下パンチ13とにより圧縮成形し、一次成形体とする。なお、上パンチ12あるいは下パンチ13には、コアロッド14が摺動可能なように中央部に孔122,132 を有する。上パンチ12および下パンチ13は、孔を区画する内周部と、ダイの内周面と摺動する外周面を区画する外周部とを有する。また、使用する原料粉末は、とくに限定する必要はなく、製品である焼結部材の用途に応じ適宜選定することが好ましい。例えば、鉄基焼結部材であれば、鉄粉等の鉄基粉末に、黒鉛粉末、合金粉末、潤滑剤等を混合した混合粉を原料粉末とすることが好ましい。
【００１７】
そして、本発明の一次圧縮成形に用いる一次成形用金型には、上パンチ11と下パンチ12のいずれか一方または両方に、内周部側および／または外周部側に面取り突起121,131 を設ける。面取り突起121,131 は、内周部または外周部の全周に亘って付設することが好ましい。
下パンチ13の内周部側に面取り突起131 を付与した場合の一次成形用金型の一例を図１に示す。図１に示すような一次成形用金型を使用して、原料粉末１を圧縮成形し一次成形体としたのち仮焼結を施すと、仮焼結体の内孔下側の内周部に面取りが施された形となる。なお、本発明では仮焼結条件は特に限定されない。使用する原料粉末に応じて決まる条件で行うことが好ましい。
【００１８】
このように、仮焼結体の内周部または外周部に面取りを施すことと、後述する二次成形用金型に付設する面取り突起とを合わせ用いることにより、その後の二次成形において二次成形用金型内におけるワーク (仮焼結体）の装入位置を一定位置とすることができる。
このように、一次成形工程で、内孔に沿った内周部側または外周部側の一方または両方に面取りを施された仮焼結体２は、ついで、二次成形金型内に装入され、二次圧縮成形を施され、ついで本焼結を施されて焼結体とされる二次成形工程を施される。
【００１９】
二次圧縮成形においては、図２に示すように一次圧縮成形と同様に、ダイ21のダイ孔に下パンチ23が挿入され、ダイ孔中央部にはコアロッド24が挿入され、さらにコアロッド24が下パンチ23の内孔232 に挿入される。ダイ21が固定された状態で下パンチ23が下降して、ダイ21の内周面とコアロッド24の外周面と下パンチ23で囲まれた部分（ダイ孔）に仮焼結体（ワーク）２を装入する。
【００２０】
二次圧縮成形において使用する二次成形用金型としては、一次成形用金型におけると同様に上パンチ22と下パンチ23のいずれか一方または両方に、内周部側および／または外周部側に面取り突起221,231 を設けた金型を使用する。なお、面取り突起221,231 は、内周部または外周部の全周に亘って付設することが好ましい。
【００２１】
また、二次圧縮成形に用いる上または下パンチの面取り突起221,231 は一次圧縮成形に用いる上または下パンチの面取り突起121,131 の寸法と同一かそれ以上の大きさの面取り突起とする。この面取り突起と、一次圧縮成形により形成された仮焼結体の面取りとにより、二次圧縮成形時のワーク（仮焼結体）２の装入位置をばらつきなく一定位置とすることができる。
【００２２】
ダイ21の内周面とコアロッド24の外周面と下パンチ23で囲まれた部分（ダイ孔）に装入された仮焼結体（ワーク）２は、仮焼結体の下側内周部の面取りと下パンチの内周部側に付設された面取り突起231 とにより、コアロッド21とワーク２とのクリアランスが全周で均一となるように固定される。これにより、再圧縮成形−本焼結後に、同軸度精度を顕著に向上させることができる。
【００２３】
下パンチの内周部側に面取り突起を付与した場合の二次成形用金型の一例を、二次圧縮成形（再圧縮成形）直前の状態で図２に示す。また、下パンチおよび上パンチの内周部側および外周部側に面取り突起を付与した場合の二次成形用金型の一例を同様に図３に示す。
ダイ孔内の一定位置に固定された仮焼結体（ワーク）２は、下降した上パンチ22により圧縮され、二次成形体（再圧縮成形体）とされる。その後、上パンチ22および下パンチ23が上昇して、二次成形体をダイ21から取り出す。
【００２４】
ダイから取り出された二次成形体は、さらに本焼結を施されて内孔付き焼結部材 (焼結体）とされる。なお、本発明では本焼結条件は特に限定されない。使用する原料粉末に応じて決まる条件で行うことが好ましい。
【００２５】
【実施例】
鉄粉に、黒鉛粉、銅粉を焼結後にＣ：0.8 質量％、Cu：1.5 質量％となるように配合し、さらに潤滑剤としてステアリン酸亜鉛を鉄粉と黒鉛粉と銅粉の合計量100 重量部に対し１重量部配合し、混合して混合粉とした。この混合粉を原料粉末として、図１に示す一次成形用金型のダイ孔に充填して、面圧：6 〜7ton／cm²で一次圧縮成形し、一次成形体とした。なお、一次成形用金型は、下プレスの内周部に面取り突起（Ｃ：0.5mm ）を有し、仮焼結後に外径40mm×内径30mm×厚さ15mmとなるように設計された金型とした。
【００２６】
これら一次成形体を、真空焼結炉中で、600 〜900 ℃の温度範囲で仮焼結する一次成形工程により、仮焼結体とした。ついでこれら仮焼結体に、図２に示す二次成形用金型を用いて、面圧：7 〜10 ton／cm²で二次圧縮成形を施し、二次成形体としたのち、1100〜1200℃の温度で本焼結を施す二次成形工程により、内孔付き焼結部材とし本発明例１とした。なお、二次成形用金型は、本焼結後に外径40mm×内径30mm×厚さ15mmの部材となるように設計された金型であり、下パンチの内周部に、仮焼結体の下側内周部に付与された面取りより大きい寸法の面取り突起（Ｃ：0.5 mm）を付設された金型とした。また、二次成形用金型と仮焼結体とのクリアランスは0.1mm （片側）に設定した。
【００２７】
また、本発明例１と同じ配合の原料粉末を、一次成形用金型として、内周部側および外周部側の両側に面取り突起（Ｃ：0.5mm ）を付設した下パンチと、内周部側および外周部側の両側に面取り突起（Ｃ：0.5mm ）を付設した上パンチを使用した金型を用い、また、二次成形用金型として、図３に示すような、内周部側および外周部側の両側に面取り突起を付設した下パンチと、内周部側および外周部側の両側に面取り突起を付設した上パンチを使用した金型を用いた以外は、本発明例１と同様な条件で一次成形工程および二次成形工程を施し、内孔付き焼結部材とし本発明例２とした。なお、二次成形用金型では、下パンチおよび上パンチに付設された面取り突起は、一次成形金型により仮焼結体に付与された面取りより大きい寸法（Ｃ：0.6 mm）とした。
【００２８】
また、比較例として、一次成形用金型、二次成形用金型として、下パンチおよび上パンチのいずれにもに面取り突起を付設しなかった金型を使用した以外は、本発明例１と同じ配合の原料粉末を、本発明例１と同様な条件の一次成形工程、二次成形工程により、内孔付き焼結部材とし、比較例とした。
これら焼結部材について、内周を基準として、外周全周のフレ量を測定し、外周の外径基準による軸心と内周の内径基準による軸心との差（mm）を求め、同軸度精度を評価した。同軸度精度は軸心の差が小さいほど向上している。
【００２９】
得られた結果を図４に示す。
図４から、本発明例１および本発明例２の同軸度はいずれも、0.04mm以下となっており、比較例の0.05mmにくらべ同軸度精度が顕著に向上していることがわかる。
【００３０】
【発明の効果】
本発明によれば、内径、および外径等の寸法精度に優れ、かつ同軸度精度に顕著に優れた内孔付き焼結部材が、簡便な方法で安価にしかも安定して製造できるという産業上格段の効果を奏する。
【図面の簡単な説明】
【図１】本発明に好適な一次成形用金型の構成の一例を模式的に示す断面図である。
【図２】本発明に好適な二次成形用金型の構成の一例を模式的に示す断面図である。
【図３】本発明に好適な二次成形用金型の構成の一例を模式的に示す断面図である。
【図４】本発明における実施例の同軸度精度を示すグラフである。
【符号の説明】
１原料粉末
11 ダイ (一次成形用）
12 上パンチ (一次成形用）
13 下パンチ (一次成形用）
14 コアロッド (一次成形用）
15 コアロッド受け治具
121 上パンチ面取り突起 (一次成形用）
122 上パンチ内孔 (一次成形用）
131 下パンチ面取り突起 (一次成形用）
132 下パンチ内孔 (一次成形用）
２ワーク（仮焼結体）
21 ダイ (二次成形用）
22 上パンチ (二次成形用）
23 下パンチ (二次成形用）
24 コアロッド (二次成形用）
25 コアロッド受け治具
221 上パンチ面取り突起
222 上パンチ内孔
231 下パンチ面取り突起
232 下パンチ内孔[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a sintered member having an inner hole, including a plurality of compression moldings, and more particularly to improvement in accuracy of coaxiality of inner and outer circumferences.
[0002]
[Prior art]
Since powder metallurgy products can be processed into a shape close to the part shape and the cutting cost can be reduced, in recent years, many are used as parts for internal combustion engines from the viewpoint of reducing the manufacturing cost of internal combustion engines. Since a considerable load is applied to the internal combustion engine component, a material having high strength and excellent sliding property is required.
[0003]
As a method for obtaining a material having high strength, that is, a high density, warm forming, two-time compression-two-time sintering method (2P2S method), sintering forging method, or the like is generally known. However, for example, a powder metallurgy product manufactured by using the 2P2S method has insufficient dimensional accuracy to completely omit the cutting process. For this reason, a sizing process or the like is added to improve the dimensional accuracy. . However, the amount of deformation by the sizing process is naturally limited, and the dimensional accuracy of the product may be insufficient depending on the dimensional accuracy before the sizing process.
[0004]
For example, for a sintered body having an inner hole, a mold in which a core rod is inserted into a mold hole (die hole) of a mold is used, a raw material powder is filled in a die hole around the core rod, and this raw material powder is used with a punch. It has been manufactured by compressing in the length direction of the core rod to form a molded body having a temporary inner hole, and further sizing to correct the shape and sintering. However, in the sintered body manufactured by such a technique, when the height is larger than the inner hole diameter, there is a problem that the inner hole diameter near the opening is smaller than the inner hole diameter in the central part.
[0005]
For example, Japanese Patent Application Laid-Open No. 61-210102 discloses an inner hole (hollow hole) using a core rod having a tapered outer peripheral wall that extends toward the opening side of the hollow hole (inner hole). A proposal has been made for a method for producing a sintered body having high accuracy. A sintered body manufactured by the technique described in JP-A-61-210102 is said to have an inner hole (hollow hole) with a high roundness.
[0006]
Japanese Patent Application Laid-Open No. 61-210106 discloses that a molded body obtained by compacting a raw material powder is subjected to induction quenching treatment to form a quenching layer on a surface layer portion of the molded body, and then subjected to sizing treatment. A method for obtaining a highly accurate sintered body has been proposed. In the technique described in Japanese Patent Laid-Open No. 61-210106, deformation caused by sizing treatment can be absorbed by the porous portion inside the quenching layer, and the dimensional accuracy is improved. However, there is a limit to the increase in the porosity of the porous portion, and there has been a limit to increasing the accuracy of the hollow hole (inner hole) by the technique described in JP-A-61-210106.
[0007]
Although the dimensional accuracy of the inner diameter and outer diameter of the sintered body having the inner hole is considerably improved by the technique as described above, the difference between the inner diameter reference axis and the outer diameter reference axis (the coaxial accuracy of the inner and outer circumferences). ) Is usually determined with accuracy during molding.
In the manufacture of camshafts that assemble a sintered body (cam) with a plurality of inner holes on the shaft, in addition to the dimensional accuracy of the inner diameter of the sintered body (cam), the outer diameter of the outer periphery of the sintered body (cam) It is required to improve the accuracy of the coaxiality between the shaft center based on the inner diameter of the sintered body (cam) and the shaft center based on the inner diameter of the inner peripheral portion of the sintered body (cam). In particular, recently, sintered bodies (cams) of different materials may be assembled on the same shaft, and further improvement of the coaxiality accuracy is desired.
[0008]
In response to such a request, for example, in Japanese Patent Laid-Open No. 2001-293531, a work (sintered body) having an inner peripheral portion and an outer peripheral portion that divide holes is arranged in a die hole and a die hole. Using a die with a core rod, insert the workpiece into the die hole, constrain the outer periphery of the workpiece with the inner periphery of the die hole, and squeeze the inner periphery of the workpiece with the outer periphery of the core rod. There has been proposed a method for improving the inner diameter accuracy of a work including a squeezing step for improving the coaxiality between an axis centered on the inner diameter of the part and an axis centered on the outer diameter of the outer peripheral part.
[0009]
JP 2001-198645 also discloses a material having a thickness larger than the thickness of the cam lobe to be manufactured, a small outer shape, and an axial hole slightly larger than the shape of the axial hole. In a mold comprising an outer mold having a wall shape complementary to the contour shape of the inner wall, a middle mold having a wall shape complementary to the shape of the axial direction hole of the cam lobe, and a lower mold having a receiving hole for engaging the bottom surface and the middle mold On the other hand, a manufacturing method of a cam lobe for an assembling camshaft is proposed in which a pressing die having the same cross-sectional shape as the cam lobe is pressed in the cold direction in the thickness direction.
[0010]
[Problems to be solved by the invention]
However, with the technology described in Japanese Patent Application Laid-Open No. 2001-198645, the manufactured cam lobe (sintered body) lacks the coaxiality accuracy and often requires finishing, which complicates the manufacturing process. There was a problem that the cost increased. In addition, the technique described in Japanese Patent Application Laid-Open No. 2001-293531 requires ironing of the inner peripheral surface of the sintered body, and may not always obtain the desired coaxiality accuracy, and requires finishing. In many cases, the manufacturing process becomes complicated and the manufacturing cost increases.
[0011]
An object of the present invention is to advantageously solve the above-described problems of the prior art and propose a method for manufacturing a sintered member with an inner hole having excellent coaxiality accuracy between the inner and outer circumferences. The term “excellent in coaxiality accuracy” as used in the present invention refers to an axis centered on the basis of the outer diameter of the outer peripheral part and an axis centered on the inner diameter of the inner peripheral part of the sintered body (cam). The state where the deviation (difference) is within 0.04 mm on average shall be said.
[0012]
[Means for Solving the Problems]
In order to achieve the above-described problems, the present inventor has further studied earnestly on factors that influence the coaxiality accuracy. As a result, the method for manufacturing a sintered body including a recompression process requires a clearance between the mold and the temporary sintered body (workpiece) at the time of recompression. It has been found that there is a degree of freedom in the loading position of the body (work), causing a deviation (difference) between the axis centered on the outer diameter and the axis centered on the inner diameter, resulting in a decrease in coaxiality accuracy. It was. The present inventor has conceived that the coaxiality accuracy is remarkably improved by adjusting the mold shape so that the pre-sintered body (workpiece) is inserted into a fixed position at the time of recompression. completed.
[0013]
That is, the present invention uses a molding die comprising a die, a core rod inserted into the center of the die hole of the die, an upper punch, and a lower punch, and at least primary compression molding and secondary compression molding. In the method for producing a sintered member with an inner hole comprising a step including: an upper punch and / or a lower punch having a chamfered protrusion on the inner peripheral portion side and / or the outer peripheral portion side, and excellent outer peripheral concentricity accuracy of which is characterized by chamfered protrusions above or below the punch used in the secondary compression molding is chamfered projection and same or greater die above or below the punch used in the primary compression molding And a method of manufacturing a sintered member with inner holes.
[0014]
The present invention also uses a primary molding die comprising a die, a core rod inserted in the center of the die hole of the die, an upper punch, and a lower punch, and the die of the primary molding die is used. The raw material powder is filled in a die hole between the core rod and the core rod, and the raw material powder is subjected to primary compression molding by the upper punch and the lower punch, and then subjected to temporary sintering to have a temporary sintered body having an inner hole. And a die hole of a secondary molding die comprising a die, a core rod inserted in the center of the die hole of the die, an upper punch, and a lower punch. And a secondary molding step in which the temporary sintered body is subjected to secondary compression molding by the upper punch and the lower punch and then subjected to main sintering to obtain a sintered body having an inner hole. In the method for producing a sintered member with an inner hole, an upper punch and / or an upper mold of the primary molding die. Alternatively, the lower punch of the primary molding die and the upper punch of the secondary molding die and / or the lower punch of the secondary molding die are arranged on the inner peripheral side and / or the outer peripheral side. has a chamfered projection, and concentricity of the outer circumferential inner and wherein said secondary compression chamfered protrusions above or below the punch used for molding can chamfered projections and same or greater above or below the punch used in the primary compression molding It is a manufacturing method of the sintered member with an inner hole excellent in accuracy.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The present invention uses a molding die composed of a die, a core rod inserted into the central portion of the die hole of the die, an upper punch, and a lower punch, and performs primary compression molding at least on the raw powder. And a secondary molding step of subjecting the primary molded body that has undergone the primary molding step to secondary compression molding (recompression molding). In the present invention, the primary molding step includes a step of performing primary compression molding to obtain a primary molded body and then pre-sintering to obtain a temporary sintered body. Further, in the secondary molding step, the primary molding step is obtained in the primary molding step. It is preferable to use a so-called 2P2S method comprising a step of subjecting the obtained temporary sintered body to re-compression molding (secondary compression molding) and further subjecting to main sintering to form a sintered body. The following description is based on the case where the 2P2S method is used, but it goes without saying that the present invention is not limited to this.
[0016]
First, in the present invention, in order to produce a sintered member with an inner hole, it comprises a die 11, a core rod 14 inserted into the center of the die 11 in the die hole, an upper punch 12, and a lower punch 13. A molding die is used. The raw material powder 1 is filled in a die hole around the core rod 14 and compression-molded by the upper punch 12 and the lower punch 13 to obtain a primary molded body. The upper punch 12 or the lower punch 13 has holes 122 and 132 in the center so that the core rod 14 can slide. The upper punch 12 and the lower punch 13 have an inner peripheral portion that defines a hole and an outer peripheral portion that defines an outer peripheral surface that slides with the inner peripheral surface of the die. Moreover, the raw material powder to be used is not particularly limited, and it is preferable to select appropriately according to the use of the sintered member which is a product. For example, in the case of an iron-based sintered member, a mixed powder obtained by mixing an iron-based powder such as iron powder with a graphite powder, an alloy powder, a lubricant, or the like is preferably used as a raw material powder.
[0017]
The primary molding die used in the primary compression molding of the present invention is provided with chamfered protrusions 121 and 131 on one or both of the upper punch 11 and the lower punch 12 on the inner peripheral portion side and / or the outer peripheral portion side. The chamfered protrusions 121 and 131 are preferably provided over the entire circumference of the inner peripheral portion or the outer peripheral portion.
FIG. 1 shows an example of a primary molding die in which a chamfered protrusion 131 is provided on the inner peripheral side of the lower punch 13. Using the primary molding die as shown in FIG. 1, when the raw powder 1 is compression molded to form a primary molded body and then subjected to temporary sintering, the inner periphery of the temporary sintered body below the inner hole is formed. The shape is chamfered. In the present invention, the pre-sintering conditions are not particularly limited. It is preferable to carry out the conditions determined according to the raw material powder to be used.
[0018]
In this way, by chamfering the inner peripheral portion or the outer peripheral portion of the temporary sintered body and using the chamfering protrusions attached to the secondary molding die, which will be described later, in the subsequent secondary molding, The charging position of the workpiece (temporarily sintered body) in the molding die can be set to a fixed position.
Thus, in the primary molding step, the temporary sintered body 2 chamfered on one or both of the inner peripheral side or the outer peripheral side along the inner hole is then charged into the secondary molding die. Then, secondary compression molding is performed, and then a secondary molding step is performed in which main sintering is performed to obtain a sintered body.
[0019]
In the secondary compression molding, as shown in FIG. 2, the lower punch 23 is inserted into the die hole of the die 21, the core rod 24 is inserted into the center of the die hole, and the core rod 24 is The punch 23 is inserted into the inner hole 232. The lower punch 23 is lowered while the die 21 is fixed, and a temporary sintered body (workpiece) 2 is formed in a portion (die hole) surrounded by the inner peripheral surface of the die 21, the outer peripheral surface of the core rod 24, and the lower punch 23. Insert.
[0020]
As for the secondary molding die used in the secondary compression molding, as in the primary molding die, either one or both of the upper punch 22 and the lower punch 23, the inner peripheral side and / or the outer peripheral side. A mold provided with chamfered protrusions 221 and 231 is used. The chamfered protrusions 221 and 231 are preferably provided over the entire circumference of the inner peripheral portion or the outer peripheral portion.
[0021]
Further, the chamfered projections 221 and 231 of the upper or lower punch used in the secondary compression molding a chamfered projection of primary compression and dimensions of the chamfered projections 121 and 131 of the upper or the lower punch for molding the same or larger than the size. By this chamfering projection and the chamfering of the temporary sintered body formed by the primary compression molding, the loading position of the work (temporary sintered body) 2 at the time of the secondary compression molding can be made constant without any variation.
[0022]
The temporary sintered body (workpiece) 2 inserted into the portion surrounded by the inner peripheral surface of the die 21, the outer peripheral surface of the core rod 24 and the lower punch 23 (die hole) is the lower inner peripheral portion of the temporary sintered body. And the chamfering protrusion 231 provided on the inner peripheral side of the lower punch are fixed so that the clearance between the core rod 21 and the workpiece 2 is uniform over the entire circumference. Thereby, the coaxiality accuracy can be remarkably improved after recompression molding-main sintering.
[0023]
An example of a secondary molding die when a chamfered protrusion is provided on the inner peripheral side of the lower punch is shown in FIG. 2 in a state immediately before secondary compression molding (recompression molding). FIG. 3 shows an example of a secondary molding die when chamfered protrusions are provided on the inner peripheral side and the outer peripheral side of the lower punch and the upper punch.
The temporary sintered body (workpiece) 2 fixed at a fixed position in the die hole is compressed by the lowered upper punch 22 to form a secondary molded body (recompression molded body). Thereafter, the upper punch 22 and the lower punch 23 are raised, and the secondary compact is taken out from the die 21.
[0024]
The secondary molded body taken out from the die is further subjected to main sintering to form a sintered member with inner holes (sintered body). In the present invention, the main sintering conditions are not particularly limited. It is preferable to carry out the conditions determined according to the raw material powder to be used.
[0025]
【Example】
Iron powder is mixed with graphite powder and copper powder after sintering so that C: 0.8 mass% and Cu: 1.5 mass%, and zinc stearate as a lubricant is added to iron powder, graphite powder, and copper powder. One part by weight was blended with 100 parts by weight and mixed to obtain a mixed powder. The mixed powder was used as a raw material powder and filled in a die hole of a primary molding die shown in FIG. 1 and subjected to primary compression molding at a surface pressure of 6 to 7 ton / cm ² to obtain a primary molded body. The primary molding die has a chamfered protrusion (C: 0.5 mm) on the inner periphery of the lower press, and is designed to have an outer diameter of 40 mm × inner diameter of 30 mm × thickness of 15 mm after pre-sintering. The type.
[0026]
These primary molded bodies were made into a temporarily sintered body by a primary molding step of presintering in a vacuum sintering furnace in a temperature range of 600 to 900 ° C. Next, these temporary sintered bodies were subjected to secondary compression molding at a surface pressure of 7 to 10 ton / cm ² using a secondary molding die shown in FIG. By a secondary forming process in which main sintering is performed at a temperature of 1200 ° C., a sintered member with an inner hole is obtained as Inventive Example 1. The secondary molding die is a die designed to become a member having an outer diameter of 40 mm, an inner diameter of 30 mm, and a thickness of 15 mm after the main sintering, and a temporary sintered body is formed on the inner peripheral portion of the lower punch. The die was provided with a chamfering protrusion (C: 0.5 mm) larger in size than the chamfering provided on the lower inner peripheral portion. The clearance between the secondary molding die and the temporary sintered body was set to 0.1 mm (one side).
[0027]
Further, a raw material powder having the same composition as that of Invention Example 1 is used as a primary molding die, a lower punch having chamfered protrusions (C: 0.5 mm) on both the inner peripheral portion side and the outer peripheral portion side, and an inner peripheral portion Using a die using an upper punch with chamfered projections (C: 0.5 mm) on both sides of the outer and outer peripheral sides, and as a secondary molding die, the inner peripheral side as shown in FIG. Example 1 of the present invention except that a die using a lower punch provided with chamfered protrusions on both sides on the outer peripheral side and an upper punch provided with chamfered protrusions on both the inner peripheral side and the outer peripheral side is used. Under the same conditions, the primary molding step and the secondary molding step were performed, and a sintered member with an inner hole was obtained as Invention Example 2. In the secondary molding die, the chamfering protrusions attached to the lower punch and the upper punch were larger than the chamfering (C: 0.6 mm) provided to the temporary sintered body by the primary molding die.
[0028]
In addition, as a comparative example, Example 1 of the present invention was used except that a mold having no chamfered protrusions on either the lower punch or the upper punch was used as a primary molding die and a secondary molding die. The raw material powder having the same composition was made into a sintered member with an inner hole by a primary molding step and a secondary molding step under the same conditions as in Invention Example 1, and used as a comparative example.
For these sintered members, the amount of flare around the outer circumference is measured with the inner circumference as a reference, and the difference (mm) between the axis center based on the outer diameter reference of the outer circumference and the axis center based on the inner diameter reference of the inner circumference is determined. Accuracy was evaluated. The accuracy of concentricity is improved as the difference in axial center is smaller.
[0029]
The obtained results are shown in FIG.
From FIG. 4, it can be seen that the coaxiality of Invention Example 1 and Invention Example 2 are both 0.04 mm or less, and the coaxiality accuracy is remarkably improved as compared with 0.05 mm of the comparative example.
[0030]
【The invention's effect】
Industrial Applicability According to the present invention, a sintered member with an inner hole, which is excellent in dimensional accuracy such as inner diameter and outer diameter, and remarkably excellent in coaxiality accuracy, can be manufactured inexpensively and stably by a simple method. There is a remarkable effect.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing an example of a configuration of a primary molding die suitable for the present invention.
FIG. 2 is a cross-sectional view schematically showing an example of the configuration of a secondary molding die suitable for the present invention.
FIG. 3 is a cross-sectional view schematically showing an example of the configuration of a secondary molding die suitable for the present invention.
FIG. 4 is a graph showing the coaxiality accuracy of an example according to the present invention.
[Explanation of symbols]
1 Raw material powder
11 Die (for primary molding)
12 Upper punch (for primary molding)
13 Lower punch (for primary molding)
14 Core rod (for primary molding)
15 Core rod receiving jig
121 Upper punch chamfered projection (for primary molding)
122 Upper punch bore (for primary molding)
131 Lower punch chamfering projection (for primary molding)
132 Lower punch bore (for primary molding)
2 Workpiece (temporary sintered body)
21 Die (for secondary molding)
22 Upper punch (for secondary molding)
23 Lower punch (for secondary molding)
24 core rod (for secondary molding)
25 Core rod receiving jig
221 Upper punch chamfering protrusion
222 Upper punch hole
231 Lower punch chamfering protrusion
232 Lower punch bore

Claims

An internal process comprising at least a primary compression molding and a secondary compression molding using a molding die comprising a die, a core rod inserted in the center of the die hole of the die, an upper punch, and a lower punch. In the method for manufacturing a sintered member with a hole, the molding die, the upper punch and / or the lower punch have chamfered protrusions on the inner peripheral side and / or the outer peripheral side, and are used for the secondary compression molding. on or perforated sintered inner chamfered projections excellent concentricity accuracy of the outer peripheral inner characterized by a chamfered projection and same or greater die above or below the punch used in the primary compression molding of the lower punch used Manufacturing method of member.

A primary molding die composed of a die, a core rod inserted into the center of the die hole of the die, an upper punch, and a lower punch is used, and between the die and the core rod of the primary molding die A raw material powder is filled in the die hole, and the raw powder is subjected to primary compression molding by the upper punch and the lower punch, and then subjected to temporary sintering to obtain a temporary sintered body having an inner hole; and The pre-sintered body is inserted into a die hole of a mold for secondary molding composed of a die, a core rod inserted in the center of the die hole of the die, an upper punch, and a lower punch, With the inner hole comprising the secondary molding step of performing the secondary compression molding of the temporary sintered body by the upper punch and the lower punch and then performing the main sintering to form a sintered body having an inner hole in the center portion. In the method for producing a sintered member, the upper punch of the primary molding die and / or the The lower punch of the primary molding die, the upper punch of the secondary molding die and / or the lower punch of the secondary molding die have chamfered protrusions on the inner peripheral side and / or the outer peripheral side. and the secondary compression on for molding or holes seizure inner excellent concentricity precision chamfered projections of the lower punch, characterized in that on or chamfered projections and same or greater of the lower punch used in the primary compression molding A manufacturing method of a binding member.